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Viewing upcoming talks containing the keyword: 8
Theoretical Physics Discussion Group
Speaker: Chris Hooley (St Andrews)
Most theoretical models of condensed matter exhibit various phases, usually classified by describing the symmetries that they break with respect to the high-temperature, completely disordered phase. Between these phases are phase transitions. Either these are continuous (in which case they are critical points themselves) or they are first-order (in which case they often end at a critical end-point). At these critical points, the average size of correlated patches of the system diverges, which provides a challenge to theory. However, remarkable progress has in fact been possible. It has been based on the idea that, at these critical points, the physics becomes scale-invariant - or, given some plausible additional assumptions, conformally invariant. Until recently this progress was restricted to two-dimensional systems, because of the special mathematical properties of the conformal group in d=2. However, in the past few years an old method - the conformal bootstrap - has had a striking renaissance, being applied with great success to problems in dimensions higher than 2. Among its other achievements, it has provided estimates of the critical exponents of the d=3 Ising model that are ten or twenty times more accurate than the best available Monte Carlo results, with just a few months' computational effort. I shall give a self-contained introduction to this technique. No prior knowledge of conformal field theory or the conformal bootstrap is required! For those interested in reading further about it, here are a couple of references:  S. El-Showk, M.F. Paulos, D. Poland, S. Rychkov, D. Simmons-Duffin, and A. Vichi, "Solving the 3D Ising model with the conformal bootstrap," Phys. Rev. D 86, 025022 (2012): http://journals.aps.org/prd/abstract/10.1103/PhysRevD.86.025022  F. Kos, D. Poland, and D. Simmons-Duffin, "Bootstrapping mixed correlators in the 3D Ising model," JHEP 11 (2014) 109: http://http://link.springer.com/article/10.1007%2FJHEP11%282014%29109
On: March 8, 2016 From: 15h00 To: 16h00View talk
Speaker: Elena Besley (Nottingham)
There are many instances in everyday life where small particles can acquire an electrical charge of the same sign. Examples include aerosol and water droplets in clouds, dust particles in space, toner particles in ink-jet printers, and suspensions of colloidal particles. As the particles carry a charge of the same sign, either positive or negative, they are expected to repel one another; however, under certain circumstances their interaction can be strongly attractive. For conducting particles, this effect was identified by William Thomson (later Lord Kelvin) who in 1845 developed a theory showing that the attraction is due to differences in the magnitude of the image charges induced in particles in cases where either their size or charge differs.1
Until recently there was no stable mathematical solution to the fundamental problem of calculating the electrostatic interaction between charged particles of dielectric material, mainly due to significant mathematical complexity of the problem. To date a variety of solutions have been offered, many of which present mathematical derivations with limited applicability, numerical complications or poor convergence at short particle separations.
I will report a comprehensive theory2,3 with universal relevance to the electrostatic properties of closely interacting particles of arbitrary size and charge.4-7 Calculations of surface charge density provide evidence of the physical effects, which cause polarisable particles carrying the same sign of charge to attract one another. The results show that attraction requires a mutual polarisation of charge, leading to regions of negative and positive surface density, at short separation distances. In this talk, the new theory will be discussed together with its relevance across multiple disciplines involving interactions of small particles. Our explanation of how particles interact with one another may also contribute to the design of thin films and surface assemblies with novel properties.
1. Thomson, W. (Lord Kelvin), J. Math. Pures Appl., 10: 364 (1845); J. Math. Pures Appl., 12: 256 (1847)
2. Bichoutskaia E., Boatwright A. L., Khachatourian A., Stace A. J., J. Chem. Phys., 133: 024105 (2010)
3. Khachatourian, A., Chan, H.-K., Stace, A. J., Bichoutskaia, E., J. Chem. Phys., 140: 074107 (2014)
4. Stace, A. J., Boatwright, A. L., Khachatourian, A., Bichoutskaia, E., J. Coll. Inter. Sci., 354: 417 (2011)
5. Stace, A. J., Bichoutskaia, E., Phys. Chem. Chem. Phys., 13: 18339 (2011)
6. Stace, A. J., Bichoutskaia, E., Soft Matter, 8: 6210 (2012)
7. B. Lindgren, E., Chan, H.-K., Stace, A. J., Besley, E. Perspective Article, Phys. Chem. Chem. Phys.
DOI: http://dx.doi.org/10.1039/C5CP07709E (2016)
On: March 9, 2016 From: 15h30 To: 16h30View talk
Physics and Astronomy Colloquia
Speaker: Dr Gaitee Hussain (ESO)
Solar-type stars display signs of magnetic activity at all wavelengths, from energetic X-ray and UV flares to variability in photometric light curves caused by large cool spots. Several factors determine the magnetic activity level observed in all of these diagnostics; the key ones being the stellar rotation rate and the internal structure of the star. In the past two decades advances in instrumentation have facilitated the direct detection of surface magnetic fields in cool stars. Combined with powerful techniques based on medical imaging principles we can actually reconstruct the detailed surface magnetic field maps on stars covering a range of evolutionary states.
Stellar magnetic fields play a particularly important role in young stars that are only a few million years old - a key stage in a young planetary system, as this is when gas giant planets form around their host stars. I will present the latest results from our surveys of young stars, showing how the surface magnetic field properties depend on their evolutionary stages. I will also show how our detailed surface maps can be used to build realistic models of the “weather” around stars that host planetary systems, and therefore better understand the environments around which planets form and evolve.
On: March 11, 2016 From: 10h00 To: 11h00View talk
Speaker: George Malliaras (EMStE)
One of the most important scientific and technological frontiers of our time lies in the interface between electronics and the human brain. Interfacing the most advanced human engineering endeavor with nature’s most refined creation promises to help elucidate aspects of the brain’s working mechanism and deliver new tools for diagnosis and treatment of a host of pathologies including epilepsy and Parkinson’s disease. Current solutions, however, are limited by the materials that are brought in contact with the tissue and transduce signals across the biotic/abiotic interface. The field of organic electronics has made available materials with a unique combination of attractive properties, including mechanical flexibility, mixed ionic/electronic conduction, enhanced biocompatibility, and capability for drug delivery. I will present examples of organic-based devices for recording and stimulation of brain activity, highlighting the connection between materials properties and device performance. I will show that organic electronic materials provide unparalleled opportunities to design devices that improve our understanding of brain physiology and pathology, and can be used to deliver new therapies.
On: March 23, 2016 From: 15h30 To: 16h30View talk
Physics and Astronomy Colloquia
Noninvasive spectrophotometry and a phototherapy as a section of the modern medical and physics research in Moscow Regional Research and Clinical Institute "MONIKI"
Speaker: Dr D A Rogatkin (Moscow Regional Research and Clinical Institute "MONIKI")
Modern semiconductor lasers as well as LEDs are widely used in medicine today. One of the biggest areas of their application are noninvasive (in vivo, in situ) diagnostics, based on principles of spectrophotometry and laser spectral analysis, and a phototherapy. This presentation is a review of selected studies in this field carried out in one of the oldest and largest Russian medical research and practical center – Moscow Regional Research and Clinical Institute (MONIKI) named after M. F. Vladimirskiy. All studies were aimed at the development and application of combined noninvasive spectrophotometry diagnostic technique in real clinical practice and in different fields of medicine, in phototherapy, for example. The specially devised multifunctional laser diagnostic system “LAKK-M” was used as a noninvasive diagnostic tool in the majority of these studies, allowing a combination of several diagnostic methods such as laser fluorescence spectroscopy, laser Doppler flowmetry, tissue reflectance oximetry, etc. in a single experiment. It allows for physicians a complex examination of the so-called blood microcirculation system - one of the primary object, which is affected in tissues at a phototherapy. All these diagnostic methods, for example, didn’t confirm the stimulation effect on the blood microcirculation in skin or mucosa at a Low Level Laser Irradiation (LLLI) with the power density below 50 mW/cm2 and irradiation time up to 5-6 minutes. Above this threshold the heating on 0,8…1 0C of tissue in the field of irradiation and the corresponding synchronous increase of all parameters of microhemodynamics were observed. The report also discusses the problems and prospects of development of researches on the blood microcirculation with the use of the non-invasive spectrophotometry.
On: April 1, 2016 From: 10h00 To: 11h00View talk
Speaker: Daniel Leznoff (Simon Fraser University, Canada)
The spectroscopic and redox properties of metallophthalocyanines (MPcs) are active areas of research. MPc complexes can be successively reduced using chemical, electrochemical, or photochemical methods to give rise to species containing reduced Pc3-, Pc4-, Pc5-, or Pc6-ligands. These species are usually generated and characterized in situ and have only very rarely been isolated for structural characterization, likely due to the extreme air and moisture sensitivity of these complexes. In particular, there are few examples of phthalocyanines with early-transition metals - despite their rich reactivity in organometallic chemistry - and thus we focused on this underdeveloped area of the periodic table with respect to new PcM complexes.
Using rigorously air- and moisture-free conditions, the isolation and structural characterization of highly reduced Pcn- (n=3,4,5) complexes – among the first ever reported - with early transition-metals, including Sc, Zr, Nb and Cr, will be described. The electronic structure of these materials will also be examined, using a combination of UV-vis-NIR and ESR spectroscopies, X-ray diffraction studies and DFT calculations.
Our efforts to prepare and characterize very rare mononuclear PcAu(II) complexes based on a prior report[2a] will also be discussed, in which we present the first synthesized and structurally characterized gold-containing phthalocyanines.[2b]
1. E.W.Y. Wong, C.J. Walsby, T. Storr, D.B. Leznoff, Inorg. Chem., 2010, 49, 3343-3350; E.W.Y. Wong, D.B. Leznoff, J. Porph. Phthalo., 2012, 16, 154-162; R. Platel, W. Zhou, T.T. Tasso, T. Furuyama, N. Kobayashi, D.B. Leznoff, Chem. Commun., 2015, 5986-89; W. Zhou, R. Platel, T.T. Tasso, T. Furuyama, N. Kobayashi, D.B. Leznoff, Dalton Trans., 2015, 44, 13955.
2. (a) A. MacCragh and W.S. Koski, J. Am. Chem. Soc., 1965, 87, 2496. (b) E.W.Y. Wong, A. Miura, M.D. Wright, Q. He, C.J. Walsby, S. Shimizu, N. Kobayashi and D.B. Leznoff Chem. Eur. J. 2012, 18, 12404.
On: April 6, 2016 From: 15h30 To: 16h30View talk