918 resultados para satellite-to-ground laser communications


Relevância:

100.00% 100.00%

Publicador:

Resumo:

En este trabajo se presentan los sistemas radar satélite y terrestres, así como los métodos de análisis de imágenes radar clásicos y avanzados para la investigación de los movimientos del terreno, haciendo énfasis en la subsidencia y los movimientos de ladera. Para ello en primer lugar se describen los distintos sensores radar disponibles así como las principales características de las imágenes radar generadas. A continuación se detallan los aspectos fundamentales de la interferometría diferencial, de los distintos métodos de interferometría diferencial avanzada y del radar terrestre. Finalmente se presentan los resultados obtenidos en distintas zonas de estudio: la subsidencia por explotación del acuífero en el área metropolitana de Murcia, la subsidencia minera y los movimientos de ladera de la Sierra de Cartagena, los movimientos de ladera de la cuenca del río Gállego y el deslizamiento del Portalet.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

In this paper we try to present the main trends of evolution of the ICT sector. Its dynamics, supported by a constant technical progress in ICs, compounded with “non convexities” such as network effects and high sunk costs, may either lead to a Schumpeter Mark I or Schumpeter Mark II competition regime. This means that in some segments, the market will be more competitive (Mark I), while in other it will be more monopolistic (Mark II). But a key trend is also the so called “convergence”. But digitization makes it cost effective to integrate different communications, information processing and entertainment systems and devices. Hence, Schumpeter Mark II grows at the core where software production dominates, while Schumpeter Mark I is established at the periphery. In this context, the European ICT industry is potentially smashed between two forces: the cost advantages of Asian countries on one hand, the inventiveness and dynamism of the US industry on the other hand. The way out of this very difficult situation is to create in Europe the conditions of restoring knowledge accumulation in a key sub-sector of ICT, that is software production. To do this, Europe can rely on its tradition of cooperation and knowledge sharing and on a set of institutions that have shown their ability to stimulate inter-regional cooperation. By concentrating on an ambitious project of open source software production in embarked systems and domestic networks, Europe could reach several objectives: to make freely accessible an essential facility, to stimulate competition, to help reaching the Lisbon objectives and to restore the European competitiveness in ICT.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Many European and American observers of the EC have criticized "intergovemmentalist" ac­ counts for exaggerating the extent of member state control over the process of European integra­ tion. This essay seeks to ground these criticisms in a "historical institutionalist" account that stresses the need to study European integration as a political process which unfolds over time. Such a perspective highlights the limits of member-state control over long-term institutional de­ velopment, due to preoccupation with shorHerm concerns, the ubiquity of unintended conse­ quences, and processes that "lock in" past decusions and make reassertions of member-state control difficult. Brief examination of the evolution of social policy in the EC suggests the limita­ tions of treating the EC as an international regime facilitating collective action among essentially sovereign states. It is ore useful to view integration as a "path-dependent" process that has pro­ duced a fragmented but still discernible "multitiered" European polity.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

INTRODUCTION In the current times of multifaceted crisis, nationalism looks, more than ever, like a positive and necessary feeling. It seems both natural and indispensable if we are to have viable political and social institutions that meet the needs and preferences of all citizens. The following paper contests this vision. Its criticism of nationalism is directed not only at its national forms, but also at any defence of collective identity based on the same model, such as the various forms of European nationalism. Furthermore, the same overriding criticism can be made of different kinds of nationalism, regardless of their more or less open and progressive political content. In order to ground our argument theoretically and practically, we will try to show that nationalism is always potentially harmful to individual rights, and unnecessary for the maintenance of a just social and political system. We will thus oppose any acritical defence of the intrinsic value of a specific community and the belief in its artificial homogeneity. The historical construction of a supposedly homogeneous community, and the insistence on its values, which are perceived as superior and binding, facilitate the absorption of the individual into the collective. As we will explain further in more details, this holistic approach is typical of communitarian approaches. In that respect, it does not really matter whether they appeal to passion or to reason, to some irrational binding features of the community or to more rational political aspects of a common identity. The main problem in nationalism is not the emotion it can trigger, it is not even its reliance on particular values. What makes nationalism problematic is, firstly, that it tends to overlook the intrinsically divisive and contradictory nature of individual and collective interests in unjust societies; secondly, that it attributes an intrinsic superiority to a particular community over others; and thirdly, that it sees politics as a means to promote the interests, values or identity of that community. As an alternative, we will very briefly advocate a cosmopolitan approach that grounds political legitimacy in a demanding approach to individual freedom, rather than in a shared collective identity. However, even if only briefly, we will also carefully distinguish our own vision of cosmopolitanism from those commonly put forward. Frequently, cosmopolitan perspectives entangle their identity frameworks with concrete political projects, without clearly explaining how the latter derive from the former. Our approach to cosmopolitanism, on the other hand, is, first and foremost, a critical vision of all communitarian postulates according to which politics should be based on some form of collective identity. Thus, we insist on the conceptual distinction between a general stance on identity issues and the more practical political ideology one stands for. In a subsequent step, we link this cosmopolitan framework with a progressive approach to individual rights. Because of our demanding approach to individual freedom, our cosmopolitanism goes hand in hand with a revival of identity-free sovereignty. It is therefore distinct from the severe condemnation of sovereignty often found in most mainstream cosmopolitan positions. Finally, instead of the frequent confusion found in public discourses and in the literature between ideals and reality, our position acknowledges the deep gulf separating these two dimensions. It therefore sketches out very general strategic principles to bring normative ideals closer to political reality.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Investigation into the earliest signs of autism in infants has become a significant sub-field of autism research. This work invokes specific ethical concerns such as use of 'at-risk' language, communicating study findings to parents and the future perspective of enrolled infants when they reach adulthood. This study aimed to ground this research field in an understanding of the perspectives of members of the autism community. Following focus groups to identify topics, an online survey was distributed to autistic adults, parents of children with autism and practitioners in health and education settings across 11 European countries. Survey respondents (n = 2317) were positively disposed towards early autism research, and there was significant overlap in their priorities for the field and preferred language to describe infant research participants. However, there were also differences including overall less favourable endorsement of early autism research by autistic adults relative to other groups and a dislike of the phrase 'at-risk' to describe infant participants, in all groups except healthcare practitioners. The findings overall indicate that the autism community in Europe is supportive of early autism research. Researchers should endeavour to maintain this by continuing to take community perspectives into account.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

This paper identifies and examines issues of relevance for increasing effectiveness of entrepreneurial management research. These issues emerged from research into entrepreneurial behaviour and underlying motivations in Sri Lanka. Understanding of socially- and culturally-bound social actors, social actions and social outputs in entrepreneurial activity requires context-sensitivity, expressed through cognisance of institutional characteristics, the interface between cultural values and business, and historical and cultural forces which impact on entrepreneurship. We suggest that this requires exploration through bottom-up translations of actions consistent with the beliefs and values of the actors involved, employing qualitative methodology to ground the reality of human behaviour in deep-rooted cultural and social contexts. Thorough interpretation of holistic case studies that are capable of capturing the actors' viewpoints brings appropriate insights to the field of entrepreneurship.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Este estudo investigou os efeitos do laser de baixa intensidade na velocidade da movimentação ortodôntica de caninos submetidos à retração inicial. A amostra constou de 26 caninos superiores e inferiores, submetidos à retração inicial realizada com mola Niti, com força de 150g. Um dos caninos foi irradiado com laser de diodo, seguindo o protocolo de aplicação: 780nm/20mW/5Jcm2/0,2J por ponto/Et=2J, nos dias 0, 3 e 7 pós-ativação, sendo que o contralateral foi considerado placebo. A retração durou em média 4 meses, num total de 9 aplicações de laser. Os modelos de cada mês foram escaneados com scanner 3D (3Shape) e as imagens tridimensionais foram analisadas por meio do Software Geomagic Studio 5, para a mensuração da quantidade de movimentação dos caninos retraídos. Foi empregada a Análise de Variância a três critérios, seguida pelo teste de Tukey (p<0,05). Para verificação da integridade tecidual, foram efetuadas radiografias periapicais iniciais e finais dos caninos retraídos e dos molares, nas quais foram avaliados uma possível reabsorção na crista alveolar, por meio da distância da crista óssea alveolar até a junção cemento-esmalte e os níveis de reabsorção radicular, por meio do índice de Levander e Malmgreen, sendo este último avaliado somente nos caninos retraídos. Para isto, foi empregado o teste não paramétrico de Wilcoxon (p<0,05). Os resultados indicaram que houve um aumento estatisticamente significante na velocidade da movimentação dos caninos irradiados comparados ao seu contralateral, em todos os tempos avaliados, como também a preservação da integridade tecidual. Com isso, concluiu-se que o laser de diodo pode acelerar a movimentação ortodôntica, podendo contribuir para a diminuição do tempo de tratamento.(AU)

Relevância:

100.00% 100.00%

Publicador:

Resumo:

This thesis presents experimental investigation of different effects/techniques that can be used to upgrade legacy WDM communication systems. The main issue in upgrading legacy systems is that the fundamental setup, including components settings such as EDFA gains, does not need to be altered thus the improvement must be carried out at the network terminal. A general introduction to optical fibre communications is given at the beginning, including optical communication components and system impairments. Experimental techniques for performing laboratory optical transmission experiments are presented before the experimental work of this thesis. These techniques include optical transmitter and receiver designs as well as the design and operation of the recirculating loop. The main experimental work includes three different studies. The first study involves a development of line monitoring equipment that can be reliably used to monitor the performance of optically amplified long-haul undersea systems. This equipment can provide instant finding of the fault locations along the legacy communication link which in tum enables rapid repair execution to be performed hence upgrading the legacy system. The second study investigates the effect of changing the number of transmitted 1s and Os on the performance of WDM system. This effect can, in reality, be seen in some coding systems, e.g. forward-error correction (FEC) technique, where the proportion of the 1s and Os are changed at the transmitter by adding extra bits to the original bit sequence. The final study presents transmission results after all-optical format conversion from NRZ to CSRZ and from RZ to CSRZ using semiconductor optical amplifier in nonlinear optical loop mirror (SOA-NOLM). This study is mainly based on the fact that the use of all-optical processing, including format conversion, has become attractive for the future data networks that are proposed to be all-optical. The feasibility of the SOA-NOLM device for converting single and WDM signals is described. The optical conversion bandwidth and its limitations for WDM conversion are also investigated. All studies of this thesis employ 10Gbit/s single or WDM signals being transmitted over dispersion managed fibre span in the recirculating loop. The fibre span is composed of single-mode fibres (SMF) whose losses and dispersion are compensated using erbium-doped fibre amplifiers (EDFAs) and dispersion compensating fibres (DCFs), respectively. Different configurations of the fibre span are presented in different parts.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

We present, for the first time, a detailed investigation of the impact of second order co-propagating Raman pumping on long-haul 100G WDM DP-QPSK coherent transmission of up to 7082 km using Raman fibre laser based configurations. Signal power and noise distributions along the fibre for each pumping scheme were characterised both numerically and experimentally. Based on these pumping schemes, the Q factor penalties versus co-pump power ratios were experimentally measured and quantified. A significant Q factor penalty of up to 4.15 dB was observed after 1666 km using symmetric bidirectional pumping, compared with counter-pumping only. Our results show that whilst using co-pumping minimises the intra-cavity signal power variation and amplification noise, the Q factor penalty with co-pumping was too great for any advantage to be seen. The relative intensity noise (RIN) characteristics of the induced fibre laser and the output signal, and the intra-cavity RF spectra of the fibre laser are also presented. We attribute the Q factor degradation to RIN induced penalty due to RIN being transferred from the first order fibre laser and second order co-pump to the signal. More importantly, there were two different fibre lasing regimes contributing to the amplification. It was random distributed feedback lasing when using counter-pumping only and conventional Fabry-Perot cavity lasing when using all bidirectional pumping schemes. This also results in significantly different performances due to different laser cavity lengths for these two classes of laser.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The spectral properties of long-period gratings (LPGs) fabricated in photonic crystal fibers using femtosecond laser pulses by the point-by-point technique, without oil-immersion of the fiber, are investigated in detail. Postfabrication spectral monitoring at room temperature showed significant long-term instability of the gratings and stable spectra only after 600 h. The stabilized spectral properties of the gratings improved with increasing annealing temperature. The observed changes in resonant wavelength, optical strength, and grating birefringence were correlated to the laser inscription energy and were further used to study the mechanism of femtosecond inscription. Furthermore, the femtosecond-laser inscribed LPGs were compared to electric-arc fabricated LPGs. Comparison of experimental results with theoretical models of LPGs and laser propagation during inscription indicate that the major processes responsible for the index change are permanent compaction and thermally induced strain, the latter can be significantly changed through annealing. © 2011 Optical Society of America.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Glass is a common form of trace evidence found at many scenes of crimes in the form of small fragments. These glass fragments can transfer to surrounding objects and/or persons and may provide forensic investigators valuable information to link a suspect to the scene of a crime. Since the elemental composition of different glass sources can be very similar, a highly discriminating technique is required to distinguish between fragments that have originated from different sources. ^ The research presented here demonstrates that Laser Induced Breakdown Spectroscopy (LIBS) is a viable analytical technique for the association and discrimination of glass fragments. The first part of this research describes the optimization of the LIBS experiments including the use of different laser wavelengths to investigate laser-material interaction. The use of a 266 nm excitation laser provided the best analytical figures of merit with minimal damage to the sample. The resulting analytical figures of merit are presented. The second part of this research evaluated the sensitivity of LIBS to associate or discriminate float glass samples originating from the same manufacturing plants and produced at approximately the same time period. Two different sample sets were analyzed ranging in manufacturing dates from days to years apart. Eighteen (18) atomic emission lines corresponding to the elements Sr, K, Fe, Ca, Al, Ba, Na, Mg and Ti, were chosen because of their detection above the method detection limits and for presenting differences between the samples. Ten elemental ratios producing the most discrimination were selected for each set. When all the ratios are combined in a comparison, 99% of the possible pairs were discriminated using the optimized LIBS method generating typical analytical precisions of ∼5% RSD. ^ The final study consisted of the development of a new approach for the use of LIBS as a quantitative analysis of ultra-low volume solution analysis using aerosols and microdrops. Laser induced breakdown spectroscopy demonstrated to be an effective technique for the analysis of as low as 90 pL for microdrop LIBS with 1 pg absolute LOD and 20 µL for aerosol LIBS with an absolute LOD of ∼100 fg.^

Relevância:

100.00% 100.00%

Publicador:

Resumo:

In this thesis, we proposed the use of device-to-device (D2D) communications for extending the coverage area of active base stations, for public safety communications with partial coverage. A 3GPP standard compliant D2D system level simulator is developed for HetNets and public safety scenarios and used to evaluate the performance of D2D discovery and communications underlying cellular networks. For D2D discovery, the benefits of time-domain inter-cell interference coordi- nation (ICIC) approaches by using almost blank subframes were evaluated. Also, the use of multi-hop is proposed to improve, even further, the performance of the D2D discovery process. Finally, the possibility of using multi-hop D2D communications for extending the coverage area of active base stations was evaluated. Improvements in energy and spectral efficiency, when compared with the case of direct UE-eNB communi- cations, were demonstrated. Moreover, UE power control techniques were applied to reduce the effects of interference from neighboring D2D links.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

One of the research programs carried out within the Czech-Ukrainian scientific co-operation is the monitoring of global solar and ultraviolet radiation at the Vernadsky Station (formerly the British Faraday Station), Antarctica. Radiation measurements have been made since 2002. Recently, a special attention is devoted to the measurements of the erythemally effective UVB radiation using a broadband Robertson Berger 501 UV-Biometer (Solar Light Co. Inc., USA). This paper brings some results from modelling the daily sums of erythemally effective UVB radiation intensity in relation to the total ozone content (TOC) in atmosphere and surface intensity of the global solar radiation. Differences between the satellite- and ground-based measurements of the TOC at the Vernadsky Station are taken into consideration. The modelled erythemally effective UVB radiation differed slightly depending on the seasons and sources of the TOC. The model relative prediction error for ground- and satellite-based measurements varied between 9.5% and 9.6% in the period of 2002-2003, while it ranged from 7.4% to 8.8% in the period of 2003-2004.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

As part of the ultrafast charge dynamics initiated by high intensity laser irradiations of solid targets,high amplitude EM pulses propagate away from the interaction point and are transported along anystalks and wires attached to the target. The propagation of these high amplitude pulses along a thinwire connected to a laser irradiated target was diagnosed via the proton radiography technique,measuring a pulse duration of 20 ps and a pulse velocity close to the speed of light. The strongelectric field associated with the EM pulse can be exploited for controlling dynamically the protonbeams produced from a laser-driven source. Chromatic divergence control of broadband laser drivenprotons (upto 75% reduction in divergence of >5 MeV protons) was obtained by winding the supportingwire around the proton beam axis to create a helical coil structure. In addition to providingfocussing and energy selection, the technique has the potential to post-accelerate the transiting protonsby the longitudinal component of the curved electric field lines produced by the helical coil lens.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The latest techniques for the fabrication of high power laser targets, using processes developed for the manufacture of Micro-Electro-Mechanical System (MEMS) devices are discussed. These laser targets are designed to meet the needs of the increased shot numbers that are available in the latest design of laser facilities. Traditionally laser targets have been fabricated using conventional machining or coarse etching processes and have been produced in quantities of 10s to low 100s. Such targets can be used for high complexity experiments such as Inertial Fusion Energy (IFE) studies and can have many complex components that need assembling and characterisation with high precision. Using the techniques that are common to MEMS devices and integrating these with an existing target fabrication capability we are able to manufacture and deliver targets to these systems. It also enables us to manufacture novel targets that have not been possible using other techniques. In addition, developments in the positioning systems that are required to deliver these targets to the laser focus are also required and a system to deliver the target to a focus of an F2 beam at 0.1Hz is discussed.