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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.
111

Electron Beam Diagnostic at the ELBE Free Electron Laser

Evtushenko, Pavel 21 October 2004 (has links)
The radiation source ELBE is a scientific user facility able to generate electromagnetic radiation as well as beams of secondary particles. The figure below shows the layout of the facility. ELBE is based on a superconducting electron linac. The linac consists of two accelerating modules and uses TESLA type nine-cell niobium cavities, two cavities in each module. The cavities were developed at DESY in the framework of the TESLA linear collider project and the X-ray free electron laser (FEL) project. The ELBE linac is designed to operate with an accelerating field gradient of 10 MV/m so that the maximum design electron beam energy at the exit of the second module is 40 MeV. The essential difference of the ELBE linac from the future TESLA and X-ray FEL linacs is that ELBE operates in the continuous wave (CW) mode. ELBE delivers an electron beam with an average current of up to 1 mA. The electron source is a DC thermionic triode delivering beam with energy of 250 keV. The gun beam quality predefines the accelerated beam quality. One application of the electron beam is the generation of bremsstrahlung in the MeV energy range. The bremsstrahlung is used for nuclear spectroscopy experiments. Another application of the electron beam is the generation of quasi-monochromatic X-rays via channeling radiation in a single crystal. Thus X-rays with an energy from 10 keV through 100 keV can be generated. The channeling radiation is used for radio-biological and bio-medical experiments. In the future the ELBE electron beam will be used to produce monoenergetic positrons for material research. One more future application of the beam is the production of neutrons by bremsstrahlung via reactions. The neutrons will be used for material research oriented toward construction of future nuclear fusion reactors. In the author’s opinion, the most exciting and elegant application of the electron beam at ELBE is the infrared FEL. There are two FELs planned to run simultaneously at ELBE. The first one, with an undulator period of 27 mm, is going to operate in the wavelength range from 3 µm through 30 µm. The second one is in the design stage only but it will be built to work at longer wavelengths from 25 µm to 150 µm where the FEL has no competition from conventional quantum lasers. While an infrared FEL makes possible a great variety of experiments it is the device most sensitive to the electron beam quality. This dissertation is dedicated to the development of beam instrumentation and the measurement of electron beam parameters at ELBE. - In Chapter #1 we review fundamentals of FEL operation, discuss the importance of the electron beam quality for the FEL and lay down the requirements imposed by the FEL on the electron beam parameters. - Chapter #2 describes measurements of the transverse emittance we did at ELBE including an explanation of the experimental methods and the measurement error analysis. The transverse emittance was measured with the multislit method in the injector where the beam is space charge dominated. The transverse emittance of the accelerated beam was measured with the quadrupole scan method since the beam is emittance dominated. - Measurements of the electron bunch length, which is in the picosecond range, are described in Chapter #3. The bunch length was estimated from a frequency domain fit of a specially constructed analytical function to the measured power spectrum of the bunch. The power spectrum was obtained as a Fourier transform of the measured autocorrelation function of the coherent transition radiation (CTR). The CTR autocorrelation function was measured with the help of a Martin-Puplett interferometer. - A system of beam position monitors was designed, built, and commissioned in the framework of this effort. The design of our stripline BPM, the corresponding electronics and software is described in Chapter #4 along with the system performance as measured with the ELBE beam.
112

The Human Error : En analys av forskningsläget kring mänskliga faktorer som sårbarhet inom IT-säkerhet / The Human Error : An analysis of the current research on human factors as vulnerabilities in IT security

Olofsson, Emilia, Rasaratnam, Sangeetha January 2024 (has links)
Ett samhälle som snabbt förändras av digitaliseringens transformerande kraft är en omfattande och debatterad fråga i vår nutid. Trots de möjligheter den ger, kvarstår utmaningar, särskilt inom IT-säkerhet. Befintlig forskning betonar främst de tekniska aspekterna och försummar det avgörande mänskliga inslaget inom IT-säkerhet. Det rådande forskningsgapet belyser det mänskliga elementet som en betydande sårbarhet för att upprätthålla säkra digitala miljöer. Medan teknologiska skydd är nödvändiga visar de sig ofta otillräckliga utan hänsyn till mänskliga faktorer. Den tänkta studien syftar till att undersöka forskningsläget kring mänskliga faktorer inom IT-säkerhet. Genom en kvalitativ litteraturstudie som primär forskningsstrategi granskas och analyseras vetenskaplig forskning och litteratur systematiskt inom det valda ämnesområdet. Resultatet presenterar i vilken omfattning olika koncept relaterade till mänskliga faktorer inom IT-säkerhet undersöks. Studien bidrar således till en teoretisk kunskapsutveckling för att stärka och skydda digital information och infrastruktur genom att identifiera områden som forskningen är begränsad kring. Denna studie strävar efter att fylla forskningsgapet genom att belysa mänskliga sårbarheter inom IT-säkerhet och vilka koncept som bör undersökas vidare. På så sätt kan studien bidra till en holistisk förståelse av IT-säkerhet, med en balans mellan teknologiska och människocentrerade tillvägagångssätt. / A society rapidly transformed by the transformative power of digitization is a comprehensive and debated issue in our contemporary times. Despite the opportunities it presents, challenges persist, particularly in IT security. Existing research primarily emphasizes the technical aspects while neglecting the crucial human element within IT security. The current research gap highlights the human element as a significant vulnerability in maintaining secure digital environments. While technological safeguards are necessary, they often prove insufficient without consideration of human factors. The intended study aims to investigate the current state of research on human factors in IT security. Through a qualitative literature review as the primary research strategy, scientific research and literature within the chosen subject area are systematically examined and analyzed. The findings present the extent to which various concepts related to human factors in IT security are explored. Thus, the study contributes to theoretical knowledge development to strengthen and protect digital information and infrastructure by identifying areas where research is limited. This study seeks to fill the research gap by highlighting human vulnerabilities in IT security and which concepts should be further investigated. In doing so, the study may contribute to a holistic understanding of IT security, balancing technological and human-centered approaches.
113

Fastighetsmäklarens upplysningsplikt :  Avseende omfattningen av upplysningsplikten gentemot köparen, med inriktning på fysiska missförhållanden hänfört till fastigheten / The magnitude of realtor’s liability to inform buyers about physical errors according to the property

Snihs, Lina January 2012 (has links)
Vid en fastighetsöverlåtelse är det mycket information som ska utbytas på kort tid, mellan köpare, säljare och mäklare vad beträffar fastighetens fysiska skick och standard. I egenskap av en lojal, opartisk och sakkunnig person avseende fastighetsförsäljningar, har mäklaren ålagts en upplysningsplikt avseende sådant kring fastighetens skick som denne iakttagit, känner till eller annars har anledning att misstänka, som kan antas ha betydelse för köparen. Räckvidden av mäklarens upplysningsplikt gentemot köparen, avseende fysiska missförhållanden enligt FML 16§ 3st. kommer att utgöra uppsatsens brännpunkt. I detta inryms att söka klar-göra vilka typer av fysiska missförhållanden som en mäklare förväntas informera en köpare om, för att inte riskera att drabbas av någon typ av påföljd. Därutöver utreds förutsägbarheten och ändamålsenligheten kring FML 16§ 3st. Bedömningen av mäklarens upplysningsplikt ska även ses utifrån köparens och säljarens inbördes ansvarsområden för faktiska fel i fastigheten, samt i vilken omfattning det anses motiverat att mäklaren ikläder sig parternas ansvarsroller. Hänsyn i bedömningen får även tas till det faktum att mäklaren åläggs en grundläggande lojalitetsplikt som denne uppbär gentemot såväl köparen som säljaren. Problematiken kan i första hand härledas till tvetydiga och tämligen oklara förarbetsuttalanden, samt frånvaron av prejudicerade rättspraxis på området. Rättsreglerna kring bestämmelsen synes därav även vara svåra att tillämpa i de lägre domstolsinstanserna och hos tillsynsmyndigheten, FMN. Därav kvarstår osäkerhet kring rättsläget avseende omfattningen av mäklarens upplysningsplikt vad beträffar fysiska missförhållanden härlett till fastigheten. / When selling a property there is much information, in regards to the property’s physical standard, which should be discussed between the parties; the realtor, the buyer and the property owner. In relation to the buyer and the property owner, the realtor will be known as a loyal, independent person that carries expert know-ledge in regards to selling property. Therefore the realtor should carry the liability to inform the buyer about physical errors according to the property, that has been found, or for some other reason will be known, or if there is a reason to suspect an error, that can be of  importance to the buyer. The focus point of this thesis is the magnitude of the realtor’s liability to inform the buyer on physical errors, according to FML 16§ 3st., and to examine what kind of physical errors that the buyer have the right to be informed of. Because if the realtor do not respect the obligations according to FML 16§ 3st., legal sanctions will be given. The author will also examine if the legal rule, FML 16§ 3st., is predictable and appropriate. To examine the magnitude of the realtor’s liability to inform the buyer on physical errors, the legal relation between the buyer and the property owner has to be taken into account according to JB 4:19§. The fact that the realtor also carries a responsibility to submit to good faith and fair dealing will also be interesting. The principal legal issue will be based on the unclear preparatory work, regarding to FML (2011:666) 16§ 3st., and the magnitude of realtor’s liability to inform the buyer on physical errors. Furthermore, there is no case law given by the Swedish Supreme Courts, and that is one more reason why the area is so hard to apply. The legal position will therefore stay unclear, according the realtor’s liability to inform the buyer about physical errors of the property.
114

Brilliant radiation sources by laser-plasma accelerators and optical undulators

Debus, Alexander 18 April 2012 (has links)
Die vorliegende Arbeit beschäftigt sich in Experiment und Theorie mit Laser-Plasma beschleunigten Elektronen und optischen Undulatoren zur Erzeugung von brillianter Synchrotronstrahlung. Zum ersten Mal wird experimentell nachgewießen, dass laserbeschleunigte Elektronenpulse kürzer als 30 fs sind. Ferner werden solche Elektronenpulse erstmalig in einem Demonstrationsexperiment durch einen magnetischen Undulator als Synchrotronstrahlenquelle genutzt. Aufbauend auf diesen experimentellen Erkenntnissen, sowie umfangreichen numerischen Simulationen zur Thomsonstreuung, werden die theoretischen Grundlagen einer neuartigen Interaktionsgeometrie für Laser-Materie Wechselwirkungen entwickelt. Diese neue, in der Anwendbarkeit sehr allgemeine Methode basiert auf raum-zeitlicher Laserpulsformung durch nichtlineare Winkeldispersion wie diese durch VLS- (varied-line spacing) Gitter erzeugt werden kann und hat den Vorteil nicht durch die Fokussierbarkeit des Lasers (Rayleighlänge) begrenzt zu sein. Zusammen mit laserbeschleunigten Elektronen ermöglicht dieser traveling-wave Thomson scattering (TWTS) benannte Ansatz neuartige, nur auf optischer Technologie basierende Synchrotronstrahlenquellen mit Zentimeter bis Meter langen optische Undulatoren. Die hierbei mit existierenden Lasern erzielbaren Brillianzen übersteigen diese bestehender Thomsonquellen-Designs um 2-3 Größenordnungen. Die hier vorgestellten Ergebnisse weisen weit über die Grenzen der vorliegenden Arbeit hinaus. Die Möglichkeit Laser als Teilchenbeschleuniger und auch optischen Undulator zu verwenden führt zu bauartbedingt sehr kompakten und energieeffizienten Synchrotronstrahlungsquellen. Die hieraus resultierende monochromatische Strahlung hoher Brillianz in einem Wellenlängenbereich von extremen ultraviolett (EUV) zu harten Röntgenstrahlen ist für die Grundlagenforschung, medizinische Anwendungen, Material- und Lebenswissenschaften von fundamentaler Bedeutung und wird maßgeblich zu einer neuen Generation ultrakurzer Strahlungsquellen und freien Elektronenlasern (FELs) beitragen. / This thesis investigates the use of high-power lasers for synchrotron radiation sources with high brilliance, from the EUV to the hard X-ray spectral range. Hereby lasers accelerate electrons by laser-wakefield acceleration (LWFA), act as optical undulators, or both. Experimental evidence shows for the first time that LWFA electron bunches are shorter than the driving laser and have a length scale comparable to the plasma wavelength. Furthermore, a first proof of principle experiment demonstrates that LWFA electrons can be exploited to generate undulator radiation. Building upon these experimental findings, as well as extensive numerical simulations of Thomson scattering, the theoretical foundations of a novel interaction geometry for laser-matter interaction are developed. This new method is very general and when tailored towards relativistically moving targets not being limited by the focusability (Rayleigh length) of the laser, while it does not require a waveguide. In a theoretical investigation of Thomson scattering, the optical analogue of undulator radiation, the limits of Thomson sources in scaling towards higher peak brilliances are highlighted. This leads to a novel method for generating brilliant, highly tunable X-ray sources, which is highly energy efficient by circumventing the laser Rayleigh limit through a novel traveling-wave Thomson scattering (TWTS) geometry. This new method suggests increases in X-ray photon yields of 2-3 orders of magnitudes using existing lasers and a way towards efficient, optical undulators to drive a free-electron laser. The results presented here extend far beyond the scope of this work. The possibility to use lasers as particle accelerators, as well as optical undulators, leads to very compact and energy efficient synchrotron sources. The resulting monoenergetic radiation of high brilliance in a range from extreme ultraviolet (EUV) to hard X-ray radiation is of fundamental importance for basic research, medical applications, material and life sciences and is going to significantly contribute to a new generation of radiation sources and free-electron lasers (FELs).
115

Hur påverkar avrundningar tillförlitligheten hos parameterskattningar i en linjär blandad modell?

Stoorhöök, Li, Artursson, Sara January 2016 (has links)
Tidigare studier visar på att blodtrycket hos gravida sjunker under andra trimestern och sedanökar i ett senare skede av graviditeten. Högt blodtryck hos gravida kan medföra hälsorisker, vilket gör mätningar av blodtryck relevanta. Dock uppstår det osäkerhet då olika personer inom vården hanterar blodtrycksmätningarna på olika sätt. Delar av vårdpersonalen avrundarmätvärden och andra gör det inte, vilket kan leda till svårigheter att tolkablodtrycksutvecklingen. I uppsatsen behandlas ett dataset innehållandes blodtrycksvärden hos gravida genom att skatta nio olika linjära regressionsmodeller med blandade effekter. Därefter genomförs en simuleringsstudie med syfte att undersöka hur mätproblem orsakat av avrundningar påverkar parameterskattningar och modellval i en linjär blandad modell. Slutsatsen är att blodtrycksavrundningarna inte påverkar typ 1-felet men påverkar styrkan. Dock innebär inte detta något problem vid fortsatt analys av blodtrycksvärdena i det verkliga datasetet.
116

Extendable ladder cover solution for swedish fire vehicles

Molbeck Blyth, Marco Aurelio, Acosta Vega, María Isabel January 2016 (has links)
The following thesis project has been done in direct collaboration with Autokaross i Floby AB Rescue Vehicle Department, in Sweden.  The report contains the design development of a protective cover against weather conditions for the extendable ladder in a fire vehicle.   The aim of the report has been to develop a functional and low cost solution cover for the FEL on a fire truck, which is allocated on the roof, with the express intention of providing adequate access and protection against weather conditions in Nordic countries, so as to prevent premature deterioration of the FEL unit. The company has set the technical and conceptual boundaries, with the help of the two previous concepts currently used, the BMC and the ACP.   The initial requirements laid out by the company were expressed through a number of specific demands which can be categorized in two main points:   Cost: Designing a solution keeping in mind cost limits, assembly cost and time, and space optimization. This was done by taking into account the two existing solutions, particularly the BMC, which represents the lowest, cost wise and function wise. Therefore it was used as the basis on which to apply improvements, rather than trying to lower the high cost on the overqualified function of the ACP.   Function: Providing the adequate protection and access to the FEL. In this case, the problem was solved by establishing the correct degree of protection relevant to the Nordic weather conditions and FEL needs, and regarding the access, this was assured by fully automating the opening/closing process with the existing extraction operating system of the FEL.     The result of this report is a concept solution which meets the company’s demands, obtained by creative detailing, together with an analysis regarding possible considerations that could improve the creative detailing result in this report in the form of future work.     The report documents the process that has taken place in exploration, concept generation, concept evaluation, concept selection, and detailed CAD development. Each section shows the requirements and adjustments taken to fulfil the company’s needs.
117

Coherent Diffractive Imaging with X-ray Lasers

Hantke, Max Felix January 2016 (has links)
The newly emerging technology of X-ray free-electron lasers (XFELs) has the potential to revolutionise molecular imaging. XFELs generate very intense X-ray pulses and predictions suggest that they may be used for structure determination to atomic resolution even for single molecules. XFELs produce femtosecond pulses that outrun processes of radiation damage and permit the study of structures at room temperature and of structural dynamics. While the first demonstrations of flash X-ray diffractive imaging (FXI) on biological particles were encouraging, they also revealed technical challenges. In this work we demonstrated how some of these challenges can be overcome. We exemplified, with heterogeneous cell organelles, how tens of thousands of FXI diffraction patterns can be collected, sorted, and analysed in an automatic data processing pipeline. We improved  image resolution and reduced problems with missing data. We validated, described, and deposited the experimental data in the Coherent X-ray Imaging Data Bank. We demonstrated that aerosol injection can be used to collect FXI data at high hit ratios and with low background. We reduced problems with non-volatile sample contaminants by decreasing aerosol droplet sizes from ~1000 nm to ~150 nm. We achieved this by adapting an electrospray aerosoliser to the Uppsala sample injector. Mie scattering imaging was used as a diagnostic tool to measure positions, sizes, and velocities of individual injected particles. XFEL experiments generate large amounts of data at high rates. Preparation, execution, and data analysis of these experiments benefits from specialised software. In this work we present new open-source software tools that facilitates prediction, online-monitoring, display, and pre-processing of XFEL diffraction data. We hope that this work is a valuable contribution in the quest of transitioning FXI from its first experimental demonstration into a technique that fulfills its potentials.
118

Mass-Selected Infrared Multiple-Photon Dissociation as a Structural Probe of Gaseous Ion-Molecule Complexes

Marta, Richard 27 August 2009 (has links)
Mass-selected infrared multiple photon spectroscopy (IRMPD), Fourier transform ion cyclotron resonance (FT-ICR) kinetic experiments, RRKM and electronic structure calculations have been performed in order to propose a complex mechanism involving the formation of the proton-bound dimer of water (H5O2+) from 1,1,3,3-tetrafluorodimethyl ether. It has been found that the reaction is facilitated by a series of sequential exothermic bimolecular ion-molecule reactions. Evidence for the dominant mechanistic pathway involving the reaction of CF2H-O=CHF+, an ion of m/z 99, with water is presented. The primary channel occurs via nucleophilic attack of water on the ion of m/z 99 (CF2H-O=CHF+), to lose formyl fluoride and yield protonated difluoromethanol (m/z 69). Association of a second water molecule with protonated difluoromethanol generates a reactive intermediate which decomposes via a 1,4-elimination to release hydrogen fluoride and yield the proton-bound dimer of water and formyl fluoride (m/z 67). The 1,4-elimination of hydrogen fluoride is found to be strongly supported by the results of both RRKM theory and electronic structure calculations. Lastly, the elimination of formyl fluoride occurs by the association of a third water molecule to produce H5O2+ (m/z 37). The most probable isomeric forms of the ions with m/z 99 and 69 were found using IRMPD spectroscopy and electronic structure theory calculations. Thermochemical information for reactant, transition and product species was obtained using MP2/aug-cc-pVQZ//MP2(full)/6-31G(d) level of theory. Ionic hydrogen bond (IHB) interactions, resulting from the association of ammonia and two of the protonated methylxanthine derivatives, caffeine and theophylline, have been characterized using mass-selected IRMPD and electronic structure calculations at the MP2/aug-cc-pVTZ//B3LYP/6-311+G(d,p) level of theory. It was found that the formation of a proton-bound dimer (PBD) of caffeine and ammonia was elusive under the experimental conditions. The low binding energy of the caffeine and ammonia PBD is responsible for the perceived difficulty in obtaining an IRMPD spectrum. The IRMPD spectrum of the PBD of theophylline and ammonia was obtained and revealed bidentate IHB formation within the complex, which greatly increased the binding energy relative to the most stable isomer of the PBD of caffeine and ammonia. The IRMPD spectra of the protonated forms of caffeine and theophylline have also obtained. The spectrum of protonated caffeine showed the dominant existence of a single isomer, whereas the spectrum of protonated theophylline showed a mixture of isomers. The mixture of isomers of protonated theophylline resulted as a consequence of proton-transport catalysis (PTC) occurring within the PBD of theophylline and ammonia. All calculated harmonic spectra have been produced at the B3LYP/6-311+G(d,p) level of theory with fundamental frequencies scaled by 0.9679; calculated anharmonic spectra have also been provided at the same level of theory and were found to greatly improve the match with the IRMPD spectra obtained in all cases. Ionic hydrogen bond (IHB) interactions, resulting from the association of caffeine and theophylline with their protonated counterparts, forming proton-bound homodimers, have been characterized using mass-selected IRMPD and electronic structure calculations at the MP2/6-311+G(2d,2p)//B3LYP/6-311+G(d,p) level of theory. It is found that the IRMPD spectra of the proton-bound homodimers of caffeine and theophylline are complicated resulting from the existence of several pairs of enantiomers separated by a narrow range of relative Gibbs free energies (298 K) of 15.6 and 18.2 kJ mol-1, respectively. The IRMPD spectrum of the proton-bound homodimer of theophylline is dominated by a unique isomer facilitated by formation of a bidentate IHB. Formation of this interaction lowers the relative Gibbs free energy of the ion to 9.75 kJ mol-1 below that of the most favourable pair of enantiomers. The IRMPD spectrum of the PBD of caffeine is complicated by the existence of at least two pairs of enantiomers with the strong likelihood of the spectral contributions of a third pair existing. The most favourable enantiomeric pair involves the formation of a O-H+⋯O IHB. However, verification of a pair of enantiomeric PBDs containing a N-H+⋯O IHB is also observed in the IRMPD spectrum of the PBD of caffeine due to the presence of three free carbonyl stretching modes located at 1731, 1751 and 1785 cm-1. The mass-selected IRMPD spectra of the sodium cation-bound dimers (SCBD) of caffeine and theophylline also have been obtained. Both the mass-selected IRMPD spectra and electronic structure calculations predict the most likely structure of the SCBDs of caffeine and theophylline to form by an efficient O⋯Na+⋯O interaction between C=O functional groups possessed by each monomer. The frequencies of the C=O-Na+ stretch are found to be nearly identical in the IRMPD spectra for both of the SCBDs of caffeine and theophylline at 1644 and 1646 cm-1, respectively. However, the degenerate free C=O symmetric and asymmetric stretches for the SCBDs of caffeine and theophylline found at 1732 and 1758 cm^(-1), respectively, demonstrating a red-shift for caffeine possibly linked to a steric interaction absent in theophylline. Free rotation about the O⋯Na+⋯O bond is found to greatly decrease the complexity of the IRMPD spectra of the SCBDs of caffeine and theophylline and demonstrates excellent agreement between the IRMPD and calculated spectra. Electronic structure calculations have been done at the MP2(full)/aug-cc-pCVTZ/6-311+G(2d,2p)//B3LYP/6-311+G(d,p) level of theory using the aug-cc-pCVTZ basis set for Na+ and all Na+-interacting heterotatoms, and the 6-311+G(2d,2p) basis set for all non-interacting atoms within the SCBDs, in order to provide accurate electronic energies. Currently, installation and implementation of a pulsed electrospray high pressure ion source mated to an existing high pressure mass spectrometer (HPMS) is underway. The new ion source will greatly increase the range of possibilities for the study of ion-molecule reactions in the McMahon laboratory. One of the unique features of the new design is the incorporation of a gas-tight electrospray interface, allowing for more possibilities than only the study of cluster-ion equilibria involving hydration (H2On⋯S+), where S+ is an ion produced by electrospray. Other small prototypical biological molecules such as amines and thiols can be used without concern for the toxicity of these species. Another unique design feature allows electrosprayed ions to associate with neutral solvent species in an electric field free reaction chamber (RC). This ensures that values of equilibrium constants determined are truly representative of ions in states of thermochemical equilibrium. The existing HPMS in the McMahon laboratory is limited to the study of small volatile organic molecules. The new ion source will permit the exploration of systems involving non-volatile species, doubly charged ions and many biologically relevant molecules such as amino acids, peptides, nucleobases and carbohydrates.
119

Mass-Selected Infrared Multiple-Photon Dissociation as a Structural Probe of Gaseous Ion-Molecule Complexes

Marta, Richard 27 August 2009 (has links)
Mass-selected infrared multiple photon spectroscopy (IRMPD), Fourier transform ion cyclotron resonance (FT-ICR) kinetic experiments, RRKM and electronic structure calculations have been performed in order to propose a complex mechanism involving the formation of the proton-bound dimer of water (H5O2+) from 1,1,3,3-tetrafluorodimethyl ether. It has been found that the reaction is facilitated by a series of sequential exothermic bimolecular ion-molecule reactions. Evidence for the dominant mechanistic pathway involving the reaction of CF2H-O=CHF+, an ion of m/z 99, with water is presented. The primary channel occurs via nucleophilic attack of water on the ion of m/z 99 (CF2H-O=CHF+), to lose formyl fluoride and yield protonated difluoromethanol (m/z 69). Association of a second water molecule with protonated difluoromethanol generates a reactive intermediate which decomposes via a 1,4-elimination to release hydrogen fluoride and yield the proton-bound dimer of water and formyl fluoride (m/z 67). The 1,4-elimination of hydrogen fluoride is found to be strongly supported by the results of both RRKM theory and electronic structure calculations. Lastly, the elimination of formyl fluoride occurs by the association of a third water molecule to produce H5O2+ (m/z 37). The most probable isomeric forms of the ions with m/z 99 and 69 were found using IRMPD spectroscopy and electronic structure theory calculations. Thermochemical information for reactant, transition and product species was obtained using MP2/aug-cc-pVQZ//MP2(full)/6-31G(d) level of theory. Ionic hydrogen bond (IHB) interactions, resulting from the association of ammonia and two of the protonated methylxanthine derivatives, caffeine and theophylline, have been characterized using mass-selected IRMPD and electronic structure calculations at the MP2/aug-cc-pVTZ//B3LYP/6-311+G(d,p) level of theory. It was found that the formation of a proton-bound dimer (PBD) of caffeine and ammonia was elusive under the experimental conditions. The low binding energy of the caffeine and ammonia PBD is responsible for the perceived difficulty in obtaining an IRMPD spectrum. The IRMPD spectrum of the PBD of theophylline and ammonia was obtained and revealed bidentate IHB formation within the complex, which greatly increased the binding energy relative to the most stable isomer of the PBD of caffeine and ammonia. The IRMPD spectra of the protonated forms of caffeine and theophylline have also obtained. The spectrum of protonated caffeine showed the dominant existence of a single isomer, whereas the spectrum of protonated theophylline showed a mixture of isomers. The mixture of isomers of protonated theophylline resulted as a consequence of proton-transport catalysis (PTC) occurring within the PBD of theophylline and ammonia. All calculated harmonic spectra have been produced at the B3LYP/6-311+G(d,p) level of theory with fundamental frequencies scaled by 0.9679; calculated anharmonic spectra have also been provided at the same level of theory and were found to greatly improve the match with the IRMPD spectra obtained in all cases. Ionic hydrogen bond (IHB) interactions, resulting from the association of caffeine and theophylline with their protonated counterparts, forming proton-bound homodimers, have been characterized using mass-selected IRMPD and electronic structure calculations at the MP2/6-311+G(2d,2p)//B3LYP/6-311+G(d,p) level of theory. It is found that the IRMPD spectra of the proton-bound homodimers of caffeine and theophylline are complicated resulting from the existence of several pairs of enantiomers separated by a narrow range of relative Gibbs free energies (298 K) of 15.6 and 18.2 kJ mol-1, respectively. The IRMPD spectrum of the proton-bound homodimer of theophylline is dominated by a unique isomer facilitated by formation of a bidentate IHB. Formation of this interaction lowers the relative Gibbs free energy of the ion to 9.75 kJ mol-1 below that of the most favourable pair of enantiomers. The IRMPD spectrum of the PBD of caffeine is complicated by the existence of at least two pairs of enantiomers with the strong likelihood of the spectral contributions of a third pair existing. The most favourable enantiomeric pair involves the formation of a O-H+⋯O IHB. However, verification of a pair of enantiomeric PBDs containing a N-H+⋯O IHB is also observed in the IRMPD spectrum of the PBD of caffeine due to the presence of three free carbonyl stretching modes located at 1731, 1751 and 1785 cm-1. The mass-selected IRMPD spectra of the sodium cation-bound dimers (SCBD) of caffeine and theophylline also have been obtained. Both the mass-selected IRMPD spectra and electronic structure calculations predict the most likely structure of the SCBDs of caffeine and theophylline to form by an efficient O⋯Na+⋯O interaction between C=O functional groups possessed by each monomer. The frequencies of the C=O-Na+ stretch are found to be nearly identical in the IRMPD spectra for both of the SCBDs of caffeine and theophylline at 1644 and 1646 cm-1, respectively. However, the degenerate free C=O symmetric and asymmetric stretches for the SCBDs of caffeine and theophylline found at 1732 and 1758 cm^(-1), respectively, demonstrating a red-shift for caffeine possibly linked to a steric interaction absent in theophylline. Free rotation about the O⋯Na+⋯O bond is found to greatly decrease the complexity of the IRMPD spectra of the SCBDs of caffeine and theophylline and demonstrates excellent agreement between the IRMPD and calculated spectra. Electronic structure calculations have been done at the MP2(full)/aug-cc-pCVTZ/6-311+G(2d,2p)//B3LYP/6-311+G(d,p) level of theory using the aug-cc-pCVTZ basis set for Na+ and all Na+-interacting heterotatoms, and the 6-311+G(2d,2p) basis set for all non-interacting atoms within the SCBDs, in order to provide accurate electronic energies. Currently, installation and implementation of a pulsed electrospray high pressure ion source mated to an existing high pressure mass spectrometer (HPMS) is underway. The new ion source will greatly increase the range of possibilities for the study of ion-molecule reactions in the McMahon laboratory. One of the unique features of the new design is the incorporation of a gas-tight electrospray interface, allowing for more possibilities than only the study of cluster-ion equilibria involving hydration (H2On⋯S+), where S+ is an ion produced by electrospray. Other small prototypical biological molecules such as amines and thiols can be used without concern for the toxicity of these species. Another unique design feature allows electrosprayed ions to associate with neutral solvent species in an electric field free reaction chamber (RC). This ensures that values of equilibrium constants determined are truly representative of ions in states of thermochemical equilibrium. The existing HPMS in the McMahon laboratory is limited to the study of small volatile organic molecules. The new ion source will permit the exploration of systems involving non-volatile species, doubly charged ions and many biologically relevant molecules such as amino acids, peptides, nucleobases and carbohydrates.
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Revisorernas kostnad av att utge en going concern- varning

Gogani, Roya, Nyrén, Jonathan January 2013 (has links)
De uppgifter som revisorn presenterar i sin revisionsberättelse bör intressenter och företag ha förtroende för. Revisorn ska vara en oberoende länk mellan intressenter och företag. Läsaren förväntar sig finna eventuella ekonomiska problem i årsredovisningen. Detta är dock inte alltid fallet. Det är viktigt att revisorerna kan göra en pålitlig bedömning över företagets möjligheter till fortsatt drift. Beslut om going concern-varning måste grunda sig på oberoende och god kunskap om företagets situation. En felaktig going concern-varning kan orsaka problem och intäktsbortfall för både företaget och revisionsbyrån. Intressenterna kan förlora förtroendet för företaget och företaget kan i sin tur byta revisor. Studien fokuserar på huruvida revisorerna kan vara sparsamma med att utge going concern-varning för att inte riskera att förlora företaget som klient och därmed förlora revisionsintäkter. Därför undersöker studien om det finns ett samband mellan förlorade revisionsarvoden och utfärdandet av en första going concern-varning bland svenska företag. Studien vill också visa ifall en going concern- varning ökar sannolikheten för konkurs den s.k. självuppfyllande profetian. Ett bidrag till tidigare forskning är att studien beaktar revisionsuppdragets längd i förhållande till going concern-varning. Från databasen Affärsdata har 432 företag selekterats ut från bokslutsåret 2009. Av dessa hade 216 erhållit en going concern- varning. Denna testgrupp har sedan jämförts med en kontrollgrupp med samma antal som varit finansiellt stressade men inte erhållit någon varning. Studien har använt SPSS som statistiskt program för att kunna göra önskade beräkningar. Studiens resultat visar at det finns ett samband mellan en första going concern-varning och revisorbyte. Studien visar också att längden på revisionsuppdraget påverkar benägenheten att ge en going concern-varning. Däremot finner undersökningen inte något belägg för den s.k. självuppfyllande profetian. / The information that the auditor provides in their audit report should be valid in the eyes of the stakeholders of the company. The auditor should be the independent link between the company and its stakeholders. When reading the audit report, one expects to find all the possible economic problems identified in it, however this is not always the case. It is crucial that the audit of a company’s going concern is reliable. Decisions regarding going concern-modified opinions should be independent and be based on valid information regarding the company’s economic situation. One faulty going concern-modified opinion can set off a whole range of issues and revenue loss for both the company and the audit firm. Consequently stakeholders can lose their trust in the company resulting in a change of audit firm. This thesis is focused on whether or not auditors might be reluctant to hand out going concern-modified opinions in fear of losing a client and the revenue associated with it. Therefore, the thesis investigates whether or not there is a relationship between lost revenue and the first instance of issuing a going concern-modified opinion for Swedish companies. This thesis is also investigating whether the issuance of a going concern-modified opinion will increase the possibility of the company going bankrupt, the so-called self-fulfilling prophecy. A contribution to the previous research regarding the going concern issue is the consideration of audit tenure. We have used 432 companies with fiscal year 2009 extracted from the database Affärsdata. Out of this selection, 216 had been issued a going concern-modified opinion. This test group is then compared to the control group with the same number of companies that were identified as financially distressed but without receiving a going concern- modified opinion. The thesis has used the statistical program SPSS to complete the calculations needed to complete the analysis. The result shows a positive relationship between the first going concern-modified opinion and the change of audit firms. The period of time the auditing requires also effects the predisposition to issue a going concern-modified opinion. However the study was unable to find any statistical evidence for the so-called self-fulfilling prophecy.

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