26 research outputs found

    Electrochemical enzyme-based biosensor array for monitoring of organic acids and ethanol in biogas processes

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    In light of steadily increasing energy demand and irreversible exhaustion of fossil fuels, further expansion of renewable energy sources is continually gaining importance. Utilization of biomass, as a widely available energy carrier, is capable of providing great contribution to sustainable energy supply. The efficient production of biogas, however, calls for an improved biomass supply chain. Economic operation of biogas plants depends in particular on reliable process monitoring. Often, process disturbances are accompanied by fluctuations in the concentration profile of some intermediates produced during the anaerobic fermentation process. Nowadays, the focus has mainly been set on volatile fatty acids (such as acetate and propionate) as an indicator for imbalanced process conditions and only little account has been taken to the relevance of other organic acids and alcohols, like lactate, formate and ethanol. In this work, an electrochemical enzyme-based biosensor array for simultaneous determination of D-lactate, L-lactate, formate and ethanol is developed. The amperometric sensing principle is based on two enzymes in each case: an analyte-specific NAD+-dependent dehydrogenase combined with a diaphorase from Clostridium kluyveri. The latter converts its substrate Fe(CN)63- to Fe(CN)64-, which generates a concentration-dependent current by oxidation at an polarized electrode. Enzymes were immobilized by chemical cross-linking with glutaraldehyde on platinum thin-film electrodes. The optimization of the biosensor performance has been investigated in regard to enzyme loading, glutaraldehyde concentration, cofactor concentration (NAD+ and Fe(CN)63-), pH value and temperature. The potential for repeated and long-term application has been proven by evaluation of operational and storage stability. Typically, enzyme-based biosensors are characterized by a high specificity due to the remarkable properties of enzymes as biological recognition element. Measurements in real samples, however, are prone to interfering effects by other electroactive species in the sample solution. The specificity of the biosensing system is determined in response to various interfering compounds and results reveal no cross-talk effects during simultaneous measurement of the four different analytes of interest. Successful practical performance for rapid and on-site analysis, has been demonstrated by quantification of D-lactate, L-lactate, formate and ethanol in various feedstocks (maize- and sugar cane silage) and spiked fermentation samples from three industrial biogas plants. Good correlation is obtained for results determined by the biosensor array in comparison to conventional commercial analytical methods applied (photometry and gas chromatography). In contrast to these techniques, the biosensor array offers the advantages of facile on-site application with a portable measurement set-up, rapid analysis time by simultaneous operation and application in untreated samples. The measuring system has also been applied for long-term monitoring of a lab-scale biogas reactor (0.01 m3) for a period of two months. Regular analysis of alcohol- and organic acid levels provides a beneficial supplementation to standard monitoring parameters, like biogas production, methane yield, pH and temperature. This additional information can help to identify changes in the microbial methane formation and potentially indicate upcoming imbalances at an early stage. For improved practical implementation of the developed biosensor array, the required cofactors have been co-immobilized on the sensor surface of screen-printed carbon electrodes. Modification with graphene oxide enables the establishment of a reagent-free biosensing system. Such biosensors can be manufactured economically by thick-film technology and used as disposable test strips for simplified on-site monitoring of several key intermediates in the biogas fermentation medium

    Femtosecond lasers for datacommunications applications

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    The work presented in this thesis details the development of all-solid-state ultrashort pulsed lasers suitable for datacommunications applications at either 1300nm or 1550nm. This is achieved through the design and construction of three different types of laser system based on the gain materials Cr⁴⁺:forsterite (chromium-doped magnesium iron silicate) and Cr⁴⁺:YAG (chromium-doped yttrium aluminium garnet). A Cr⁴⁺:forsterite based system is the first laser that is presented. This configuration utilises a relatively novel GalnNAs semiconductor device to initiate the generation of 130fs pulses around 1300nm. Although GalnNAs devices have previously been used to generate pulses of light in the picosecond domain, this is the first time ultrashort pulses have been achieved in the femtosecond domain. As such, it has been possible to use the results from this laser system to further the understanding of various dynamics of GalnNAs devices. An SBR mode-locked Cr⁴⁺:YAG laser system introduces the concept of Femtosecond pulse generation around 1550nm. This is done in order to lay the necessary foundations for understanding the motivation and physics behind high pulse repetition frequency (prf) all-solid state femtosecond lasers suitable for datacommunications applications. Details are then given for the construction and operation of a simple 3-element Cr⁴⁺:YAG laser that generates 70fs pulses at a prf greater than 4GHz. The success of this system leads to the development of a compact and robust engineered prototype with a footprint of 215x 106mm². Integration of the high prf laser systems into novel optical time division multiplexing/wavelength division multiplexing (OTDM/WDM) based assessments prove successful with the demonstration of a datacommunications system capable of generating 1.36Tb/s. This still remains to be the only system capable of achieving such a high capacity from a single source and demonstrates the ongoing success of femtosecond lasers through continued research and development

    Evolutionary genomics : statistical and computational methods

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    This open access book addresses the challenge of analyzing and understanding the evolutionary dynamics of complex biological systems at the genomic level, and elaborates on some promising strategies that would bring us closer to uncovering of the vital relationships between genotype and phenotype. After a few educational primers, the book continues with sections on sequence homology and alignment, phylogenetic methods to study genome evolution, methodologies for evaluating selective pressures on genomic sequences as well as genomic evolution in light of protein domain architecture and transposable elements, population genomics and other omics, and discussions of current bottlenecks in handling and analyzing genomic data. Written for the highly successful Methods in Molecular Biology series, chapters include the kind of detail and expert implementation advice that lead to the best results. Authoritative and comprehensive, Evolutionary Genomics: Statistical and Computational Methods, Second Edition aims to serve both novices in biology with strong statistics and computational skills, and molecular biologists with a good grasp of standard mathematical concepts, in moving this important field of study forward

    Medida del perfil de índice de refracción en fibra óptica mediante el método de reflexión

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    En este proyecto, se ha desarrollado un sistema para la medida del perfil de índice de refracción en fibras ópticas mediante la técnica de reflexión. Se ha diseñado un sistema automatizado de medida controlado por LabVIEW, que realiza mediciones locales de reflectividad Fresnel equiespaciadas entre sí 1 um. El programa en LabVIEW convierte estas medidas de reflectividad en un perfil bidimensional de índice de refracción, y posteriormente aplica un ajuste no lineal por mínimos cuadrados de manera iterativa, calculando los cuatro parámetros caracterísiticos del perfil de índice de refracción en una fibra de índice gradual: índice máximo del núcleo (n1), diferencia relativa de índice de refracción (-), radio del núcleo (a) y exponente (-). El sistema se ha probado sobre fibras de dos tipos (sílice y CYTOP), ambas con núcleo de 62;5 um. Las pruebas se realizaron con latiguillos comerciales conectorizados FC/PC, y se midieron de manera no destructiva, sin retirar ni los conectores ni la cubierta de la fibra.In this project, a system was developed for measurement of refractive index profile in optical fibers by reflection method. A LabVIEW-controlled automatized measurement system was designed, that performs local Fresnel reflectivity measurements separated each other by 1 um. LabVIEW code translates these reflectivity measurements into a bidimmensional refractive index profile, and then applies a non-linear least square fitting in an iterative way, finding the four representative parameters of the refractive index profile in a graded-index optical fiber: maximum core index (n1), relative index difference (-), core radius (a), and index exponent (-). The system has been tested with two different fibers (silica and CYTOP), both with 62;5 um cores. Tests were performed on commercial fiber patchcords (FC/PC connectorized), in a non destructive way without removal of connectors nor fiber’s jacket.Ingeniería Técnica en Electrónic

    On-Chip Magnetorelaxometry Using Planar Hall Effect Magnetic Field Sensors

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    I de senere år er der opstået en interesse for at udvikle lab-on-a-chip systemer, der potentielt kan benyttes som point-of-care biosensorer. Fordelen ved point-of-care biosensorer er at de straks kan analysere prøver udtaget fra patienter og der derved undgas spildtid ved at sende prøven til et laboratorium for at blive analyseret. Mange forskellige udlæsningsmetoder kan benyttes til point-of-care biosensorer, heriblandt magnetiske udlæsningsmetoder, hvilke er specielt interessante da de fleste biologiske prøver er umagnetiske. Målet med denne afhandling er at udforske mulighederne og begrænsningerne ved at brugeplanar Hall effekt magnetisk felt sensorer til at måle magnetorelaksometry af magnetiske kugler. Dette kan benyttes som udlæsningsmetode for volumen-baseret biodetektion, ved at måle ændringer af magnetiske kuglers hydrodynamiske diameter forsaget af binding til analytter. Traditionelt måles magnetorelaksometry ved at måle AC susceptibilitet med store dyre instrumenter, der ikke let kan integreres med lab-on-a-chip systemer. Fordelene ved planar Hall effekt sensorer er at de er små og derfor let integreres som udlæsningsmetode i lab-on-a-chip systemer.I denne afhandling er den teoretiske baggrund udledt for hvordan magnetorelaksometry måles med planar Hall effect sensorer. Dette inkluderer en beskrivelse af relaksationsmekanismer for magnetiske kugler i både tids og frekvens domænerne, hvordan planar Hall effekt sensorer kan måle relaksation af magnetiske kugler uden brug af eksterne magnetfelter samt estimater for dekræfter, der påvirker magnetiske kugler i nærheden af planar Hall effekt sensorer.Temperatur afhængigheden af målinger med planar Hall effekt sensorer er undersøgt. Herunder hvordan sensor signalerne afhænger af temperaturen og hvordan den Brownske relaksation af magnetiske kugler påvirkes. Det vises at magnetiske kuglers hydrodynamiske diametre kan bestemmes udfra AC susceptibilitetsmålinger med planar Hall effect sensorer, når temperaturenog væskens viskositet er kendte.AC susceptibilitetsmålinger på magnetiske kugler er påvist mulige for to forskellige sensor geometrier, planar Hall effekt kryds sensorer og planar Hall effekt bro sensorer. Med de benyttede geometrier, viste bro sensorerne at give seks gange signalet målt med kryds sensorerne uden at tilføje signifikant mere støj til målingerne. Et studie hvor koncentrationen af magnetiske kugler med diametre på 40 nm blev varieret viste, at hydrodynamiske diametre kan bestemmes for koncentrationer over 64 μg/mL, og tilstedeværelsen af magnetiske kugler kan spores ned til 16 μg/mL. Når det er sagt, så giver højere koncentrationer større signaler og hermed kan de hydrodynamiske diametre bestemmes mere nøjagtigt.Herudover er det påvist at planar Hall effekt sensorer kan benyttes i frekvens området fra DC til 1 MHz. Dette brede frekvensområde tillader at måle den Brownske relaksation of magnetiske kugler med diametre fra 10 nm til 250 nm. Det viste sig dog at 250 nm ikke er egnede til målinger med planar Hall effect sensorer, da de bliver indfanget af magnetostatiske kræfter fra sensor stacken.Eksperimenter udført med magnetiske kugler med streptavidin blandet med biotin-konjugeret bovine serum albumin viser at planar Hall effekt sensorer kan måle tilstedeværelsen af biotinkonjugeret bovine serum albumin i nanomolar området. Til slut er målinger med planar Hall effect sensorer foretaget for at detektere DNA coils fremstillet ved rolling circle amplicering. Disse resultater viser at DNA coils kan detekteres ned til koncentrationer pa 4 pM, hvilket er sammenligneligt med hvad der er opnået på lignende prøver målt med kommercielt tilgængeligt måleudstyr. Planar Hall effect sensorer har dog den fordel at de er betydelig mindre, simplere og potentielt billigere.In recent years there has been an increasing interest in developing lab-on-a-chip devices that potentially can be used as point-of-care biosensors. The advantage of point-of-care biosensors is that they can analyze samples obtained from patients immediately, cutting away the time needed for sending the sample to a laboratory for analysis. Many different read out techniques can be used for point-of-care biosensors, among these are magnetic readouts, which are especially interesting because most biological samples are non-magnetic. The goal of this thesis is to explore the possibilities and limitations of using planar Hall effect magnetic field sensors to measure magnetorelaxomety of magnetic beads. This can be used as the readout principle for volume-based biosensing, by detecting changes in the hydrodynamic diameter of magnetic beads due to binding of analytes. Traditionally magnetorelaxomety is measured by AC susceptibility measurements performed with large expensive instruments, which cannot easily be integrated with a lab-on-a-chip system. The advantages of planar Hall effect sensors are that they are small and can easily be integrated as the readout method for a lab-ona-chip device.In this thesis, the theoretical background for how magnetorelaxometry is measured using planar Hall effect sensors is derived. This includes a description of the relaxation mechanism of magnetic beads in both the time and frequency domains, how the planar Hall effect sensors are utilized for measuring the relaxation of magnetic beads without the need of any external fields and estimates of the forces that influence magnetic beads near a planar Hall effect sensor. The temperature dependence of measurements using planar Hall effect sensors is investigated.This is done both with respect to how the sensor signals depend on temperature and how temperature influences the Brownian relaxation of magnetic beads. It is shown that the hydrodynamic diameter of the magnetic beads can be extracted from AC susceptibility measurements with planar Hall effect sensors when the temperature and dynamic viscosity of the liquid in which the beads are suspended are known.AC susceptibility measurements of beads are shown to be possible using two different sensor geometries, planar Hall effect cross sensors and planar Hall effect bridge sensors. For the geometries used, the bridge sensor yields an amplification of the bead signals by a factor of six compared to the cross sensor without significant noise being added to the measurements. A study varying the concentration of magnetic beads with a nominal diameter of 40 nm shows that the hydrodynamic diameters can be extracted reliably for concentrations down to 64 _g/mL, and the presence of beads can be detected down to 16 _g/mL. However, higher bead concentration leads to higher signal and thereby hydrodynamic diameters can be extracted more reliably.Furthermore, it is shown that the planar Hall effect can be operated at frequencies ranging from DC to 1 MHz. This wide range of frequencies allows for measuring Brownian relaxation of magnetic beads with nominal diameters ranging from 10 nm to 250 nm. However, it is not appropriate to use beads as large as 250 nm with the planar Hall effect sensors as they are captured by magnetostatic forces from the sensor stack.Experiments with streptavidin coated beads and biotin-conjugated bovine serum albumin show that planar Hall effect sensors can detect the presence of biotin-conjugated bovine serum albumin in the nanomolar range. Finally, measurements are performed to detect DNA-coils formed by rolling amplification using planar Hall effect bridge sensors. These results show that DNA-coils can be detected in concentrations down to 4 pM, which is comparable to what has been obtained for similar samples using commercially available measurement equipment. However, the planar Hall effect sensor have the advantage of being considerably smaller, much more simple and potentially cheaper.<br/

    Papers on anthropology XIX

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    Eelkäija: Tartu Ülikooli toimetised. Antropoloogia-alaseid töid, ISSN 0207-4575http://www.ester.ee/record=b1339521*es

    A User-Defined Approach for Reverse Engineering Tool to Visualize, Understand and Re-document Existing Software Systems (UDARE)

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    Pemahaman sesuatu perisian sedia ad~khususnya sistem legasLialah satu tugas~rumit.-Pembangun-atau pengemaskini perisian perlu mempelajari kod sumber sebelum menukar program terlibat dengan bantuan mana-mana dokumen atau tanpa dokumen. Banyak produk CASE (Kejuruteraan Peri sian Berbantukan Komputer) atau alat telah muncul untuk membantu pengemaskini perisian yang menghadapi ketiadaan dokumentasi atau ia tidak terkemaskini terutamanya dokumen reka bentuk yang menyediakan maklumat paling terperinci mengenai sistem perisian. Understanding an existing software system particularly a legacy system is a tedious task. Software developers or maintainers need to study the source codes prior to changing the affected programs with the aid of any documents or even without any document. Many CASE (Computer-Aided Software Engineering) products or tools have emerged to assist software maintainers who are confronted with absence of documentation or outdated documentation particularly design document that provides the most detail information about a software system

    Molecular epidemiology of African swine fever in East Africa

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    African swine fever (ASF), a hemorrhagic disease of domestic pigs, is caused by a large enveloped icosahedral arbovirus of the Asfivirus genus in the family Asfarviridae . It has a linear, covalently close-ended, double stranded DNA (dsDNA) genome, 170 – 190 kbp in size. Warthogs (Phaecochoerus aethiopicus ), bushpigs (Potamochoerus porcus ) and soft ticks of the Ornithodoros genus are natural reservoirs of ASF virus (ASFV) in Africa. Serological differentiation between field strains is not possible and as no vaccine is available, control relies on stamping out and strict zoosanitary practices. In order to identify possible sources of virus and prevent further introductions, ASFVs need to be differentiated on genotype basis. Genotyping of East African ASFV isolates was achieved in this study by characterization of the C-terminal region of the major capsid protein gene, p72 . Thirteen genotypes were identified among East African sylvatic and domestic hosts. Of significance was the recovery of an apparently geographically restricted homogenous domestic pig cycle in the region, as well as the presence of viruses of the ESACWA genotype, formerly believed to be confined to Europe, South America, the Caribbean Islands and West Africa. Due to the conserved nature of the p72 gene, intra-genotypic relationships of viruses recovered from a homogeneous domestic pig-associated lineage, genotype VIII, could not be resolved. In an attempt to address this short-coming, genetic characterization of the Central Variable Region (CVR) within the 9-RL open reading frame (ORF) of the central conserved region of ASFV genome was conducted. Eight groups were resolved, some of which confirmed prolonged periods of circulation of a particular virus type, whilst others confirmed transboundary transmission of the disease. The complexity of ASF epidemiology in East Africa exemplified by the presence of a sylvatic and domestic pig cycle, multiple genotypes within countries and identical genotypes shared by multiple countries, was revealed. The East African ASFV molecular epidemiological database created in this study will be of great assistance to veterinary officials implementing prevention and outbreak control strategies.Dissertation (MSc)--University of Pretoria, 2007.Zoology and Entomologyunrestricte
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