Shared Disk database systems offer a high flexibility for parallel transaction and query processing. This is because each node can process any transaction, query or subquery because it has access to the entire database. Compared to Shared Nothing, this is particularly advantageous for scan queries for which the degree of intra-query parallelism as well as the scan processors themselves can dynamically be chosen. On the other hand, there is the danger of disk contention between subqueries, in particular for index scans. We present a detailed simulation study to analyze the effectiveness of parallel scan processing in Shared Disk database systems. In particular, we investigate the relationship between the degree of declustering and the degree of scan parallelism for relation scans, clustered index scans, and non-clustered index scans. Furthermore, we study the usefulness of disk caches and prefetching for limiting disk contention. Finally, we show the importance of dynamically choosing the degree of scan parallelism to control disk contention in multi-user mode.

No description available.

Two state of the art finite element reduction techniquespreviously validated against the direct finite element method,one based on classical modal analysis and another based oncomponent mode synthesis, are applied for efficient mistunedfree vibration and forced response analysis of several bladeddisk geometries. The methods are first applied to two testcases in order to demonstrate the differences in computationalefficiency as well as to validate the methods againstexperimental data. As previous studies have indicated, nonoticeable differences in accuracy are detected for the currentapplications, while the method based on classical modalanalysis is significantly more efficient. Experimental data(mistuned frequencies and mode shapes) available for one of thetwo test cases are compared with numerical predictions, and agood match is obtained, which adds to the previous validationof the methods (against the direct finite element method). The influence of blade-to-blade coupling and rotation speedon the sensitivity of bladed disks to mistuning is thenstudied. A transonic fan is considered with part span shroudsand without shrouds, respectively, constituting a high and alow blade-to-blade coupling case. For both cases, computationsare performed at rest as well as at various rotation speeds.Mistuning sensitivity is modelled as the dependence ofamplitude magnification on the standard deviation of bladestiffnesses. The finite element reduction technique based onclassical modal analysis is employed for the structuralanalysis. This reduced order model is solved for sets of randomblade stiffnesses with various standard deviations, i.e. MonteCarlo simulations. In order to reduce the sample size, thestatistical data is fitted to a Weibull (type III) parametermodel. Three different parameter estimation techniques areapplied and compared. The key role of blade-to-blade coupling,as well as the ratio of mistuning to coupling, is demonstratedfor the two cases. It is observed that mistuning sensitivityvaries significantly with rotation speed for both fans due toan associated variation in blade-to-blade coupling strength.Focusing on the effect of one specific engine order on themistuned response of the first bending modes, it is observedthat the mistuning sensitivity behaviour of the fan withoutshrouds is unaffected by rotation at its resonant condition,due to insignificant changes in coupling strength at thisspeed. The fan with shrouds, on the other hand, shows asignificantly different behaviour at rest and resonant speed,due to increased coupling under rotation. Comparing the twocases at resonant rotor speeds, the fan without shrouds is lessor equally sensitive to mistuning than the fan with shrouds inthe entire range of mistuning strengths considered. This thesis’scientific contribution centres on themistuning sensitivity study, where the effects of shrouds androtation speed are quantified for realistic bladed diskgeometries. However, also the validation of two finite elementreduction techniques against experimental measurementsconstitutes an important contribution. / NR 20140805

As our society becomes increasingly digitalized, there is an ever-increasing need for forensic tools to become faster and faster. This paper was made to help the Police and other digital forensic investigators choose the fastest disk imaging tool while still maintaining the integrity of the imaged disk. To answer this, an experiment including 162 disk imaging tests was done, with an active imaging and verification time of over 160 hours. The results were analyzed with the help of a scoring system and statistical significance tests. The paper also aimed to show if there is any difference when making images of disks that are filled to 100% compared to disks filled to 50%, and which of the disk imaging tools that handles it best. The results of the experiment showed that Guymager was the fastest disk imaging tool among the tested alternatives. It also illustrated that the speed was affected by the disks being filled to 50% as opposed to 100%. Guymager showed the best performance improvement using the EWF_E01 format, and OSForensics showed the biggest improvement when imaging using the DD format.

Generic Ericsson Processor boards are general purpose hardware platforms which provide generic processing services. They support the Unified Extensible Firmware Interface Specification. They have several network interfaces available and they are connected to Ericsson’s laboratory network. Several servers are also connected to this network. These boards require periodic firmware upgrades. They also require acquiring new firmware components and data files. Currently, an application to download or upload files from and to Ericsson’s laboratory servers when an Operating System has not already been booted does not exist. Therefore, the files have to be transferred to USB drives which are connected later to the boards in order to transfer the files. This is a time consuming operation which decreases Ericsson’s productivity. In addition, although Generic Ericsson Processor boards have an optional solid-state drive as secondary storage, Ericsson wants to be able to operate without it. This is because this secondary storage is not always available and Ericsson does not want to use it when the Generic Ericsson Processor boards are operating before an Operating System has been loaded. They prefer to use Random Access Memory storage. This project is focused on studying possible solutions for those two problems. Several file transfer protocols are analyzed. Several file system solutions mounted on Random Access Memory are also explored. A Trivial File Transfer Protocol client application and a Random Access Memory Disk driver prototype are designed, implemented and tested. They are tailored to work on a pre-boot environment, when the boards have not booted an Operating System yet, in Ericsson’s laboratory network. Finally, a secure file transfer protocols’ study is developed. This study will be used to assess Ericsson on the optimal secure file transfer protocol choice in order to implement possible secure future versions of the system.

In the present work we study the properties of accretion tori orbiting black hole. Our approach to this problem comes from the solving of general relativistic magnetohydrodynamic equations, which follow from conservation of the energy-momentum tensor, the particle number and from Maxwell's equations. We solve these equations by numerical methods which are described in Chapter 1. The formalism of tori which we consider here is described in Chapter 2. We are interested in tori with constant density of angular momentum and Fishbone-Moncrief tori mainly. We study accretion rates in these tori when the mass of black hole is increased suddenly and so the equilibrium in the torus is corrupted. For tori with constant density of angular momentum we study the influence of the presence of toroidal magnetic field on accretion rates.

No description available.

HD 106906 is a young, binary stellar system, located at ~103.3 parsecs away in the Lower Centaurus Crux (LCC) group. This system is completely unique among known systems in that it contains an asymmetrical debris disk, as well as an 11 M(Jup) planet companion, at a separation of ~735 AU. Only 4 other systems are known to contain both a disk and detected planet, where HD 106906 is the only one in which the planet has apparently been ejected. Furthermore, the debris disk is nearly edge on, and extends roughly from 70 AU to >500 AU, where previous polarimetric studies with HST have shown the outer regions to have high asymmetry. The presence of a planet companion sparks questions about the origin of this asymmetry. To better understand the structure and composition of the disk, deeper data have been taken with the Gemini Planet Imager (GPI), which we have used to perform a deep polarimetric study of HD 106906’s asymmetrical debris disk. The data were taken in the H-band, and were supplemented with both J- and K1-band polarimetric data which have been obtained through one of GPI’s Large and Long Programs (LLP). Polarimetry is important in the study of debris disks in scattered light, as it helps us constrain their dust grain characteristics, as well as allowing us to obtain high-contrast images. Modelling the disk, along with an empirical analysis of our data, supports a disk that is asymmetrical in surface brightness and structure, as well as a disk that is highly eccentric. These results will be discussed in terms of possible sources of asymmetry, such as dynamical interaction with the planet companion HD 106906b. / Graduate / 2021-07-26

Cette thèse s’intéresse aux signatures spectroscopiques des nano-particules carbonées dans l’infrarouge proche et moyen dans les disques protoplanétaires. Ces signatures sont largement observées dans le milieu interstellaire et les galaxies et représentent ainsi un outil essentiel pour étudier les conditions physiques qui y règnent. Notamment, leur étude dans les environnements circumstellaires d’étoiles de type Herbig contribue à notre connaissance de la formation des systèmes planétaires et du cycle de la matière dans la Voie lactée. Même si la poussière ne représente qu’un faible pourcentage de la matière galactique, elle est essentielle dans la formation d’espèces chimiques complexes, le chauffage photo-électrique du gaz, la balance énergétique ou ladynamique des structures. Ainsi, elle participe directement à l’évolution des disques protoplanétaires.Ce travail s’appuie notamment sur les données d’observations spectroscopiques résolues spatialement obtenues avec l’instrument NaCo au VLT dans l’infrarouge proche entre 3 et 4 μm. Le modèle THEMIS fournit un cadre d’interprétation pour les observations en proposant un modèle physique de la poussière dans lequel les propriétés optiques sont calculées en considérant la composition, la structureet la taille de populations de grains. THEMIS propose un scénario d’évolution de celle-ci au travers des différentes phases du milieu interstellaire.Les résultats obtenus montrent que des particules carbonées sub-nanométriques ayant une forte aromaticité sont présentes de manière étendue et structuréeà la surface des disques protoplanétaires. Leur degré d’aromaticité augmente avec l’intensité du champ de rayonnement de l’étoile. De plus, l’observation de ces particules près de l’étoile suggère leur renouvellement continu. La odélisation de l’émission de la poussière dans les conditions des disques met enévidence les contributions des différentes populations selon la longueur d’onde et les conditions d’irradiation.Ce travail s’inscrit dans la préparation de la mission du James Webb Space Telescope qui permettra d’observer notamment les disques ptrotoplanétaires surune large gamme infrarouge (0.6-28 μm). Ce travail a également conduit à la production de deux articles, un publié et l’autre soumis dans la revue Astronomy & Astrophysics. / This thesis focuses on spectroscopic signatures of carbon nanoparticles in the near and mid-infrared in protoplanetary disks. These signatures are widely observed in the interstellar medium and galaxies and thus represent an essential tool for studying their physical conditions. In particular, their study in the circumstellar environments of Herbig stars contributes to our knowledge of the formation of planetary systems and the dust cycle in the MilkyWay. Even if dust represents only a small percentage of galactic matter, it is key to the formation of complex chemical species, photoelectric gas heating, energy balance or structural dynamics. Thus, it participates directly in the evolution of protoplanetary disks.This work is based in particular on spatially resolved spectroscopic observation data obtained with the NaCo instrument at the VLT in the near infrared between 3 and 4 μm. The THEMIS model provides an interpretative framework for observations by proposing a physical dust model in which optical properties are calculated by considering the composition, structure and size of grain populations. THEMIS proposes a scenario of its evolution through the different phasesof the interstellar medium.The results obtained show that carbon sub-nanoparticles with high aromaticity are present in a widespread and structured manner at the surface ofprotoplanetary disks. Their degree of aromaticity increases with the intensity of the stellar radiation field. Moreover, the observation of these particles close to the star suggests their continuous replenishment. Modelling the dust emission under disk conditions highlights the contributions of dust populations according to the wavelength and the radiation field.This work is related to the preparation of the James Webb Space Telescope mission which will allow to observe protoplanetary disks over a wide infrared range (0.6-28 μm) with a resolution of 0.1”. This work also led to the production of two articles, one published and the other submitted to the journal Astronomy & Astrophysics.

This thesis concerns the control of an adaptive passive vibration neutralizer and the feasibility of miniaturizing this type of tunable vibration neutralizer for small-scale applications. An analytical model for the adaptive passive vibration neutralizer is derived and compared to experimental results. A tuning algorithm is derived from a curve-fit of experimental tests on the specific neutralizer. A more generic tuning algorithm is also developed, which does not require testing of the neutralizer for optimal control. Both tuning algorithms are tested using a chirp forcing function to simulate drift in the excitation frequency of a host structure. Computer simulation and experimental results are given for these tests. A novel low-cost, small-scale vibration neutralizer is constructed from packing bubble-wrap. Analytical models for the stiffness are calculated, and experimental data is used to derive a damped mass-spring model. Miniaturization of vibration neutralizers is described, and many of the pitfalls in design are discussed. Theoretical tuning frequencies of possible adaptive passive vibration neutralizers at different scales are included. The goal for these miniaturized vibration neutralizers is vibration control in computer hard drives. A hard drive is analyzed for vibration problems. Included are plots of the velocities of the read-write head and spindle. Limitations of the measurement equipment are discussed, and directions for future work on small-scale tunable vibration neutralizers are outlined. / Master of Science