Viewing upcoming talks in: Physics and Astronomy Colloquia
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Physics and Astronomy ColloquiaA multi-tracer view on galaxies since cosmic noon: census, scaling relations and evolution
Speaker: Dr Stijn Wuyts (University of Bath)
Studies of the structural evolution of galaxies since the peak epoch of cosmic star formation 10 billion years ago have matured in recent years by combining the power of deep imaging lookback surveys and highly multiplexed integral-field spectroscopy. With observations from the rest-frame ultraviolet to infrared we not only have a census of the stars within galaxies, but also probe their dust, ionised and molecular gas content. Using diagnostics of gravitational and non-gravitational motions I will discuss the disk nature and mass budget of star-forming galaxies at cosmic noon, their turbulent interstellar medium, and the feedback processes responsible for large-scale galactic outflows. I will contrast early star-forming galaxies to their quiescent counterparts at the same epoch, and will draw connections to their likely descendants at the present day.
On: November 1, 2019 From: 10h00 To: 11h00
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Physics and Astronomy ColloquiaPolaritonic networks as a route to unconventional computing
Speaker: Prof. Natalia Berloff (University of Cambridge)
Polariton ic networks for large scale hard optimisation Natalia G. Berloff Department of Applied Mathematics and Theoretical Physics, University of Cambridge and Skolkovo Institute of Science and Technology Recently several gain - dissipative platforms based on the networks of optical parametric oscillators [1], coupled lasers [2] and various non - equilibrium Bose - Einstein condensates such as exciton - polariton[3], atomic [4] and photon [5] condensates have been proposed as analogue Hamiltonian simulators for solving large - scale hard optimisation problems. Such platforms use an approach to finding the global minimum of spin Hamiltonians which is different from quantum annealers or quantum computers. However, in general, the parameters of such spin Hamiltonians when realised by gain - dissipative simulators depend on the no de occupancies that are not known a priori , which limits the simulators applicability to the classes of problems easily solvable by classical computations. I show how to overcome this difficulty and formulate algorithms for solving the NP - hard large - scale optimisation problems such as constant modulus continuous quadratic optimisation [6] and quadratic binary optimisation for any general matrix [7] . T o solve such problems any gain - dissipative simulator has to implement a feedback mechanism for the dynamical adjustment of the gain and coupling strengths , so that occupancy of each node is the same. I will illustrate the work of such a simulator using the polariton graph platform that we recently realised in experiments [3]. The estimates of the time operation of the physical implementation of the gain - dissipative simulato rs for large matrices s uggest the speed - up of the several orders of magnitude in comparison with classical computations [8] . Besides acting as analog Hamiltonian optimizers, the networks of exciton - polaritons are a flexible universal platform to realise a vast array of known and extensively studied systems of coupled oscillators such as Kuramoto, Sakaguchi - Kuramot o, Stuart - Landau, Lang - Kobayashi oscillators and beyond [9 ]. The networks of polariton condensates are therefore capable of implementing various regimes producing Chimera states, exotic spin glasses and large scale secondary synchronization of oscillations , probe new exotic dynamical regimes and to create novel states of matter.
References: [1] Marandi, A., et al. Network of time - multiplexed optical parametric oscillators as a coherent Ising machine . Nat. Phot. 8 , 937 - 942 (2014). [2] Nixon, M., et al. Observing geometric frustration with thousands of coupled lasers. Phys. Rev. Lett. 110 , 184102 (2013). [3] Berloff, N. G. et al. Realizing the classical XY Hamiltonian in polariton simulators. Nat. Mat . 16 (11), 1120 (2017). [4] Vaidya, D. V. et al. Tunable - range, photon - mediated atomic interactions in multimode cavity QED. Phys. Rev. X 8 (1), 011002 (2018). [5] Dung, D. et al. Variable potentials for thermalized light and coupled condensates. Nat. Phot. 11 (9), 565 (2017) [6] Kalinin K.P. and N.G. Berloff "Networks of non - equilibrium condensates for global optimization" New J . of Phys ., 20 113023 (2018) [7] Kalinin K. P. and N.G.Berloff "Simulating Ising and Potts models and external fields with non - equilibrium condensates," Phys . Rev . Lett s ., 121 , 235302 (2018) [ 8 ] Kalinin K.P. and N.G.Berloff "Global optimization of spin Hamiltonians with gain - dissipative systems," Sci . Rep ., 8 ,17791 (2018) [9] Kalinin K.P. and N.G.Berloff “ Polaritonic network as a paradigm for dynamics of coupled oscillators ” , arXiv:1902.09142 Download PDFOn: November 8, 2019 From: 10h00 To: 11h00
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Physics and Astronomy ColloquiaEPR of heme proteins in mesoporous matrices – a successful match between spectroscopy, protein research, and hybrid material and biosensor development
Speaker: Prof. Sabine Van Doorslaer (Antwerp University)
The incorporation of proteins in mesoporous materials provides a promising tool to create new hybrid materials for biosensing or biocatalysis applications. The confinement of the proteins in these materials may stabilize the protein structure and even improve protein activity, but finding the optimal incorporation conditions and best protein-matrix matches is not trivial. This requires not only an in-depth understanding of the biochemical working of the used proteins under diverse chemical conditions and knowledge of the characteristics of the mesoporous host, it also calls for a variety of characterization tools that can probe the individual components as well as the hybrid materials. Although simple optical absorption techniques can be used to follow the adsorption and incorporation of the proteins, the faith of the proteins inside the synthetic host needs to be addressed by different techniques. Using the example of the incorporation of heme proteins, more specifically globins and peroxidases, in mesoporous titania and silica, it will be shown that EPR can provide unique information that cannot be obtained by other characterization methods. Moreover, EPR can play a role in monitoring and understand radical-formation reactions during the working of the final electrochemical biosensor. This requires developments of improved in-situ EPR hydrodynamic electrochemical cells, allowing fast and easy replacement of parts and adjustments to electrodes.
On: November 15, 2019 From: 10h00 To: 11h00
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Physics and Astronomy ColloquiaWhat we learned from the first interstellar comets, ‘Oumuamua and Borisov, and what we can do with the next ones
Speaker: Dr Colin Snodgrass (University of Edinburgh)
In 2017 a strange object was discovered by near-Earth asteroid surveys, with the appearance of a small asteroid, but an orbit that showed it to have come from another star. I will describe what we learned about this object, called ‘Oumuamua, and what we are now learning about the second interstellar object, comet Borisov, which was discovered in September this year and is currently being observed as it approaches the Sun. In addition to what we can measure with telescopes, I will also describe a newly approved ESA space mission that may one day investigate an interstellar object up close: Comet Interceptor.
On: November 22, 2019 From: 10h00 To: 11h00
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Physics and Astronomy ColloquiaHow does silicate dust form around oxygen-rich AGB stars?
Speaker: Prof John Plane ()
On: November 29, 2019 From: 10h00 To: 11h00
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