A generalised equivalent storm model for long-term statistics of ocean waves

This is the final version of the article. Available from Elsevier via the DOI in this record.To calculate the return periods of individual wave or crest heights, the long-term distribution of sea states must be combined with the short-term distribution of individual wave or crest heights conditional on sea state. This is normally achieved using an equivalent storm model to parameterise the distribution of the maximum wave or crest height in a storm. A new equivalent storm model is introduced that generalises the approach of Tromans and Vanderschuren (1995). The generalised equivalent storm (GES) method is significantly simpler than equivalent storm methods that model the temporal evolution of the significant wave height in a storm. The GES method is applied to long time series of wave buoy measurements for deep and shallow water sites and demonstrated to be more accurate than existing methods at representing the statistical characteristics of measured storms. Return periods of crest heights from the GES method are shown to be more robust to uncertainties in the fitted models of the equivalent storm parameters than estimates from temporal evolution methods such as the equivalent triangular storm and equivalent power storm model.This work was partly funded through EPSRC grant EP/R007519/1

All-optical generation and photoassociative probing of sodium Bose-Einstein condensates

We demonsatrate an all optical technique to evaporatively produce sodium Bose-Einstein condensates (BEC). We use a crossed-dipole trap formed from light near 1060 nm, and a simple ramp of the intensity to force evaporation. In addition, we introduce photoassociation as diagnostic of the trap loading process, and show that it can be used to detect the onset of Bose-Einstein condensation. Finally, we demonstrate the straightforward production of multiple traps with condensates using this technique, and that some control over the spinor state of the BEC is achieved by positioning the trap as well.Comment: 8 pages, 10 figure

Comparison of analytical and numerical solutions for wave interaction with a vertical porous barrier

This is the final version. Available on open access from Elsevier via the DOI in this record.Analytical solutions for wave interaction with a vertical porous barrier are presented. The analytical solutions are derived using two different methods for taking the depth-average of the pressure drop across the porous barrier. Both solutions assume that the evanescent modes in the wave field can be neglected. The results from the analytical models are compared to results from an iterative boundary element method (BEM) model. The BEM model shows that neglecting evanescent modes is a reasonable assumption for long waves, but that for short waves the velocity through the porous wall from the evanescent modes can be up to 25% of the velocity from the progressive modes at the free surface. However, the effect of neglecting the evanescent modes has only a small effect on the depth-averaged velocity through porous wall and the analytical models derived using depth-averaged assumptions are shown to give good agreement with the BEM model for the reflection coefficient, horizontal force and overturning moment on the porous barrier. The analytical models are used to investigate the effects of the drag and inertia coefficients of the porous barrier on the behaviour of the solution. It is shown that for fixed values of the drag coefficient, wave frequency and amplitude, the solutions for the reflection coefficient lie on approximately semicircular arcs on the complex plane, with the position on the arc determined by the inertial coefficient. This places bounds on the size of the phase change in the reflected and transmitted wave which are possible. The analytical models are also used to derive the asymptotic behaviour of the solution in long and short waves. The implications of the results for more general cases of wave interaction with porous structures are discussed.Engineering and Physical Sciences Research Council (EPSRC

A model to map levelised cost of energy for wave energy projects

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.An economic model has been developed which allows the spatial dependence of wave energy levelised cost of energy (LCOE) to be calculated and mapped in graphical information system (GIS) software. Calculation is performed across a domain of points which define hindcast wave data; these data are obtained from wave propagation models like Simulating WAves Nearshore (SWAN). Time series of metocean data are interpolated across a device power matrix, obtaining energy production at every location. Spatial costs are calculated using Dijkstra's algorithm, to find distances between points from which costs are inferred. These include the export cable and operations, the latter also calculated by statistically estimating weather window waiting time. A case study is presented, considering the Scottish Western Isles and using real data from a device developer. Results indicate that, for the small scale device examined, the lowest LCOE hotspots occur in the Minches. This area is relatively sheltered, showing that performance is device specific and does not always correspond to the areas of highest energy resource. Sensitivity studies are performed, examining the effects of cut-in and cut-out significant wave height on LCOE, and month on installation cost. The results show that the impact of these parameters is highly location-specific.The authors wish to thank Albatern Ltd, the industrial partner of the research project, for their funding and support in sponsoring the lead author. In addition, the Energy Technology Institute (ETI) and Research Councils UK Energy Programme who have funded this research through the IDCORE programme (grant number: EP/J500847/1)

Simulation of Jahn-Teller-Dicke Magnetic Structural Phase Transition with Trapped Ions

We study theoretically the collective E$\otimes$e Jahn-Teller-Dicke distortion in a system of trapped ions. We focus in the limit of infinite range interactions in which an ensemble of effective spins interacts with two collective vibrational modes with U(1) symmetric couplings. Our model is exactly solvable in the thermodynamical limit and it is amenable to be solved by exact numerical diagonalization for a moderate number of ions. We show that trapped ions are ideally suited to study the emergence of spontaneous symmetry breaking of a continuous symmetry and magnetic structural phase transition in a mesoscopic system.Comment: 19 pages, 7 figure

A BEM model for wave forces on structures with thin porous elements

This is the final version. Available on open access from Elsevier via the DOI in this record. A boundary element method (BEM) model is presented for wave forces on structures composed of solid and porous surfaces, where the porous surface can be subject to either a linear or quadratic pressure–velocity relation. In the case of the quadratic relation, the solutions to the radiation and diffraction problems cannot be superimposed to obtain a solution for body motions in waves. Instead, a solution method is proposed which solves for the motion response and wave forces on the body simultaneously. Solutions for the radiation and diffraction problems are then obtained as special cases. Hydrodynamic identities and expressions for the mean drift force for combined solid-porous bodies are also derived. It is shown that in the case of a quadratic pressure drop, the hydrodynamic coefficients are no longer symmetric and the Haskind relation must be modified to account for the pressure drop across the porous surface. The BEM solution is verified against an analytical calculations and results for the excitation and mean drift forces are shown to agree well. A case study is presented for a floating truncated cylinder, with a concentric porous outer cylinder. It is shown that the porous outer cylinder significantly increases the damping at low frequencies, where wave radiation damping is low, leading to a lower motion response.Engineering and Physical Sciences Research Council (EPSRC

Feasibility study of mooring lines design for a floating tidal turbine platform using double hull structure

The aim of this paper is to study the mooring tension characteristics on a tidal energy converter (TIC) platform considering i) a horizontal and ii) a vertical tidal turbine. The study examines numerically the feasibility of a catenary mooring line for a modular tidal energy platform. A modular platform is designed and modelled with two floating hulls and anchored by studlink catenary mooring chains on the seabed. Vertical and horizontal axis turbines which have similar Cp are selected and modelled separately. The effect of those turbines on the mooring system are compared and the results informs lifetime of the mooring component for each turbine connection. The hydrodynamic model with no turbine is firstly developed and validated against an experiment with 1:12 scale ratio. The starboard fore mooring line tension, platform surge and pitch displacements are validated against the experiment. The model results show identical signal frequency with slightly different magnitude from the experiment. The mooring tension under vertical and horizontal tidal turbine operations in the particular environment is further examined. The result shows that the mooring line using selected vertical axis turbine experiences higher tension. For platform motions, the horizontal turbine generates slightly larger displacement in surge. However the pitch motion record shows equal displacement under both turbine operations. The selected vertical axis tidal turbine also produces longer lifetime mooring components

Mycotoxin Adducts on Human Serum Albumin: Biomarkers of Exposure to Stachybotrys chartarum

OBJECTIVE: Despite the growing body of evidence showing adverse health effects from inhalation exposure to the trichothecene-producing mold Stachybotrys chartarum, controversy remains. Currently, there are no reliable assays suitable for clinical diagnosis of exposure. We hypothesized that satratoxin G (SG)–albumin adducts may serve as biomarkers of exposure to this fungus. DESIGN: We studied the formation of adducts of SG with serum albumin in vitro using Western blots and mass spectrometry (MS) and searched for similar adducts formed in vivo using human and animal serum. RESULTS: Samples of purified human serum albumin that had been incubated with increasing concentrations of SG showed concentration-dependent albumin bands in Western blots developed with anti-SG antibodies. MS analysis found that as many as 10 toxin molecules can be bound in vitro to one albumin molecule. The sequencing of albumin-adduct tryptic peptides and the analysis of pronase/aminopeptidase digests demonstrated that lysyl, cysteinyl, and histidyl residues are involved in the formation of these adducts. Serum samples from three patients with documented exposure to S. chartarum similarly revealed lysine–, cysteine–, and histidine–SG adducts after exhaustive digestion, affinity column enrichment, and MS analysis. These adducts were also found in the sera from rats exposed to the spores of S. chartarum in contrast to control human subjects and control animals. CONCLUSIONS: These data document the occurrence of SG–albumin adducts in both in vitro experiments and in vivo human and animal exposures to S. chartarum. RELEVANCE TO CLINICAL PRACTICE: SG–amino acid adducts may serve as reliable dosimeter biomarkers for detection of exposure to S. chartarum