Estudio cinético de la descomposición catalizada de peróxido de hidrógeno sobre carbón activado

The kinetic study of decomposition of hydrogen peroxide catalyzed by activated carbon was carried out. The effect of concentrations of reactants and temperature were experimentally studied. Kinetic data were evaluated using differential method of initial rates of reaction. When a typical kinetic law for reactions in homogeneous phase is used, first order of reaction is obtained for hydrogen peroxide and activated carbon, and activation energy of 27 kJ mol-1 for the reaction was estimated. Experimentally was observed that surface of activated carbon is chemically modified during decomposition of hydrogen peroxide, based on this result a scheme of reaction was proposed and evaluated. Experimental data fits very well to a Langmuir- Hinshelwood kinetic model and activation energy of 40 kJ mol-1 was estimated for reaction in heterogeneous phase.

O experimento de Clement-Desormes no século XXI

The Clement-Desormes experiment is reviewed. By reason of a finite difference between the pressure within the system and its surroundings, Bertrand and McDonald have criticized the usual consideration of the adiabatic expansion as reversible. Garland, Nibler and Shoemaker oppose, defining regions through virtual boundaries where the surroundings do not operate. For Holden, the use of virtual boundaries is expendable. Experiments cannot support a hypothesis testing due to experiment's intrinsic uncertainty. The role of polytropy in uncertainty is discussed. Both thermodynamic definitions and kinetic model depict the real processes as irreversible phenomena and the reversible ones as a limiting hypothetical case.

Application of simulated annealing in simulation and optimization of drying process of Zea mays malt

Kinetic simulation and drying process optimization of corn malt by Simulated Annealing (SA) for estimation of temperature and time parameters in order to preserve maximum amylase activity in the obtained product are presented here. Germinated corn seeds were dried at 54-76 °C in a convective dryer, with occasional measurement of moisture content and enzymatic activity. The experimental data obtained were submitted to modeling. Simulation and optimization of the drying process were made by using the SA method, a randomized improvement algorithm, analogous to the simulated annealing process. Results showed that seeds were best dried between 3h and 5h. Among the models used in this work, the kinetic model of water diffusion into corn seeds showed the best fitting. Drying temperature and time showed a square influence on the enzymatic activity. Optimization through SA showed the best condition at 54 ºC and between 5.6h and 6.4h of drying. Values of specific activity in the corn malt were found between 5.26±0.06 SKB/mg and 15.69±0,10% of remaining moisture.

Acidic dissolution of iron oxides and regeneration of a ceramic filter medium

The dewatering of iron ore concentrates requires large capacity in addition to producing a cake with low moisture content. Such large processes are commonly energy intensive and means to lower the specific energy consumption are needed. Ceramic capillary action disc filters incorporate a novel filter medium enabling the harnessing of capillary action, which results in decreased energy consumption in comparison to traditional filtration technologies. As another benefit, the filter medium is mechanically and chemically more durable than, for example, filter cloths and can, thus, withstand harsh operating conditions and possible regeneration better than other types of filter media. In iron ore dewatering, the regeneration of the filter medium is done through a combination of several techniques: (1) backwashing, (2) ultrasonic cleaning, and (3) acid regeneration. Although it is commonly acknowledged that the filter medium is affected by slurry particles and extraneous compounds, published research, especially in the field of dewatering of mineral concentrates, is scarce. Whereas the regenerative effect of backwashing and ultrasound are more or less mechanical, regeneration with acids is based on chemistry. The chemistry behind the acid regeneration is, naturally, dissolution. The dissolution of iron oxide particles has been extensively studied over several decades but those studies may not necessarily be directly applicable in the regeneration of the filter medium which has undergone interactions with the slurry components. The aim of this thesis was to investigate if free particle dissolution indeed correlates with the regeneration of the filter medium. For this purpose, both free particle dissolution and dissolution of surface adhered particles were studied. The focus was on acidic dissolution of iron oxide particles and on the study of the ceramic filter medium used in the dewatering of iron ore concentrates. The free particle dissolution experiments show that the solubility of synthetic fine grained iron oxide particles in oxalic acid could be explained through linear models accounting for the effects of temperature and acid concentration, whereas the dissolution of a natural magnetite is not so easily explained by such models. In addition, the kinetic experiments performed both support and contradict the work of previous authors: the suitable kinetic model here supports previous research suggesting solid state reduction to be the reaction mechanism of hematite dissolution but the formation of a stable iron oxalate is not supported by the results of this research. Several other dissolution mechanisms have also been suggested for iron oxide dissolution in oxalic acid, indicating that the details of oxalate promoted reductive dissolution are not yet agreed and, in this respect, this research offers added value to the community. The results of the regeneration experiments with the ceramic filter media show that oxalic acid is highly effective in removing iron oxide particles from the surface of the filter medium. The dissolution of those particles did not, however, exhibit the expected behaviour, i.e. complete dissolution. The results of this thesis show that although the regeneration of the ceramic filter medium with acids incorporates the dissolution of slurry particles from the surface of the filter medium, the regeneration cannot be assessed purely based upon free particle dissolution. A steady state, dependent on temperature and on the acid concentration, was observed in the dissolution of particles from the surface even though the limit of solubility of free iron oxide particles had not been reached. Both the regeneration capacity and efficiency, with regards to the removal of iron oxide particles, was found to be temperature dependent, but was not affected by the acid concentration. This observation further suggests that the removal of the surface adhered particles does not follow the dissolution of free particles, which do exhibit a dependency on the acid concentration. In addition, changes in the permeability and in the pore structure of the filter medium were still observed after the bulk concentration of dissolved iron had reached a steady state. Consequently, the regeneration of the filter medium continued after the dissolution of particles from the surface had ceased. This observation suggests that internal changes take place at the final stages of regeneration. The regeneration process could, in theory, be divided into two, possibly overlapping, stages: (1) dissolution of surface-adhered particles, and (2) dissolution of extraneous compounds from within the pore structure. In addition to the fundamental knowledge generated during this thesis, tools to assess the effects of parameters on the regeneration of the ceramic filter medium are needed. It has become clear that the same tools used to estimate the dissolution of free particles cannot be used to estimate the regeneration of a filter medium unless only a robust characterisation of the order of regeneration efficiency is needed.

Extraction of polymeric galactoglucomannans from spruce wood by pressurized hot water

The major type of non-cellulosic polysaccharides (hemicelluloses) in softwoods, the partly acetylated galactoglucomannans (GGMs), which comprise about 15% of spruce wood, have attracted growing interest because of their potential to become high-value products with applications in many areas. The main objective of this work was to explore the possibilities to extract galactoglucomannans in native, polymeric form in high yield from spruce wood with pressurised hot-water, and to obtain a deeper understanding of the process chemistry involved. Spruce (Picea abies) chips and ground wood particles were extracted using an accelerated solvent extractor (ASE) in the temperature range 160 – 180°C. Detailed chemical analyses were done on both the water extracts and the wood residues. As much as 80 – 90% of the GGMs in spruce wood, i.e. about 13% based on the original wood, could be extracted from ground spruce wood with pure water at 170 – 180°C with an extraction time of 60 min. GGMs comprised about 75% of the extracted carbohydrates and about 60% of the total dissolved solids. Other substances in the water extracts were xylans, arabinogalactans, pectins, lignin and acetic acid. The yields from chips were only about 60% of that from ground wood. Both the GGMs and other non-cellulosic polysaccharides were extensively hydrolysed at severe extraction conditions when pH dropped to the level of 3.5. Addition of sodium bicarbonate increased the yields of polymeric GGMs at low additions, 2.5 – 5 mM, where the end pH remained around 3.9. However, at higher addition levels the yields decreased, mainly because the acetyl groups in GGMs were split off, leading to a low solubility of GGMs. Extraction with buffered water in the pH range 3.8 – 4.4 gave similar yields as with plain water, but gave a higher yield of polymeric GGMs. Moreover, at these pH levels the hydrolysis of acetyl groups in GGMs was significantly inhibited. It was concluded that hot-water extraction of polymeric GGMs in good yields (up to 8% of wood) demands appropriate control of pH, in a narrow range about 4. These results were supported by a study of hydrolysis of GGM at constant pH in the range of 3.8 – 4.2 where a kinetic model for degradation of GGM was developed. The influence of wood particle size on hot-water extraction was studied with particles in the range of 0.1 – 2 mm. The smallest particles (< 0.1 mm) gave 20 – 40% higher total yield than the coarsest particles (1.25 – 2 mm). The difference was greatest at short extraction times. The results indicated that extraction of GGMs and other polysaccharides is limited mainly by the mass transfer in the fibre wall, and for coarse wood particles also in the wood matrix. Spruce sapwood, heartwood and thermomechnical pulp were also compared, but only small differences in yields and composition of extracts were found. Two methods for isolation and purification of polymeric GGMs, i.e. membrane filtration and precipitation in ethanol-water, were compared. Filtration through a series of membranes with different pore sizes separated GGMs of different molar masses, from polymers to oligomers. Polysaccharides with molar mass higher than 4 kDa were precipitated in ethanol-water. GGMs comprised about 80% of the precipitated polysaccharides. Other polysaccharides were mainly arabinoglucuronoxylans and pectins. The ethanol-precipitated GGMs were by 13C NMR spectroscopy verified to be very similar to GGMs extracted from spruce wood in low yield at a much lower temperature, 90°C. The obtained large body of experimental data could be utilised for further kinetic and economic calculations to optimise technical hot-water extractionof softwoods.

Silicon-containing species in used lube oil re-refining

Nowadays, the re-refining of the used lube oils has gained worldwide a lot of attention due to the necessity for added environmental protection and increasingly stringent environmental legislation. One of the parameters determining the quality of the produced base oils is the composition of feedstock. Estimation of the chemical composition of the used oil collected from several European locations showed that the hydrocarbon structure of the motor oil is changed insignificantly during its operation and the major part of the changes is accounted for with depleted oil additives. In the lube oil re-refining industry silicon, coming mainly from antifoaming agents, is recognized to be a contaminant generating undesired solid deposits in various locations in the re-refining units. In this thesis, a particular attention was paid to the mechanism of solid product formation during the alkali treatment process of silicon-containing used lube oils. The transformations of a model siloxane, tetramethyldisiloxane (TMDS), were studied in a batch reactor at industrially relevant alkali treatment conditions (low temperature, short reaction time) using different alkali agents. The reaction mechanism involving solid alkali metal silanolates was proposed. The experimental data obtained demonstrated that the solids were dominant products at low temperature and short reaction time. The liquid products in the low temperature reactions were represented mainly by linear siloxanes. The prolongation of reaction time resulted in reduction of solids, whereas both temperature and time increase led to dominance of cyclic products in the reaction mixture. Experiments with the varied reaction time demonstrated that the concentration of cyclic trimer being the dominant in the beginning of the reaction diminished with time, whereas the cyclic tetramer tended to increase. Experiments with lower sodium hydroxide concentration showed the same effect. In addition, a decrease of alkali agent concentration in the initial reaction mixture accelerated TMDS transformation reactions resulting in solely liquid cyclic siloxanes yields. Comparison of sodium and potassium hydroxides applied as an alkali agent demonstrated that potassium hydroxide was more efficient, since the activation energy in KOH presence was almost 2-fold lower than that for sodium hydroxide containing reaction mixture. Application of potassium hydroxide for TMDS transformation at 100° C with 3 hours reaction time resulted in 20 % decrease of solid yields compared to NaOH-containing mixture. Moreover, TMDS transformations in the presence of sodium silanolate applied as an alkali agent led to formation of only liquid products without formation of the undesired solids. On the basis of experimental data and the proposed reaction mechanism, a kinetic model was developed, which provided a satisfactory description of the experimental results. Suitability of the selected siloxane as a relevant model of industrial silicon-containing compounds was verified by investigation of the commercially available antifoam agent in base-catalyzed conditions.

Partial substitution of nitrite by chitosan and the effect on the quality properties of pork sausages

The aim of the study was to evaluate the influence of partial nitrite replacement by chitosan on the quality of Ham Visking (a type of pork sausages). Five Ham Visking formulations were elaborated modifying the sodium nitrite (0.011; 0.016 or 0.0212%) and chitosan concentrations (0.25 or 0.5%) in the products. Sausages were stored at 4 ºC and physicochemical, microbiological, and sensorial evaluations were performed in order to estimate their shelf life. Chitosan can be used in pork sausages without affecting ensory attributes such as color although the panelists detected textural differences among the samples with chitosan, which suggests that there is some influence of deacetylation degree of chitosan on the textural behavior of sausages which still needed to be explained for a successful application of chitosan in meat products. The reduction of residual sodium nitrite did not affect the color and flavor of such products, but the use of chitosan increasedsignificantly the shelf life of sausages.

Alterations of palm oil (Elaeis guineensis) in the continuous industrial par frying of breaded chicken snacks

The physical and chemical alterations in palm oil during continuous industrial par frying of breaded chicken snacks were evaluated using a pseudo first-order kinetic model. The acidity index, refractive index, concentration of polar compounds, viscosity, color, and absorbance (232 and 268 nm) of 238 samples of the frying oil collected during 26 days of production were analyzed. For all of the analyses, the results of the oil were below the limits recommended for oil disposal, indicating that the processing conditions were safe and that under these experimental conditions the oil remained suitable for frying. The linear regressions were significant for refractive index, content of polar compounds, and lightness (L*). The content of polar compounds was determined using a cooking oil tester, and it had the best fit to the proposed model and can be used as an effective index for monitoring palm oil during the continuous par frying of breaded chicken snacks. The high turnover rate of the oil was important for maintaining the oil in good running conditions.

Thermal inactivation of polyphenoloxidase and peroxidase in Jubileu clingstone peach and yeast isolated from its spoiled puree

The thermal inactivation of yeast isolated from spoiled Jubileu peach puree and that of polyphenoloxidase (PPO) and peroxidase (POD) in cv. Jubileu, which is widely cultivated in southern Rio Grande do Sul state, Brazil, were studied. PPO and POD were extracted using the protein powder method and submitted to partial purification by precipitation followed by dialysis. The enzymatic activity was determined measuring the increase in absorbance at 420 nm for PPO and 470 nm for POD. The yeast used in this investigation was isolated from spoiled Jubileu peach puree at 22 °Brix, with total initial microbial count of 22 × 10² UFCmL- 1. Stock cultures were maintained on potato dextrose agar (PDA) slants at 4 °C and pH 5 for later use for microbial growth. In all cases, kinetic analysis of the results suggests that the thermal inactivation was well described by a first-order kinetic model, and the temperature dependence was significantly represented by the Arrhenius law. Both enzymes were affected by heat denaturation, and PPO was more thermostable. PPO was also more thermosTable than the yeast isolated from peach puree. The D60-values were 1.53 and 1.87 min for PPO and yeast isolated from spoiled Jubileu peach puree, respectively.

Étude fonctionnelle du cotransporteur Na+/glucose (hSGLT1) : courant de fuite, vitesse de cotransport et modélisation cinétique

Les résultats présentés dans cette thèse précisent certains aspects de la fonction du cotransporteur Na+/glucose (SGLT1), une protéine transmembranaire qui utilise le gradient électrochimique favorable des ions Na+ afin d’accumuler le glucose à l’intérieur des cellules épithéliales de l’intestin grêle et du rein. Nous avons tout d’abord utilisé l’électrophysiologie à deux microélectrodes sur des ovocytes de xénope afin d’identifier les ions qui constituaient le courant de fuite de SGLT1, un courant mesuré en absence de glucose qui est découplé de la stoechiométrie stricte de 2 Na+/1 glucose caractérisant le cotransport. Nos résultats ont démontré que des cations comme le Li+, le K+ et le Cs+, qui n’interagissent que faiblement avec les sites de liaison de SGLT1 et ne permettent pas les conformations engendrées par la liaison du Na+, pouvaient néanmoins générer un courant de fuite d’amplitude comparable à celui mesuré en présence de Na+. Ceci suggère que le courant de fuite traverse SGLT1 en utilisant une voie de perméation différente de celle définie par les changements de conformation propres au cotransport Na+/glucose, possiblement similaire à celle empruntée par la perméabilité à l’eau passive. Dans un deuxième temps, nous avons cherché à estimer la vitesse des cycles de cotransport de SGLT1 à l’aide de la technique de la trappe ionique, selon laquelle le large bout d’une électrode sélective (~100 μm) est pressé contre la membrane plasmique d’un ovocyte et circonscrit ainsi un petit volume de solution extracellulaire que l’on nomme la trappe. Les variations de concentration ionique se produisant dans la trappe en conséquence de l’activité de SGLT1 nous ont permis de déduire que le cotransport Na+/glucose s’effectuait à un rythme d’environ 13 s-1 lorsque le potentiel membranaire était fixé à -155 mV. Suite à cela, nous nous sommes intéressés au développement d’un modèle cinétique de SGLT1. En se servant de l’algorithme du recuit simulé, nous avons construit un schéma cinétique à 7 états reproduisant de façon précise les courants du cotransporteur en fonction du Na+ et du glucose extracellulaire. Notre modèle prédit qu’en présence d’une concentration saturante de glucose, la réorientation dans la membrane de SGLT1 suivant le relâchement intracellulaire de ses substrats est l’étape qui limite la vitesse de cotransport.

Étude structure/fonction des cotransporteurs Na+/glucose

Cette thèse porte sur l’étude de la relation entre la structure et la fonction chez les cotransporteurs Na+/glucose (SGLTs). Les SGLTs sont des protéines membranaires qui se servent du gradient électrochimique transmembranaire du Na+ afin d’accumuler leurs substrats dans la cellule. Une mise en contexte présentera d’abord un bref résumé des connaissances actuelles dans le domaine, suivi par un survol des différentes techniques expérimentales utilisées dans le cadre de mes travaux. Ces travaux peuvent être divisés en trois projets. Un premier projet a porté sur les bases structurelles de la perméation de l’eau au travers des SGLTs. En utilisant à la fois des techniques de modélisation moléculaire, mais aussi la volumétrie en voltage imposé, nous avons identifié les bases structurelles de cette perméation. Ainsi, nous avons pu identifier in silico la présence d’une voie de perméation passive à l’eau traversant le cotransporteur, pour ensuite corroborer ces résultats à l’aide de mesures faites sur le cotransporteur Na/glucose humain (hSGLT1) exprimé dans les ovocytes. Un second projet a permis d’élucider certaines caractéristiques structurelles de hSGLT1 de par l’utilisation de la dipicrylamine (DPA), un accepteur de fluorescence dont la répartition dans la membrane lipidique dépend du potentiel membranaire. L’utilisation de la DPA, conjuguée aux techniques de fluorescence en voltage imposé et de FRET (fluorescence resonance energy transfer), a permis de démontrer la position extracellulaire d’une partie de la boucle 12-13 et le fait que hSGLT1 forme des dimères dont les sous-unités sont unies par un pont disulfure. Un dernier projet a eu pour but de caractériser les courants stationnaires et pré-stationaires d’un membre de la famille des SGLTs, soit le cotransporteur Na+/myo-inositol humain hSMIT2 afin de proposer un modèle cinétique qui décrit son fonctionnement. Nous avons démontré que la phlorizine inhibe mal les courants préstationnaires suite à une dépolarisation, et la présence de courants de fuite qui varient en fonction du temps, du potentiel membranaire et des substrats. Un algorithme de recuit simulé a été mis au point afin de permettre la détermination objective de la connectivité et des différents paramètres associés à la modélisation cinétique.

Dégradation chimique et biologique de neuf contaminants émergents dans les eaux de surfaces et les effluents primaires d’eaux usées municipales

Un protocole inspiré du test de simulation 309 de l’Organisation de coopération et de développement économiques (OCDE) nous a permis de mesurer la dégradation chimique (excluant la photolyse) dans des eaux de surface de même que la dégradation chimique et biologique de neuf contaminants émergents dans l’effluent d’un décanteur primaire d’eau usée municipale. Les données étaient compatibles avec le modèle de cinétique de pseudo ordre un. Les résultats démontrant une persistance de plus d’un an dans les eaux de surface et de 71 jours dans l’effluent du décanteur primaire suggèrent que les dégradations chimique et biologique ne contribuent pas significativement à la diminution de: atrazine, déséthylatrazine, carbamazépine et diclofénac dans la phase aqueuse des systèmes testés. Les autres composés se sont dégradés à différents niveaux. Le 17ß-estradiol ainsi que l’éthinylestradiol, la noréthindrone, la caféine et le sulfaméthoxazole ont tous été sujet à la dégradation biologique dans les effluents du décanteur primaire d’eau usée avec des constantes de dégradation k et des demi-vies t1/2 mesurées allant respectivement de 0.0082 à 0.59 j-1 et de 1.2 à 85 jours. Les paramètres de cinétique mesurés peuvent être combinés aux concentrations typiques des composés à l’étude dans un décanteur primaire d’eau usée pour y calculer leur vitesse de dégradation. Cependant, puisque les décanteurs primaires dans les usines de traitement d’eaux usées ont généralement des temps de résidence de quelques heures seulement, il est improbable que les neufs contaminants émergents à l’étude diminuent significativement par ces processus durant leur passage dans le compartiment.

Caractérisation structurale et thermodynamique de la reconnaissance du substrat par le ribozyme VS de Neurospora

Les interactions ARN/ARN de type kissing-loop sont des éléments de structure tertiaire qui jouent souvent des rôles clés chez les ARN, tant au niveau fonctionnel que structural. En effet, ce type d’interaction est crucial pour plusieurs processus dépendant des ARN, notamment pour l’initiation de la traduction, la reconnaissance des ARN antisens et la dimérisation de génome rétroviral. Les interactions kissing-loop sont également importantes pour le repliement des ARN, puisqu’elles permettent d’établir des contacts à longue distance entre différents ARN ou encore entre les domaines éloignés d’un même ARN. Ce type d’interaction stabilise aussi les structures complexes des ARN fonctionnels tels que les ARNt, les riborégulateurs et les ribozymes. Comme d’autres ARN fonctionnels, le ribozyme VS de Neurospora contient une interaction kissing-loop importante. Celle-ci est impliquée dans la reconnaissance du substrat et se forme entre la tige-boucle I (stem-loop I, SLI) du substrat et la tige-boucle V (stem-loop V, SLV) du domaine catalytique. Des études biochimiques ont démontré que l’interaction kissing-loop I/V, dépendante du magnésium, implique trois paires de bases Watson-Crick (W-C). De plus, cette interaction est associée à un réarrangement de la structure du substrat, le faisant passer d’une conformation inactive dite unshifted à une conformation active dite shifted. Les travaux présentés dans cette thèse consistent en une caractérisation structurale et thermodynamique de l’interaction kissing-loop I/V du ribozyme VS, laquelle est formée de fragments d’ARN représentant les tige-boucles I et V dérivées du ribozyme VS (SLI et SLV). Cette caractérisation a été réalisée principalement par spectroscopie de résonance magnétique nucléaire (RMN) et par titrage calorimétrique isotherme (isothermal titration calorimetry, ITC) en utilisant différents complexes SLI/SLV dans lesquels l’ARN SLV est commun à tous les complexes, alors que différentes variations de l’ARN SLI ont été utilisées, soit en conformation shiftable ou preshifted. Les données d’ITC ont permis de démontrer qu’en présence d’une concentration saturante de magnésium, l’affinité d’un substrat SLI preshifted pour SLV est extrêmement élevée, rendant cette interaction plus stable que ce qui est prédit pour un duplexe d’ARN équivalent. De plus, l’étude effectuée par ITC montre que des ARN SLI preshifted présentent une meilleure affinité pour SLV que des ARN SLI shiftable, ce qui a permis de calculer le coût énergétique associé au réarrangement de structure du substrat. En plus de confirmer la formation des trois paires de bases W-C prédites à la jonction I/V, les études de RMN ont permis d’obtenir une preuve structurale directe du réarrangement structural des substrats SLI shiftable en présence de magnésium et de l’ARN SLV. La structure RMN d’un complexe SLI/SLV de grande affinité démontre que les boucles terminales de SLI et SLV forment chacune un motif U-turn, ce qui facilite l’appariement W-C intermoléculaire. Plusieurs autres interactions ont été définies à l’interface I/V, notamment des triplets de bases, ainsi que des empilements de bases. Ces interactions contribuent d’ailleurs à la création d’une structure présentant un empilement continu, c’est-à-dire qui se propage du centre de l’interaction jusqu’aux bouts des tiges de SLI et SLV. Ces études de RMN permettent donc de mieux comprendre la stabilité exceptionnelle de l’interaction kissing-loop I/V au niveau structural et mènent à l’élaboration d’un modèle cinétique de l’activation du substrat par le ribozyme VS. En considérant l’ensemble des données d’ITC et de RMN, l’étonnante stabilité de l’interaction I/V s’explique probablement par une combinaison de facteurs, dont les motifs U-turn, la présence d’un nucléotide exclu de la boucle de SLV (U700), la liaison de cations magnésium et l’empilement de bases continu à la jonction I/V.

Nanocrystalline Ge Flash Memories: Electrical Characterization and Trap Engineering

Conventional floating gate non-volatile memories (NVMs) present critical issues for device scalability beyond the sub-90 nm node, such as gate length and tunnel oxide thickness reduction. Nanocrystalline germanium (nc-Ge) quantum dot flash memories are fully CMOS compatible technology based on discrete isolated charge storage nodules which have the potential of pushing further the scalability of conventional NVMs. Quantum dot memories offer lower operating voltages as compared to conventional floating-gate (FG) Flash memories due to thinner tunnel dielectrics which allow higher tunneling probabilities. The isolated charge nodules suppress charge loss through lateral paths, thereby achieving a superior charge retention time. Despite the considerable amount of efforts devoted to the study of nanocrystal Flash memories, the charge storage mechanism remains obscure. Interfacial defects of the nanocrystals seem to play a role in charge storage in recent studies, although storage in the nanocrystal conduction band by quantum confinement has been reported earlier. In this work, a single transistor memory structure with threshold voltage shift, Vth, exceeding ~1.5 V corresponding to interface charge trapping in nc-Ge, operating at 0.96 MV/cm, is presented. The trapping effect is eliminated when nc-Ge is synthesized in forming gas thus excluding the possibility of quantum confinement and Coulomb blockade effects. Through discharging kinetics, the model of deep level trap charge storage is confirmed. The trap energy level is dependent on the matrix which confines the nc-Ge.

Technical note: A proposed method to determine the extent of degradation of a feed in the rumen from the degradation profile obtained with the in vitro gas production technique using feces as the inoculum

A method is proposed to determine the extent of degradation in the rumen involving a two-stage mathematical modeling process. In the first stage, a statistical model shifts (or maps) the gas accumulation profile obtained using a fecal inoculum to a ruminal gas profile. Then, a kinetic model determines the extent of degradation in the rumen from the shifted profile. The kinetic model is presented as a generalized mathematical function, allowing any one of a number of alternative equation forms to be selected. This method might allow the gas production technique to become an approach for determining extent of degradation in the rumen, decreasing the need for surgically modified animals while still maintaining the link with the animal. Further research is needed before the proposed methodology can be used as a standard method across a range of feeds.