Laboratory and field experiments measured urea uptake and assimilation with ¹⁴C⁻ and ¹⁵N-urea and by disappearance of dissolved urea. A modified diacetyl monoxime method was developed, which accurately and precisely determined dissolved urea concentrations in seawater. In the Strait of Georgia, chlorophyll α (chl α) specific uptake rates of ammonium (NH₄⁺) and urea were greatest in stratified water; whereas, chl α specific uptake rates of nitrate (NO₃⁻) were greatest in frontal water. Ammonium and urea regeneration rates were calculated by a mass balance method and the rates were similar. Differences between measurements of particulate nitrogen, dissolved NH₄⁺, NO₃⁻ and urea, and ¹⁵N uptake were used to explain the dominant N transformations in frontal and stratified seawater. Uptake rates measured by ¹⁴C-urea were ca. 1.4 times faster than those determined by ¹⁵N-urea in the Sargasso Sea. Turnover times of urea in the surface-mixed layer were ca. 12 h. Within some seawater samples, phytoplankton utilized urea at rates which approximated the maximum rates of utilization. In a nitrate-sufficient culture of Thaiassiosira pseudonana (clone 3H) (Hustedt) Hasle and Heimdal, urea uptake rates measured by three methods disagreed; whereas, no discrepancies occurred in a nitrate-starved culture. NH₄⁺ was released from cells after urea was taken up and was later reabsorbed. A model of urea uptake and assimilation by T. pseudonana is proposed. An obligate selenium (Se) requirement for growth of T. pseudonana was demonstrated in axenic culture in artificial seawater. The addition of 10⁻⁹ M SeO₃²⁻ to culture medium was sufficient for good growth of this alga; SeO₄²⁻ was only effective at concentrations greater than 10⁻⁷ M. To elucidate the biochemical role of Se in T. pseudonana, cells were cultured in medium containing 10⁻⁹ M Na₂ ⁷⁵SeO₃. Two soluble polypeptides of 21 and 29 kD contained ⁷⁵Se. Glutathione peroxidase was detected on non-denaturing polyacrylamide gels and ⁷⁵Se co-migrated with the enzyme. It was concluded that Se is an essential element for growth of T. pseudonana due, in part, to the presence of the selenoenzyme glutathione peroxidase. / Science, Faculty of / Botany, Department of / Graduate

Yes / Solid urea is the largest nitrogen fertilizer product which is produced in two forms of granules and prills. Although the chemical properties of both prills and granules remain similar, their different physical and mechanical properties are distinguishable and make them suitable for different application either as fertilizer or raw materials for chemical industry. The objective of this work is to analyses physical and mechanical properties of urea granules produced in two different plants in Malaysia using fluidized bed process and compare them with the imported urea prills to the country; hence make a process-product relationship for urea finishing processes. Results of size distribution of the samples show that the most of the granules fall in the size range between 2.82 and 3.06 mm, whereas the prills size is around 1.65 mm. Strength measurement using side crushing test also shows that the prills with the average failure load of 3.80 N remain significantly weaker than the granules with failure load of 10-17 N. Strength distribution of the particles also shows that a more uniform strength distribution is observed for the prills than the granules. It is concluded that the urea prilling process is the finishing process which produces the weaker and the more uniform size and strength of the particles than the fluidized-bed granulation process.

The addition of Tier 2 standards by United States Environmental Protection Agency (EPA) has increased focus on light-duty vehicle emissions. In this study, a diesel-electric hybrid vehicle was used for testing under the Challenge X program. The diesel engine was powered by a 20% soy-based biodiesel - 80% diesel blend, and the electric motor received its energy from a 330 volt Nickle Metal Hydride battery pack. The diesel engine, notorious for high emissions of nitrogen oxides (NOx) and particulate matter (PM), requires aftertreatment of these emissions to achieve Tier 2 EPA compliance. The primary focus of this thesis is use of a urea injection selective catalytic reduction (SCR) system to reduce NOx emissions. Also, a diesel particulate filter (DPF) was employed for PM reduction purposes. Significant decreases in both NOx and PM emissions were achieved.

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Thesis (M.S.)--Miami University, Dept. of Zoology, 2007. / Title from first page of PDF document. Includes bibliographical references (p. 17-19).

I och med nuvarande och kommande lagkrav för utsläpp från tunga lastbilar finns en efterfrågan på utvecklade strategier för utsläppsminskning. För att kontrollera utsläppen av kväveoxider (NOx) används katalytisk omvandling med AdBlue (vätskeblandning av urea och vatten).  AdBlue-dropparna förångas av avgaserna eller på en förångningsyta där en väggfilm kan skapas som i sin tur kan öka risken för utfällningar av urea. Därför finns ett behov av ett reglersystem för att minimera risken för utfällning,  Målet med detta examensarbete var att skapa en bättre förståelse för hur risken för utfällning av urea kan relateras till den nuvarande kalibreringen på Scania och föreslå hur det nuvarande reglersystemet kan förbättras. Tester uppdelat i två delar genomfördes i en provcell. Först testades ureadoseringen i pulser där doseringsmängden, förångningstiden och pulsfrekvensen varierades. Därefter testades varierat avgasflöde mellan två flöden genom att ändra ramptiden.  Genom visuella inspektioner visade det sig att pulserna med urea behöver längre förångningstid än vad den aktuella kalibreringen anger. Detta för att minska risken av utfällningar. Vid dosering av urea över den stationära förångningskapaciteten skapades väggfilmen längre bort från doseringsenheten. Detta leder till mindre effektiv användning av den doserade urean. För varierat avgasflöde med de valda ramptidena förändrades inte risken för utfällning. Därför skulle det nuvarande styrsystemet kunna förbättras genom att inkludera en längre tid för förångning mellan ureadoseringspulserna. / With current and upcoming emission legislation for heavy-duty transport, there is a demand for improved emission abatement strategies. To control nitrogen oxide (NOx) emissions, catalytic conversion with AdBlue (a liquid mixture of urea and water) is used. Droplets of AdBlue are evaporated by the exhaust gas or on an evaporation surface where a wall film can be created. A wall film increases the urea deposit risk which in turn causes problems. Consequently, there is a need for a control system to minimize the risk of urea deposits. The target of this thesis was to create a better understanding of how the urea deposit risk can be related to the current control calibration at Scania and to suggest how the current control system could be improved. Tests were performed in an engine testbed, in two parts. Firstly, varying of urea dosing was tested in pulses where the dosing amount, evaporation time and pulse frequency were varied. Secondly, the exhaust flow rate was varied between two flows by changing the ramp time. Through visual inspections, it was shown that the urea dosing pulses need longer evaporation time than the current control calibration states, to reduce the build-up of urea deposits. Furthermore, when dosing urea above the stationary evaporation capacity, the wall film was created further away from the dosing unit, thus, leading to less efficient use of the injected urea. For varying exhaust flow rate, the chosen ramp times did not change the urea deposit risk. Therefore, the current control system could be improved by including longer time for evaporation between the urea injection pulses.

Call number: LD2668 .T4 1960 H55

Drip irrigation lines placed 15 cm deep or 5 cm shallow below soil surface and furrow irrigation were compared on calcareous soils of southern Arizona. Crops grown were zucchini squash (Cucurbita pepo L.) 1982 and 1983 summers, and cabbage (Brassica oleracea var. capitata L.), 1982 fall. Furrows received a preplant application of phosphorus (P) at a rate of 100 kg P₂O₅/ha. Urea phosphate (UP) (17-44-0) solution was injected twice in drip lines during the growing season to give a total rate of 100 kg P₂O₅/ha on cabbage and 50 kg P₂O₅/ha on squash. Deep drip lines produced 52 and 34% higher yield than shallow drip in squash 1982 and 1983 experiments respectively. Deep drip yields were comparable to fertilized furrow yields with half the water and half the fertilizer rate of the furrow used by the deep drip. Unfertilized furrow yielded least. Application of UP in deep drip raised PO₄-P and NO₃-N concentration in squash leaves to comparable values in fertilized furrow plants. Shallow drip and unfertilized furrow plants had low nutrient concentrations. Soil analysis for NaHCO₃ extractable P and NO₃-N showed higher levels under drip than furrow treatments. Available P increased to 20 cm from emitters. EC was lower under drip than furrow. Soil pH was reduced by 0.5 units around emitters. Soil moisture in root zone was highest under furrows. Deep drip had more moisture than shallow drip. Injection of UP reduced water pH to 1.8 which prevented P precipitation. Cabbage yields were comparable under all fertilized treatments. Deep drip yielded 19% higher than shallow drip. Tissue analysis showed higher nutrient concentration under drip than furrow treatments. Soil analysis showed higher available P and NO₃-N and lower EC and pH under drip than furrow treatments. Mobility of PO₄ from UP was about 20 cm in soil columns. Rate of P fixation was high. Reduction in pH followed same pattern of P mobility. Root growth and distribution was more extensive under deep than shallow drip. Roots concentrated around deep UP zone in transparent cylinders.