Quantum phases of vortices in rotating Bose-Einstein condensates

We investigate the ground states of weakly interacting bosons in a rotating trap as a function of the number of bosons, N, and the average number of vortices, N(V). We identify the filling fraction nu identical with N/N(V) as the parameter controlling the nature of these states. We present results indicating that, as a function of nu, there is a zero temperature phase transition between a triangular vortex lattice phase, and strongly correlated vortex liquid phases. The vortex liquid phases appear to be the Read-Rezayi parafermion states.     

An application of the capacitance matrix method to accommodate masked land areas and island circulations in a primitive equation ocean model

The capacitance matrix method has been implemented in a primitive equation ocean model to accommodate islands and portions of irregular coastal boundaries that cannot be treated adequately by boundary-fitted orthogonal curvilinear co-ordinates. The algorithm preserves the ability to solve the streamfunction equation using fast and accurate elliptic solvers that require a rectangular computational domain. By superposition of a set of island Green functions, the solution is adjusted to ensure continuity of pressure around each island. The implementation is tested by comparison with an analytic solution for wind-driven flow in a closed basin similar to the southwest Pacific Ocean.     

Two-pion production in deuteron-deuteron collisions at low energies

The cross-section for the dd →^4Heππ reaction is estimated near threshold in a two-step model where a pion created in a first interaction produces a second pion in a subsequent interaction. This approach, which describes well the rates of 2π and η production in the pd →^3Heππ and dd →^4Heη reactions, leads to predictions that are much too low compared to experiment. Alternatives to this and the double-Δ model will have to be sought to explain these data.     

Sudden death of a symmetry

Spin polarization symmetries of Dirac particles in the presence of (1 ±β)V(r) potentials are discussed. The effects of a symmetry breaking term εV(r) are explored and applied to proton and anti-proton scattering on nuclei in the framework of Dirac optical models.     

Modified meson-nucleus optical potentials

We argue that the energy dependence of the meson-nucleus optical potential should be treated in a more dynamical fashion. When this is done, some of the difficulties found in phenomenological applications are eliminated.     

Stretching of polymer chains by fluctuating flow fields

We investigate polymer stretching by fluctuating flow fields via numerical solutions of the Brownian dynamics of multibead polymer chains taking into account nonlinear elasticity, hydrodynamic interactions and good solvent, excluded volume interaction effects. By varying the scaling exponent of the energy spectrum whilst keeping the same Reynolds and Deborah numbers, as well as microscale length and turnover times, we show that steeper spectra are associated with stronger stretching. We compute the probability density functions of chain length, and explain their main features by examining explicit molecular histories. We quantify the interaction between strain rate tensor structure and chain geometry as a means of understanding better the different stretching mechanisms in mild, moderate and strong polymer stretching regimes.     

Morse theory for the space of Higgs <Emphasis Type="Italic">G</Emphasis>–bundles

Fix a C ^∞ principal G–bundle E⁰_G{E^0_G} on a compact connected Riemann surface X, where G is a connected complex reductive linear algebraic group. We consider the gradient flow of the Yang–Mills–Higgs functional on the cotangent bundle of the space of all smooth connections on E⁰_G{E^0_G}. We prove that this flow preserves the subset of Higgs G–bundles, and, furthermore, the flow emanating from any point of this subset has a limit. Given a Higgs G–bundle, we identify the limit point of the integral curve passing through it. These generalize the results of the second named author on Higgs vector bundles.