Diego Antonio López-García

Most e-voting schemes make use of central servers. Users are obliged to trust these servers, which represent a vulnerability of the scheme. In the last few years, a very small group of schemes has been published that overcomes this handicap by using a peer-to-peer (P2P) approach. These are known as boardroom e-voting schemes, whereby users take the role of the servers. They act as managers of the process: they cast votes, keep a record of them, and verify the cryptographic operations made by others. Nevertheless, ballots must fulfill certain constraints which conflict with the possibilities of recent debate tools. These tools allow users to decide what to vote on, thus enabling the ballot frame to remain unknown before the voting process. The scheme presented here is a new boardroom voting protocol. It provides privacy, eligibility, and verifiability among other relevant features. The key advantage of this system is its high degree of flexibility, due to the absence of a need to impose any constraint on the ballots. This paper includes experimental results with two debate groups.

Mixnets are an instrument to achieve anonymity. They are generally a sequence of servers that apply a cryptographic process and a permutation to a batch of user messages. Most use asymmetric cryptography, with the high computational cost that this entails. The main objective of this study is to reduce delay in mixnet nodes. In this sense, this paper presents a new scheme that is based only on symmetric cryptography. The novelty of this scheme is the use of binary graphs built by mixnet nodes. The root node collects user keys and labels without knowing their owners. After feeding each node by its graph, they can establish a random permutation and relate their keys to the incoming batch positions through labels. The differences with previous symmetric schemes are that users do not need long headers and nodes avoid the searching process. The outcomes are security and efficiency improvements. As far as we know, it is the fastest mixnet system. Therefore, it is appropriate for high-throughput applications like national polls (many users) or debates (many messages).

This work proposes a means of reducing maritime transport emissions by combining electric ship propulsion with waste heat recovery systems. This solution was derived from the application of a literature-review based methodology, the findings of which were formulated as a paradigm consisting of a combination of electric ship propulsion with MVDC networks and waste heat recovery systems. This paradigm was then validated through modelling and simulation. Real-time simulations were deployed to evaluate the integration of the heat recovery system, specifically an Organic Rankine Cycle, into the MVDC network of the ship. The results of the simulations showed that an appropriate design of the DC network topology and control system is required for the ship to perform correctly under any scenario. It was concluded that replacing the passive rectifiers of the generators with controlled rectifiers improved the voltage profile of the MVDC network. In addition, it was inferred that the design of the global controller is essential for the integration of the heat recovery system.

This research work presents a techno-economic analysis of a biomass gasification plant fueled with residues from the olive oil and almond industries for combined heat and power generation in the agrifood sector. The experimental plant consists of a downdraft fixed bed gasifier, a producer gas cleaning and cooling system and a spark-ignition engine–generator set as a power generation unit, which generates about 10–12 kW of rated electric power. With an average consumption between 13–14 kg/h of exhausted olive pomace pellets as feedstock, the producer gas volumetric flow rate was 31 Nm³/h (vol. %: 19.2 H₂, 12.9 CO, 1.9 CH₄, 19.2 CO₂, 46.7 N₂). The average cold gas efficiency was nearly 63%. This work also addresses the characterization and potential application of the carbonaceous solid residue (biochar), discharged from the gasifier at 1.7 kg/h. Finally, an economic feasibility analysis was developed, wherein the payback period ranges between 5–9 years.

The hybridization of vehicles is a viable step toward overcoming the challenge of the reduction of emissions related to road transport all over the world. To take advantage of the emission reduction potential of hybrid electric vehicles (HEVs), the appropriate design of their energy management systems (EMSs) to control the power flow between the engine and the battery is essential. This work presents a systematic literature review (SLR) of the more recent works that developed EMSs for HEVs. The review is carried out subject to the following idea: although the development of novel EMSs that seek the optimum performance of HEVs is booming, in the real world, HEVs continue to rely on well-known rule-based (RB) strategies. The contribution of this work is to present a quantitative comparison of the works selected. Since several studies do not provide results of their models against commercial RB strategies, it is proposed, as another contribution, to complete their results using simulations. From these results, it is concluded that the improvement of the analyzed EMSs ranges roughly between 5% and 10% with regard to commercial RB EMSs; in comparison to the optimum, the analyzed EMSs are nearer to the optimum than commercial RB EMSs.

This paper proposes the use of a remote laboratory assigned to students online practical activities. The hands-on laboratory has a power system where the practical part of subjects related to photovoltaic can be taught. It consists of photovoltaic modules or a programmable source, a low-cost DC/DC buck-boost converter and a load. The remote laboratory is managed by a dsPIC30F microcontroller which serves as a link between the web server and the power system. Thus, the behavior of a photovoltaic system can be studied. It allows to obtain the characteristic curves under different conditions, the supervision of control strategies to track the maximum power point and even the design of the maximum power point tracking algorithms. At the same time, the students’ activities are tracked for pedagogical purposes. The obtained data suggest that the online laboratory facilitates the autonomy of the learners to conduct experiments and have a positive effect on students’ motivation.

Debates have been used to develop critical thinking within teaching environments. Many learning activities are configured as working groups, which use debates to make decisions. Nevertheless, in a classroom debate, only a few students can participate; large work groups are similarly limited. Whilst the use of web tools would appear to offer a convenient solution, none of those currently available provides an automated system for organizing contributions into a logical structure, or for making decisions. To address this problem, this paper describes a new tool for managing and structuring debates over the Internet, and presents the results of a series of trials in an educational context. The tool enables users to post opinions and proposals, and to make multiple group decisions. The main advantages are that it does not require a moderator, and all contributions are automatically arranged into an intuitive structure. Thus, it enabled large groups to carry out bigger projects. Empirical results showed that it also encouraged the involvement of all the students in debates and allowed the participation of each student to be evaluated. The tool demonstrated its advantages over traditional oral debates and, as far as we are aware, it incorporates features not found in any other comparable web tool.