An integrated open-coastal biogeochemistry, ecosystem and biodiversity observatory of the eastern Mediterranean – the Cretan Sea component of the POSEIDON system

There is a general scarcity of oceanic observations that concurrently examine air–sea interactions, coastal–open-ocean processes and physical–biogeochemical processes, in appropriate spatiotemporal scales and under continuous, long-term data acquisition schemes. In the Mediterranean Sea, the resulting knowledge gaps and observing challenges increase due to its oligotrophic character, especially in the eastern part of the basin. The oligotrophic open Cretan Sea's biogeochemistry is considered to be representative of a greater Mediterranean area up to 106&thinsp;km2, and understanding its features may be useful on even larger oceanic scales, since the Mediterranean Sea has been considered a miniature model of the global ocean. The spatiotemporal coverage of biogeochemical (BGC) observations in the Cretan Sea has progressively increased over the last decades, especially since the creation of the POSEIDON observing system, which has adopted a multiplatform, multivariable approach, supporting BGC data acquisition. The current POSEIDON system's status includes open and coastal sea fixed platforms, a Ferrybox (FB) system and Bio-Argo autonomous floats that remotely deliver fluorescence as a proxy of chlorophyll-a (Chl-a), O2, pH and pCO2 data, as well as BGC-related physical variables. Since 2010, the list has been further expanded to other BGC (nutrients, vertical particulate matter fluxes), ecosystem and biodiversity (from viruses up to zooplankton) variables, thanks to the addition of sediment traps, frequent research vessel (R/V) visits for seawater–plankton sampling and an acoustic Doppler current profiler (ADCP) delivering information on macrozooplankton–micronekton vertical migration (in the epipelagic to mesopelagic layer). Gliders and drifters are the new (currently under integration to the existing system) platforms, supporting BGC monitoring. Land-based facilities, such as data centres, technical support infrastructure, calibration laboratory and mesocosms, support and give added value to the observatory. The data gathered from these platforms are used to improve the quality of the BGC-ecosystem model predictions, which have recently incorporated atmospheric nutrient deposition processes and assimilation of satellite Chl-a data. Besides addressing open scientific questions at regional and international levels, examples of which are presented, the observatory provides user-oriented services to marine policy makers and the society, and is a technological test bed for new and/or cost-efficient BGC sensor technology and marine equipment. It is part of European and international observing programs, playing a key role in regional data handling and participating in harmonization and best practices procedures. Future expansion plans consider the evolving scientific and society priorities, balanced with sustainable management.</p

Photonic devices based on οptical fiber for telecommunication applications

In this thesis, all-optical processing for the functionalities of second and third generation optical networks is studied in one hand by means of parametric processes and on the other hand by taking advance of cross phase modulation in highly non-linear optical fibers. Through the first part of this thesis an analytical study on the noise characteristics of parametric amplifiers operating at the linear regime is provided taking also into account that the zero dispersion wavelength mapping along fiber’s length varies its value. In the same part of this thesis a 2R polarization insensitive regenerator based on dual pump parametric processes in fiber is proposed and theoretically studied. Two novel fiber based photonic devices, which based on cross phase modulation in highly non-linear fibers, are proposed in the second part of this thesis. The first proposed fiber device is an all optical ultrafast (160 Gbps) reconfigurable (XOR, OR, AND, NAND, OR, NOR, NOT) photonic logic gates and the second device is an all optical ultrafast (40 Gbps) photonic differentiator which have the ability to produce fist-order and second-order temporal derivatives of an optical RZ modulated signal® Στα πλαίσια τη διατριβή μελετώνται νέες τεχνικές αμιγώς οπτικής επεξεργασίας σήματος για οπτικά δίκτυα δεύτερης και τρίτης γενιάς που βασίζονται τόσο σε παραμετρικές διατάξεις καθώς και στην αξιοποίηση του μη γραμμικού φαινομένου της ετεροδιαμόρφωσης φάσης σε οπτικές ίνες με υψηλο συντελεστή μη γραμμικότητας. Στο πρώτο σκέλος της εργασίας αυτής παρέχεται μία θεωρητική ανάλυση των ιδιοτήτων θορύβου των παραμετρικών διατάξεων οπτικής ίνας για την περίπτωση που η τιμή του μήκους κύματος μηδενικής χρωματικής διασποράς μεταβάλλεται κατά μήκος της οπτικής ίνας που χρησιμοποιείται. Στην συνέχεια της εργασίας αυτής μελετάται θεωρητικά και αριθμητικά μια προτεινόμενη διάταξη αμιγώς οπτικής αναγέννησης ανεξάρτητης της πολωτικής κατάστασης του σήματος που βασίζεται εξολοκλήρου σε παραμετρικούς ενισχυτές που χρησιμοποιούν δύο κύματα άντλησης. Στο δεύτερο σκέλος της εργασίας αυτής προτείνονται δύο νέες τεχνικές αμιγώς οπτικής επεξεργασίας τηλεπικοινωνιακών σημάτων που αξιοποιούν τις ιδιότητες της ετεροδιαμόρφωσης φάσης σε οπτικές ίνες με υψηλό συντελεστή μη γραμμικότητας. Η πρώτη τεχνική προτείνει την υλοποίηση ενός υψίρρυθμου (160 Gbps) φωτονικού υπολογιστή εκτέλεσης πολλαπλών λογικών πράξεων (XOR, OR, AND, NAND, OR, NOR, NOT) και η δεύτερη τεχνική προτείνει την υλοποίηση ενός αμιγώς οπτικού διαφοριστή υψίρρυθμών (40 Gbps) οπτικών σημάτων για την παραγωγή χρονικών παραγώγων πρώτης και δεύτερης τάξης των οπτικών σημάτων που εισέρχονται σε αυτόν

On-device Crop Disease Prediction: A realistic case for vineyards

Internet of Things (IoT) is one of the next big concepts to support societal changes and economic growth, with the help of Artificial Intelligence and edge computing. A whole new range of applications that leverage data and metadata from connected IoT devices provide novel human-centric services in areas such as smart agriculture. In this paper, we investigate the efficiency of executing ML-based crop disease prediction on a commercial drone device and demonstrate its potential in vineyards. We conduct inference of the trained models on several IoT and edge devices’ processors and demonstrate the potential for real-time decision-making and therefore enabling targeted treatment for affected areas for optimizing crop protection strategies

Operation properties of a reconfigurable photonic logic gate based on cross phase modulation in highly nonlinear fibers

The operation features of a 160   Gb / s reconfigurable all-optical logic gate based on cross phase modulation in highly nonlinear fibers are numerically investigated for six logic functions (XOR, OR, NAND, NOR, NOT, and AND). High bit rate operation is numerically demonstrated for a wide input signal wavelength range (&gt; 20   nm). Performance enhancement of the proposed setup operating at 160   Gb / s for different signal wavelengths is exhibited by using a 2R regenerator based on the self-phase modulation effect in highly nonlinear fibers at the gate&apos;s output. The operation of the multi-functional logic gate is investigated considering either a pulsed or a continuous wave probe. © 2008 Elsevier Inc. All rights reserved

Impact of dispersion fluctuations on the noise properties of fiber optic parametric amplifiers

The effects of zero-dispersion wavelength (ZDWL) fluctuations on the noise characteristics of fiber optical parametric amplifiers (FOPAs) are investigated. The numerical derivation of the noise figure (NF) in terms of the amplifier operating conditions and the magnitude of ZDWL fluctuations is achieved by utilizing a simulation method based on the three-coupled propagation equations. The numerical analysis shows that the average NF of FOPAs is increased compared with the case of uniform dispersion, especially at high-gain operation. Apart from the NF, the gain-to-NF ratio is also evaluated to assess the amplifier performance for a variety of amplifier operating conditions and dispersion profiles

Blockchain Technology: Financial Sector Applications Beyond Cryptocurrencies

Blockchain technology was initially employed as the public transaction ledger for cryptocurrencies. However, beyond cryptocurrencies, blockchain technology has been recently considered for a plethora of other applications as it encapsulates unique properties including decentralization, security, transparency and anti-tampering. Such properties are particularly advantageous for variety of prominent issues experienced in the financial sector. As a result, blockchain technology holds the potential to revolutionize the financial industry by altering the way in which different services are conducted in the financial industry. In this paper, we outline five different financial industry use cases that are expected to be radically transformed by the use of blockchain technology

Numerical investigation of a 160-Gb/s reconfigurable photonic logic gate based on cross-phase modulation in fibers

A simple reconfigurable all-optical logic gate based on cross-phase modulation in highly nonlinear fibers is numerically demonstrated. Fine performance at 160 Gb/s is obtained for five logic functions (XOR, OR, NAND, NOR and NOT). The implementation simplicity and the high-bit-rate operation make the proposed device suitable for ultrafast applications in the emerging all-optical networks. © 2007 IEEE