• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 776
  • 513
  • 233
  • 155
  • 107
  • 98
  • 85
  • 27
  • 27
  • 19
  • 18
  • 16
  • 15
  • 15
  • 8
  • Tagged with
  • 2455
  • 337
  • 164
  • 141
  • 134
  • 129
  • 110
  • 107
  • 104
  • 104
  • 91
  • 82
  • 80
  • 79
  • 78
  • 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.
141

Non-abelian Littlewood–Offord inequalities

Tiep, Pham H., Vu, Van H. 10 1900 (has links)
In 1943, Littlewood and Offord proved the first anti-concentration result for sums of independent random variables. Their result has since then been strengthened and generalised by generations of researchers, with applications in several areas of mathematics. In this paper, we present the first non-abelian analogue of the Littlewood Offord result, a sharp anti-concentration inequality for products of independent random variables. (C) 2016 Elsevier Inc. All rights reserved.
142

Measurement of the Atomic-oxygen Concentration under Simulated Upper Atmosphere Conditions

Grable, Weliko C. 01 1900 (has links)
This thesis describes an experimental technique for measuring the atomic-oxygen concentration under simulated upper atmosphere conditions.
143

The Relationship of Dose to Plasma Concentration with Acute Ingestion of Amitriptyline

Williams, Teresa Lynn 05 1900 (has links)
The high concentrations of amitriptyline found in blood at autopsy, indicating a large amount of ingested drug, is often contradictory to the prescription available. Using dogs as the animal model it was found that there was a large variance between the dose given and its plasma amitriptyline concentration during the acute phase of absorption. Factors that were found to be important were the amitriptyline to nortriptyline (as metabolite) ratio, the nature of the specimen, and the collection site. The calculation of the dose from an acute ingestion of amitriptyline resulting in death cannot be accurately determined from a single specimen collected at autopsy.
144

A Comparison Between Reading and Listening in Comprehension and Retention of Certain Language Concepts in the Third Grade

Gay, Marcella 08 1900 (has links)
This thesis compares reading verses listening comprehension in third grade students. The problem under consideration is to determine whether it is easier for a third-grade child to understand a given meaning when that meaning is presented to him in spoken words than it is when the meaning is presented in printed words,
145

Optimisation and evaluation of boron analysis for pressurized Water reactor plants

Tasana, Nomalanga Gloria January 2016 (has links)
Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2016. / Boron concentration analysis is an important and critical analysis performed by the Analytical Chemistry Laboratory at Koeberg Nuclear Power Station (KNPS), because boron controls reactivity and the concentration determination is a Technical Specification Parameter (safety parameter). Hence accurate, precise results for boron concentration produced by laboratories and on-line analysers are important because of their operational implications associated with reactivity control and also for nuclear safety. The project focused on comparing the quality of chemical analysis results of boron produced by analysis techniques/ methods used at Koeberg Nuclear Power Station namely; Potentiometric Titration, Atomic Absorption Spectrophotometry (Flame) and UV-VIS Azomethine-H method. The methods were described, optimised, evaluated and compared in terms of uncertainty of measurement, accuracy, precision, analysis range, limitations, appropriateness and applicability for boron analysis in 2500 mg B/kg concentration range. For Potentiometric Titration method, the measurement uncertainty = 2500 ±16 mg B/kg, accuracy= 0.2%, precision= 0.08% the range of analysis= 5-800 mg B/kg. For Atomic Absorption Spectrophotometry (Flame) the measurement uncertainty= 2500 ±51 mg B/kg, accuracy= 0.12%, precision= 0.44% the range of analysis= 0 -500 mg B/kg. For UV-VIS Azomethine-H the measurement uncertainty= 2500 ±72 mg B/kg, accuracy= 0.08%, precision= 0.44% the range of analysis= 0 -10 mg B/kg. The INPOs 95% accuracy and precision criteria for boron is ± 1%. So these techniques could be used for boron analysis in PWR. Based on the evaluation and assessments mentioned above; the Potentiometric Titration was found to be the most preferred method for boron analysis for Pressurised Water Reactors followed by Atomic Absorption Spectrophotometry (Flame) that can be of good use in determining boron especially in waste samples and samples with complex matrices. The UV-VIS Azomethine-H methods can only be used when it is really necessary to determine very low levels of boron between 0- 10mg B/kg of which it was never required before. Since it is specifically the B-10 isotope that is responsible for the ability to control reactivity, the implementation of isotopic boron analysis (by Inductively Coupled Plasma – Mass Spectrometry) at KNPS is explained and the advantage of the programme is illustrated. Although the current state of instrumental capabilities is adequate for 10B isotope determination, further work of optimising the methodology for even better results is recommended.
146

Effects of Molecular Weight and Solution Concentration on Electrospinning of PVA

Tao, Jing 13 June 2003 (has links)
"The effects of molecular weight (Mw) and concentration (c) on the structure of electrospun PVA have been studied. Experiments have been conducted for Mw values ranging from 9000 g/mol to 124,000 g/mol. The concentration was varied from 5 to 35 wt %. Data were acquired for several solvents including water, Dimethyl Sulfoxide, Ethylene Glycol and N-Methyl Pyrrolidone. The transient phenomena occurring during jet breakdown were examined by high speed digital photography. The structure in the electrospun polymer was analyzed by scanning electron microscopy. The fiber diameter distribution for various conditions was characterized by optical image analysis. The effects of additives such as NaCl and Poly Ethylene Glycol on the structure have been studied. The results indicate that a minimum Mw and c corresponding to [h]c ~ 5 or Capillary number, Ca ~ 0.5 is necessary for forming a fibrous structure. As Mw or c increase, the fiber diameter becomes larger and a broader distribution of fibers may be obtained. The average diameter of the fiber, D, follows a Power law relationship: D (nm) = 18.6([h]c)1.11. Round fibers may be obtained at low Mw and c, while flat fibers are observed at high Mw and c. The transition from round to flat fibers appears to begin at [h]c ~ 12. At any [h]c, there is a minimum Capillary and Ohnesorge numbers at which fibers are stabilized and a maximum at which viscous effects become dominant. The addition of NaCl lowers the average fiber diameter in PVA samples with a high molecular weight. Electrospinning can be used to produce nanofibers of PVA with various architectures. "
147

Nitrification in preplant N-P fertilizer bands and Ph effects on nitrification

Betzen, Nicholas Mark January 2011 (has links)
Vita. / Digitized by Kansas Correctional Industries
148

Distribution of Dissolved Trace Metals and Carbon System Parameters in the Surface Waters of the Hillsborough River and Tampa Bay

Elliott, Matthew Matthias 22 October 2014 (has links)
This work represents a first look at the general spatial distribution of trace metals and the inorganic carbon system in the surface waters of Tampa Bay. Tampa Bay's chemical environment bears many influences ranging from hydrological and geological to anthropogenic and meteorological. A large y-shaped estuary on the west-central side of the Florida Peninsula, Tampa Bay extends over 400 square miles and has a 2200 square mile watershed that includes extensive swamps, scrub, agricultural lands and densely urbanized areas. Reaching 37 miles from the northernmost point of Old Tampa Bay to the mouth of the estuary near the Sunshine Skyway Bridge, it is home to the largest port in Florida, and overall places 17th in the nation for tonnage. In addition to its ports, Tampa Bay supports the requirements of a broad range of industries including: ship building and repair, power generation, wastewater processing, development, and recreational and commercial fishing. The region experiences high rainfall during the summer and much reduced rainfall during the remaining portions of the year. The bay has a broad gradient of mixing intensities, with residence times ranging from 100+ days in Old Tampa Bay to less than 20 days at the mouth. Seventy-one percent of Tampa Bay's freshwater input is delivered by four primary rivers: the Hillsborough, Alafia, Manatee and Little Manatee; and the region is strongly influenced by spring outflow from the Floridan Aquifer. The largest river, the Hillsborough, spans 54 miles from the Green Swamp to its mouth in Hillsborough Bay. Samples were collected over a two-week period in January of 2013 along 13 sites on the Hillsborough River and 26 stations in Tampa Bay. Metal concentration analyses were conducted on twelve elements using inductively coupled plasma mass spectrometry (ICP-MS). These twelve elements included sodium, lithium, magnesium, calcium, strontium, barium, vanadium, molybdenum, manganese, nickel, antimony, and uranium. Within Tampa Bay, sodium, lithium, and magnesium exhibited strongly conservative behavior (showing simple two-end-member mixing). Calcium, strontium, molybdenum, and uranium show quasi-conservative behavior, with localized deviations from simple mixing of fresh water and seawater end members. The remaining elements showed variable behavior driven by solubility, redox reactions, and/or unique localized inputs based on local geology. Comparisons of baywater calcium concentrations and the concentrations of lithium, magnesium, strontium and barium revealed simple relationships that are promising for use in interpretations of otolith chemistry of teleosts and some agnatha (Campana, 1999; Carlström, 1963). Samples were collected from both the river and the bay for CO2 system analyses. Spectrophometric pH measurements were obtained using purified m-Cresol Purple (mCP) and the procedures of Liu et al. (2011). Dissolved inorganic carbon (DIC) was processed according to CDIAC's Guide to Best Practices, SOP:2 (Dickson, Sabine, & Christian, 2007). Total alkalinity samples were processed using the spectrophotometric procedures of Yao and Byrne (1998). Dissolved inorganic carbon in the bay ranged between 3500 µMol/L and 2250 µMol/L and, in the Hillsborough River, peaked at 3700 µMol/L just below the Green Swamp. A comparison of measured total alkalinity and calculated alkalinity (obtained using pH and DIC and CO2sys software) demonstrated the presence of substantial organic base concentrations within the bay.
149

Proton and iron capture mechanisms of Bacillus sp. strain TA2.A1 at alkaline pH values

McMillan, Duncan George Glenn, n/a January 2008 (has links)
The thermoalkaliphilic Bacillus sp. strain TA2.A1 was able to grow in pH-controlled batch culture containing a fermentable growth substrate (i.e. sucrose) from pH 7.5 to 10.0 with no significant change in specific growth rate, suggesting that this bacterium is a facultative alkaliphile. However, when strain TA2.A1 was grown on non-fermentable carbon sources like succinate, no growth was observed until the external pH was > 9.0, suggesting this bacterium is an obligate alkaliphile. Growth on succinate at pH 9.5 was sensitive to both carbonyl cyanide m-chlorophenylhydrazone (CCCP) and monensin revealing that both the proton and sodium motive force ([Delta][mu][H⁺] and [Delta][mu][Na⁺], respectively) were obligate requirements for growth at alkaline pH values. Transport of succinate was driven by a chemical gradient of Na⁺ ([Delta]pNa⁺) that was strictly coupled to [Delta][Psi]. A single transport system was detected for the uptake of succinate, with an apparent K[m] of 19 [mu]M and V[max] of 0.45 nmol succinate/min/mg protein. Succinate transport was pH-dependent, and showed optimal activity at pH values greater than 8.5. Other C₄-dicarboxylates (e.g. malate, fumarate) inhibited the uptake of succinate suggesting that the permease was general for other C₄-dicarboxylates. Cytochrome content, succinate dehydrogenase oxidoreductase, and F₁F₀-ATPase activities were lower in membranes from strain TA2.A1 cells grown at pH 7.5 compared to those cultured at 9.5. These data suggest that oxidative phosphorylation-linked processes are down-regulated at neutral pH values, an observation that mirrored oxygen consumption profiles of strain TA2.A1 in whole cells. To study this phenomenon at a molecular level, we measured ATP synthesis by the F₁F₀-ATP synthase from strain TA2.A1 as a function of pH. The strain TA2.A1 F₁F₀-ATP synthase had a pH optimum for ATP synthesis of 9.0-9.5, and significantly lower rates of ATP synthesis observed below pH 9.0. Analysis of the atp operon from the thermoalkaliphilic Bacillus sp. strain TA2.A1 and comparison with other atp operons from alkaliphilic bacteria reveals the presence of a conserved lysine residue at position 180 (Bacillus sp. strain TA2.A1 numbering) within the a subunit of these F₁F₀-ATP synthases. We hypothesize that the basic nature of this residue is ideally suited to capture protons from the bulk phase at high pH. To test this hypothesis, a heterologous expression system for the ATP synthase from Bacillus sp. TA2.A1 (TA2F₁F₀) was developed in Escherichia coli DK8 ([Delta]atp). Amino acid substitutions were made in the a subunit of TA2F₁F₀ at position 180. Lysine (aK180) was substituted for the basic residues histidine (aK180H) or arginine (aK180R), and the uncharged residue glycine (aK180G). ATP synthesis experiments were performed in ADP plus P[i]-loaded right-side out membrane vesicles energized by ascorbate-phenazine methosulfate. When these enzyme complexes were examined for their ability to perform ATP synthesis over the pH range from 7.0 to 10.0, TA2F₁F₀ and aK180R showed a similar pH profile having optimum ATP synthesis rates at pH 9.0 to 9.5 with no measurable ATP synthesis at pH 7.5. Conversely, aK180H and aK180G showed maximal ATP synthesis at pH�s 8.0 and 7.5, respectively. ATP synthesis under these conditions for all enzyme forms was sensitive to DCCD. These data strongly imply that amino acid residue K180 is a specific adaptation within the a subunit of TA2F₁F₀ to facilitate proton capture at high pH. At pH values near the pK[a] of K180, the trapped protons readily dissociate to reach the subunit c binding sites but this dissociation is impeded at neutral pH values causing either a blocking of the proposed H⁺ channel and/or mechanism of proton translocation, and hence ATP synthesis is inhibited. The mechanisms where by alkaliphilic bacteria obtain iron remains unknown. Growth of strain TA2.A1 at pH 9.5 in the presence of the artificial iron chelators ethylenediamine O-hydroxyphenylacetic acid (EDDHA) and 2�2� dipyridal revealed that iron is an important requirement for aerobic growth at alkaline pH values. Furthermore, biochemical analysis showed that Bacillus alcalophilus and Bacillus pseudofirmus both synthesized orange catecholate siderophores, whilst Bacillus halodurans synthesized a hydroxamate siderophore. These tests showed that strain TA2.A1 synthesized both orange catecholate and hydroxamate siderophore/s. Attempts to purify the catecholate were unsuccessful. No homologues of previously identified non-ribosomal peptide synthase (NRPS) genes in Bacillus subtilis and B.halodurans were detected in the genome of strain TA2.A1 using both PCR and Southern hybridization using known non-ribosomal peptide synthase genes.
150

Physical modelling of mixing between rectangular jets present in tangentially fired brown coal boilers.

Scarsella, Alessio Angelo January 2007 (has links)
Large scale power generation commences with the combustion of coal or other fuel, which in turn converts high pressure water into steam which then drives a turbine thus generating electricity. Burning high moisture coal, such as lignite, for power generation implies that a significant amount of energy is wasted in vaporising the moisture, which could otherwise be used in the steam raising process. This implies that more moist coal would be required to drive the same process than if the coal was drier, thus increasing the amount of combustion products such as greenhouses gases. Introducing a dried coal in an existing boiler will significantly change the heat flux profiles, which could result in boiler damage or excessive fouling. Flame temperature is influenced by the supply of reactants; in most cases the limiting reactant will be oxygen. The supply of oxygen (through air) to a pneumatically transported coal stream and subsequent reaction is controlled by the localised fluid mechanics or ‘mixing’. This research aims to provide an understanding of the mixing process between the pneumatically transported coal and air in brown coal fired boilers by modelling the individual jets. The effects of the change in velocity ratio for the air (secondary) jets and fuel (primary) jets of rectangular burners typical of those found in brown coal fired boilers has been studied experimentally and is reported in this thesis. In particular, scientific analysis was used to investigate the physical mechanisms which control fuel-air mixing, and to quantify the concentration of primary and secondary fluid. The concentration data was used in a regression model in conjunction with a reactive combustion model, developed from a 1:30 scale cold model of the Yallourn W’ stage 2 boiler, in order that overall boiler performance can be assessed. This overall study is fundamental as a result of the questions raised concerning the future of brown coal in modern society. A qualitative flow visualisation study of the unconfined 1:30 scaled primary, and two adjacent rectangular jets, was conducted using single colour planar laser induced fluorescence. The characteristics of the jet flow were examined by imaging individually seeded primary and secondary jets and were visualised through four different planes longitudinally, on the axes of each jet. In addition, a transverse qualitative and quantitative study on the rectangular jets was also conducted for the individually seeded jets, and was visualised through planes of flow perpendicular to the direction flow, specifically at axial stations of x/D =0.1, 0.2, 0.5, 1, 2, 4, 6 and 8. The flow characteristics were also examined under different co-flow conditions, particularly secondary to primary jet velocity ratios (λ) of 0, 0.55, 1.4, 2.8, 3.6 and ∞. This quantitative data yields the basis for a 3D regression model to predict fuel-air mixing in actual boilers. A semi-quantitative investigation into some geometrical modifications on the rectangular jets was also conducted at velocity ratios of λ=0, 0.55 and 1.4. The rectangular nozzles were fitted with base plates orientated at 90 degrees and 60 degrees to the direction of flow. The longitudinal flow visualisation study highlighted the effect of velocity ratio on the flow field of the primary and secondary jets. In particular it showed that the main structures of the primary and secondary jets are sensitive to the co-flowing conditions. The primary jet also experienced the formation of coherent structures close to the bluff body re-circulation region for λ>2.8. The quantitative transverse analysis of the rectangular jets showed that the primary jet and secondary jets close to the nozzle exit plane distorted with a change in co-flowing conditions. The primary jet experienced distortion for λ>1.4, and the secondary jets experienced distortion for λ <1.4. A plausible mechanism for this “distortion” can be explained by different co-flowing conditions altering the velocity gradients of the jet, thus changing the denomination of the counter rotating vortices present in the corners of rectangular jets, allowing them to alter jet shape. The transverse quantitative analysis of the rectangular jets allowed for graphical representation of the normalised concentration of the primary and secondary jets in the radial direction and the centreline mixture fraction decay. The analysis of the latter showed that the primary jet, under all co-flow conditions, reached self-similarity at approximately x/D =4, whereas the secondary jets did so at x/D =2. The primary jets observed greater rates of centreline dilution at high velocity ratios, whereas the secondary jets did so at λ=0.55. The quantification of the centreline concentration decay obeyed the inverse rate law for all co-flowing conditions. The first order decay constant K₁, was found to be heavily dependant on velocity ratio. The planar transverse quantitative data of the primary and secondary jets was used with the method of weighted squares to develop a regression model that would three-dimensionally reproduce the scalar mixing field as a function of velocity ratio. The regression model reproduces scalar quantities for λ=0 and λ=0.55 to 3.6 for the primary jet and λ=0.55 to 3.6 and ∞ for the secondary jet, and is capable of predicting primary and secondary bulk fluid concentrations within 30 to 40 % of the measured values. A sensitivity analysis on the regression model revealed that it is highly responsive to the momentum-controlling region between the jets with a change in velocity ratio. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297627 / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2007

Page generated in 0.1609 seconds