Wind Turbine Blade Radar Signatures in the Near Field:Modeling and Experimental Confirmation

This paper presents methods and results in modeling wind turbine dynamic radar signatures in the near field. The theoretical analysis begins with the simpler case of modeling wind turbine blades as rectangular plates. The theoretical radar signature for the wind turbine in the near field is formulated and its main peculiarities are investigated. Subsequently, the complex shape of the blades is considered and the corresponding radar signatures are modeled. Theoretical modeling is confirmed for both cases via experimental testing in laboratory conditions. It is shown that the experimental results are in good accordance with the theoretically predicted signatures

Comparative study of clearing and prescribed burning treatments for fuel reduction in forest fire prevention in the municipality of Cabrillanes (León)

29 páginas, figuras[ES] Los incendios forestales suponen un gran problema ambiental, ya que cada vez son más grandes y virulentos, por eso es tan importante aplicar medidas de prevención. En este estudio se comparan dos métodos preventivos para la reducción de combustible forestal: la quema controlada y el desbroce. El estudio se ha realizado en un matorral de alta montaña dominado por Calluna vulgaris, en una zona situada al norte de la provincia de León con gran recurrencia de incendios forestales, en tres parcelas por tratamiento. Se estudian las variables de riqueza y cobertura de herbáceas y riqueza, cobertura y altura de las especies leñosas, además, de la cobertura de suelo descubierto. Los resultados indican que, con la quema prescrita, el estrato herbáceo es el que mejor se ha recuperado, junto con una pequeña cobertura de suelo descubierto. Con respecto a las especies leñosas, no se encontraron diferencias entre los tratamientos de quema y desbroce, pero sí se mostró que los tratamientos afectaron negativamente a su regeneración[EN] Forest fires represent a major environmental problem, as they are becoming larger and more virulent, and that is why it is so important to apply preventive measures. In this study, two different preventive methods for forest fuel reduction are being compared: controlled burning and clearing. The study was carried out in a high mountain scrubland dominated by Calluna vulgaris, located in the northern area of the province of León with a high recurrence of forest fires, in three plots per treatment. The variables of herbaceous richness and cover, richness, cover and height of woody species, as well as bare ground cover, were studied. The results indicate that, with prescribed burning, the herbaceous stratum is the one that has recovered the best, with a lower cover in bare ground. Regarding woody species, no differences were found between the burning and clearing treatments, but it was shown that the treatments had a negative effect on their regeneratio

Optimized frequency comb spectrum of parametrically modulated bottle microresonators

The formation of optical frequency combs (OFCs) by the parametric modulation of optical microresonators is commonly described by lumped-parameter models. However, these models do not consider the actual spatial distribution of the parametric modulation (SDPM). Here, we show that the effect of the SDPM becomes of special importance for an elongated SNAP bottle microresonator (SBM) having shallow nanometre-scale effective radius variation along its axial length. The advantage of SBMs compared to microresonators with different shapes (e.g., spherical and toroidal) is that SBMs, remaining miniature, can have resonant spectrum with much smaller free spectral range and no dispersion. Therefore, SBMs can be used to generate OFCs with much lower repetition rates. We consider the resonant and adiabatic modulation of parabolic SBMs and show that it is possible to improve the flatness and increase the bandwidth of the generated OFC spectra by optimising the SDPM. We suggest that the determined optimal SDPM can be experimentally realized using piezoelectric, radiation pressure, and electro-optical excitation of an SBM.Comment: 16 pages, 6 figure

Controlled transportation of light by light at the microscale

We show how light can be controllably transported by light at microscale dimensions. We design a miniature device that consists of a short segment of an optical fiber coupled to transversally oriented input-output microfibers. A whispering gallery soliton is launched from the first microfiber into the fiber segment and slowly propagates along its mm-scale length. The soliton loads and unloads optical pulses at designated input-output microfibers. The speed of the soliton and its propagation direction is controlled by the dramatically small, yet feasible to introduce, permanently or all-optically, nanoscale variations of the effective fiber radius

Addressing the permutational flow shop scheduling problem through constructive heuristics: A statistical comparison

Flow shop problem has been addressed by many researchers around the world. Different heuristic methods has been developed to deal with this kind of problems. Nevertheless, it is necessary to explore the impact that the bottleneck machine has on the performance of each heuristic. In this article an F6 || Cmax (Makespan) flow shop is tackled with different well-known heuristics in open literature, such as Palmer, Johnson, Gupta, CDS, NEH and PAS and their impact on Cmax was measure. The methodology used seeks to find the possible relationship between the different bottleneck machines and the result obtained from each of the heuristics. For this experiment, there were 302 scenarios with six machines in series, in which each machine had a parity number of scenarios in which it was the bottleneck. The values of Cmax obtained for each heuristic were compared against the result of corresponding MILP (Mixed Integer Liner Problem) problem. The results show that the performance of the NEH heuristic is superior in each scenario, regardless of the bottleneck, but also shows a variable behavior in each heuristic, taking into account the bottleneck machine

Optimized frequency comb spectrum of parametrically modulated bottle microresonators

Optical frequency combs generated by parametric modulation of optical microresonators are usually described by lumped-parameter models, which do not account for the spatial distribution of the modulation. This study highlights the importance of this spatial distribution in the Surface Nanoscale Axial Photonics (SNAP) platform, specifically for elongated SNAP bottle microresonators with a shallow nanometre-scale effective radius variation along its axial length. SNAP bottle microresonators have much smaller free spectral range and may have no dispersion compared to microresonators with other shapes (e.g., spherical and toroidal), making them ideal for generating optical frequency combs with lower repetition rates. By modulating parabolic SNAP bottle microresonators resonantly and adiabatically, we show that the flatness and bandwidth of the optical frequency comb spectra can be enhanced by optimizing the spatial distribution of the parametric modulation. The optimal spatial distribution can be achieved experimentally using piezoelectric, radiation pressure, and electro-optical excitation of a SNAP bottle microresonator

Rectangular SNAP microresonator fabricated with a femtosecond laser

Surface nanoscale axial photonics (SNAP) microresonators, which are fabricated by nanoscale effective radius variation (ERV) of the optical fiber with subangstrom precision, can be potentially used as miniature classical and quantum signal processors, frequency comb generators, and ultraprecise microfluidic and environmental optical sensors. Many of these applications require the introduction of nanoscale ERV with a large contrast α, which is defined as the maximum shift of the fiber cutoff wavelength introduced per unit length of the fiber axis. The previously developed fabrication methods of SNAP structures, which used focused CO2 and femtosecond laser beams, achieved α∼0.02 nm∕μm. Here we develop a new, to the best of our knowledge, fabrication method of SNAP microresonators with a femtosecond laser, which allows us to demonstrate a 50-fold improvement of previous results and achieve α∼1 nm∕μm. Furthermore, our fabrication method enables the introduction of ERV that is several times larger than the maximum ERV demonstrated previously. As an example, we fabricate a rectangular SNAP resonator and investigate its group delay characteristics. Our experimental results are in good agreement with theoretical simulations. Overall, the developed approach allows us to reduce the axial scale of SNAP structures by an order of magnitude