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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.
391

Design tandemového válce / Design of Tandem Roller

Otruba, Radim January 2015 (has links)
The thesis deals with the design of the tandem roller with autonomous control. The proposal takes into account the technical nature of the machine and conceptual image of construction equipment intended for compaction work . To solve this problem the basic characteristic elements of autonomous means have been defined and subsequently applied to the proposal. An ergonomic aspect when operating and servicing the machine also has been taken into account. The final draft has been prepared and described in the practical part.
392

Characterization of tandem organic solar cells

Timmreck, Ronny 08 October 2015 (has links)
The tandem solar cell concept is a promising approach to improve the efficiency of photovoltaic devices. However, characterization of tandem solar cell devices is challenging since correct efficiency determination demands special experimental infrastructure as well as suitable characterization procedures. Even though the appropriate IEC and ASTM measurement standards define all that very precisely, they cannot be applied without special care to organic photovoltaics (OPV) because they were originally developed for inorganic devices. As a consequence, nowadays almost all tandem organic solar cell publications are not using correct characterization procedures, often resulting in questionable efficiency values. The aim of this work is developing a measurement procedure for tandem organic solar cells assuring their correct characterization. Therefore, at first the existing standards and measurement procedures for tandem solar cells are reviewed and challenges when applying these standards to organic solar cells are identified. As main challenges the relatively low fill factors and distinct nonlinearities of organic solar cells are identified. As preliminary experiments, single junction organic solar cells are investigated to analyze the influence of measurement parameters like bias irradiance, bias voltage, and chopper frequency on the external quantum efficiency (EQE) of organic solar cells. This results in parameter sets assuring minimized artifacts for the subsequent EQE determination of the subcells of tandem organic solar cells. The main part of this thesis presents the detailed characterization of a tandem OPV example device. First, EQE is measured and validated by two independent institutes. The EQE results are used to calculate the illumination conditions to reach AM1.5g conditions for both subcells with a multi-source sun simulator. The resulting efficiency value under standard reporting conditions (SRC) is found to be 5% lower than the efficiency measured with a single-source sun simulator. A full spectrometric characterization shows that differing fill factors of the subcells are the reason for this behavior. To overcome the main reason for the complicated measurement procedure of tandem solar cells, the inaccessibility of the individual subcells, three different approaches for the jV-characteristics determination of the subcells are presented. The so-called Bias Voltage Approach is based on EQE-measurements under varying bias voltage and needs no additional electrical contacts. Therefore, it can be applied to existing devices. The Voltage Contact Approach as well as the Current Contact Approach require in changed stack designs. Therefore, they cannot be applied to existing devices but give more accurate results. Finally, a procedure for characterizing tandem organic solar cells is formulated. This procedures aims at giving practical advice how to characterize tandem organic solar cells to achieve results conforming to the measurement standards and being as accurate and reproducible as possible. Hence, this thesis attempts to establish standards for a correct measurement of tandem organic solar cells of which other emerging solar cell technologies can profit as well.
393

Využití alkenylboronových kyselin v tandemové cyklizaci/Suzukiho couplingu / Use of alkenylboronic acids in the tandem cyclisation/Suzuki cross-coupling

Klanicová, Kristýna January 2020 (has links)
This thesis deals with the synthesis of polycyclic compounds using tandem cyclisation/Suzuki cross-coupling, by modification of the method developed by our research group. This thesis mainly investigates the scope of the tandem reaction with aliphatic boronic acids or their esters. The products of the palladium catalyzed reaction then underwent electrocyclization to form an aromatic ring. The polycyclic skeleton, containing the aromatic core, is found in a considerable amount of natural substances with biological activity. The structure of the compounds prepared herein is similar to miltiorin D or commiphorane A.
394

Models and Algorithms for Sorting Permutations with Tandem Duplication and Random Loss

Hartmann, Tom 25 April 2019 (has links)
A central topic of evolutionary biology is the inference of phylogeny, i. e., the evolutionary history of species. A powerful tool for the inference of such phylogenetic relationships is the arrangement of the genes in mitochondrial genomes. The rationale is that these gene arrangements are subject to different types of mutations in the course of evolution. Hence, a high similarity in the gene arrangement between two species indicates a close evolutionary relation. Metazoan mitochondrial gene arrangements are particularly well suited for such phylogenetic studies as they are available for a wide range of species, their gene content is almost invariant, and usually free of duplicates. With these properties gene arrangements of mitochondrial genomes are modeled by permutations in which each element represents a gene, i. e., a specific genetic sequence. The mutations that shape the gene arrangement of genomes are then represented by operations that rearrange elements in permutations, so-called genome rearrangements, and thereby bridge the gap between evolutionary biology and optimization. Many problems of phylogeny inference can be formulated as challenging combinatorial optimization problems which makes this research area especially interesting for computer scientists. The most prominent examples of such optimization problems are the sorting problem and the distance problem. While the sorting problem requires a minimum length sequence of rearrangements that transforms one given permutation into another given permutation, i. e., it aims for a hypothetical scenario of gene order evolution, the distance problem intends to determine only the length of such a sequence. This minimum length is called distance and used as a (dis)similarity measure quantifying the evolutionary relatedness. Most evolutionary changes occurring in gene arrangements of mitochondrial genomes can be explained by the tandem duplication random loss (TDRL) genome rearrangement model. A TDRL consists of a duplication of a consecutive set of genes in tandem followed by a random loss of one copy of each duplicated gene. In spite of the importance of the TDRL genome rearrangement in mitochondrial evolution, its combinatorial properties have rarely been studied. In addition, models of genome rearrangements which include all types of rearrangement that are relevant for mitochondrial genomes, i. e., inversions, transpositions, inverse transpositions, and TDRLs, while admitting computational tractability are rare. Nevertheless, especially for metazoan gene arrangements the TDRL rearrangement should be considered for the reconstruction of phylogeny. Realizing that a better understanding of the TDRL model is indispensable for the study of mitochondrial gene arrangements, the central theme of this thesis is to broaden the horizon of TDRL genome rearrangements with respect to mitochondrial genome evolution. For this purpose, this thesis provides combinatorial properties of the TDRL model and its variants as well as efficient methods for a plausible reconstruction of rearrangement scenarios between gene arrangements. The methods that are proposed consider all types of genome rearrangements that predominately occur during mitochondrial evolution. More precisely, the main points contained in this thesis are as follows: The distance problem and the sorting problem for the TDRL model are further examined in respect to circular permutations, a formal concept that reflects the circular structure of mitochondrial genomes. As a result, a closed formula for the distance is provided. Recently, evidence for a variant of the TDRL rearrangement model in which the duplicated set of genes is additionally inverted have been found. Initiating the algorithmic study of this new rearrangement model on a certain type of permutations, a closed formula solving the distance problem is proposed as well as a quasilinear time algorithm that solves the corresponding sorting problem. The assumption that only one type of genome rearrangement has occurred during the evolution of certain gene arrangements is most likely unrealistic, e. g., at least three types of rearrangements on top of the TDRL rearrangement have to be considered for the evolution metazoan mitochondrial genomes. Therefore, three different biologically motivated constraints are taken into account in this thesis in order to produce plausible evolutionary rearrangement scenarios. The first constraint is extending the considered set of genome rearrangements to the model that covers all four common types of mitochondrial genome rearrangements. For this 4-type model a sharp lower bound and several close additive upper bounds on the distance are developed. As a byproduct, a polynomial-time approximation algorithm for the corresponding sorting problem is provided that guarantees the computation of pairwise rearrangement scenarios that deviate from a minimum length scenario by at most two rearrangement operations. The second biologically motivated constraint is the relative frequency of the different types of rearrangements occurring during the evolution. The frequency is modeled by employing a weighting scheme on the 4-type model in which every rearrangement is weighted with respect to its type. The resulting NP-hard sorting problem is then solved by means of a polynomial size integer linear program. The third biologically motivated constraint that has been taken into account is that certain subsets of genes are often found in close proximity in the gene arrangements of many different species. This observation is reflected by demanding rearrangement scenarios to preserve certain groups of genes which are modeled by common intervals of permutations. In order to solve the sorting problem that considers all three types of biologically motivated constraints, the exact dynamic programming algorithm CREx2 is proposed. CREx2 has a linear runtime for a large class of problem instances. Otherwise, two versions of the CREx2 are provided: The first version provides exact solutions but has an exponential runtime in the worst case and the second version provides approximated solutions efficiently. CREx2 is evaluated by an empirical study for simulated artificial and real biological mitochondrial gene arrangements.
395

Simulations of silicon detector response in nuclear fission experiments : A study of the plasma delay time in an experiment performed at the Tandem lab

Lekander, Moa Li, Aliyali, Alan January 2020 (has links)
The goal of the project was to simulate a typical silicon detectorresponse in an experiment made at the Tandem lab in Uppsala. The plasma delay time was analyzed by simulating the experiment. Three different models of the plasma delay time were introduced and their effects on time of flight measurements were studied. A continuation of the main goal was to see if the inserted PDT models could be extracted from the simulations when being treated as a pseudo experiment, to see theoverall effectiveness of the experiment. When comparing the final simulations with actual measurements, it was concluded that the main properties of the detector response had been featured and that the simulations were successful. The successful extraction of the inserted plasma delay times and their dependencies on energy also proved that the experiment was a good one. The result of the project was that one of the models seemed to have a strong mass dependence, however with no clear dependence on the energy. The other two models showed a somewhat similar dependence on energy. One of the two models also showed a relatively weak mass dependence.
396

Design of LED setup for measuring tandem solar cell subcell J-V behaviour

Bergström, Kristina, Kamalmaz, Mohammed Nour, Lindvall, Erik January 2022 (has links)
The need to accurately measure multi-junction (MJ) tandem solar cells' subcell current-voltage characteristics is increasing due to the vital information they provide about the efficiency, stability, and longevity of the cells. These measurements are rather difficult compared to their counterpart single-layer solar cell measurements. The purpose of this project is to construct an instrument that is able to successfully bias multiple subcells in a tandem solar cell. This would allow accurate measurements of the J-V behaviours of individual subcells within the stack and by extent, allow analysis to optimise future tandem cell technology. The instrument made is a controllable multi-chromatic light-emitting diode array, consisting of six wavelength-different LEDs ranging between ultraviolet and infrared light, which the intensity of is controlled bya slider control Graphical User Interface (GUI). This instrument will bemounted on a laboratory station at the institution of solar cell technology, Ångström laboratory. Although not perfect, the instrumentcan provide sufficient background light for biasing subcells of an MJ solar cell for a wide selection of cell band gaps
397

Validation of a Next Generation Sequencing based method for chimerism analysis in clinical practice

Högberg, Maria January 2022 (has links)
Hematopoietic stem cell transplantation (HSCT) is used to treat patient with hematological diseases such as leukemia and genetic conditions such as sickle cell anemia. After HSCT the patients are supervised for signs of relapse of disease or rejection of transplanted cells. This is done by using chimerism analysis. At the department of clinical genetics at Akademiska sjukhuset fragment analysis of short tandem repeats is used for chimerism analysis, which is to be replaced by a Next generation sequencing (NGS) based method called Devyser chimerism, which includes an IVDR labelled kit. The aim of this project was to validate the new method for chimerism analysis. DNA samples from twelve HSCT patients and their donors were analyzed with Devyser chimerism and the results were compared to the results from the current method. The sensitivity of the new method was tested by analysis of artificial chimerism samples from blood donors. The results from the comparison showed a good correlation between methods (R2 = 0,9864) and the sensitivity of the method was confirmed to be 0,1% mixed chimerism. There was some difficulty in identifying enough informative markers for re-transplanted patients two had separate donors. This is a known problem for chimerism analysis in general and not a specific problem to the new method and will not be a hindrance for the implementation of Devyser chimerism at the clinical laboratory.
398

Možnosti klinického využití jednoduchých a tandemových rázových vln. / Possibilities of clinical use single and tandem shock waves.

Zeman, Jan January 2016 (has links)
Shock waves have been used in medicine for more than 30 year. At the beginning was mainly use for lithotripsy, but today is also applied in other fields of medicine, such as orthopedics, rheumatology and others. Single shock wave is one shock that usually is repeated every 1-1.5 seconds. By contrast tandem shock waves are two shocks consecutively (ideal interval between shocks is from 8 to 15 microseconds), that are repeated. In this work we investigated the clinical use of single and tandem shock waves that are generated entirely new source. It is based on the principle of multichannel discharge. It was found that a single shock wave can destroy the union between bone and bone cement, this effect could be used in orthopedics. Single and tandem shock wave can damage the tumor in vivo, but the principle damage is different. Tandem shockwave is able to cause damage in a depth of acoustically homogeneous medium and enhances the effect of chemotherapy. It would therefore be possible to used single and tandem shock waves in oncology either alone, or their combination with other chemicals. Functional sample of clinically usable applicator of shock waves with a new source was made for these applications. Powered by TCPDF (www.tcpdf.org)
399

Gold(I)-Catalyzed Synthesis of Polycyclic Frameworks Related to Terpenes: Selective Divergent Synthesis of Fused Carbocycles

Barabe, Francis January 2013 (has links)
Gold catalysis has become an important tool to achieve highly chemoselective p-acid activation. Exceptional reactivity and selectivity are often encountered under mild reaction conditions. These properties have made gold(I) complexes suitable catalysts for tremendous applications in the total synthesis of natural products. The first chapter will highlight a number of total syntheses using gold catalysis as a key step. The second chapter will cover our application of the gold(I)-catalyzed 6-endo-dig carbocyclization for the synthesis of bridgehead-substituted scaffolds and its use toward the synthesis of PPAP natural products. This research has opened our eyes to the utility of biphenylphosphine ligands, particularly JohnPhos, in gold(I)-catalysis. The reactivity and selectivity exhibited by gold(I) complexes is modulated by the nature of the ancillary ligand. Recent research rationalizes the impact of these ligands on the divergent reactivity observed between cationic and carbenoid intermediates. Our desire to favor the 6-endo-dig pathway has led us toward the discovery of another example of the diagonal reactivity that NHC carbene and biphenylphosphine ligands can bring to gold(I)-catalysis. Chapter three will explain the development of a selective gold-catalyzed synthesis of fused carbocycles . Our selective divergent synthesis of fused carbocycles, combined with the Diels–Alder reaction, has brought new synthetic opportunities. Chapter four will describe our approach toward the synthesis of various polycyclic diterpene-related frameworks. Starting with a unique linear precursor, we have developed a new “one-pot” process for the synthesis of three different polycyclic compounds related to the terpenoid family. The facile modulation of the linear precursor and the use of different dienophiles during the Diels–Alder reaction could enable the synthesis of diverse polycyclic analogues based on three principal frameworks. The gold(I)-catalyzed synthesis of fused carbocycles reached some limitations during our study. Regioselective control was found to be substantially more challenging, with terminal alkynes or alkynes bearing a sterically and electronically neutral methyl substituent. In chapter five, we will discuss how the complementarity of silver(I) catalysis to gold(I) catalysis enabled the selective divergent synthesis of three different fused carbocycles from a unique precursor. Moreover, copper(I) catalysis has given access to the 6-endo-dig pathway on terminal alkynes without the formation of a vinylidene intermediate.
400

Fundamentals and Applications of Ion Mobility Using 3D Printed Devices

Robert Louis Schrader (11115012) 22 July 2021 (has links)
<p>Advancements in 3D printing technology have provided (1) easy access to low-cost, open- source robotics, and (2) a fast fabrication technique for analytical devices among others. Using the robotics of a 3D printer, a mass spectrometry-based reaction screening device was built as a low- cost, modest throughput alternative to expensive, very fast systems. Using the 3D printer for fabrication, ion mobility devices were fabricated. Fundamental studies of the motion of ions in these devices were performed in addition to applications of ion mobility-mass spectrometry using a 3D printed drift tube ion mobility spectrometer.</p><p><br></p><p>With only simple modification, 3D printer kits provide nearly all the necessary parts for a functional reaction screening device. Replacing the hotend assembly with custom parts to hold a syringe, precise volumes of reaction mixtures can be dispensed, and high voltage applied to the needle for direct analysis of solutions by mass spectrometry. Direct analysis of reaction mixtures in a 96-well microtiter plates was completed in approximately 105 minutes (~65 seconds per reaction mixture, including washing of syringe). Following analysis, product distributions derived from the electrospray mass spectra were represented as heatmaps and optimum reaction conditions were determined. Using low-cost, open-source hardware, a modest throughput for reaction screening could be achieved using electrospray ionization mass spectrometry.</p><p><br></p><p>The manipulation of ions at reduced pressures is very well understood, whereas the efficient manipulation of ions at atmospheric pressure is far less understood. Using 3D printing, multiple iterations of atmospheric pressure drift tube ion mobility spectrometers were fabricated with one and two turns in the drift path. Optimum electrode geometries for ion transmission and resolution were determined by both simulation and experiment. Racetrack effects, where ions on the inside of turns have a shorter path than ions on the outside, were determined to be highly detrimental to resolving power. Drift tubes with two turns in opposite directions (a chicane) corrected for racetrack effects and had only marginally poorer resolving power than a straight drift tube. Additionally, ion intensities were nearly identical between optimized straight and turned ion paths, showing that these manipulations can be done with high efficiency. The focusing of ions at reduced pressure using RF ion funnels at reduced pressure can have nearly 100 percent transmission. At atmospheric pressure, RF fields are not nearly as efficient at focusing ions. By using non-uniform DC fields at atmospheric pressure, ions can be focused, but not nearly to the extent as at reduced pressure.</p><p><br></p><div><div><div><p>The coupling of atmospheric pressure drift tube ion mobility with ion trap mass spectrometry is inefficient due to the mismatch in duty cycle between the two instruments. For this reason, increasing the amount of data collected from a single experiment is of high importance. Fourier transform ion mobility increases the duty cycle from less than 1% to 25%. When ions are fragmented in the mass spectrometer, they maintain the frequency characteristic of the precursor. Therefore, ions can be fragmented without isolation in the ion trap (reducing duty cycle further) and related precursors and product ions identified through their drift time. Two-dimensional tandem mass spectrometry is a method to collect all tandem mass spectrometry information in a single scan. When coupled with ion mobility, this data can be used to generate functional group- specific ion mobility spectra where ion intensity is measured along a precursor or neutral loss scan line. This was demonstrated for a lipid sample in which head-group specific ion mobility spectra were obtained using head-group specific precursor and neutral loss scan lines.</p></div></div></div>

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