Aspects of SWATH Design and Evaluation

This thesis describes research intended to extend and enhance the existing SWATH design capability developed at the University. The thesis commences (Chapter 2) with a brief general review of all design aspects relevant to the balanced evaluation and comparison of monohull and SWATH vessels. SWATH vessel performance in each of these areas is analysed individually, and where possible quantified in relation to that of corresponding monohull ships. This chapter is intended to highlight the range and extent of the variations existing in SWATH / monohull design and operability characteristics. Chapters 3, 4 and 5 of the thesis describe studies aimed at improving our understanding of the often neglected although fundamental aspects of damage stability, manoeuvring and wave induced global loading. These design topics were selected for investigation after the preliminary review highlighted shortfalls in the availability and reliability of relevant information. Chapter 3 addresses the question of damage stability. Results from an extensive parametric study undertaken to explore the damage stability characteristics of SWATH vessels are presented and discussed. Secondly the relationships thus established between design geometry and damage stability are utilized in the construction of 'FSEP1'; a design program which estimates damaged stability characteristics at the preliminary design stage. Chapter 4 investigates the manoeuvring performance of SWATH ships. Following a thorough literature survey, conventional (monohull) manoeuvring theory is applied and adapted to create a manoeuvring prediction tool for SWATH vessels; 'SWATHMAN'. This program will estimate required rudder areas in order to achieve a specified manoeuvring performance. Conversely the program will estimate the likely turning performance for a specified rudder area. The program incorporates propeller acceleration effects and caters for control fins mounted in and outwith the slipstream. Chapter 5 reviews aspects of wave loading in the structural design of SWATH ships. It is widely acknowledged that wave induced side force leading to a transverse bending moment is the dominant form of environmental loading for these vessels. All available methods for the calculation / estimation of this force were therefore identified and applied to the vessels T-AGOS 19 and the M. V. Patria. Short term extreme value prediction methods are applied in order to determine likely lifetime values of design extreme loading. Empirically derived estimates are compared with those produced by the application of rigorous three dimensional potential theory, and conclusions on the applicability of the methods are drawn. Finally chapter 6 outlines a method for the overall mission based evaluation of alternative monohull and SWATH designs. This comparison is based on all relevant features of the two concepts. Features and characteristics of both hullforms are identified and assigned a priority level. The priority level assigned includes consideration of the vessel's intended role and operating profile. Through application of this technique the chapter aims to provide guidance for the designer selecting hullforms for both general and specific roles

A faint red stellar halo around an edge-on disc galaxy in the Hubble Ultra Deep Field

We analyse the detailed structure of a highly-inclined (i>~80 degrees) disc galaxy which lies within the Hubble Ultra Deep Field (UDF). The unprecedented depth of the UDF data allow disc and extraplanar emission to be reliably traced to surface brightness levels of mu_{V,i,z}~29-30 mag/arcsec^2 (corresponding to rest-frame equivalents of mu_{g,r,i}~28-29 mag/arcsec^2) in this redshift z=0.32 system. We detect excess emission above the disc which is characterised by a moderately-flattened (b/a~0.6) power-law (I proportional to R^(-2.6)). The structure and colour of this component are very similar to the stellar halo detected in an SDSS stacking analysis of local disc galaxies (Zibetti, White and Brinkmann 2004) and lend support to the idea that we have detected a stellar halo in this distant system. Although the peculiar colours of the halo are difficult to understand in terms of normal stellar populations, the consistency found between the UDF and SDSS analyses suggests that they cannot be easily discounted.Comment: 5 pages, 5 figures, accepted for publication in MNRAS Letters. Figure 1 substantially degraded, full resolution version available at http://www.mpa-garching.mpg.de/~zibetti/UDFhalo.pd

Capturing the time-varying drivers of an epidemic using stochastic dynamical systems

Epidemics are often modelled using non-linear dynamical systems observed through partial and noisy data. In this paper, we consider stochastic extensions in order to capture unknown influences (changing behaviors, public interventions, seasonal effects etc). These models assign diffusion processes to the time-varying parameters, and our inferential procedure is based on a suitably adjusted adaptive particle MCMC algorithm. The performance of the proposed computational methods is validated on simulated data and the adopted model is applied to the 2009 H1N1 pandemic in England. In addition to estimating the effective contact rate trajectories, the methodology is applied in real time to provide evidence in related public health decisions. Diffusion driven SEIR-type models with age structure are also introduced.Comment: 21 pages, 5 figure

Sexually Transmitted Infections: Perceived Knowledge Versus Actual Knowledge

Sexually transmitted infections (STIs) continue to be a serious problem, with potentially severe consequences. Past research has found that people may not seek out treatment for STIs because they do not know what symptoms to look for (Greenberg et al., 2002). The present study investigated many aspects of STI knowledge, including perceived knowledge and actually knowledge. Moreover, this study added a novel and applied aspect to the assessment of STI knowledge: visual knowledge. Overall, participants performed poorly on the actual STI knowledge, however, those who rated their knowledge as high performed significantly better than those who rated their knowledge as low. The data revealed two significant predictors of actual STI knowledge, level of STI education and number of previously contracted STIs. In addition, it was found that participants performed better on the written portion of the test than the visual portion of the test. The authors content that increased education may assist in reducing the transmission of sexually transmitted diseases

Deep UV Luminosity Functions at the Infall Region of the Coma Cluster

We have used deep GALEX observations at the infall region of the Coma cluster to measure the faintest UV luminosity functions (LFs) presented for a rich galaxy cluster thus far. The Coma UV LFs are measured to M_UV = -10.5 in the GALEX FUV and NUV bands, or 3.5 mag fainter than previous studies, and reach the dwarf early-type galaxy population in Coma for the first time. The Schechter faint-end slopes (alpha = -1.39 in both GALEX bands) are shallower than reported in previous Coma UV LF studies owing to a flatter LF at faint magnitudes. A Gaussian-plus-Schechter model provides a slightly better parametrization of the UV LFs resulting in a faint-end slope of ~ -1.15 in both GALEX bands. The two-component model gives faint-end slopes shallower than -1 (a turnover) for the LFs constructed separately for passive and star forming galaxies. The UV LFs for star forming galaxies show a turnover at M_UV ~ -14 owing to a deficit of dwarf star forming galaxies in Coma with stellar masses below M*=10^8 Msun. A similar turnover is identified in recent UV LFs measured for the Virgo cluster suggesting this may be a common feature of local galaxy clusters, whereas the field UV LFs continue to rise at faint magnitudes. We did not identify an excess of passive galaxies as would be expected if the missing dwarf star forming galaxies were quenched inside the cluster. In fact, the LFs for both dwarf passive and star forming galaxies show the same turnover at faint magnitudes. We discuss the possible origin of the missing dwarf star forming galaxies in Coma and their expected properties based on comparisons to local field galaxies.Comment: accepted for publication in Ap

The Specific Globular Cluster Frequencies of Dwarf Elliptical Galaxies from the Hubble Space Telescope

The specific globular cluster frequencies (S_N) for 24 dwarf elliptical (dE) galaxies in the Virgo and Fornax Clusters and the Leo Group imaged with the Hubble Space Telescope are presented. Combining all available data, we find that for nucleated dEs --- which are spatially distributed like giant ellipticals in galaxy clusters --- S_N(dE,N)=6.5 +- 1.2 and S_N increases with M_V, while for non-nucleated dEs --- which are distributed like late-type galaxies --- S_N(dE,noN)=3.1 +- 0.5 and there is little or no trend with M_V. The S_N values for dE galaxies are thus on average significantly higher than those for late-type galaxies, which have S_N < 1. This suggests that dE galaxies are more akin to giant Es than to late-type galaxies. If there are dormant or stripped irregulars hiding among the dE population, they are likely to be among the non-nucleated dEs. Furthermore, the similarities in the properties of the globular clusters and in the spatial distributions of dE,Ns and giant Es suggest that neither galaxy mass or galaxy metallicity is responsible for high values of S_N. Instead, most metal-poor GCs may have formed in dwarf-sized fragments that merged into larger galaxies.Comment: 12 pages (uses aaspp4.sty), 2 figures, 1 table, to appear in the Astrophysical Journa