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.

Abstract
This paper models a novel demand response (DR) trading strategy. In this model, the DR aggregator obtains the DR from the end-users via two types of DR programs, i.e. a time-of-use (TOU) program and an incentive-based DR program. Then, it offers this DR to the wholesale market. Three consumer sectors, namely residential, commercial and industrial, are included in this problem. The DR program is dependent on their corresponding load profiles during the studied time horizon. This paper uses a mixed-integer linear programming (MILP) problem and it is solved using the CPLEX solver through a stochastic programming approach in GAMS. The risk measure chosen to represent the load uncertainty of the users who are participating in the DR program is Conditional Value-at-Risk (CVaR). The proposed problem is simulated and assessed through a case study of a test system. The results indicate that the industrial loads play a major role in the power system and this directly affects the DR program. Moreover, the risk-averse decision-maker in this model favors a reduced participation in the DR programs when compared to a decision-maker who is risk-neutral, since the risk-averse decision maker prefers to be more secure against uncertainties. In other words, an increase in risk factor results in a decrease in the participation rate of the consumers in DR programs.

Abstract