• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 189
  • 83
  • 30
  • 25
  • 17
  • 8
  • 5
  • 4
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 497
  • 497
  • 158
  • 144
  • 89
  • 77
  • 73
  • 54
  • 44
  • 44
  • 39
  • 38
  • 35
  • 35
  • 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.
1

Skin effect measurements of the bulk modulus of potassium

Loveday, J. S. January 1987 (has links)
No description available.
2

Physical properties of cyclic and linear poly(dimethylsiloxanes)

Orrah, D. J. January 1987 (has links)
No description available.
3

Conformation and crystallinity in polymers - a study using novel Raman techniques

Royaud, Isabelle Anne-Marie January 1989 (has links)
No description available.
4

Effect of polyacrylamides on the physical properties of some light-textured soils.

Phillips, Shane January 2007 (has links)
The work presented in this thesis represents a combination of laboratory and field experiments designed to explain some field observations I made on some coarse sands in South Australia in 1999: that much of the irrigation water and nutrients applied to the sands under drip-irrigation simply passed through the root zone leaving the crops water-stressed shortly after irrigation events. There was clearly only minimal lateral spread of the water in these coarse sands. However, by applying small concentrations of polyacrylamide or ‘PAM’ in the irrigation water, the crops seemed to do better. Furthermore the timing of irrigation events appeared to be more flexible on the PAM-treated properties. I found this intriguing and saw an opportunity to increase the lateral spread of water in the root zone and thereby increasing the stored volume and residence time of water. By retaining more water in the rootzone, there was potential to save a considerable amount of costly irrigation water, and also improve crop production and quality. With encouragement from my then employer (Elders Pty Ltd) and from Ciba Specialty Chemicals Australia, I undertook to explore my findings in greater detail and to attempt to explain them based on some ‘hard’ (experimental) evidence. Increasing the lateral spread of water under drippers in coarse-textured soils requires water to be retained in the root zone for longer periods during irrigation, but the practical methods for doing this are limited to: • Altering the pore size distribution to create a finer average range of pore sizes, either by compaction or by stabilization of smaller pores using organic matter or additions of clay. • Reducing the wettability of the soil so that less water can be taken in and the soil never becomes saturated. (This of course risks surface runoff and suboptimal placement of irrigation water). • Altering the physical properties of irrigation water (eg. viscosity, surface tension) so that it interacts differently with soil pores and moves through them more slowly. The aim of the research was therefore to evaluate the potential for some commercially available PAMs to reduce hydraulic conductivity and to increase water retention on some drip-irrigated coarse sandy soils of South Australia and Victoria. I worked with two commonly available anionic polyacrylamides, designated PAM-1011 and PAM-135, and measured ponded infiltration in laboratory columns of seven different sandy soils from around South Australia and Victoria. I varied the concentration of the polymer within the range typically used in the field (0, 1 and 10 ppm for PAM-1011; 0, 2.5 and 25 ppm for PAM-135) and I also varied the quality of the irrigation water used to mix the PAM solutions in terms of salinity and sodicity (distilled water, 10 and 20 mmol(+) salt/L, using either sodium chloride, calcium chloride, or both). I measured the effects of PAM on pore-size distribution of one of the sands (by the water retention characteristic), on water repellence of the soils (by measuring water droplet penetration times), and the kinematic viscosity of the PAM solutions at various concentrations with various qualities of irrigation water. I also set up transparent cases of sand to observe infiltration and wetting behaviour of the PAM solution. Finally, with some understanding of how the physical and chemical properties of the PAMs, I conducted a field trial to measure the soil water matric potential at various depths and locations around drippers in vine rows receiving PAM in the irrigation water. Laboratory findings: The polymer PAM-1011 significantly reduced the steady-state infiltration rate in all sands, and it did this with relatively modest concentrations (< 10 ppm). The polyacrylamide PAM-135 was not effective for this purpose, which indicated that the chemical properties of the polymer (not investigated here) influenced its physical behaviour. Further work with PAM-135 was therefore discontinued in favour of PAM-1011. The effectiveness of PAM-1011 in reducing steady-state infiltration rates was related to changes in the properties of the irrigating solution caused by PAM-1011 rather than by a change in the properties of the soils to which it is applied. For example, PAM-1011 had only minimal (if any) influence on the pore size distribution (water retention) of a coarse sandy soil and had no significant impact on water repellence (wettability) of another sandy soil. It did, however, have a large impact on the kinematic viscosity of the irrigating solution, and the more PAM-1011 that was dissolved, the more viscous the solutions became. The effectiveness of PAM-1011 in reducing steady-state infiltration rates was reduced in salty irrigation water, and there was evidence to suggest that cation-effects may have been involved. When PAM-1011 was dissolved in distilled water, infiltration rates were reduced by the greatest amount. When PAM-1011 was dissolved in salty water containing the monovalent cation, sodium, infiltration rates were not reduced as much; furthermore, if the solvent water contained the divalent cation, calcium, PAM-1011 was even less effective than in sodium-rich water. Thus electrolytes affected the physical conformation of PAM-1011 solutions, altering viscosity. To overcome the salt-water effects, higher concentrations of PAM-1011 needed to be used. The cation-effects were primarily related to the way each cation interacted with the polymer to alter its kinematic viscosity. PAM-1011 in distilled water had the greatest viscosity, while PAM-1011 in sodium-rich water had a lower viscosity, and PAM-1011 in calcium-rich water had the lowest viscosity. A practical implication from this is that irrigators using salty waters will need to dissolve more PAM-1011 in their water-sources to increase the viscosity and thus gain the retarding effects of the polymer on infiltration rates. The data suggest that the amount of polymer required to overcome the salt effects is about 10 ppm PAM-1011. Rates as low as 1 ppm can be used when irrigators have access to high-quality water with < 10 mmol(+) salt/L present. Visual observations of the wetting fronts during infiltration showed that irrigation water containing PAM-1011 at between 1 and 10 ppm reduced the depth of percolation and increased its lateral spread in coarse sands. Field study: The field work was largely unsuccessful because shortly after the treatments were applied, a 1-in-100 year hailstorm struck that completely wiped out the vegetation on the vines in the study. I spent most of the season simply trying to keep the vines alive and to recover some of the leaf area for future years. Overall, however, this work identified the ability of PAM-1011 to reduce water movement through the root zone of coarse sands, and demonstrates the potential to conserve a great deal of water – a significant move toward higher water- and nutrient-use efficiencies on the coarser textured soils in the Murray-Darling Basin. / Thesis (M.App.Sc.) -- University of Adelaide, School of Earth and Environmental Sciences, 2007
5

Clay mineralogy and its effect on physical properties in the Gulf of Mexico northwestern continental slope

Berti, Debora 17 February 2005 (has links)
The clay mineral composition of sediments deposited in the last six oxygen isotope stages in the Gulf of Mexico continental slope was characterized. Smectite and illite were found to be the two major clay minerals of the clay fraction while kaolinite, chlorite and quartz were present in the clay fraction but in less proportions. Variations in clay mineral abundances, especially in the relative abundances of smectite and illite, were identified in relation to climate changes. Smectite was the most abundant mineral in sediments of the current (stage 1) and last interglacial maxima (stage 5) while illite dominates the clay min-eralogy of sediments from the last glacial maximum (stage 2). Relationships between clay mineralogy and physical properties were investigated as well. Significant positive correla-tions were found between Atterberg limits with the smectite content of the bulk sediment and with clay content. However, the relationship with smectite yielded a significantly higher correlation coefficient. Smectite and clay content also affect the natural water con-tent of sediments and its changes with depth.
6

Clay mineralogy and its effect on physical properties in the Gulf of Mexico northwestern continental slope

Berti, Debora 17 February 2005 (has links)
The clay mineral composition of sediments deposited in the last six oxygen isotope stages in the Gulf of Mexico continental slope was characterized. Smectite and illite were found to be the two major clay minerals of the clay fraction while kaolinite, chlorite and quartz were present in the clay fraction but in less proportions. Variations in clay mineral abundances, especially in the relative abundances of smectite and illite, were identified in relation to climate changes. Smectite was the most abundant mineral in sediments of the current (stage 1) and last interglacial maxima (stage 5) while illite dominates the clay min-eralogy of sediments from the last glacial maximum (stage 2). Relationships between clay mineralogy and physical properties were investigated as well. Significant positive correla-tions were found between Atterberg limits with the smectite content of the bulk sediment and with clay content. However, the relationship with smectite yielded a significantly higher correlation coefficient. Smectite and clay content also affect the natural water con-tent of sediments and its changes with depth.
7

The development of genetic algorithms and fuzzy logic for geoscience applications

Cuddy, Steven John January 2003 (has links)
This thesis describes how I have researched and developed new methods for the prediction of rock physical properties using genetic algorithms and fuzzy logic (GAFL).  These techniques are improvements on conventional methods providing two original but dissimilar tools for formation evaluation and reservoir characterisation. The premise behind the use of fuzzy logic in this context is that a reservoir can be broken down into several lithotypes, each having characteristic statistical distributions for electrical log values.  Fuzzy logic attempt to uncover the relationships between these distributions.  Genetic algorithms use a feedback technique that assumes a continuous functional relationship between the electrical log values and rock properties, generating and testing equations that fit predicted and observed responses.  Complex non-linear equations are “evolved” until the best fit is obtained.  Genetic algorithms provide the functional form of the equation as well as the constant parameters of the relationship. I have modified conventional GAFL techniques so that they can be more precisely calibrated and applied to geoscience problems more successfully.  This research analysed the characteristics of large data sets from several North Sea and Middle Eastern fields, and led to the design of software that automatically calibrates GAFL in a way that is less sensitive to noise and data outliers.  I describe the applications of these new techniques to permeability, litho-facies, porosity and shear velocity prediction;  the repair of poor electrical logs and the modelling of shaly sand equations. Permeability governs the movement of fluids through reservoir rocks and is therefore a critical input into reservoir models.  Permeability estimation is extremely challenging, as it is difficult to measure directly using current sub-surface logging technology.  GAFL was applied to predict permeability in the Northern North Sea oil fields.  The newly developed software provides an important and visual indication of the uncertainty associated with the predicted permeabilities.
8

Water veins in polycrystalline ice

Mader, Heidy Marita January 1992 (has links)
No description available.
9

The determination of lithology from core physical properties measurements

Clark, Paula Ann 16 August 2006 (has links)
I performed statistical analysis of shipboard physical properties data from the Ocean Drilling Program to investigate relationships between the physical properties data and the lithology of deep ocean cores. The use of non-invasive experiments on deep-sea core samples offers a near real-time view of sediments and requires little user interaction or interpretation. The speed, density, and accuracy of these experiments make efficient use of limited space and expensive ship time. The fact that these experiments are noninvasive also allows for further post-cruise studies. For the study I chose Leg 162 (July-September 1995 in the North Atlantic) for the density of data, the experiments performed, the quantity and quality of post-cruise publications and the influence of different, yet dominant, environments. Combining similar lithologies across a Leg increased sample size and offered a more statistically normalized sample. Interpolation of the physical properties data matched the intervals used for the lithological determinations. Statistical methods included univariate and multivariate correlation matrices, mean and standard deviations, the significance of the correlations, and a model equation for each lithology and the Leg as a whole. By looking at the physical properties, one can estimate the lithology. This research is important because sedimentological and geophysical approaches can be merged to offer a more accurate, more detailed view of the depositional history of oceanic cores. Through statistical analysis of geophysical data, the findings duplicate the findings of the sedimentologists without the painstaking examinations typical of this type of research. Performing experiments and analysis quickly and accurately with minimal operator error allows for immediate discussions and results. Use of this research as a data verification tool provides the ability to distinguish data acquisition problems and misidentifications. This application has proven invaluable for allowing a non-sedimentologist quantitative insight into the lithology.
10

Comparison of the physical properties for five different commercial root canal sealers

Hifeda, Nedda 28 September 2016 (has links)
AIM:  to evaluate the flow, working time, setting time, film thickness and solubility of a novel root canal sealers (MTA Fillapex) in comparison with a zinc oxide-eugenol– based sealer (Tubli-Seal), epoxy resin-based sealers (AH 26), a calcium hydroxide-based sealer (Apexit Plus), and a silicone-based sealer (ReokkoSeal Automix). MATERIALS AND METHODS: ISO 6876/20012 specifications were followed except for the solubility test. Solubility was measured by the amount of material extracted from the specimens left in water over 24 hr period. Film thickness was measured as the distance between weighted glass slides containing a standard quantity of sealer. Flow was assessed by rate of sealer extrusion through a standard bore diameter, after unit time. Working time was taken as the point at which flow rate was reduced by 10%. The indentation test using a modified Gilmore needle was employed to investigate the setting times. RESULTS: ReokkoSeal Automix and MTA Fillapex were the least soluble, whilst Tubli- Seal was the most unstable in water. Also, Tubli-Seal had the highest film thickness. All sealers showed comparable flow rates. The working time varied from 30 min for MTA Fillapex to 4 hr for AH 26. The range of setting times recorded was from 64 min for Tubli-Seal Xpress to more than 5 hr for AH 26. CONCLUSIONS: MTA Fillapex and RoekoSeal Automix showed the greatest stability in Solution. The film thickness values in increasing order were: AH26 < Apexit plus = RoekoSeal Automix < MTA Fillapex < Tubli-Seal Xpress. The flow rates for Tubli-Seal xpress, AH26, and RoekoSeal Automix are statistically similar, while Apexit plus and MTA Fillapex are statistically similar. The working times for all sealers were greater than 30 min. AH26 did not set when incubated in volumes sufficient to fill the test matrices. / 2018-09-28T00:00:00Z

Page generated in 0.0941 seconds