Diss. (sammanfattning) Umeå : Univ., 2007. / Härtill 5 uppsatser.

Analysis of urinary hormone levels can be used to identify sex and breeding patterns in amphibians. This is especially important for ensuring the survival of endangered species. The most common way to determine hormone levels is enzyme-linked immunosorbent assay (ELISA); however, there is the possibility of cross-reactivity with this technique, and only one hormone can be monitored per plate, limiting efficiency. In this study, the effectiveness of liquid chromatography coupled to mass spectrometry (LC-MS/MS) was evaluated in terms of sensitivity, repeatability, and through-put in monitoring hormone levels in Anaxyrus boreas boreas (boreal toads). Urine samples were collected from ten different female Boreal toads over a three-year period and monitored for estrone, â-estradiol, estriol, 17á-ethinylestradiol, corticosterone, testosterone, and progesterone. To account for differences in urine concentration, creatinine (a metabolic breakdown product) was used to normalize all samples as it is typically present at a constant concentration. Prior to chromatographic analysis, all samples underwent a solid phase extraction (SPE) clean-up. Hormones in the estrogen class were derivatized via dansylation prior to analysis to enhance detection sensitivity. An Agilent 1290 Liquid Chromatograph coupled to an Agilent 6460 Triple Quadrupole Mass Spectrometer was used to quantitate hormone levels. The extraction method developed proved to be reliable and reproducible with percent recoveries in quality control samples ranging from 80%-120%. Using LC-MS/MS and derivatization, limits of quantitation as low as 0.001 parts-per-billion (ppb) were achieved for estrogens and 0.100 ppb for androgens. Ultimately, the method optimized for hormone analysis using LC-MS/MS showed to be as reliable as ELISA while also being less expensive per sample and more robust.

Yes / The analysis of organic residues from archaeological materials has become increasingly important to our understanding of ancient diet, trade and technology. Residues from diverse contexts have been retrieved and analysed from the remains of food, medicine and cosmetics to hafting material on stone arrowheads, pitch and tar from shipwrecks, and ancient manure from soils. Research has brought many advances in our understanding of archaeological, organic residues over the past two decades. Some have enabled very specific and detailed interpretations of materials preserved in the archaeological record. However there are still areas where we know very little, like the mechanisms at work during the formation and preservation of residues, and areas where each advance produces more questions rather than answers, as in the identification of degraded fats. This chapter will discuss some of the significant achievements in the field over the past decade and the ongoing challenges for research in this area. / Full text was made available in the Repository on 15th Oct 2015, at the end of the publisher's embargo period.

Four commercially available methods used for the analysis of low-level Chlorine Dioxide (ClO2) concentrations in drinking water were evaluated for accuracy and precision and ranked according to cost, efficiency and ease of the methods under several conditions that might be encountered at water treatment plants. The different analytical methods included: 1.The DPD (N, N-diethyl-p-phenylenediamine) method 2.Lissamine Green B (LGB) wet-chemical method 3.Palintest® kit LGB 4.Amperometric titration All these tests were performed with standard 1.0 mg/L ClO2 either alone or in the presence of different chlorine species, including chlorite ion (ClO2-, 0.5 mg/L), chlorate ion (ClO3-, 0.5 mg/L) and chlorine (Cl2, 1.0 mg/L). The tests were performed with four different matrices, with different concentrations of 0.1 mg/L ClO2, 0.5 mg/L ClO2 and 1.0 mg/L ClO2 at a constant temperature of 20oC and at different temperatures of 0oC, 10oC and 20oC at a fixed ClO2 concentration of 1.0 mg/L. None of the four methods produced the desired level of either accuracy or precision. For all four methods, interference to the measured ClO2 concentration from the addition of ClO2-, ClO3-, and Cl2 was minimal when the methods were performed according to specifications. The Palintest® was the best all-round method because it was easy to perform, performed well at all concentrations tested, and its colored product was stable. The HACH® DPD method was also easy to perform and gave the best results when measuring concentrations of 1.0 mg/L ClO2. The DPD method was less accurate than the Palintest® at lower concentrations. The DPD colored product that formed upon reaction of ClO2 and DPD was unstable, making it necessary to measure the intensity of the colored product at exactly 1 minute. The amperometric titration and lissamine green methods were more cumbersome and time-consuming to perform than either the DPD or Palintest® methods; for this reason they are less desirable for routine use. / Master of Science

New liquid phase microextraction (LPME) has been optimized. Plastic adapter with tapered tip was used as extraction device. Concentration of analytes was determined by GC-MS. Face centered design was used to optimize LPME and the results were evaluated by Minitab 16 programme. Volume of sample, volume of extraction solvent, stirring rate, extraction time, ionic strength and time after microextraction were optimized. Response of system was defined as the sum of the peak relative areas. Toluene, tetrachlorethylene, ethylbenzene, xylenes, mesitylene and naphthalene were the studied analytes. Methylhexadecanoate was used as an internal standard. Optimal system conditions were as follows: 20 mL sample volume, 300 μL extraction solvent volume, 20 minutes, stirring speed 700 rpm, no addition of salt, and time after microextraction 3.5 minutes. Determination coefficient was 0.9700 and the lack-of-fit was insignificant which indicated good agreement of the model with the experimental data. The preconcentration factor ranged from 26 (tetrachlorethylene) to 39 (xylenes). The microextraction yield was varied from 39.5% (tetrachlorethylene) to 59.1% (p-xylene and m-xylene). The new method was tested by analyzing real samples of tap water, river water and water from the sewage treatment plant. The samples were...

As estatinas são substâncias que inibem a síntese de colesterol. Por não existir métodos analíticos simples e de baixo custo para determinação quantitativa de pravastatina sódica, fluvastatina sódica, atorvastatina cálcica e rosuvastatina cálcica, o objetivo desta pesquisa foi desenvolver, validar e comparar os métodos por cromatografia líquida de alta eficiência e espectrofotometria direta e derivada no ultravioleta para a determinação quantitativa de estatinas em comprimidos. Os métodos cromatográficos foram realizados em coluna LiChrospher® RP-18 com fase móvel composta de metanol-água e pH ajustado a 3,0 com ácido fosfórico. Os métodos espectrofotométricos foram validados utilizando NaOH 0,1 M como solvente. A análise estatística com os testes t e F, não mostraram diferença significativa entre os métodos propostos ao nível de confiança de 95%. Os métodos são simples, eficientes e podem ser utilizados em análises de rotina para o controle de qualidade de estatinas em comprimidos. / The statins are substances that inhibit the synthesis of cholesterol. There is no simple and low cost analytical methods for quantitative determination of pravastatin sodium, fluvastatin sodium, atorvastatin calcium and rosuvastatin calcium; the objective of this research was to develop, to validate and to compare the methods as high performance liquid chromatography and ultraviolet direct and derivative spectrophotometry for quantitative determination of statins in tablets. The chromatographic methods were carried out with a LiChrospherB RP-18 column with a mobile phase composed of methanol-water and pH adjusted to 3.0 with phosphoric acid. The spectrophotometric methods were validated using NaOH 0.1 M as solvent. The statistical analysis using tests t and F, did not show significant difference between the methods considering the 95% confidence level. The methods are simple, efficient and can be used in routine analyses for quality control of statins in tablets.

Reaction-diffusion systems and delay differential equations have been extensively used over the years to model and study the dynamics of infectious diseases. In this thesis we consider two aspects of disease dynamics: spatial dynamics in a reaction-diffusion epidemic model with nonlinear incidence rate, and a delayed epidemic model with combined effects of latency and temporary immunity. The first part of the thesis is devoted to the analysis of stability and pattern formation in an SIS-type epidemic model with nonlinear incidence rate. By considering the dynamics without spatial component, conditions for local asymptotic stability are obtained for general values of the powers of nonlinearity. We prove positivity, boundedness, invariant principle and permanence of our model. The next generation matrix method is used to derive the corresponding basic reproductive number R0, and the Routh-Hurwitz criterion is used to show that for R0 ≤ 1, the disease-free equilibrium is found to be locally asymptotically stable, for R0 > 1, a unique endemic steady state exists and is found to be locally asymptotically stable. In the presence of diffusion, Turing instability conditions are established in terms of system parameters. Numerical simulations are performed to identify the spatial regions for spots, stripes and labyrinthine patterns in the parameter space. Numerical simulations show that the system has complex and rich dynamics and can exhibit complex patterns, depending on the recovery rate r and the transmission rate β. We have discovered that whenever the transmission rate exceeds the recovery rate the system exhibits stripe patterns which correspond to a disease outbreak, and in the opposite case the system settles on spot patterns which imply the absence of disease outbreaks. Also, we find that increasing the power q can lead to epidemic outbreak even at lower values of the transmission rate β. All numerical simulations use an Implicit-Explicit (IMEX) Euler's method, which computes diffusion terms in Fourier space and reaction terms in the real space. Numerical approximation of the model is benchmarked to prove stability of the numerical scheme, and the method is shown to converge with the correct order. Experimental order of convergence (EOC) and estimates for the error in both L2, H1 and maximum norms have also been computed. Also, we compare our results to those on infectious diseases and our model shows good predictions. In the second part of this thesis, we derive and analyse a delayed SIR model with bilinear incidence rate and two time delays which represent latency Τ1 and temporary immunity Τ2 periods. We prove both local and global stability of the system equilibria in the case when there are no time delays, i.e. both the latency and temporary immunity periods are set to zero. For the case when there is only latency (Τ1 > 1, Τ2 = 0) and the case when the two time delays are identical (Τ1 = Τ2 = Τ ), we show that the endemic steady state is always stable for any parameter values. For the case when there is only temporary immunity (Τ2 > 0, Τ1 = 0) and the case when there are both latency and temporary immunity in the system (Τ1 > 0, Τ2 > 0), we prove the existence of periodic solutions arising from the Hopf bifurcation. The endemic steady state undergoes Hopf bifurcation giving rise to stable periodic solutions. For the last two cases, we show interesting regions of (in)stability of the endemic steady state in the different parameter regimes. We find that by varying the transmission rate β, the natural death rate γ and the disease-induced death rate μ increase the regions of (in)stability. Also, we find that the dynamics of the system is richer when we have the two time delays in the model. Analytical results are supported by extensive numerical simulations, illustrating temporal behaviour of the system in different dynamical regimes. Finally, we relate our results to modelling infectious diseases and our results show good predictions of safety and epidemic outbreak.

This thesis is concerned with the study of the important effect of the gradient term in parabolic problems. More precisely, we study the global existence or nonexistence of solutions, and their asymptotic behaviour in finite or infinite time. Particularly when the power of the gradient term can increase to the power function of the solution. This thesis consists of five parts. (i) Steady-State Solutions, (ii) The Blow-up Behaviour of the Positive Solutions, (iii) Parabolic Liouville-Type Theorems and the Universal Estimates, (iv) The Global Existence of the Positive Solutions, (v) Viscous Hamilton-Jacobi Equations (VHJ). Under certain conditions on the exponents of both the function of the solution and the gradient term, the nonexistence of positive stationary solution of parabolic problems with gradient terms are proved in (i). In (ii), we extend some known blow-up results of parabolic problems with perturbation terms, which is not too strong, to problems with stronger perturbation terms. In (iii), the nonexistence of nonnegative, nontrivial bounded solutions for all negative and positive times on the whole space are showed for parabolic problems with a strong perturbation term. Moreover, we study the connections between parabolic Liouville-type theorems and local and global properties of nonnegative classical solutions to parabolic problems with gradient terms. Namely, we use a general method for derivation of universal, pointwise a priori estimates of solutions from Liouville type theorems, which unifies the results of a priori bounds, decay estimates and initial and final blow up rates. Global existence and stability, and unbounded global solutions are shown in (iv) when the perturbation term is stronger. In (v) we show that the speed of divergence of gradient blow up (GBU) of solutions of Dirichlet problem for VHJ, especially the upper GBU rate estimate in n space dimensions is the same as in one space dimension.

This thesis is concerned with modelling the spread of diseases amongst host populations and the epidemics that result from this process. We are primarily interested in how networks can be used to model the various heterogeneities observable in real-world populations. Firstly, we start with the full system of Kolmogorov/master equations for a simple Susceptible-Infected-Susceptible (SIS) type epidemic on an arbitrary contact network. From this general framework, we rigorously derive sets of ODEs that describe the exact dynamics of the expected number of individuals and pairs of individuals. We proceed to use moment closure techniques to close these hierarchical systems of ODEs, by approximating higher order moments in terms of lower order moments. We prove that the simple first order mean-field approximation becomes exact in the limit of a large, fully-connected network. We then investigate how well two different pairwise approximations capture the topological features of theoretical networks generated using different algorithms. We then introduce the effective degree modelling framework and propose a model for SIS epidemics on dynamic contact networks by accounting for random link activation and deletion. We show that results from the resulting set of ODEs agrees well with results from stochastic simulations, both in describing the evolution of the network and the disease. Furthermore, we derive an analytic calculation of the stability of the disease-free steady state and explore the validity of such a measure in the context of a dynamically evolving contact network. Finally, we move on to derive a system of ODEs that describes the interacting dynamics of a disease and information relating to the disease. We allow individuals to become responsive in light of received information and, thus, reduce the rate at which they become infected. We consider the effectiveness of different routes of information transmission (such as peer-to-peer communication or mass media campaigns) in slowing or preventing the spread of a disease. Finally, we use a range of modelling techniques to investigate the spread of disease within sheep flocks. We use field data to construct weighted contact networks for flocks of sheep to account for seasonal changes of the flock structure as lambs are born and eventually become weaned. We construct a range of network and ODE models that are designed to investigate the effect of link-weight heterogeneity on the spread of disease.

This thesis discusses a two dimensional non-smooth dynamical system described by an autonomous ordinary differential equation. The right hand side of the differential equation is assumed to be discontinuous. We provide a local theory of existence, uniqueness and exponential asymptotic stability and state a formula for the basin of attraction. Our conditions are sufficient. Thetheory generalizes smooth dynamical systems theory by providing contraction conditions for two nearby trajectories at a jump. Such conditions have only previously been studied for a two dimensional nonautonomous differential equation. We provide an example of the theory developed in this thesis and show that we can determine stability of a periodic orbit without explicitly calculating it. This is the main advantage of our theory. Our conditions require to define a metric. This however, can turn out to be a difficult task, and at present, we do not have a method for finding such a metric systematically. The final part of this thesis considers an application of a nonsmooth dynamical system to biomechanics. We model an elderly person stepping over an obstacle. Our model assumes stiff legs, and suggests a gait strategy to overcome an obstacle. This work is in collaboration with Professor Wagner's research group at Institute for Sport Science at the University of Mϋnster. However, we only present work developed independently in this thesis.