• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 3100
  • 1587
  • 348
  • 316
  • 300
  • 275
  • 155
  • 67
  • 67
  • 54
  • 48
  • 47
  • 45
  • 45
  • 45
  • Tagged with
  • 7558
  • 2185
  • 1429
  • 964
  • 841
  • 832
  • 754
  • 753
  • 559
  • 497
  • 463
  • 435
  • 415
  • 414
  • 400
  • 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.
131

Solar House

Nawas, Yousef Ibrahim 01 April 2004 (has links)
The Solar House is an investigation that resulted from an inter-disciplinary, design built competition ( the Solar Decathlon). This event was sponsored by the U.S. Department of Energy in an atempt to integrate architecture, technology, and dwelling. The investigation focused on making a house using matter as a conduit to the spiritual, by emphasising two different natures in contrasting conditions. At the same time inclusive of all the technological aspects of a building that operates on solar energy, embedded with the complexities of building systems and new materials. / Master of Architecture
132

Chemical bath deposition of II-VI compound thin films

Oladeji, Isaiah Olatunde 01 January 1999 (has links)
No description available.
133

Optimisation, design, development, and trial of a low-cost solar oven with novel concentrator geometry

Berryman, Ian January 2016 (has links)
A promising and novel solar concentrator design has been thoroughly investigated and optimised. A prototype concentrator based on this novel geometry was validated using ray tracing techniques. This ray tracing demonstrated the comparative performance of this novel concentrator in regards to equivalent parabolic dishes. The effect of mirror surface normal errors on performance was established using Monte-Carlo based ray tracing code, which agreed well with the optical performance of this prototype which was determined experimentally. A need for low-cost solar cookers to replace bio-mass worldwide was identified, and the concentrator design was then developed as a low-cost solar oven. Despite existing in some number, no current design is able to achieve high performance at low-cost. An industrial partner, Dytecna, was initially involved in the process of this development of the system as a solar cooker. In support of a field trial for the solar cooker developed with Dytecna, a detailed thermal model of the oven was developed. A low-cost lightmeter was constructed and calibrated in order to measure the direct normal irradiance during the field trial in Italy. Laboratory work provided baseline results for the heating of various thermal masses in the oven. The Italian field trials provided a wealth of feedback into the design of the system and many valuable results. The solar cooker was able to bring 0.75L of water to the boil in 33 minutes with an average heat throughput of 203W. Important benchmark results and practical experience of several competing receiver materials was obtained; further lab testing provided more accurate measurements of the receivers' performances. The experiences of the Italian field trial were fed back into the design of a subsequent prototype, intended for a much larger field trial in Tanzania. Improvements in the hotplate, receiver material, and the oven were all incorporated into the design. Additionally, the structure of the solar cooker was redesigned to incorporate a low-cost wooden construction. Supporting work was conducted for the month long trial in which 8 solar cookers would be distributed to families in Tanzania. The field trial in Tanzania provided a wealth of user feedback into the design. At the same time the new solar cooker exceeded previously established performances in Italy. The new design was able to provide an average of 246W of heat to 1kg of water, which was brought to boiling point in 25 minutes. This represents a heating efficiency of 66% compared to the incident solar flux on the hotplate. In response to findings during the Tanzanian trials, further laboratory work was conducted into establishing the reflectivities of low-cost candidate mirror materials. Throughout all phases of the project the design of the solar cooker was refined and improved with the goal of a solar cooker design that could reach price-point, performance, and usability standards which would ensure market success.
134

Performance studies of a working solar home

Bryan, Austin David January 1977 (has links)
Thesis. 1977. M.Arch.--Massachusetts Institute of Technology. Dept. of Architecture. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCH. / Bibliography : p. 89. / by A. David Bryan. / M.Arch.
135

The impact of sunspot rotation on solar flares

Walker, Andrew Philip January 2018 (has links)
Solar flares are one mechanism to release stored magnetic energy in the Sun’s atmosphere. This thesis aims to determine whether sunspot rotation can inject the energy required for solar flares into the corona. This thesis investigates the relationship between sunspot rotation and solar flares, and the impact that sunspot rotation has on the strength and frequency of flare events. A robust analysis tool is developed which uses continuum images of the Sun to determine the rotation of sunspots. This tool is used throughout the thesis, first on the active region 11158, in an in-depth case study of the rotation and flaring properties of the region as it traverses the solar disc. The case study develops analysis techniques, such as introducing sunspot selection criteria, which are used in the following statistical studies. The first statistical study involves the analysis of the rotation and flaring properties of a sample of all sunspots that meet the selection criteria within all X-class flaring regions since the launch of the Solar Dynamics Observatory. As this first statistical study is biased towards higher flare-energy active regions, a second unbiased statistical study is carried out on all sunspots that meet the sunspot selection criteria between 1 May 2013 and 31 August 2013. The results of these statistical studies are combined and analysed, concluding that sunspot rotation injects enough energy (and in the majority of cases, an excess of energy) to account for the energy output by solar flare radiation. On average, the radiated bolometric flare energy outputs 65.6% of the injected energy due to the absolute sunspot rotation for the X-class flare sample, and 59.2% for the four-month sample.
136

False alarms in the forecasting of Solar Energetic Particle events

Swalwell, Bill January 2018 (has links)
Solar Energetic Particles (SEPs) are known to be accelerated by high-energy events in the Sun's corona: coronal mass ejections (CMEs) with high speed, solar flares with high peak emission in soft X-rays, or a combination of the two. SEPs, however, are not detected following all fast CMEs or intense flares. Those large solar events, which might reasonably have been expected to produce SEPs at Earth but which failed to do so, may be termed “false alarms”. In this work, two simple SEP forecasting algorithms are defined: one (algorithm A.1) is based upon the observation of a magnetically well-connected CME with a speed of 1,500 km/s or greater (a ``fast CME''), and the other (algorithm A.2) is based upon the observation of a magnetically well-connected X class flare. The algorithms were applied to historical data sets to ascertain which produced an enhancement of >40 MeV protons, and which were false alarms. The algorithms have been evaluated using standard verification scores. Both algorithms correctly forecast approximately the same percentage of SEP events (47% and 49% respectively); the false alarm ratio for algorithm A.1, however, was much lower than for A.2 (29% and 51% respectively). Both algorithms failed to forecast almost the same number of SEP events (53% for A.1, and 51% for A.2). The parameters of the false alarms were compared to those of the SEP-producing events. False alarm fast CMEs tended to be associated with flares of class less than M3; X class flares which were either not associated with any CME, or were associated with a CME slower than 500 km/s, were false alarms. A third forecasting algorithm, based upon these results, was defined. This algorithm, which takes into account parameters of both CMEs and flares, performed better than either A.1 or A.2, correctly forecasting a significantly greater percentage of SEP events than both (68%), having a false alarm ratio similar to A.1 (30%), but missing a significantly lower percentage (32%) of SEP events. A small number of case studies were carried out. It was found that for accurate forecasting of SEP events it may not be sufficient simply to consider the accelerating events, but that the location of the heliospheric current sheet relative to the site of the solar event and of the Earth's footpoint may be an important consideration. SEP forecasts produced by the SPARX simulation were evaluated with a view to providing a benchmark against which future versions of the model may be tested.
137

Three-dimensional topology of the magnetic field in the solar corona

Lee, Daniel Thomas January 2018 (has links)
This thesis investigates the topology of the magnetic field in the solar corona, due to a variety of source configurations and types. To fully understand the complex behaviour of the Sun's magnetic field, it is important to have a complete description of the features present in its structure. The magnetic topologies due to network source configurations are investigated using both the point source description and the continuous source description. A series of case studies involving an emerging bipole in a hexagonal arrangement to simulate a supergranular cell are studied. This has a particular focus on the behaviour of coronal nulls located in the topology, and a particular case may form the underpinning of a model for polar plumes. A new topological feature, called a null-like point, is defined by relaxing the definition of a magnetic null point. Separatix-like surfaces, originating from null-like points, allow quasi-separatrix layers to be found in magnetic topologies due to continuously distributed sources. The squashing factor, Q, is mapped across the source configuration, highlighting the locations of the quasi-separatrix layers. Finally, an algorithm is developed which automatically detects and classifies magnetic events local to X-ray bright points (XBPs). Significant peaks are identified in the gradients of flux curves (positive, negative and absolute flux) local to XBP footpoints, allowing instances of flux emergence and cancellation to be identified and linked to the onset and demise of the XBPs studied. The algorithm correctly classifies 90% of all emergence and cancellation events related to the studied XBPs.
138

Alternative back contact for CIGS solar cells built on sodium-free substrates

Söderström, Wilhelm January 2011 (has links)
It is widely known that the element sodium plays a vital role in providing highefficiency CIGS solar cells and that when cells are built on sodium free substrates theyneed an alternative (a substitute) sodium source. In this study a molybdenum-sodiumcompound has been deposited, investigated and evaluated as an alternative backcontact layer containing sodium. The compound had a 5 at % sodium concentrationand it was manufactured by an Austrian company called Plansee. The aim of the studywas to create an equivalent back contact in the sense of sodium delivery, conductivityand adhesion compared to a normal molybdenum back contact on a soda lime glass. The experimental part of the study started with the construction of complete cells,which were fabricated and measured. This work took place at the ÅngströmLaboratory, Uppsala University, Sweden. The characteristics of the layer and the cellswere analyzed by current voltage measurements, quantum efficiency measurementsand secondary ion mass spectrometry analysis. Cell manufacturing involved sputtering,co evaporation and chemical deposition processes. Results show that the molybdenum-sodium compound increases the efficiency of acell built on a sodium-free substrate. Efficiencies reached 8 % for cells without sodiumin the molybdenum and these cells produced 67 % efficiency and 80 % open circuitvoltage of the reference value. Cells with sodium in the back contact layer produced90 % of the efficiency and 95% of the open circuit voltage relative to the references.The best cell with the molybdenum-sodium compound reached an efficiency of 13.3%. This implies that the new back contact layer acts as a sodium source but the cellshave 1-2 % lower efficiency than the reference cells built on soda lime glass. Othercharacteristics of the layer as conductivity and adhesion show no significant differenceto an ordinary molybdenum back contact. Measurements also indicate that the sodium is probably located inside themolybdenum grains and just a small amount is found at the boundaries and in betweenthe grains. Sodium inside the molybdenum grains is difficult to extract and thereforenot enough sodium will diffuse into the CIGS layer. The conclusions drawn from this study are that the molybdenum-sodium compoundhelps to increase the efficiency of a CIGS solar cell built on a sodium-free substrate,but it does not deliver enough sodium to constitute a substitute sodium source.
139

Analysis of a solar occultation experiment from the space shuttle Columbia

Bhattacharya, Yajnavalkya. January 1997 (has links)
Thesis (M. Sc.)--York University, 1997. Graduate Programme in Earth and Space Science. / Typescript. Includes bibliographical references (leaves 83-85). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ27334.
140

An evaluation of the performance of a solar boiler equipped with a parabolic cylinder type mirror

Bowman, John Patrick, 1935- January 1959 (has links)
No description available.

Page generated in 0.0505 seconds