Type-1.5 superconductivity in multiband systems: the effects of interband couplings

In contrast to single-component superconductors, which are described at the level of Ginzburg-Landau theory by a single parameter \kappa and are divided in type-I \kappa1/\sqrt{2} classes, two-component systems in general possess three fundamental length scales and have been shown to possess a separate "type-1.5" superconducting state. In that state, as a consequence of the extra fundamental length scale, vortices attract one another at long range but repel at shorter ranges, and therefore should form clusters in low magnetic fields. In this work we investigate the appearance of type-1.5 superconductivity and the interpretation of the fundamental length scales in the case of two bands with substantial interband couplings such as intrinsic Josephson coupling, mixed gradient coupling and density-density interactions. We show that in the presence of substantial intercomponent interactions of the above types the system supports type-1.5 superconductivity with fundamental length scales being associated with the mass of the gauge field and two masses of normal modes represented by mixed combinations of the density fields.Comment: 19 pages, v.2: various additions, v.3: journal version (minor improvements in presentation

Magnetic field delocalization and flux inversion in fractional vortices in two-component superconductors

We demonstrate that, in contrast to the single-component Abrikosov vortex, in two-component superconductors vortex solutions with exponentially screened magnetic field exist only in exceptional cases: in the case of vortices carrying an integer number of flux quanta, and in a special parameter limit for half-quantum vortices. For all other parameters the vortex solutions have delocalized magnetic field with a slowly decaying tail. Furthermore, we demonstrate a new effect which is generic in two-component systems but has no counterpart in single-component systems: on exactly half of the parameter space of the $U(1)\times U(1)$ Ginzburg-Landau model, the magnetic field of a generic fractional vortex inverts its direction at a certain distance from the vortex core.Comment: Replaced with published version. 4 pages, 3 figure

Prothoracic region of acalypterate diptera : a) morphology, b) taxonomic significance

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Chiral CP^2 skyrmions in three-band superconductors

It is shown that under certain conditions, three-component superconductors (and in particular three-band systems) allow stable topological defects different from vortices. We demonstrate the existence of these excitations, characterized by a $CP^2$ topological invariant, in models for three-component superconductors with broken time reversal symmetry. We term these topological defects "chiral $GL^{(3)}$ skyrmions", where "chiral" refers to the fact that due to broken time reversal symmetry, these defects come in inequivalent left- and right-handed versions. In certain cases these objects are energetically cheaper than vortices and should be induced by an applied magnetic field. In other situations these skyrmions are metastable states, which can be produced by a quench. Observation of these defects can signal broken time reversal symmetry in three-band superconductors or in Josephson-coupled bilayers of $s_\pm$ and s-wave superconductors.Comment: minor presentation changes; replaced journal version; 30 pages, 21 figure

On the dynamics of topological solitons

This thesis investigates the dynamics of lump-like objects in non-integrable field theories, whose stability is due to topological considerations. The work concerns three different low dimensional ((1 + 1)- and (2 + l)-dimensional) systems and addresses the questions of how the topology and metric structure of physical space, the quantum mechanics of the basic field quanta and intersoliton interactions affect soliton dynamics. In chapter 2 a sine-Gordon system in discrete space, but with continuous time, is presented. This has some novel features, namely a topological lower bound on the energy of a kink and an explicit static kink which saturates this bound. Kink dynamics in this model is studied using a geodesic approximation which, on comparison with numerical simulations, is found to work well for moderately low kink speeds. At higher speeds the dynamics becomes significantly dissipative, and the approximation fails. Some of the dissipative phenomena observed are explained by means of a dispersion relation for phonons on the spatial lattice. Chapter 3 goes on to quantize the kink sector of this model. A quantum induced potential called the kink Casimir energy is computed numerically in the weak coupling approximation by quantizing the lattice phonons. The effect of this potential on classical kink dynamics is discussed. Chapter 4 presents a study of the low-energy dynamics of a CP(^1) lump on the two-sphere in the geodesic approximation. By considering the isometry group inherited from globalsymmetries of the model, the structure of the induced metric on the unit-charge moduli space is so restricted that the metric can be calculated explicitly. Some totally geodesic submanifolds are found, and the qualitative features of motion on these described. The moduli space is found to be geodesically incomplete. Finally, chapter 5 contains an analysis of long range intervortex forces in the abelian Higgs model, a massive field theory, extending a point source. approximation previously only used in massless theories. The static intervortex potential is rederived from a new viewpoint and used to model type II vortex scattering. Velocity dependent forces are then calculated, providing a model of critical vortex scattering, and leading to a conjecture for the analytic asymptotic form of the metric on the two-vortex moduli space

Easy plane baby skyrmions

The baby Skyrme model is studied with a novel choice of potential, $V=1/2 \phi_3^2$. This "easy plane" potential vanishes at the equator of the target two-sphere. Hence, in contrast to previously studied cases, the boundary value of the field breaks the residual SO(2) internal symmetry of the model. Consequently, even the unit charge skyrmion has only discrete symmetry and consists of a bound state of two half lumps. A model of long-range inter-skyrmion forces is developed wherein a unit skyrmion is pictured as a single scalar dipole inducing a massless scalar field tangential to the vacuum manifold. This model has the interesting feature that the two-skyrmion interaction energy depends only on the average orientation of the dipoles relative to the line joining them. Its qualitative predictions are confirmed by numerical simulations. Global energy minimizers of charges B=1,...,14,18,32 are found numerically. Up to charge B=6, the minimizers have 2B half lumps positioned at the vertices of a regular 2B-gon. For charges B >= 7, rectangular or distorted rectangular arrays of 2B half lumps are preferred, as close to square as possible.Comment: v3: replaced with journal version, one new reference, one deleted reference; 8 pages, 5 figures v2: fixed some typos and clarified the relationship with condensed matter systems 8 pages, 5 figure

Comparison of Fish Assemblages and Water Quality in Two Marinas in the British Virgin Islands

Eutrophication is a widespread problem in tropical marine environments that leads to the increase of nutrients in a water body, usually nitrate and phosphate, and is usually associated with the discharge of untreated sewage, intensive farming or fertilizer-enriched agricultural runoff (Wu 1999). Common symptoms are increased N and P levels, increased macroalgal production in shallow areas, reduced dissolved oxygen, loss of seagrass and coral habitats and changes in the fish community (Hallock and Schlager 1986, Granelli et al. 1990, Valiela 1995, Hemminga and Duarte 2000). Direct chemical testing to establish pollution levels can be difficult because of sharp pollution gradients, rapid dilution effects, changing tides and currents, variable pollutant concentrations, varying pollution activities, unavailability of water quality test kits, a prohibitive range of pollutants to test for and high testing costs (Resh et al. 1995). Many of these problems can be countered with bioassessment methods that use biotic indicators to assess ecosystem integrity (Karr 1981, Noss 1990, Wright et al. 1993, Chessman 1995). Biotic indicators of pollution have several advantages over chemical methods: they are broad-ranged, detect many forms of pollution, reflect pollution history and indicate overall health of the system. Animal bioindicators should be: 1) sufficiently sensitive to disturbance, 2) widely distributed, 3) capable of living in a wide range of conditions, 4) relatively independent of sample size, 5) easy and cost effective to study, 6) able to differentiate between natural and man-made disturbance, and 7) relevant to ecologically significant phenomena (Noss 1990). Fish meet many of these criteria and have been included in several freshwater bioassessment protocols, sometimes referred to as biological integrity indices (Larkin and Northcote 1969, Karr 1981, Karr 1990, Hughes et al. 1998). Marine fish have been widely used as indicators of coral cover and overfishing (Bell and Galzin 1984, Findley and Findley 1985, Roberts 1995, Russ and Alcala 1998), but few studies have successfully used marine fish assemblages as indicators of pollution. One reason is that it is difficult to determine the direct effects of pollution on marine fish assemblages because natural experiments are usually confounded by habitat alteration due to dredging, siltation and pollution. This study aims to assess the potential of marine fishes as bioindicators using artificial reefs as habitat controls in 2 marinas with different pollution levels

STN keys for the identification of adult european syrphidae 2012

The identification keys presented here include a key to the genera of European Syrphidae and Microdontidae and keys to the species of various genera. They do not comprise a comprehensive set of keys to the identification of European syrphid species. While every effort has been made to ensure that each key is as self-contained and accurate as possible it is not suggested that these keys be used in isolation from other literature on identification of European syrphids. In the StN Species Accounts volume (Speight, 2012) information is given for each species on identification literature, sources of figures of the male terminalia, sources of coloured illustrations of the adult fly etc., together with suggestions (where appropriate) of additional features to use for identification purposes. That information is not repeated here. A genus for which an StN key to the European species exists is indicated in the generic key following the name of the genus, by the phrase “see StN key to European species”. Various syrphid genera are represented in Europe by no more than one species. For these, the generic key provides a mechanism for identification to species level and the name of the European species is given in the generic key, following the name of the genus. This volume is presented in two sections, an English section and a French section. The key to European syrphid genera appears only in the English section. But all of the keys to the species of individual genera appear in both sections. Each key is dated, to show when it was most recently updated. The keys to the species of individual genera are presented in alphabetical order of the genera they cover, under Microdontidae and Syrphidae. No grouping is made of genera in subfamilies or tribes. For further information on the known European species in each genus the StN Species Accounts volume (Speight, 2012) should be consulted. There is unfortunately no standard set of English-language terms used for morphological features in taxonomic literature on Syrphidae. Contrasting accounts are provided by Thompson (1999) and Speight (1987). Part 3 of the present volume presents a Glossary of the terms used for morphological features in the StN keys, together with figures showing those features