Dissipative Liouville Cosmology: A Case Study

We consider solutions of the cosmological equations pertaining to a dissipative, dilaton-driven off-equilibrium Liouville Cosmological model, which may describe the effective field theoretic limit of a non-critical string model of the Universe. The non-criticality may be the result of an early-era catastrophic cosmic event, such as a big-bang, brane-world collision etc. The evolution of the various cosmological parameters of the model are obtained, and the effects of the dilaton and off-shell Liouville terms, including briefly those on relic densities, which distinguish the model from conventional cosmologies, are emphasised.Comment: 19 pages latex, 11 eps figures incorporate

To the Crucible: An Irish engagement with the Greek crisis and the Greek left

A monumental drama is playing out before our eyes. It is a true Greek tragedy. The plot: A society is being pushed to its limits. The denouement is not yet determined, but survival is at stake and prospects are precarious. Greece is at the sharp end of a radical and risky experiment in how far accumulation by dispossession can go, how much expropriation can be endured, how far the state can be subordinated to the market. It is a global narrative, but the story is a few episodes ahead here. Greece is the crucible. It is a caldron where concentrated forces are colliding in a process that will bring forth either a reconfiguration of capitalism or the dawn of its demise

Characterisation of Single Biomolecules With Optoplasmonic Resonators

Biomolecules can be detected through induced changes in the optical whispering-gallery mode (WGM) resonance in a circularly symmetric dielectric. The spatial and temporal confinement of light in a WGM is further complemented by coupling to the localised surface plasmons (LSPs) of metallic nanoparticles attached to the WGM resonator. LSP-WGM hybridisation allows for the optical readout of single-molecule surface reactions on gold nanoantennae, the mechanisms for which are not yet fully understood from a theoretical perspective. The specificity of this modality is, moreover, a subject of intense research. In this thesis, we propose three strategies for characterising molecules with light. The first strategy is a prototype polarimeter that differentiates chirality based on a signal-reversible Faraday effect in a magneto-optical WGM microcavity. Thermal tuning integrated into the resonator minimises geometrical birefringence, in turn maximising Faraday rotation to optimise chiral sensitivity. There we endeavour to resolve single-molecule chirality. Without engineering reconsiderations, however, the polarimeter is found to be limited to bulk chiral analysis. The second strategy is an (optoplasmonic) LSP-WGM resonator with chiral gold nanoantennae. Signals from the molecules conjointly show a correlation with the molecular weight and diffusivity of detected DL-cysteine and poly-DL-lysine. Aside from these features, the sensing site heterogeneity on the chiral gold nanoparticles impedes chiral discrimination. The third strategy is a novel reaction scheme adapted to the optoplasmonic sensor. Aminothiol linkers functionalise the gold surface via amine-gold anchoring, setting up cyclical interactions with thiolated analytes by thiol/disulfide exchange. Unexpected perturbations in the LSP-WGM resonance are observed, such as linewidth oscillation without resonance shift attributed to optomechanical coupling between LSPs and the vibrational modes in a given analyte. This offers a new form of spectroscopy wherein single biomolecules could be characterised by their mass, size, and composition through monitoring secondary parameters of the optoplasmonic resonance.European Commissio

Ultracold gases far from equilibrium

Ultracold atomic quantum gases belong to the most exciting challenges of modern physics. Their theoretical description has drawn much from classical field equations. These mean-field approximations are in general reliable for dilute gases in which the atoms collide only rarely with each other, and for situations where the gas is not too far from thermal equilibrium. With present-day technology it is, however, possible to drive and observe a system far away from equilibrium. Functional quantum field theory provides powerful tools to achieve both, analytical understanding and numerical computability, also in higher dimensions, of far-from-equilibrium quantum many-body dynamics. In the article, an outline of these approaches is given, including methods based on the two-particle irreducible effective action as well as on renormalisation-group theory. Their relation to near-equilibrium kinetic theory is discussed, and the distinction between quantum and classical statistical fluctuations is shown to naturally emerge from the functional-integral description. Example applications to the evolution of an ultracold atomic Bose gas in one spatial dimension underline the power of the methods. The article is compiled from the notes for lectures held at 46. Internationale Universitaetswochen fuer Theoretische Physik 2008 in Schladming, Austria.Comment: 59 pages, 26 figures; Compiled from notes for lectures held at 46. Internationale Universitaetswochen fuer Theoretische Physik 2008 in Schladming, Austria. To be published in Eur. Phys. J. Special Topic

Strategies for applying active seismic subglacial till characterization methods to valley glaciers

Thesis (M.S.) University of Alaska Fairbanks, 2017Subglacial materials play an important role in glacier dynamics. High pore-pressure, high porosity (dilatant) tills can contribute to high basal motion rates by deforming. Amplitude Variation with Angle (AVA) analysis of seismic reflection data uses the relationship between basal reflectivity and reflection incidence angle to characterize the subglacial material. This technique can distinguish between dilatant tills and less-porous, non-deforming (dewatered) tills due to their distinctive reflectivity curves. However, noise from crevasses and glacier geometry effects can complicate reflectivity calculations, which require a source amplitude derived from the bed reflection multiple. We use a forward model to produce synthetic seismic records, including datasets with and without visible bed reflection multiples. The synthetic data are used to test source amplitude inversion and crossing angle analysis, which are amplitude analysis techniques that do not require absolute reflectivity calculations. We and that these alternative methods can distinguish subglacial till types, as long as reflections from crevasses do not obscure the bed reflection. The forward model can be used as a planning tool for seismic surveys on glaciers, as it can predict AVA success or failure based on crevasse geometries from remote sensing data and glacier bed geometry from radar or from a worst-case-scenario assumption of glacier bed shape. Applying lessons from the forward model, we perform AVA on a seismic dataset collected from Taku Glacier in Southeast Alaska in March 2016. Taku Glacier is a valley glacier thought to overlay thick sediment deposits. It has been the subject of numerous studies focusing on its ice-sediment interactions. Our analysis indicates that Taku Glacier overlies unconsolidated tills with porosity values greater than 33 %, though because of uncertainties due to the lack of a bed reflection multiple, it is possible that the tills are not dilatant

Photonic crystal antireflection coatings, surface modes, and impedances

We present a rigorous definition of a wave impedance for 2D rectangular and triangular lattice photonic crystals (PCs), in the form of a matrix. Reflection and transmission at an interface between PCs can be represented by matrices that relate the Bloch mode (eigenmode) amplitudes in the two PCs; we show that these matrices, which are multi-mode generalisations of reflection and transmission coefficients, may be calculated from the PCs' impedances that we define. Given the impedances and Bloch factors (propagation constants) of a collection of PCs, the reflection and transmission properties of arbitrary stacks of these PCs may be calculated efficiently using a few matrix operations. Therefore our definition enables PC-based antireflection coatings to be designed efficiently: some computationally expensive simulations are required in an initial step to find a range of PCs' impedances, but then the reflectances of every coating that consists of a stack of these PCs can be calculated without any further simulations. We first define the PC impedance from the transfer matrix of a single PC layer (i.e., a grating). Since transfer matrix methods are not especially widespread, we also present a method and associated source code to extract a PC's propagating and evanescent Bloch modes from a scattering calculation that can be performed by any off-the-shelf field solver, and to calculate impedances from the extracted modal fields. Finally, we put our method to use. We apply it to design antireflection coatings, nearly eliminating reflection at a single frequency for one or both polarisations, or lowering it across a larger bandwidth. We use it to find surface modes at interfaces between PCs and air, and their projected band structures. We use the impedance to define effective parameters for PC homogenisation, and we briefly describe how our definition has been used to dispersion engineer a PC waveguide