Space Division Multiplexing (SDM) is a key technology to cope with the bandwidth limitations of single mode fibers. Multi-Core Fibers (MCFs) are considered as a promising candidate technology to implement SDM, due to their low inter-core crosstalk (ICXT), experimentally proven in laboratory prototypes. Among the different channel allocation options making use of the newly enabled space dimension, the so-called spatial super-channel (Spa-SCh) is the most likely solution to be implemented, given the inherent cost reduction of the joint-switching operation (i.e., jointly switching a spectrum portion in all MCF cores at once). This work targets the cost-effective Spa-SCh allocation over MCF-enabled Flex-Grid optical core networks. To this goal, state-of-the-art 22-core MCFs are assumed, although the proposed solutions are applicable to any MCF type. In particular, we propose and evaluate a partial-core assignment as a cost-effective strategy to improve spectrum utilization and save Capital Expenditure (CapEx) costs by minimizing the number of optical transceivers used per Spa-SCh. Numerical results reveal that reductions up to 44% and 33% in the number of active transceivers in the network can be obtained in national- and continental-wide backbone networks, respectively, without affecting the network Grade-of-Service (GoS), measured in terms of Bandwidth Blocking Probability (BBP). To evaluate the impact of the ICXT, we also compare the performance of the MCF scenarios under study against equivalent Multi-Fiber (MF) ones. From the obtained results, ICXT in MCF scenarios requires the utilization of less efficient modulation formats, which reduces the admissible offered network load by up to 17% for a 1% BBP target. Furthermore, this lower spectral efficiency also demands an increase of the symbol rate per sub-channel up to a 26%, a key indicator of the modulator electronic complexity.
Rodriguez-Gomez, A.; Sicard, M.; Granados, M.; Ben Chahed, E.; Muñoz, C.; Barragan, R.; Comeron, A.; Rocadenbosch, F.; Vidal, E. Sensors Vol. 17, num. 12, p. 1-16 DOI: 10.3390/s17122957 Data de publicació: 2017-12-20 Article en revista
A new architecture for the measurement of depolarization produced by atmospheric
aerosols with a Raman lidar is presented. The system uses two different telescopes: one for
depolarization measurements and another for total-power measurements. The system architecture
and principle of operation are described. The first experimental results are also presented,
corresponding to a collection of atmospheric conditions over the city of Barcelona.
Sarmiento, S.; Altabas, J.; Izquierdo, D.; Garces, I.; Spadaro, S.; Lazaro, J.A. Journal of optical communications and networking Vol. 9, num. 12, p. 1116-1124 DOI: 10.1364/JOCN.9.001116 Data de publicació: 2017-12 Article en revista
Architectural changes are required for the underlying networks to support the expected Internet data traffic volume growth caused by the popularization of cloud services, 5G-based services, and social networks, to provide a highly dynamic connectivity. Cost-effective and energy-efficient solutions for flexible network subsystems are required to provide future sustainable networks. In this paper, we present a cost-effective dense wavelength division multiplexing (DWDM) reconfigurable optical add/drop multiplexer (ROADM) design enabling optical metro–access networks convergence. The cost-effective DWDM ROADM capabilities also have been assessed in an ultradense wavelength multiplexing (u-DWDM) ring network scenario. In particular, achievable network throughput has been considered.
Oikonomakou , M.; Antonopoulos, A.; Alonso, L.; Verikoukis, C. IEEE transactions on vehicular technology Vol. 66, num. 12, p. 11352-11365 DOI: 10.1109/TVT.2017.2719404 Data de publicació: 2017-12 Article en revista
The anticipated explosion in the total data traffic load will impose to mobile network operators (MNOs) the necessity to densify their networks to provide coverage. At the same time, since MNOs plan their networks according to their high-peak traffic load, base station (BS) underutilization during the low traffic hours raises the issue of unnecessary power consumption and excessive cost. In this paper, we plan to study the energy and cost efficiency of a heterogeneous network (HetNet) that is a cooperation result of many MNOs. Each MNO is owner of a HetNet, composed of eNodeBs and small cells and they cooperate by sharing their infrastructure and by switching off a part of it. BS type and traffic load constitute switching off criteria and a roaming-cost-based user association scheme is used to roam traffic to neighboring BSs. We assess the cost alterations created by the possible MNO coalitions and we propose a bankruptcy game to allocate the obtained cost to the cooperative MNOs and to motivate them thus to maintain their sharing agreement instead of following a non-cooperative tactic. The bankruptcy game uses Shapley Value to portray each MNO's contribution to cost savings. The MNOs’ satisfaction from their payoffs (i.e., the allocated cost) and the overall fairness of the method are evaluated. According to the extracted results, the proposed switching off scheme achieves significant improvement of energy efficiency for the studied network, while the proposed bankruptcy game achieves a balanced and satisfactory cost allocation for different MNO traffic loads.
Continuous descent operations with controlled times of arrival at one or several metering fixes could enable environmentally friendly procedures without compromising terminal airspace capacity. This paper focuses on controlled time of arrival updates once the descent has been already initiated, assessing the feasible time window (and associated fuel consumption) of continuous descent operations requiring neither thrust nor speed-brake usage along the whole descent (i.e. only elevator control is used to achieve different metering times). Based on previous works, an optimal control problem is formulated and numerically solved. The earliest and latest times of arrival at the initial approach fix have been computed for the descent of an Airbus A320 under different scenarios, considering the potential altitudes and distances to go when receiving the controlled time of arrival update. The effects of the aircraft mass, initial speed, longitudinal wind and position of the initial approach fix on the time window have been also investigated. Results show that time windows about three minutes could be achieved for certain conditions, and that there is a trade-off between robustness facing controlled time of arrival updates during the descent and fuel consumption. Interestingly, minimum fuel trajectories almost correspond to those of minimum time.
The microstructural evolution of an Al–Zn–Mg–Cu alloy under continuous heating over the temperature range of 298 to 648 K (25 to 375 °C) is characterized by focused ion beam-scanning electron microscopy, transmission electron microscopy, and atom probe tomography. The chemical composition, dimensions, number density, and volume fraction of precipitates are measured comprehensively. Quantitative measurements of Guinier-Preston zones volume fraction and ¿'/¿ phase volume fraction are correlated to the viscoelastic response of the Al–Zn–Mg–Cu alloy with temperature in the studied range. This provides valuable evidence indicating that observed variations in the viscoelastic behavior of the Al–Zn–Mg–Cu alloy may be associated with phase transformations involving Guinier-Preston zones and phases ¿' and ¿.
Moreno, F.J.; Rumipamba Zambrano, R.; Pavón, P.; Perello, J.; Gene, J. M.; Spadaro, S. Journal of optical communications and networking Vol. 9, num. 11, p. 1041-1050 DOI: 10.1364/JOCN.9.001041 Data de publicació: 2017-11-01 Article en revista
To effectively keep pace with the global IP traffic growth forecasted in the years to come, flex-grid over multi-core fiber (MCF) networks can bring superior spectrum utilization flexibility, as well as bandwidth scalability far beyond the non-linear Shannon’s limit. In such a network scenario, however, full node switching re-configurability will require enormous node complexity, pushing the limits of current optical device technologies with prohibitive capital expenditures. Therefore, cost-effective node solutions will most probably be the key enablers of flex-grid/MCF networks, at least in the short- and mid-term future. In this context, this paper proposes a cost-effective reconfigurable optical add/drop multiplexer (ROADM) architecture for flex-grid/MCF networks, called CCC-ROADM, which reduces technological requirements (and associated costs) in exchange for demanding core continuity along the end-to-end communication. To assess the performance of the proposed CCC-ROADM in comparison with a fully flexible ROADM (i.e., a fully non-blocking ROADM, called FNB-ROADM in this work) in large-scale network scenarios, a novel lightweight heuristic to solve the route, modulation, core, and spectrum assignment problem in flex-grid/MCF networks is presented in this work, whose goodness is successfully validated against optimal ILP formulations previously proposed for the same goal. The obtained numerical results in a significant number of representative network topologies with different MCF configurations of 7, 12, and 19 cores show almost identical network performance in terms of maximum network throughput when deploying CCC-ROADMs versus FNB-ROADMs, while decreasing network capital expenditures to a large extent.
A compromise solution to increase flight efficiency in cruise, but without penalising capacity (or even safety), would be perhaps to remove (or relax) the minimum rate of climb (ROC) constraint and/or to reduce the height of the step climbs in cruise. In this paper, the benefits (in terms of total operating costs) and the associated impact on the air traffic management (ATM) of such “relaxed cruise” operations are quantified for a representative medium-haul aircraft under different scenarios, by means of an in-house trajectory optimisation software. Results show that by reducing the minimum ROC from 500 to 300 ftmin-1, whilst keeping the step climb height according to current reduced vertical separation minima (RVSM) standard would give a good compromise between cost savings and impact on the ATM.
In this study, the author formally proves that designing attribute-based encryption schemes cannot be easier than designing identity-based encryption schemes. In more detail, they show how an attribute-based encryption scheme which admits, at least, and policies can be combined with a collision-resistant hash function to obtain an identity-based encryption scheme. Even if this result may seem natural, not surprising at all, it has not been explicitly written anywhere, as far as they know. Furthermore, it may be an unknown result for some people: Odelu et al. in 2016 and 2017 have proposed both an attribute-based encryption scheme in the discrete logarithm setting, without bilinear pairings, and an attribute-based encryption scheme in the RSA setting, both admitting and policies. If these schemes were secure, then by using the implication proved in this study, one would obtain secure identity-based encryption schemes in both the RSA and the discrete logarithm settings, without bilinear pairings, which would be a breakthrough in the area. Unfortunately, the author presents here complete attacks of the two schemes proposed by Odelu et al.
Mesodiakaki, A.; Zola, E.; Kassler, A.J. ACM International Conference on Modeling, Analysis and Simulation of Wireless and Mobile Systems p. 179-186 DOI: 10.1145/3127540.3127560 Data de presentació: 2017-11 Presentació treball a congrés
With the advance of fifth generation (5G) networks, network density needs to grow significantly in order to meet the required capacity demands. A massive deployment of small cells may lead to a high cost for providing fiber connectivity to each node. Consequently, many small cells are expected to be connected through wireless links to the umbrella eNodeB, leading to a mesh backhaul topology. This backhaul solution will most probably be composed of high capacity point-to-point links, typically operating in the millimeter wave (mmWave) frequency band due to its massive bandwidth availability. In this paper, we propose a mathematical model that jointly solves the user association and backhaul routing problem in the aforementioned context, aiming at the energy efficiency maximization of the network. Our study considers the energy consumption of both the access and backhaul links, while taking into account the capacity constraints of all the nodes as well as the fulfillment of the service-level agreements (SLAs). Due to the high complexity of the optimal solution, we also propose an energy efficient heuristic algorithm (Joint), which solves the discussed joint problem, while inducing low complexity in the system. We numerically evaluate the algorithm performance by comparing it not only with the optimal solution but also with reference approaches under different traffic load scenarios and backhaul parameters. Our results demonstrate that Joint outperforms the state-of-the-art, while being able to find good solutions, close to optimal, in short time.
As the number of Access Points and stations sharing the unlicensed ISM (Industrial Scientific Medical) bands increases, interference diminishes the theoretical performance of 802.11 standard. This paper presents results of the performance of an IEEE 802.11b/g network in a public facility infrastructure which needed to deploy more than a thousand access points to provide an IIoT (Industrial Internet of the Things) item location service. As a first step to better analyze such network characteristics, this work studies the channel occupancy, the RSSI (Received Signal Strength Indicator) variation and the throughput of a static and mobile station. The study also analyzes the performance of Voice over IP over the wireless network. The results reveal the inefficient use of the wireless medium in a large 802.11 network due to multiple
radio propagation conditions.
LoRaWAN is a flagship Low-Power Wide Area Network (LPWAN) technology that has highly attracted much attention from the community in recent years. Many LoRaWAN end-devices, such as sensors or actuators, are expected not to be powered by the electricity grid; therefore, it is crucial to investigate the energy consumption of LoRaWAN. However, published works have only focused on this topic to a limited extent. In this paper, we present analytical models that allow the characterization of LoRaWAN end-device current consumption, lifetime and energy cost of data delivery. The models, which have been derived based on measurements on a currently prevalent LoRaWAN hardware platform, allow us to quantify the impact of relevant physical and Medium Access Control (MAC) layer LoRaWAN parameters and mechanisms, as well as Bit Error Rate (BER) and collisions, on energy performance. Among others, evaluation results show that an appropriately configured LoRaWAN end-device platform powered by a battery of 2400 mAh can achieve a 1-year lifetime while sending one message every 5 min, and an asymptotic theoretical lifetime of 6 years for infrequent communication.
Next generation 5G networks will rely on virtualized Data Centers (vDC) to host virtualized network functions on commodity servers. Such Network Function Virtualization (NFV) will lead to significant savings in terms of infrastructure cost and reduced management complexity. However, green strategies for networking and computing inside data centers, such as server consolidation or energy aware routing, should not negatively impact the quality and service level agreements expected from network operators. In this paper, we study how robust strategies that place virtual network func- tions (VNF) inside vDC impact the energy savings and the protection level against resource demand uncertainty. We propose novel optimization mod- els that allow the minimization of the energy of the computing and network infrastructure which is hosting a set of service chains that implement the VNFs. The model explicitly provides for robustness to unknown or impre- cisely formulated resource demand variations, powers down unused routers, switch ports and servers, and calculates the energy optimal VNF placement and network embedding also considering latency constraints on the service chains. We propose both exact and heuristic methods. Our experiments were carried out using the virtualized Evolved Packet Core (vEPC), which allows us to quantitatively assess the trade-off between energy cost, robust- ness and the protection level of the solutions against demand uncertainty. Our heuristic is able to converge to a good solution in a very short time, in comparison to the exact solver, which is not able to output better results in a longer run as demonstrated by our numerical evaluation. We also study the degree of robustness of a solution for a given protection level and the cost of additional energy needed because of the usage of more computing and network elements.
Vincenzi, M.; Antonopoulos, A.; Kartsakli, E.; Vardakas, J.; Alonso, L.; Verikoukis, C. IEEE Wireless communications Vol. 24, num. 5, p. 118-125 DOI: 10.1109/MWC.2017.1700138 Data de publicació: 2017-10-01 Article en revista
The explosive data traffic demand in the context of the 5G revolution has stressed the need for network capacity increase. As the network densification has almost reached its limits, mobile network operators are motivated to share their network infrastructure and the available resources through dynamic spectrum management. Although some initial efforts have been made in this direction by concluding sharing agreements at a coarse granularity (i.e., months or years), the 5G developments require fine timescale agreements, mainly enabled by network slicing. In this article, taking into account the radical changes foreseen for next generation networks, we provide a thorough discussion of the challenges that network slicing brings in the different network parts, while introducing a new entity capable of managing the end-to-end slicing in a coherent manner. In addition, according to the paradigm shift of operators sharing their resources in a common centralized pool, we design a cooperative game to study the potential cooperation aspects among the participants. The experimental results highlight the performance and financial gains achievable by operators through multi-tenant slicing, providing them with the necessary incentives for network upgrade toward 5G.
Timing points used in running races and other competition events are generally based on radio-frequency identification (RFID) technology. Athletes' times are calculated via passive RFID tags and reader kits. Specifically, the reader infrastructure needed is complex and requires the deployment of a mat or ramps which hide the receiver antennae under them. Moreover, with the employed tags, it is not possible to transmit additional and dynamic information such as pulse or oximetry monitoring, alarms, etc. In this proposal, we present a system based on Bluetooth Low Energy which allows complete real-time position monitoring of the users using mobile phones on the organizer side and BLE sensors on the participants’ side. Along with the proposal, we present a complete architecture and an extensive analysis of metrics which are determinant for evaluating the performance of the proposed system: detection probability, range, mobility patterns of runners in real races, detection delay, packet collision, energy consumption, performance under high sensor density, etc. All these results, obtained through both experimental measurements and computer simulation, will demonstrate the viability and benefits of the system against other alternatives for the intended application.
Continuous Descent Operations with Controlled Times of Arrival (CTA) at one or several metering fixes could enable environmentally friendly procedures without compromising capacity. This type of flight operation requires advanced on-board systems not only able to compute a plan satisfying Required Times of Arrival (RTAs), but also to safely and efficiently guide the aircraft during the execution of the descent such that RTAs are accurately accomplished. The primary aim of this paper is to compare the performance (in terms of environmental impact mitigation and ability to fulfill operational constraints) of four guidance strategies: tactical, strategic, hybrid and Model Predictive Control (MPC). A high fidelity flight simulator has been configured, and several descents to Barcelona-El Prat airport (Spain) have been simulated in presence of weather forecast and aircraft performance modeling errors. Results show that MPC is the most robust in terms of energy and time deviation, providing at the same time excellent environmental impact mitigation.
State-of-the-art weather data obtained from numerical weather predictions are unlikely to satisfy the requirements
of the future air traffic management system. A potential approach
to improve the resolution and accuracy of the weather predictions
could consist on using airborne aircraft as meteorological sensors,
which would provide up-to-date weather observations to the sur-
rounding aircraft and ground systems. This paper proposes to use
Kriging, a geostatistical interpolation technique, to create short-
term weather predictions from scattered weather observations
derived from surveillance data. Results show that this method
can accurately capture the spatio-temporal distribution of the
temperature and wind fields, allowing to obtain high-quality local,
short-term weather predictions and providing at the same time
a measure of the uncertainty associated with the prediction.
The use of metal matrix composites (MMC) has increased steadily in the last two decades. Conventional MMC are usually produced by addition of either Al2O3 or SiC particles, or their combinations, into molten pure metals or alloys. However, when preparing the MMC through melting routes, there is significant loss of those costly particles, making fabrication more expensive. Lightweight MMC are important and researchers are urged to develop cheaper production techniques. In this work, the viscoelastic response of a novel aluminum metal matrix composite (AMC) is measured. The studied AMC, with A356 alloy matrix, was produced with a novel technique which allows incorporating reinforcement consisting of Al2O3, SiC and C, novel ceramic particles developed indigenously from colliery shale, avoiding the addition of costly reinforcing agents like Al2O3 or SiC in the matrix. The experimental results, obtained with a dynamic-mechanical analyzer, are compared to those for pure aluminum and commercial aluminum alloys 7075 (Al–Zn–Mg), 2024 (Al–Cu–Mg), 6061 and 6082 (Al–Mg–Si alloys). The objective of this research is to characterize the influence of the temperature, loading frequency and microstructure on the viscoelastic behavior of this novel, low-cost AMC, and to establish the interest of this AMC for applications like, for instance, damping systems, compared to the mentioned alloys.
Let S be a set of n points in real three-dimensional space, no three collinear and not all co-planar. We prove that if the number of planes incident with exactly three points of S is less than (Formula presented.) for some (Formula presented.) then, for n sufficiently large, all but at most O(K) points of S are contained in the intersection of two quadrics. Furthermore, we prove that there is a constant c such that if the number of planes incident with exactly three points of S is less than (Formula presented.) then, for n sufficiently large, S is either a regular prism, a regular anti-prism, a regular prism with a point removed or a regular anti-prism with a point removed. As a corollary to the main result, we deduce the following theorem. Let S be a set of n points in the real plane. If the number of circles incident with exactly three points of S is less than (Formula presented.) for some (Formula presented.) then, for n sufficiently large, all but at most O(K) points of S are contained in a curve of degree at most four.
One of the major contributions to aircraft operational costs corresponds to maintenance. This is a time consuming and expensive process, but necessary, for instance, to detect early formation of cracks, monitoring crack growth, and for removing or fixing parts with repairs to regain their original strength. Thus, repair technologies play an important role in minimizing the aircraft operational costs, and airlines pay careful attention to these technologies to improve their efficiency and revenue. Aircraft repair patches are usually made of aluminium or composites. Composites have very high strength to weight ratio compared to aluminium but, when riveted, they may lose nearly 60% of their total strength and carrying capacity. In spite of these drawbacks, the aviation industry still uses nowadays riveting of composites as common practice. This work analyses and compares the performance of several configurations of aircraft repair patches; particularly, riveted lap joints consisting of aluminium or composite substrates repaired with aluminium or composite doublers. Each of the studied joints consists of two substrate plates separated by a gap of 12.7 mm (simulating and induced crack or hole), repaired with two doublers riveted to the substrate plates, with a total of eight rivets. The performance is computed numerically using commercial Finite Element Analysis (FEA) code ABAQUS for the riveted joints with substrate-doubler configurations as follows: aluminium alloy (AA)-AA, AA-Carbon fibre reinforced polymer (CFRP), CFRP-CFRP and CFRP-AA. For the different configurations, the joints are loaded with their limit load (7.5 kN) and ultimate load (11.3 kN), as derived from experimental results, and the stresses at various locations on the substrates are compared. The experiments and simulations presented in this work are compliant with FAR 25.571 requirements.
The viscoelastic response of commercial 6061 and 6082 (Al–Mg–Si) alloys was measured with a dynamic-mechanical analyzer (DMA) as a function of both the temperature (in the range 30 to 425ºC) and the loading frequency (in the range 0.01 to 150 Hz). The time-temperature superposition (TTS) principle has proven useful in studying the mechanical relaxations and in obtaining master curves for the viscoelastic behavior of amorphous materials. In this work, a similar approach is used for the studied Al–Mg–Si alloys. In particular, the TTS principle is applied to experimental viscoelastic data obtained with the DMA (i.e., the storage and loss moduli) for the studied alloys, both in the as-received condition (the T6 temper) and after application of solution treatment. The analysis allows first to obtain the corresponding master curves, and second to study the mechanical relaxations responsible for the viscoelastic behavior of the alloys. For the storage modulus it was possible to identify a master curve for a low temperature region (below 150ºC) and, for both the storage and loss moduli, it was possible to identify another mater curve for a high temperature region (above 320ºC). The different temperature dependencies of the shift factors for the identified master curves, manifested by different activation energies in the Arrhenius expressions for the shift factor, are due to the occurrence of microstructural changes and variations in the relaxation mechanisms between the mentioned temperature regions.
Cojocaru, E.; Rebassa, A.; Torres, S.; Garcia-berro, E. Monthly notices of the Royal Astronomical Society Vol. 470, num. 2, p. 1442-1452 DOI: 10.1093/mnras/stx1326 Data de publicació: 2017-09-11 Article en revista
We present a Monte Carlo population synthesis study of white dwarf-main sequence (WD+MS) binaries in the Galactic disc aimed at reproducing the ensemble properties of the entire population observed by the Sloan Digital Sky Survey (SDSS) Data Release 12. Our simulations take into account all known observational biases and use the most up-to-date stellar evolutionary models. This allows us to perform a sound comparison between the simulations and the observational data. We find that the properties of the simulated and observed parameter distributions agree best when assuming low values of the common envelope efficiency (0.2-0.3), a result that is in agreement with previous findings obtained by observational and population synthesis studies of close SDSSWD+MS binaries.We also show that all synthetic populations that result from adopting an initial mass ratio distribution with a positive slope are excluded by observations. Finally, we confirm that the properties of the simulated WD+MS binary populations are nearly independent of the age adopted for the thin disc, on the contribution of WD+MS binaries from the thick disc (0-17 per cent of the total population) and on the assumed fraction of the internal energy that is used to eject the envelope during the common envelope phase (0.1-0.5).
Garcia, D.; Gonzalez, M.; Hueltes, A.; Collado, J.; Mateu, J.; Gonzalez, J.; Kreuzer, S.; Aigner, R. IEEE International Ultrasonics Symposium p. 1-4 DOI: 10.1109/ULTSYM.2017.8091793 Data de presentació: 2017-09-08 Presentació treball a congrés
This work presents a broadband characterization and modeling of the second harmonic nonlinear response in Bulk acoustic wave (BAW) resonators. The proposed circuit model is based on the constitutive equations describing the behavior of all materials used on the different layers of the resonator. These constitutive equations are extended for both the linear and nonlinear domain, and allow to explain all the features observed in the nonlinear response over all the characterized bandwidth. This circuit model is used to explain the nonlinear effects occurring in two different BAW resonators, and concludes that in addition to the well-known nonlinear behavior of the main piezoelectric layer, other layers of the Bragg mirror also contribute to the overall nonlinear response.
Rodriguez Cantalapiedra, I.; Alvarez-Lacalle, E.; Peñaranda, A.; Echebarria, B. Chaos : an interdisciplinary journal of nonlinear science Vol. 27, num. 9, p. 093928-1-093928-13 DOI: 10.1063/1.5000709 Data de publicació: 2017-09-07 Article en revista
In the heart, rapid pacing rates may induce alternations in the strength of cardiac contraction, termed pulsus alternans. Often, this is due to an instability in the dynamics of the intracellular calcium concentration, whose transients become larger and smaller at consecutive beats. This alternation has been linked experimentally and theoretically to two different mechanisms: an instability due to (1) a strong dependence of calcium release on sarcoplasmic reticulum (SR) load, together with a slow calcium reuptake into the SR or (2) to SR release refractoriness, due to a slow recovery of the ryanodine receptors (RyR2) from inactivation. The relationship between calcium alternans and refractoriness of the RyR2 has been more elusive than the corresponding SR Ca load mechanism. To study the former, we reduce a general calcium model, which mimics the deterministic evolution of a calcium release unit, to its most basic elements. We show that calcium alternans can be understood using a simple nonlinear equation for calcium concentration at the dyadic space, coupled to a relaxation equation for the number of recovered RyR2s. Depending on the number of RyR2s that are recovered at the beginning of a stimulation, the increase in calcium concentration may pass, or not, over an excitability threshold that limits the occurrence of a large calcium transient. When the recovery of the RyR2 is slow, this produces naturally a period doubling bifurcation, resulting in calcium alternans. We then study the effects of inactivation, calcium diffusion, and release conductance for the onset of alternans. We find that the development of alternans requires a well-defined value of diffusion while it is less sensitive to the values of inactivation or release conductance.
Las enfermedades respiratorias son una de las causas principales de muerte y enfermedad en Europa y el mundo. Una de las más importantes es la Enfermedad Pulmonar Obstructiva Crónica (EPOC) asociada principalmente a la bronquitis crónica y al enfisema pulmonar. Los pacientes con EPOC durante una Insuficiencia Respiratoria Aguda (IRA) requieren ventilación mecánica para asistir o sustituir su función pulmonar, donde la selección y configuración del modo ventilatorio constituye un paso esencial durante el tratamiento y la recuperación del paciente.La evolución del conocimiento fisiopatológico y de la tecnología ha generado una gran variedad de modos de ventilación diseñados para aumentar la ventilación alveolar, reducir el trabajo respiratorio, mejorar el acoplamiento entre la ventilación y la perfusión y optimar la oxigenación de la sangre arterial. Sin embargo, en la práctica clínica suelen ser desaprovechados muchos de los beneficios que estos ofrecen debido a: 1) la complejidad y diversidad de modos ventilatorios y marcas de ventiladores, y 2) la falta de herramientas que ayuden a la selección y configuración adecuada de estos en función de las características específicas de cada paciente. Se han estudiado diversos modelos del sistema respiratorio para reforzar el conocimiento sobre el mecanismo de control ventilatorio que dicho sistema adopta en condiciones normales y patológicas. Sin embargo, la unión entre el sistema de control respiratorio y los ventiladores mecánicos sigue siendo un campo de investigación abierto, dado que antes de configurar el ventilador resulta fundamental conocer y predecir apropiadamente su patrón respiratorio y los parámetros que lo afectan.El objetivo principal de esta tesis es el desarrollo y evaluación de nuevos simuladores computacionales que permitan predecir apropiadamente la respuesta dinámica respiratoria de sujetos sanos y enfermos respiratorios ante demandas ventilatorias y ventilación mecánica asistida. En esta tesis diversos modelos del sistema respiratorio son analizados. Modificaciones en su modelado, ajustes en sus parámetros y estudios comparativos fueron realizados con el fin de predecir adecuadamente la respuesta del sistema respiratorio en sujetos sanos y patológicos durante demandas ventilatorias incrementadas. Además, una herramienta computacional, basada en un modelo que integra las características más relevantes de los modelos analizados y de un ventilador mecánico, ha sido desarrollada para simular la interacción paciente-ventilador.Las principales contribuciones de la tesis son: 1) Una nueva estimación del trabajo mecánico respiratorio con una mayor interpretación fisiológica y cuya minimización permite predecir mejor la respuesta del sistema de control. 2) Un modelo completo del sistema respiratorio que predice adecuadamente la respuesta tanto en régimen transitorio como estacionario de un sujeto sano ante demandas ventilatorias incrementales. Dicho modelo utiliza una planta respiratoria de intercambio y sensado de gases mejorada y algoritmos de optimización más apropiados. 3) Un modelo completo del sistema respiratorio que predice adecuadamente la respuesta de enfermedades pulmonares obstructivas y restrictivas. Dicho modelo incorpora la simplificación de una planta mecánica respiratoria conocida, detallada y completa que se aproxima cuadráticamente para su integración computacional en el modelo del sujeto sano anterior. Parámetros mecánicos de tres submodelos para cada enfermedad son también propuestos 5) Un simulador computacional con una interfaz amigable e interactiva, que incluye el modelo anterior de un paciente y de un ventilador mecánico. Dicha herramienta a la que ya se le han hecho pruebas de usabilidad, ha sido utilizada con éxito en cursos para médicos, investigadores y estudiantes.Tales herramientas buscan brindar medios para asistir a médicos en la configuración de ventiladores y en la comprensión de la interacción paciente-ventilador.
Corpas, R.; Hernández, A.; Porquet, D.; Hernández, C.; Bosch, F.; Ortega, A.; Comellas, F.; de la Rosa, E.; Sanfeliu, C. Neuropharmacology Vol. 123, p. 221-232 DOI: 10.1016/j.neuropharm.2017.06.014 Data de publicació: 2017-09-01 Article en revista
Brain inflammaging is increasingly considered as contributing to age-related cognitive loss and neurodegeneration. Despite intensive research in multiple models, no clinically effective pharmacological treatment has been found yet. Here, in the mouse model of brain senescence SAMP8, we tested the effects of proinsulin, a promising neuroprotective agent that was previously proven to be effective in mouse models of retinal neurodegeneration. Proinsulin is the precursor of the hormone insulin but also upholds developmental physiological effects, particularly as a survival factor for neural cells. Adeno-associated viral vectors of serotype 1 bearing the human proinsulin gene were administered intramuscularly to obtain a sustained release of proinsulin into the blood stream, which was able to reach the target area of the hippocampus. SAMP8 mice and the control strain SAMR1 were treated at 1 month of age. At 6 months, behavioral testing exhibited cognitive loss in SAMP8 mice treated with the null vector. Remarkably, the cognitive performance achieved in spatial and recognition tasks by SAMP8 mice treated with proinsulin was similar to that of SAMR1 mice. In the hippocampus, proinsulin induced the activation of neuroprotective pathways and the downstream signaling cascade, leading to the decrease of neuroinflammatory markers. Furthermore, the decrease of astrocyte reactivity was a central effect, as demonstrated in the connectome network of changes induced by proinsulin. Therefore, the neuroprotective effects of human proinsulin unveil a new pharmacological potential therapy in the fight against cognitive loss in the elderly.
The device discovery process is one of the most crucial aspects in real deployments of sensor networks. Recently, several works have analyzed the topic of Bluetooth Low Energy (BLE) device discovery through analytical or simulation models limited to version 4.x. Non-connectable and non-scannable undirected advertising has been shown to be a reliable alternative for discovering a high number of devices in a relatively short time period. However, new features of Bluetooth 5.0 allow us to define a variant on the device discovery process, based on BLE scannable undirected advertising events, which results in higher discovering capacities and also lower power consumption. In order to characterize this new device discovery process, we experimentally model the real device behavior of BLE scannable undirected advertising events. Non-detection packet probability, discovery probability, and discovery latency for a varying number of devices and parameters are compared by simulations and experimental measurements. We demonstrate that our proposal outperforms previous works, diminishing the discovery time and increasing the potential user device density. A mathematical model is also developed in order to easily obtain a measure of the potential capacity in high density scenarios.
The ¿h-product that is referred in the title was introduced in 2008 as a generalization of the Kronecker product of digraphs. Many relations among labelings have been obtained since then, always using as a second factor a family of super edge-magic graphs with equal order and size. In this paper, we introduce a new labeling construction by changing the role of the factors. Using this new construction the range of applications grows up considerably. In particular, we can increase the information about magic sums of cycles and crowns.
This paper compares different optimization strategies for the minimization of flight and passenger delays at two levels: pre-tactical, with on-ground delay at origin, and tactical, with airborne delay close to the destination airport. The optimization model is based on the ground holding problem and uses various cost functions. The scenario considered takes place in a busy European airport and includes realistic values of traffic. A passenger assignment with connections at the hub is modeled. Statistical models are used for passenger and connecting passenger allocation, minimum time required for turnaround and tactical noise; whereas uncertainty is also introduced in the model for tactical noise. Performance of the various optimization processes is presented and compared to ration by schedule results.
Xu, Y.; Dalmau, R.; Prats, X. Transportation research. Part C, emerging technologies Vol. 81, num. August 2017, p. 137-152 DOI: 10.1016/j.trc.2017.05.012 Data de publicació: 2017-08-01 Article en revista
This paper introduces a linear holding strategy based on prior works on cruise speed reduction, aimed at performing airborne delay at no extra fuel cost, as a complementary strategy to current ground and airborne holding strategies. Firstly, the equivalent speed concept is extended to climb and descent phases through an analysis of fuel consumption and speed from aircraft performance data. This gives an insight of the feasibility to implement the concept, differentiating the case where the cruise flight level initially requested is kept and the case where it can be changed before departure in order to maximize the linear holding time. Illustrative examples are given, where typical flights are simulated using an optimal trajectory generation tool where linear holding is maximized while keeping constant the initially planned fuel. Finally, the effects of linear holding are thoroughly assessed in terms of the vertical trajectory profiles, range of feasible speed intervals and trade-offs between fuel and time. Results show that the airborne delay increases significantly with nearly 3-fold time for short-haul flights and 2-fold for mid-hauls to the cases in prior works.
An n×n production matrix for a class of geometric graphs has the property that the numbers of these geometric graphs on up to n vertices can be read off from the powers of the matrix. Recently, we obtained such production matrices for non-crossing geometric graphs on point sets in convex position [Huemer, C., A. Pilz, C. Seara, and R.I. Silveira, Production matrices for geometric graphs, Electronic Notes in Discrete Mathematics 54 (2016) 301–306]. In this note, we determine the characteristic polynomials of these matrices. Then, the Cayley-Hamilton theorem implies relations among the numbers of geometric graphs with different numbers of vertices. Further, relations between characteristic polynomials of production matrices for geometric graphs and Fibonacci numbers are revealed.
In a (1 : q) Maker-Breaker game, one of the central questions is to find (or at least estimate) the maximal value of q that allows Maker to win the game. Based on the ideas of Bednarska and Luczak [Bednarska, M., and T. Luczak, Biased positional games for which random strategies are nearly optimal, Combinatorica, 20 (2000), 477–488], who studied biased H-games, we prove general winning criteria for Maker and Breaker and a hypergraph generalization of their result. Furthermore, we study the biased version of a strong generalization of the van der Waerden games introduced by Beck [Beck, J., Van der Waerden and Ramsey type games, Combinatorica, 1 (1981), 103–116] and apply our criteria to determine the threshold bias of these games up to constant factor. As in the result of [Bednarska, M., and T. Luczak, Biased positional games for which random strategies are nearly optimal, Combinatorica, 20 (2000), 477–488], the random strategy for Maker is again the best known strategy.
In this extended abstract, we present the first combinatorial scheme for counting labeled 4-regular planar graphs through a complete recursive decomposition. More precisely, we show that the exponential generating function counting labeled 4-regular planar graphs can be computed effectively as the solution of a system of equations. From here we can extract the coefficients by means of algebraic calculus. As a by-product, we can also compute the algebraic generating function counting labeled 3-connected 4-regular planar maps.
Mekikis, P. V.; Antonopoulos, A.; Kartsakli, E.; Alonso, L.; Verikoukis, C. IEEE transactions on consumer electronics Vol. 63, num. 3, p. 291-299 DOI: 10.1109/TCE.2017.014904 Data de publicació: 2017-08-01 Article en revista
In spite of the significant advancements in wireless connectivity, the static form of the network infrastructure cannot guarantee an uninterrupted operation of the ever-growing wireless consumer electronics in emergency situations such as natural disasters. In such occasions, employing flexible aerial nodes can tackle this issue by recovering the communication rapidly, when the need for connectivity is of utmost importance. In this paper, we study the use of aerial nodes for communication recovery after a communication breakdown. We provide an analytical model of the recovery probability that demonstrates the capabilities of such networks. In the performance evaluation, we show the effects of the altitude and the distance between the aerial nodes on the recovery probability and verify them with simulations. Moreover, we introduce our testbed and preliminary experimental work that shows promising results for aerial networks. Finally, we discuss useful insights for the network design and present some open issues that exist in this field.
Perez-Romero, J.; Sanchez, J.; Sallent, J.; Whitehead, A. International Conference on Engineering Applications of Neural Networks p. 680-692 DOI: 10.1007/978-3-319-65172-9_57 Data de presentació: 2017-08 Presentació treball a congrés
The application of Artificial Intelligence (AI)-based knowledge discovery mechanisms for supporting the automation of wireless network operations is envisaged to fertilize in future Fifth Generation (5G) systems due to the stringent requirements of these systems and to the advent of big data analytics. This paper intends to elaborate on the demonstration of knowledge discovery capabilities in the context of the architecture proposed by the Small cEllS coordinAtion for Multi-tenancy and Edge services (SESAME) project that deals with multi-operator cloud-enabled small cells. Specifically, the paper presents the considered demonstration framework and particularizes it for supporting an energy saving functionality through the classification of cells depending on whether they can be switched off during certain times. The framework is illustrated with some results obtained from real small cell deployments.
Elayoubi, K.; Rissons, A.; Lacan, J.; Saint-Antonin, L.; Le Kernec, A.; Sotom, M.; Belmonte, A. Opto-Electronics and Communications Conference p. 1 Data de presentació: 2017-07-31 Presentació treball a congrés