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  • 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.
31

Stanovení aminoglutethimidu pomocí HPLC-ED na uhlíkových pastách / Determination of aminoglutethimide using HPLC-ED on carbon pastes

Vlachová, Karolína January 2010 (has links)
In this thesis, the determination of AGT, sooner used as anticancer drug, especially for the treatment of breast cancer in postmenopausal women or for the treatment of prostate cancer, by high performance liquid chromatogramy with UV spectrophotometric detection (HPLC-UV) and electrochemical detection (HPLC-ED) on carbon paste electrodes (CPEs) was studied. CPEs were prepared from glassy carbon microspheres and different pasting liquids - routinely used mineral oil (CPE-MO) and less commonly used tricresylphosphate (CPE-TCP) and silicone oil (CPE-SO). The concentration dependences of AGT were measured by HPLC-UV with detection wavelength 242 nm, by HPLC-ED with a working potencial of +1,3 V for CPE-MO and + 1,1 V for CPE-TCP in mobile phase containing phosphate buffer (pH 4) and methanol 50:50 (v/v). The following limits of detection were achieved - 3,6. 10-7 mol.l-1 for UV spectrophotometric detection, 2,5. 10-7 mol.l-1 for electrochemical detection with CPE-MO and 9,7. 10-7 mol.l-1 for electrochemical detection with CPE-TCP. AGT was also determined in model samples of urine. With HPLC-UV it was not possible to detect AGT, because of the interferences of other compounds. With HPLC-ED on CPE-MO the limit of detection 5,2. 10-7 mol.l-1 AGT was achieved. KEY WORDS Aminoglutethimide HPLC with UV...
32

Impact of ingredient selection on rheological properties of a semi-liquid syrup model for use in pulp/paste candy

Stangl, Kimberly January 1900 (has links)
Master of Science / Food Science / Sajid Alavi / Pulp/paste candy is popular in Mexico and is gaining popularity around the world. Pulp/paste candy is characterized as a soft, semi-fluid candy with particles in a colloidal suspension, typically squeezed out of the package for consumption. It is made by hydrating gums in water and mixing them with corn syrup, acid, powdered/pulverized sugar, and other minor ingredients yielding a product around 80°Brix and pH between 2-3. Over time the sucrose in the candy tends to invert, causing two types of failure: package leakage and solidification in package. Based on the findings of previous work from Molina-Rubio et al. (2010), a modified semi-liquid syrup model system was created with corn syrup, sugar, gums, and water. The model system was used to identify the influence these ingredients had on viscosity and texture since these factors are linked to the typical modes of failure in pulp/paste candy. An oscillatory sweep was used on a controlled force rheometer to identify the linear viscoelastic range. Oneway ANOVA with Tukey HSD was used to compare % total solids levels with complex viscosity at 0.1 rad/sec (there was a significant difference between all levels) and minimum tan (delta) (mid and high level were similar). Using a stepwise method, ANOVA models were generated that showed statistically significant effects on complex viscosity for gum level and sugar level as well as interactions (p < 0.05) between invert syrup-water, gum-water, and sugar type-water. The type of gum and the amount of corn syrup used didn’t significantly impact on the viscosity of the system. Using probe tests helped to analyze samples that were too thick for the rheometer. Analysis showed an inflection point for exponentially increased hardness (85-93%TS) that should be further investigated. The stepwise regression model generated for stickiness showed that the invert syrup-water interaction was significant along with gum type. These results are applicable to the confectionery industry and can help companies test and create a candy that meets the packaging and shelf life constraints that they desire. Targeting invert syrup-water levels and the hydration of the gum will have the most impact on the final product’s viscosity and stickiness, which are important for primary package filling and storage. To create an easy to eat candy, no invert syrup should be used in formulation and gellan gum would be better to use than xanthan. Higher solids (> 85%) should also be avoided since it would create a candy that is harder to squeeze out of the package due to higher viscosity and textural hardness.
33

Temperature Dependence of the Leachability of Cemented Paste Backfill

Bull, Andrew 05 March 2019 (has links)
Underground mining is a mineral acquisition technique that is critical to global economies, and human technological advancements. As shallow resource reserves are depleted, mine depths are increasing to accommodate global mineral demand. Increases in mine throughputs and excavation depths pose increased environmental concerns. Tailings surface disposal, and underground mine support are two considerable environmental and geotechnical factors of concern in current day mining. Underground waste disposal has been adopted by the mining industry in many forms. Cemented paste backfill (CPB) is a common best management practice developed to tackle these two specific resource industry related issues worldwide. CPB is a cement-stabilized material composed of tailings, water, and hydraulic binder. Tailings disposal areas on the earth’s surface are reduced by disposing of tailings in subsurface stopes that have been previously excavated. This increases underground safety by providing structural support to the mine. There are also economic benefits to this practice, as the additional support allows for adjacent pillars to be excavated. Although CPB greatly reduces tailings exposure to atmospheric elements, there are still underground environmental factors that must be considered with respect to environmental performance. CPBs are porous media, meaning they are susceptible to leaching of naturally occurring metals that are no longer in a stable condition as they were when incorporated in the parent rock. Arsenic and lead are metals of concern due to their association with many ore bodies. Leaching of these unstable metals may be influenced by the backfill curing temperature and the chosen hydraulic binder. Curing temperatures may be influenced by geographic location, local stope geology and depth, hydration and transport, among others. Hydraulic binders are chosen based on availability, cost, and desired mechanical properties of the paste. In this research, the effect of curing temperature and binder composition on the leachability of CPB are studied. ASTM C 1308 leaching protocol is used to determine the leachability of six CPBs. In addition, microstructural techniques (Powder X-Ray Diffraction, Mercury Intrusion Porosimetry, and Scanning Electron Microscopy) are used to relate the microstructural properties of the CPB to the leaching characteristics. Results reveal that CPBs cured with ordinary Portland cement (OPC) leach significantly less than CPBs cured with an OPC/Blast furnace slag (Slag) binder (50% blending ratio) as a result of CH consumption in slag hydration. Both CH and C-S-H are responsible for immobilizing arsenic in cement stabilized materials. OPC-CPBs contain greater relative quantities of CH, which aids in arsenic immobilization. Between the range of 2°C and 35°C OPC-CPB performed better at lower curing temperatures. Lower curing temperatures are favoured in OPC-CPB because the pore surface greater than the threshold pore diameter is reduced. Alternatively, OPC/Slag-CPB exhibited a decrease in cumulative mass leached at higher curing temperatures. The difference in cumulative mass leached by the OPC/Slag-CPBs is also related to the pore surface, and threshold pore diameter.
34

Remineralization effectiveness of MI Paste Plus - a clinical pilot study

Clark, Sarah Elizabeth 01 May 2011 (has links)
Purpose: The purpose of this study is to evaluate the effectiveness of MI Paste Plus™ in increasing remineralization and improving the esthetic appearance of white spot lesions in patients who have been treated with fixed orthodontic appliances. Material and Methods: A total of twelve subject participants aged twelve to twenty years were selected in this pilot study. The six treatment group subjects were treated with MI Paste PlusTM every three weeks in-office (4 applications) and via invisible retainer every night for a total of 12 weeks. The in-office application consisted of a 1 minute 35% phosphoric acid and a 5 minute MI Paste PlusTM contact time. At home, the subjects went about their routine oral hygiene practices, but added MI Paste PlusTM to their invisible retainer before bedtime which was worn throughout the night. Photographs and quantitative light-induced fluorescence (QLF) were used to calculate white spot lesion area and ∆F values respectively. Results: A significant difference was found in the control group for the area of the white spot lesion in antimere teeth #6 and #11. When analyzing the white spot lesion area in the treatment group, significant differences were found in tooth #6, antimere teeth #6 and #11, antimere teeth #8 and #9, as well as all teeth. ∆F values for all teeth in both the control and treatment groups were significant. Conclusion: In-office and at home treatment with MI Paste Plus™ showed a statistically significant reduction in photographic lesion area when compared to controls. Both MI Paste Plus™ and a fluoride toothpaste will provide some remineralization of white spot lesions.
35

“Potential Distribution Channel of Thai Seasoning Pastes in Sweden” : “Potential Distribution Channel of Thai Seasoning Pastes in Sweden” / “Potential Distribution Channel of Thai Seasoning Pastes in Sweden” : “Potential Distribution Channel of Thai Seasoning Pastes in Sweden”

Romfahthai, Sujinun, Phetpakdeechai, Wichittra January 2010 (has links)
Globo Foods Co., Ltd. has good opportunity to export five Thai seasoning        paste products to Sweden (Västerås). By setting the price as low initial price, sell firstly at ICA Maxi Hälla and Coop Extra in Västerås, use attractive promotion and advertising for Swedish people. This result is from valid, reliable primary and secondary data in order to be guideline and useful information to Globo Foods Co., Ltd. and also can adapt to fit the result with Thai seasoning pastes from other companies or other kind of products to enter to Västerås,Sweden.
36

Non-Linear Drying Diffusion and Viscoelastic Drying Shrinkage Modeling in Hardened Cement Pastes

Leung, Chin K. 2009 May 1900 (has links)
The present research seeks to study the decrease in diffusivity rate as relative humidity (RH) decreases and modeling drying shrinkage of hardened cement paste as a poroviscoelastic respose. Thin cement paste strips of 0.4 and 0.5 w/c at age 3 and 7 days were measured for mass loss and shrinkage at small RH steps in an environmental chamber at constant temperature. Non-linear drying diffusion rate of hardened cement was modeled with the use of Fick's second law of diffusion by assuming linearity of diffusion rate over short drops of ambient relative humidity. Techniques to determine drying isotherms prior to full equilibration of mass loss, as well as converting mass loss into concentration of water vapor were developed. Using the measured water vapor diffusivity, drying shrinkage strain was modeled by the theory of poroviscoelasticity. This approach was validated by determining viscoelastic properties from uniaxial creep tests considering the effect of aging by the solidification theory. A change in drying diffusion rate at different RH was observed in the 0.4 and 0.5 w/c pastes at different ages. Drying diffusion rate decreases as RH drops. This can be attributed to a change in diffusion mechanisms in the porous media at smaller pore radius. Shrinkage modeling with an average diffusion coefficient and with determined viscoelastic parameters from creep tests agreed well compared to the shrinkage data from experiments, indicating that drying shrinkage of cement paste may be considered as a poroviscoelastic reponse.
37

Early Age Mechanical Behavior and Stiffness Development of Cemented Paste Backfill with Sand

Abdelaal, Abdullah 05 January 2012 (has links)
Rapid delivery of backfill to support underground openings attracted many mines to adopt paste backfilling methods. As a precaution to prevent liquefaction and to improve the mechanical performance of backfills, a small portion of a binder is added to the paste to form the cemented paste backfill (CPB). Recently, adding sand to mine tailings (MT) in CPB mixes has attracted attention since it enhances the flow and mechanical characteristics of the pastefill. This thesis investigates the effects of adding sand to CPB on the undrained mechanical behavior of the mixture (CPBS) under monotonic and cyclic loads. Liquefaction investigations took place at the earliest practically possible age. Beyond this age, the present research focused on characterizing the evolution of stiffness and obtaining the values of the stiffness parameters that could be useful for designing and modeling backfilling systems. The liquefaction investigation involved monotonic compression and extension triaxial tests. Neither flow nor temporary liquefaction was observed for all cemented and uncemented specimens under monotonic compression, while temporary liquefaction was observed for all specimens under monotonic extension. The addition of binder and sand to MT was found to slightly strengthen the pastefill in compression while weakening it in extension. Under cyclic loading, the addition of sand negatively impacted the cyclic resistance. However, binder was found to be more effective in the presence of sand. All specimens exhibited a cyclic mobility type of response. The evolution of effective stiffness parameters for two CPB-sand mixtures was monitored in a non-destructive triaxial test for five days. Self-desiccation was found to not be influential on the development of early age stiffness. Moreover, a framework is suggested to predict the undrained stiffness at degrees of saturation representative of the field. The credibility of the proposed test in providing stiffness parameters at representative strain levels of the field was verified.
38

Development and Standardization of the NIST Rapid Sulphate Resistance Test

Aleksic, Mila 14 December 2010 (has links)
The NIST miniature paste prism test was developed to assess sulphate resistance of cements faster than the commonly used ASTM C 1012 test. The goal of this research is to address the current limitations regarding the NIST procedure to determine the optimum testing parameters and to establish appropriate expansion limits. A range of variables including details of specimen design, curing regime, water-to-cementitious materials ratio, and prism length were tested on the materials with a wide range of sulphate performance. The findings of the study demonstrate that even though it can yield results in only three months, the NIST test can provide an erroneous differentiation between certain cementitious materials. Reliability and repeatability of the test results can be improved by using longer specimens and longer curing times. The NIST test can be used as a preliminary screening test, but users need to be aware of its limitations.
39

Early Age Mechanical Behavior and Stiffness Development of Cemented Paste Backfill with Sand

Abdelaal, Abdullah 05 January 2012 (has links)
Rapid delivery of backfill to support underground openings attracted many mines to adopt paste backfilling methods. As a precaution to prevent liquefaction and to improve the mechanical performance of backfills, a small portion of a binder is added to the paste to form the cemented paste backfill (CPB). Recently, adding sand to mine tailings (MT) in CPB mixes has attracted attention since it enhances the flow and mechanical characteristics of the pastefill. This thesis investigates the effects of adding sand to CPB on the undrained mechanical behavior of the mixture (CPBS) under monotonic and cyclic loads. Liquefaction investigations took place at the earliest practically possible age. Beyond this age, the present research focused on characterizing the evolution of stiffness and obtaining the values of the stiffness parameters that could be useful for designing and modeling backfilling systems. The liquefaction investigation involved monotonic compression and extension triaxial tests. Neither flow nor temporary liquefaction was observed for all cemented and uncemented specimens under monotonic compression, while temporary liquefaction was observed for all specimens under monotonic extension. The addition of binder and sand to MT was found to slightly strengthen the pastefill in compression while weakening it in extension. Under cyclic loading, the addition of sand negatively impacted the cyclic resistance. However, binder was found to be more effective in the presence of sand. All specimens exhibited a cyclic mobility type of response. The evolution of effective stiffness parameters for two CPB-sand mixtures was monitored in a non-destructive triaxial test for five days. Self-desiccation was found to not be influential on the development of early age stiffness. Moreover, a framework is suggested to predict the undrained stiffness at degrees of saturation representative of the field. The credibility of the proposed test in providing stiffness parameters at representative strain levels of the field was verified.
40

Development and Standardization of the NIST Rapid Sulphate Resistance Test

Aleksic, Mila 14 December 2010 (has links)
The NIST miniature paste prism test was developed to assess sulphate resistance of cements faster than the commonly used ASTM C 1012 test. The goal of this research is to address the current limitations regarding the NIST procedure to determine the optimum testing parameters and to establish appropriate expansion limits. A range of variables including details of specimen design, curing regime, water-to-cementitious materials ratio, and prism length were tested on the materials with a wide range of sulphate performance. The findings of the study demonstrate that even though it can yield results in only three months, the NIST test can provide an erroneous differentiation between certain cementitious materials. Reliability and repeatability of the test results can be improved by using longer specimens and longer curing times. The NIST test can be used as a preliminary screening test, but users need to be aware of its limitations.

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