HD 169142 is an excellent target for investigating signs of planet-disk interaction due to previous evidence of gap structures. We perform J-band (similar to 1.2 mu m) polarized intensity imaging of HD 169142 with VLT/SPHERE. We observe polarized scattered light down to 0 ''.16 (similar to 19 au) and find an inner gap with a significantly reduced scattered-light flux. We confirm the previously detected double-ring structure peaking at 0 ''.18 (similar to 21 au) and 0 ''.56 (similar to 66 au) and marginally detect a faint third gap at 0 ''.70-0 ''.73 (similar to 82-85 au). We explore dust evolution models in a disk perturbed by two giant planets, as well as models with a parameterized dust size distribution. The dust evolution model is able to reproduce the ring locations and gap widths in polarized intensity but fails to reproduce their depths. However, it gives a good match with the ALMA dust continuum image at 1.3 mm. Models with a parameterized dust size distribution better reproduce the gap depth in scattered light, suggesting that dust filtration at the outer edges of the gaps is less effective. The pileup of millimeter grains in a dust trap and the continuous distribution of small grains throughout the gap likely require more efficient dust fragmentation and dust diffusion in the dust trap. Alternatively, turbulence or charging effects might lead to a reservoir of small grains at the surface layer that is not affected by the dust growth and fragmentation cycle dominating the dense disk midplane. The exploration of models shows that extracting planet properties such as mass from observed gap profiles is highly degenerate.

Problems with the low back resulting from diseases of the lumbar disc account for much human suffering and medical expense. Through early identification of changes in the disc, Magnetic Resonance Imaging offers a potential method for recognition of those at risk of low back trouble. An understanding of the chemical and structural basis of the MR image will therefore be of great help in understanding the degenerative mechanism itself. With this in mind, NMR studies of human intervertebral discs were performed to extract data that could be correlated with different stages of degeneration. In vitro samples of anulus fibrosus and nucleus pulposus of grades II and IV discs were examined. The Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence was used to obtain T₂ relaxation data, which were analysed with a non-negative least squares algorithm and presented as a continuous spectrum of exponentials. An inversion-recovery sequence was used to obtain T₁ data which were analysed with the same algorithm, then presented as a discrete exponential spectrum. The same procedures were used to produce relaxation times from samples of isolated disc collagen and proteoglycan. Also, T₂ relaxation data were obtained with a twelve-echo CPMG imaging sequence from healthy volunteers, and these data analysed with the same procedure used for in vitro data. In vivo and in vitro results were compared and found to agree in terms of the T₂ relaxation values. Most change between grades occurred in the nucleus, where both T₁ and T₂ values decreased from grade II to grade IV. The results of the proteoglycan and collagen studies support the theory that structure, not chemical composition, is responsible for the observed changes in relaxation times. Based on estimates of the percentages of protons in the nucleus due to water, proteoglycan and collagen, tentative assignments were made to the components of the T₂ spectra for grades II and IV nucleus, and these were supported by the results of all parts of the study. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Jatos e discos de acreção associados a objetos galácticos e extragalácticos tais como, microquasares (i.e., buracos negros de massa estelar presentes em alguns sistemas binários estelares), núcleos ativos de galáxias (NAGs) e objetos estelares jovens (OEJs), frequentemente exibem eventos de ejeção de matéria quase periódicos que podem fornecer importantes informações sobre os processos físicos que ocorrem nas suas regiões mais internas. Entre essas classes de objetos, os microquasares com emissão transiente em raios-X vêm sendo identificados em nossa Galáxia desde a última década, e tal como os NAGs e quasares distantes, alguns desses sistemas também produzem jatos colimados com velocidades aparentemente superluminais, não deixando dúvidas de que se tratam de um gás ejetado com velocidades relativísticas. Um exemplo amplamente observado em comprimentos de onda do rádio aos raios-X é o microquasar GRS 1915+105 (e.g., Dhawan et al.,2000), que foi o primeiro objeto galáctico a exibir evidências de um jato com movimento aparentemente superluminal (Mirabel e Rodríguez, 1998, 1994). Um modelo para explicar a origem dessas ejeções superluminais, bem como a emissão rádio sincrotrônica em flares não muito diferentes dos que ocorrem na coroa solar, foi desenvolvido por de Gouveia Dal Pino e Lazarian (2005), onde é invocado um processo de reconexão magnética violenta entre as linhas de campo magnético que se erguem do disco de acreção e as linhas da magnetosfera da fonte central. Em episódios de acreção onde a razão entre a pressão efetiva do disco e a pressão magnética diminui para valores menores ou da ordem de 1 e as taxas de acreção se aproximam da taxa crítica de Eddington, a reconexão pode tornar-se violenta e libera grandes quantidades de energia magnética em pouco tempo. Parte dessa energia aquece o gás, tanto da coroa quanto do disco, e parte acelera as partículas a velocidades relativísticas por um processo de Fermi de primeira ordem, pela primeira vez estudado em zonas de reconexão magnética por esses autores, produzindo um espectro sincrotrônico de lei de potência com índice espectral comparável às observações. Neste trabalho realizamos um estudo complementar, iniciado por Piovezan (2009), no qual generalizamos o modelo acima descrito para o caso dos NAGs. Nesse estudo, constatamos que a atividade de reconexão magnética na região coronal, na base de lançamento do jato, pode explicar a origem das ejeções relativísticas, dos microquasares aos NAGs de baixa luminosidade (tais como galáxias Seyfert e LINERS). A potência liberada em eventos de reconexão magnética em função das massas dos buracos negros dessas fontes, de 5 massas solares a 10^10 massas solares, obedece a uma correlação que se mantém por todo esse intervalo, abrangendo 10^9 ordens de magnitude. Essa correlação implica em uma dependência quase linear (em um diagrama log-log), aproximadamente independente das características físicas locais dos discos de acreção dessas fontes. Além do mais, ela é compatível com o chamado plano fundamental, obtido empiricamente, que correlaciona a emissão rádio e raios-X dos microquasares e NAGs às massas dos seus buracos negros (veja Merloni et al., 2003). Assim, o modelo de de Gouveia Dal Pino e Lazarian (2005), oferece uma interpretação física simples para a existência dessa correlação empírica, como devida à atividade magnética coronal nessas fontes. Já os quasares e NAGs mais luminosos não satisfazem à mesma correlação, possivelmente porque a densidade ao redor da região coronal nessas fontes é tão alta que mascara a emissão devida à atividade magnética. A emissão rádio nesses casos deve-se, possivelmente, a regiões mais externas do jato supersônico, onde ele já expandiu o suficiente para tornar-se opticamente fino e visível, e onde os elétrons relativísticos são possivelmente produzidos em choques (veja também de Gouveia Dal Pino et al., 2010a,b). Paralelamente, investigamos a formação de eventos de reconexão magnética através de simulações magnetohidrodinâmicas axissimétricas (2.5D-MHD), da interação entre o campo magnético poloidal ancorado no disco de acreção viscoso (satisfazendo ao modelo padrão de Shakura e Sunyaev, 1973) e a magnetosfera dipolar da fonte central em rotação. Para esse fim, consideramos condições iniciais semelhantes às dos OEJs. Nos testes preliminares aqui realizados, a reconexão magnética das linhas ocorre em presença de uma resistividade numérica, que não é intensa o bastante para determinar um processo de reconexão a taxas da ordem da velocidade de Alfvén, ou seja, ela é essencialmente lenta. Ainda assim, pudemos identificar alguns dos efeitos previstos pelo modelo de reconexão magnética rápida aqui estudado. Por exemplo, verificamos que a frequência e a intensidade com que eventos de reconexão magnética podem ocorrer é sensível tanto à topologia inicial do campo magnético do sistema quanto às taxas de acreção do disco (como previsto pelo modelo de de Gouveia Dal Pino e Lazarian, 2005), de modo que tais eventos ocorrem de forma mais eficiente em regimes de alta taxa de acreção. Finalmente, além da investigação sobre o desenvolvimento de eventos de reconexão magnética, pudemos também examinar a partir das simulações a formação natural de funis de acreção, os quais são colunas de acreção que conduzem gás do disco para a superfície da fonte central através das linhas do campo magnético. Os resultados desse estudo foram comparados com as observações de funis de acreção de objetos estelares jovens. / Jets and accretion disks associated with galactic and extragalactic objects such as microquasars (i.e., stellar-mass black holes occurring in some binary stellar systems), active galactic nuclei (AGNs) and young stellar objects (YSOs), often exhibit quasi-periodic ejections of matter that may offer important clues about the physical processes that occur in their inner regions. Among these classes of objects, microquasars with transient emission in X-rays have been identified in our Galaxy since the last decade and like AGNs and distant quasars, some of them also produce collimated jets with apparent superluminal speeds, leaving no doubt that we are also dealing with ejected gas with relativistic velocities. One example widely investigated from radio wavelengths to X-rays is the microquasar GRS 1915+105 (e.g., Dhawan et al.,2000), which was the first Galactic object to show evidence of a jet with apparent superluminal motion (Mirabel e Rodríguez, 1998, 1994). A model to explain the origin of the superluminal ejections and the synchrotron radio emission in flares which are not very different from those occurring in the solar corona, was developed by de Gouveia Dal Pino e Lazarian (2005), where they invoked a process of violent magnetic reconnection between the magnetic field lines that arise from the accretion disk and the lines of the magnetosphere of the central source. In accretion episodes where the ratio between the effective disk pressure and magnetic pressure decreases to values smaller than the unity and the accretion rate approaches the critical Eddington rate, the reconnection may become violent and releases large amounts of magnetic energy in a short time. Part of this energy heats the coronal and the disk gas and part accelerates particles to relativistic velocities through a first-order Fermi-like process, which was investigated for the first time in magnetic reconnection by these authors and results a synchrotron radio power-law spectrum that is compatible to the observations. In the present work we conducted a complementary study, initiated by Piovezan (2009), which generalize the model described above for the case of AGNs. We found that the activity due to magnetic reconnection in the coronal region, at the base of the launching jet, can explain the origin of relativistic ejections from microquasars to low luminous AGNs (LLAGNs, such as Seyfert galaxies and LINERs). The power released by magnetic reconnection events as a function of the black hole masses of these sources, between 5 solar mass and 10^10 solar mass, obeys a correlation that is maintained throughout this interval, spanning 10^9 orders of magnitude. This correlation implies an almost linear dependence (in a log-log diagram), which is approximately independent of the physical properties of the accretion disks of these sources. Moreover, it is compatible with the so-called fundamental plan obtained empirically, which correlates the radio and X-rays emission of microquasars and AGNs with the masses of their black holes (see Merloni et al., 2003). Thus, the model of de Gouveia Dal Pino e Lazarian (2005) provides a simple physical interpretation for the existence of this empirical correlation as due to coronal magnetic activity in these sources. More luminous AGNs and quasars do not seem to obey the same correlation, possibly because the density around the coronal region in these sources is so high that it \"masks\" the emission due to the magnetic activity. The radio emission in these cases is possibly due regions further out of the supersonic jet, where it has already expanded enough to become optically thin and visible and where the relativistic electrons are probably accelerated in shocks (see also de Gouveia Dal Pino et al., 2010a,b). In addition, we investigated the development of magnetic reconnection events through axisymmetric magnetohydrodynamic simulations (2.5D-MHD) of the interaction between the poloidal magnetic field that arises from the viscous accretion disk (which satisfies the standard model of Shakura e Sunyaev, 1973) and the dipolar magnetosphere of the rotating central source. To this aim, we considered initial conditions which are compatible to those of YSOs. In the preliminary tests conducted here, magnetic reconnection occurs in the presence of numerical resistivity only, which is not intense enough to determine a process of reconnection with rates of the order of the Alfvén speed, i.e., it is essentially slow. Nevertheless, we were able to identify some of the effects predicted by the model of fast magnetic reconnection studied here. For example, we found that the frequency and strength with which events of magnetic reconnection can occur is sensitive to both the initial topology of the magnetic field of the system and the accretion disk rates (as predicted by the model of de Gouveia Dal Pino e Lazarian, 2005), so that such events occur more efficiently under high accretion rates. Finally, besides the investigation of the development of magnetic reconnection events, we could also examine in our numerical studies the natural formation of funnel flows which are accretion columns that transport gas from the accretion disk to the surface of the central source along the magnetic field lines. The results of these studies were compared with the observations of funnel flows in young stellar objects.

Due to the Three Mile Island accident in 1979 the Swedish government took the decision in 1986 to impose a pressure relief system for Swedish BWR’s which prevents containment overpressure in case of LOCA. This pressure relief system consists of a rupture disks in two different systems, non-filtered system 361 and filtered system 362. During a steam line break it is not clear if an unjustified activation of rupture disk 361 or 362 could possibly occur. If significant amount of nitrogen will leak out from the containment then, there is a risk of low pressure in the containment (e.g. due to activation of containment spray) with leaking rupture disks, which might cause air inflow to the containment and burning of hydrogen, so conditions of activation of rupture disk must be studied. The main objective of this master thesis is the investigation of conditions of activation of rupture disk in BWR containment filtering system. In order to find out these conditions specific software called GOTHIC has been used. The methodology of this master thesis has been modeling different containments with GOTHIC software; this thesis work will go from a simple GOTHIC model, that consist in nine lumped control volumes connected by flow paths, until a more complex GOTHIC model that consist in a combination of lumped and 3D control volumes, connected among them by flow paths and 3D connectors. A large LOCA in the upper part of the reactor vessel will be considerate, due to this severe accident; conditions for the activation of the rupture disk will be complying. It has to be mentioned that pressure in the lumped modeling will be lower than pressure in the 3D volumes. Activation time for the lumped modeling will be 8,5 seconds after the steam break for system 362 and activation time for 3D modeling will be 2,8 seconds for system 362 as well. In neither case 361 system will be activated. Considering this is a nuclear safety study and accuracy must be a key point, for further investigations it might be more than advisable using 3D control volumes instead of lumped control volumes. It has to be mentioned also that due to there is no experimental data, uncertainty regarding to the results exist, and if a further safety analysis want to be done, sensitive study of the parameters implemented on GOTHIC software should be performed in the future.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18790号 / 理博第4048号 / 新制||理||1582(附属図書館) / 31741 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 中村 卓史, 教授 鶴 剛, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20918号 / 理博第4370号 / 新制||理||1627(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 上田 佳宏, 准教授 野上 大作, 教授 太田 耕司 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

No description available.

Current computer systems fill the demand of operating systems and applications for ever greater amounts of random access memory by paging the least recently used data to the hard disk drive. This paging process is called "virtual memory," to indicate that the hard disk drive is used to create the illusion that the computer has more random access memory than it actually has. Unfortunately, the fastest hard disk drives are over five orders of magnitude slower than the DRAM they are emulating. When the demand for memory increases to the point that processes are being continually saved to disk and then retrieved again, a process called "thrashing" occurs, and the performance of the entire computer system plummets. This thesis sought to find alternatives for home and small business computer users to the hard disk drive for virtual memory which would not suffer from the same long delays. Virtual memory is especially important for older computers, which often are limited by their motherboards, their processors and their power supplies to a relatively small amount of random access memory. Thus, this thesis was focused on improving the performance of older computers by replacing the hard disk drive with faster technologies for the virtual memory. Of the different technologies considered, flash memory was selected because of its low power requirements, its ready availability, its relatively low cost and its significantly faster random access times. Two devices were evaluated on a system with a 512MB of RAM, a Pentium 4 processor and a SATA hard disk drive. Theoretical models and a simulator were developed, and physical performance measurements were taken. Flash memory was not shown to be significantly faster than the hard disk drive in virtual memory applications.

A highly durable optical disk has been developed for data archiving. This optical disk uses tellurium as the write layer and carbon as a dielectric and oxidation prevention layer. The sandwich style CTeC film was deposited on polycarbonate and silicon substrates by plasma sputtering. These films were then characterized with SEM, TEM, EELS, ellipsometry, ToF-SIMS, etc, and were tested for writability and longevity. Results show the films were uniform in physical structure, are stable, and able to form permanent pits. Data was written to a disk and successfully read back in a commercial DVD drive.

A vast majority of coal and mineral cleaning and upgrading processes involve the addition of water. The water allows the movement of particles throughout the processing plant and the upgrading of the material. When the process is complete the finished product must be dewatered. This is due to storage concerns, in which the water takes up a majority of the space, and high transportation costs, in which no compensation is obtained from the buyer for the shipment of the liquid. Dewatering is accomplished by many devices, with the two most common pieces of equipment being the screen-bowl centrifuge and disk filter. This thesis tests and compares the effect of reagents on dewatering using the screen-bowl centrifuge and disk filter. Coal was obtained from the Upper Banner, Pittsburgh No. 8, Taggart, and Dorchester seams, crushed and ground to the desired size, and run through the dewatering circuits. The results showed that the moisture content of the product can be greatly reduced in the disk filter while being only slightly reduced in the screen-bowl centrifuge. It was also shown that the recovery can be slightly increased in the screen-bowl centrifuge. Overall, with the addition of reagents, the disk filter outperformed the centrifuge in both recovery and moisture content. A model was also developed for the screen-bowl centrifuge. The results from the screen-bowl tests helped in the development of this model. This model can be used to predict the moisture content of the product, the recovery, particle size distribution of the effluent and particle size distribution of the product. The model also predicted how the product moisture and recovery were affected by changing the feed flow rate, feed percent solids, centrifuge speed, and particle size distribution. / Master of Science