• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 7502
  • 5679
  • 2412
  • 1647
  • 1617
  • 506
  • 385
  • 321
  • 267
  • 256
  • 207
  • 157
  • 153
  • 132
  • 127
  • Tagged with
  • 24248
  • 3199
  • 3191
  • 2698
  • 2168
  • 1598
  • 1506
  • 1497
  • 1463
  • 1334
  • 1277
  • 1250
  • 1231
  • 1223
  • 1181
  • 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.
271

Integrated and multi-period design of diesel hydrotreating process

Ahmad, Muhammad Imran January 2009 (has links)
Hydrotreating processes play a vital role in petroleum refineries to meet the increasing demand of transportation fuels. The recent trends in processing of heavier crudes with higher sulphur contents and more stringent product specifications for cleaner transportation fuels, such as ultra-low sulphur diesel, are resulting in more severe operating conditions and higher hydrogen consumption of hydrotreating processes. In order to carry out any revamp or design projects for improving the performance and efficiency of hydrotreating units molecular kinetic models of hydrotreating reactions may be required to provide detailed and accurate information of the composition and properties of hydrotreating products. The overall hydrotreating process consisting of the hydrotreater, the separation system and the associated heat recovery system need to be modelled on a consistent basis of detailed characterisation of petroleum fractions and the interactions of these individual subsystems with each other and with the refinery hydrogen network handled simultaneously for overall process optimisation. A molecular pathways level model of diesel hydrotreating reactions using the molecular type and homologous series matrix is employed for prediction of detailed molecular level information of composition and properties of diesel hydrotreating products. The molecular type and homologous series matrix representation of petroleum fractions is a detailed characterisation approach that represents the composition of a stream in a matrix in terms of the carbon number range and compound classes existing in the petroleum fraction. A new strategy is developed for estimation of physical properties of middle distillate and heavy petroleum fractions with molecular type and homologous series matrix representation using group contribution methods.
272

A spectral Lagrange-Galerkin method for convection-dominated diffusion equations

Ware, Antony Frank January 1991 (has links)
No description available.
273

Monopoles on 3-manifolds

McAllister, Ian January 1995 (has links)
No description available.
274

A theory of learning and personal development based on a double helix model

Robinson, Margret D. H. January 1987 (has links)
No description available.
275

Carbon allocation in barley plants

Farrar, S. C. January 1985 (has links)
No description available.
276

Studies in process analysis and control in batch reactors

Diez-Lazaro, Alvaro January 2002 (has links)
This work is part of a number of projects dealing with the development of novel techniques for better analysis and control of chemical processes carried out in batch reactors. The problems of pH measurement and sampling, linked to the implementation of NMR and HPLC on-line analysers, are presented as key areas in this development work. Also, part of the engineering work summarised in this thesis assisted the work of other researchers who participated in the project. In the area of sampling, the difficulties associated with the collection of representatives samples from agitated vessels are introduced. Also, the ideas of calibration and modelling of sampling systems are presented. Modelling tests were used to optimise the design and development of a fast sampling loop system to obtain representative samples from stirred vessels. In addition to this, the modelling studies also assisted the work of other researchers in the project who needed the kinetic and heat-exchange parameters for the process of esterification of crotonic acid. The fast sampling loop was shown to be adequate for the implementation of a low-field NMR system for on-line analysis. The development of discrete samplers designed to collect, dilute and deliver representative samples for LC analysis is also covered in this work. A Mark IV prototype of LC sampler was tested and developed to acceptable levels. In the area of pH measurement the advantages and disadvantages of the use of thermally grown iridium-oxide electrodes are introduced. Their response was compared to that of standard glass electrodes and found to be faster, more stable at high temperatures and no alkaline error was observed. However, the problem of drift of the signals was not fully overcome and it is presented as the limiting factor in the use of the sensors for on-line industrial measurements. Finally, a new type of total iridium-oxide probe is presented.
277

Secondary materials in water treatment

Välikangas, T. (Taru) 13 February 2017 (has links)
In the World the availability of the clean drinking water is a serious problem. The appearance of this problem is different in developed and developing countries. Even though water treatment technologies are widely studied and improved, the developing countries do not have the same economic capacities to utilize the sufficient treatment methods. This thesis concentrates on the utilization of secondary materials in water treatment as adsorbents. These materials are potential for the low-cost treatment of water. For the testing of the secondary materials, two pollutants were chosen as model compounds: organic pharmaceutical diclofenac and inorganic arsenic As(V), since they have been recognized to be problematic in water treatment. Two industrial by-products were chosen as secondary materials to be tested as adsorbents. Sachtofer is a by-product from titanium dioxide TiO2 production and Red mud is a waste material originating from aluminium oxide Al2O3 production. Third material tested was sand from Brazil obtained via cooperation with the Federal Institute of Goias in Goiania, Brazil. In this thesis a commercial adsorbent CFH-12 (Kemira) was chosen as a reference material. The literature part of the thesis contains theoretical considerations on the utilization of adsorption in water treatment. In addition the effect of organic and inorganic impurities in water bodies are discussed in a general level. The experimental part of the thesis presents first the characterization results of the secondary materials. The specific surface areas (BET) were measured for all the secondary materials. The surface structures were studied with scanning electron microscopy (SEM). For some of the adsorbents, the pH of the point of zero charge was determined as well as the elemental composition with XRF. One part of this thesis concentrated on studying the effect of pre-treatment on the adsorption efficiency of the materials. In this case, the adsorption materials were washed with distilled water and treated with hydrochloric acid. The adsorption experiments were carried out as batch experiments. Diclofenac concentration during the experiments was analyzed with spectrophotometry and HPLC. The best removal, i.e. 16% of diclofenac was achieved with HCl-activated Brazilian sand. With Red mud the HCl-activated sample was the most effective with 8% removal. The HCl-activated Sachtofer removed only 4% of diclofenac. The change in the arsenic concentration during the experiments was analyzed by ICP-MS. With Sachtofer, all three pre-treated samples removed 100% of arsenic. All Red mud and Brazilian sand samples were able to remove arsenic in significant amount. Though, after HCl-activation, the removal of arsenic was higher giving 98% for Red mud and 100% for the Brazilian sand. The diclofenac removal was assumed to be difficult and the 16% removal was a quite good result. The problem seems to be too high pH. By adjusting pH to a lower level, the higher removal efficiency might be achievable. All arsenic removal results were promising, and with all the material samples the removal was higher than 90%. These results confirm that the secondary materials are potential adsorbents for in water treatment. With certain adsorbents, the removal was high even without any pre-treatment. This is economically interesting possibility that should be studied more, especially due to the possibility of improving the water treatment in developing countries. / Puhtaan juomaveden puute on todellinen ongelma maailmassa. Se on ongelma jossa erityisesi kehittyvät ja kehittyneet maat ovat eriarvoisessa asemassa. Vaikka vedenpuhdistusprosesseja tutkitaan paljon ja ne ovat pitkälle kehittyneitä, ei kehittyvillä mailla ole välttämättä taloudellisia resursseja hyödyntää riittävää vedenpohditus tekniikkaa. Tässä työssä on tutkittu kierrätysmateriaalien hyötykäyttöä adsorbentteinä vedenpuhdistuksessa. Puhdistettaviksi malliaineeksi valittiin orgaaninen lääkeaine diklofenakki sekä epäorgaaninen arseeni As(V), koska niiden on havaittu aiheuttavan ongelmia nykyisissä vedenpuhdistusprosesseissa. Adsorptiomateriaaleina tässä työssä käytettiin teollisuuden sivutuotteina syntyneitä Sachtoferia joka on titaanidioksidin valmistuksen sivutuote, sekä punaliejua, joka alumiinioksidin valmistuksessa syntynyttä jätemateriaalia. Kolmantena materiaalina testattiin Brasilialaista -hiekkaa, jota saatiin tutkimustarkoituksiin yhteistyön kautta, Federal Institute of Goias, Goiania, Brasilia toimittamana. Työhön haluttiin valita myös yksi kaupallinen adsorptiomateriaali joka toimisi referenssimateriaalina, ja tämän vuoksi valitsimme adsorptiomateriaaliksi Kemiran CFH-12 -tuotteen. Työn kirjallisuus osiossa selvitetään adsorption teoriaa sekä sen hyödyntämistä vesienpuhdistuksessa. Myös orgaanisen ja epäorgaanisten haitta-aineiden vaikutuksia veden laatuun tarkastellaan yleisellä tasolla. Kokeellisen osan alussa työssä käytettyjen adsorbenttien ominaisuuksia tutkittiin erilaisilla menetelmillä, joilla arvioitiin materiaalien kykyä adsorboida malliaineita. Materiaaleille määritettiin mm. pH jossa materiaalin pintavaraus on nolla (point of zero charge). Lisäksi materiaaleille tehtiin BET-analyysi ominaispinta-alan selvittämiseksi ja niiden pintaa ja rakennetta tutkittiin elektronimikroskoopilla. Osalle aineista tehtiin myös alkuaineanalyysi. Työssä haluttiin myös tutkia vaikuttaisiko materiaalien esikäsittely adsorptiotehokkuuteen. Tämän vuoksi adsorptiomateriaaleja pestiin tislatulla vedellä sekä käsiteltiin suolahapolla. Adsorptiokokeet toteutettiin laboratoriomittakaavassa panoskokeina. Diklofenakin pitoisuutta seurattiin kokeen aikana spektrofotometrillä sekä HPLC analyysi menetelmällä. Paras tulos diklofenakin poistossa saatiin HCl -aktivoidulla Brasilialaisella hiekalla, jolloin poistuma oli 16 %. Punaliejulla käsitellyistä näytteistä paras poistuma, 8 %, saatiin myös HCl -aktivoidulla näytteellä. HCl -aktivoidulla Sachtoferilla poistuma oli vain 4 %. Arseenin pitoisuuden muutosta kokeen aikana analysoitiin ICP-MS menetelmällä. Kaikkilla kolmella Sachtofer -näytteellä arseenin poistuma oli 100 %. Kaikki punalieju ja Brasilialainen hiekka näytteet adsorboivat arseenia merkittävästi. Kuitenkin HCl -käsitellyillä näytteillä poistuma oli paras, punaliejulle 98 % ja Brasilialaiselle hiekalle 100 %. Diklofenakin poistamisen vedestä oletettiin olevan haastavaa, ja saavutettu 16 % poistuma oli hyvä tulos. Ongelmana diklofenakin poistossa oli todennäköisesti liian korkea pH ja mikäli pH:ta onnistutaan säätämään enemmän happamaksi, poistuma voisi olla korkeampi. Arseenin adsorptio kokeiden tulokset olivat todella lupaavia, ja kaikilla materiaaleilla poistuma oli vähintään 90 %. Näiden tulosten perusteella voidaan todeta että kierrätysmateriaalit ovat hyvin potentiaalinen vaihtoehto vedenkäsittelyadsorbenteiksi. Osa materiaaleista toimi arseenin poistossa tehokkaasti myös ilman esikäsittelyä. Tämä on taloudelliselta kannalta mielenkiintoinen tulos, jota tulisi tutkia lisää, erityisesti kehittyvien maiden vedenpuhdistuksen tehokkuuden parantamiseksi.
278

The Time and Process used to write a Case Study

Herfors, David January 2016 (has links)
The time and process used to write a case study depends on several factors. There are different things to consider to save time and to make the process easier. First of all the author might need a certain skillset and experience. Second is to understand the importance of being prepared. It takes much time to write a case study and if the preparations are not taken in seriously consideration it may jeopardize the whole study. A deadline and timeline for the process is necessary to control the outcome. Normally the process involves a case study release form and a success letter where the last approval is made before the publication of the case study is done.
279

The Development of Criteria for the Design of an Ideal Environment for Interpretation

Elkins, William David 12 1900 (has links)
The problem with which this study was concerned was the development of criteria for design of an environment for interpretation. The study analyzed the art of interpretation as a communicative process, derived criteria for design from the spatial requirements indicated by the analysis, and presented a sample design based on the criteria.
280

Product Management: the Decision Process

Pahl, Shane D. 05 1900 (has links)
This thesis builds upon several theoretical ideas. The first of which is the anthropologists’ transition into the corporate context and the particular type of skills and value that someone with anthropological training can bring to operations management. As anthropology is relatively new and unfamiliar to corporations, anthropologists are often hired without explicit knowledge of how they will address organizational problems. Frequently, this incremental relationship building between the anthropologist and the organization leads to shifting project goals which come only after the anthropologist is able to reveal initial findings to someone who has the power to grant the anthropologist further access to employees and company information. This refocusing comes from a building of trust that is crucially important for the anthropologist’s ability to identify social issues, which is the anthropologist’s expertise. In order to develop the context of this project the following paragraphs will explain in more detail and expand into particular cases in which anthropologists have helped organizations to identify and manage social, organizational problems. As a relationship needs to be built between the anthropologist and the organization, here I argue that there needs to be continual relationship building between anthropological, design, and management theories to optimally solve organizational problems.

Page generated in 0.0907 seconds