Valence band spectroscopy in V-grooved quantum wires

We present a combined theoretical and experimental study of the anisotropy in the optical absorption of V-shaped quantum wires. By means of realistic band structure calculations for these structures, we show that detailed information on the heavy- and light-hole states can be singled out from the anisotropy spectra {\em independently of the electron confinement}, thus allowing accurate valence band spectroscopy.Comment: To be published in Appl. Phys. Lett. (8 pages in REVTeX, two postscipt figures

Brane World in a Topological Black Hole Bulk

We consider a static brane in the background of a topological black hole, in arbitrary dimensions. For hyperbolic horizons, we find a solution only when the black hole mass assumes its minimum negative value. In this case, the tension of the brane vanishes, and the brane position coincides with the location of the horizon. For an elliptic horizon, we show that the massless mode of Randall-Sundrum is recovered in the limit of large black hole mass.Comment: Latex, 8 pages, v2: Additional references, to appear in MPL

Hybridization of multi-objective deterministic particle swarm with derivative-free local searches

The paper presents a multi-objective derivative-free and deterministic global/local hybrid algorithm for the efficient and effective solution of simulation-based design optimization (SBDO) problems. The objective is to show how the hybridization of two multi-objective derivative-free global and local algorithms achieves better performance than the separate use of the two algorithms in solving specific SBDO problems for hull-form design. The proposed method belongs to the class of memetic algorithms, where the global exploration capability of multi-objective deterministic particle swarm optimization is enriched by exploiting the local search accuracy of a derivative-free multi-objective line-search method. To the authors best knowledge, studies are still limited on memetic, multi-objective, deterministic, derivative-free, and evolutionary algorithms for an effective and efficient solution of SBDO for hull-form design. The proposed formulation manages global and local searches based on the hypervolume metric. The hybridization scheme uses two parameters to control the local search activation and the number of function calls used by the local algorithm. The most promising values of these parameters were identified using forty analytical tests representative of the SBDO problem of interest. The resulting hybrid algorithm was finally applied to two SBDO problems for hull-form design. For both analytical tests and SBDO problems, the hybrid method achieves better performance than its global and local counterparts

The effect of pre-curing UV-irradiation on the crosslinking of silicone rubber

A recent work made use of selective pre-curing UV-irradiation and its effect on the kinetics of reaction of heat-cure silicone elastomers to spatially tune its viscoelastic properties and design architected solid membranes. The present study adds to the possibility of controlling the local properties of spatially graded materials by exploring the effect of key processing parameters such as the UV dose and the silicone mix thickness on the vulcanization kinetics. Dynamic Differential Scanning Calorimetry measurements have been performed showing that, over the conditions explored, the higher the UV dose, the slower the kinetics reaction. Additionally, complete crosslinking was always reached. Companion modeling effort using the Kissinger reaction model is attempted and the effects of processing parameters on the apparent activation energy are discussed. This work is a crucial first step towards the control of the processing settings needed to design architected silicone rubber membranes with spatially controlled mechanical property gradients obtained from a unique macromolecular network

Self-T-Dual Brane Cosmology and the Cosmological Constant Problem

We consider a codimension-one brane embedded in a gravity-dilaton bulk action, whose symmetries are compatible with T-duality along the space-like directions parallel to the brane, and the bulk time-like direction. The equations of motions in the string frame allow for a smooth background obtained by the union of two symmetric patches of AdS space. The Poincar\'{e} invariance of the solution appears to hold independently of the value of the brane vacuum energy, through a self-tuning property of the dilaton ground state. Moreover, the effective cosmology displays a bounce, at which the scale factor does not shrink to zero. Finally, by exploiting the T-duality symmetry, we show how to construct an ever-expanding Universe, along the lines of the Pre-Big Bang scenario.Comment: Minor corrections, comments & references added. Accepted for publicatio

The O&M driven design of a multi-row platform tidal project

This is the author accepted manuscript. The final version is available from EWTEC via the link in this recordA number of tidal projects with different design, sizes and conceptual approaches, have been developed in recent years. While the technology has proven to be effective in converting tidal streams into electric energy, the economic viability is still far from being achieved due to unforeseen complications following the installation of the devices. In this paper, the authors provide an overview of the major challenges tidal energy developers should consider in order to design a viable tidal energy device. In addition, based on past field experiences, the typical issues encountered by offshore contractors during the deployment of one or an array of devices are presented. Therefore, paying special attention to the operational requirements of the devices, the solutions to these offshore challenges are proposed. Hence, a novel tidal concept is presented, using lifecycle O&M costs as a top driver for the development of the device. Subsequently, the iterative improvement of the project is achieved by means of a verified and calibrated integrated framework, based on Monte Carlo simulation and evolutionary algorithms, in order to support the decision-making process and management of the assets. Thus, the pivotal role of computational tools to improve the profitability of the project while ensuring satisfactory levels of availability and reliability is highlighted, and the potential for cost reduction in the design of a tidal energy project, in order to achieve financial viability, is shown.European Regional Development Fund (ERDF

The Management of Lake Como

This paper presents a new and heuristic approach for improving the performance of multipurpose reservoirs already in operation. The main characteristic of the method is that the analyst must first learn from the past experience of the manager and synthesize it into a very simple operating rule. Then, the analyst must point out with the help of the manager what the acceptable modifications of such a rule are. Only after these phases have been carried out can possible improvements in the management be obtained by using standard optimization techniques. The method has been applied to the case of Lake Como, (Northern Italy), and the results are quite satisfactory since the major objectives of the management can be substantially improved. The average duration of the floods on the lake shores and the mean volume of the water deficits in the downstream agricultural areas are about halved, without lowering the mean yearly electricity production of the downstream run-of-river plants. Moreover, the advantages of a revision of the active storage and of a possible protection of the shores of the town of Como are also investigated. All the results of this study had a direct impact on the management of the lake. In fact, the proposed operating rule has been programmed on a microcomputer, which is now used every day by the manager as an essential support for his final decision; the active storage was lowered in June 1982 by the Ministry of Public Works, and the sunken part of Como town will be soon repaved and elevated by the Municipality

On the Analysis of a Wave Energy Farm with Focus on Maintenance Operations

Wave energy has a promising technical potential that could contribute to the future energy mix. However, costs related to the deployment of wave energy converters (WECs) are still high compared to other technologies. In order to reduce these costs, two principle options are available, a reduction in cost and an increase in productivity. This paper presents a reliability-based computational tool to identify typical decision problems and to shed light on the complexity of optimising a wave power farm. The proposed tool is used to investigate productivity and availability of a wave energy farm during 10 years of operational life. A number of optimization possibilities to improve productivity, namely vessel choice, maintenance regime, failure rate and component redundancy, are then explored in order to assess their effectiveness. The paper quantifies the yield increase and provides a practical approach to evaluate the effectiveness of strategic and operational decision options. Results, in terms of the variations in productivity and availability of the farm, are analysed and discussed. Conclusions highlight the importance of reliability-centred simulations that consider the specific decision parameters throughout the operational life to find suitable solutions that increase the productivity and reduce the running cost for offshore farms.The work in this paper has been conducted within the multinational Initial Training Network (ITN) OceaNET, funded under the PEOPLE Programme (Marie Curie Actions) of European Union’s FP7. Mojo Maritime have provided access to Mermaid to support, and for integration with, this research

A decision support model to optimise the operation and maintenance strategies of an offshore renewable energy farm

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.In order to accelerate the access into the energy market for ocean renewables, the operation and maintenance (O & M) costs for these technologies must be reduced. In this paper a reliability-based simulation tool for the optimization of the management of an offshore renewable energy (ORE) farm is presented. The proposed tool takes into account the reliability data of the simulated devices and estimations on the energy produced to create a series of results in terms of availability and maintainability of the farm. The information produced supports operational and strategic decision making regarding the O & M for offshore farms. A case study simulating a conceptual tidal energy project, consisting of an array of two tidal turbines located off the north coast of Scotland, is presented to show some of the results achievable with this model. The proposed methodology, although ado pted for a tidal farm here, is generally applicable to other kinds of ORE farms.This research has been conducted within the multinational Initial Training Network (ITN) OceaNET, funded under the People Programme (Marie Curie Actions) of the European Union's Seventh Framework ProgrammeFP7/2007-2013/under REA grant agreement no 607656. Mojo Maritime have provided access to Mermaid to support, and for integration with, this research

Cytometric analysis, genetic manipulation and antibiotic selection of the snail embryonic cell line Bge from Biomphalaria glabrata, the intermediate host of Schistosoma mansoni.

The invertebrate cell line, Bge, from embryos of the snail Biomphalaria glabrata, remains to date the only established cell line from any species of the Phylum Mollusca. Since its establishment in 1976 by Eder Hansen, few studies have focused on profiling its cytometrics, growth characteristics or sensitivity to xenobiotics. Bge cells are reputed to be challenging to propagate and maintain. Therefore, even though this cell line is a noteworthy resource, it has not been studied widely. With growing interest in functional genomics, including genetic transformation, to elucidate molecular aspects of the snail intermediate hosts responsible for transmission of schistosomiasis, and aiming to enhance the convenience of maintenance of this molluscan cell line, we deployed the xCELLigene real time approach to study Bge cells. Doubling times for three isolates of Bge, termed CB, SL and UK, were longer than for mammalian cell lines - longer than 40 h in complete Bge medium supplemented with 7% fetal bovine serum at 25 °C, ranging from ∼42 h to ∼157 h when 40,000 cells were seeded. To assess the potential of the cells for genetic transformation, antibiotic selection was explored. Bge cells were sensitive to the aminonucleoside antibiotic puromycin (from Streptomyces alboniger) from 5 μg/ml to 200 ng/ml, displaying a half maximal inhibitory concentration (IC50) of ∼1.91 μg/ml. Sensitivity to puromycin, and a relatively quick kill time (<48 h in 5 μg/ml) facilitated use of this antibiotic, together with the cognate resistance gene (puromycin N-acetyl-transferase) for selection of Bge cells transformed with the PAC gene (puroR). Bge cells transfected with a plasmid encoding puroR were partially rescued when cultured in the presence of 5 μg/ml of puromycin. These findings pave the way for the development of functional genomic tools applied to the host-parasite interaction during schistosomiasis and neglected tropical trematodiases at large