School of Physical Sciences

Methane (CH4), the second most important greenhouse gas directly emitted by human activity, is removed from the atmosphere via chemical degradation. The chemical sink of CH4 is influenced by temperature and the chemical composition of the atmosphere. It is further an important source of water vapour in the stratosphere and affects the ozone concentration in the troposphere and the stratosphere via secondary feedbacks.

The talk will focus on the role of these chemistry-climate interactions in numerical simulations with the chemistry-climate model EMAC perturbed by either CO2 or CH4 increase. For both forcing agents, CO2 and CH4 , so called rapid radiative adjustments are assessed in simulations with prescribed sea surface temperatures, as well as climate feedbacks in respective simulations using an interactive oceanic mixed layer.

The simulation set-up uses CH4 emission fluxes instead of prescribed CH4 concentrations at the lower boundary so that changes of the chemical sink can feed back on the atmospheric CH4 concentration without constraints.

The results show a shortening of the CH4 lifetime and, accordingly, a reduction of the CH4 mixing ratios in a warming and moistening troposphere. This decrease in CH4 also affects the response of tropospheric ozone.

Furthermore, recently an additional radiation scheme was implemented into the EMAC model, which represents the direct radiative effect of CH4 better and also accounts for the absorption by CH4 in the solar shortwave spectrum. With the new radiation scheme the effective radiative forcing for the same perturbation of CH4 emissions is larger, and individual rapid radiative adjustments, e.g. of clouds, are changed.

Zoom link: https://us02web.zoom.us/j/89826306833?pwd=cnNHSG9OWHRjVngzMGVMc2F0NnA4dz09

• Speaker: Laura Stecher, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre (Engl: German Aerospace Center, Institute of Atmospheric Physics)
• Tuesday 07 May 2024, 11:30-12:30
• Venue: Chemistry Dept, Unilever Lecture Theatre and Zoom.
• Series: Centre for Atmospheric Science seminars, Chemistry Dept.; organiser: .

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The massless Dirac equation with a Coulomb potential is interesting both from a physical and a mathematical point of view; it appears in some physical models, for instance the 2D equation is used to describe the dynamics of carbon atoms in a sheet of non-perfect graphene, and on the mathematical side the homogeneity of degree -1 of the potential seems to have a critical behavior, as |x| goes to infinity, since Strichartz estimates are known to hold for potentials that decay faster and there are examples of potentials decaying slower such that the corresponding flows do not disperse. In this talk I will present a recent result concerning Strichartz estimates for the solutions of the massless Dirac-Coulomb equation in 2 and 3 dimension with additional angular regularity. It extends the result on R3 of Cacciafesta-Séré-Zhang and provides completely new estimates on R2. As an application we will discuss a local well-posedness result for a nonlinear system.

• Speaker: Elena Danesi
• Monday 29 April 2024, 14:00-15:00
• Venue: MR13.
• Series: Partial Differential Equations seminar; organiser: Dr Greg Taujanskas.

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We present some theoretical and experimental results on the dynamics of two phase turbulent buoyant plumes – both with particles and with bubbles – to demonstrate some of the effects of phase separation on the overall flow patterns, and flow behaviour and some of the instabilities that arise as a result. 

ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales

• Speaker: Andy Woods (National and Capodistrian University of Athens)
• Thursday 02 May 2024, 16:00-17:00
• Venue: Seminar Room 1, Newton Institute.
• Series: Isaac Newton Institute Seminar Series; organiser: nobody.

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The study of wave propagation on black hole spacetimes has been an intense field of research in the past decades. This interest has been driven by the stability problem for black holes and by questions related to scattering theory. On Kerr black holes, the analysis of Maxwell’s equations and the equations of linearized gravity, can be simplified by introducing the Teukolsky equation, which offers the advantage of being scalar in nature. After explaining this reduction, I will present a result providing the large time leading-order term for initially localized and regular solutions of the Teukolsky equation, valid for the full subextremal range of black hole parameters and for all spins. I will explain how such a development follows naturally from the precise analysis of the resolvent operator on the real axis. Recent advances in microlocal analysis are crucially used to establish the existence and mapping properties of the resolvent.

• Speaker: Pascal Millet (Ecole Polytechnique)
• Monday 06 May 2024, 14:00-15:00
• Venue: MR13.
• Series: Partial Differential Equations seminar; organiser: Dr Greg Taujanskas.

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TBA

• Speaker: Luis García (UCL)
• Tuesday 14 May 2024, 14:30-15:30
• Venue: MR13.
• Series: Number Theory Seminar; organiser: Jef Laga.

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TBA

• Speaker: Beth Romano (King's College London)
• Tuesday 28 May 2024, 14:30-15:30
• Venue: MR13.
• Series: Number Theory Seminar; organiser: Jef Laga.

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We present some theoretical and experimental results on the dynamics of two phase turbulent buoyant plumes – both with particles and with bubbles – to demonstrate some of the effects of phase separation on the overall flow patterns, and flow behaviour and some of the instabilities that arise as a result. 

ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales

• Speaker:
• Thursday 02 May 2024, 16:00-17:00
• Venue: Discussion Room, Newton Institute.
• Series: Isaac Newton Institute Seminar Series; organiser: nobody.

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I will talk about anomalous diffusion in two problems at two very different length scales. (A) Compressible turbulence at the scale of parsecs. One of the cornerstones of incompressible turbulence is the Richardson’s law which states that the mean of the square of the distance between two Lagrangian particles grows as the cube of time:  R2 \sim t3. I will show from numerical simulations that this does not hold in shock dominated turbulence.  We will then generalize the multifractal model to include shocks and thereby rationalize the generalization of Richarson’s law to compressible turbulence. (B) Cell membrane at the scale of micrometers. Experiments show that the cell membrane is an exotic two-dimensional material which has both solid like and fluid like properties. An example of the former is the existence of a non-zero elastic shear modulus.  Evidence in support of the fluid like behavior are: (1) tether formation (2) lateral diffusion, simple of anomalous, of lipid molecules. We construct a model that can capture both of these aspects.  (A) is done in collaboration with Sadhitro De and Rahul Pandit, pre-print ( arXiv:2311.06836 ) .   (B) is done in collaboration with Vikash Pandey, pre-print(  arXiv:2404.12211).

ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales

• Speaker: Dhrubaditya Mitra (NORDITA)
• Wednesday 01 May 2024, 11:30-12:30
• Venue: Seminar Room 1, Newton Institute.
• Series: Isaac Newton Institute Seminar Series; organiser: nobody.

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The interplay of gravity with mass density inhomogeneities introduces natural (thermal) convection and represents the essential mechanism by which heat is transported in natural flows. Simultaneously, natural flows are often far more extended in the horizontal direction than in the vertical one. Motivated by these two observations and the various geo- and astrophysical applications (e.g. the solar convection zone), 3-dimensional Rayleigh-Bénard convection as the paradigm of thermal convection has been studied. This talk will cover some recent results from studying the impact of thermal (and mechanical) boundary conditions on large-scale flow structures in Rayleigh-Bénard convection by means of direct numerical simulations. It will be shown that thermal boundary conditions are crucial to the formation of long-living large-scale (turbulent) flow structures. In particular, a slow transient aggregation process — that only stops once the horizontal extent of the domain is reached — can be found once the fluid layer is subjected to Neumann-type constant heat flux boundary conditions. As a result, the temperature field in the domain is separated into one extended hot and another extended cold region. We trace this mechanism of self-organisation of flow structures back to secondary instabilities as well as an inverse cascade in spectral space. The talk will finish with a brief overview of our work on the identification of those large-scale flow structures by the use of unsupervised machine learning based on Lagrangian particle data.   Selected references [1] P P Vieweg, J D Scheel and J Schumacher, “Supergranule aggregation for constant heat flux-driven turbulent convection”, Phys. Rev. Research 3, 013231 (2021). DOI : 10.1103/PhysRevResearch.3.013231 [2] P P Vieweg, “Large-scale flow structures in turbulent Rayleigh-Bénard convection: Dynamical origin, formation, and role in material transport” (PhD thesis, TU Ilmenau, Germany, 2023). DOI : 10.22032/dbt.58334

ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales

• Speaker: Philipp Patrick Vieweg (University of Cambridge)
• Tuesday 30 April 2024, 11:30-12:30
• Venue: Seminar Room 1, Newton Institute.
• Series: Isaac Newton Institute Seminar Series; organiser: nobody.

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Two observational methods are currently being used to monitor post-deployment vaccine effectiveness against infection: the obvious crude method comparing rate of testing positive for infection per head of vaccinated population with that rate per head of unvaccinated population; and the test-negative case control (TNCC) method. The two methods give very different results. Various parties’ preference for choice of method appears to broadly coincide with their vested interests in getting the result that method gives. We want to know whether either method is reliable.

We suggest how this question could be examined, and will share what conclusions we reach.

• Speaker: Roger Sewell
• Thursday 02 May 2024, 19:15-21:30
• Venue: MRC Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge CB2 7EF.
• Series: Cambridge Statistics Discussion Group (CSDG); organiser: Peter Watson.

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Abstract not available

• Speaker: Dr Laura Filion, University of Utrecht
• Wednesday 20 November 2024, 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 Arcminute Microkelvin Imager – Large Array has been instrumental in the study of radio transients. In this talk I will give an overview of the current extragalactic transients monitoring program which is running on AMI -LA. To demonstrate the power of AMI -LA in improving our shock physics in extragalactic transients I will go through two examples of events where AMI -LA has been instrumental. Starting with the most relativistic systems: GRBs have been observed by AMI -LA from as early as 2012 with the ALARRM rapid follow up system. GRB 221009A , also known as the brightest of all time, has demonstrated the unparalleled temporal coverage achievable with AMI -LA from a few hours to over 100 days post burst. AMI -LA has also enabled us to draw conclusions that wouldn’t be possible with other facilities such as the jetted tidal disruption event AT2022cmc that was first reported in 2022. Due to the high cadence light curve with AMI -LA, we were able to prove for the first time, in a model independent manner that the radio emission originated from a highly relativistic outflow. Such a result has been vital in terms of our understand of tidal disruption events and can now infer the presence of off-axis jets such as AT2018hyz.

• Speaker: Dr. Lauren Rhodes (University of Oxford)
• Tuesday 30 April 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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Complex cellular landscapes of proteins include the dense, liquid-like droplet state and the solid-like amyloid state, in addition to the native state. The amyloid state, which is often pathological, can be formed through the deposition pathway from the native state and through the condensation pathway from the droplet state. I present a uniform framework to describe both pathways and identify mutations biasing towards these aggregation mechanisms. The droplet landscape model is a sequence-based, generic approach that simultaneously estimates the probability of droplet formation and the likelihood of state conversion. The method exploits that the interactions driving the droplet state sample disordered binding modes, whereas those governing the amyloid state sample ordered binding modes, which can simultaneously be estimated from sequence without information on the interaction partners. In addition, we predict the multiplicity of binding modes, that a given protein region can sample under different cellular conditions. I will demonstrate the application of the droplet landscape approach to both pathological and functional aggregates, in particular predicting mutations associated with amyotrophic lateral sclerosis and those facilitating muscle lineage development.

References M. Vendruscolo, M Fuxreiter (2022) Protein Condensation Diseases: Therapeutic Opportunities. Nat Commun 13, 5500, doi: 10.1038/s41467-022-32940-7 Hatos A, Tosatto SCE , Vendruscolo M, Fuxreiter M. (2022) FuzDrop on AlphaFold: visualizing the sequence-dependent propensity of liquid-liquid phase separation and aggregation of proteins. Nucleic Acids Res. 50(W1), W337 -44 Gönczi M., Teixeira JMC , Barrera-Vilarmau S., Mediani L. , Antoniani F. , Nagy TM, Fehér K., Ráduly Z., Ambrus V., Tőzsér J., Barta E., Kövér KE., Csernoch L., Carra S. , Fuxreiter M. (2023) Alternatively spliced exon regulates context-dependent MEF2D higher-order assembly during myogenesis Nature Communications 14, 1329. Horvath A, Vendruscolo M, Fuxreiter M. (2022) Sequence-based Prediction of the Cellular Toxicity Associated with Amyloid Aggregation within Protein Condensates Biochemistry 61, 2461-2469.

• Speaker: Professor Monika Fuxreiter, University of Padova
• Wednesday 01 May 2024, 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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“Consider a spherical cow in the vacuum…” – that’s how most physics problems start. A very simplified version of the real world that we can wrap our heads around and find answers using pencil and paper. Numerical models that simulate the components of the climate system are no different: we start simple and build it up as scientific knowledge of the system advances and technology allows us to explore smaller-scale processes. My research focuses on understanding ice-ocean interactions, focusing on the behaviour of icebergs and their impacts in the polar oceans, using said models. Join me as I explain my journey towards drawing a cow that looks less like a balloon and more like a quadruped.

• Speaker: Juliana Marson, University of Manitoba
• Wednesday 01 May 2024, 14:00-15:00
• Venue: BAS Seminar Room 1; https://bas-ac-uk.zoom.us/j/93676773793.
• Series: British Antarctic Survey - Polar Oceans seminar series; organiser: Dr Birgit Rogalla.

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Abstract not available

• Speaker: Hannah Dawson, University of Tasmania
• Wednesday 22 May 2024, 13:00-14:00
• Venue: BAS Seminar Room 1; https://bas-ac-uk.zoom.us/j/91268978510.
• Series: British Antarctic Survey - Polar Oceans seminar series; organiser: Dr Birgit Rogalla.

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Abstract not available

• Speaker: Professor Rachel Bearon, Professor of Mathematical Biology and Executive Dean of the Faculty of Natural, Mathematical & Engineering Sciences, KCL
• Thursday 16 May 2024, 12:00-13:00
• Venue: Centre for Mathematical Sciences MR2, CMS.
• Series: Rouse Ball Lectures; organiser: Sarah Jefferys.

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“Consider a spherical cow in the vacuum…” – that’s how most physics problems start. A very simplified version of the real world that we can wrap our heads around and find answers using pencil and paper. Numerical models that simulate the components of the climate system are no different: we start simple and build it up as scientific knowledge of the system advances and technology allows us to explore smaller-scale processes. My research focuses on understanding ice-ocean interactions, focusing on the behaviour of icebergs and their impacts in the polar oceans, using said models. Join me as I explain my journey towards drawing a cow that looks less like a balloon and more like a quadruped.

• Speaker: Juliana Marson, University of Manitoba
• Wednesday 01 May 2024, 14:00-15:00
• Venue: BAS Seminar Room 1; zoom.
• Series: British Antarctic Survey - Polar Oceans seminar series; organiser: Dr Birgit Rogalla.

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Abstract not available

• Speaker: Speakers to be confirmed
• Friday 17 May 2024, 14:00-17:00
• Venue: MR2.
• Series: Fluid Mechanics (DAMTP); organiser: Professor Grae Worster.

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Abstract not available

• Speaker: Jan Gutowski (Surrey)
• Tuesday 07 May 2024, 16:00-17:00
• Venue: CMS, MR9.
• Series: Mathematical Physics Seminar; organiser: Professor Maciej Dunajski.

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Abstract not available

• Speaker: Lionel Mason (Oxford)
• Tuesday 14 May 2024, 16:00-17:00
• Venue: CMS, MR9.
• Series: Mathematical Physics Seminar; organiser: Professor Maciej Dunajski.

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