Temporal filtering for Montgomery self-imaging under dispersive transmission

We present what we believe is a new method to introduce self-imaging properties under dispersive transmission of single or multiple light pulses with different temporal characteristics. By properly performing a temporal filtering into a given input signal it can produce an output signal having a spectral content satisfying the Montgomery condition, thereby allowing self-imaging of this signal under further dispersive transmission. An array of fiber loops performs the filtering operation on the input signal. We show some numerical simulations with a single light pulse as an input signal to verify the feasibility of the method and demonstrate the effects of the several involved parameters on both the pulse shape and the noise level.     

Analysis of the main factors affecting the evaluation of the radon dose in workplaces: the case of tourist caves

High concentrations of radon exist in several workplaces like tourist caves mainly because of the low ventilation rates existing at these enclosures. In this sense, in its 1990 publication, the ICRP recommended that high exposures of radon in workplaces should be considered as occupational exposure. In developed caves in which guides provide tours for the general public great care is needed for taking remedial actions concerning radon, because in some circumstances forced ventilation may alter the humidity inside the cave affecting some of the formations or paintings that attract tourists. Tourist guides can work about 1900 h per year, so the only option to protect them and other cave workers from radon exposure is to apply an appropriate system of radiation protection mainly based on limitation of exposure by restricting the amount of time spent in the cave. Because of the typical environmental conditions inside the caves, the application of these protecting actions requires to know some indoor air characteristics like particle concentration, as well as radon progeny behaviour in order to get more realistic effective dose values In this work the results of the first two set of radon measurements program carried out in 10 caves located in the region of Cantabria (Spain) are presented.     

Does mixing affect the setting of injectable bone cement? An ultrasound study

Experimental calcium sulphate bone cement has been tested by ultrasounds to characterise its progressive setting through the evolution of several acoustic properties. The acoustic impedance z(t), the density ρ (t) and the speed of sound c(t) versus the curing time have been monitored during the viscous-to-solid transition of the cement as a function of different mixing conditions. Injectability tests were also performed and the results have been related to the acoustic properties measured previously. It has been observed that further mixing after cement’s constituency, and before the initial setting time of the cement, drastically affects both the characteristic setting times and the injectability of the cement.     

Ruthenium purple-mediated microelectrode biosensors based on sol-gel film

Ruthenium Purple (RP), an analogue of Prussian Blue, has potentially advantageous electrochemical characteristics. We now demonstrate its use in microelectrode biosensors for the first time. An RP layer was grown on, and remained stably anchored to, the surface of gold microelectrodes at physiological pH ranges. Crucially, it retained its electrochemical activity in sodium-based phosphate buffers. The RP microelectrodes displayed electrocatalytic reduction of hydrogen peroxide at 0 to -50 mV (vs Ag/AgCl). To fabricate biosensors on the RP microelectrodes, we used a sol-gel film electrodeposition technique to create ATP and hypoxanthine biosensors as examples of the methodology. These RP-mediated biosensors displayed excellent performance including the following: high selectivity against interferences such as 5HT, ascorbic acid, urate, and acetaminophen; high sensitivity with wide linear calibration range; and good stability. These attractive characteristics demonstrate that RP can be universally employed as an electron mediator in fabrication of highly selective oxidase-based microelectrode biosensors. Furthermore, given their ability to operate in the presence of physiological levels of Na+, the RP-mediated biosensors can be potentially applied to the in vitro and in vivo measurement of physiological signaling substances.     

Implications of low breakdown voltage of component subcells on external quantum efficiency measurements of multijunction solar cells

The electrical and optical coupling between subcells in a multijunction solar cell affects its external quantum efficiency (EQE) measurement. In this study, we show how a low breakdown voltage of a component subcell impacts the EQE determination of a multijunction solar cell and demands the use of a finely adjusted external voltage bias. The optimum voltage bias for the EQE measurement of a Ge subcell in two different GaInP/GaInAs/Ge triple‐junction solar cells is determined both by sweeping the external voltage bias and by tracing the I–V curve under the same light bias conditions applied during the EQE measurement. It is shown that the I–V curve gives rapid and valuable information about the adequate light and voltage bias needed, and also helps to detect problems associated with non‐ideal I–V curves that might affect the EQE measurement. The results also show that, if a non‐optimum voltage bias is applied, a measurement artifact can result. Only when the problems associated with a non‐ideal I–V curve and/or a low breakdown voltage have been discarded, the measurement artifacts, if any, can be attributed to other effects such as luminescent coupling between subcells. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of mechanically milled powder and high pressure on spark plasma sintering of Mg–Cu–Gd metallic glasses

In this study a gas atomized Mg₆₅Cu₂₅Gd₁₀ amorphous powder was mechanically milled and consolidated by spark plasma sintering (SPS) at a high pressure (500 MPa) at different temperatures (443, 433, and 423 K) to provide an insight into the consolidation and mechanical behavior of Mg-based metallic glasses. Microstructural evolution in the vicinity of the interfaces of SPSed Mg–Cu–Gd BMG powders was characterized using scanning and transmission electron microscopy, and the associated amorphous phase transformation and thermal stability were analyzed using X-ray diffraction and differential scanning calorimetry. The results show that interfacial bonding between amorphous particles was enhanced by the disruption of surface oxides as well as by structural relaxation of the milled powder and the presence of high pressure during SPS. A finite element method with COMSOL software was also applied to investigate and explain the powder packing density, localized heating, and temperature distribution during SPS.     

Mine Water for Energy and Water Supply in the Central Coal Basin of Asturias (Spain)

The Asturian Central Coal Basin (NW Spain) is generally characterized by moderately porous and permeable rocks, such as sandstone, limestone, and shale. Groundwater mostly flows through open fractures, voids, and decompression zones associated with coal mining. Exploitation of water resources in former coal mines could contribute to the economic well-being of communities affected by closure. The potential value of mine water associated with the flooded Barredo and Figaredo mine shafts near the town of Mieres was studied. This reservoir could supply water for 60,000 people; this could possibly be doubled by co-managing the river flow and underground resources. We studied the potential recovery of energy from the thermal value of this mine water (using water-to-water heat pumps). Two district heating systems are proposed: a low-temperature network (35 °C) for domestic heating and a very-low temperature network (20 °C) for large users, such as shopping centres, that need both heating and cooling. Return flow to the reservoir can generate electricity by means of micro-turbines. Preliminary estimates of profitability appear favourable, along with a sizable reduction in CO₂ emissions compared to natural gas heating. Extrapolation of these results to other mine water reservoirs in Central Asturias implies a potential of 40 million m³ per year for water supply, and an energy supply capacity close to 260,000 thermal MWh per year.     

Enhanced balancing Neumann–Neumann preconditioning in computational fluid and solid mechanics

In this work, we propose an enhanced implementation of balancing Neumann–Neumann (BNN) preconditioning together with a detailed numerical comparison against the balancing domain decomposition by constraints (BDDC) preconditioner. As model problems, we consider the Poisson and linear elasticity problems. On one hand, we propose a novel way to deal with singular matrices and pseudo‐inverses appearing in local solvers. It is based on a kernel identification strategy that allows us to efficiently compute the action of the pseudo‐inverse via local indefinite solvers. We further show how, identifying a minimum set of degrees of freedom to be fixed, an equivalent definite system can be solved instead, even in the elastic case. On the other hand, we propose a simple implementation of the algorithm that reduces the number of Dirichlet solvers to only one per iteration, leading to similar computational cost as additive methods. After these improvements of the BNN preconditioned conjugate gradient algorithm, we compare its performance against that of the BDDC preconditioners on a pair of large‐scale distributed‐memory platforms. The enhanced BNN method is a competitive preconditioner for three‐dimensional Poisson and elasticity problems and outperforms the BDDC method in many cases. Copyright © 2013 John Wiley & Sons, Ltd.     

International relocation and production geography in the European automobile components sector: the case of Spain

This article, based on the various approaches to location theory, analyses relocation processes in the Spanish automobile components industry in order to explain the importance of internal factors at both corporate and production plant levels. While acknowledging that location advantages play a relevant role, we show that changes in production geography can, to a great extent, be explained by corporate strategies, other decision-making mechanisms and firms’ characteristics. The results obtained from an empirical study during the period 2001–2008 show that the search for lower labour costs and corporate restructuring in order to achieve global production efficiency are the main factors determining relocation in the Spanish sector. These processes are facilitated by the operational flexibility of the multinational firms that dominate the sector. Lean supply and technological requirements are the main barriers to such processes of production plant mobility. From the point of view of practical relevance, the article shows that these logistic and technological determinants should be considered by managers in their relocation decisions not only in terms of cost efficiency but also in terms of the risks involved in relocation processes. Any relocation project must include measures to mitigate such risks.     

Evolutionary algorithms applied to reliable communication network design

Several evolutionary algorithms (EAs) applied to a wide class of communication network design problems modelled under the generalized Steiner problem (GSP) are evaluated. In order to provide a fault-tolerant design, a solution to this problem consists of a preset number of independent paths linking each pair of potentially communicating terminal nodes. This usually requires considering intermediate non-terminal nodes (Steiner nodes), which are used to ensure path redundancy, while trying to minimize the overall cost. The GSP is an NP-hard problem for which few algorithms have been proposed. This article presents a comparative study of pure and hybrid EAs applied to the GSP, codified over MALLBA, a general purpose library for combinatorial optimization. The algorithms were tested on several GSPs, and asset efficient numerical results are reported for both serial and distributed models of the evaluated algorithms.