• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 215
  • 69
  • 42
  • 33
  • 23
  • 14
  • 4
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 453
  • 453
  • 89
  • 88
  • 67
  • 63
  • 63
  • 46
  • 43
  • 40
  • 35
  • 31
  • 30
  • 29
  • 28
  • 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.
111

Studie av lågenergibyggnader inför projektering av nära-nollenergi förskolor / Study of low energy buildings in preparation of near zero energy preschool projects

Nilsson, Daniel, Hallberg, Vilhelm January 2016 (has links)
Purpose: Production and utilization of buildings contributes immensely to global carbon dioxide emissions. The construction sector today accounts for over a third of global energy use will increase as the world population increases. According to the EU Directive from 2010, all new buildings in EU member countries as of December 31, 2020 are to be classified as near-zero energy buildings (NZEB). The goal is to investigate the various energy-affecting measures of the involved architects, structural engineers and planners that can improve the energy performance of a kindergarten to be closer to near-zero and identify obstacles that make it more difficult to achieve NZEB. Method: The investigation strategies for the project are qualitative methods in the form of semi-structured interviews with architects, planners and ventilation engineers for six different kindergartens. The interviews were conducted by telephone in which the questions were sent in advance to those interviewed. Mail interviews were conducted early on which resulted in either short answers or not answers at all. The energy performance documents of the different kindergartens were analyzed to get information about the different energy performances. Findings: The result does not contain a solution as to what the near-zero energy definition is or how to define it, but is more like guidance concerning what factors you can influence to get closer to near-zero energy for a kindergarten. Recurring problems surfacing in the interviews is that not all the involved roles have been able to influence predetermined choices of shape and space that, among other things, contribute to a limited space for services that planners are having difficulty influencing afterwards. Implications: The result helps contribute to making sure buildings are built in a more energy-efficient way and by such reducing the construction sector's share of the global energy consumption. The building's energy efficiency may not contribute to poor indoor climate in such a way that it affects children's health in a negative manner. This results in a need for careful planning where all parties can contribute with their best energy efficiency solutions without being too limited by the architectural constraints of shape and space. Alternatively, better communication between planners and architects in the earlier stages. Good planning contributes to a better result. Limitations: The result is based on Swedish kindergartens in a Nordic climate and should not be applied in countries without a Nordic climate. The result is not only applicable to kindergartens but is largely applicable to most similar buildings. Contact with more architects, constructional engineers, planners and more kindergartens would have given a better result.
112

Nízkoenergetické stavby ako zdroj úspory energie / Low-energy buildings as a source of energy savings

Smoleňová, Daniela January 2009 (has links)
The issue of low energy construction is currently actual and often discussed topic. The main reason is continuously increasing consumption and price of energy. Additionally, projections show this trend is not going to rapidly change in the upcoming years. The construction of buildings in low energy standard should become one of the most significant sources in energy savings in European Union for the upcoming period. Low energy constructions in contrast with standard constructions are distinguished not only because of low energy consumption and lower operating expenses but also for its favorable impact on the environment. The main purpose of this thesis will be the assessment of economical effectiveness of current low energy constructions and underline the importance of energy saving constructions by using LCA method as one of the possibilities in increasing the quality of environment.
113

Nanoemulsões produzidas pelo método do ponto de inversão da emulsão (EIP) para encapsulação de curcumina: parâmetros de produção, estabilidade físico-química e incorporação em sorvete / Curcumin- loaded nanoemulsions produced by emulsion inversion point (EIP) method: process parameters, physico-chemical stability and incorporation in ice cream

Borrin, Thaís Ribeiro 13 July 2015 (has links)
A curcumina possui uma grande variedade de propriedades benéficas para a saúde humana. Devido a este fato, a indústria alimentícia tem aumentado a aplicação deste bioativo como aromatizante, conservante e aditivo para substituição dos corantes amarelos artificiais. No entanto, incorporar a curcumina em formulações alimentícias pode ser problemático porque sua molécula hidrofóbica tem baixa solubilidade em água e é muito sensível à luz. Os métodos de encapsulação em nanoemulsões podem tornar viável a proteção do curcuminoide, bem como permitir sua dispersibilidade em água. O objetivo do presente trabalho de Mestrado foi produzir nanoemulsões encapsulando curcumina pelo método do ponto de inversão da emulsão (EIP, emulsion inversion point), determinando parâmetros de operação que viabilizem um futuro escalonamento do processo e incorporação das dispersões em sorvete de massa sabor abacaxi. Os parâmetros de produção foram ajustados como: tipo e concentração de tensoativo (razão SOR), concentração de óleo de soja, tipo e concentração de cosolvente, tipo de impelidor/ velocidade de agitação e vazão de entrada da fase aquosa. As porcentagens de curcumina encapsulada foram 0,03, 0,07 e 0,10%. Dentre estas, a concentração de 0,07% foi a mais viável para a aplicação no sorvete de massa sabor abacaxi, por apresentar melhor distribuição de tamanho de gotícula (diâmetro hidrodinâmico), não apresentar variação significativa de oxidação lipídica, boa manutenção da curcumina encapsulada (70%) e, consequentemente, a sua cor, apresentando maior estabilidade do parâmetro TCD por um período de 60 dias. Os testes reológicos não mostraram mudança na estrutura de nanoemulsões com a encapsulação de curcumina. Das formulações testadas para sorvete de abacaxi contendo curcumina, a formulação usando nanoemulsões substituindo 50% da mistura comercial (B) teve uma maior aceitação de cor, sabor e aroma, sendo compatível com a formulação comercial (A). Esta formulação (B) e aquela com substituição completa da mistura comercial (C) apresentaram uma maior estabilidade quanto à manutenção da cor durante o período do estudo. Os testes reológicos não mostraram diferença estrutural entre as formulações testadas para sorvete de abacaxi. Indicando que não houve influência nas características estruturais do sorvete contendo nanoemulsão com curcumina encapsulada. / Curcumin has several beneficial properties and the food industry has been trying to increase the use of curcumin as flavoring, conservant or as a replacer of artificial yellow dyes. However, incorporating curcumin can be difficult due to its hydrophobicity and low water solubility, as well as high sensitivity to light. Encapsulation in nanoemulsions can be an interesting technological alternative to encapsulate and protect the curcuminoid. The objective of this study was to produce nanoemulsions encapsulating curcumin by the low-energy method EIP (emulsion inversion point), determining operating parameters that enable a future escalation of the process and incorporation of dispersions in pineapple ice cream. The production parameters were adjusted as: type and concentration of surfactante, soybean oil concentration, type and concentration of cosolvent, impeller type/speed stirring and flow of the aqueous phase. The percentages of encapsulated curcumin were 0.03, 0.07 and 0.10%. The concentration of 0.07% was the most viable for application in pineapple ice cream, for presenting better distribution of droplet size (hydrodynamic diameter), do not presente of significant changes in lipid oxidation, good maintenance of encapsulated curcumin (70%) and therefore its color, with greater stability of the TCD parameter for a period of 60 days. The rheological tests showed no change in the nanoemulsions structure with encapsulating curcumin. Among the formulations tested for pineapple ice cream incorporating encapsulated curcumin, the formulation using nanoemulsions replacing 50% of the commercial mixture (B) had a better acceptance of color, flavor and aroma and it is compatible with the commercial formulation (A). This formulation (B) and that with complete replacement of the commercial mixture (C) had a higher stability and maintenance of color during the storage period. The rheological tests showed no structural difference between the formulations tested for pineapple ice cream, indicating no influence on the structural characteristics of the ice cream containing nanoemulsion with encapsulated curcumin.
114

The activation of stable isotopes, their migration in soil and groundwater at a radionuclide production facility : a case study in Faure, Cape Town, South Africa

Marazula, Thandazile January 2018 (has links)
Thesis (MTech (Environmental Management))--Cape Peninsula University of Technology, 2018. / The iThemba Laboratory for Accelerator Based Sciences (iThemba LABS or iTL), a facility governed by the National Research Foundation (NRF) based in Cape Town has embarked on a project called the South African Isotope Facility (SAIF). Part of the SAIF will be a project called the Low Energy Radioactive Ion Beam (LERIB) for the production of radioactive beams with the Separated Sector Cyclotron (SSC). The LERIB project is anticipated to generate significant prompt sources of ionising radiation such as neutrons displaced by protons during bombardment of targets. At present, the facility has 3 - 5 m thick concrete walls designed to shield against 200 MeV neutrons. The floor thickness varies from each vault according to the behaviour and characteristics of the produced radiation. The LERIB facility concrete floor is envisioned to be 1 m thick. Insufficient floor shielding might expose the sub-surface strata below the floor with ionising radiation. Some matter in the exposed strata might undergo activation and consequently produce undesirable radioactive isotopes. Exposure to radioactive isotopes can pose potential risks to the general public and the receiving environment. In the sub-surface, the activated isotopes can spread through the soil and groundwater bodies. Groundwater being mobile in nature might act as conduit for activated isotopes to migrate in the subsurface. The half-lives of the formed radionuclides were used to estimate the distance the radionuclides can migrate in the sub-surface before decay. The X-Ray Fluorescence (XRF) and Inductive Coupled Plasma - Mass Spectrometry (ICP-MS) were used to quantify the mass fraction of elements from soil and groundwater samples. The Inductive Coupled Plasma - Optical Emission Spectrometry (ICP-OES) was used to measure dissolved metals of major and minor oxides in groundwater samples. These scientific techniques were applied in order to measure mass fractions of elements present in the sub-surface anticipated to be exposed with neutron radiation. Results revealed that the sub-surface in the study site constitutes Si, Al, Na and Fe in abundance. This suggests that, these elements might have a high probability to undergo activation compared to those occurring at lower concentrations, such as minor and trace elements. However the neutron capture cross-section for these elements varies and hence some elements such as Si and Al were not activated. To investigate elements measured from the ICP-MS, ICP-OES and XRF which might undergo activation, soil and water samples were irradiated for an hour with neutrons from a Beryllium target from a range of 0 – 66 MeV energy. The results revealed that activating the sub-surface with neutron radiation will result to the formation of short and long-lived unstable isotopes. However, isotopes with long half-lives such as 22Na, 52Mn, 54Mn and 46Sc only occurred in soil samples and none measured from the water samples except a short-lived isotope 24Na. These results agrees with the reviewed literature that, water being a product of two hydrogens and one oxygen, with 1H from H2O considered to be a good neutron moderator should have absorbed the neutrons so as to reduce neutron capture cross-sections.
115

Electronic Structure and Surface Physics of Two-dimensional Material Molybdenum Disulfide

Jin, Wencan January 2017 (has links)
The interest in two-dimensional materials and materials physics has grown dramatically over the past decade. The family of two-dimensional materials, which includes graphene, transition metal dichalcogenides, phosphorene, hexagonal boron nitride, etc., can be fabricated into atomically thin films since the intralayer bonding arises from their strong covalent character, while the interlayer interaction is mediated by weak van der Waals forces. Among them, molybdenum disulfide (MoS₂) has attracted much interest for its potential applications in opto-electronic and valleytronics devices. Previously, much of the experimental studies have concentrated on optical and transport measurements while neglecting direct experimental determination of the electronic structure of MoS₂, which is crucial to the full understanding of its distinctive properties. In particular, like other atomically thin materials, the interactions with substrate impact the surface structure and morphology of MoS₂, and as a result, its structural and physical properties can be affected. In this dissertation, the electronic structure and surface structure of MoS₂ are directly investigated using angle-resolved photoemission spectroscopy and cathode lens microscopy. Local-probe angle-resolved photoemission spectroscopy measurements of monolayer, bilayer, trilayer, and bulk MoS₂ directly demonstrate the indirect-to-direct bandgap transition due to quantum confinement as the MoS₂ thickness is decreased from multilayer to monolayer. The evolution of the interlayer coupling in this transition is also investigated using density functional theory calculations. Also, the thickness-dependent surface roughness is characterized using selected-area low energy electron diffraction (LEED) and the surface structural relaxation is investigated using LEED I-V measurements combined with dynamical LEED calculations. Finally, bandgap engineering is demonstrated via tuning of the interlayer interactions in van der Waals interfaces by twisting the relative orientation in bilayer-MoS₂ and graphene-MoS₂-heterostructure systems.
116

Hyperchanneling of low energy ions on the platinum(111) and gold(110) surfaces and ion scattering spectrometry of ferroelectric lithium tantalate. / Hyperchanneling of low energy ions on the Pt(111) and Au(110) surfaces and ion scattering spectrometry of Ferroelectric LiTaO3 / CUHK electronic theses & dissertations collection

January 2002 (has links)
"May 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.
117

Optimisation of timber frame closed panel systems for low energy buildings

Amigo, Jesus Menendez January 2017 (has links)
The United Kingdom published a legally binding document to reduce national greenhouse gas emissions by year 2020 up to 34% against the 1990 levels. This target also fulfils the Europe 2020 strategy of 20% carbon emission reductions by year 2020 (EC, 2010). Emissions due to space heating count for around 60% of the total domestic emissions (DCLG, 2012). The report “Rethinking Construction” published in 1998 emphasised the opportunities to improve the quality and efficiency of the UK construction sector (Egan, 1998). More recently, a framework has been published by the Government to tackle fuel poverty by building more energy efficient homes (DECC, 2015). In terms of energy performance, Passivhaus is recognised as one of the most energy efficient and researched construction standards which requires an exceptionally high-level of insulation and airtightness. Closed-panel timber frames are a relatively new system in UK with an opportunity for growth. These advanced panels are pre-fitted in the factory, reducing the on-site work. However, closed-panel systems present a more complex sole plate fixing detail which can have an undesirable long-term impact on the structural and thermal performance of the building. The work presented in this thesis investigates the structural considerations, racking performance, of timber frame closed panel systems for future building regulations. The thesis underlines the significance of structural stability, serviceability and detailing in relationship with long-term thermal efficiency and airtightness, according to Passivhaus standard. An experimental study was carried out to investigate the structural racking performance of advanced closed panel systems. A comparison was made between the behaviour of the timber frame panels and the analytical PD 6693-1. A set of different wall panel built-ups is presented for optimised Passivhaus design, including thermal bridge-free sole plate details. A timber frame racking software application was developed to optimise the structural design of shear walls. A parametric study was carried out with this tool to generate efficient timber frame wall design tables for different applied racking loads and U-values. The software application also allows for direct specification of robust sole plate base fixings and thermal bridge free details.
118

Reordering at the gas-phase polysulfide-passivated InP and GaAs surfaces.

January 1996 (has links)
by So King Lung, Benny. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 102-109). / ABSTRACT --- p.v / ACKNOWLEDGEMENTS --- p.vii / LIST OF FIGURES --- p.viii / LIST OF TABLES --- p.xiii / Chapter Chapter 1 --- Background of the study --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Surface passivation techniques --- p.3 / Chapter 1.2.1 --- Sulfide solution passivation --- p.3 / Chapter 1.2.2 --- Gas-phase sulfide passivation --- p.4 / Chapter 1.3 --- Surface structure of sulfide-passivated surface --- p.5 / Chapter 1.4 --- Objectives of the present study --- p.7 / Chapter Chapter 2 --- Instrumentation --- p.9 / Chapter 2.1 --- Introduction --- p.9 / Chapter 2.2 --- X-ray photoelectron spectroscopy (XPS) --- p.9 / Chapter 2.2.1 --- The development of XPS --- p.9 / Chapter 2.2.2 --- Basic principle of XPS --- p.9 / Chapter 2.2.3 --- Quantitative analysis of XPS --- p.14 / Chapter 2.2.3.1 --- Atomic concentration of a homogenous material --- p.14 / Chapter 2.2.3.2 --- Layer structure --- p.15 / Chapter 2.2.3.3 --- Simulation of XPS atomic concentration ratios from proposed surface structural models --- p.17 / Chapter 2.2.4 --- XPS experiment --- p.19 / Chapter 2.3 --- Low energy electron diffraction (LEED) --- p.21 / Chapter 2.3.1 --- The development of LEED --- p.21 / Chapter 2.3.2 --- Basic principle of LEED --- p.23 / Chapter 2.3.3 --- LEED experiment --- p.28 / Chapter 2.3.3.1 --- The ultra high vacuum chamber (UHV) --- p.28 / Chapter 2.3.3.2 --- The electron gun --- p.28 / Chapter 2.3.3.3 --- The sample --- p.30 / Chapter 2.3.3.4 --- The detector system --- p.30 / Chapter Chapter 3 --- Surface treatments --- p.31 / Chapter 3.1 --- Semiconductor wafers --- p.31 / Chapter 3.2 --- Cleaning procedure --- p.31 / Chapter 3.3 --- Polysulfide passivation --- p.33 / Chapter Chapter 4 --- Gas-phase polysulfide passivation of the InP(100) surface --- p.37 / Chapter 4.1 --- Introduction --- p.37 / Chapter 4.2 --- Sulfide-assisted reordering at the InP(100) surface --- p.38 / Chapter 4.2.1 --- Gas-phase polysulfide-treated InP( 100) surface --- p.38 / Chapter 4.2.2 --- Further annealing of the gas-phase polysulfide-treated surface --- p.47 / Chapter 4.2.3 --- Comparison with the UV/O3-HF treatment --- p.48 / Chapter 4.2.4 --- Sulfide at the interface of SiNx/InP --- p.49 / Chapter 4.3 --- Conclusions --- p.53 / Chapter Chapter 5 --- Gas-phase polysulfide passivation of the GaAs(lOO) surface --- p.55 / Chapter 5.1 --- Introduction --- p.55 / Chapter 5.2 --- Gas-phase poly sulfide-passivated GaAs( 100) surface --- p.56 / Chapter 5.2.1 --- Surface structure of the as-treated surface --- p.56 / Chapter 5.2.2 --- Surface structure after further annealing --- p.64 / Chapter 5.2.3 --- Mechanism of the gas-phase polysulfide passivation --- p.67 / Chapter 5.3 --- Conclusions --- p.68 / Chapter Chapter 6 --- Gas-phase polysulfide passivation of the GaAs(100) surface --- p.69 / Chapter 6.1 --- Introduction --- p.69 / Chapter 6.2 --- Reordering at the gas-phase polysulfide-passivated GaAs(100) surface --- p.70 / Chapter 6.2.1 --- Adsorption of polysulfide on the GaAs(100) surface --- p.70 / Chapter 6.2.2 --- Ordered sulfide at the GaAs(l 10) surface --- p.73 / Chapter 6.2.3 --- Further analysis of the LEED pattern --- p.80 / Chapter 6.3 --- Conclusions --- p.83 / Chapter Chapter 7 --- Sulfide Solution passivation of the GaAs(100) surface --- p.84 / Chapter 7.1 --- Introduction --- p.84 / Chapter 7.2 --- Sulfide solution passivation on the GaAs(l 10) surface --- p.85 / Chapter 7.2.1 --- Etching of sulfide solution on the GaAs(l 10) surface --- p.85 / Chapter 7.2.2 --- Annealing of sulfide solution-passivated GaAs( 110) surface --- p.88 / Chapter 7.2.3 --- Further analysis of the LEED pattern --- p.92 / Chapter 7.2.4 --- Shift of XPS peak position during annealing --- p.95 / Chapter 7.3 --- Conclusions --- p.97 / Chapter Chapter 8 --- Conclusions and further work --- p.99 / Chapter 8.1 --- Conclusions --- p.99 / Chapter 8.2 --- Further work --- p.100 / References --- p.102
119

Molecular Dynamics Studies of Low-Energy Atom Impact Phenomena on Metal Surfaces during Crystal Growth

Adamovic, Dragan January 2006 (has links)
It is a well-known fact in the materials science community that the use of low-energy atom impacts during thin film deposition is an effective tool for altering the growth behavior and for increasing the crystallinity of the films. However, the manner in which the incident atoms affect the growth kinetics and surface morphology is quite complicated and still not fully understood. This provides a strong incentive for further investigations of the interaction among incident atoms and surface atoms on the atomic scale. These impact-induced energetic events are non-equilibrium, transient processes which complete in picoseconds. The only accessible technique today which permits direct observation of these events is molecular dynamics (MD) simulations. This thesis deals with MD simulations of low-energy atom impact phenomena on metal surfaces during crystal growth. Platinum is chosen as a model system given that it has seen extended use as a model surface over the past few decades, both in experiments and simulations. In MD, the classical equations of motion are solved numerically for a set of interacting atoms. The atomic interactions are calculated using the embedded atom method (EAM). The EAM is a semi-empirical, pair-functional interatomic potential based on density functional theory. This potential provides a physical picture that includes many-atom effects while retaining computational efficiency needed for larger systems. Single adatoms residing on a surface constitute the smallest possible clusters and are the fundamental components controlling nucleation kinetics. Small two-dimensional clusters on a surface are the result of nucleation and are present during the early stages of growth. These surface structures are chosen as targets in the simulations (papers I and II) to provide further knowledge of the atomistic processes which occur during deposition, to investigate at which impact energies the different kinetic pathways open up, and how they may affect growth behavior. Some of the events observed are adatom scattering, dimer formation, cluster disruption, formation of three-dimensional clusters, and residual vacancy formation. Given the knowledge obtained, papers III and IV deal with growth of several layers with the aim to study the underlying mechanisms responsible for altering growth behavior and how the overall intra- and interlayer atomic migration can be controlled by low-energy atom impacts. / <p>On the day of the defence date the status of article II was Accepted.</p>
120

Investigating the Gamma-ray Strength Function in 74Ge using the Ratio Method

Sowazi, Khanyisa January 2018 (has links)
>Magister Scientiae - MSc / An increasing number of measurements reveal the presence of a low-energy enhancement in the gamma-ray strength function (GSF). The GSF, which is the ability of nuclei to absorb or emit rays, provides insight into the statistical properties of atomic nuclei. For this project the GSF was studied for 74Ge which was populated in the reaction 74Ge(p,p')74Ge* at a beam energy of 18 MeV. The data were collected with the STARS-LIBERACE array at Lawrence Berkeley National Laboratory. Silicon detector telescopes were used for particle identi cation and rays in coincidence were detected with 5 clover-type high-purity germanium detectors. Through the analysis particle- - coincidence events were constructed. These events, together with well-known energy levels, were used to identify primary rays from the quasicontinuum. Primary rays from a broad excitation energy region, which decay to six 2+ states could be identi ed. These states and the associated primary rays are used to measure the GSF for 74Ge with the Ratio Method [1], which entails taking ratios of e ciency-corrected primary -ray intensities from the quasicontinuum. Results from the analysis of the data and focus on the existence of the low-energy enhancement in 74Ge will be discussed. The results are further discussed in the context of other work done on 74Ge using the ( , ') [2], (3He,3He') [3] and ( , ') [4] reactions.

Page generated in 0.0388 seconds