No description available.

No description available.

Kinetics of the reactions of amoxycillin sodium and potassium clavulanate alone and in combination were investigated in the liquid and frozen states at selected pH values of 2.0, 4.6 and 7.0. A stability indicating HPLC assay was developed to perform simultaneous quantification of these compounds validated under stressed conditions.Amoxycillin and clavulanate degradation obeyed first-order kinetics under all conditions of this study. The effect of temperature, buffer, concentrations and complexation were investigated. Both compounds showed acceleration in rates due to general acid catalysis from buffer species. The buffer catalysis rate constants due to total phosphate and total acetate at 55 degrees celsius were 5.84x10(subscript)-1 (mol dm(subscript)-3)(subscript)-1 h(subscript)-1 and 1.53 X10(subscript)-1 (mol dm(subscript)-3)(subscript)-1 h(subscript)-1 for amoxycillin, 2.33 (mol dm(subscript)-3)(subscript)-1 h(subscript)-1 and 4.4x10(subscript)-1 mol dm(subscript)-3)(subscript)-1 h(subscript)-1 for clavulanate respectively. The buffer independent rate constant values were obtained and interpreted according to the available literature data. Increase in the initial concentration of amoxycillin or clavulanate did not change the first-order rate constant values of these antibiotics significantly at liquid state temperatures. However in the buffer systems, the rate of hydrolysis of amoxycillin in the combination was significantly subject to clavulanate catalysis. This novel finding was influenced by phosphate buffer concentration. A kinetic model was proposed and the second-order catalytic rate constant values at pH 7.0 and 55 degrees celsius were estimated for clavulanate catalysis of amoxycillin (k(subscript)cvc) to be k(subscript)cvc = 1.75 X10(subscript)2 (mol dm(subscript)-3)(subscript)-1 h(subscript)-1 and for phosphate catalyzed of clavulanate catalysis of ++ / amoxycillin (k(subscript)phccv) as k(subscript)phccv = 2.87 (mol dm(subscript)-3)(subscript)-1 h(subscript)-1.The temperature dependence of the rate of amoxycillin sodium degradation over the pH range evaluated did not change significantly. However the E(subscript)a values of potassium clavulanate decreased slightly with increase in pH. Both the compounds showed similar E(subscript)a values at pH 4.6 in acetate system. Hence 71.2 kJ mol(subscript)-1 for amoxycillin and 75.1 kJ mol(subscript)-1 for clavulanate.The investigation on complexation effects by HPbetaCD on the rate of hydrolysis of amoxycillin and clavulanate indicated no significant change in the rate of reaction of amoxycillin in the acetate buffer system. But the rate of clavulanate hydrolysis in combination was decreased by approximately 10%. The rate constant within the cyclodextrin complex and the stability constant of the complex obtained for clavulanate at pH 4.6 and 55 degrees celsius were k(subscript)c = 1.54x 10(subscript)-1 h(subscript)-1 and K(subscript)c = 74.2 (mol dm(subscript)-3)(subscript)-1.Extrapolation of the rate constant values to the frozen state from the liquid state data indicated marked acceleration of the rate of amoxycillin and clavulanate in all the pH values investigated. The highest acceleration in rate recorded was 15.0 fold for clavulanate in the hydrochloric acid system and the lowest value was 4.4 fold for amoxycillin at -7.3 degrees celsius. The rate constant values obtained were interpreted in terms of the concentration model (Pincock and Kiovsky 1966), phase-temperature relationship of the solutes, buffer catalysis, pH change and polymerization reactions.In the hydrochloric acid system a kinetic model was deduced providing adequate explanation of the experimental results. The stabilizing effect of sodium chloride used for maintaining constant ionic strength (mu=0.5) was ++ / enormous in this system. The shelf-life of amoxycillin was increased from 2.2 h to 58.3 h at -7.3 degrees celsius when sodium chloride was included in the system. It also stabilized the rates of the reactions significantly in the buffer systems.The buffer systems used in this study stabilized the rates of the reaction of both the drug compounds considerably. The shelf-life of amoxycillin in phosphate buffer was 621.3 h at -13.5 degrees celsius and in acetate buffer the shelf-life of clavulanate was 71.9 h at the same temperature. These are the highest shelf-life values recorded so far in the literature for amoxycillin and clavulanate at this frozen temperature.

No description available.

<p> In this thesis, the current-voltage (I-V) behaviour of Liquid Organic Field-Effect Transistor (LOFET) was systematically studied with respect to the gate voltage, channel length and channel fluid. LOFETs in both internal and external gate modes were successfully fabricated in four-probe configuration. </p> <p> It was discovered that the effect of gate voltage on the source-to-drain current of LOFETs was significant. The drain current clearly increased when the gate voltage increased. This phenomenon was found in all LOFETs samples with different channel fluids and channel lengths. In addition, it was also proved that anions are the majority carriers in LOFETs. The concentration of anions inside the LOFET channel increased while applying a larger voltage to the gate, resulted in an increase of the drain current. This achievable gate modulation set up a solid foundation for further research on the manipulation of ionic and molecular species. </p> <p>It was also obtained that the drain current was changed with variable channel lengths. The current through the LOFET channel decreased while the channel length increased. At the same time, the difference between drain current in various channels evidently increased when the gate voltage increased from 0 to 5V. This was found to be due to the anion concentration change with varying gate voltages. </p> <p> The drain currents through LOFET channels filled with fluids of different polarities were also measured. It was observed that when the polarity of the molecule increased from that of 4,4'-Dihydroxybiphenyl to that of 2-Amino-4 Phenylphenol, the drain current increased significantly. At the same time, the difference between drain current in specific solutions was also more significant, when applying higher voltage to the gate. Combining these results with the gate modulation above, there is great potential of developing new sensing techniques and even logic operation in the future. </p> <p> This work represents a step towards a new group of cheap and effiecient electronic components of LOFETs. Guided by systemic observations from the effects of gate voltage, channel length and fluid structure, there is no doubt that LOFET will become a more attractive research topic because of its promising advantages, such as easy fabrication, low cost and its highly sensitive response. </p> / Thesis / Master of Applied Science (MASc)

Este trabalho investiga a termodifusão em coloides magnéticos através da técnica de varredura Z. O ponto de partida é a generalização do modelo de lente térmica, supondo o surgimento de um gradiente de concentração dos grãos magnéticos devido ao gradiente de temperatura causado pelo feixe de laser sobre a amostra. A partir do uso da técnica de varredura Z foi possível o estudo do coeficiente Soret (S IND.T) em ferrofluidos iônicos, surfactados e citrados, em amostras com baixa concentração de grãos (fração volumétrica de Fe, ø, menor que 1%). Na generalização do modelo de lente térmica que efetuamos, consideramos que a variação no índice de refração da amostra, em uma experiência de varredura Z, depende da variação da intensidade do feixe laser (I), da variação da temperatura (T) e da variação da concentração de grãos magnéticos (ø), onde C IND.N, C IND.T e C IND.S são seus respectivos parâmetros adimensionais no modelo. Uma vez que o tempo característico da termodifusão é da ordem de segundos, uma varredura Z com pulsos da ordem de 20ms é utilizada para a determinação de C IND.N. C IND.T é obtido independentemente por meio de métodos de óptica linear.Após a determinação de C IND.N e C IND.T, uma varredura Z com duração de pulso da ordem de 1 segundo é feita para determinar C IND.S e, posteriormente, o coeficiente Soret. A partir do comportamento da curva de evolução temporal da tranmitância com pulsos de 1 segundo pode-se determinar o sinal do coeficiente Soret. O sinal está relacionado com a tendência dos grãos de migrarem para a região mais fria (termofóbico, S IND.T>0) ou mais quente (termofílico, S IND.T<0) da amostra, dependendo de suas características físico-químicas. Mostramos que o módulo de S IND.T é proporcional a ø, em concordância com resultados obtidos para soluções mais concentradas (ø1) através da técnica de Espalhamento Rayleigh Forçado. Uma possível origem física para os comportamentos termofóbico e termofílico dos fluidos magnéticos poderia estar relacionada a mudanças na intensidade das forças que mantêm o equilíbrio coloidal, por ação da temperatura. / This work explores the thermodiffusion in magnetic colloids through the Z-Scan technique. The starting point is the generalization of the thermal lens model based on the assumption that the concentration gradient of the magnetic grains emerges due to the temperature gradient caused by the laser beam on the sample. By using the Z-Scan technique it was possible to study the Soret coefficient (ST) for ionic, surfacted and citrated ferrofluids in samples with low concentration of grains (Fe volumetric percentage, ø, less than 1%). In this thermal lens model generalization, we have considered that the refraction índex variation in a Z-Scan experiment depends on the laser beam intensity (I), the temperature variation (T) and the variation of the magnetic grains concentration (ø), where CN, CT and CS are their respective dimensionless parameters in the model. As characteristic time of thermodiffusion is of the order of seconds, a Z-Scan with pulses around 20 ms is used in order to determine CN. CT is obtained independently by using lenear optics methods. After the determination of CN and CT, a Z-Scan with pulses around 1 second is made in order to determine CS and, Consequently, the Soret coefficient. Through the behavior of the time dependent transmittance with 1-second pulses we were able to determine the sign of the Soret coefficient. The sign is related to the tendency of the grains to migrate to the colder region (thermophobic, ST>0) or to the warmer region (thermophilic, ST<0) of the sample, depending on its physical-chemical characteristics. We have showed that the ST module is proportional to ø, in agreement with the results for higher concentration solutions (ø1%) obtained through Forced Rayleigh Scattering. A possible physical originfor the thermophobic and thermophilic behavior of magnetic fluids could berelated to changes in the intensity of the forces that keep the colloidal balance, by means of temperature.

The way our brain works is still an open question, but one thing seems to be clear: biological neural systems are computationally powerful, robust and noisy. Natural nervous system are able to control limbs in different scenarios with high precision. As neural networks in living beings communicate through spikes, modern neuromorphic systems try to mimic them by using spike-based neuron models. This thesis is focused on the advancement of neurorobotics or brain inspired robotic arm controllers based on artificial neural network architectures. The architecture chosen to implement those controllers was the spike neuron version of Reservoir Computing framework, called Liquid State Machines. The main goal is to explore the possibility of using brain inspired neural networks to control a robot by demonstration. Moreover, it aims to achieve systems robust to environmental noise and internal structure destruction presenting a graceful degradation. As the validation, a series of action learning experiments are presented where simulated robotic arms are controlled. The investigation starts with a 2 degrees of freedom arm and moves to the research version of the Rethink Robotics Inc. collaborative humanoid robot Baxter. Moreover, a proof-of- concept experiment is also done using the real Baxter robot. The results show Liquid State Machines, when endowed with an extra external feedback loop, can be also employed to control more complex humanoid robotic arms than a simple planar 2 degrees of freedom one. Additionally, the new parallel architecture presented here was capable to withstand noise and internal destruction better than a simple use of multiple columns also presenting a graceful degradation behaviour.

Spiking neural networks have, in recent years, become a popular tool for investigating the properties and computational performance of large massively connected networks of neurons. Equally as interesting is the investigation of the potential computational power of individual spiking neurons. An overview is provided of current and relevant research into the Liquid Sate Machine, biologically inspired artificial STDP learning mechanisms and the investigation of aspects of the computational power of artificial, recurrent networks of spiking neurons. First, it is shown that, using simple structures of spiking Leaky Integrate and Fire (LIF) neurons, a network n(P), can be built to perform any program P that can be performed by a general parallel programming language. Next, a form of STDP learning with normalisation is developed, referred to as STDP + N learning. The effects of applying this STDP + N learning within recurrently connected networks of neurons is then investigated. It is shown experimentally that, in very specific circumstances Anti-Hebbian and Hebbian STDP learning may be considered to be approximately equivalent processes. A metric is then developed that can be used to measure the distance between any two spike trains. The metric is then used, along with the STDP + N learning, in an experiment to examine the capacity of a single spiking neuron that receives multiple input spike trains, to simultaneously learn many temporally precise Input/Output spike train associations. The STDP +N learning is further modified for use in recurrent networks of spiking neurons, to give the STDP + NType2 learning methodology. An experiment is devised which demonstrates that the Type 2 method of applying learning to the synapses of a recurrent network — effectively a randomly shifting locality of learning — can enable the network to learn firing patterns that the typical application of learning is unable to learn. The resulting networks could, in theory, be used to create to simple structures discussed in the first chapter of original work.

Neste trabalho apresentamos uma revisão de métodos de simulação de energia eletrostática de sistemas de cargas e uma proposta de adaptação de algoritmo ultilizado na literatura de sistemas gravitacionais para estudo das propriedades estatísticas de sistemas coulombianos. Na primeira parte do estudo, revisamos os fundamentos teóricos do método de Ewald e suas condições de aplicabilidade, procurando esclarecer as referências mais importantes no assunto, que são de difícil compreensão, gerando equívocos na utilização do termo de dipolo. Detalhamos o estudo sobre a análise da convergência da série em que a técnica se baseia, bem como sua interpretação física mostrando a equivalência entre as duas abordagens . Na segunda parte do trabalho analisamos os fundamentos do Fast Multipole Method desenvolvido para interação gravitacional, para o qual construímos programas em linguagem C para uma versão na rede. Criamos um algoritmo que denominamos Fast Multipole Monte Carlo (FMMC) e desenvolvemos um programa para cálculo das propriedades termodinâmicas de sistemas coulombianos. Os programas são testados comparando resultados para a energia e propriedades térmicas do modelo LRPM com resultados de simulação através de cálculo direto. / In this work we present a review of methods of simulation for the electrostatic energy of charged systems and an adaptation of an algorithm from the literature on gravitational systems for the study of the statistical properties of Coulomb systems. In the first part of the work, we review the fundamentals for the theoretical method of Ewald and its conditions of applicability, seeking to clarify the most important references on the subject, which because of the involved mathematics, have led to misuse of the so-called dipole correction. We detail the study on the convergence of the series for the electrostatic potential on which the Ewald technique is based, as well as the physical interpretation given elsewhere, showing the equivalence between the two approaches. In the second part of this work, we analyse the foundations of the Fast Multipole Method developed for gravitational interactions, and present programs in C language for a network version of neutral charged systems. Finally, an algorithm, which we name Fast Multipole Monte Carlo, and the corresponding code for calculating the thermodynamic properties of Coulomb systems are presented. The programs are tested by comparing results for the energy and thermal properties of the Lattice Restricted Primitive model with results of simulations based on direct calculations for the Coulomb energies.

Este trabalho investiga a termodifusão em coloides magnéticos através da técnica de varredura Z. O ponto de partida é a generalização do modelo de lente térmica, supondo o surgimento de um gradiente de concentração dos grãos magnéticos devido ao gradiente de temperatura causado pelo feixe de laser sobre a amostra. A partir do uso da técnica de varredura Z foi possível o estudo do coeficiente Soret (S IND.T) em ferrofluidos iônicos, surfactados e citrados, em amostras com baixa concentração de grãos (fração volumétrica de Fe, ø, menor que 1%). Na generalização do modelo de lente térmica que efetuamos, consideramos que a variação no índice de refração da amostra, em uma experiência de varredura Z, depende da variação da intensidade do feixe laser (I), da variação da temperatura (T) e da variação da concentração de grãos magnéticos (ø), onde C IND.N, C IND.T e C IND.S são seus respectivos parâmetros adimensionais no modelo. Uma vez que o tempo característico da termodifusão é da ordem de segundos, uma varredura Z com pulsos da ordem de 20ms é utilizada para a determinação de C IND.N. C IND.T é obtido independentemente por meio de métodos de óptica linear.Após a determinação de C IND.N e C IND.T, uma varredura Z com duração de pulso da ordem de 1 segundo é feita para determinar C IND.S e, posteriormente, o coeficiente Soret. A partir do comportamento da curva de evolução temporal da tranmitância com pulsos de 1 segundo pode-se determinar o sinal do coeficiente Soret. O sinal está relacionado com a tendência dos grãos de migrarem para a região mais fria (termofóbico, S IND.T>0) ou mais quente (termofílico, S IND.T<0) da amostra, dependendo de suas características físico-químicas. Mostramos que o módulo de S IND.T é proporcional a ø, em concordância com resultados obtidos para soluções mais concentradas (ø1) através da técnica de Espalhamento Rayleigh Forçado. Uma possível origem física para os comportamentos termofóbico e termofílico dos fluidos magnéticos poderia estar relacionada a mudanças na intensidade das forças que mantêm o equilíbrio coloidal, por ação da temperatura. / This work explores the thermodiffusion in magnetic colloids through the Z-Scan technique. The starting point is the generalization of the thermal lens model based on the assumption that the concentration gradient of the magnetic grains emerges due to the temperature gradient caused by the laser beam on the sample. By using the Z-Scan technique it was possible to study the Soret coefficient (ST) for ionic, surfacted and citrated ferrofluids in samples with low concentration of grains (Fe volumetric percentage, ø, less than 1%). In this thermal lens model generalization, we have considered that the refraction índex variation in a Z-Scan experiment depends on the laser beam intensity (I), the temperature variation (T) and the variation of the magnetic grains concentration (ø), where CN, CT and CS are their respective dimensionless parameters in the model. As characteristic time of thermodiffusion is of the order of seconds, a Z-Scan with pulses around 20 ms is used in order to determine CN. CT is obtained independently by using lenear optics methods. After the determination of CN and CT, a Z-Scan with pulses around 1 second is made in order to determine CS and, Consequently, the Soret coefficient. Through the behavior of the time dependent transmittance with 1-second pulses we were able to determine the sign of the Soret coefficient. The sign is related to the tendency of the grains to migrate to the colder region (thermophobic, ST>0) or to the warmer region (thermophilic, ST<0) of the sample, depending on its physical-chemical characteristics. We have showed that the ST module is proportional to ø, in agreement with the results for higher concentration solutions (ø1%) obtained through Forced Rayleigh Scattering. A possible physical originfor the thermophobic and thermophilic behavior of magnetic fluids could berelated to changes in the intensity of the forces that keep the colloidal balance, by means of temperature.