Abstract
This paper reports the development of a power recycling network for a wireless radio-frequency (RF) transmitter combiner. The transmitter makes use of two RF power amplifiers (PAs) in an outphasing architecture, connected at the output by a 180-degree hybrid combiner. In general, to provide isolation between the PAs and prevent nonlinear distortion, an isolation resistor is usually applied at the four-port combiner. However, the main drawback of such approach is the power dissipated at the isolation port, which drastically reduces the overall power efficiency of the outphasing transmitter. In the present work, the isolation port is replaced by an active network that provides the required input impedance for isolation, at the same time it converts the RF signal into dc, feeding it back to the transmitter power supply. Hence, this way, one recycles the power that would be lost in the isolating resistor. The proposed active network comprises a circulator, a resonant rectifier and a dcdc converter that can be regulated by a maximum power point tracking (MPPT) algorithm. Simulation results for this power recycling system are provided, denoting 61-percent maximum efficiency achieved for an increase of 22-percent peak efficiency for QAM signals with a bandwidth of 250-kHz and carrier frequency equal to 250-MHz when operating at 41-miliwatt output power.

Abstract
The rise of smart manufacturing environments, characterized by high quantity of data/information available, contributes to a growing interest and research towards the use of immersive technologies not only in factories but also across entire value chains. New immersive technologies and devices are being developed to improve cooperation within Collaborative Networks (CNs), especially in the human-machine hybrid networks context. The application of these technologies in such complex environments expands substantially the modes how information is delivered and used, which may exacerbate one of the oldest problems of cognitive ergonomics: information overload. Therefore, this work presents applications of immersive technologies in manufacturing into the perspective of "information work" and "immersive human-centered manufacturing systems". A framework is proposed to be developed in a FabLab to understand the worker needs and interactions. This FabLab aims to demonstrate the potential/real application of immersive technologies, towards the enhancement of the human worker cognitive capabilities.

Abstract
Hash tries are a trie-based data structure with nearly ideal characteristics for the implementation of hash maps. In this paper, we present a novel, simple and scalable hash trie map design that fully supports the concurrent search, insert and remove operations on hash maps. To the best of our knowledge, our proposal is the first that puts together the following characteristics: (i) be lock free; (ii) use fixed size data structures; and (iii) maintain the access to all internal data structures as persistent memory references. Our design is modular enough to allow different types of configurations aimed for different performances in memory usage and execution time and can be easily implemented in any type of language, library or within other complex data structures. We discuss in detail the key algorithms required to easily reproduce our implementation by others and we present a proof of correctness showing that our proposal is linearizable and lock-free for the search, insert and remove operations. Experimental results show that our proposal is quite competitive when compared against other state-of-the-art proposals implemented in Java.

Abstract
Purpose This study explores the contribution that tech startups can provide in the fight against COVID-19. The Tech4Covid movement is presented to that effect, which has joined several Portuguese tech startups. This initiative gathers more than 5,000 volunteers and 28 ongoing projects in several interdisciplinary areas, including science, technology, health and education. Design/methodology/approach Two qualitative methods are adopted: the case study and the field research technique. This joint approach allows exploring in-depth the relevance and impact of the different areas included in Tech4Covid movement. Data were collected both from primary sources, namely by the authors' participation in the movement and by the use of secondary sources from each project. Findings The findings reveal three main areas in which the 28 ongoing projects can be categorized, respectively: support to health professionals and hospital equipment, health and education services and business and leisure. These projects offer direct and indirect contributions to the fight against COVID-19. From a perspective, they were initially designed to support health professionals in gathering protective equipment and supporting screening for suspicious cases. From another perspective, they also offer indirect benefits to citizens and the local economy. Originality/value This paper addresses a recent phenomenon with a dramatic impact on public health, social and economic dimensions. The study provides essentially practical contributions by revealing how Portuguese technological startups were organized and worked together to respond to the COVID-19 pandemic. It is expected this study will serve as a reference for other countries and communities that intend to replicate this model.

Abstract
The Trombe wall is a passive solar system that can improve buildings energy efficiency. Despite the studies already developed in this field, more research is needed to assess the possibility of its integration in buildings avoiding user intervention. In this study, the influence of air vent management and materials' heat storage capacity upon its thermal performance, particularly in the temperature fluctuation and indoor conditions, was discussed. Comparing two days with similar solar radiation (SR) for non-ventilated (NVTW) and ventilated (VTW) Trombe walls, a differential of 43 degrees C between the external surface temperature and the one in the middle of the massive wall was verified for NVTW, while for VTW this value was 27 degrees C, reflecting the heat transfer by air convection, which reduced greenhouse effect, solar absorption and heat storage. A cooling capacity greater than 50% was verified for VTW compared to NVTW during night periods. An algorithm for the Trombe wall's automation and control was proposed considering SR as variable. Air vents and external shading devices should be open when SR exceeds 100 W/m(2) and closed for 50 W/m(2) to obtain at least 20 degrees C inside the room. Closing for 50 W/m(2) and opening for values lower that 20 W/m(2) is suggested for summer periods.

Abstract
The operational transconductance amplifier (OTA) is, probably, the most relevant building block in analog circuits. However, its design has become particularly difficult in deep nanoscale CMOS technologies. Consequently, during the past decade, several inverter-based continuous-time and switched-capacitor (SC) amplifier circuit solutions have been proposed to overcome the limitations imposed by deep-submicron processes. Inverters scale friendly with the technology downscaling, but their applicability depends on some key performance parameters such as, energy-efficiency, die area, low-frequency (DC) gain, gain-bandwidth product (GBW) and linearity versus output-swing (OS). This paper presents three inverter-based SC amplifiers, namely a single inverter, a three-stage inverter, and a three-stage inverter with a multipath. The key performance parameters are simulated and fairly compared. The impact of their linearity on systems, depending on the application, is also discussed.