11 research outputs found

    Beyond the noise : high fidelity MR signal processing

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    This thesis describes a variety of methods developed to increase the sensitivity and resolution of liquid state nuclear magnetic resonance (NMR) experiments. NMR is known as one of the most versatile non-invasive analytical techniques yet often suffers from low sensitivity. The main contribution to this low sensitivity issue is a presence of noise and level of noise in the spectrum is expressed numerically as “signal-to-noise ratio”. NMR signal processing involves sensitivity and resolution enhancement achieved by noise reduction using mathematical algorithms. A singular value decomposition based reduced rank matrix method, composite property mapping, in particular is studied extensively in this thesis to present its advantages, limitations, and applications. In theory, when the sum of k noiseless sinusoidal decays is formatted into a specific matrix form (i.e., Toeplitz), the matrix is known to possess k linearly independent columns. This information becomes apparent only after a singular value decomposition of the matrix. Singular value decomposition factorises the large matrix into three smaller submatrices: right and left singular vector matrices, and one diagonal matrix containing singular values. Were k noiseless sinusoidal decays involved, there would be only k nonzero singular values appearing in the diagonal matrix in descending order providing the information of the amplitude of each sinusoidal decay. The number of non-zero singular values or the number of linearly independent columns is known as the rank of the matrix. With real NMR data none of the singular values equals zero and the matrix has full rank. The reduction of the rank of the matrix and thus the noise in the reconstructed NMR data can be achieved by replacing all the singular values except the first k values with zeroes. This noise reduction process becomes difficult when biomolecular NMR data is to be processed due to the number of resonances being unknown and the presence of a large solvent peak

    Effet de la microstructure sur les propriétés excitoniques des polymères semi-conducteurs semi-cristallins

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    Les polymères semi-conducteurs semicristallins sont utilisés au sein de diodes électroluminescentes, transistors ou dispositifs photovoltaïques organiques. Ces matériaux peuvent être traités à partir de solutions ou directement à partir de leur état solide et forment des agrégats moléculaires dont la morphologie dicte en grande partie leurs propriétés optoélectroniques. Le poly(3-hexylthiophène) est un des polymères semi-conducteurs les plus étudiés. Lorsque le poids moléculaire (Mw) des chaînes est inférieur à 50 kg/mol, la microstructure est polycristalline et composée de chaînes formant des empilements-π. Lorsque Mw>50 kg/mol, la morphologie est semicristalline et composée de domaines cristallins imbriquées dans une matrice de chaînes amorphes. À partir de techniques de spectroscopie en continu et ultrarapide et appuyé de modèles théoriques, nous démontrons que la cohérence spatiale des excitons dans ce matériau est légèrement anisotrope et dépend de Mw. Ceci nous permet d’approfondir la compréhension de la relation intime entre le couplage inter et intramoléculaire sur la forme spectrale en absorption et photoluminescence. De plus, nous démontrons que les excitations photogénérées directement aux interfaces entre les domaines cristallins et les régions amorphes génèrent des paires de polarons liés qui se recombinent par effet tunnel sur des échelles de temps supérieures à 10ns. Le taux de photoluminescence à long temps de vie provenant de ces paires de charges dépend aussi de Mw et varie entre ∼10% et ∼40% pour les faibles et hauts poids moléculaires respectivement. Nous fournissons un modèle permettant d’expliquer le processus de photogénération des paires de polarons et nous élucidons le rôle de la microstructure sur la dynamique de séparation et recombinaison de ces espèces.Microstructure plays a crucial role in defining the optoelectrical properties of conjugated polymeric semiconductors which can be used in light harvesting and generating devices such as organic light emitting diodes, field effect transistors or photovoltaic devices. These polymers can be processed from solution or solidstate and form photophysical aggregates, consequently providing a complex network which controls the fate of any photogenerated species. poly(3-hexylthiopene) is one of the most studied polymeric semiconductor. In this material, the molecular weight (Mw) of the polymer governs the microstructure and highly impact the optical and electronic properties. Below Mw≈ 50 kg/mol, the polymer chains forms polycrystalline domains of π-stacked molecules while high Mw (>50 kg/mol) consists of a two-phase morphology of molecularly ordered crystallites that are embedded in amorphous regions. Such morphology provides a bidimensionnal network hosting both neutral excitations, known as Frenkel excitons, and polarons. By means of steady-state and ultrafast spectroscopy experiment and backed up theoretical modeling, we demonstrate that the spatial coherence of such excitations are anisotropic in the lattice and depends on the Mw of the polymer, providing a deep understanding of the interplay between interchain (excitonic) and intrachain coupling in polymer aggregates. Moreover, we show that direct excitation at the interface between molecularly ordered and amorphous regions generates tightlybound charge pairs which decay via quantum tunneling over >10 ns. The yield of delayed photoluminescence arising from the recombination of those charge pairs varies between ∼10% and ∼40% for low and high Mw films respectively. We provide a quantitative model that describes the photogeneration process of those geminate polaron pairs and determine the role of the microstructure in the charge separation and recombination processes

    Two-dimensional spectroscopy of γ-aminobutyric acid on a clinical MRI scanner

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    Measurement of the cerebral metabolite y-aminobutyric acid (GABA) has been performed on clinical MRI scanners using a variety of magnetic resonance spectroscopy (MRS) techniques. MRS studies of GABA are difficult, especially at 1.5T due to low in-vivo concentrations and overlapping of higher concentration metabolites. Unlike spectral editing methods, two-dimensional (2D) MRS allows the simultaneous measurement of GABA and other, more traditional metabolites. This work evaluates three implementations of 2D MRS for both in-vitro and in-vivo GABA measurement on a clinical MRI scanner.Existing spectroscopy sequences were used to develop a protocol for performing 2D Jresolved MRS without a dedicated sequence. GABA was measured in-vitro at concentrations approaching normal physiological levels and volunteer results allowed assignment of the 3.01ppm GABA resonance at its J-coupling frequency (7.4Hz). However, the prolonged scan time of over two hours prevented practical application of this approach.A far more efficient method of acquiring 2D J-resolved spectra is achieved with a dedicated 2D J-resolved sequence. An optimised set of acquisition parameters was produced to allow GABA measurement with maximum SNR, and without macromolecule contamination, in 35 minutes. Since the reproducibility of the sequence must be sufficient to detect physiological changes, a formal reproducibility study was performed acquiring three measures of reproducibility at six concentrations of GABA, using a standard volume head coil, 3"- and 5"- surface coils. To our knowledge, this is the first such reproducibility study dedicated to 2D J-resolved GABA measurement, and as such, could have significant implications on the interpretation of in-vivo results. In-vivo 2D J-resolved spectra were acquired and compared well to the published results, allowing assignment of the 3.0Ippm GABA (plus macromolecule) peak (J = 7.4Hz). In the first reported 2D J-resolved spectra specifically designed to reduce the macromolecule contribution by optimising the echo time range, assignment of the in-vivo 3.01 ppm GABA peak was less convincing.As an alternative to 2D J-resolved spectroscopy, preliminary testing of 2D correlation spectroscopy (COSY) showed that it was not as sensitive or robust for either in-vitro or invivo GABA measurement. Although provisional assignment of the 3.01 ppm GABA peak was made, in their current form, neither technique is suitable for pure GABA measurement at 1.5T

    Automated Analysis of Quantitative NMR Spectra

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    NMR spectroscopy is an invaluable tool for structure elucidation in chemistry and molecular biology, which is able to provide unique information not easily obtained by other analytical methods. However, performing quantitative NMR experiments and mixture analysis is considerably less common due to constraints in sensitivity/resolution and the fact that NMR observes individual nuclei, not molecules. The advances in instrument design in the last 25 years have substantially increased the sensitivity of NMR spectrometers, diminishing the main weakness of NMR, while increases in field strength and ever more intricate experiments have improved the resolving power and expanded the attainable information. The minimal need for sample preparation and its non-specific nature make quantitative NMR suitable for many applications ranging from quality control to metabolome characterization. Furthermore, the development of automated sample changers and fully automated acquisition have made high-throughput NMR acquisition a more feasible and attractive, yet expensive, possibility. This work discusses the fundamental principles and limitations of quantitative liquid state NMR spectroscopy, and tries to put together a summary of its various aspects scattered across literature. Many of these more subtle features can be neglected in simple routine spectroscopy, but become important when extracting quantitative data and/or when trying to acquire and process vast amounts of spectra consistently. The original research presented in this thesis provides improved methods for data acquisition of quantitative 13C detected NMR spectra in the form of modified INEPT based experiments (Q-INEPT-CT and Q-INEPT-2D), while software tools for automated processing and analysis of NMR spectra are also presented (ImatraNMR and SimpeleNMR). The application of these tools is demonstrated in the analysis of complex hydrocarbon mixtures (base oils), plant extracts and blood plasma samples. The increased capability of NMR spectroscopy, the rising interest in metabolomics and for example the recent introduction of benchtop NMR spectrometers are likely to expand the future use of quantitative NMR in the analysis of complex mixtures. For this reason, the further development of robust, accurate and feasible analysis methods and tools is essential.NMR-spektroskopia on keskeinen mm. kemiassa ja molekyylibiologiassa käytetty analyysimenetelmä, joka perustuu atomiydinten havaitsemiseen voimakkaassa magneettikentässä radioaaltojen avulla. Menetelmä soveltuu erityisen hyvin molekyylirakenteiden selvittämiseen, ja sillä voidaan saada tietoa myös molekyylien kolmiulotteisesta rakenteesta sekä niiden välisistä interaktioista. NMR-spektroskopia on myös epäselektiivinen menetelmä, jolla on helppo tutkia erityyppisiä näytteitä ilman monimutkaista esikäsittelyä. Perinteisesti NMR-spektroskopian heikkoutena on ollut spektrometrien kalleus ja huono herkkyys, joka on rajannut sen käyttöä laimeiden näytteiden ja etenkin seosten analysoinnissa. Laitteistojen ja analyysitekniikoiden parantuminen viimeisten 20-30 vuoden aikana on kuitenkin kohentanut tilannetta merkittävästi, ja NMR-spektroskopian käyttäminen seosten kvantitatiiviseen analyysiin on selvässä kasvussa. Etenkin metaboliittien analysoimisesta erilaisista biologisista näytteistä on muodostunut tärkeä sovellus. Tätä kehitystä on vauhdittanut myös näytteenkäsittelyn ja spektrien prosessoinnin automaation kehittyminen, joka helpottaa suurien näytemäärien tutkimista. Suurin osa NMR-spektrien käsittelyyn tarkoitetuista ohjelmistoista ei kuitenkaan vielä ole suunniteltu ensisijaisesti suurten näytesarjojen tai seosten analysointiin. Tämä työ keskittyy kvantitatiiviseen NMR-spektroskopiaan ja sen sovelluksiin. Työssä kehitettiin kvantitatiivisia NMR-menetelmiä (pulssisarjat), sekä spektrien analyysiin soveltuvia ohjelmistotyökaluja (ImatraNMR ja SimpeleNMR), joiden tavoitteena on etenkin suurten näytesarjojen automaattisen analysoinnin helpottaminen. Kehitettyjä työkaluja käytettiin hiilivetyseosten (perusöljyt) ja kasviekstraktien analysointiin, mutta niitä voidaan soveltaa myös moniin muihin näytesarjoihin tai esimerkiksi reaktioseosten analysointiin

    DEFINITION OF AN ADVANCED PROCESS FOR THE PRODUCTION OF LOW ENVIRONMENTAL IMPACT CONTAINERS AS POTENTIAL ALTERNATIVE TO PLASTICS

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    For decades, petroleum-based synthetic polymers, commonly known as plastics, have become one of the most appealing materials used for a wide variety of applications. Nevertheless, currently, conventional petroleum-based plastics represent a serious problem for global pollution because remain for hundreds of years in the environment when discarded. In order to reduce dependence on fossil resources, bioplastic materials are being proposed as safer and more sustainable alternatives. Bioplastics are bio-based and/or biodegradable materials, typically derived from renewable sources. Among different resources, food waste is attracting more and more attention in the research field of bioplastics’ production. The sources of food waste include household, commercial, industrial and agricultural residues. In fact, every year, around one-third of all food resources produced for human consumption are lost or wasted. Although European Union guidelines stated that food waste should preferentially be used as animal feed, in some cases, it became illegal because of disease control concerns and other times its nutritional value is very poor. On the other hand, the production of bioplastics from food waste is a renewable, sustainable process, in which materials are fabricated from carbon neutral resources, thus aligning itself with the principles of the circular bioeconomy. However, the conversion of fruit and vegetable by-products into eco-friendly materials with mechanical and hydrodynamic performances comparable to those of fuel-based plastics still remains a challenge. In this thesis, different approaches have been investigated for the valorization of fruit and vegetable wastes to produce low environmental impact materials, as a potential alternative to plastics with application in the field of food packaging. In the first section, apple waste and tomato peel by-products have been used as fillers to fabricate starch-based biocomposites. The mechanical characterization of the samples showed their suitability for covering purposes, since a ductile and soft behaviour was exhibited. In the second section, an avocado by-product extract has been incorporated to an ethyl cellulose matrix for the production of impregnated paper with enhanced durability. Since fruit wastes can contain potential pathogens and physical and chemical contaminants which can be released when used as additive for active packaging, a preliminary untargeted metabolomic characterization of the extract was conducted by LC-ESI(-)-Q Exactive-Orbitrap- MS/MS. The lipid components detected in the extract proved to be useful additives to improve paper hydrophobicity, preventing food browning and moisture loss. In general, the addition of all tested wastes (apple waste, tomato peel and avocado by-products) has proved to be useful to increase the biodegradability of the fabricated biomaterials. Hence, the environmental benefits associated with their recovery are proposed as a driving force to expand their further use for these purposes. The upcycling of food waste through the production of value-added products is an ideal and practical end use, allowing to save huge economic and energy losses

    Innovations in the Food System: Exploring the Future of Food

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    Innovations in Food Systems should be: Inclusive: ensuring economic and social inclusion for all food system actors, especially smallholders, women, and youth; Sustainable: minimizing negative environmental impacts, conserving scarce natural resources, and strengthening resiliency against future shocks; Efficient: producing adequate quantities of food for global needs while minimizing postharvest loss and consumer waste; Nutritious and healthy: enabling the consumption of a diverse range of healthy, nutritious, and safe foods. These are ambitious goals that will require multidisciplinary effort—from engineering to life sciences, biotechnology, medical sciences, social sciences, and economic sciences. New technologies and scientific discoveries are the solutions to the increasing demand for sufficient, safe, healthy, and sustainable foods influenced by the increased public awareness of their importance
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