Using simulation to compare Aircraft Boarding Strategies

The boarding process has a very important role in t he objective of increase the efficiency, profitability, and customer satisfaction of an airline industry. It is one of the significant elements of the turnaround time, a slow boarding process might lead to financial issues to the company and, of course, cu stomer complaints. In this paper are analyzed three boarding strategies presenting a model and an easy to use tool that implements it. The study suggest that differences exists among them, and proposes the most efficient strategy.Peer ReviewedPostprint (published version

A simulation study regarding different aircraft boarding strategies

The airline industry is constantly subject to the search of new methods in order to increase efficiency, profitability, and customer satisfaction. Since airlines only generate revenue when their airplanes are on the air, the time they spend at the airports should be the shortest possible. Hence, the airplane turnaround time becomes a process which airlines pay special attention on. The boarding process has a very important role, since it is one of the significant elements of the turnaround time, and a slow boarding process might lead to many kinds of problems to the airline, from financial issues to customer complaints. This paper analyzes the major interferences among the passengers that cause delays in boarding times, and after comparing the different aircraft boarding strategies, it proposes the most efficient strategy.Peer ReviewedPostprint (published version

Students have their say: factors involved in students' perception on their engineering degree

This is an Accepted Manuscript of an article published by Taylor & Francis in European Journal of Engineering Education on 02-11-2021, available online: http://www.tandfonline.com/10.1080/03043797.2021.1977244[EN] Higher Education institutions strive to continuously improve to meet students' expectations. Thus, it is vital to understand the factors involved in students' perceptions on their degree and on the quality of the teaching received. Engineering degrees require specific conditions due to their complex practical lessons and the need for high applicability, and our aim is to identify what affects the quality of the teaching delivered to our engineering students. Previous research on Higher Education focused on students' perception has been based on closed response questionnaires, which do not provide enough information. Hence, we asked students to freely make remarks, positive and/or negative on an open response questionnaire, and the qualitative analysis of their answers led to the description of a four-category figure (Teacher, Subject, Student, and Degree) revealing students' perceptions. Open response questionnaires offer administrators valuable information, as a complement to the quantitative analysis based on closed response questionnaires.Aznar-Mas, LE.; Atarés Huerta, LM.; Marin-Garcia, JA. (2021). Students have their say: factors involved in students' perception on their engineering degree. European Journal of Engineering Education. 46(6):1007-1025. https://doi.org/10.1080/03043797.2021.19772441007102546

Paper-based chromatic toxicity bioassay by analysis of bacterial ferricyanide reduction

Water quality assessment requires a continuous and strict analysis of samples to guarantee compliance with established standards. Nowadays, the increasing number of pollutants and their synergistic effects lead to the development general toxicity bioassays capable to analyse water pollution as a whole. Current general toxicity methods, e.g. Microtox®, rely on long operation protocols, the use of complex and expensive instrumentation and sample pre-treatment, which should be transported to the laboratory for analysis. These requirements delay sample analysis and hence, the response to avoid an environmental catastrophe. In an attempt to solve it, a fast (15 min) and low-cost toxicity bioassay based on the chromatic changes associated to bacterial ferricyanide reduction is here presented. E. coli cells (used as model bacteria) were stably trapped on low-cost paper matrices (cellulose-based paper discs, PDs) and remained viable for long times (1 month at -20 °C). Apart from bacterial carrier, paper matrices also acted as a fluidic element, allowing fluid management without the need of external pumps. Bioassay evaluation was performed using copper as model toxic agent. Chromatic changes associated to bacterial ferricyanide reduction were determined by three different transduction methods, i.e. (i) optical reflectometry (as reference method), (ii) image analysis and (iii) visual inspection. In all cases, bioassay results (in terms of half maximal effective concentrations, EC50) were in agreement with already reported data, confirming the good performance of the bioassay. The validation of the bioassay was performed by analysis of real samples from natural sources, which were analysed and compared with a reference method (i.e. Microtox). Obtained results showed agreement for about 70% of toxic samples and 80% of non-toxic samples, which may validate the use of this simple and quick protocol in the determination of general toxicity. The minimum instrumentation requirements and the simplicity of the bioassay open the possibility of in-situ water toxicity assessment with a fast and low-cost protocolPostprint (author's final draft

Thermal analysis of the plasma membrane Ca 2+ - ATPase

Abstract The plasma membrane Ca 2+ -ATPase is a well known enzyme in eucaryotes able to extrude calcium to the extracellular space in order to restore intracellular calcium to very low levels. This ATPase needs plasma membrane lipids such as acidic phospholipids in order to maintain its activity. In this study, we investigated the role that calcium and cholesterol play on the thermal stability of the Ca 2+ -ATPase isolated from cardiac sarcolemma and erythrocyte membranes. Calcium showed a stabilizing and protective effect when the enzyme was exposed to high temperatures. This stabilizing effect showed by calcium was potentiated in the presence of cholesterol. These protection effects were reflected on several thermodynamic parameters such as T 50 , ∆H vh and apparent ∆G, indicating that calcium might induce a conformational change stabilized in the presence of cholesterol that confers enzyme thermostability. The effect shown by cholesterol on ∆H vh and apparent ∆H ‡ open the possibility that this lipid decreases cooperativity during the induced transition. Despite that a binding site for cholesterol has not been identified in the plasma membrane Ca 2+ -ATPase, our results supports the proposal that this lipid interacts with the enzyme in a direct fashion. (Mol Cel

Numerical and experimental study of the time-dependent states and the slow dynamics in a von Ka´rma´n swirling flow

The characteristics of time-dependent swirling flows in a von Ka´rma´n configuration are investigated numerically up to Reynolds number Re¼3000 (based on the angular velocity and the radius of the cylinder), and experimentally within turbulent regimes. Experimental results are analyzed together with the periodic and aperiodic flow obtained numerically. In the present configuration, the fluid is contained in a cylindrical cavity with aspect ratio (height to radius) !¼2 and the motion is driven by the exact counter rotation of the end walls while the sidewall is at rest. Spectral direct numerical simulations show that for this geometry the axisymmetric base flow becomes unstable to non-axisymmetric perturbations with azimuthal wavenumber m¼1 through a subcritical bifurcation, and the corresponding flow exhibits a pattern with one cat’s eye in the axial-azimuthal planes. Increasing the Reynolds number the flow becomes unstable to non-axisymmetric steady perturbations with even azimuthal wavenumbers, and the corresponding flows exhibits a two cat’s eyes pattern. The occurrence of cat’s eye pattern in radial-azimuthal surfaces was observed in this and other aspect ratio cavities and is associated with vortices in 3D steady flows with characteristic azimuthal modes [Nore, C., Tuckerman, L.S., Daube, O. and Xin, S., The 1 : 2 mode interaction in exactly counter-rotating von Ka´rma´n swirling flow, J. Fluid Mech., 2003, 477, 51–88; Lackey, T.C. and Sotiropoulos, F., Relationship between stirring rate and Reynolds number in the chaotically advected steady flow in a container with exactly counter-rotating lids, Phys. Fluids, 2006, 18, 1–14]. Timedependent regimes are obtained numerically when the value of the Reynolds number is Re"1500. The time dependency is associated with a pulsation of the two vortices found in the steady regime. Experimental visualizations and measurements show that in turbulent regimes the flow also exhibits two vortices, but in this case they travel in the azimuthal direction with a frequency compatible with the frequency obtained in the numerical simulations at much lower Reynolds number. The azimuthal drift of these vortices is associated with the asymmetry of the mean azimuthal flow with respect to the equatorial plane

Optimization of low-efficiency traffic in OpenFlow Software Defined Networks

Abstract — This paper proposes a method for optimizing bandwidth usage in Software Defined Networks (SDNs) based on OpenFlow. Flows of small packets presenting a high overhead, as the ones generated by emerging services, can be identified by the SDN controller, in order to remove header fields that are common to any packet in the flow, only during their way through the SDN. At the same time, several packets can be multiplexed together in the same frame, thus reducing the number of sent frames. Four kinds of small-packet traffic flows are considered (VoIP, UDP and TCP-based online games, and ACKs from TCP flows). Both IPv4 and IPv6 are tested, and significant bandwidth savings (up to 68 % for IPv4 and 78 % for IPv6) can be obtained for the considered kinds of traffic

Cultural and socio-economic impacts of Mediterranean marine protected areas

Marine protected areas (MPAs) may be important for protecting the marine environment, but they may also have substantial socio-cultural impacts about which very little is currently known, or acknowledged. In the Mediterranean, few data are available on the socio-economic consequences of MPAs. The present study reviews the existing data on MPAs in Spain, France, Italy and Greece. A general increase in tourist activities in Mediterranean MPAs is evident, as are increases in the abundances of larger fish species, although there are no data indicating yields for fisheries increase adjacent to MPAs. A large increase in the number of divers and vessels using MPAs has already had impacts on natural benthic communities as a result of diver damage, mooring and the feeding of large fish by divers. Emphasis has been given in only a few MPAs to promoting public awareness of these impacts. Although the conservation of nature should be considered the fundamental objective of MPAs, neglecting their social, cultural and economic impacts has at times led to poor local consensus, if not hostility. We believe that planning and managing MPAs should be conducted on a multidisciplinary basis. Nonetheless, no single model can be considered valid for the whole Mediterranean. The very variable characteristics of coastal areas, from those of small uninhabited islands to those of cities, require different weightings to be assigned for each factor in order to achieve a durable equilibrium and realize the original objectives of each MPA. Only with such flexibility of management will it be possible to reach a greater understanding of the MPA system and create a lasting consensus in favour of conservation, a consensus which would mean an overwhelming majority of people actively avoiding damaging nature and preventing others from doing so.This paper was realized with funds from the EU CEC DGXII–MAST III contract number: MAS3-ct97–0155