A multi-objective formulation of improving flexibility in the operation of electric power systems: Application to mitigation measures during the coronavirus pandemic

The coronavirus pandemic has infected more than 23 million people worldwide by August 2020 along with more than 800,000 deaths. To face this pandemic, a joint effort among different areas has been required. In this context, the correct supply of basic services is the key to enhance the complex circumstance. The operation of the electric power systems is needed to ensure the answer to the situation. Basic services in areas of health, security, food, and communications depend on the electricity supply. Consequently, this paper introduces a multi-objective procedure that enhances the operations of power systems under these circumstances. It considers geographical areas that are affected by coronavirus cases and their effects on the personnel of power plants. To obtain the best combinations of total cost and protection of the workers, lexicographic optimization is implemented. The effectiveness of this approach is studied by solving two test cases: a 6-bus system and the Argentine Electric System with real data about the infection cases. The effects on the electricity generation and transportation stages are studied. The results allow identifying critical areas and proposing corrective actions. The method can reach feasible solutions with a low computational requirement.Fil: Alvarez, Gonzalo Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo y Diseño. Universidad Tecnológica Nacional. Facultad Regional Santa Fe. Instituto de Desarrollo y Diseño; Argentin

Diffusion and perfusion MRI and applications in cerebral ischaemia

Two MRI techniques, namely diffusion and perfusion imaging, are becoming increasingly used for evaluation of the pathophysiology of stroke. This work describes the use of these techniques, together with more conventional MRI modalities (such as T1, and T2 imaging) in the investigation of cerebral ischaemia. The work was performed both in a paediatric population in a whole-body clinical MR system (1.5 T) and in an animal model of focal ischaemia at high magnetic field strength (8.5 T). For the paediatric studies, a single shot echo planar imaging (EPI) sequence was developed to enable the on-line calculation of maps of the trace of the diffusion tensor. In the process of this development, it was necessary to address two different imaging artefacts in these maps: eddy current induced image shifts, and residual Nyquist ghost artefacts. Perfusion imaging was implemented using an EPI sequence to follow the passage through the brain of a bolus of a paramagnetic contrast agent. Computer simulations were performed to evaluate the limitations of this technique in the quantification of cerebral blood flow when delay in the arrival and dispersion of the bolus of contrast agent are not accounted for. These MRI techniques were applied to paediatric patients to identify acute ischaemic events, as well as to differentiate between multiple acute events, or between acute and chronic events. Furthermore, the diffusion and perfusion findings were shown to contribute significantly to the management of patients with high risk of stroke, and in the evaluation of treatment outcome. In the animal experiments, permanent middle cerebral artery occlusion was performed in rats to investigate longitudinally the acute MRI changes (first 4-6 hours) following an ischaemic event. This longitudinal analysis contributed to the understanding of the evolution of the ischaemic lesion. Furthermore, the findings allowed the acute identification of tissue 'at risk' of infarction

Adjustment of optically measured leaf traits to patterns of solar spectral irradiance in plant taxa from high elevations and from forest understoreys

The attenuation of radiation in forest canopies has been studied in depth within the photosynthetically active radiation (PAR, 400-700 nm), but we are still lacking knowledge on how the spectral composition of ultraviolet radiation (UV-B 280-315 nm, UV-A 315-400 nm) varies. Advances in knowledge on the effects of UV radiation has led to growing interest in its study as a trigger of regulatory responses in plants, rather than as a stressor, which is now considered to be rare in plants growing under natural conditions. Furthermore, a growing number of studies suggest that there are complex interactions in perception, signalling and responses of plants to solar spectral irradiance. My dissertation research is focussed on the acclimation and adaptation of leaf flavonoids to solar radiation in plant taxa from contrasting environments assessed through the study of optically measured leaf traits. These responses were studied in forest understorey taxa growing in a seasonally dynamic, but mostly low UV radiation environment, and in taxa growing at high elevation experiencing a high UV radiation environment in a "common garden" setting. More precisely, we examined: 1) how understorey spectral irradiance changes across shade, leaf-shade and sunflecks through the spring and among different forest stands, 2) how optically measured leaf traits and leaf flavonoids in understorey plants change through the growing season, 3) how these patterns relate to seasonal changes in spectral irradiance especially those in UV region, 4) do the patterns of optically measured leaf traits from a large set of taxa, mainly growing at high elevation, follow their patterns of phylogenetic relatedness and 5) how do their leaf traits relate to climatic conditions at their original collection sites. To study these questions, we adopted relatively new monitoring approaches, enabling us both to measure simultaneously the in situ spectral irradiance from the UV to near infra-red (NIR) regions, and leaf flavonols/flavones in vivo repeatedly with a leaf-clip in the field. Our analysis revealed a hierarchy among those factors affecting spectral composition of solar radiation in forest understoreys; most importantly understorey position (sunflecks, shade or radiation transmitted through the canopy of leaves), then stand composition, and date during spring. We found the optically measured leaf flavonol/flavone index (Iflav) in forest understorey species to be plastic and to adjust to changes in climatic conditions. Furthermore, species' leaf retention strategy (e.g., summer green, overwintering leaves) and new leaf production were found to affect the Iflav of plants. All these factors are reflected in the seasonal trends we describe in leaf flavonoids, measured optically (Iflav) and via leaf extracts, across understorey plant communities. For mountain environments, our objectives were to determine factors that underpin leaf flavonoid accumulation of high elevation taxa and whether patterns in optically measured leaf traits followed their phylogenetic relatedness or climatic conditions at their origin. Both these patterns could potentially constrain plant responses. To see if either pattern was present, we tested for a phylogenetic signal particularly in Iflav from a large set of taxa growing in a high-elevation environment and the relationship of mean Iflav of plants to climatic variables. The tests for a phylogenetic signal (Pagel's λ, range from 0 to 1) gave intermediate fitted λ values with significant results for Iflav and anthocyanin index (Iant), while for the smaller set of taxa growing in Kumpula Botanical Garden (southern Finland) only chlorophyll index (Ichl) showed significant results. Despite the relatively low signal for Iflav, we identified certain genera with mainly positive local autocorrelations (local Moran's I) meaning they contained species showing either with mostly high or mostly low leaf trait values. This suggests potential limitations in their leaf flavonol/flavone accumulation responses. Hence, some of these genera may be less well prepared against higher maximum UV radiation and may encounter constraints in migrating upwards, if other compensatory photoprotection mechanisms fail. We did not find a relationship between Iflav and climate at the plants' origin, while our results suggested UV irradiance in the plants' current microhabitat to be important, albeit not the only driver for flavonoid accumulation. In most taxa, we did not find a clear indication of constraints on leaf flavonoid accumulation, thus no evidence that high UV radiation is a detrimental factor in their environment. The values of these optically measured leaf traits represent the outcome of complex interactions between the evolutionary and biogeographical history, and acclimation to the current growing conditions of the plants. In general across the three studies, these results provide evidence that optically measured leaf traits related to flavonoid accumulation are largely flexible and acclimate to local changes in the environment, as well as adjusting over the growing season.Metsien kenttäkerroksen valo-oloja ja niiden muutoksia keväällä latvuston sulkeutumisen myötä on tutkittu paljon erityisesti niillä aallonpituuksilla, joita kasvit hyödyntävät fotosynteesissä (400-700 nm). Ultraviolettisäteilyn (UV) muutoksista metsien kenttäkerroksessa tiedetään sitä vastoin verraten vähän. UV-säteily (UV-B 280-315 nm, UV-A 315-400 nm) muodostaa pienen osan maanpäällisestä auringon kokonaissäteilystä, mutta sen tiedetään olevan tärkeä kasvien vasteiden stimuloija. Auringon säteilyn eri aallonpituuksien vaikutukset kasveihin eivät ole suoraviivaisia, vaan niihin liittyy monimutkaisia vuorovaikutussuhteita aina valon havainnoinnista tuotettuun vasteeseen asti, esimerkiksi fotoreseptorien signalointireittien komponenttien välillä. Eräs usein havaittu kasvien vaste UV-säteilylle on tuottaa ja kerryttää sekundaarisia aineenvaihduntatuotteita (kuten flavonoideja), jotka osaltaan suojaavat kasveja säteilyn haitallisilta vaikutuksilta (engl. photoprotection). Tässä väitöskirjassa tutkin kasvien lehtien flavonoidien akklimaatiota ja adaptaatiota auringon säteilyyn kahdessa hyvin erilaisissa ympäristöissä. Metsän kenttäkerrosta luonnehtii tyypillisesti alhainen auringon säteilytaso ja lyhytaikainen korkea säteilytaso valoaukoissa. Vuoristoissa UV-säteilyarvot sitä vastoin ovat usein korkeita, ja siellä tutkimme eri puolilta maailmaa tuotuja kasveja samassa ympäristössä. Tutkimme 1) miten metsän kenttäkerroksen auringon säteilyn määrä ja säteilyn suhteellinen määrä spektrin eri aallonpituuksilla muuttuvat keväällä eri latvustoisissa metsiköissä, 2) miten aluskasvuston lehtien flavonoidien määrä muuttuu kasvukauden aikana, mitattuna optisesti sekä määrittäen lehtiuutteista, 3) miten nämä muutokset vertautuvat auringon säteilyn ja erityisesti UV-alueen säteilyn muutoksiin keväällä, 4) noudattavatko vuoristossa kasvavien kasvilajien optisesti mitatut lehtien ominaisuudet taksonien evolutiivisia sukulaisuussuhteita ja 5) korreloivatko nämä mitatut lehtien ominaisuudet kasvien alkuperäisen keräyspaikan ilmasto-olojen kanssa. Käytimme näiden kysymysten tutkimiseen tekniikoita, jotka mahdollistivat laajan (UV-säteilystä lyhyeen infrapunasäteilyyn) auringon säteilyspektrin mittauksen samanaikaisesti. Lehtien flavonoidipitoisuuden mittaamiseen käytimme optista laitetta (Dualex Scientific+), joka mahdollisti toistuvan seurannan kasvia vahingoittamatta. Havaitsimme, että auringon säteilyspektriin metsien kenttäkerroksessa vaikuttivat eniten varjostuksen määrä (umbra, penumbra, valolaikku) sekä laskevassa järjestyksessä metsikkö (eroavat puulajit, tiheys) ja ajankohta kevään aikana. Kasvien flavonoidi-indeksissä havaittiin plastisuutta ja muutoksia vallitsevien ympäristömuuttujien mukaisesti. Lisäksi kasvien lehtistrategiat, sekä uusien lehtien tuotanto vaikuttivat kasvien lehtien flavonoidi-indeksiin. Vuoristossa kasvavien lajien lehtien ominaisuuksien mahdollisia rajoitteita tutkittiin testaamalla niiden fylogeneettinen signaali (Pagel's λ), sekä korrelaatio kasvien alkuperäisen ympäristön ilmastomuuttujien ja lehtien ominaisuuksien välillä. Emme havainneet korrelaatiota kasvien alkuperäisten ilmasto-olojen sekä flavonoidi-indeksin välillä, mikä viittaa kasvien akklimaatioon niiden nykyiseen ympäristöönsä. Lisäksi havaitsimme, että lehtien ominaisuuksien (flavonoidi- ja antosyaani-indeksi) fylogeneettinen signaali oli heikko mutta merkitsevä, ja pienemmästä lajiryhmästä, mitkä kasvoivat Kumpulan kasvitieteellisessä puutarhassa (Etelä-Suomi) ainoastaan klorofylli-indeksi antoi merkitsevän tuloksen. Lähemmässä tarkastelussa (local Moran's I) erotimme sukuja, joiden lajit osoittivat samankaltaisuutta (paikallinen positiivinen autokorrelaatio) lehtien ominaisuuksissa, pääasiassa joko korkeita tai alhaisia indeksiarvoja. Tämä viittaa siihen, että näissä suvuissa flavonoidien kerääntyminen voi olla evolutiivisten sukulaisuussuhteiden mukaisesti rajoittunutta. Tämä voi mahdollisesti vaikeuttaa joidenkin lajien kohdalla migraatiota vuoristossa -varsinkin suvuissa, joissa havaitsimme pääasiassa matalia flavonoidi-indeksin arvoja. Emme kuitenkaan löytäneet selkeää merkkiä rajoitteista vuoristoissa kasvavien lajien lehtien flavonoidien akkumuloitumisessa, joten todisteita korkean UV-säteilyn haitoista niiden nykyisessä ympäristössä ei ollut. Kaiken kaikkiaan tuloksemme osoittavat, että optisesti mitatut lehtien ominaisuudet, liittyen lehtien flavonoidien kertymiseen, ovat joustavia ja akklimoituvat paikallisiin ympäristön muutoksiin, mukaan lukien kasvukauden aikaiset muutokset

Learning and recognition by a dynamical system with a plastic velocity field

Learning is a mechanism intrinsic to all sentient biological systems. Despite the diverse range of paradigms that exist, it appears that an artificial system has yet to be developed that can emulate learning with a comparable degree of accuracy or efficiency to the human brain. With the development of new approaches comes the opportunity to reduce this disparity in performance. A model presented by Janson and Marsden [arXiv:1107.0674 (2011)] (Memory foam model) redefines the critical features that an intelligent system should demonstrate. Rather than focussing on the topological constraints of the rigid neuron structure, the emphasis is placed on the on-line, unsupervised, classification, retention and recognition of stimuli. In contrast to traditional AI approaches, the system s memory is not plagued by spurious attractors or the curse of dimensionality. The ability to continuously learn, whilst simultaneously recognising aspects of a stimuli ensures that this model more closely embodies the operations occurring in the brain than many other AI approaches. Here we consider the pertinent deficiencies of classical artificial learning models before introducing and developing this memory foam self-shaping system. As this model is relatively new, its limitations are not yet apparent. These must be established by testing the model in various complex environments. Here we consider its ability to learn and recognize the RGB colours composing cartoons as observed via a web-camera. The self-shaping vector field of the system is shown to adjust its composition to reflect the distribution of three-dimensional inputs. The model builds a memory of its experiences and is shown to recognize unfamiliar colours by locating the most appropriate class with which to associate a stimuli. In addition, we discuss a method to map a three-dimensional RGB input onto a line spectrum of colours. The corresponding reduction of the models dimensions is shown to dramatically improve computational speed, however, the model is then restricted to a much smaller set of representable colours. This models prototype offers a gradient description of recognition, it is evident that a more complex, non-linear alternative may be used to better characterize the classes of the system. It is postulated that non-linear attractors may be utilized to convey the concept of hierarchy that relates the different classes of the system. We relate the dynamics of the van der Pol oscillator to this plastic self-shaping system, first demonstrating the recognition of stimuli with limit cycle trajectories. The location and frequency of each cycle is dependent on the topology of the systems energy potential. For a one-dimensional stimuli the dynamics are restricted to the cycle, the extension of the model to an N dimensional stimuli is approached via the coupling of N oscillators. Here we study systems of up to three mutually coupled oscillators and relate limit cycles, fixed points and quasi-periodic orbits to the recognition of stimuli

Frequency- and amplitude- modulated semiconductor laser frequency combs

Chip-scale coherent semiconductor light sources generating optical frequency combs currently revolutionize mid-infrared on-chip spectroscopy, near-infrared optical communications and nonlinear microscopy. Their key advantages is the efficient generation of narrow and equidistant spectral lines or laser modes with a fixed phase relationship across a broadband spectral region. An attractive realization of such combs is based on nanostructured semiconductor lasers with semiconductor quantum dots forming their active region. In this thesis, frst, the formation of two types of optical frequency combs in a semiconductor quantum dot laser is presented: in-phase synchronization of the intermode beatings, leading to optical pulses, and the splay-phase synchronization, leading to quasi continuous wave optical output. Both states can be generated on demand in a single semiconductor laser. By varying the laser design and the biasing conditions, frequency- and amplitude-modulated combs can be generated on demand. Second, based on their identifed particular temporal characteristics, a novel technique to determine the sensitivity of semiconductor laser frequency combs to optical feedback, is presented. Results suggest, that amplitude-modulated semiconductor laser frequency combs are less sensitive to optical feedback than frequency-modulated semiconductor laser frequency combs. The developed insights are expected to elevate semiconductor laser frequency combs in current and future integrated photonic circuits in optical communications, where unavoidable optical feedback from downstream active and passive components deteriorates comb stability