Design and implementation of a simulator to explore cooperation in distributed environments

La manca de recursos computacionals dels ordinadors personals, afegit al increment de requeriments cada vegada mes patent en el software actual, està demanant urgentment a una redefinició dels paradigmes de computació que hi havia fins ara. Les xarxes de computació distribuïda son una de les solucions que actualment s'estan valorant per resoldre el problema de la manca de recursos hardware. No obstant, la aplicació d'aquestes solucions es veu aturada per la manca de coneixement sobre el seu funcionament i la necessitat tecnològica de resoldre reptes que la recerca i la innovació encara no han descobert com encarar. Un dels problemes pendents és com generar la suficient confiança entre els usuaris i per tant, assegurar un cert nivell de cooperació dins de la xarxa, o el que és el mateix: una col·laboració bidireccional. Aquest projecte de màster pretén explorar els diferents mecanismes basats en incentius i topologies per promoure la cooperació utilitzant com a eina un simulador capaç de valorar aquests indicadors sobre múltiples topologies de xarxa, aplicacions i estratègies sobre sistemes GRID distribuïts. Per tant, una primera part est`a enfocada a l'estudi de la cooperació e identificar quins paràmetres poden portar-la a terme, i quins no influeixen. El segon objectiu és la creació d'una eina prou modular i potent com per extreure suficients conclusions de la seva utilització sobre diferents escenaris i, finalment, una ultima part centrada en l'anàlisi de resultats i la creació d'un protocol de negociació verificable per la compartició de recursos en xarxes distribuïdes

Understanding collaboration in volunteer computing systems

Volunteer computing is a paradigm in which devices participating in a distributed environment share part of their resources to help others perform their activities. The effectiveness of this computing paradigm depends on the collaboration attitude adopted by the participating devices. Unfortunately for software designers it is not clear how to contribute with local resources to the shared environment without compromising resources that could then be required by the contributors. Therefore, many designers adopt a conservative position when defining the collaboration strategy to be embedded in volunteer computing applications. This position produces an underutilization of the devices’ local resources and reduces the effectiveness of these solutions. This article presents a study that helps designers understand the impact of adopting a particular collaboration attitude to contribute with local resources to the distributed shared environment. The study considers five collaboration strategies, which are analyzed in computing environments with both, abundance and scarcity of resources. The obtained results indicate that collaboration strategies based on effort-based incentives work better than those using contribution-based incentives. These results also show that the use of effort-based incentives does not jeopardize the availability of local resources for the local needs.Peer ReviewedPostprint (published version

An Analysis of the Consequences of the General Data Protection Regulation on Social Network Research

This article examines the principles outlined in the General Data Protection Regulation in the context of social network data. We provide both a practical guide to General Data Protection Regulation--compliant social network data processing, covering aspects such as data collection, consent, anonymization, and data analysis, and a broader discussion of the problems emerging when the general principles on which the regulation is based are instantiated for this research area

Bell-state measurement exceeding 50% success probability with linear optics

Bell-state projections serve as a fundamental basis for most quantum communication and computing protocols today. However, with current Bell-state measurement schemes based on linear optics, only two of four Bell states can be identified, which means that the maximum success probability of this vital step cannot exceed $50\%$. Here, we experimentally demonstrate a scheme that amends the original measurement with additional modes in the form of ancillary photons, which leads to a more complex measurement pattern, and ultimately a higher success probability of $62.5\%$. Experimentally, we achieve a success probability of $(57.9 \pm 1.4)\%$, a significant improvement over the conventional scheme. With the possibility of extending the protocol to a larger number of ancillary photons, our work paves the way towards more efficient realisations of quantum technologies based on Bell-state measurements

Studio clinico sul coinvolgimento aortico nelle metastasi linfonodali lombo-aortiche da carcinoma testicolare

Gli Autori passano brevemente in rassegna la letteratura interna - zionale sulla frequenza dell’interessamento vascolare (vena cava infe - riore ed aorta) nelle metastasi linfoghiandolari lombo-aortiche da neoplasie del testicolo. Presentano, quindi, un caso venuto alla loro osservazione ed operato di linfoadenectomia lombo-aortica da carci - noma misto del testicolo sinistro con infiltrazione dell’aorta sottorenale e, quindi, con conseguente resezione in blocco anche di un trat - to dell’aorta e sua sostituzione con protesi in dacron. Sulla base dei casi riportati in letteratura e del paziente da loro operato, gli Autori rilevano la possibilità di ottenere discreti risultati di sopravvivenza anche in questi stadi avanzati della malattia

Design and implementation of a simulator to explore cooperation in distributed environments

La manca de recursos computacionals dels ordinadors personals, afegit al increment de requeriments cada vegada mes patent en el software actual, està demanant urgentment a una redefinició dels paradigmes de computació que hi havia fins ara. Les xarxes de computació distribuïda son una de les solucions que actualment s'estan valorant per resoldre el problema de la manca de recursos hardware. No obstant, la aplicació d'aquestes solucions es veu aturada per la manca de coneixement sobre el seu funcionament i la necessitat tecnològica de resoldre reptes que la recerca i la innovació encara no han descobert com encarar. Un dels problemes pendents és com generar la suficient confiança entre els usuaris i per tant, assegurar un cert nivell de cooperació dins de la xarxa, o el que és el mateix: una col·laboració bidireccional. Aquest projecte de màster pretén explorar els diferents mecanismes basats en incentius i topologies per promoure la cooperació utilitzant com a eina un simulador capaç de valorar aquests indicadors sobre múltiples topologies de xarxa, aplicacions i estratègies sobre sistemes GRID distribuïts. Per tant, una primera part est`a enfocada a l'estudi de la cooperació e identificar quins paràmetres poden portar-la a terme, i quins no influeixen. El segon objectiu és la creació d'una eina prou modular i potent com per extreure suficients conclusions de la seva utilització sobre diferents escenaris i, finalment, una ultima part centrada en l'anàlisi de resultats i la creació d'un protocol de negociació verificable per la compartició de recursos en xarxes distribuïdes

Adaptive phase estimation through a genetic algorithm

Quantum metrology is one of the most relevant applications of quantum information theory to quantum technologies. Here, quantum probes are exploited to overcome classical bounds in the estimation of unknown parameters. In this context, phase estimation, where the unknown parameter is a phase shift between two modes of a quantum system, is a fundamental problem. In practical and realistic applications, it is necessary to devise methods to optimally estimate an unknown phase shift by using a limited number of probes. Here we introduce and experimentally demonstrate a machine learning-based approach for the adaptive estimation of a phase shift in a Mach-Zehnder interferometer, tailored for optimal performances with limited resources. The employed technique is a genetic algorithm used to devise the optimal feedback phases employed during the estimation in an offline fashion. The results show the capability to retrieve the true value of the phase by using few photons, and to reach the sensitivity bounds in such small probe regime. We finally investigate the robustness of the protocol with respect to common experimental errors, showing that the protocol can be adapted to a noisy scenario. Such approach promises to be a useful tool for more complex and general tasks where optimization of feedback parameters is required

Enhanced geometries of macroporous silicon photonic crystals for optical gas sensing applications

A macroporous silicon photonic crystal is designed and optimized theoretically for its use in gas sensing applications and IR optical filters. Light impinges perpendicularly onto the sample surface (vertical propagation) so a three-dimensional (3d) structure is used. For gas sensing, a sharp resonance is desired in order to isolate an absorption line of the gas of interest. The high Q-factors needed mandate the use of a plane defect inside the PhC to give rise to a resonant mode inside the bandgap tuned to the gas absorption line. Furthermore to allow gas passage through the device, an open membrane is required. This can affect the mechanical resilience. To improve the strength of the photonic crystal the pores are extended after the “active” 3d part. The number of modulations, and the extension length have been optimized to obtain the largest Q-factor with reasonable transmitted power. These proposed structures have been experimentally performed, probing an enhancement of almost an order of magnitude in the Q-factor in respect with the basic case. Simulations considering CO2 have been performed showing that the proposed structures are promising as precise optical gas sensors.Peer ReviewedPostprint (author's final draft

Bandgap widening in macroporous silicon photonic crystals by multiperiodic structures

Large bandgaps with low transmission in 3D macroporous silicon photonic crystals have been proved as an interesting technology for the development of optical filters and spectroscopic MIR gas sensors. The aim of this study is the investigation of different bandgap widening methods based on multiperiodic structures for 3D macroporous silicon photonic crystals. To do so, chirped modulations and structures with different periodicity groups have been modelled and theoretically analysed by means of 3D FDTD simulations. They have revealed that by using different decreasing periodicity groups, bandgaps with null transmission and widths as high as 1800 nm, 4 times the original single periodicity photonic crystal bandgap, can be obtained. Furthermore, it has been shown that a resonant cavity with a 20% transmission can be placed in a 1 µm wide bandgap. The results open a way to use this type of structures not only for gas sensing but also for other purposes such as wide stop-band filters, selective filters or broadband mirrors.Peer ReviewedPostprint (published version