• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 89
  • 68
  • 11
  • 9
  • 6
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 299
  • 299
  • 299
  • 113
  • 81
  • 69
  • 57
  • 47
  • 39
  • 35
  • 34
  • 33
  • 30
  • 25
  • 25
  • 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.

X-ray scattering from magnetic metallic multilayers

Hase, Thomas Paul Anselm January 1998 (has links)
Study of structure and interface morphology of magnetic thin films is crucial in obtaining a better understanding of the coupling mechanisms in such systems. In this thesis various x-ray scattering techniques are applied to a series of Co/Cr trilayers, Cu/Co multilayers and spin valve structures. It is demonstrated that modifications to the distorted wave Born approximation allow the modelling of grazing incidence diffuse scatter originating from graded systems such as Co/Cr. Grazing incidence scattering techniques are also employed to investigate the out of plane correlations of lateral roughness in Cu/Co multilayers, as well as in miscible trilayer structures. The use of soft x-rays in the investigation of 3d transition metal multilayers is also presented. Such experiments are sensitive to the component of magnetisation aligned with the direction of the incident beam. In a series of magnetisation experiments, the dependence of the x-ray scatter sensitive to this component of magnetisation are analysed. For the first time evidenced is found for correlated magnetic roughness, which has lateral correlation lengths far greater than the structural roughness length scales. This magnetic roughness is measured in detail, and the correlation length is found to vary with applied field direction. Grazing incidence x-ray fluorescence is applied to two spin valve structures. These experiments provide a direct measure of buried layer thicknesses which is not possible by other x-ray scattering techniques. This novel method for the determination of the copper layer thickness in spin valves shows the versatility of non-destructive x-ray methods for the characterisation of magnetic metallic multilayers.

Reflectivity studies of non-critical interfaces in binary liquid mixtures

Howse, Jonathan R. January 1999 (has links)
No description available.

X-Ray Fluorescence Measurements Of Molten Aluminum Elemental Composition

Duren, Leigh C 09 January 2008 (has links)
The aluminum industry is in need of high-speed in-situ elemental identification technology for molten metals. wTe Corporation of Bedford, MA was granted funds to research this technology for aluminum through the Advanced Technology Program (ATP) of the National Institute of Standards and Technology (NIST). As a secondary metal scrap processor, wTe Corporation is interested in increasing the value of scrap and better identification technology is one way of doing this. With better identification technology, foundries and smelters will be more confident in the melt chemistry and more apt to use secondary aluminum which decreases the energy required for processing by approximately 85%. wTe Corporation is exploring two avenues for in-situ molten metal identification: Laser Induced Breakdown Spectroscopy (LIBS) and X-Ray Fluorescence (XRF). The objectives of this work were to contribute to developing XRF technology for in-situ identification of molten metal by establishing a method of data instrumentation and analysis for XRF to determine aluminum melt composition, investigate the major alloying elements in the Al380 alloy series and determine the relationship between intensity and concentration, and to determine the effect of temperature on XRF Spectra. The XRF instrumentation development and the technical challenges associated with high temperature measurements are presented. The relationship between intensity and concentration is presented for three alloys within the 380 alloy series, and lastly it is observed that there are significant differences between liquid and solid spectra and that a calibration curve for liquid data is necessary. Several hypotheses are given as to why this difference between liquid and solid state spectra may occur.

Lithic Analysis at a Late Prehistoric Coastal Site in the Samoan Archipelago

Hawkins, Megan T. 2009 December 1900 (has links)
This thesis presents a lithic attribute and geochemical analysis of the lithic material recovered from coastal site of Fatumafuti, on Tutuila Island, in the Samoan archipelago during 1050-520 BP. The goal of this thesis is to clarify the nature of stone tool production and to add to our current understanding of the cultural transformations from Lapita to a Polynesian identity. To complete this goal four research questions are addressed. What is the stage of reduction (cha ne operatoire) at Fatumafuti? Does the assemblage vary over space and time? Where did the source material come from? And, what was the organization of lithic craft production? Specifically, is there evidence for specialization? The lithics at Fatumafuti contain multiple segments in the technical sequence of tool manufacture (cha ne operatoire). The two major segments are middle stage and late stage reduction, and two minor segments are early stage reduction and tool rejuvenation. Expedient tools found on site indicate that prehistoric groups did not rely on a completely curated technology. Tool manufacture was geared toward producing a variety of tools, as opposed to a specific product. Production was most intense towards the coastal portion of the site during the earlier cultural component and then shifted towards the talus base during the later cultural component. Using non-destructive Energy Dispersive X-Ray Fluorescence (EDXRF), elemental concentrations were analyzed and compared to those of Tataga-matau, Lau?agae, Asiapa and Alega. One, possibly two, sources were utilized at this site; however, they are not chemically similar to Tatagamatau, Lau'agae, Asiapa and Alega. I conclude that people of Fatumafuti practiced independent household production at the end of the Aceramic and beginning of the Recent period. Either the intensification of lithic craft production that is seen during the height of complex chiefdoms is not seen at Fatumafuti, or these social transformations had not yet taken hold. With more cases that date to this time, we may find that Samoan chiefdoms had not attained full complexity at this point.

Journeys of Our Ancestors: Conservation Science Approaches to the Analysis of Cultural Material

O'Grady, Caitlin Rose January 2009 (has links)
The application and use of non-destructive portable x-ray fluorescence (XRF) analysis is a critical tool in the preservation and interpretation of cultural material. Portable XRF instrumentation produce elemental compositional data that is used to reconstruct current artifact composition, which can be related to materials and methods of manufacture, technological practice, as well as object condition and presence of corrosion surfaces. Portable XRF analysis is used to assess a variety of material classes utilized in artifact manufacture. The dissertation research is based on a series of three case studies that represent typical groups of material culture commonly encountered in conservation and conservation science research.Conservators and conservation scientists frequently undertake analysis and interpretation of disparate groups of materials. Often, these objects are tied together by research questions or themes directed by outside influences including preservation issues requiring action; curatorial research interests; museum exhibition programs; as well as many other cultural heritage stakeholders. To this end, both non-destructive and destructive tools that provide measurements of interest play critical roles in analysis. The case studies have been designed to answer common compositional questions relating to (a) bulk analysis of Chinese coins, (b) characterization of Southwestern ceramic colorants, and, (c) chemical examination of post-depositional manganese dioxide accretions occurring on archaeological ceramic materials. They evaluate the value of data produced using effectiveness of non-destructive portable XRF analysis for the interpretation of archaeological materials. The case studies provide a template for the development of conservation science research, predicated on object preservation, which produce meaningful data for the interpretation and conservation of the analyzed archaeological artifacts. Portable XRF provides useful data that is used to successfully interpret archaeological materials through (a) classification of metal alloys that can be related to published coin data, (b) identification of ceramic colorants and production technologies, and, (c) characterization of post-depositional product composition when used with established visual typologies.

Developing a methodology for the non-destructive analysis of British soft-paste porcelain

Dunster, Joanna Margaret January 2016 (has links)
Soft-paste porcelain was produced in Britain in great quantities between the mid-18th and early 19th centuries. Due to industrial secrecy and the complexities of creating a product that would survive high-temperature firing, a range of paste recipes was employed by dozens of factories. This has resulted in an array of porcelains which vary in their elemental composition and mineralogy. This research carries out a meta-analysis of the published data for porcelain bodies and glazes and concludes that some discrimination can be achieved using the major and minor elemental composition of the bodies, and that for the glazes intra-factory variation is often greater than inter-factory variation in composition. A pilot investigation of the trace elemental composition of British porcelain is carried out using Laser Ablation Inductively Coupled Plasma Mass Spectroscopy, which finds compositional groups corresponding to different sources of clay and silica raw materials. In the interests of preserving intact objects, there is recognised a need for a non-destructive method for analysing British porcelain, in order to provenance and date objects. Such a method would rely on data from the surface of the object, which is typically covered by glaze and over-glaze coloured enamels, and this research demonstrates that the formulae used for the glaze and enamels are in some cases characteristic of the factory, or workshop, and period at which they were created. Hand-Held XRF analysis is used to analyse the glaze, underglaze blue and polychrome enamels on a selection of porcelain objects from different factories, and compositional traits are identified that allow some factories and periods to be distinguished. Glass standards are developed, which are representative of the glaze and enamel composition, and which could allow X-ray fluorescence (XRF) data to be calibrated for fully quantitative results.


LODWICK, JEFFREY CLARK 02 September 2003 (has links)
No description available.


Ma, Jieqi January 2019 (has links)
This thesis explores the use of skin iron concentration, assessed using a portable x- ray fluorescence (PXRF) analyzer, as an indicator of liver iron concentration. Ultrasound images were acquired from four sites on human cadavers: thenar eminence (TE), between the metacarpophalangeal joint 1 and 2 (MJ), patella (P), and plantar arch (PA). Skin thickness was subsequently measured using boundary detection software applied to the ultrasound images. Skin iron concentrations, from the same sites, were obtained directly from 13 cadavers using a PXRF analyzer. As the iron concentrations determined using PXRF may have been impacted due to beam attenuation through the skin, these iron concentrations were subsequently corrected using the Beer-Lambert Law accounting for the skin thickness at each site. Huber XRF is a bulk tissue measurement system that was used to measure iron concentrations from the extracted samples of the four sites. The skin iron concentrations determined using both PXRF and Huber XRF were compared to evaluate the agreement between the two methods. As such, samples from the four sites were extracted and the iron concentrations of the extracted samples were measured using a Huber X-Ray Fluorescence (XRF) analyzer as the control. A statistically significant relationship with a p-value of <0.01 and a strong correlation with a R2 value of 0.87 was seen between the corrected skin iron concentrations determined using PXRF and the skin iron concentrations determined using Huber XRF analysis of the extracted samples. Thus, the skin iron concentrations obtained using PXRF are representative of the skin iron concentrations collected by Huber XRF. For further validation, liver samples were obtained from 6 of the 13 cadavers and the liver iron concentrations were assessed using Huber XRF. The non- corrected PXRF, corrected PXRF and the Huber XRF skin iron concentrations were then compared with the liver iron concentrations. The relationships between iron concentrations measured at the PA site and in the liver were found to be statistically significant with strong correlations (R2 = 0.94 for Huber XRF, R2 = 0.87 for non-corrected PXRF, and R2 = 0.95 for corrected PXRF). Therefore, the skin iron concentrations at the PA site determined by PXRF and determined by Huber XRF analysis of skin samples could be used in the future as a surrogate marker for the liver iron concentrations in humans. / Thesis / Master of Science (MSc)

Grundämnesanalys på S:t Hans individer : Ett metodologiskt arbete med µXRF / An element analysis on the individuals of S:t Hans : a methodological study using µXRF.

Sjögren, Phillip January 2019 (has links)
The practice of using X-Ray fluorescence analysis as a method in ar-chaeological, forensic and osteological studies have resulted in a vast amount of data. It is time and cost efficient, and the method of µXRF element analysis has been of great use to archaeologists, forensic an-thropologists and osteologists to understand dietary customs, techno-logical trade patterns, understanding of diagenesis, elemental accumu-lation in bone and more. Moreover, the method has been crucial due to its non-destructive nature since bones and ancient artifacts are fragile and thus a nonde-structive method is preferable. This essay will give the reader an intro-duction to the basics of micro X-Ray fluorescence analysis and will explore the possibilities of trace elements in right (dexter) and left (sinister) thighbones (femur) on a medieval population in Visby Got-land, namely Sankt Hans. The reader will also come to know the fun-damental principles, applications, strengths and weaknesses of mi-croX-Ray fluorescence, as well as its limitations. Keywords: µXRF, non-destructive, data, method, left, right, thigh-bone, elements, analysis.

Spent Nuclear Fuel Self-Induced XRF to Predict Pu to U Content

Stafford, Alissa Sarah 2010 August 1900 (has links)
The quantification of plutonium (Pu) in spent nuclear fuel is an increasingly important safeguards issue. There exists an estimated worldwide 980 metric tons of Pu in the nuclear fuel cycle and the majority is in spent nuclear fuel waiting for long term storage or fuel reprocessing. This study investigates utilizing the measurement of x-ray fluorescence (XRF) from the spent fuel for the quantification of its uranium (U) to Pu ratio. Pu quantification measurements at the front end of the reprocessing plant, the fuel cycle area of interest, would improve input accountability and shipper/receiver differences. XRF measurements were made on individual PWR fuel rods with varying fuel ages and final burn-ups at Oak Ridge National Laboratory (ORNL) in July 2008 and January 2009. These measurements successfully showed that it is possible to measure the Pu x-ray peak at 103.7 keV in PWR spent fuel (~1 percent Pu) using a planar HPGe detector. Prior to these measurement campaigns, the Pu peak has only been measured for fast breeder reactor fuel (~40 percent Pu). To understand the physics of the measurements, several modern physics simulations were conducted to determine the fuel isotopics, the sources of XRF in the spent fuel, and the sources of Compton continuum. Fuel transformation and decay simulations demonstrated the Pu/U measured peak ratio is directly proportional to the Pu/U content and increases linearly as burn-up increases. Spent fuel source simulations showed for 4 to 13 year old PWR fuel with burn-up ranges from 50 to 67 GWd/MTU, initial photon sources and resulting Compton and XRF interactions adequately model the spent fuel measured spectrum and background. The detector simulations also showed the contributions to the Compton continuum from strongest to weakest are as follows: the fuel, the shipping tube, the cladding, the detector can, the detector crystal and the collimator end. The detector simulations showed the relationship between the Pu/U peak ratio and fuel burn-up over predict the measured Pu/U peak but the trend is the same. In conclusion, the spent fuel simulations using modern radiation transport physics codes can model the actual spent fuel measurements but need to be benchmarked.

Page generated in 0.0749 seconds