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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
211

Virtual Sites for Nucleic Acids : Verifying force field parameters for nucleic acids using MD

Jakobsson, Ellen January 2023 (has links)
No description available.
212

Study of nucleophilic aromatic substitution with diaryliodonium salts / Läran om nukleofil aromatisk substitution med diaryliodonium salter

Ubillos, Micaela January 2021 (has links)
No description available.
213

PREPARATION AND CHARACTERIZATION OF EPOXY-BASED MONOLITHIC SORBENTS FOR CHROMATOGRAPHY

Quoc Nguyen, Trung January 2021 (has links)
This ‘scouting’ work aimed to investigate the possibility of using non-aromatic monomers to prepare porous monolithic materials by utilizing varying compositions under spinodal decomposition and step polymerization. 1,3,5-Triglycidyl isocyanurate (TEPIC) was employed as a main molecular structural scaffold. Factors such as stepwise curing temperature and ratios of monomers and solvents have been explored by multi-variate experimental design and analysis. For the material characterization, specific sur-face area analysis (by the BET method) and scanning electron microscopy (SEM) were used to determine the monolith’s total surface areas, monolith morphologies, and skele-ton structures. The most promising material (NEM-15), having a specific surface area of 2.8 m2/g and 3-D skeleton, was in situ synthesized in capillary columns (I.D. 25, 50, 75, and 100 μm) for further chromatographic evaluation.
214

Different chemical environments effect on the structural stability of a phytochrome construct : Optimization for crystallographic experiments

Salomonsson, Arvid January 2022 (has links)
No description available.
215

Could fluorinated pharmaceuticals have an impact on the EOF amount in human blood?

Alvén Fimmerstad, Tilda January 2022 (has links)
Recent studies have discovered an increasing amount of unknown organofluorine in human blood. This increase insinuate that humans might be exposed to potentially new and unidentified organofluorine compounds. Currently there is a large gap between the amount of per- and polyfluorinated substances (PFAS) being monitored and the number of PFAS existing. Due to regulations of legacy PFAS like perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), production have shifted to new PFAS, mainly short-chains (C4-C6). New approaches have been made in order to discover these emerging PFAS, for example total oxidizable precursor (TOP) assay and extractable organofluorine (EOF) analysis. Though, these methods are non-specific and therefore useful in screening of fluorinated compounds. In today’s pharmaceutical market, a lot of drugs contain fluorine, and there is a current increase in number of fluorinated pharmaceuticals. Since EOF analysis measures all organofluorine that can be extracted, the presence of fluorinated pharmaceuticals in a sample may contribute to the EOF amount. However, if fluorinated pharmaceuticals do co-extract during sample preparation for common PFAS analysis is not yet known. This study evaluates if selected pharmaceuticals (fluoxetine, seproxetine, celecoxib and ciprofloxacin) will be co-extracted during ion pair extraction, a common extraction for EOF analysis. The extraction was first optimized in order to gain a good extraction efficiency for the pharmaceuticals. Ion pair solution adjusted to different pH’s (pH 3-4, pH 10 and pH 12) was tested, celecoxib had a good recovery independent of what pH was used (95%-102%), fluoxetine and seproxetine were only extractable at high pH’s (10 and 12) and had a recovery of around 90%, ciprofloxacin, however, could not be extracted no matter a low or high pH. The extraction was then conducted both with a pH of 10 and with a low pH (3-4) on human sera samples (n=6); the sera samples included 3 samples where subjects had been taking fluoxetine and 3 control samples. When analysis of the extracted sera samples was performed, no detectable level of pharmaceutical including its known metabolite seproxetine was found. An EOF and TF analysis of the sera samples were also performed. The EOF analysis could however not indicate any presence of pharmaceutical due to contamination in the procedural blanks. The TF analysis indicated vaguely a higher amount of total fluorine in the sera samples where subjects had taken fluoxetine compared to the control group; however, the large variation between the two groups make it hard to draw any conclusion. Since fluoxetine, seproxetine and celecoxib could be extracted when spike tests were performed, hypothetically they could contribute to the EOF amount. However, since no detectable level was found in the sera samples after extraction it cannot be stated for sure that these pharmaceuticals can be extracted from human blood, using ion-pair extraction. The unanswered question here is if the pharmaceutical is present in some other form in the sera samples, which cannot be extracted, or if it is even present at all.
216

Analysis and Valorization of Bark from Silver Birch, Scots Pine, and Norway Spruce : Compositional analysis of bark from common Swedish trees in forestry, to optimize sustainability procedures and monetary value of bark residue

Lindbäck, Isak January 2022 (has links)
Silver birch, Scots pine, and Norway spruce are the three most common types of trees in Sweden and make up to 90% of standing volume in Swedish forests (Skogsstyrelsen 2015, 3). With millions of cubic meters of wood being cut down annually, bark and other residues that cannot be used for sawn timber is left over and burnt for energy. Since bark makes up ~10-15% of harvested volume, it is a prime target for valorization and could be incorporated into preexisting procedures or used as feedstock for new processes. Bark samples obtained from the above-mentioned tree species were characterized by analyzing the chemical composition and the susceptibility to hydrothermal pretreatment and enzymatic saccharification. The study helps to understand and compare the fundamental properties of the three bark materials and determine the potential for utilization in a biorefinery context. Chemical compositional analysis of the three bark types were performed. All bark types were high in ethanol extractives (mass fraction 23.6-27.4%, dry weight). Pine and spruce bark showed similarities in chemical composition with respect to arabinan (3.5-5.2%), galactan (2.0%), glucan (18.9%), mannan (1.9%), xylan (1.8%), total lignin (33.9%) and total ash (2.7-3.7%). However, the bark of birch varied mainly in the composition of lignin and carbohydrate content, i.e., arabinan (2.5%), galactan (1.2%), glucan (8.1%), mannan (0.8%), xylan (3.3%), total lignin (50.2%) and total ash (2.0%). Hydrothermal pretreatment at a lower combined severity (CS 2.5) seems to be more efficient for birch bark than at CS 3.3. However, the bark material of the softwood species seemed to be more susceptible to enzymatic saccharification than the hardwood species. There was a clear differentiation in the chemical composition of the hardwood and softwood bark material. Birch bark was rich in ethanol extractives, total lignin or lignin-like substances, and hemicelluloses (especially xylan). Whereas pine and spruce bark has higher fractions of ash and glucan. Comparison of the effect of enzymatic hydrolysis between samples showed clear increases in glucose concentration over time for pine and spruce. However, values for birch were much lower as it was more recalcitrant
217

Method evaluation for probing DNA sorption to clay minerals : Evaluation of fluorescent and spectroscopic quantification of DNA as well as DNA interactions of Kaolinite and Montmorillonite

Wangdell, Oskar January 2022 (has links)
The association of DNA/RNA to mineral surfaces is an emerging field with widespread applications from biotechnological solutions to paleogenetics. Evaluating available methods to quantify adsorption will be essential to further investigate how to control and predict loading of DNA onto minerals. This study aims to test some of the available techniques for DNA quantification by investigating sorption onto Montmorillonite (Mnt) and Kaolinite (Kao) clay minerals, exchanged with different counter-cations. UV-Vis spectroscopy was successfully used in quantifying bulk DNA. Fluorescent techniques showed less reproducibility in this study but is inherently a more sensitive method demanding a more sophisticated protocol. In theory, with the right sample preparations the method can be both selective and sensitive. With pure samples and lacking a defined fluorescent protocol UV-Vis was determined to be the method of choice. To test the influence of different counter-cations, Mnt and Kao clays were washed and exchanged with Na+, K+, Ca2+, and Mg2+ and used in the DNA sorption experiments. In solutions with monovalent ions, DNA associated strongest to Kao while in solutions with divalent ions DNA associated strongest to Mnt, as quantified by the sorption coefficient Kd. Overall, the Kd values increased in the order of Na+ < K+ < Ca2+ < Mg2+ for both minerals, with the major difference between the results being the case of monovalent and divalent cations which is in agreement with previous studies. Interestingly, when confirming mineralogy of the clay samples using powder XRD, an additional first order reflection was found in samples prepared at high temperatures (<80˚C) indicating a composite material. The distance and higher temperatures required suggest single stranded DNA could be intercalated in the Na+-exchanged Mnt. Further investigations of what ionic property determines the facilitation of DNA adsorption and the suspected DNA intercalation should be conducted.
218

Temperature-dependent waterbinding on potassiumbirnessite : A potential sorbent for atmospheric water harvesting

Oderstad, Hanna January 2022 (has links)
The nanolayered manganese oxide birnessite (MnO2) is a naturally occurring mineralin soils and sediments. Its ability to capture and store water within its interlayers, andits great solar absorptivity, could be a part of the solution to global water shortage.Sorbent-based atmospheric water harvesting is a potential technology to increase thewater supply in arid areas. Fundamental studies on potential sorbents, such asbirnessite, is essential for further progress. To investigate how the nanometric waterfilms in birnessite act over a range of temperatures, Fourier Transform Infraredspectroscopy was used during 21-point adsorption/desorption isotherm cycles atconstant temperatures, from 30 to 80 °C. All spectra were analyzed and interpreted inthe computational environment of Matlab. The result showed that the water bindingin birnessite is temperature dependent, and it lose as much as half of its efficiency whenincreasing the temperature from 30 to 80 °C.
219

Adsorption studier av antimikrobiella komponenter på olika adsorption : Adsorption vid gränssnittet fast/vätska

Sukkar, Hiam January 2022 (has links)
In this study, we examined the effects of temperature, heat treatment which were heated in oven for an hour in 200 ℃, and solvent on the adsorption isotherm for thymol and benzoic acid on the three surfaces (modified calcium carbonate, silica gel, and perlite). For the first effect, the adsorption isotherm for benzoic acid on modified calcium carbonate was determined at temperatures of 25, 35, 45 and 55 ℃ in ethanol solvent. While for the last two effects, the adsorption isotherm for ethanol, acetonitrile, and n-heptane solutions wasdetermined at 25 ℃. UV-spectrophotometer measurements have been conducted todetermine the amount of adsorbed. The main purpose of this project is to examine the antimicrobial substances benefits which prolong food shelf life. However, it’s better to place those substances in so called food pads than to add it directly to the food. That certainly reduces the bacterial growth in the food pads. A grater amount of thymol was found to be adsorbed in n-heptane than the other solutions, additionally, a greater amount of benzoic acid was seen in ethanol than it was in acetonitrile or n-heptane. Sometimes the adsorption capacity has a large effect during heat treatment, while other times it has a small effect. The study also showed that the amount of benzoic acid adsorbed on modified calcium carbonate increases as temperature decreases
220

Standardization and optimization of index for 28 day strength for cement made from standard clinker / Optimering och standardisering av 28-dygns hållfasthetsindex för cement tillverkat av standard klinker

Hermansson, Anton January 2020 (has links)
This project regards the prediction of 28 day compressive strengths of cement. Using traditional multivariate analysis in combination with Artificial Neural Networks indexes have been developed which makes these predictions possible. Compressive strength is highly dependent on the cement hydration and clinker reactivity and literature on these topics have been studied followed by statistical analyses in Unscrambler X (Camo AS) and the Neural Networks model developed at Heidelberg Technology Center (HTC). After studying the theory behind compressive strength, some key parameters are identified including the Alite content, particle sizes as well as a variety of other parameters. Following this, a data set has been collected and formatted for the use in the project. Data on cement properties including compressive strength has been compiled by the quality engineer in Slite making the data collection simple. Having the data, the procedure includes a start with traditional multivariate analysis in Unscrambler to identify significant parameters in an effort of reducing the number of variables in the final model. In Unscrambler, Partial Least Squares regression has been used with uncertainty analysis as a selected option for parameter selection. Following the analysis in Unscrambler, the data set for each cement type is inserted into the neural networks models and the significant parameters are selected to act as input data, predicting either 1d or 28d strength. Before insertion into the Neural Networks model, the parameters are manually vetted with support of the literature and the accepted theories on cement hydration as correlations not necessarily mean that there is a causal link. Results are presented using the verification set of these indexes, indicating the prediction capacity of the indexes. Scenarios have also been used to study the underlying correlations between various properties and the compressive strengths. The results have shown good performance of the indexes created, and the procedure has proven to be fast and effective in creating these indexes. This opens up possibilities of using similar approaches to other areas of the plant in the future efforts to improve environmental and financial sustainability. Included in the final section of the report are also a few recommendations that would simplify the future work on this topic.

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