Nano-Power Integrated Circuits for Energy Harvesting

The energy harvesting research field has grown considerably in the last decade due to increasing interests in energy autonomous sensing systems, which require smart and efficient interfaces for extracting power from energy source and power management (PM) circuits. This thesis investigates the design trade-offs for minimizing the intrinsic power of PM circuits, in order to allow operation with very weak energy sources. For validation purposes, three different integrated power converter and PM circuits for energy harvesting applications are presented. They have been designed for nano-power operations and single-source converters can operate with input power lower than 1 μW. The first IC is a buck-boost converter for piezoelectric transducers (PZ) implementing Synchronous Electrical Charge Extraction (SECE), a non-linear energy extraction technique. Moreover, Residual Charge Inversion technique is exploited for extracting energy from PZ with weak and irregular excitations (i.e. lower voltage), and the implemented PM policy, named Two-Way Energy Storage, considerably reduces the start-up time of the converter, improving the overall conversion efficiency. The second proposed IC is a general-purpose buck-boost converter for low-voltage DC energy sources, up to 2.5 V. An ultra-low-power MPPT circuit has been designed in order to track variations of source power. Furthermore, a capacitive boost circuit has been included, allowing the converter start-up from a source voltage VDC0 = 223 mV. A nano-power programmable linear regulator is also included in order to provide a stable voltage to the load. The third IC implements an heterogeneous multisource buck-boost converter. It provides up to 9 independent input channels, of which 5 are specific for PZ (with SECE) and 4 for DC energy sources with MPPT. The inductor is shared among channels and an arbiter, designed with asynchronous logic to reduce the energy consumption, avoids simultaneous access to the buck-boost core, with a dynamic schedule based on source priority.

Many-core Algorithms for Combinatorial Optimization

Combinatorial Optimization is becoming ever more crucial, in these days. From natural sciences to economics, passing through urban centers administration and personnel management, methodologies and algorithms with a strong theoretical background and a consolidated real-word effectiveness is more and more requested, in order to find, quickly, good solutions to complex strategical problems. Resource optimization is, nowadays, a fundamental ground for building the basements of successful projects. From the theoretical point of view, Combinatorial Optimization rests on stable and strong foundations, that allow researchers to face ever more challenging problems. However, from the application point of view, it seems that the rate of theoretical developments cannot cope with that enjoyed by modern hardware technologies, especially with reference to the one of processors industry. In this work we propose new parallel algorithms, designed for exploiting the new parallel architectures available on the market. We found that, exposing the inherent parallelism of some resolution techniques (like Dynamic Programming), the computational benefits are remarkable, lowering the execution times by more than an order of magnitude, and allowing to address instances with dimensions not possible before. We approached four Combinatorial Optimization’s notable problems: Packing Problem, Vehicle Routing Problem, Single Source Shortest Path Problem and a Network Design problem. For each of these problems we propose a collection of effective parallel solution algorithms, either for solving the full problem (Guillotine Cuts and SSSPP) or for enhancing a fundamental part of the solution method (VRP and ND). We endorse our claim by presenting computational results for all problems, either on standard benchmarks from the literature or, when possible, on data from real-world applications, where speed-ups of one order of magnitude are usually attained, not uncommonly scaling up to 40 X factors.

Effetti del chitosano su composti polifenolici in colture cellulari di vite: aspetti molecolari e metabolici

Polyphenols, including flavonoids and stilbenes, are an essential part of human diet and constitute one of the most abundant and ubiquitous group of plant secondary metabolites. The level of these compounds is inducible by stress or fungal attack, so attempts are being made to identify likely biotic and abiotic elicitors and to better understand the underlying mechanism. Resveratrol (3,5,4’-trihydroxystilbene), which belongs to the stilbene family, is a naturally occurring polyphenol, found in several fruits, vegetables and beverages including red wine. It is one of the most important plant polyphenols with proved benefic activity on animal health. In the last two decades, the potential protective effects of resveratrol against cardiovascular and neurodegenerative diseases, as well as the chemopreventive properties against cancer, have been largely investigated. The most important source of polyphenols and in particular resveratrol for human diet is grape (Vitis vinifera). Since stilbenes and flavonoids play a very important role in plant defence responses and enviromental interactions, and their effects on human health seem promising, the aim of the research of this Thesis was to study at different levels the activation and the regulation of their biosynthetic pathways after chitosan treatment. Moreover, the polyphenol production in grape cells and the optimisation of cultural conditions bioreactor scale-up, were also investigated. Cell suspensions were obtained from cv. Barbera (Vitis vinifera L.) petioles and were treated with a biotic elicitor, chitosan (50 μg/mL, dissolved in acetic acid) to promote phenylpropanoid metabolism. Chitosan is a D-glucosamine polymer from fungi cell wall and therefore mimes fungal pathogen attack. Liquid cultures have been monitored for 15 days, measuring cell number, cell viability, pH and grams of fresh weight. The endogenous and released amounts of 7 stilbenes (trans and cis isomers of resveratrol, piceid and resveratroloside, and piceatannol), gallic acid, 6 hydroxycinnamic acids (trans-cinnamic, p-coumaric, caffeic, ferulic, sinapic and chlorogenic acids), 5 catechines (catechin, epicatechin, epigallocatechin-gallate (EGCG), epigallocatechin and epicatechin-gallate) and other 5 flavonoids (chalcon, naringenin, kaempferol, quercetin and rutin) in cells and cultural medium, were measured by HPLC-DAD analysis and total anthocyanins were quantified by spectrophotometric analysis. Chitosan was effective in stimulating trans-resveratrol endogenous accumulation with a sharp peak at day 4 (exceeding acetic acid and water controls by 36% and 63%, respectively), while it did not influence the production of the cis-isomer. Compared to both water and acetic acid controls, chitosan decreased the release of both trans- and cis-resveratrol respect to controls. No effect was shown on the accumulation of single resveratrol mono-glucoside isomers, but considering their total amount, normalized for the relative water control, it was possible to evidence an increase in both accumulation and release of those compounds, in chitosan-treated cells, throughout the culture period and particularly during the second week. Many of the analysed flavonoids and hydroxycinnamic acids were not present or detectable in trace amounts. Catechin, epicatechin and epigallocatechin-gallate (EGCG) were detectable both inside the cells and in the culture media, but chitosan did not affect their amounts. On the contrary, total anthocyanins have been stimulated by chitosan and their level, from day 4 to 14, was about 2-fold higher than in both controls, confirming macroscopic observations that treated suspensions showed an intense brown-red color, from day 3 onwards. These elicitation results suggest that chitosan selectively up-regulates specific biosynthetic pathways, without modifying the general accumulation pattern of other flavonoids. Proteins have been extracted from cells at day 4 of culture (corresponding to the production peak of trans-resveratrol) and separated by bidimensional electrophoresis. The 73 proteins that showed a consistently changed amount between untreated, chitosan and acetic acid (chitosan solvent) treated cells, have been identified by mass spectrometry. Chitosan induced an increase in stilbene synthase (STS, the resveratrol biosynthetic enzyme), chalcone-flavanone isomerase (CHI, that switches the pathway from chalcones to flavones and anthocyanins), pathogenesis-related proteins 10 (PRs10, a large family of defence proteins), and a decrease in many proteins belonging to primary metabolisms. A train of six distinct spots of STS encoded by the same gene and increased by chitosan, was detected on the 2-D gels, and related to the different phosphorylation degree of STS spots. Northern blot analyses have been performed on RNA extracted from cells treated with chitosan and relative controls, using probes for STS, PAL (phenylalanine ammonia lyase, the first enzyme of the biosynthetic pathway), CHS (chalcone synthase, that shares with STS the same precursors), CHI and PR-10. The up-regulation of PAL, CHS and CHI transcript expression levels correlated with the accumulation of anthocyanins. The strong increase of different molecular weight PR-10 mRNAs, correlated with the 11 PR-10 protein spots identified in proteomic analyses. The sudden decrease in trans-resveratrol endogenous accumulation after day 4 of culture, could be simply explained by the diminished resveratrol biosynthetic activity due to the lower amount of biosynthetic enzymes. This might be indirectly demonstrated by northern blot expression analyses, that showed lower levels of phenylalanine ammonia lyase (PAL) and stilbene synthase (STS) mRNAs starting from day 4. Other possible explanations could be a resveratrol oxidation process and/or the formation of other different mono-, di-glucosides and resveratrol oligomers such as viniferins. Immunolocalisation experiments performed on grape protoplasts and the subsequent analyses by confocal microscope, showed that STS, and therefore the resveratrol synthetic site, is mostly associated to intracellular membranes close to the cytosolic side of plasma membrane and in a smaller amount is localized in the cytosol. STS seemed not to be present inside vacuole and nucleus. There were no differences in the STS intracellular localisation between the different treatments. Since it was shown that stilbenes are largely released in the culture medium and that STS is a soluble protein, a possible interaction of STS with a plasma membrane transporter responsible for the extrusion of stilbenes in the culture medium, might be hypothesized. Proteomic analyses performed on subcellular fractions identified in the microsomial fraction 5 proteins taking part in channel complexes or associated with channels, that significantly changed their amount after chitosan treatment. In soluble and membrane fractions respectively 3 and 4 STS and 6 and 3 PR-10 have been identified. Proteomic results obtained from subcellular fractions substantially confirmed previous result obtained from total cell protein extracts and added more information about protein localisation and co-localisation. The interesting results obtained on Barbera cell cultures with the aim to increase polyphenol (especially stilbenes) production, have encouraged scale up tests in 1 litre bioreactors. The first trial fermentation was performed in parallel with a normal time-course in 20 mL flasks, showing that the scale-up (bigger volume and different conditions) process influenced in a very relevant way stilbenes production. In order to optimise culture parameters such as medium sucrose amount, fermentation length and inoculum cell concentration, few other fermentations were performed. Chitosan treatments were also performed. The modification of each parameter brought relevant variations in stilbenes and catechins levels, so that the production of a certain compound (or class of compounds) could be hypothetically promoted by modulating one or more culture parameters. For example the catechin yield could be improved by increasing sucrose content and the time of fermentation. The best results in stilbene yield were obtained in a 800 mL fermentation inoculated with 10.8 grams of cells and supplemented with chitosan. The culture was fed with MS medium added with 30 g/L sucrose, 25 μg/mL rifampicin and 50 μg/mL of chitosan, and was maintained at 24°C, stirred by marine impeller at 100 rpm and supplied of air at 0.16 L/min rate. Resveratroloside was the stilbene present in the larger amount, 3-5 times more than resveratrol. Because resveratrol glucosides are similarly active and more stable than free resveratrol, their production using a bioreactor could be a great advantage in an hypothetical industrial process. In my bioreactor tests, stilbenes were mainly released in the culture medium (60-80% of the total) and this fact could be another advantage for industrial applications, because it allows recovering the products directly from the culture medium without stopping the fermentation and/or killing the cells. In my best cultural conditions, it was possible to obtain 3.95 mg/L of stilbenes at day 4 (maximum resveratrol accumulation) and 5.13 mg/L at day 14 (maximum resveratroloside production). In conclusion, chitosan effect in inducing Vitis vinifera defense mechanisms can be related to its ability to increase the intracellular content of a large spectrum of antioxidants, and in particular of resveratrol, its derivates and anthocyanins. Its effect can be observed at transcriptional, proteomic (variation of soluble and membrane protein amounts) and metabolic (polyphenols production) level. The chitosan ability to elicit specific plant matabolisms can be useful to produce large quantities of antioxidant compounds from cell culture in bioreactor.

The Enhanced Single-dish Control System and wide surveys of compact sources

The Italian radio telescopes currently undergo a major upgrade period in response to the growing demand for deep radio observations, such as surveys on large sky areas or observations of vast samples of compact radio sources. The optimised employment of the Italian antennas, at first constructed mainly for VLBI activities and provided with a control system (FS – Field System) not tailored to single-dish observations, required important modifications in particular of the guiding software and data acquisition system. The production of a completely new control system called ESCS (Enhanced Single-dish Control System) for the Medicina dish started in 2007, in synergy with the software development for the forthcoming Sardinia Radio Telescope (SRT). The aim is to produce a system optimised for single-dish observations in continuum, spectrometry and polarimetry. ESCS is also planned to be installed at the Noto site. A substantial part of this thesis work consisted in designing and developing subsystems within ESCS, in order to provide this software with tools to carry out large maps, spanning from the implementation of On-The-Fly fast scans (following both conventional and innovative observing strategies) to the production of single-dish standard output files and the realisation of tools for the quick-look of the acquired data. The test period coincided with the commissioning phase for two devices temporarily installed – while waiting for the SRT to be completed – on the Medicina antenna: a 18-26 GHz 7-feed receiver and the 14-channel analogue backend developed for its use. It is worth stressing that it is the only K-band multi-feed receiver at present available worldwide. The commissioning of the overall hardware/software system constituted a considerable section of the thesis work. Tests were led in order to verify the system stability and its capabilities, down to sensitivity levels which had never been reached in Medicina using the previous observing techniques and hardware devices. The aim was also to assess the scientific potential of the multi-feed receiver for the production of wide maps, exploiting its temporary availability on a mid-sized antenna. Dishes like the 32-m antennas at Medicina and Noto, in fact, offer the best conditions for large-area surveys, especially at high frequencies, as they provide a suited compromise between sufficiently large beam sizes to cover quickly large areas of the sky (typical of small-sized telescopes) and sensitivity (typical of large-sized telescopes). The KNoWS (K-band Northern Wide Survey) project is aimed at the realisation of a full-northern-sky survey at 21 GHz; its pilot observations, performed using the new ESCS tools and a peculiar observing strategy, constituted an ideal test-bed for ESCS itself and for the multi-feed/backend system. The KNoWS group, which I am part of, supported the commissioning activities also providing map-making and source-extraction tools, in order to complete the necessary data reduction pipeline and assess the general system scientific capabilities. The K-band observations, which were carried out in several sessions along the December 2008-March 2010 period, were accompanied by the realisation of a 5 GHz test survey during the summertime, which is not suitable for high-frequency observations. This activity was conceived in order to check the new analogue backend separately from the multi-feed receiver, and to simultaneously produce original scientific data (the 6-cm Medicina Survey, 6MS, a polar cap survey to complete PMN-GB6 and provide an all-sky coverage at 5 GHz).

The effect of osmolytes on protein fold stability at the single-molecule level

By pulling and releasing the tension on protein homomers with the Atomic Force Miscroscope (AFM) at different pulling speeds, dwell times and dwell distances, the observed force-response of the protein can be fitted with suitable theoretical models. In this respect we developed mathematical procedures and open-source computer codes for driving such experiments and fitting Bell’s model to experimental protein unfolding forces and protein folding frequencies. We applied the above techniques to the study of proteins GB1 (the B1 IgG-binding domain of protein G from Streptococcus) and I27 (a module of human cardiac titin) in aqueous solutions of protecting osmolytes such as dimethyl sulfoxide (DMSO), glycerol and trimethylamine N-oxide (TMAO). In order to get a molecular understanding of the experimental results we developed an Ising-like model for proteins that incorporates the osmophobic nature of their backbone. The model benefits from analytical thermodynamics and kinetics amenable to Monte-Carlo simulation. The prevailing view used to be that small protecting osmolytes bridge the separating beta-strands of proteins with mechanical resistance, presumably shifting the transition state to significantly higher distances that correlate with the molecular size of the osmolyte molecules. Our experiments showed instead that protecting osmolytes slow down protein unfolding and speed-up protein folding at physiological pH without shifting the protein transition state on the mechanical reaction coordinate. Together with the theoretical results of the Ising-model, our results lend support to the osmophobic theory according to which osmolyte stabilisation is a result of the preferential exclusion of the osmolyte molecules from the protein backbone. The results obtained during this thesis work have markedly improved our understanding of the strategy selected by Nature to strengthen protein stability in hostile environments, shifting the focus from hypothetical protein-osmolyte interactions to the more general mechanism based on the osmophobicity of the protein backbone.

Electrochemical surface modification of Single walled carbon nanotubes and graphene-based electrodes for (bio)sensing applications

Sensors are devices that have shown widespread use, from the detection of gas molecules to the tracking of chemical signals in biological cells. Single walled carbon nanotube (SWCNT) and graphene based electrodes have demonstrated to be an excellent material for the development of electrochemical biosensors as they display remarkable electronic properties and the ability to act as individual nanoelectrodes, display an excellent low-dimensional charge carrier transport, and promote surface electrocatalysis. The present work aims at the preparation and investigation of electrochemically modified SWCNT and graphene-based electrodes for applications in the field of biosensors. We initially studied SWCNT films and focused on their topography and surface composition, electrical and optical properties. Parallel to SWCNTs, graphene films were investigated. Higher resistance values were obtained in comparison with nanotubes films. The electrochemical surface modification of both electrodes was investigated following two routes (i) the electrografting of aryl diazonium salts, and (ii) the electrophylic addition of 1, 3-benzodithiolylium tetrafluoroborate (BDYT). Both the qualitative and quantitative characteristics of the modified electrode surfaces were studied such as the degree of functionalization and their surface composition. The combination of Raman, X-ray photoelectron spectroscopy, atomic force microscopy, electrochemistry and other techniques, has demonstrated that selected precursors could be covalently anchored to the nanotubes and graphene-based electrode surfaces through novel carbon-carbon formation.