Mae'r cynnwys hwn ar gael yn Saesneg yn unig.
We run a regular programme of seminars for staff and students.
All seminars will take place in Queen's Buildings North, Room N/3.28 unless otherwise stated.
This seminar will focus on three absorbing lines of research into nanophotonics, representing three consecutive time scales of the physics involved. It will begin with the first experimental observation of a chiroptical effect that was predicted 40 years ago [1,2]. Next, it will consider the smallest backjets (‘nanojets’) ever created and will discuss how they can serve to assemble novel metamaterials [3,4]. Finally, drawing inspiration from steampunk science fiction, it will illustrate how a vapour stabilization technique can greatly enhance quantum sensors . When light shines on metal nanoparticles (NPs), it is initially (fs timescale) absorbed by the electrons. These electrons give rise to “instantaneous” nonlinear optical processes, such as second harmonic (SH) generation, whereby two photons at the fundamental frequency are converted into a single photon at twice that frequency \Omega. This SH generation is promising for applications, based on frequency conversion (for laser manufacturing), on nonlinear optical characterization[6,7] (e.g. microscopy) and on metasurfaces (for ultrathin telecom components). Our team recently demonstrated that in chiral metal NPs (those that lack mirror symmetry) the intensity of light, scattered at the SH frequency, is proportional to the chirality, see Fig. 1 [in the poster]. This effect was predicted 40 years ago, it is >10,000 more sensitive than corresponding linear optical effects and it could enable safer pharmaceuticals.
Taking little other than common cuticle, loaded with a small amount of melanin, butterflies have evolved some stunning metasurfaces. Often only microns thick, these act as selective reflectors and polarizers as well as being sometimes very strong scatterers (white) or very strong absorbers (black) of electromagnetic radiation. Similarly surface-structured metals, metasurfaces, can lead to unexpected effects: for example selective absorption, even at long wavelengths where metals are expected to behave as almost perfect mirrors, or even negative refraction.
The membranes of cells are made for a large part of lipids assembled in bilayers. Membranes behave as 2D-liquid, but they also have peculiar mechanical properties since they can be bent in the perpendicular direction, as well as stretched. The Brownian motion of inclusions embedded into membranes, such as trans-membrane proteins is not trivial and has been well described by the long-time accepted Saffman-Delbrück model. However, rich behavior arises for inclusions with non-symmetric shapes, that locally bend membranes. Coupling between inclusions' distribution and density can be observed as well as deviation to inclusion mobility described by Saffman-Delbrück. I will illustrate with some examples these peculiar properties specific to fluid membranes, and discuss some consequences for living cells.
Supernovae are the incredibly luminous deaths of stars that play vital roles in chemical enrichment, galaxy feedback mechanisms, and stellar evolution. In particular, Type Ia supernovae, the explosions of white dwarf stars in binary systems, were instrumental in the discovery of dark energy. However, what are their progenitor systems, and how they explode, remains a mystery. There is increasing observational evidence that there are multiple ways in which white dwarfs can explode. I will review the status of what we know about the stellar systems that produce Type Ia supernovae, as well as discuss the recently discovered zoo of peculiar transients that are also predicted to result from the explosions of white dwarfs, such as He-shell mergers, tidal disruption events, violent mergers. Distinguishing between these explosion scenarios and understanding their diversity is vital for producing the best samples for future precision measurements of the cosmological parameters.
Despite the fact that most of the radiation emitted in the universe since the Big Bang is in the THz range, readily available THz sources did not emerge until the end of the 20th century. Also, the detection of THz waves was proven to be very challenging. Altogether slowed down the adoption of THz waves (and technology), making this spectral window sandwiched between the optical and microwave regimes (ca. 0.3 – 3 THz; wavelength range between 1 mm and 0.1 mm) relatively unexplored. A great deal of effort is now carried out to develop such spectrum as it holds promise for next generation of wireless communication, medical diagnosis, security applications (chemical fingerprinting and standoff screening) and industrial control processes. The potential of THz in these realms arises from the ability of THz radiation to provide more bandwidth than microwaves/millimetre-waves and to pass through many optically opaque materials (e.g., clothing, paper, etc.), as well as the fact that specific rotations, vibrations or librations of molecules and molecular aggregates occur in this frequency range. In addition, THz radiation is non-ionizing and safe, unlike X-rays. Terahertz time-domain spectroscopy has emerged as a main spectroscopic modality to fill this so-called THz-gap and this seminar will showcase the use of the technique for two applications: (1) development of flexible low-loss low-dispersion waveguides ('cables'); (2) understanding of the extraordinary transmission phenomenon.
To be confirmed.
To be confirmed.
Our basic picture of condensed matter involves drawing a distinction between 'order' and 'disorder', as evidenced, respectively, by Bragg peaks and blobs or rings of scattering. However, modern, high resolution X-ray and neutron scattering sources can resolve a third type of scattering: 'pinch points' - near singularities in the structure factor that indicate special type of highly correlated state that is neither entirely ordered, nor entirely disordered. In this talk I will explain how pinch points are in part an illusion and in part an important diagnostic of a very special state. To explain this, I will refer to several types of material and meta-material, including water ice, spin ice, artificial spin ice, ionic solids and models of dipolar liquids, electrolytes and superfluids. I will also point out analogies with general physics.
Astrometry from space has unique advantages over ground-based observations: the all-sky coverage, relatively stable and temperature- and gravity-invariant operating environment delivers precision, accuracy and sample volume several orders of magnitude greater than ground-based results. Even more importantly, absolute astrometry is possible. The European Space Agency Cornerstone mission Gaia is delivering that promise. Gaia provides 5-D phase space measurements, 3 spatial coordinates and two space motions in the plane of the sky, for a representative sample of the Milky Way’s stellar populations (over 1 billion stars, being ~1% of the stars over 50% of the volume). Full 6-D phase space data is delivered from line-of-sight (radial) velocities for the 300million brightest stars. These data make substantial contributions to astrophysics and fundamental physics on scales from the Solar System to cosmology, from asteroids to gravitational waves. A few example results illustrating the rapidly changing understanding of the history of our Milky Way will be given.
To be confirmed.
To be confirmed.
To be confirmed.
Microelectromechanical (MEMS) and nanoelectromechanical systems (NEMS) are ideal candidates for exploring quantum fluids, since they can be manufactured reproducibly, cover the frequency range from hundreds of kilohertz up to gigahertz and usually have very low power dissipation.
Their small size offers the possibility of probing the condensate on scales comparable to, and below, the coherence length. That said, there have been hitherto no successful measurements of NEMS res- onators in the liquid phases of helium.
Here we report the operation of doubly-clamped aluminum nanocantilevers in superfluid 4He at temperatures spanning the superfluid transition. The devices are shown to be very sensitive detectors of the superfluid density and the normal fluid damping. We use nanomechanical resonators with extremely high quality factor to probe superfluid 4He at millikelvin temperatures, as well.
The high sensitivity of these devices to thermal excitations in the environment makes it possible to drive them using the momentum transfer from phonons generated by a nearby heater. This so-called phonon wind is a reverse thermomechanical effect that until now has never been demonstrated.
Analysing, constructing, and translating between graphical, pictorial, and mathematical representations of physics ideas and reasoning flexibly through them (representational competence) is a key characteristic of expertise. It is challenging for learners to develop, but little instruction is explicitly designed with this purpose in mind.
This talk will focus on the role of interactive computer simulations with appropriate scaffolding in supporting representational learning. We have been developing combined simulation-tutorials for the learning of quantum mechanics, whereby students first work on problems independently, constructing representations they will later see in the simulation, followed by further problems with simulation support.
This talk will describe the structure and sequencing of the simulation-tutorials and present results from pre-, mid- and post-tests to assess student learning.