Browsing by Issue Date, starting with "2011-04"
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- Using social networks theory as a complementary perspective to the study of organizational changePublication . Ferreira, Manuel Portugal; Armagau, SunguThis paper contributes to the literature on organizational change by examining organizations as social entities embedded in inter-organizational networks. In contrast with extant research that focuses on macro environmental and internal factors to explain organizational change, we put forth the social network surrounding the firm as a major driver of any change process. Specifically, we examine organizational change as driven by the organizations’ positions and relations in an interorganizational network, and advance a set of theory driven propositions on innovation, imitation, inertia, structural equivalence and structural positioning. Our conceptual discussion demonstrates that inter-organizational networks are important in complementing the macroenvironment and internal organizational factors for the study of organizational changes. We conclude with a discussion on normative implications for organizations and avenues for future research.
- Blind men and the elephant : how to cope with european mobility finantial cutbacksPublication . Boa-Ventura, Ana Cecília; Silva, José ManuelDonald Puchala's metaphor of the blind men and the elephant is used to stress what the authors consider to be the current situation with the financial aid cutbacks from the European Commission: each of one of the member states is able to see only part of the problem and cannot see the whole picture. How can we cope with the consequences of having less students in mobility programs and more strategies to increase mobility in our own universities? We will share with you (1) how Portugal is trying to solve this problem, (2) the data from the past 2 years from our National Agency’s new policies and (3) the results of a case study of the Polytechnic Institute of Leiria, regarding incoming and outgoing Erasmus students for the 2010/2011 academic year.
- A 130 nm CMOS LNA for 30 GHz applicationsPublication . Ribeiro, R.; Moreira Mendes, Luís Miguel; Vaz, J. C.; Rosario, M. J.; Freire, J. C.This paper presents the design of a 30 GHz low noise amplifier in a 130 nm CMOS technology. The amplifier is based on a cascode topology. The circuit uses autotransformers in the input and output matching networks. This design approach eliminates the necessity of the use of source degeneration and allows obtaining an ultra compact LNA. The amplifier presents a forward gain (S21) of 7.4 dB at 30 GHz with a bandwidth of 10 GHz, input and output VSWRs better than 1.22:1 and a noise figure of 3.7 dB. The LNA is unconditionally stable and consumes only 7 mW when supplied with 1.2 V. The amplifier fits an area of 0.08 mm2, which is one of the smallest areas reported.
- Computational complexity reduction methods for multiscale recurrent pattern algorithmsPublication . Francisco, Nelson C.; M. M. Rodrigues, Nuno; Silva, Eduardo A. B. da; Carvalho, Murilo B. de; Faria, SergioThe Multidimensional Multiscale Parser algorithm was originally proposed as a generic lossy data compression algorithm. An high degree of adaptivity and versatility allowed it to outperform state-of-the-art transform-based compression methods for a wide range of applications, from still images, compound documents, or even ECG's, just to name a few. However, as other pattern matching algorithms, it presents a high computational complexity. In this paper, we investigated several techniques that allowed to considerably reduce both the encoder's and the decoder's computational complexity, with marginal R-D performance losses. The most important reduction was achieved on the decoder, that reduced up to 95% the time required by the previous method. These improvements contribute to affirm MMP as an alternative to traditional transform-based encoders, approaching its computational complexity with that of transform-based algorithms.
- Development and performance analysis of a real time high-resolution channel sounder - IF stagePublication . Ferreira, D.; Caldeirinha, RafaelThis paper presents an intermediate frequency (IF) stage of a swept time delayed cross-correlation (STDCC) channel sounder. The proposed topology employs the real-time sliding correlation technique of pseudo-random (PN) sequences, enabling amplitude and Doppler spectrum measurements and analysis of multipath components. It makes use of recent technologies, specifically in the generation and transmission of PN sequences, which allows for an easy adjustment of the main specifications of the sounder. The system presented here has been tested and validated by using a PN sequence at 1GHz chip rate, which allows for a time-delay resolution of consecutive multipath components of 2ns. The dynamic range at the IF stage's input was measured to be around 40 to 50 dB. The results presented are also compared with the VNA frequency sweep method.
- Stereo image coding using dynamic template-matching predictionPublication . Lucas, L. F. R.; M. M. Rodrigues, Nuno; Silva, E. A. B. da; Faria, SergioTemplate matching (TM) has been originally proposed as a texture synthesis tool. However, it has been successfully exploited for spatial and inter-frame prediction in video coding. In this paper we investigate the use of TM prediction for stereo image coding. In order to efficiently encode stereo images, the TM algorithm was optimized for stereo disparity prediction. Additionally, we have used the state-of-the-art pattern matching based algorithm, the Multidimensional Multiscale Parser (MMP), to encode images predicted with the proposed scheme. Experimental results of the developed stereo image encoder show that TM is able to efficiently exploit the redundancy between stereo views. The use of the new prediction method with MMP also achieves important coding gains over the state-of-the-art transform based H.264/AVC standard, for stereo image coding.
- Efficient scalable coding of video summaries using dynamic GOP structuresPublication . Ferreira, Lino; Cruz, L.; Assunção, PedroA method to efficiently encode an arbitrary video summary with temporal scalability and dynamic Group of Pictures (GOP) structures is proposed in this paper. The video summary is encoded as the base layer of a Scalable Video Coding (SVC) bitstream using a novel approach, which matches the summary frames available in temporal segments onto corresponding dynamic GOP structures. An algorithm is devised to compute variable GOP sizes along with an efficient independent prediction structure for the summary. The results show that the proposed method can be used to encode arbitrary video summaries with increased efficiency in the temporal base layer and negligible loss of R-D performance in the whole scalable sequence
- Advanced time-domain techniques for strongly nonlinear RF circuit simulation: Recent developments and remaining challengesPublication . Oliveira, Jorge; Pedro, J. C.Simulating modern wireless communication systems is today a hot topic. Serious difficulties arise when these systems are composed of strongly nonlinear highly heterogeneous circuits operating in multiple time scales. In this sense, this paper provides a general overview on the existing time-domain simulation techniques, as the ones encountered in commercial packages, or the ones recently published in the literature. Some new results will be introduced by presenting a comparison between the most relevant univariate and multivariate time domain techniques, in terms of computational efficiency.
- Analysis of the dRET input parameters under varying wind conditions at 20 GHzPublication . Morgadinho, S.; Caldeirinha, Rafael; Fernandes, Telmo, Telmo Rui Carvalhinho Cunha, Telmo R.; Richter, J.In this paper, the discrete Radiative Energy Transfer (dRET) theory is addressed as a means to the model dynamic effects through vegetation at millimetre-wave frequencies. The proposed approach, suggests the use of the dRET input parameters time-variant properties, to achieve the modelling of time-variant effects. Analysis of the input parameters time-variability, and its effect on the directional spectra is performed, in order to assess the feasibility of the proposed model approach.
- ArQoS®: System to monitor QoS/QoE in VoIPPublication . S. Cardeal; Neves, Filipe; Soares, S.; Tavares, F.; Assunção, PedroThe evolution of telecommunications technology from circuit to packet switching, in which the Internet is the great paradigm, offers nowadays more flexibility in services and higher efficiency in the transport infrastructure that was not experienced before. As consequence, several new services have emerged. Among them, Voice over IP (VoIP) is, indubitably, one of the most popular, mainly because it allows anyone to make low cost voice calls, making it a very attractive service. This is perhaps one of the main factors responsible for the fast development of VoIP technology. However, IP networks were not designed for services with real time requirements and factors like delay, jitter, codec distortions and packet loss lead to degradations that directly influence de VoIP user experience. The quality experienced by these users is highly dependent on network conditions and also on the subjective experience perceived by them. Thus, new challenges have brought with this evolution of telecommunications networks. In order to meet the assigned Service Level Agreement (SLA's), service providers around the world need to monitor and guarantee the agreed Quality of Service (QoS) to its customers. Consequently, an emergent way to measure QoS arises in the field of the telecommunications sector: the Quality of Experience (QoE) assessment and monitor that takes into account that subjective experience. Thus, a new challenging need arises: the development of systems and methods for assessing quality of experience, such that, network operators and service providers can actually know how users evaluate the quality of the service provided to them. In this paper, a system for assessing QoS/QoE is described: the ArQoS®. This is an integrated system provided by Portugal Telecom Inovação (PTIn) which implements QoE assessment methods to assess the networks performance and their telecommunications services. Beyond the existing methods already supported by the system, a novel QoE monitor for VoIP services was recently integrated as a result of fundamental research carried out at PTIn Labs. The ArQoS® is a probing system based on different types of probes, actually comprising two systems operating in two different modes: the active system (intrusive mode) and the passive system (non-intrusive mode).