• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 8
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 23
  • 5
  • 4
  • 4
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 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.
11

Coops hållbarhetsarbete : En fallstudie om hur ett ord kan påverka organisationskulturen

Alberius, Adam, Lundin, Martin January 2018 (has links)
In the light of corporate scandals, pressure has increased on organizations to communicate information related to their corporate social responsibility (CSR). In order to keep up with the increased pressure on social commitment, organizations’ self-descriptions may be future-oriented rather than reflections of reality. The future-oriented communication may improve the organizational culture and thereby motivate staff to perform more efficiently. On the other hand, if the organization does not fulfill their CSR communication it could lead to internal skepticism. This thesis constitutes a case study of the organization Coop, comprising whether the relationship between its CSR communication and the internal perception of Coop’s CSR work in store has affected their organizational culture.   In order to answer How does Coop communicate it sustainability work through its external communication? and How does the staff perceive Coop's sustainability work? a qualitative content analysis and interviews with Coop’s staff have been conducted. The theoretical framework consists of Nils Brunsson’s (2006) theory about Organized hypocrisy, and Christensen's (1997) Autocommunication.   A conclusion that can be made from the results of this thesis, is that the image communicated from Coop (regarding their sustainability work) does not seem to be fully aligned with the staff’s perception of Coop’s sustainability work. Coop’s definition of their sustainability work had only been acknowledged by some, whereas half of the staff had individual interpretations of Coop’s sustainability work. The various definitions of sustainability among the staff led to various attitudes towards Coop’s sustainability work, which ultimately resulted in a fragmented organizational culture.
12

Development of New Bioorthogonal Strain-Promoted Alkyne-Nitrone Cycloaddition Methodology for Applications in Living Systems

Chigrinova, Mariya January 2014 (has links)
Nitrones are alternatives to azides in rapid strain-promoted 1,3-dipolar cycloadditions with cyclooctynes. To evaluate the differences between nitrones and azides we have performed kinetic studies of strain-promoted alkyne-nitrone cycloaddition (SPANC) reactions of biarylazacyclooctynone (BARAC) with various acyclic and cyclic nitrones. The reactions were conducted under pseudo first-order reaction conditions using UV-visible spectroscopy. The reactivity of the acyclic nitrones was evaluated by varying the stereoelectronic and steric character of substituents at both the α-aryl and nitrogen positions. Cyclic nitrone reactivity was assessed according to the size of the ring and additional steric and strain effects. The obtained second-order rate constants for reactions of BARAC with cyclic nitrones were found to be greater than those for acyclic nitrones. However, all nitrones employed in the kinetic studies herein displayed significantly greater reactivity than azides in the analogous cycloadditions with BARAC. It is of particular note that the five-membered cyclic nitrones showed exceptional reactivity and, if used as rapid alternatives to azides in reactions with BARAC, can increase the reaction rates by up to 50 fold. An attempt to synthesize an allylated BARAC analogue is also described; the rearrangement reaction leading to the unexpected products is reported. The reaction rate for the novel rearrangement under both neutral and acidic conditions was obtained and plausible mechanisms for formation of products are proposed. Based on the results reported herein we anticipate that development of a labelling probe based on BARAC and a five-membered cyclic nitrone would allow for significant decrease of the concentrations of labelling reagents, thereby minimizing reaction time and reagent usage in life sciences applications. Nevertheless, a possible labelling decrease due to side reactions should be given consideration for prolonged labelling.
13

BASE- AND VISIBLE LIGHT-PROMOTED ACTIVATION OF ARYL HALIDES UNDER TRANSITION-METAL-FREE CONDITIONS: APPLICATIONS AND MECHANISTIC STUDIES

Lei Pan (11740286) 20 December 2021 (has links)
Aromatic rings are universal motifs in natural products, pharmaceuticals, agrochemicals, and wide variety of organic materials. Aromatic halides are widely used as synthetic precursors in all these applications. Therefore, tremendous effort has been devoted to activate aryl halides in the past decades. The common methods to activate aryl halides require the use of transition-metals either in the form of Grignard reagents or through the use of transition-metal catalysis. <br>Over the past decade, photoredox catalysis has attracted significant attention as a cogent tool to develop greener synthetic processes and enable new molecular activation pathways under mild conditions. The most common of these approaches uses a photoredox/nickel dual catalytic cycle.<br>While this technology has greatly expanded the toolbox of organic chemists, this method still requires expensive rare-metal-based catalyts. Herein, we present a series of visible light-induced methods that are transition-metal-free. These new base-promoted transformations and their mechanistic work will be discussed in the following order:<br>We will first present our discovery that the dimsyl anion enables visible-light-promoted charge transfer in cross-coupling reactions of aryl halides. This work was applied to the synthesis of unsymmetrical diaryl chalcogenides. This method has a broad scope and functional group tolerance. An electron-donor-acceptor (EDA) complex between a dimsyl anion and the aryl halide is formed during the reaction and explains the observed aryl radical reactivity observed.<br>Then, a visible-light-induced borylation and phosphorylation of aryl halides under mild conditions was developed. Inspired by the mechanistic breakthroughs observed in the previous work. The mechanism of this reaction also involves an aryl radical that is presumed to be formed also via an EDA complex. In other work, a photo-induced phosphonation of ArI using N,N-diisopropylethylamine (DIPEA) and trialkyl phosphites was developed. This method uses very mild conditions, which allowed the preparation a wide variety of functionalized aromatic phosphonates derivatives, including natural products and medicinal compounds. Finally, a photochemical amination of amides was developed via a C(sp 3 )–H bond functionalization<br>process under visible light irradiation. This reaction showed good functional group compatibility without the use of external radical initiators, strong oxidants, or heat source. An EDA complex between N-bromophthalimide and LiOtBu is formed during the reaction.
14

Molecular Mass Dependent Mechanical Properties of Metal-free Click Hydrogels

Wang, Huifeng 29 May 2015 (has links)
No description available.
15

TRANSITION METAL CATALYZED REARRANGEMENT OF DIMETHYL VINYLCYCLOBUTENE DICARBOXYLATES DERIVATIVES TO DIMETHYL CYCLOHEXADIENE DICARBOXYLATES AND PHTHALATES

Lovchik, Martin Alan 11 October 2001 (has links)
No description available.
16

Forsterite Dissolution Kinetics: Applications and Implications for Chemical Weathering

Olsen, Amanda Albright 02 August 2007 (has links)
Silicate minerals are the most common mineral group in the earth's crust so it is not surprising that their weathering reactions dominate the chemistry of many earth surface processes. This project used forsterite as a model system to identify the important factors that affect silicate mineral dissolution rates and grain lifetimes in the weathering environment. I determined an empirical rate law for forsterite dissolution of forsterite in oxalic acid solutions: based on a series of 124 semi-batch reactor experiments over a pH range of 0 to 7 and total oxalate concentrations between 0 and 0.35 m at 25°C. These experiments show that oxalate-promoted dissolution rates depend upon both oxalate concentration and pH. I propose a reaction mechanism in which a hydrogen ion and an oxalate ion are simultaneously present in the activated complex for the reaction that releases H4SiO4 into solution. By analogy, I propose that water acts as a ligand in the absence of oxalate. I also ran 82 batch reactor experiments in magnesium and sodium sulfate and magnesium and potassium nitrate solutions. These experiments show that ionic strength up to 12 m, log mMg up to 4 m, and log mSO4 up to 3 m have no effect on forsterite dissolution rates. However, decreasing aH2O slows forsterite dissolution rates. The effect of decreasing dissolution rates with decreasing aH2O is consistent with the idea that water acts as a ligand that participates in the dissolution process.Forsterite dissolution rate data from previously published studies were combined with results from my experiments and regressed to produce rate laws at low and high pH. For pH < 5.05 or and for pH > 5.05 or I then developed a diagram that shows the effect rate-determining variables on the lifetime of olivine grains in weathering environments using these rate laws. / Ph. D.
17

Promoted ignition testing : an investigation of sample geometry and data analysis techniques

Suvorovs, Terese January 2007 (has links)
Metallic materials and oxygen can be a volatile combination when accompanied by ignition mechanisms. Once ignited, metallic materials can readily burn in high pressure oxygen atmospheres, releasing an enormous amount of energy and potentially destroying equipment, space missions and resulting in the loss of life. The potential losses associated with these fires led to research into the conditions under which metal fires propagate. Several organisations, including the American Society for Testing and Materials (ASTM) and the International Organisation for Standardisation (ISO), have published recommended standard test practices with which to assess the relative flammability of metallic materials. These promoted ignition tests, so called because samples are ignited with an overwhelming source of energy, are typically used to examine two important parameters as an indication of a metallic material's flammability: Threshold Pressure (TP) and the Regression Rate of the Melting Interface (RRMI). A material's TP is the minimum pressure at which it burns, therefore, TPs of different materials can be compared to assess which materials are most suited for a range of high pressure applications. The RRMI is a useful measure for ranking materials, particularly if they have the same TP, but can be used as a ranking method irrespective of TP. In addition, it is a crucial parameter to aid in understanding the complex burning process and is one of the few experimental parameters that can be measured. Promoted ignition test standards specify a standard sample geometry to use when performing the test, typically a 3.2 mm diameter cylindrical rod. The recent addition of a 3.2 × 3.2 mm square rod as an optional standard sample geometry raises the issue of how the geometry of a sample affects its flammability. Promoted ignition test results for standard geometries are often applied to assess the flammability risk for the complex geometries of real components within oxygen systems, including regulators, valves, piping etc. Literature shows that sample geometry has a significant effect on material rankings when rankings are based on testing of standard geometries, for example, cylindrical rods, compared to non-standard geometries, for example, sintered filters and meshes. In addition, the RRMI has been shown to be dependent on a sample's cross-sectional area (XA). However, it remains unclear, from a simple heat transfer analysis, why the RRMI is dependent on XA or how the shape of a sample affects its melting rate. These questions are particularly relevant since understanding how sample geometry affects burning contributes to two important research goals: to be able to accurately model and predict the flammability risk of a metallic component without the need for physical testing, and to understand the effects of different sample geometries on their relative flammabilities within the standard tests used. Promoted ignition tests were conducted on iron rods with cylindrical, rectangular and triangular cross sections for a range of XAs. Their RRMIs were measured and analysed using a statistical approach which allowed differences in RRMI to be quantitatively assessed. Statistically significant differences in RRMI were measured for rods with the same XA but of different shape. Furthermore, the magnitude of the difference was dependent on XA. Triangular rods had the fastest RRMIs, followed by rectangular rods and then cylindrical rods. Differences in RRMI based on rod shape are due to heat transfer effects and the dynamic motion of the attached molten mass during the drop cycle. The corners of the rectangular and triangular rods melt faster due to their locally higher Surface Area to Volume ratio (SA/V). This dynamic effect increases the area of contact between the molten mass and the solid rod (solid liquid interface (SLI)) which facilitates increased heat transfer to the rod resulting in a faster RRMI. This finding highlights the importance of the SLI in the heat transfer process. Although the SLI is largely dependent on the XA, the shape of the rod causes subtle changes to the size of the SLI and thus affects heat transfer, burning and observed RRMI. The relationship between rod diameter, test pressure and Extent of Reaction (ER), the proportion of metal that reacts (oxidises) whilst attached to the burning rod, was investigated. During promoted ignition testing of iron rods of varying diameter the detached drops were rapidly quenched by immersion in a water bath. Microanalysis techniques were used to qualitatively assess the ER as a function of pressure and rod diameter. It was found that the pressure dramatically affects ER. High pressure tests resulted in a slag mass consisting of oxide, with no unreacted iron, whereas low pressure tests resulted in a significant fraction of unreacted iron within the slag. This indicates that the ER contributes directly to the observed increase in RRMI with increasing test pressure. At high pressures the ER is not affected by rod diameter, since all available liquid metal reacted, but at low pressures ER is a function of rod diameter, ER decreases as XA increases. This thesis also investigates the analysis of promoted ignition test data through suitable statistical methods. Logistic regression is identified as an appropriate method for modelling binary burn/no-burn test data. The relationship between the reaction probability, defined as the probability that a sample will undergo sustained burning, and pressure, is evaluated for two different data sets. The fits of the logistic regression models are assessed and found to model the available data well. The logistic regression method is contrasted with the confidence levels associated with binary data based on the Bernoulli distribution. It is concluded that a modelling approach is beneficial in providing an overall understanding of the transition between pressures where no burning occurs and pressures where burning is expected.
18

"Mandem vir seus parentes": a Sociedade Promotora de Imigração em São Paulo (1886-1896) / "Ask to come their relatives": in Immigration Promoted Society in São Paulo (1886-1896)

Petri, Kátia Cristina 21 October 2010 (has links)
Made available in DSpace on 2016-04-27T19:30:06Z (GMT). No. of bitstreams: 1 Katia Cristina Petri.pdf: 1199355 bytes, checksum: 25e61b6271a78f1de2adf44d1e344a7d (MD5) Previous issue date: 2010-10-21 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / I propose a reflection on the question of work in coffee plantations in São Paulo and how the discussions, which have sought alternantives for the rural labor with the end of slavery, were conducted. We can not say that immigration was a consensus among the farmers, by contrast, throughout the period that it was present, immigration was the target of criticism from different parts of society. The time clipping has, in Immigration Promoted Society, a mounting of the whole apparatus around the arrival of immigrants, through the correspondence sent by their relatives and friends. is in chronological Society Promoting Immigration This aspect is what makes difference between the immigrant project from the other ones which were set previously, or even in the period of its operation, that is, even being the link of the significant immigrant influx, Promoter is going to take as prerogative an indication to immigrate. Only listed families, that were under the auspices of the project, therefore, is a grant program for immigration, only through it is that the subsidy was paid, both for those who immigrated under his responsibility, as the spontaneous who requesting reimbursement or even those who traveled with the encouragement of the general government / Proponho uma reflexão sobre a questão do trabalho na lavoura cafeeira paulista e como foram conduzidos os debates que buscavam alternativas para o trabalho rural com fim da escravidão. Não podemos afirmar que a imigração foi um consenso entre os produtores rurais, pelo contrário, durante todo o período que esteve presente foi alvo de críticas de diferentes setores da sociedade. O recorte cronológico tem na Sociedade Promotora de Imigração a montagem de todo aparato em torno da vinda dos imigrantes, através das correspondencias enviadas pelos seus parentes e amigos. Esse aspecto é o que diferencia seu projeto imigrantista dos que foram estabelecidos anteriormente ou, até, no período de seu funcionamento, ou seja, mesmo sendo o elo da significativa corrente imigratória a Promotora vai adotar como prerrogativa a indicação para imigrar. Somente famílias, indicadas, é que estavam sob a tutela do projeto, portanto, é um programa de subvenção para a imigração, somente por meio dela é que o subsídio era pago, tanto para aqueles que imigravam sob sua responsabilidade, como os espontâneos que solicitavam reembolso ou mesmo aqueles que viajavam com o incentivo do governo geral
19

Transition Metal-Mediated Syntheses of Yohimbane and Indolizidine Alkaloids / Übergangsmetall-vermittelte Synthesen von Yohimban- und Indolizidinalkaloiden

Agarwal, Sameer 27 May 2005 (has links) (PDF)
Polycyclic nitrogen containing heterocycles form the basic skeleton of numerous alkaloids and physiologically active drugs. Alloyohimbane was obtained from 3,4-dihydro-â-carboline using an iron-mediated [2+2+1] cycloaddition as the key-step. The bis-TMS-diyne was conveniently obtained by the C-alkylation of 3,4-dihydro-â-carboline followed by N-alkylation. Demetalation of the iron-complex followed by hydrogenation, E-ring expansion, and reduction provided alloyohimbane, a structurally and biologically interesting substance, via a linear eight-step sequence in 7% overall yield based on 3,4-dihydro-â-carboline. Another sequence provided (±)-alloyohimbane and (±)-3-epi-alloyohimbane in nine steps. The pyrrole unit occurs in a variety of naturally occurring compounds, pharmaceutical products and polymers. A novel two-step procedure for the synthesis of pyrroles by addition of a propargyl Grignard reagent to a Schiff base and subsequent silver(I)-promoted oxidative cyclization of the resulting homopropargylamine has been developed. The generality of this reaction was proven by the synthesis of a broad variety of substituted pyrroles using silver(I)-promoted cyclization. A three-step synthesis of (±)-harmicine, a natural product isolated from the Malaysian plant Kopsia griffithii having strong anti-leishmania activity, from 3,4-dihydro-â-carboline is achieved by addition of 3-trimethylsilylpropargyl Grignard reagent, Ag(I)-promoted oxidative cyclization to a pyrrole, and chemoselective hydrogenation of pyrrole ring. Total synthesis of anti-tumor active crispine A and biologically active 1,2,3,5,6,10b-hexahydropyrrolo[2,1-a]isoquinoline have been achieved in three steps using silver(I)-promoted oxidative cyclization as key step.
20

Transition Metal-Mediated Syntheses of Yohimbane and Indolizidine Alkaloids

Agarwal, Sameer 02 June 2005 (has links)
Polycyclic nitrogen containing heterocycles form the basic skeleton of numerous alkaloids and physiologically active drugs. Alloyohimbane was obtained from 3,4-dihydro-â-carboline using an iron-mediated [2+2+1] cycloaddition as the key-step. The bis-TMS-diyne was conveniently obtained by the C-alkylation of 3,4-dihydro-â-carboline followed by N-alkylation. Demetalation of the iron-complex followed by hydrogenation, E-ring expansion, and reduction provided alloyohimbane, a structurally and biologically interesting substance, via a linear eight-step sequence in 7% overall yield based on 3,4-dihydro-â-carboline. Another sequence provided (±)-alloyohimbane and (±)-3-epi-alloyohimbane in nine steps. The pyrrole unit occurs in a variety of naturally occurring compounds, pharmaceutical products and polymers. A novel two-step procedure for the synthesis of pyrroles by addition of a propargyl Grignard reagent to a Schiff base and subsequent silver(I)-promoted oxidative cyclization of the resulting homopropargylamine has been developed. The generality of this reaction was proven by the synthesis of a broad variety of substituted pyrroles using silver(I)-promoted cyclization. A three-step synthesis of (±)-harmicine, a natural product isolated from the Malaysian plant Kopsia griffithii having strong anti-leishmania activity, from 3,4-dihydro-â-carboline is achieved by addition of 3-trimethylsilylpropargyl Grignard reagent, Ag(I)-promoted oxidative cyclization to a pyrrole, and chemoselective hydrogenation of pyrrole ring. Total synthesis of anti-tumor active crispine A and biologically active 1,2,3,5,6,10b-hexahydropyrrolo[2,1-a]isoquinoline have been achieved in three steps using silver(I)-promoted oxidative cyclization as key step.

Page generated in 0.0865 seconds