Browsing by Issue Date, starting with "2017-10"
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- Light field image Coding using high-order intrablock predictionPublication . Monteiro, Ricardo J. S.; Nunes, Paulo J. L.; Rodrigues, Nuno M. M.; Faria, Sérgio M. M. deThis paper proposes a two-stage high-order intrablock prediction method for light field image coding. This method exploits the spatial redundancy in lenslet light field images by predicting each image block, through a geometric transformation applied to a region of the causal encoded area. Light field images comprise an array of microimages that are related by complex geometric transformations that cannot be efficiently compensated by state-of-the-art image coding techniques, which are usually based on low-order translational prediction models. The two-stage nature of the proposed method allows us to choose the order of the prediction model most suitable for each block, ranging from pure translations to projective or bilinear transformations, optimized according to an appropriate rate-distortion criterion. The proposed higher order intrablock prediction approach was integrated into a high efficiency video coding (HEVC) codec and evaluated for both unfocused and focused light field camera models, using different resolutions and microlens arrays. Experimental results show consistent bitrate savings, which can go up to 12.62%, when compared to a lower order intrablock prediction solution and 49.82% when compared to HEVC still picture coding.
- Contextualização da Simulação Clínica e seus Benefícios TeóricosPublication . Duarte, Hugo Miguel Santos
- Lighting the Wireless World: The Promise and Challenges of Visible Light CommunicationPublication . Figueiredo, Mónica; Alves, Luis Nero; Ribeiro, CarlosLight-emitting diodes (LEDs) are becoming increasingly ubiquitous. They can be found in illumination appliances, phones, TVs, advertising panels, dashboards, and traffic signals, among others. Most illumination applications are becoming LED based, mainly due to their long operational lifetime and high energy efficiency, which is nowadays higher than 100 lm/W [1]. Other benefits include enhanced sustainability, a compact form factor, easier maintenance, and lower cost. For these reasons, LED lighting is expected to have a market share of 84% in the general illumination market by 2030 [2]. However, there is another characteristic that is not being fully exploited: LEDs are capable of switching their light intensity at a rate that is imperceptible to the human eye. This property has been used for dimming purposes but can also be utilized in the opportunistic deployment of value-added services based on visible light communication (VLC). Since 2011, VLC technology has gained momentum, supported by the release of the IEEE 802.15.7 draft standard [3] that defines the physical and medium-access control layers. This norm specifies data rates of up to 96 megabits/s for indoor and outdoor applications [3]. Since then, several research demonstrators have shown that VLC is capable of achieving gigabits-per-second transmission with commercial off-the-shelf red-green-blue (RGB) and phosphorescent white LEDs [4]. This is the result of the increasing attention that this technology has attracted in both the research community and global society in recent years. Figure 1 illustrates this trend over the last five years by depicting the number of results for the search term visible light communication conducted using the IEEE Xplore online library and Google search engine. A key VLC requirement is that it must be based on illumination-grade LEDs and comply with the illumination requirements and safety recommendations [5]. Also, data transmission should have minimal impact on LED performance, such as color temperature, color rendering index, and lifetime [6]. Most state-of-the-art VLC demonstrators have already proved they can achieve data rates compatible with the envisioned applications, but they do not address lighting quality issues. Thus, further investigation is still necessary to guarantee the seamless integration of lighting and communication services, which is crucial for the general deployment of this technology [7]. A pertinent question that one might ask is, “Why use light signals when we can use radio-frequency (RF) signals to communicate?” The visible light spectrum can be used synergistically with common radio technology. First, as the available RF bandwidth is limited, highly regulated, and increasingly congested, it may be helpful to use a portion of the spectrum that is unlicensed, currently largely unused, and amenable to spatial reuse. This is especially relevant in the realm of technologies beyond fifth generation (5G), where the density of users and devices with communication needs is predicted to scale up exponentially. Second, there are many application scenarios where the use of radio signals raises concerns related to e-smog, privacy, and security. Third, in scenarios where line of sight (LOS) and locality are important and the illumination infrastructure is already deployed (e.g., offices, stores, or vehicles), VLC can be a complement to current RF communications. Finally, light can be a good medium for low-cost and/or low-latency short-range links for near-field communications or high-bandwidth download links. Table 1 shows the most relevant visible light and RF signal characteristics, highlighting their complementarity. Broadcasting content to end users is the most natural service envisioned for directional technologies such as VLC. Luminaires are supposed to transmit a low- [8] or high-data-rate service [9] for end users located in their illumination area. However, VLC can also be used for full duplex communication, as long as the uplink and downlink can be separated [10]. This can be done by division in wavelength, in time, or in code or by resorting to spatial isolation. Alternatively, VLC can be combined with RF in heterogeneous networks [11]; VLC provides a high-capacity, uncongested, and unregulated downlink path, while RF is used in the uplink, where congestion is less likely. In the past couple of years, several interesting surveys have been published on VLC. Some are focused on physical-layer techniques [12], while others cover medium-access protocols [13], networking techniques and sensing [14], and lighting requirements [15]. A survey on more general optical wireless communications can be found in [16]. In this article, we provide a brief state-of-the-art overview of the technology and the main upcoming challenges.
- Da jurisprudência sieckmann ao regulamento (UE) 2015/2424. Evolução no registo das marcas olfativas na União Europeia?Publication . Lucas, EugénioA obrigatoriedade de representação gráfica da marca exigida no Regulamento (CE) nº 40/94 para o registo da marca comunitária impossibilitava a registo de uma marca olfativa na União Europeia. Com a jurisprudência Sieckmann (Processo C-273/00) o TJUE - Tribunal de Justiça da União Europeia aceita que as marcas possam ser sinais não visíveis, como aromas ou sons, mas rejeitou o pedido de registo de uma marca olfativa argumentando com a dificuldade de representação gráfica.
- The Impacts of Perceptions of Justice and Organizational Support on Employee Performance: The Moderating Role of Satisfaction with Management, in the Portuguese ContextPublication . Coelho, Arnaldo; Virgolino, Ana; Ribeiro, Neuza; Weersma, L.The objective of this paper is to identify the impact of perceived organizational justice (POJ) and perceived organizational support (POS) on the individual performance (IP) of employees and on burnout (BUR), considering the moderating role of satisfaction with organizational management (SOM). The study uses a structured questionnaire to gather self-reporting data from a cross-sectional sample of 407 employees. Structural equation modeling (SEM) is used to test the proposed hypotheses, and a multi-group analysis is conducted to find how the perception SOM can impact on the suggested relationships. The results show that POJ and POS have a positive impact on psychological contract (PC) and affective commitment (AC). Happiness (HAP) and AC have a positive impact on IP and PC has a negative impact on the BUR. It was also possible to conclude that SOM moderates the relationships between PC and BUR and, between leader-member exchange (LMX) and AC. This investigation provides a better understanding and integration of these concepts and relationship of moderation in a single study and provides a model that depicts a chain of important effects that may inform strategies to secure positive human resources management outcomes.
- NonDestructive Techniques for the Assessment and Preservation of Historic StructuresPublication . Gonçalves, Luísa M. S.; Rodrigues, Hugo; Gaspar, FlorindoThe preservation of the built heritage has long been a public concern, mainly due to fears about the loss of identity, history and heritage of populations. The main concerns are the conservation and restoration of monuments that usually represent important events in the history of a city or a country. More recently, urban residents and policymakers have become aware of the abandonment or degradation of old city cores, leading to mischaracterisation of the buildings and ways of living. To preserve history and promote building and urban renewal, considering the basic principles of the preservation process, it is important to introduce the least possible disturbance. To start with, the diagnostic process is a key aspect, especially to investigate the construction characteristics and the damage to materials, and to find structural and nonstructural problems. To start any process, a visual inspection, a study and knowledge of the original construction methods and materials and historical repair techniques can help but may not be sufficient, and the use of conventional techniques to complement the information needed can result in an insufficient understanding or in extensive and unnecessary intrusions in the construction. In recent years, the rapid growth of science and research, combined with the industry and the need to gather more and accurate information, have led to the fast development of nondestructive testing methodologies that allow the architectural archaeology to be studied, the structural assessment to be supported and information to be given about the material properties. Each technique can be used for a specific purpose, but, in some cases, only a combination of techniques is reliable and gives an accurate interpretation of the data acquired. The fundamental contribution and aim of this book is to give a full overview of several case studies where different nondestructive techniques have been applied, in several cases using multidisciplinary approaches, which aim to highlight the importance of the information acquired and encourage the use of these techniques in future studies. The book brings together 16 chapters focused on nondestructive testing techniques applied at the urban building level and also applied to monumental buildings, archaeology and cultural heritage, bringing together more than 40 international researchers and experts in the field, who are the source of practical case studies supported by a theoretical background.
- Hospital center website: Usability, accessibility and mobile optimizationPublication . Santos, Marisa Alexandra Monteiro; Piedade, Maria Beatriz; Távora, Vítor Noronha eIn this article it is presented and described the process of design, development, implementation and validation of the Middle Tagus Hospital Center’s website. It was intended to create a communication and disclosure tool of important and helpful information, it would be to meet the needs of users and health professionals. The website should respond to current technological issues, particularly those relating to the design, accessibility and mobile access. The website evaluation and validation process presented in this article included the development of usability and accessibility tests. The tests results are also presented and discussed. The evaluation and validation process prove the website utility, usability, accessibility and mobile optimization.
- Mobile augmented reality in cultural heritage context: Current technologiesPublication . Marto, Anabela G.R.; Sousa, A. Augusto de; José Marques Gonçalves, AlexandrinoThe use of augmented reality has a great potential applied to several areas, in particular, for cultural heritage context where it became possible to display, in loco, virtual elements which complement the user’s real scenario. Due to technological advances, differentiated ways of experience this technology has been explored, providing to common user, the access to this technology, until recently, quite limited, especially, in public locations. This article presents a work which includes implementation and evaluation of distinct applications of augmented reality – using smartphones – based on different techniques and tools. The evaluation intends to identify a solution to be implemented in a cultural heritage context, namely, the ruins of the Museu Monográfico de Conimbriga.
- Optical digital to analog conversion performance analysis for indoor set-up conditionsPublication . Dobesch, Aleš; Alves, Luis Nero; Wilfert, Otakar; Ribeiro, Carlos GasparIn visible light communication (VLC) the optical digital to analog conversion (ODAC) approach was proposed as a suitable driving technique able to overcome light-emitting diode’s (LED) non-linear characteristic. This concept is analogous to an electrical digital-to-analog converter (EDAC). In other words, digital bits are binary weighted to represent an analog signal. The method supports elementary on–off based modulations able to exploit the essence of LED’s non-linear characteristic allowing simultaneous lighting and communication. In the ODAC concept the reconstruction error does not simply rely upon the converter bit depth as in case of EDAC. It rather depends on communication system set-up and geometrical relation between emitter and receiver as well. The paper describes simulation results presenting the ODAC’s error performance taking into account: the optical channel, the LED’s half power angle (HPA) and the receiver field of view (FOV). The set-up under consideration examines indoor conditions for a square room with 4 m length and 3 m height, operating with one dominant wavelength (blue) and having walls with a reflection coefficient of 0.8. The achieved results reveal that reconstruction error increases for higher data rates as a result of interference due to multipath propagation.
- Estimation Through Array-Based Group TestsPublication . Oliveira Martins, João Paulo; Felgueiras, Miguel; Santos, RuiPooling individual samples for batch testing is a common procedure for reducing costs. The recent use of multidimensional array algorithms, due to the emergence of robotic pooling, is an innovative way of pooling. We show that the two-dimensional array-based group tests can provide accurate estimates for the prevalence rate even for situations in which the traditional estimators, applied to one-dimensional arrays, are not valid. Hence, a computational script was developed to determine which prevalence rate estimate minimizes the sum of the squared deviations between the number of observed and expected rows and columns whose pooled sample had a positive test result. © 2017, National Statistical Institute. All rights reserved.