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Physics Colloquia

Fridays at 1200hrs In Newman F


12 October 2007 The role of the cryosphere in the climate system
Jeff Ridley, the Met Office

Predictions of sea level rise require an understanding the behaviour of the cryosphere with changing climatic forces and the feedbacks on the climate system. The cold high latitude ocean is a crucial sink for atmospheric carbon, and controls the overturning of the deep ocean. This talk describes how climate models may be used to ascertain the contribution of ice sheets and glaciers to sea level rise, and their potential to shut down the ocean conveyor. The impact of natural variability in regional atmospheric and ocean circulation on high latitude processes is compared with that of climate feedbacks from sea ice and cloud. The reduction of uncertainties in sea level rise prediction requires the development of new physical processes.

19 October 2007 From transit spectroscopy to direct detection: a roadmap to exoplanet characterization
Giovanna Tinetti, University College London

In the past decade, more than 250 planets orbiting other stars (extrasolar planets) were discovered using indirect detection techniques. Most recent observations of primary and secondary eclipses with Hubble Space Telescope and Spitzer of transiting extrasolar giant planets (EGPs), suggest that emitted and transmitted spectra of EGPs can be used to infer many properties of their atmospheres and internal structure, including chemical element abundances, cloud/haze optical properties, temperature-pressure profiles, density and evolution. Larger and technologically more challenging concept missions have been proposed to directly detect exoplanets in the near future. These projects are expected to provide our first opportunity to study spectroscopically the global characteristics of Super-Earths and Earth-size planets beyond our solar system, and even search for signs of habitability and life. To understand our ability to characterize Giant and Terrestrial exoplanets, we have generated synthetic planetary spectra (emitted, reflected and transmitted) of these exotic environments, using a set of chemistry, climate and radiative transfer models. This presentation will focus on the detectability of spectral signatures of crucial atmospheric molecules and surface characteristics with present and future observations.

26 October 2007 QED in a Pencil Trace
Kostya Novoselov, University of Manchester

When one writes by a pencil, thin flakes of graphite are left on a surface. Some of them are only one angstrom thick and can be viewed as individual atomic planes cleaved away from the bulk. This strictly two dimensional material called graphene was presumed not to exist in the free state and remained undiscovered until the last year. In fact, there exists a whole class of such two-dimensional crystals. In grapheme, electrons move with little scattering over huge (submicron) distances as if they were completely insensitive to the environment only a couple of angstroms away. Moreover, electron transport in graphene is governed by the Dirac equation so that they mimic relativistic particles with zero rest mass.

2 November 2007 Geometry, light, and a wee bit of magic
Ulf Leonhardt, University of St. Andrews

Invisibility devices, quantum levitation and optical black holes have something in common: they use the fact that dielectric media act as effective geometries, changing the way light perceives space and time. In this lecture, these connections will be elucidated.

9 November 2007 Water at model membranes: structure, dynamics and biomolecular sensing
Mischa Bonn, FOM Institute AMOLF, Amsterdam.

The interaction of lipids with water drives the self-assembly process of biological membranes. It has been a challenge to elucidate the detailed role of water in biomolecular processes, including those occurring at the membrane surface. We use surface-specific vibrational spectroscopies to study the properties of the one molecular layer water directly interacting with model membranes. Our results reveal marked differences between membrane-bound water and other types of interfacial water.

16 November 2007 Evidence that Drug Molecules Eat Their Way Through Membranes
Oscar Ces, Imperial College London.

To get to their site of action drug molecules must cross multiple cell membrane barriers. At present they are believed to do so by one of two major mechanisms: active or passive translocation. Passive translocation involves diffusion, with the concentration gradient across membranes acting as the driving force. Active transport on the other hand is mediated by special carrier proteins and is of particular relevance to larger drug molecules. These mechanisms however are not yet fully understood and do not account for many experimental observations. This presentation highlights our observation that one of the largest classes of pharmaceutical drug molecules, the cationic amphiphilic drugs, or CADs, do so via a novel mechanism driven by a catalytic reaction that degrades the membrane. Our results demonstrate that the entire process, from drug adsorption to drug release within micelles occurs on a timescale of seconds, compatible with in vivo drug diffusion rates. Given the rate at which this occurs it is probable that this process is a significant mechanism for drug transport.

23 November 2007 Measuring the electric dipole moment of the neutron - a very small measurement with very big consequences
David Wark, Imperial College London/Rutherford Appleton Laboratory

First pointed out in the 60s, in order to get from a Big Bang of pure energy to our current universe (which is strongly dominated by matter) the laws of physics must be different for particles and antiparticles (a phenomenon called CP violation). IF CP violation exists beyond the Standard Model, it is quite likely to induce a static electric dipole moment in the neutron. This talk will discuss this theoretical background and then concentrate on efforts to observe such an effect using ultra-cold neutrons. This involves cooling neutrons to a fraction of a degree Kelvin, at which point they travel at walking pace, can be controlled with water valves and bath plugs, and stored in a bottle like milk. The neutrons are then used to make an "atomic clock", and measurements of shifts in the frequency of that clock when subjected to a high electric field hold out the promise of finally giving an answer to the question: Why is the Universe made of matter?

30 November 2007 Gravitational Lensing as a Universal Astrophysical Tool: Giant Arcs, Multiple Quasars and Extrasolar Planets
Joachim Wambsganss, Astronomisches Rechen Institut, Heidelberg

Deflection of light by gravity was predicted by Einstein's Theory of General Relativity and observationally confirmed in 1919. Only in 1979, gravitational lensing became an observational science when the first doubly imaged quasar was discovered. Today lensing is a booming part of astrophysics and cosmology. A whole suite of lensing phenomena have been investigated since: multiple quasars, giant luminous arcs, quasar microlensing, galactic microlensing, Einstein rings, arclets, weak gravitational lensing and cosmic shear. The most recent lensing application is the detection of extrasolar planets. Lensing has contributed significant new results in areas as different as the cosmological distance scale, mass determination of galaxy clusters, physics of quasars, searches for dark matter in galaxy halos, structure of the Milky Way, stellar atmospheres and exoplanets. A guided tour through some of these lensing applications will illustrate that gravitational lensing has established itself as a very useful universal astrophysical tool.


For more details contact Euan Hendry.


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