A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item The Effects of Liquid Alkane Fuel Structure on Catalyst-Enhanced Combustion(2018) Dube, Grant; Oran, Elaine S; Lee, Ivan C; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The U.S. Army is developing micro-combustors for use in soldier-portable power generation systems. Many of the challenges associated with micro-combustion can be potentially overcome using a catalyst, but the effects of the catalyst on ignition under the low temperature, atmospheric conditions seen in the field are not well understood. To better understand catalytic ignition phenomena under these conditions, a Catalytic Ignition and Emissions Tester (CIET) was developed and used to investigate the effects of liquid alkane fuel structure during catalyst enhanced ignition. Various mixtures of n-octane and iso-octane, as well as single component n-dodecane and n-hexadecane, were chosen as simple, surrogate test fuels to represent gasoline, jet fuel, and diesel, respectively. Fuel reactivity was shown to decrease with increased branching for all metrics tested while the effects of chain length were less definitive. The global apparent activation energies of all fuels tested were found to be in the range of 41-61 kJ/mol with 95% confidence, significantly lower than those previously reported for non-catalytic hydrocarbon combustion (>100 kJ/mol).Item Dependence of the perpendicular anisotropy in Co/Au multilayers on the number of repetitions(American Institute of Physics, 2003-05-15) Gubbiotti, G.; Carlotti, G.; Albertini, F.; Casoli, F.; Bontempi, E.; Depero, L. E.; Mengucci, P.; Di Cristoforo, A.; Koo, H.; Gomez, R. D.The correlations between structure and magnetism in [Co(0.9 nm)/Au(5 nm)]XN multilayer films with different number of repetitions N510, 30, and 50, have been studied by the combined use of complementary structural and magnetic techniques, such as x-ray reflectivity, x-ray diffraction, and transmission electron microscopy, alternating gradient force magnetometry, magnetic force microscopy and Brillouin light scattering. On increasing the value of N, an overall improvement of the multilayer quality is observed which corresponds to a change in the micromagnetic structure and to an enhancement of the perpendicular anisotropy. These effects have been attributed to a reduction of the magnetostatic energy associated with the formation of perpendicular magnetic domains in multilayers with increasing number of layers repetitions.Item SYNTHESIS OF POROUS FILMS FROM NANOPARTICLE AGGREGATES AND STUDY OF THEIR PROCESSING-STRUCTURE-PROPERTY RELATIONSHIPS(2005-12-09) Ogunsola, Oluwatosin Abiola; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Porous films made from titania nanoparticle aggregates have a variety of uses in high surface area applications such as gas sensors, photocatalysts in treatment of wastewater and air pollutants, optical filters, and photovoltaic electrodes for low cost solar cells. A hybrid process based upon gas-to-particle conversion and particle precipitated chemical vapor deposition was used to synthesize porous films of titania nanoparticle aggregates. The residence time of particles in the reactor was varied and the influence on particle morphology and mechanical properties was studied. An increase in residence time resulted in an increase in primary particle diameter but did not significantly affect aggregate diameter, over the range of residence times considered in this study. The Young's modulus is shown to increase with a decrease in primary particle diameter. A study of the effect of post processing annealing on the particle morphology and mechanical properties was conducted. Increasing the annealing temperature resulted in particle growth at different temperatures and aggregate growth only at the highest temperature studied. The Young's modulus, however, shows only an influence of aggregate diameter, increasing as aggregate diameter increased. It is interesting to note that annealing did not result in a significant increase in Young's modulus or hardness until most of the surface area was lost. This suggests that annealing may not be the most effective process for strengthening films, if preservation of high surface area is desired. To better understand the effect of change in particle and aggregate diameters on Young's modulus, Monte Carlo and continuum methods were employed to explore structure-property relationships. A Monte Carlo method was used to simulate particle deposits and a finite element method was used to calculate the Young's modulus from strain energy of the deposits simulated. The results of this study indicate that a decrease in particle diameter increases the Young's modulus, especially below 15 nm. Aggregate size was not seen to have any effect on the Young's modulus, for the range of aggregate sizes considered. The results of these studies can be used to optimize the mechanical properties of titania films, made up of nanoparticle aggregates, for different desired applications.Item Construction Project Organizational Structuring(2005-04-20) Salgado, Carlos; Baecher, Gregory B; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents an extended research study of project organizational structuring design, using Mintzberg's design parameters of organization and Lucas' IT-enabled variables on construction building project organizations. To the design parameters of unit grouping, unit size, liaison devices, planning and control systems, decision-making system and design of positions, this dissertation study simultaneously considers virtual components, technological leveling, technological matrixing, electronic linking and communications. This study used Yin's multiple case holistic design approach for this extended research study with data from major successful building construction projects to illustrate the use of this extended view and compare its findings. Based on this extended research study, this dissertation develops a practical methodology for construction project organizational structuring design. Furthermore, this dissertation applied Robbins' measures of organization structure (complexity, formalization and centralization) for corroboration.