• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 3508
  • 2887
  • 949
  • 530
  • 467
  • 428
  • 325
  • 127
  • 113
  • 85
  • 83
  • 53
  • 49
  • 49
  • 49
  • Tagged with
  • 11479
  • 977
  • 881
  • 761
  • 711
  • 669
  • 597
  • 505
  • 488
  • 480
  • 442
  • 432
  • 404
  • 403
  • 402
  • 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.
531

Efficient C-O and C-N bond forming cross-coupling reactions catalyzed by core-shell structured Cu/Cu2O nanowires

Elshewy, Ahmed M. 12 1900 (has links)
Oxygen and Nitrogen containing compounds are of utmost importance due to their interesting and diverse biological activities. The construction of the C-O and C–N bonds is of significance as it opens avenues for the introduction of ether and amine linkages in organic molecules. Despite significant advancements in this field, the construction of C-O and C–N bonds is still a major challenge for organic chemists, due to the involvement of harsh reaction conditions or the use of expensive catalysts or ligands in many cases. Thus, it is a challenge to develop alternative, milder, cheaper and more reproducible methodologies for the construction of these types of bonds. Herein, we introduce a new efficient ligand free catalytic system for C-O and C-N bond formation reactions.
532

DENSITY FUNCTIONAL THEORY STUDIES ON THE STRUCTURAL EVOLUTION AND CATALYTIC REACTIVITY OF MOLYBDENUM-BASED CATALYSTS FOR METHANE CONVERSION

Zhang, Tianyu 01 December 2019 (has links)
Methane is an abundant resource existing in the form of natural and shale gas, and molybdenum-based catalysts, including molybdenum oxides and carbides, are the commonly used components in catalysts for converting methane to value-added chemicals. Therefore, understanding the catalytic mechanism underlying the methane conversion over molybdenum-based catalysts is key to designing highly efficient catalysts and optimizing the operating conditions. In this dissertation, I focus on the structural evolution from oxide to carbides and catalytic reactivity of the molybdenum-based catalysts for methane conversion based on the result from density functional theory (DFT) computational studies.First, the surface chemistry and reactivity of α-MoO3 toward C-H bond activation of methane by breaking the first C-H bond on the MoO3 (010) surface were used to evaluate various functionals of the DFT method. Our results indicate that surface reduction of α-MoO3 (010) occurs preferably through releasing the terminal oxygen atoms, generating oxygen vacancies while exposing the reduced Mo centers. These oxygen vacancies tend to be separated from each other at a higher density due to the repulsive interactions. Furthermore, the reduced α-MoO3 (010) surface promotes methane activation kinetically and thermodynamically by reducing the activation barrier for the first C-H bond breaking and stabilizing the product state as compared with those on the stoichiometric surface. There is a synergy between the reduced Mo active site and surface lattice oxygen for C-H bond cleavage. In addition, the performance of different functionals, including the pure-GGA PBE functional with the semi-empirical vdW correction and the meta-GGA SCAN functional, has been investigated. With the meta-GGA functional, we can predict the bulk structure of α-MoO3 more accurately while reproducing the thermal chemistry of MoO3. On the other hand, the reactivity based on the PBE functional is qualitatively consistent with that from the SCAN functional.We then conducted a systematic study of methane activation and conversion over the Mo-terminated surfaces derived from different phases of Mo2C carbides, i.e. the (001) surface of α-Mo2C and the (100) surface of β-Mo2C. The results show that Mo-terminated Mo2C with lower carburization in its subsurface (β-Mo2C) possesses a superior reactivity toward methane activation, resulting in a complete dissociation of methane to carbon adatom on the surface. This carbon adatom causes further carburization of the surface, lowering the reactivity toward methane activation. Moreover, the carburization occurs more easily in the near surface layers of Mo2C than in the bulk. Although carburization lowers the activities for methane activation, it promotes C-C coupling for dimerization of the (CH)ad species, resulting in (C2H2)ad on the Mo-terminated surfaces. On the deep carburized molybdenum carbide (MoC) surfaces, we mapped out the elementary steps of CH4 dissociation and possible mechanisms for forming the C2 species. The results indicate that the Mo-terminated MoC surfaces derived from different bulk phases (α- and δ-) of MoC possess a similar mechanism to that on the noble-metal surfaces for methane dissociation, i.e., CH4 dissociates sequentially to (CH)ad with both kinetic and thermodynamic feasibilities while breaking the last C-H bond in (CH)ad is highly activated. As such, C-C coupling through dimerization of the (CH)ad species occurs more readily, resulting in (C2H2)ad on the Mo-terminated surfaces. Such (C2H2)ad species can dehydrogenate easily to other C2 adsorbates such as (C2H)ad and (C2)ad. Consequently, these C2 species from CH4 dissociation will likely be the precursors for producing long chain hydrocarbons and/or aromatics on molybdenum carbide based catalysts.
533

Utveckling av bokningssystem med .NET / Development of Booking Application using. NET

AMIRI DEHBAREZ, AHMAD January 2013 (has links)
Examensarbetet har utförts åt det nystartade företaget Idop AB:s vägnar och har inneburit en vidareutveckling av ett befintligt webbaserad bokningssystem för det specifika företaget. Huvudsyftet har varit att leverera en webbaserad bokningskalender där uthyrare kan lägga ut sina objekt samtidigt som intressenter kan boka dessa objekt. Dessa objekt kan omfattas av till exempel lägenheter, stugor och så vidare. Då projektet kräver att utvecklare och kund har ett nära samarbete valdes Skalning Agil metod som är en Agil metod, för att bäst uppnå detta syfte. Utvecklingen utav bokningssystemet skedde i en .NET miljö där programmeringsspråket var C#. För datalagring hade företaget Idop valt SQL server och interaktion med databasen sker genom Entity Framework. Resultatet av projektet blev en bokningskalender där uthyraren lägger ut sina lediga objekt för uthyrning under specifika datum samt uppger pris för den lediga perioden. Även intressenterna har nu möjlighet att preliminär boka ett specifikt objekt vid önskat datum. I rapporten förekommer mer detaljerad beskrivning av ovanståendenämnda punkter samt slutsatsen av projektet. / This project has been carried out on the recently started company Idop AB's behalf and has led to a further development of an existing webbased booking system for the mentioned company. The main goal has been to deliver a web-based booking calendar where advertiser can place their items while stakeholders can book these items. These items may be subject to such houses, cottages and so on. The project requires developers and customers to work closely, Scaling Agile Methods which is an agile method, was chosen for this purpose in order to best achieve this aim. The development of the booking system was written in a .NET environment in which the programming language was C#. For database, the company Idop AB had chosen SQL server and for interaction with the database Entity Framework. The outcome of the project was an online based booking calendar where the owners outsource their vacant properties for rent during specific dates and report the prices for the vacant period. The stakeholders are now able to make a preliminary booking of a specific object at the desired date. The report present more detailed description of the above mentioned points and the conclusion of the project.
534

Utveckling av dynamiskt verktyg mot REST-API i C#

Franzén, Emil, Karlsson, Andreas January 2018 (has links)
In February 2018 the students Andreas Karlsson and Emil Franzén contacted Danfoss Power Solutions in Älmhult, shortly after they were offered to perform a thesis. A thesis about developing an SDK in the programming language C# for Danfoss Power Solutions newly developed API, PLUS+1 System API 2.0. As a part of the thesis a mini service tool was to be created to show the powers of the SDK and then evaluate the SDK by letting a company perform a usability test. By the end of May an SDK was delivered written in C# along with a mini service tool for use in demonstration. But because of time issues there were no usability test performed.
535

Development of the routine laboratory diagnosis of activated protein c resistance and its evaluation in a population of pregnant women

Munster, Marion 10 1900 (has links)
A Research Report submitted to the Faculty of Medicine, University of the Witwatersrand, in part fulfilment of the requirements for the degree of Master of Medicine in the branch of Haematology Johannesburg, October 1997 / Venous thromboembolic disease is a common health problem. It contributes considerably to morbidity as well as to mortality. Thrombosis usually occurs due to an underlying risk factor which may be environmental or genetic in origin. The recently described activated Protein C (APC) resistance is the commonest cause of familial thrombophilia documented to date. The molecular lesion is a single point mutation in the factor V (FV) gene which abolishes a cleavage site whereby it is normally inactivated by APC. This defect, termed the FV Leiden mutation, is highly prevalent in normal Caucasian populations. Although it would appear to have arisen due to a founder effect, there is a paucity of data concerning non-Caucasian populations. / IT2018
536

Design and Simulation of All-CMOS Temperature-Compensated gm-C Bandpass Filters and Sinusoidal Oscillators

Parajuli, Purushottam 16 August 2011 (has links)
No description available.
537

Ruthenium(II) arene complexes for asymmetric catalysis

Zhu, Zhenyu 09 August 2019 (has links)
Within the last few years, a significant contribution to the discovery of sp2C−H activation processes and useful applications for cross-coupling C−C bond formation has been achieved by the use of ruthenium(II) arene catalysts. The aim of this thesis is to describe a modular approach for the synthesis of several ruthenium(II) arene complexes with the potential for C−H activation. Another cutting-edge field, catalytic enantioselective functionalization of C−H bonds by transitional metal catalysts, has also been realized within the last few years. It represents a highly atom- and step-economic approach toward the generation of structural complexity. However, the majority of current methodologies rely on the usage of late third- row transition metals such as pallidum, iridium and rhodium. There is a need that motivates the search for cheaper, relative earth abundant metals that could have similar catalytic ability. Herein is also represented a preliminary study of a ruthenium(II)-catalyzed enantioselective access to chromane moiety enabled by chiral transient directing group.
538

Studies of the Endothelial Protein C Receptor

Pepler, Laura January 2016 (has links)
The endothelial protein C receptor (EPCR) binds to protein C (PC) and increases the rate of activated protein C (APC) generation by the thrombin-thrombomodulin (TM) complex. APC exerts anticoagulant, anti-inflammatory, and cytoprotective effects, which are EPCR-dependent. The thrombin-TM complex is also a potent activator of thrombin activable fibrinolysis inhibitor (TAFI), leading to impaired clot lysis. Mutations and polymorphisms identified in the EPCR gene, which can affect the efficiency of PC activation, have been associated with an increased risk of thrombosis. In this thesis we investigate the impact of impaired PC binding to EPCR on coagulation, inflammation, and fibrinolysis using novel in vitro and in vivo models. Using a murine model that harbours a variant of EPCR that does not bind PC (R84A), we demonstrate that upon thrombotic challenge, there is an increase in thrombin generation and fibrin deposition in the lungs. Upon inflammatory challenge, impaired PC/EPCR interactions also result in increased thrombin generation and increased neutrophil infiltration into the lungs. Using cells that express TM and a human variant of EPCR that does not bind PC (R96C), we demonstrate that clot lysis is delayed in normal plasma independent of TAFI activation, suggesting PC and TAFI do not compete for activation by the thrombin-TM complex. In contrast, delayed clot lysis in plasma deficient of PC is a result of greater TAFI activation by the thrombin-TM complex. Taken together, impairment of the PC pathway contributes to thrombosis through pro-coagulant, pro-inflammatory and anti-fibrinolytic mechanisms. Interestingly, mice with EPCR variant R84A, develop bone marrow failure and splenomegaly, revealing a novel role for EPCR in the bone marrow. Taken together, PC/EPCR interactions regulate the coagulation, inflammation, and fibrinolytic pathways, which may have a significant impact on maintaining hematopoietic homeostasis. / Thesis / Doctor of Philosophy (PhD) / Under normal conditions, blood is maintained in a fluid state. Upon injury or infection, the blood begins to form a clot to prevent bleeding. Once bleeding has stopped the clot is dissolved and blood regains its fluid state. The formation of a blood clot is a serious and potentially life threatening disease. A blood clot formed inside a blood vessel can block the flow of blood through the circulation, leading to organ damage. Approximately 50% of blood clots are caused by known genetic or environmental factors, leaving 50% of blood clots caused by unknown factors. In this thesis we investigate the unknown factors that contribute to blood clotting. In patients who have experienced blood clots with no known cause, we have identified genetic mutations in a blood vessel wall protein, known as the endothelial protein C receptor (EPCR) that renders it non-functional. We demonstrate both in vitro and in vivo that non-functional EPCR not only leads to the formation of a blood clot but also delays the removal of the blood clot. Our in vivo studies have also revealed a previously unknown role for EPCR in the bone marrow, likely through its effects on blood coagulation. Taken together, loss of EPCR function contributes to the development of clot formation and likely impacts other organ systems.
539

A Study of C^13 and C^14 Isoptope Effects Effects in Some Unidirectional Processes

Stevens, William 04 1900 (has links)
<p> The c^13 isotope effect in acid and alkaline hydrolysis of both ethyl and tertiary butyl benzoate-carboxyl-c^14 have been measured. Significant isotope effects were found in all the hydrolyses except acid hydrolysis of the tertiary butyl oster. These results are additional evidence for the suggestion of Choen and Schneider that alkyl oxygen rather than normal acyl oxygen bond cleavage occurs when tertiary butyl benzoate is hydrolyzed in acid solution. No appreciable c^13 isotope effect was found to occur in thermal, aqueous, or acid-catalysed decarboxylation of anthranilic acid. From this observation and other experimental evidence, it is concluded that anthranilic acid decarboxylates by a bimolecular process in which the attack of the hydrogen ion is rate controlling. It is further suggested that the hydrogen ion attack is on the zwitterion at the c carbon position. Both the c^13 and the c^14 isotope effect in the decarboxylation of mesitoic acid were measured using a mass spectrometer. The c^14 isotope effect was found to be two and one half times the magnitude of the c^13 isotope effect instead of twice as present theory predicts. </p> / Thesis / Doctor of Philosophy (PhD)
540

Sensitivity comparisons of the insect Centroptilum triangulifer to Ceriodaphnia dubia and Daphnia magna using standard reference toxicants; NaCl, KCl and CuS04

Hammer, Katherine A. 18 September 2012 (has links)
No description available.

Page generated in 0.0715 seconds