Single-mode, optical-fiber sensors and tunable wavelength filters based on the resonant excitation of metal-clad modes

The resonant excitation of metal-clad modes, including fundamental and higher-order modes, in a multilayer structure deposited on the polished cladding of a single-mode optical fiber is theoretically analyzed and experimentally demonstrated. The excitation of metal-clad modes is shown as a resonant power transfer from the fiber to the metal-clad mode that takes place for an external refractive-index value such that the effective index of the metal-clad mode reaches the cladding level. The observed attenuation on the TM polarization provides a suitable transducing mechanism for refractive-index sensor devices as well as the principle for developing tunable wavelength-polarized filters with a wide range of optical performance characteristics.     

Supply chain networks servicing upstream operations in oil and gas fields after the shale revolution

The recent irruption of shale resources in the oil and gas (O&G) industry has dramatically changed the paradigm for managing upstream operations. Unconventional production is largely driven by drilling new wells, yielding a much larger scale of material and service flows that need to be efficiently planned. This article presents an optimization framework for the design of integrated supply chain networks (SCNs) servicing upstream operations. Novel aspects addressed in this work are the integrated planning of material and service supplies; the economies of scale in operating, transportation and capital expenditures; the concept of waiting cost to quantify production losses; and the reverse flow of materials within closed-loop supply chains. The merits of the proposed approach are assessed through real-world case studies from the Argentine O&G industry. Optimal designs yield significant cost savings and confirm that the integrated planning of the SCN is critical for O&G operators after the shale revolution.     

Incorporation of Alpha‐Linolenic Acid and Enhancement of n‐3 Fatty Acids in Nile Tilapia: a Factorial Design

A 2² factorial design (two factors at two levels, in triplicate) was performed to investigate the influence of factors A (time of treatment, 15 and 30 days) and B (chia oil content in a supplemented diet, at 2.1 and 4.2 %) in three responses of interest referring to: (a) the incorporation of alpha‐linolenic acid (LNA) in lipids of Nile tilapia fillet; (b) the enhancement of n‐3 fatty acids; and (c) the decrease in the omega‐6/omega3 (n‐6/n‐3) ratio in fish. Factors A and B were significant in the three regression models obtained and the interaction AB was a significant contributor to the LNA and n‐6/n‐3 ratio. Analysis of variance suggested three significant and predictive mathematical models. Response surfaces analyses from designs indicated higher LNA and n‐3 contents and a lower n‐6/n‐3 ratio using both factors A and B in the higher levels (30 days of treatment and 4.2 % of chia oil in the diet for fish) chosen for this study.     

The environmental bill of material and technology routing: an integrated LCA approach

This paper deals with the environmental bill of material and technology routing: evaluating components and process impacts on the environmental strategy map through an integrated LCA approach. It introduces these two new elements in the definition of new approaches to complement environmental and financial considerations into a single sustainability indicator. The basic idea presented is that each component of a specific product has a certain environmental burden and consequently contributes to the environmental footprints. Those contributions are identified as environmental performance points (EPP). When an item is routed through different technology processes to build the final product, it keeps contributing to the overall environmental burden. These contributions are again identified as EPP. The sum of all EPPs, categorized by footprints, provides the basis for creation of the characteristic environmental performance strategy map, previously developed by the authors of this paper. This new approach allows wide flexibility: the impact of changing a component, material or a production process will be reflected immediately on the map.     

Evaluation and assessment of reliability and availability software for securing an uninterrupted energy supply

The significance of reliability, availability and maintainability (RAM) in recent years increased due to rising energy cost and the competitive market. These issues have a considerable effect on the energy generation and potential saving as well. RAM can be assessed by implementing effective software tools generating adequate models. They also provide results visualization via a tabular and/or graphical representation. Various software tools have been selected, tested and a brief overview drawn. It has been a wide selection; however, most of the information available has been driven by marketing and sales features. This work focuses on the main features of several promising complex reliability packages and its target is a balanced assessment of their main features.     

Synthesis of regional networks for the supply of energy and bioproducts

This article presents a method for the synthesis of regional renewable energy supply chains, based on Mixed-Integer Linear Programming (MILP). This method addresses the challenges presented by biomass resources. The main challenges are the distributive and varied availabilities regarding both location and time. This work also aims to maximise the economically viable utilisation of resources, accounting for the competition between energy and food production. A four-layer supply chain superstructure has been developed, which includes the harvesting, preparation, core processing and distribution of products. This considered system’s boundaries involve a region, which is then divided into zones for optimising conversion operations and transportation flows. An MILP model has been formulated with profit maximisation as the optimisation criterion. The environmental impact is evaluated by the carbon footprint. The sensitivity of the optimal solutions is analysed for different regions’ sizes, transportation costs, pre-processing alternatives and the co-production of food and energy.     

InP based semiconductor structures for radiation detection

We report the preparation of semi-insulating InP single crystals of p-type conductivity and intentionally undoped p-type epitaxial layers for radiation detection. We focus on (i) the growth of InP single crystals doped with copper by the Czochralski technique and their subsequent temperature annealing to convert them to a semi-insulating (SI) state of p-type conductivity, and (ii) the growth of thick (>10 μm) p-type InP layers by liquid phase epitaxy with an admixture of Pr and Dy. Grown layers and single crystals were examined by low-temperature photoluminescence spectroscopy, capacitance-voltage and temperature dependent Hall measurements. An efficient purification due to rare earth (RE) admixture has been observed and layers grown with the addition of Pr and Dy exhibit the change of electrical conductivity from n to p at certain RE concentration in the melt. Dominant acceptors responsible for conductivity conversion have been identified. Three types of detection structures exploiting the Schottky or Schottky like contacts on pure and SI p-type InP or exploiting the p–n junction were designed.     

An adaptive finite element scheme to solve fluid-structure vibration problems on non-matching grids

This paper deals with the computation of the vibration modes of a system consisting of a linear elastic solid interacting with an acoustic fluid. A finite element method based on meshes for each medium not matching on the fluid-solid interface is analyzed. Optimal order of convergence is proved for the approximation of the eigenfunctions, as well as a double order for the eigenvalues. Numerical tests confirming the theoretical results and showing the advantage of using non-matching grids are reported. Finally, an a posteriori error estimator for this method is introduced and combined with a mesh refinement strategy. The efficiency of this adaptive technique is tested with further numerical experiments. Received: 30 January 2001 / Accepted: 30 May 2001