Continuous monitoring of mining induced strain in a road pavement using fiber Bragg grating sensors

Abstrakt Få samhällsproblem har under de senaste åren mött så allmän uppmärksamhet som ungdomsbrottsligheten. Den polisanmälda ungdomsbrottsligheten har i stort sett följt brottslighetens utvecklingskurva avseende antal begångna brott, denna kurva visar en tydlig ökning sedan efterkrigstiden. Detta är en komparativ uppsats som är inriktad på ungdomsbrottsligheten i två av Malmö stadsdelar där vi undersöker antalet polisanmälda ungdomar till socialtjänsten mellan åren 2007-2009. Vi har studerat vilka brott ungdomarna var anmälda, analyserat brottstrender och i den mån det var möjligt granskat hur könsfördelningen har sett ut. Vi har undersökt vilka insatser som tillämpas från socialtjänstens håll för att motverka ungdomsbrottslighet samt förhindra fortsatt brottslighet hos redan polisanmälda ungdomar samt granska hur socialsekreterare vid våra undersökningsverksamheter upplever och uppfattar ungdomsbrottsligheten. Våra resultat har delvis ställts i relation till hur ungdomsbrottsligheten enligt tidigare forskning och redan befintlig statistik ser ut i Sverige. Vi har i uppsatsen använt oss av kvalitativ och kvantitativ datainsamlingsmetod samt ställt analysavsnitt och diskussionsavsnitt i relation till tidigare forskning och den av Travis Hirschis konstruerade teorin om sociala band. Studiens resultat visar bland annat att antalet polisanmälningar till socialtjänsterna har ökat, att killar begår fler brott än tjejer, att brottstyperna skiljer sig åt beroende på kön samt att ett mindre antal ungdomar ansvarar för en stor del av socialtjänsternas inkomna polisanmälningar

Acousto-optic attenuation filters based on tapered optical fibres

This paper studies the acousto-optic interaction induced by an acoustic flexural wave among the optical propagation modes supported by tapered optical fibres. We have investigated the evolution of the acousto-optic resonance condition as the fibre is progressively tapered, showing that the taper radius can be regarded as a new degree of freedom in the design of acousto-optic filters. Finally, we demonstrate a novel acousto-optic filter based on nonuniform tapers for dynamic gain flattening of optical fibre amplifiers

Metodología para la tipificación y caracterización estructural de paisajes en comarcas forestales españolas

The Forest Resources Management Plans are basic planning tools of the current Spanish Forest Law. Landscape ecology principles and methods on a regional scale are applicable to these Plans. This paper, part of ECOPORF project, proposes a methodology for the classification of landscapes in forest districts and the characterization of their structure. The definitive Landscape Types integrate the abiotic variables used in a previous Land Classification and the biotic information provided by the Spanish Forest Map (1:50.000). The calculation of certain landscape indices determines the characteristic composition and configuration of each Landscape Type. Finally, a method is proposed for the design of stratified sampling in landscape monitoring studies. This methodology provides a basic starting point for further development of Forest Resources Management Plans.Los Planes de Ordenación de los Recursos Forestales constituyen un instrumento básico de planificación forestal de la actual Ley de Montes (43/2003) española. La escala comarcal de esta figura es adecuada para la aplicación de conceptos y métodos relativos a la ecología del paisaje. Así, en este trabajo, encuadrado dentro del proyecto ECOPORF, se muestra una metodología para el establecimiento de una tipología de paisajes en comarcas forestales y su posterior caracterización estructural. Para ello, a partir de variables abióticas, se desarrolla un modelo de Clasificación Territorial que sirve como base para la definición y delimitación de Tipos de Paisaje, en la que se integra la información biótica proveniente del Mapa Forestal de España (1:50.000). El cálculo de determinados índices de paisaje en los diferentes Tipos permite definir su composición y configuración características. Por último, en el trabajo se propone un método para la selección de cuadrículas muestrales, con utilidad para la realización de estudios de monitorización del paisaje. El conocimiento obtenido tras el seguimiento de la metodología mostrada supone un punto de partida fundamental para el desarrollo de las siguientes fases de la elaboración de un Plan de Ordenación de los Recursos Forestales

Dispersive properties of quasi-phase-matched optical parametric amplifiers

The dispersive properties of non-degenerate optical parametric amplification in quasi-phase-matched (QPM) nonlinear quadratic crystals with an arbitrary grating profile are theoretically investigated in the no-pump-depletion limit. The spectral group delay curve of the amplifier is shown to be univocally determined by its spectral power gain curve through a Hilbert transform. Such a constraint has important implications on the propagation of spectrally-narrow optical pulses through the amplifier. In particular, it is shown that anomalous transit times, corresponding to superluminal or even negative group velocities, are possible near local minima of the spectral gain curve. A possible experimental observation of such effects using a QPM Lithium-Niobate crystal is suggested.Comment: submitted for publicatio

Semi-natural habitats support biological control, pollination and soil conservation in Europe:A review

Semi-natural habitats are integral to most agricultural areas and have the potential to support ecosystem services, especially biological control and pollination by supplying resources for the invertebrates providing these services and for soil conservation by preventing erosion and run-off. Some habitats are supported through agri-environment scheme funding in the European Union, but their value for ecosystem service delivery has been questioned. An improved understanding of previous research approaches and outcomes will contribute to the development of more sustainable farming systems, improve experimental designs and highlight knowledge gaps especially for funders and researchers. Here we compiled a systematic map to allow for the first time a review of the quantity of evidence collected in Europe that semi-natural habitats support biological control, pollination and soil conservation. A literature search selected 2252 publications, and, following review, 270 met the inclusion criteria and were entered into the database. Most publications were of pest control (143 publications) with less on pollination (78 publications) or soil-related aspects (31). For pest control and pollination, most publications reported a positive effect of semi-natural habitats. There were weaknesses in the evidence base though because of bias in study location and the crops, whilst metrics (e.g. yield) valued by end users were seldom measured. Hedgerows, woodland and grassland were the most heavily investigated semi-natural habitats, and the wider landscape composition was often considered. Study designs varied considerably yet only 24% included controls or involved manipulation of semi-natural habitats. Service providers were commonly measured and used as a surrogate for ecosystem service delivery. Key messages for policymakers and funders are that they should encourage research that includes more metrics required by end users, be prepared to fund longer-term studies (61% were of only 1-year duration) and investigate the role of soils within semi-natural habitats in delivering ecosystem services

Advances and new applications using the acousto-optic effect in optical fibers

This work presents a short review of the current research on the acousto-optic mechanism applied to optical fibers. The role of the piezoelectric element and the acousto-optic modulator in the excitation of flexural and longitudinal acoustic modes in the frequency range up to 1.2 MHz is highlighted. A combination of the finite elements and the transfer matrix methods is used to simulate the interaction of the waves with Bragg and long period gratings. Results show a very good agreement with experimental data. Recent applications such as the writing of gratings under the acoustic excitation and a novel viscometer sensor based on the acousto-optic mechanism are discussed

Effects of random phase and amplitude errors in optical fiber Bragg gratings

This paper studies the influence of random phase and amplitude fabrication errors on the performance of optical filters based on fiber Bragg gratings (FBGs). In particular, we analyze two effects of particular importance for optical communications: the excess crosstalk induced in apodized gratings commonly used in wavelength-division-multiplexing (WDM) systems, and the time-delay fluctuations that appear in chirped gratings employed to compensate the fiber dispersion. A statistical model is presented to explain these effects in terms of the coherence length of the grating fabrication procedure

Nondestructive characterization of fiber couplers by a local perturbation method

A technique for the nondestructive characterization of fiber couplers is demonstrated. A CO2 laser beam is scanned along the coupler length inducing a local perturbation to the coupler eigenmodes. Information about the power evolution and the coupling-constant variation along the coupler length can be obtained by applying an asymmetric and symmetric perturbation, respectively. Experimental results of the characterization of a half- and a full-cycle fiber coupler using this technique are presented

Advanced fibre Bragg gratings for high performance dispersion compensation in DWDM systems

The increasing application of DWDM transmission schemes with bit rates of 10 Gb/s and 50 GHz channel spacing places a strict requirement on dispersion management. The use of chirped fibre Bragg gratings to compensate the dispersion of fibre links is a well-known approach that has become increasingly prevalent over recent years. An ideal dispersion compensator should either provide continuous operation over the full bandwidth of a transmission system, or be capable of being closely packed with other such devices in order that every available DWDM channel can be transmitted. These criteria have, to date, been difficult to fulfill with grating technology: a single dispersion compensating grating with a bandwidth of &gt;30nm needs to be several metres in length raising questions of fabrication practicality and packaging concerns; traditional short (&lt;10cm) chirped gratings, which may be packaged athermally and are more straightforward to fabricate, have a low bandwidth filling-factor, and a non-linear group delay response. In this paper, we present, for the first time, experimental results of gratings designed by a newly-developed layer-peeling inverse-scattering algorithm for single-channel dispersion compensation compatible with 50 GHz DWDM channel spacing. Gratings made by this design procedure have a very high bandwidth utilisation factor, both in terms of reflectivity and linear group delay. They are designed to accommodate RZ signals on a 50 GHz grid, but alternatively will provide high ASE rejection on a 100 GHz grid whilst maintaining a broad useable bandwidth. We believe that this approach overcomes the limitations normally associated with short chirped gratings, whilst retaining their desirable fabrication and packaging characteristics. <br/