Assessment of Seagrass Floral Community Structure from Two Caribbean Marine Protected Areas

Seagrass communities represent spatially complex and biomass producing systems comprised of intermixed seagrass and algal species. We investigated shallow water communities from two Marine Protected Areas (MPAs) in the Caribbean: St. John, United States Virgin Islands and Cayos Cochinos, Honduras. St. John sites (4) lie within the Virgin Islands National Park and the Coral Reef National Monument and are designated within an UNESCO Biosphere Reserve. Honduran sites (4) lie within the designated Marine National Monument. Our results indicate that both MPAs were dominated by Thalassia testudinum with spatial coverage and shoot density significantly greater in Honduras. Many sites also showed substantial cover of Syringodium filiforme, which was significantly greater in St. John. Most major algal groups showed significant differences between MPAs and among sites within locations. Specifically, Halimeda, Penicillus, Udotea, Galaxaura, and Dictyosphaeria were significantly more abundant in Honduras, while Padina and Avrainvillea were significantly greater from St. John. Additionally, only Honduran sites showed the presence of coral colonies (Montastrea and Porites) within their seagrass beds. Floral community level analyses demonstrated significant differences among almost all site comparisons suggesting relatively distinct floral communities exist within each of these regions, but both MPAs maintain high spatial coverage of seagrasses providing critical ecosystem services

Fashion retailing – past, present and future

This issue of Textile Progress reviews the way that fashion retailing has developed as a result of the application of the World Wide Web and information and communications technology (ICT) by fashion-retail companies. The review therefore first considers how fashion retailing has evolved, analysing retail formats, global strategies, emerging and developing economies, and the factors that are threatening and driving growth in the fashion-retail market. The second part of the review considers the emergence of omni-channel retailing, analysing how retail has progressed and developed since the adoption of the Internet and how ICT initiatives such as mobile commerce (m-commerce), digital visualisation online, and in-store and self-service technologies have been proven to support the progression and expansion of fashion retailing. The paper concludes with recommendations on future research opportunities for gaining a better understanding of the impacts of ICT and omni-channel retailing, through which it may be possible to increase and develop knowledge and understanding of the way the sector is developing and provide fresh impetus to an already-innovative and competitive industr

The talbot effect : Fresnel diffraction of amplitude and phase gratings

Ph.D.Donald C. O'She

Broadband Variable Transmission Sphere for Fizeau Interferometry

Transmission spheres used in interferometry are specified by f-number and source wavelength. In this paper, we explore a broadband variable transmission sphere (BVTS) system based on freeform Alvarez lenses that enables variable operation across a broad range of f-numbers and wavelengths. Potential applications and performance tradeoffs are discussed in comparison to conventional spherical transmission spheres. Simulation results are presented for f/15 to f/80 configurations from visible to long-wave infrared sources in a Fizeau interferometer. Simulation results highlight that spherical, coma, and astigmatism impose limits on surface measurement quality

Fabrication Of Micro Optics On Coreless Fiber Segments

Fabrication of micro optics for fiber optics applications is a challenge due to their size and the issues associated with alignment of the optics to single-mode fibers. This study summarizes a method for fabricating diffractive optical elements on the ends of coreless fiber segments for passive alignment to single-mode fibers. Results are presented for passively aligned diffractive lens elements used for both collimation and beam shaping. © 2003 Optical Society of America

Predictive models for the Strehl ratio of diamond-machined optics

International audienceThis paper provides a practical connection between the Strehl ratio as an optical performance metric and manufacturing parameters for diamond machined optics. The choice of fabrication parameters impacts residual mid-spatial frequency groove structures over the part's surface, which reduce optical performance. Connections between the Strehl ratio and the fabrication parameters are studied using rigorous Rayleigh-Sommerfeld simulations for a sample optical system. The connections are generalized by incorporating the shape of diamond-machined groove structures and the effects of optical path differences for both transmissive and reflective optics. This work validates the analytical representation of the Strehl ratio as a Fourier transform of a probability density that relates to surface errors. The result is a practical tool that can be used to guide the choice of machining parameters to achieve a targeted optical performance

Micro-Transfer Molding Of Su-8 Micro-Optics

SU-8 is a very promising polymer for micro-optics. It is mechanically robust with high thermal and chemical resistance, has high transmission at visible and near-infrared wavelengths, and has relatively high refractive index after curing. While lithographic patterning of SU-8 is relatively common, molding of SU-8 is more difficult due to challenges with solvent removal and cross linking. In this paper, we discuss techniques for micromolding of micro- and nano-optics in SU-8. Elastomeric mold templates are first cast from master structures fabricated using standard techniques. The elastomeric templates are then used in low pressure molding processes to produce high-fidelity refractive and diffractive micro-optics in SU-8. The use of the elastomeric replica mold enables realization of a wider variety of optical surfaces than can be achieved with conventional lithographic patterning in SU-8, and further enables conformal fabrication of SU-8 micro-optics on non-planar surfaces. Molding processes and experimental results for both thin (diffractive) and thick (refractive) elements are presented. Replication of SU-8 micro-optics on both planar and non-planar surfaces, and hybrid processes combining molding and lithographic exposure are demonstrated