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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.

Mars : plasma environment and surface

Carlsson, Ella January 2008 (has links)
This doctoral thesis treats parts of the solar wind interaction with the Martian atmosphere and the water-related features known as gullies. The composition of the escaping plasma at Mars has been investigated in an analysis of data from the IMA sensor, which is a part of the ASPERA-3 instrument suit onboard the European satellite Mars Express. The goal of the investigation is to determine if there are any high abundances of escaping ion species incorporating carbon, such as in CO_2^+ . The most abundant ion species was found to be O^+ and O_2^+, followed by CO_2^+. The following ratios were identifed: CO_2^+/O^+ = 0:2 and O_2^+ /O^+ = 0:9. The escaping plasma, in form of ion beam events, has also been correlated to the magnetic anomalies found on the surface, where no clear association was found. Similar ion beams have also been detected on Venus, which does not have any crustal magnetic fields, and hence the fields are not required for the formation process of the beams. The ion beams' dependence of the direction of the solar wind convection electric field has also been studied, where a correlation was found, suggesting that the ion beams are accelerated by this field. The studies mentioned above are important in order to understand the evolution of Mars and its atmosphere, as well as plasma acceleration processes at non-magnetized planetary bodies. On 5 December 2006 the ASPERA instruments of both Venus Express and Mars Express detected a large enhancement in their respective background count level. These readings are associated with events of SEPs (Solar Energetic Particles), which are believed to be coupled with the CMEs (Coronal Mass Ejection) identified 43 ¡ 67 hours after the SEPs. The CMEs occurred on the far side of the sun (with respect to the locations of Venus and Mars), which indicates that these events can a®ect the space weather in areas situated 90 degrees in both azimuthal directions in the heliosphere with respect to the target. During this event the heavy ion outflow from the atmosphere of Mars increased by one order of magnitude, suggesting that EUV flux levels significantly affect the atmospheric loss from unmagnetized bodies. The gully formations have been investigated with data from the MOC, MOLA and TES instruments onboard the satellite Mars Global Surveyor. The features suggest that there has been fluvial erosion on the surface of Mars. The shallow and deep aquifer models remain the most plausible formation theories. Gully formation processes are important to understand since their eroding agent may be liquid water. / Godkänd; 2008; 20080206 (ysko)

Studies of plasma-facing materials and macromolecules using scanning probe microscopy

Almqvist, Nils January 1995 (has links)
The main topic of this thesis is experimental analysis of material surfaces using scanning probe microscopies. These microscopes are used for characterization through high-resolution topographical imaging, but also for controlled modification of surfaces and molecules. The surface characterization includes evaluation and development of fractal methods for surface roughness determination. The term modification is used for manipulating the structures on a microscale by scraping them with a tiny tip. The major application of this technique in the present work is the analysis of effects induced by plasma-surface interactions. Such studies are fundamental in the understanding of erosion and deposition processes on the first wall in controlled fusion devices. In this work, scanning probe microscopes were for the first time used for studying such plasma-facing materials. Both the surface structure and composition have to be known in order to evaluate new wall-materials for fusion reactors. The materials studied here are graphites, SiC/Al coatings, graphite-silicon mixtures and various silicon carbide based composites. They were all exposed to plasmas, either to lowenergy deuterium plasmas and ions in laboratory experiments, or to the plasma in a socalled tokamak. The results show the usefulness of these high-resolution microscopes in the study of plasma-surface interaction. Several other surface sensitive techniques were also applied, at the home laboratories of our collaborators, the most important ones being Rutherford backscattering spectroscopy and nuclear reaction analysis. The scanning probe microscopy in combination with the ion-beam analysis made it possible to trace fine structural features on the surfaces and to measure the surface roughness. The main results are: (i) the detection of the initial stages of bubble/blister formation on CSi mixtures, SiC/AI coatings and graphites; (ii) the morphological changes and the physical properties of the silicon carbide composites; (iii) the distinction of radiation damages on different phases of multicomponent composites; (iv) the estimation of layer thickness with scanning probe microscopy; (v) the determination of the structure of codeposited layers formed during exposure in a tokamak; (vi) the uptake of deuterium by the materials. The atomic force microscope has also been used to study the human protein spectrin, and we managed to image free spectrins with molecular resolution in an almost natural environment. The elongated spectrin macromolecule was found to be 100 rim long and 5 nm broad. Indications of a substructure were observed. The force between the sensor tip and the molecules was crucial, both for sample movement, manipulation and image resolution. Therefore, the instrument was rebuilt to operate with so called tapping-mode in liquid. Preliminary results with this method on spectrin are presented. / Godkänd; 1995; 20070410 (ysko)

Nanostructured carbon materials under extreme conditions

Mases, Mattias January 2012 (has links)
Godkänd; 2012; 20111220 (matmas); LICENTIATSEMINARIUM Ämnesområde: Fysik/Physics Examinator: Professor Alexander Soldatov, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Professor Alfonso San Miguel, Labor. of the physical properties of Nanomaterials, University Lyon 1, France Tid: Tisdag den 24 januari 2012 kl 10.00 Plats: E246 Studion, Luleå tekniska universitet

The fundamental structure of matter

Hansson, Johan January 1998 (has links)
The subject of this thesis is "the fundamental structure of matter, that is, the quest of understanding the deepest level of the physical world, and the interactions relevant at that level. The hope is that, as one goes deeper, the laws are going to be simpler, not necessarily in mathematical terms, but in conceptual terms. The goal is fewer and fewer ad hoc assumptions, inspiring and driving the pursuit for the fundamental structure of matter. The thesis consists of an introductory part, giving a broad overview of where the subject stands today, and of a more detailed part, containing our own contributions to the advances of this knowledge. Six reproduced papers are appended at the end. There we treat the fundamental structure of matter on three different levels. The first three papers are concerned with the inner structure of particles (hadrons) that interact via the strong nuclear force. Here we have investigated the interactions of the so-called quarks inside hadrons, taking into account also their spin structure. Besides protons and neutrons, we have also studied more exotic particles containing quarks, so-called mesons, that are only produced in high-energy collision processes. Om a more fundamental, but speculative, level we have constructed a new model for an underlying substructure common to both quarks and leptons (particles unaffected by the strong interaction), i.e., all particles that build up matter. We also investigate some of the physical consequences of this model, particularly the possibility of radiative neutrino decay. On the large scale, we analyse the origin of the so-called dark matter in the Universe, which we propose is composed out of enormous lumps exclusively made of quarks, without any "normal" hadrons. We also explore the connection of this phenomenon to the mysterious bursts of gammarays seen in astrophysics. / Godkänd; 1998; 20061123 (haneit)

Warped D-Brane Inflation and Toroidal Compactifications

Stålhammar, Marcus January 2017 (has links)
We set out on the ambitious journey to fuse inflation and string theory. We first give a somewhat extensive, yet free from the most complicated details, review of string inflation, discussing concepts as flux compactifications, moduli stabilization, the η-problem and reheating. Then, we consider two specific configurations of type II supergravity; type IIB on T6 with D3-branes and O3-planes, and type IIA on a twisted torus with D6-branes and O6-planes. In both cases, we calculate the scalar potential from the metric ansatzes, and try to uplift it to one of de-Sitter (dS) type. In the IIA-case, we also derive the scalar potential from a super- and Kähler potential, before we search for stable dS-solutions.

Simulation and optimization of a multi-TW few-cycle optical parametric synthesizer

Hallberg, Oskar January 2017 (has links)
The Light Wave Synthesizer 20 (LWS20) is an Optical Parametric Synthesizer (OPS) system used for relativistic attosecond physics research. The LWS20 performs OPS through the means of multiple two-color pumped Noncollinear Optical Parametric Chirped Pulse Amplification (NOPCPA) stages. NOPCPA is basedon the nonlinear optical effect Optical Parametric Amplification (OPA) which is only described analytically through simplified expressions. A natural route around this difficulty is through the means of numerical models. In this thesis a (2+1) dimensional simulation software [1], [2] is used to simulate the four currently present NOPCPA stages of the LWS20, operated under two different options. The simulationwill be key to the planned upgrade of the LWS20, propelling the system fromthe current 16 TW power [3] to the wanted 100 TW power domain. It is shown that the used software is able to, with some caveats, emulate the results achieved in a laboratory environment and that the two operational options are optimized under slightly different settings. Furthermore, some barely documented, albeit crucial, features of the simulation software have been exposed, indicating that it is not very well optimized for simulating the OPA processes of the LWS20. By increasing the pump energy of the simulation beyond the realisticlevel it is still possible to attain relatively realistic amplification and thus the software ought to prove a valuable tool for the planned system upgrade. Some alternative approaches to the continuation of the simulations are presented which would further increase the software’s usefulness in the process of expanding theLWS20. Historically, the LWS20 has been operated successfully under the sameconditions under the two possible operational options, but the simulations clearly show that an optimized set-up for one option is far from optimal for the other option. Therefore, there is a possibility to further optimize the LWS20, an idea worth pursuing in future experiments.

Physical properties and structural stability of carbon nanotubes under extreme conditions

Noël, Maxime January 2014 (has links)
Carbon nanotubes (CNTs) have attracted an immense attention of the research community since reporting on this system by S. Ijima in 1991. A "single-walled" CNT (SWCNT) can be considered as a rolled-up single-layer graphene - a one atom-thick layer of carbon atoms arranged in a hexagonal lattice. This cylindrical object being just about 1 nm in diameter and up to a few centimeters long can be considered as a quasi-one-dimensional system. Several nanotubes "inserted" one into another build a so-called multi-walled CNT. CNTs exhibit outstanding mechanical, thermal and electronic properties which make this material a promising candidate for numerous applications - reinforced composite materials, nano-electronics, molecular sensors and drug delivery systems to name just a few. CNTs possess tensile strength 10 and 5 times higher than that of steel and Kevlar, respectively, that creates a great prospective for their use as reinforcing units in materials subjected to high-impact dynamic loads/stress (bullet-proof jackets, for example). Nonetheless, to date there are no reports on experimental study of CNTs behavior at extreme dynamic loads which may substantiate such prospective. In addition, several theoretical predictions indicate a possibility of CNTs transformation into new structural forms at extreme pressures. The goal of this work is a systematic study of structural properties and exploration possibility of synthesis of new materials from CNTs under extreme pressures/stress.In a set of experiments purified SWCNTs were subjected to high dynamic (shock) pressures up to 52 GPa. Recovered from each pressure step sample was characterized by High Resolution Transmission Electron Microscopy (HRTEM) and Raman spectroscopy. We observed a gradual increase of defects concentration on the CNT surface with pressure along with shortening and "un-zipping" of the tubes and an onset of the complete CNT destruction at 26 GPa shock which sets-up a limit for certain practical applications of this kind of material. Further increase of the dynamic load to 35 and 52 GPa led to CNT transformation into a mixture of disordered sp²/sp³- bonded carbon atoms with nano-sized graphene clusters. No CNT polymerization or coalescence was observed contrary to some theoretical predictions. For comparison, we conducted a separate experiment on the same CNT material under static compression up to 36 GPa in a diamond anvil cell (DAC). The system evolution was monitored in-situ during the high-pressure run using Raman spectroscopy. Examination of the material recovered from high pressure revealed that certain fraction of the CNTs survived exposure to 36 GPa though similar damages were introduced to the nanotubes as in the shock experiments evidenced by the Raman spectra. This result testifies a substantial difference in the processes of CNT destruction by dynamic vs static compression.A separate set of experiments in DACs was aimed at in-situ monitoring of the Raman spectra (in particular G-band) during pressure evolution and establishing the level of static pressure which causes a complete destruction of SWCNTs from the same batch as used in similar experiments at the dynamic compression. Pressure dependence of G-band, G(p), exhibited several peculiarities at approximately 15, 45 and 60 GPa which we associate with collapse of large (1.2 nm) and small (∼1 nm) diameter CNTs, and an onset of nanotubes transformation to a new phase respectively. Raman spectra of the sample recovered after 58 GPa static compression exhibit no RBM signal, large G-band broadening and high D/G peak intensity ratio that testifies for CNT destruction. Pressure increase to 100 GPa resulted in a substantial altering of Raman spectrum of the recovered sample - appearance of characteristic features of highly disordered sp²-and sp³-bonded carbons which may stem from interlinked nano-sized graphene clusters.Change of CNTs structure results in the altering of their electronic properties thus structure evolution of the CNTs with pressure may be followed by monitoring electrical resistance change with pressure. In a series of experiments we conducted in-situ electrical resistance (R) measurements of the SWCNTs under static pressures up to 45 GPa (temperature range 293 - 395 K) in a conductive DAC. Isobaric temperature dependence of the resistance indicated that the nanotube sample is comprised predominantly of semiconducting CNTs. A set of anomalies observed in R(p) at room temperature we interpret as a sequential, diameter-dependent collapse of the CNTs. Raman characterization of the samples after the pressure cycling confirmed reversibility of these structural transitions for at least certain CNT species accompanied by a substantial increase of CNT defects density. No indication of nanotubes polymerization was observed.Although thermal conductivity of individual CNTs is excellent (5 times better than that of copper) heat conduction becomes far less efficient in "conventional" system, i.e. when the tubes form bundles/ropes which may lead to a risk of CNT destruction by overheating. Therefore probing CNTs response to extreme heat (temperature) is important both for testing capabilities of the nanotube material and developing methods of its proper characterization. We followed temporal evolution of the Raman spectra of bundled SWCNTs exposed to high laser irradiance in both air and argon atmosphere. Temperature threshold for CNT destruction in air appeared to be lower than that in Ar, the fact indicating importance of the CNTs oxidation for their structural integrity. We show that primary damage occurs in resonant with excitation laser CNTs which act as photon energy absorbers. We show that smaller diameter and metallic nanotubes are less stable to high irradiance/heat flux than their large diameter/semiconducting counterparts. Remarkably, some small diameter, non-resonant CNTs were destroyed indirectly, i.e. via overheating induced by neighbor CNTs in resonance (photon absorbers). We demonstrate the importance of laser heating effects on Raman characterization of nanotubes.Even though carbon nanotubes exhibit susceptibility to extreme pressure/stress and high laser irradiance/overheating their potential for use in very demanding applications is not yet challenged: for example SWCNT destruction under dynamic compression occurs at pressure exceeding 20 times the typical threshold levels in ballistic impact. Cold compression of nanotubes also opens up perspectives of synthesis of new carbon phases with superior mechanical properties. / Godkänd; 2014; 20141216 (maxnoe); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Maxime Noël Ämne: Fysik/Physics Avhandling: Physical Properties and Structural Stability of Carbon Nanotubes Under Extreme Conditions Opponent: Professor David Dunstan, School of Physics and Astronomy, Queen Mary, University of London, London, Ordförande: Professor Alexander Soldatov, Avd för materialvetenskap, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Fredag den 30 januari, kl 10.00 Plats: E231, Luleå tekniska universitet

Modeling and simulation of particle dynamics in microfluidic channels

Söderqvist, Hampus January 2017 (has links)
No description available.

Development of methods and software for rapid quality control in fluoroscopy / Utveckling av metoder och mjukvara för snabb kvalitetskontroll av genomlysningsutrustning

Khosamadi, Majid January 2021 (has links)
Background: Fluoroscopy is a common imaging technique which uses X-ray to derive a real time imaging of patient anatomy to determine diagnosis and positioning of patients for interventional procedures. It is therefore important that the fluoroscopy systems maintain their performance. Assessment of image quality parameters (such as: low contrast resolution, uniformity, homogeneity and detection of defective pixels and artifacts) is one way to assess if they maintain their performance. This study aims to develop and implement a Matlab script to do a remote Quality Control (QC) and set up tolerance levels on different types of fluoroscopy systems.                                        Method: Three fluoroscopy systems were used in this project, Siemens Axiom Artis Zee MP, Siemens Cios Alpha and Ziehm Vision RFD. There were two setups used in the study for image acquisition by adding a 2 mm Cu filter as the attenuating material placed directly on the X-ray tube. A Cylindrical aluminum contrast detail of dimension 4 mm thick and 6 mm diameter was placed in the middle of X-ray field (Setup 1 on patient couch and setup 2 directly on the flat panel detector). The fluoroscopic images were acquired with and without contrast detail over a period of six month. The image quality parameter SNR2rate was determined from signal and background images while other quality parameters such as kerma-area product rate PKA, rate, uniformity, homogeneity, low contrast resolution, SNR, defective pixels and artefact detection were examined and determined from the background images. Two additional supporting experiments were performed, one with a chest phantom and 13 cm PMMA and the other one a human visual detection 4-AFC experiment.                 Result: The image quality index SNR2rate and the dose rate index PKA, rate, the low contrast resolution parameter (LCRP), uniformity, homogeneity and SNR values were within ±2 standard deviation for repeated measurements in each system. Nevertheless, the result indicates that Siemens Axiom Artis Zee MP has the best performance while Ziehm Vision RFD has the worst performance between these three systems. The result from the defective pixel method indicate that for 20 % tolerance there were no defective pixels for Siemens Axiom and Cios Alpha. Ziehm Vision had also no defective pixels for 30 % tolerance. The artefact detection shows that artefact level is high for fluoroscopy systems and Ziehm Vision RFD has artefact level more than 50 % tolerance.  The chest phantom experiment indicate that SNR2rate varies considerably over the lung anatomy as expected.           The 4-AFC experiment indicates that the effective time was 0.14 s for human observers to integrate the information in the live image.           Conclusion: The methods developed and implemented in this project were successfully able to determine and assess the image quality parameters such as SNR2rate,PKA, rate, low contrast resolution, uniformity, homogeneity, SNR and detection of defective pixels. Further effort is needed for installation of Matlab script on our local server, connection with Excel program and internal website (SharePoint) and adding more clinical fluoroscopy systems to do remote QC in Region Östergötland.

Measure of macrocoherence

Bernhardsson, Patrik January 2021 (has links)
Macrocoherence is the concept of quantum mechanics being scaled up to the macroscopic level where everyday physical systems should inhibit quantum mechanical properties, however this is not what is observed. Through the use of Leggett-Garg inequalities, one can infer if there is a fundamental quantum mechanical behavior of the system being observed. Then, using violations of these inequalities, this paper discusses the possibility of extracting useful measures of how macroscopic a system can be. Utilizing an analogy with the measures of locality through Bell's inequalities, the scope of what a measure should consist of is discussed. A measure should be proper in the sense that a baseline of 0 should be obtained from system that never violates an LGI. Further, it is proposed that a measure should extend naturally to all orders of LGIs without ranking quantum systems differently. With these in mind two measures are proposed, one utilizing the integral over the violated area of a LGI over time whereas the other uses inner products over a matrix defined elementwise as a specified LGI. The measures scopes are discussed and their applications are showcased for some analytical quantum systems. Though functional, the measures are found to lack a resource tied to its value complicating the conceptualization of what is being measured. It is concluded that a new effort to find a true measure of macrocoherence should start from the concept of a resource.

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