1,721,016 research outputs found
Microengineered analytical tools for cell-based studies in environmental monitoring, pharmacology and neuroscience
No full textMonitoring cells’ Tehavior in-vitro and evaluation of their response to different types of stimulations are the major oTjectives in cell-Tased studies. The results of these studies answer questions on the physiology of the cells, cell-to-cell signaling and impact of external stimulations on the cells. Exploiting cells for oTtaining such information has Teen applied for detection of toxicants in the environment, studying the pathology of diseases, development of new drugs and exploring cellular mechanisms and functions of living organisms. This thesis is mainly focused on investigation of novel tools with simple working principles and innovative approaches for studying cells in-vitro. The developed tools are designed with an uncomplicated faTrication procedure, and are intended to Te integrated in an automated standalone system. In environmental monitoring using cell-Tased systems, cultured cells are exposed to samples and their response is monitored to detect the samples’ cytotoxicity. These samples need to Te pretreated Tefore introducing them into the cell culture. This pretreatment includes adjustment of temperature, osmolality and pH. On-site automatic adjustment of osmolality and pH is not reported in the literature. One of the developed tools in this thesis is a fully automatic device for in-line adjustment of these two parameters ruling out the drawTacks of the conventional methods including particularly dilution of the samples and denaturation of their ingredients. In order to monitor the metaTolism of the cells Tefore and after stimulation, measuring the concentration of glucose and lactate in a few microliter sample oTtained from the culture medium is studied. For this measurement, an enzyme-Tased SU-8 microreactor cartridge with amperometric detection of hydrogen peroxide is designed and faTricated. In comparison to previously reported approaches in which the Tiosensors are implemented inside the cell culture, measuring the metaTolites in an extracted sample from the culture medium prevents contamination of the cells’ microenvironment and crosstalk Tetween the adjacent Tiosensors. The characterization of the cartridge and the role of SU-8 as a suTstrate for immoTilization of enzymes are investigated. It is revealed that the aging and hard Taking of the SU-8 suTstrate Tefore the enzyme immoTilization as well as the sample flow-rate have an impact on the cartridge response. In environmental or pharmaceutical samples applied to cell-Tased systems, the presence of toxicants with inhiTitory effects on enzymes, or electroactive agents that can interfere with the amperometric measurement can limit the application of enzyme-Tased Tiosensors for detecting the metaTolites in the culture medium. Therefore, a protocol for sample preparation is investigated in this thesis that enaTles the application of enzymes and amperometric methods in such measurements. The Tenefits of using the cartridge and the protocol are demonstrated in monitoring the effect of Triton X-100, CuCl2 and acetaminophen on glucose and lactate metaTolism of Caco-2 epithelial cells. The cartridge design enaTles measuring analyte concentrations as low as a few nanomolars using a stopped-flow protocol. Thus, it can Te an appropriate tool for detection of neurotransmitters in a neuronal cell-culture. ImmoTilizations of glutamate oxidase and choline oxidase enzymes in the SU-8 microreactors are investigated. The cartridge caliTration curves for measuring glutamate and choline over a period of 7 days are presented. Furthermore, a compartmentalized neuronal cell-culture device that enaTles the sampling from the regions where the extrasynaptic neurotransmitters are released is presented. In addition to the capaTility of stimulation of the cells chemically, a suTstrate with microelectrodes is faTricated to provide the possiTility of applying electrical stimulations to the cells. A sampling microchannel is structured in the device where the synaptic clefts form. The liquid content of this microchannel will Te transferred to the cartridge for detection of the neurotransmitters realized upon electrical or chemical stimulation of the cultured neuronal populations. Culturing rat’s hippocampal neurons on this device, revealed the TiocompatiTility of the culture device over a period of 20 days. Furthermore, Ty immunostaining of the cells, the formation of synapses containing glutamate and GABA neurotransmitter vesicles in the sampling microchannel was oTserved. The compartmentalized neuronal cell-culture and the microreactor cartridge for in-vitro monitoring of neurotransmitters can Te applied for studying neuromudulation and synaptic plasticity as well as for neurotoxicological or neuropharmacological assessments.SAMLA
Microengineered Electrochemical Tools for in-situ Monitoring of Marine Environment
Get PDFMeasuring the concentration of different compounds in aquatic ecosystem and understanding their impact on the environment are some of the main objectives in the environmental monitoring field. Trace metals, nutrients, volatile organic compounds (VOCs), biotoxins and algaes are among the most important targets of such assessment. Their quantification at an appropriate time scale is crucial in order to understand their dynamics in the marine biogeochemical processes. In situ continuous monitoring is the key to achieve these objectives. This thesis is focused on the development of new micro-engineered tools for improving the performance of electroanalytical techniques by exploiting microfabrication techniques. The developed devices were fabricated by using different techniques, such as thin-film technology, printing and additive manufacturing techniques. The quantification of nutrients is hampered by the high sodium chloride content present in the seawater. Literature is weak concerning systems which provide a selective removal of chloride with respect to other ions. One of the developed tools of this thesis is an environmentally-friendly microfluidic platform for selective sodium chloride removal prior to nutrients detection: chloride removal occurs upon bulk electrolysis in a thin-layer configuration and a ten times-fold reduction was achieved. Trace metals speciation may vary continuously reflecting changing in aquatic system physicochemical conditions. Their quantification is commonly achieved by voltammetric techniques. Voltammetric probes have been reported in literature for detection of trace metals such as lead, cadmium, copper and zinc. The core of these systems is a miniaturized sensor composed by an array of microelectrodes serving as WE and a CE. The reference electrode is a crucial component for the functioning of such sensors however its integration is still challenging. The second tool developed in the framework of this thesis is a three-electrode on-chip sensor for the detection of trace metals, where RE integration is achieved by using a PVC membrane plasticized with ionic liquids as diffusion barrier on top of a silver/silver chloride electrode. These sensors were capable to detect trace metals, but further improvement is required for their quantification. Marine biotoxins are compounds with toxic activity that accumulate in fish and shellfish. Among the various species of biotoxins, another target of this work is saxitoxin, a low molecular weight neurotoxin. Its detection is hindered by its low concentration, therefore a pre-concentration unit is required. Another herein developed tool is a simple microfluidic platform predisposed for pre-concentration of saxitoxin; its working principle is based on the binding of the saxitoxin to a specific aptamer and its release upon a temperature increase. VOCs, such as hydrocarbons and chlorinated hydrocarbons, are considered as significant indicators of urban and industrial pollution. Mid-infrared fiber-optic evanescent wave sensors constitute one of the most promising approaches for continuous VOCs pollution monitoring in seawater. In this thesis a microfluidic platform designed to optimize the enrichment of the polymer layer coating the fiber with the target analytes is developed. The optimization of the device design allowed the simultaneous detection of ten VOCs species. All the tools developed are intended to be integrated in submersible probes for in situ deployment.LMT
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Furfural:Enhancing production via boronate esters
Get PDFAs a way of combatting climate change, biomass can be used as an alternative to fossil resources. A promising route is through the platform chemical furfural, a molecule that can not only be easily created from biomass (i.e. the C5-sugars that make up most of the hemicellulose, predominantly xylose) but can also be transformed into a wide array of other molecules. Current processes for producing furfural have a molecular selectivity of 50 % from sugar to furfural and a large energy requirement, which needs to be addressed before furfural can be used as a keystone in the energy transition.One of the ways to improve the furfural yield is via the boronate route. In this route, xylose first reacts with a boronic acid to produce a boronate ester. As the sugar is hydrophilic but the ester hydrophobic, this allows for the sugar to be extracted from a (dilute) aqueous stream. The second step of the process is hydrolyzing the ester back to xylose and subsequently dehydrating it in an acidic aqueous medium to form furfural. As the equilibrium for both sugar/ester and furfural is towards the organic phase, their concentration in the aqueous phase is low. This suppresses the amount of byproduct formed, improving the yield of furfural.In this thesis, the viability of the boronate route is researched. By both performing the first and second step of the process in practice and modelling it, a final design of a 50 ktpa furfural plant can be made, allowing for the determination of the (economic) viability of the process. Various aspects of the process are investigated, such as the choice of chemicals and reaction conditions in both steps of the process. Most data is obtained with a model solution of pure xylose in water, but some experiments are replicated with acid hydrolysate of sugarcane bagasse, validating that the process will deliver similar results when actual biomass is used
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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