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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.
61

Materiais nanoestruturados sintéticos tipo esmectitas: sua síntese, caracterização e aplicação em nanocompósitos de polietileno

Bueno, Marcos Roberto Paulino January 2008 (has links)
Materiais naturais nanoestruturados, tipo smectita, têm sido amplamente usados em nanocompósitos poliméricos, com ganhos expressivos em muitas propriedades. Porém, devido a sua natureza polar, seu uso em nanocompósitos de poliolefinas apresenta uma série de problemas. Entre esses problemas está a dificuldade de esfoliação na matriz, o que geralmente resulta um sistema não nano-estruturado e, por conseqüência, com pouco ou nenhum ganho em propriedades. Para tentar resolver esse problema, materiais tipo esmectita têm sido modificados com sais de amônio quartenário. Esses, por sua vez, possuem características tóxicas, impedindo seu uso em embalagens de alimentos. Com o objetivo de estudar uma nova alternativa que contorne esses problemas, dois materiais lamelares nano-estruturados, tipo esmectita, contendo grupos alquila ligados por ligação sigma com a rede inorgânica, foram sintetizados. Ambos apresentaram excelente ordem mesoestrutural. Um dos materiais sintetizados, formado por um Alsilsesquioxano lamelar, contendo alto teor de cadeia alquila entre as lamelas inorgânicas, foi usado na formação de compósito de polietileno. Comparativamente, uma argila natural, modificada com sais de amônio quaternário (Cloisite 15A), foi usada para fins comparativos. Os compósitos, então obtidos, foram caracterizados para avaliar diferenças microestruturais, morfológicas e mudanças em suas propriedades mecânicas e reológicas. Comparativamente à argila comercial Cloisite 15A, os compósitos contendo os materiais sintéticos apresentaram reologia diferenciada, melhor resistência ao impacto e ao Tensofissuramento Acelerado pelo Ambiente (ESCR). / Nanostructured natural materials, as smectites, have been widely used in polymeric nanocomposites, with significant gains in many properties. However, due to its polar nature, the use in nanocomposites of polyolefins presents a series of drawbacks. Among these problems, its difficulty exfoliation in the matrix, which generally results in a system not nanostructured and, consequently, with little or no gain on properties. To try to resolve this problem, materials type smectite have been modified with quaternary ammonium salts. These salts, in turn, have toxic characteristics, preventing its use in food packaging. In order to study a new alternative that bypasses these problems, two lamellar nanostructured materials, like smectite, with alkyl groups containing sigma links connected to lamellar inorganic network, were synthesized. Both materials had excellent mesostructural order. One of the synthesized materials, formed by a lamellar Al-silsesquioxane, containing high levels of alkyl chain between the inorganic lamella, was used in the formation of a polyethylene composite. Commercial natural clay, modified with quaternary ammonium salts (Cloisite 15A), was used for comparative purposes. The composites then obtained, were characterized to assess microstructural differences, morphological change, and its mechanical and rheological properties. Comparatively to commercial clay (Cloisite 15A), the composites containing synthetic materials, showed differented rheologics properties, better impact resistance and better Environmental Stress Cracking Resistance (ESCR).
62

Solid-state reactions in co-crystals: applications in synthetic chemistry and materials science

Dutta, Saikat 01 May 2010 (has links)
Chemistry is on the verge of a new era where the attention of chemists has shifted from covalent bonds to noncovalent interactions and their use as a predictable way to guide reactions pathways and product formation. Nature synthesizes elegant molecules under mild conditions and the designed syntheses have been demonstrated to be largely dependent on recognition, self-assembly and templating effects between molecular building blocks. Although covalent synthesis in fluidic medium via supramolecular control has been achieved with limited success, organic solid state has been of particular interest since it avoids solvent effects, and is able to provide unique materials with remarkable stereoselectivity under environment-friendly conditions. Although reactions in solids have resulted in a number of remarkable discoveries in chemistry and materials science, solid-state synthesis is generally not considered as a mainstream synthetic medium and solid-state reactions are seldom appreciated as an efficient way to access molecular targets. Owing to the limited number of solid-state reactions and the uncontrollable nature of crystal packing, solid state has not been utilized readily as a primary synthetic medium. In this context, reactions conducted in multicomponent molecular assemblies or co-crystals have been attracting much attraction in recent years as a general way of controlling the reactivity of molecules in solid state. A molecular component in the multicomponent molecular solid, acting as a linear template, has been shown to preorganize molecules in a modular way via intermolecular interactions and engineer their physical and/or chemical properties. The [2+2]photodimerization of olefins is a successful demonstration how templated solid state synthesis can efficiently synthesize complex targets that are synthetically challenging via conventional routes. In this dissertation, the generality and synthetic applicability of the templated synthetic approach in solid state will be described. How supramolecular interactions in molecular co-crystals precisely guide covalent bond formation in order to construct complex molecular targets will be demonstrated. Finally, co-crystallization will be shown as a general way to control optical properties in crystals.
63

The Effects Of Varying Plating Variables On The Morphology Of Palladium Nanostructures For Hydrogen Sensing Applications

Ortiz, Ophir 13 October 2004 (has links)
Present state-of-the-art hydrogen sensors are limited by a number of defects such as poisoning effects, slow response, and/or the range of concentrations that can be detected. Thus, hydrogen sensors are currently under investigation. In the search for the ultimate sensor, a variety of materials have been employed as the sensing layer. One of these materials is palladium. Palladium is widely used for hydrogen sensing due to its high selectivity and property of spontaneously absorbing hydrogen. Thin and thick film palladium hydrogen sensors have been reported, as well as palladium nanostructures. Specifically, palladium nanowires for hydrogen sensing have had improved results relative to other types of sensors; these have been reported with a response time down to 75ms and do not suffer from poisoning effects. Additionally, the fabrication of these nanostructures via electrodeposition is simple and cost efficient. For this reason, palladium nanostructures were chosen as the front-end for a novel hydrogen sensor. The nanostructures were to be employed as the sensing front-end of a Surface Acoustic Wave (SAW) sensor. It was theorized that the response time would be vastly improved if these were used as opposed to a thin or thick palladium film due to the decreased hydrogen diffusion distance, which is a result of the structures being one-dimensional. Because it was theorized that the dimensions of the nanostructures play an integral role in the response time to hydrogen, control of the morphology was required. This control was achieved by varying the plating variables in the electrodeposition experiments. The plating variables investigated were deposition potential, time, and counter-electrode area. The dimensions of the resulting nanostructures were measured via Scanning Electron Microscopy (SEM) and correlated to the conditions of the electrodeposition experiments. Nanowires under 40nm were successfully fabricated.
64

A Template-Based Code Generator for the OpenModelica Compiler

Lindberg, Rickard January 2010 (has links)
<p>A new, template-based code generator has been implemented for the OpenModelica compiler. All data needed for target code generation has been collected in a new data structure that is then sent to templates which generate target code based on that data. This simplifies the implementation of the code generator and also makes it possible to write a different set of templates to generate target code in a different language.</p><p>The new, template-based code generator currently only supports generation of target code for simulating Modelica models. In that scenario it translates models roughly at the same speed as the old code generator.</p>
65

High Density Single Crystalline GaN Nanodot Arrays Fabricated Using Template-Assisted Selective Growth

Wang, Yadong, Zang, Keyan, Chua, Soo-Jin, Fonstad, Clifton G. Jr. 01 1900 (has links)
High density, uniform GaN nanodot arrays with controllable size have been synthesized by using template-assisted selective growth. The GaN nanodots with average diameter 40nm, 80nm and 120nm were selectively grown by metalorganic chemical vapor deposition (MOCVD) on a nano-patterned SiO2/GaN template. The nanoporous SiO2 on GaN surface was created by inductively coupled plasma etching (ICP) using anodic aluminum oxide (AAO) template as a mask. This selective regrowth results in highly crystalline GaN nanodots confirmed by high resolution transmission electron microscopy. The narrow size distribution and uniform spatial position of the nanoscale dots offer potential advantages over self-assembled dots grown by the Stranski–Krastanow mode. / Singapore-MIT Alliance (SMA)
66

Standardizing Requirements Specification for IT Sourcing

Zeller, Martin, Hultgren, Eric January 2013 (has links)
This thesis considers standardizing service requirement specification for IT sourcing. The potential benefits a standardization of service requirements writing combined with Scania IT:s developing strategy have created a need for an investigation about how requirements standardization for IT sourcing could be done. This thesis is built upon three different approaches, requirements engineering, service oriented requirement engineering and best practices. Combined, these different approaches comprise the theory model RSB that will be used in the requirements standardization work. The strategies for collecting data, the authors choose embedded case study. The main problem at Scania IT regarding requirements specification in sourcing is the absence of a standard. The service requirements specifications varies in quality and execution, which causes communication problems. In order to standardize the requirements specification, the authors of this thesis have developed a standardization model consisting of three phases. A template is developed and presented in this thesis, the template is also included in the standardization phases model. The template created in this thesis, based on the RSB-model combined with the empirics, shows how a standard template can be designed. This study also suggests a three-phase model for working with standardization in the future. The standardization model suggest a requirements management software connected to a database.
67

A Template-Based Code Generator for the OpenModelica Compiler

Lindberg, Rickard January 2010 (has links)
A new, template-based code generator has been implemented for the OpenModelica compiler. All data needed for target code generation has been collected in a new data structure that is then sent to templates which generate target code based on that data. This simplifies the implementation of the code generator and also makes it possible to write a different set of templates to generate target code in a different language. The new, template-based code generator currently only supports generation of target code for simulating Modelica models. In that scenario it translates models roughly at the same speed as the old code generator.
68

Applying Knowledge Management to Requirement Analysis of Software Development

Chang, Chien-hung 01 September 2005 (has links)
How to create, classify, store and share the external and internal knowledge effectively will be the main competitive advantages of a company in the new era of knowledge economy. It is extremely important to the software industry, an industry that is highly intensive in both knowledge and human power. Requirement Analysis is the first phase in software development process and is an important development base for the other phases. Therefore, it becomes the key success factor for a software product. This paper proposes a requirement construction procedure. First, it expresses the users' important requirements through requirement capture and requirement transformation process, with related tables and interface blueprints. Secondly, it transforms the interface blueprints into abstract templates and meta-templates based on the abstraction of the interface blueprints through the requirement structure analysis procedure. Based on these templates and meta-templates, it can create a knowledge management framework using the special features of objects and encapsulation. Then, the requirement-knowledge is able to be stored, integrated and reused effectively. Lastly, this paper uses the ERP of steel industry in a software company as an example. It applies the knowledge modeling process of requirement analysis by a case demonstrated in practice. The result of this research provides the tables and templates for a company to create a requirement analysis knowledge management system. This system may help analysts to analyze requirements, and hopefully, reduce the time in software development and enhance the quality of software products.
69

Personal Workflow Systems in Support of Inter-process Integration

Tu, Jiun-Kai 21 July 2003 (has links)
In our daily lives, people constantly need to schedule their activities to meet their personal goals. Many of these activities involve the interaction with organization sectors, which must follow certain regulations in terms of input data, doable time and places. These regulations form personal processes. In previous work, [Chen01] proposed a personal process model that define a personal process as a set of tasks and a coordination on the tasks and a personal workflow system architecture. However, the proposed system is solely to facilitate a mobile user in deciding when, where, and how to process a task. We have noticed that many processes initiated by an individual often involve business processes coming from different organizations. Our objective in this thesis is to revise the personal process model proposed in [Chen01] by incorporating business processes existing in different sectors, developing a simpler query method, and extending personal workflow architecture in support of the new model. In our architecture, the management of personal processes involves three parties: the service provider, the template provider and the PWFMS. The service providers supply personal processes, each of which enable users to achieve a specific goal, and keep track of the status of executed tasks. The template providers incorporate several personal processes from different service providers and form a useful template for a user. The PWFMSs assist users in managing personal processes. In order to prove our idea, we implemented a prototype of the architecture.
70

Application of Template Update to Visual Servo for a Deformable Object

Chou, Cheng-te 04 August 2008 (has links)
A monocular visual servo system for a target with variable shape has been developed in this paper. It consists of two parts: an image-processing unit and a servo control unit. For the image-processing unit, the motion between the target and image center is determined by a template match approach. The image is grabbed by the camera equipped on a Pan-Tilt robot and the robot is controlled to track the target by maintaining the target on the image center. However, the template needs to be updated when the target deforms. For the servo control unit, the movement is estimated by the Kalman filter technique to enhance the tracking performance of the visual servo system.

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