M.A. / CD-ROM products provide access to information by means of different modes of interaction, often on the same database. Although command language is still widely recognized as the interaction mode which retrieves the most relevant references, it is regarded as difficult to use because of its complex structure. More user friendly modes, for example, menu and direct manipulation are viewed as being more accessible to the up-and-coming end-user. The purpose of this study was to determine by means of an empirical study whether the retrieval effectiveness between two modes of interaction on the same database differed significantly. A literature survey pointed out the unique characteristics of existing modes. It was also established that the traditional measures of retrieval effectiveness through relevance and precision could not be applied in this research. A method was devised in which the results of the two modes were compared. The empirical study was done on the command and form fill-in modes of Wilson Business Abstracts. Total results retrieved through each mode were compared, as well as the ease of entering the search by means of appropriate search facilities for each mode. The results of the research revealed that the presence of unique search facilities in a mode results in better retrieval effectiveness. Searches in both modes also require specific ways of input for optimum quality retrieval and thus has implications for intensive training in search methods.

L'objectif de cette thèse est d'étudier la formation de tourbillons dans la zone morte des disques protoplanétaires. Un code numérique 3D compressible a été mis au point et utilisé pour cette étude. Deux instabilités hydrodynamiques sont envisagées pour former les tourbillons: l'instabilité de Rossby et l'instabilité barocline.La première entraine la fragmentation d'une sur-densité annulaire en une chaîne de tourbillons qui se rattrapent les uns les autres et finissent par fusionner en un seul tourbillon qui reste stable sur de très longues durées lorsque son rapport d’aspect est suffisamment grand, et possède une structure quasi bidimensionnelle. En revanche, les tourbillons tridimensionnels de petits rapport d'aspect sont affectés par l’instabilité elliptique qui les détruits en quelques rotations. Seuls persistent ceux de grand rapport d'aspect.L'instabilité barocline, fondamentalement non linéaire, produit des tourbillons à partir de perturbations d'amplitude finies ; ces tourbillons sont ensuite amplifiés et fusionnent en tourbillons plus gros si le disque est stratifié de façon instable et s’il permet aussi le transfert de chaleur. Deux types de transfert thermique ont été envisagés pour étudier cette instabilité qui conduit alors à des différences significatives dans la structure des tourbillons formés. Le rapport d'aspect étant lié à la vorticité, l'amplification des tourbillons se traduit par une diminution de leur rapport d'aspect, et les rend donc sujet à l'instabilité elliptique. Cependant, ils ne sont pas détruit et gardent une structure tourbillonnaire grâce à l'amplification barocline. / The objective of this thesis is to study the formation of vortices in the dead-zone of protoplanetary disks. A 3D compressible numerical code has been performed and used for this study. Two hydrodynamical instabilities are considered for vortex formation: the Rossby wave instability and the baroclinic instability.The first one leads tp the fragmentation of an annular bump into a chain of vortices that catch one another and merge in a single vortex; this vortex remains stable on very long durations when its aspect ratio is large enough and has a quasi two-dimensional structure. In contrast, tridimensional small aspect ratios vortices are affected by the elliptical instability and are destroyed in a few rotation periods. Only vortices with large aspect ratios can survive.The baroclinic instability, a basically non-linear one, can produce vortices from small amplitude perturbations; these vortices are then amplified and merge in bigger vortices if the disk is unstably stratified and also permits heat transfer. Two types of heat transfer have been considered leading to significant differences in the structures of the resulting vortices. As aspect ratio and vorticity are strongly related, the baroclinic amplification reduces the aspect ratio and, so, make the vortex sensitive to the elliptical instability. However, such vortices are not destroyed and keep a vertical structure thanks to the baroclinic amplification.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, February 2013. / This case study supports the National Department of Education’s (DoE) strategy of integrating information and communication technologies (ICTs) into the curriculum delivery in all South African schools to enhance teaching and learning. It examined the influence of a Mindset’s multimedia digital versatile disk (DVD) instruction of chemical systems core knowledge area, a section in the grade 11 Physical Science curriculum. The main emphasis was directed at examining the influence that the DVD material would have on learners’ understanding of scientific processes and concepts in that particular section. Secondary to this objective, it looked at the attitudes and perceptions of learners and their teacher towards the classroom integration of the DVD material, also taking note of the challenges and benefits attributed to the integration itself. This study was based on the distributive cognition framework which has its roots in the socio-cultural and situated learning theories. The framework suggests that the learning process of the scientific concepts by learners is situated in a social learning environment, where learning is mediated by technological tools and artifacts (Valanides & Angeli, 2008). Under this cognitive theory the learner is positioned at the centre of the learning environment that is formulated by other people (i.e. other learners, the teacher and the community), the learning material (i.e. the content) and learning resources (i.e. physical and technological tools).Learning therefore is regarded as a social process where other people and the learning resources actively interact (Hollan, Hutchkins & Kirsh, 2000). Through the DVD’s visuals and explanations, the artificial mining environment was brought into the classroom enabling learners to be exposed to the scientific processes involved in the mining industry as a social real world activity which learners could associate with. That on its own could enhance the comprehension of content. A quasi experimental design was adopted with two grade 11 Physical Science classes from the same school, one used as an experimental group and the other one as a control group. The study sample consisted of 56 learners, 24 in the control group and 32 in the experimental group. Both classes were taught the same content by the same teacher without using the DVD lessons for a period of three weeks. Thereafter, the experimental group was exposed to the multimedia-supported lessons for three more weeks (i.e. the teacher used the DVD lessons to supplement his traditional teaching methods) while during the same period the control group was taught the same content for the same duration using the traditional teaching methods only. The pre-test and post-test measures were administered on both groups using the same instruments in order to check if the difference in the teaching approach had a positive impact or not. In addition, the data was collected in the form of questionnaires and interviews for attitudes and perceptions about using the DVD material for teaching and learning. The null hypothesis tested was: “the mean result of the experimental group would be the same or lower than that of the control group”. The t-test results showed that there was no statistical difference between the performances of the two groups hence upholding the null hypothesis. Descriptively, the results showed that learners regarded a multimedia-supported learning environment as an exciting one. They mentioned that it posed more benefits than challenges. The teacher also displayed positive attitude and perceptions about using the DVD material for teaching and learning as he indicated that it is a useful teaching tool.

Protoplanetary discs, composed of gas and dust, usually surround young stellar objects and serve two main purposes: they determine the accretion of matter onto the central object and also represent sites of planet formation. The accretion proceeds through the transport of angular momentum outwards allowing the disc matter to fall towards the centre. A mechanism responsible for the transport can be turbulence, waves or other coherent structures originating from various instabilities in discs that could, in addition, play a role in the planet formation process. For an understanding of these instabilities, it is necessary to study perturbation dynamics in differentially rotating, or sheared media. Thus, this thesis focuses on new aspects in the perturbation dynamics in non-magnetised protoplanetary discs that arise due to their self-gravity and velocity shear associated with the disc’s differential rotation. The analysis is carried out in the framework of the widely employed local shearing box approximation. We start with 2D discs and then move on to 3D ones. In 2D discs, there are two basic perturbation types/modes – spiral density waves and vortices – that are responsible for angular momentum transport and that can also contribute to accelerating planet formation. First, in the linear regime, we demonstrate that the vortical mode undergoes large growth due to self-gravity and in this process generates density waves via shear-induced linear mode coupling phenomenon. This is noteworthy, because commonly only density waves are considered in self-gravitating discs. Then we investigate vortex dynamics in the non-linear regime under the influence of self-gravity by means of numerical simulations. It is shown that vortices are no longer well-organised and long-lived structures, unlike those occurring in non-self-gravitating discs. They undergo recurring phases (lasting for a few disc rotation periods) of formation, growth and eventual destruction. We also discuss the dust trapping capability of such transient vortices. Perturbation dynamics in 3D vertically stratified discs is richer, as there are more mode types. We first consider non-axisymmetric modes in non-self-gravitating discs and then only axisymmetric modes in the more complicated case when self-gravity is present. Specifically, in non-self-gravitating discs with superadiabatic vertical stratification, motivated by the recent results on the transport properties of incompressible convection, we show that when compressibility is taken into account, the non-axisymmetric convective mode excites density waves via the same shear-induced linear mode coupling mechanism mentioned above. These generated density waves transport angular momentum outwards in the trailing phase, and we suggest that they may aid and enhance the transport due solely to convection in the non-linear regime, where the latter becomes outward. In the final part of the thesis, we carry out a linear analysis of axisymmetric vertical normal modes in stratified self-gravitating discs. Although axisymmetric modes do not display shear-induced couplings, their analysis provides insight into how gravitational instabilities develop in the 3D case and their onset criterion. We examine how the structure of dispersion curves and eigenfunctions of 3D modes are influenced by self-gravity, which mode first becomes gravitationally unstable and thus determines the onset criterion and nature of the gravitational instability in stratified discs. We also contrast the more exact instability criterion obtained with our 3D model with that of density waves in 2D discs. Based on these findings, we discuss the origin of 3D behaviour of perturbations involving noticeable disc surface distortions, as seen in some numerical simulations of self-gravitating discs.

Made available in DSpace on 2014-06-11T19:31:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-12-18Bitstream added on 2014-06-13T19:19:56Z : No. of bitstreams: 1 soares_ta_dr_jabo.pdf: 1734974 bytes, checksum: 8d54e9e4e3cc5af52880f71df0be7d31 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O plantio direto consiste em um sistema de manejo conservacionista da produção agrícola, que promove a melhoria das condições físicas, químicas e biológicas do solo. Desta forma, o objetivo do presente trabalho foi a avaliação de sistemas de acabamento de semeadura existentes no mercado nacional, utilizados em semeadoras de precisão para plantio direto, assim como novas propostas, levando em conta fatores que afetam a germinação das sementes e a emergência das plântulas no campo. O experimento foi conduzido na Fazenda Experimental do Instituto Agronômico do Paraná – IAPAR, em Londrina, utilizando-se o delineamento experimental em blocos ao acaso, com oito tratamentos e quatro repetições para a cultura do feijão e três repetições para a cultura da soja. Os tratamentos foram constituídos de oito sistemas de acabamento de semeadura, dotados de componentes com e sem aterramento, sistemas de controle de profundidade de sementes e rodas compactadoras. Foram avaliadas variáveis do solo, das sementes e parâmetros de desempenho das unidades semeadoras. Conclui-se que os discos aterradores melhoram os resultados das unidades de semeadura, beneficiando a operação em diferentes aspectos e aumentando a emergência. As rodas controladoras de profundidade paralelas melhoram os resultados dos discos aterradores, inclusive os de emergência. As rodas compactadoras lisas não são indicadas, pois promovem problemas de selamento superficial. As rodas compactadoras em “V” apresentaram bons resultados, mas as rodas compactadoras com garras e sulcos internos tendem a ser melhores / No-till is a system of conservation management of agricultural production, which promotes the improvement of the physical, chemical and biological soil conditions. Thus, the purpose of this study was to evaluate the systems finish seeding on the market in Brazil, used in precision seeders for no-till planters, as well as new proposals, considering factors that affect seed germination and emergence seedlings in the field. The experiment was conducted at the Experimental Farm of the Agronomic Institute of Paraná – IAPAR, in Londrina, using the randomized block planning with eight treatments and four repetitions for the cultivation of beans and three repetitions for soybean. Treatments consist of eight systems of finish seeding that having components with and without ground finish systems, depth of seed and compactor wheels. Was evaluated soil variables, seeds variables and performance parameters of seeding units. It was concluded that soil cover disks improve the seeding units performance, benefit the operation in different aspects and increasing the emergency. Parallel depth controller wheels improve results of soil cover discs, including the emergency. The flat compactor wheels are not recommended, because they promote soil surface sealing problems. The wheels in V had good results, but the wheels with grip and internal ridges tend to be better

In this thesis we analyse X-ray data of accretion powered low mass and high mass X-ray binaries to understand the nature of their accretion mechanisms by searching for some clues of viscous time-scales of their accretion discs, if they have, in their low frequency power density spectra created from their long-term X-ray observations, or by doing pulse timing analysis with much shorter X-ray data to detect the effects of torque fluctuations caused by the accreting material on the pulsar. The low mass and high mass X-ray binaries we analysed have breaks in their power density spectra, which are attributed to the role of viscosity in the formation of accretion discs. Although, the time-scales corresponding to these break frequencies are smaller than the predictions of the Standard theory of accretion discs, the sources give consistent results among themselves by displaying the expected correlation between their break and orbital frequencies. The correlation curve of LMXBs implies thicker appearing accretion discs than those assumed by the theory. The dichotomy of the HMXBs on this curve points out the different origins of accretion that these sources may have, and offers a way to distinguish the stellar-wind fed systems from the Roche-lobe overflow systems. The timing and spectral analysis of Swift J1626.6-5156 reveal a correlation between the spin-up rate and the luminosity of the source implying that the pulsar is accretion-powered. This correlation together with the characteristics of the X-ray spectra enables us to estimate the magnetic field and the distance of the source. The AXP 1E 2259+586 does not display any signs of viscous time-scale in its low frequency power density spectra, and its pulse timing analysis gives a much smaller torque noise value than that expected from accretion powered pulsars. In addition, the analysis results presented in this thesis reveal magnetar-like glitches which differ than those of radio pulsars, due to the presence of the strong magnetic field of the pulsar. These results eliminate the possibility that the AXP is an accretion-powered pulsar.

No description available.

Thesis (B.A.)--Haverford College, Dept. of Economics, 2008. / Includes bibliographical references.

Thesis (Master of Engineering in Ocean Engineering)--University of California at Berkeley, 2004. / "January 2005." Description based on title screen as viewed on May 25, 2010. DTIC Descriptor(s): Fluid Dynamics, Lagrangian Functions, Equations Of Motion, Acceleration, Formulations, Grids, Continuum Mechanics, Gaussian Quadrature, Derivatives (Mathematics), Compact Disks, Boundary Value Problems, Polynomials, Interpolation, Pressure, Operators (Mathematics). DTIC Identifier(s): Multimedia (CD-Rom), Moving Grids, Meshless Discretization, Lifs (Lagrange Implicit Fraction Step), Lagrangian Dynamics, Meshless Operators, Mlip (Multidimensional Lagrange Interpolating Polynomials), Flux Boundary Conditions, Radial Basis Functions Includes bibliographical references (58-59).

Thesis (Ph. D.)--Louisiana State University and Agricultural and Mechanical College, 2004. / Includes bibliographical references. Also available online (PDF file) by a subscription to the set or by purchasing the individual file.