Chemical and Biomolecular Engineering Theses and Dissertations

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Creep Rupture Properties of Tin Tested at Constant Stress
(1954) Breen, John E.; Huff, Wilbert J.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
This investigation was initiated to study the creep characteristics of a simple, relatively pure, material at constant stress as compared to that tested at constant load. Tin was selected for the investigation. A series of creep tests were run to rupture at constant stress and constant load. The test variables were adjusted in these tests so that time to rupture varied from approximately 300 minutes to 33500 minutes (5 hours to 558 hours) at room temperature, and from 40 minutes to 2500 (0.67 hours to 41.7 hours) at 200 degrees F.
Battery Studies with Particular Reference to Organic Depolarizers
(1955) Monson, William L.; Huff, W. J.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
Since Volta's invention of the first primary cell, using silver and zinc, numerous other cell combinations have been studied, covering a wide variety of anode and cathode materials. The latter have included both inorganic and organic substances capable of electrochemical reduction, although, historically, organic cathode materials have received very much less attention than the inorganic. It was the purpose of this investigation to study the actual behavior of a selected number of quinones as depolarizers in primary cells. Performance of experimental cells was compared with cells of the usual dry cell composition but of the same size and construction as cells of experimental composition. The results show that certain substituted anthraquinones possess good depolarizing ability as measured by discharge voltage and coulombic capacity. Energy output in some cases was higher than that of the manganese dioxide control cells (zinc anodes in all cases) because of higher effective coulombic capacities. A qualitative study of the effect of substituents on the discharge voltages of various quinones showed that cell working voltages were much more sensitive to quinone substitution than were the calculated reversible potentials. Also, in the case of nitro-substituted anthraquinones more coulombic capacity was obtained than could be accounted for by the simple reduction to the corresponding hydroquinone. The possibility of a reduction of the nitro-group of this compound was considered. Substances investigated were benzoquinone, naphthoquinone, anthraquinone, and certain of their derivatives, using various electrolytes. The size of the experimental cells was such that about 0.2 gram of the various depolarizers could be studied conveniently.
Thermal Displacement in Copper-Gold Alloys
(1971) Gilmore, Charles M.; Bolsaitis, P.; Skolnick, L.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The thermal displacements and Debye temperatures are determined for single crystals of copper and Cu-Au solid solutions including Cu3Au of four degrees of long range order (0.0, 0.53; 0.8, .98). Other solid solution compositions studied were .91Cu-.09Au and .2Cu-.8Au. At the .91Cu-.09Au composition a one week anneal produced a nonequilibrium structure. After a one month anneal the thermal displacements decreased to a value nearly equal to the value for pure Cu. The thermal displacements in the quenched .75Cu-.25Au crystal were also nearly equal to the value for pure Cu, but the thermal displacements increased as the Cu3Au crystal approached the equilibrium condition of full order. In the Cu3Au crystals, which were partially or fully ordered, the thermal displacements of the individual Cu and Au atoms were determined. It was observed that the vibration amplitudes of the Cu atoms are not isotropic in this diatomic cubic crystal. The vibrations of the Au atoms are equal in the [110] and [001] directions within experimental uncertainty. Also, the thermal displacements decrease as the crystal is changed from fully ordered to fully disordered. This is consistent with calculations of the vibrational spectrum for ordered and disordered Cu3Au. The static displacements for the partially ordered S = .80 crystal were also determined from the same experiments as the thermal displacements. An Einstein model was developed to calculate thermal displacements and Einstein frequencies from interatomic potentials. The calculated thermal displacements are 10 to 20 percent less than the experimental values. This is due to the simplifying assumptions in the model. The model calculation and the experimental results do agree on the changes in the thermal displacements with alloying. The Einstein model is also used to calculate the vibrational entropy in alloys.
Local Atomic Arrangments and Solution Strengthening of Ta-Mo and Ta-Nb Alloys
(1975) Predmore, Roamer Edward; Arsenault, Richard J.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Ta-Nb alloys are shown to form random solid solutions by x-ray diffuse scattering measurements. These alloys have equal size atoms in their pure state with lattice parameters that are invariant in composition, obey Vegard's law, and exhibit an absence of solid solution hardening and an absence of fracture embrittlement at high solute concentrations. Ta-Mo atoms of about 5% difference in atomic size form short range ordered solid solutions with large atomic displacement effects. The Ta-Mo, and Ta-W, Nb-Mo and Nb-W alloys have in common a lattice parameter that varies in composition with a negative deviation from Vegard's Law. There is also a negative heat of mixing which is well correlated with short range order. In addition, all these alloys show linear solid solution hardening to high solute concentrations at room temperature and fracture embrittlement at high solute concentrations. Diffuse ex-ray scattering measurements on Ta-Mo alloys give the short range order parameters and atomic size displacements. The hardening is attributed to a combination of size effect induced substitutional solid solution hardening and short range order induced hardening.
An Investigation of Blast Waves Generated by Constant Velocity Flames
(1977) Luckritz, Robert Thomas; Marchello, Joseph M.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The relevant flow field parameters associated with the generation and propagation of blast waves from constant velocity flames were systematically studied through numerical integrations of the non-steady equations for mass, momentum, and energy. The flow was assumed to be that of an adiabatic inviscid fluid obeying the ideal gas law and the flame was simulated by a working fluid heat addition model. The flame velocity was varied from infinitely fast (bursting sphere) through velocities characterized by the nearly constant pressure deflagration associated with low Mach number laminar flames. The properties noted included peak pressure, positive impulse, energy distribution, and the blast wave flow field. Results were computed for the case of a methane-air mixture assuming an energy density, q = 8.0, an ambient specific heat ratio, Yo = 1.4 and a specific heat ratio behind the flame, Y4 = 1.2. In the source volume, as the flame velocity decreased to Mach 4.0 the overpressure increased. For flame velocities below Mach 4.0 the overpressure decreased, and approach the acoustic solution originally developed by Taylor. In the far field the overpressure curves for supersonic flame velocities coalesced to a common curve at approximately 70% of Baker's pentolite correlation. Far field overpressures for subsonic flame velocities decreased as the flame velocity decreased. For the flame velocities investigated the near field impulse was greater than the impulse from Baker's pentolite correlation. In the far field the flame generated impulse decreased to 60 to 75% of the pentolite impulse. In cases where the flow was expected to reduce to a self-similar solution and/or show Rayleigh line behavior it did. The calculations showed that the flow field behaved normally where expected, and for flow velocities where steady state behavior is not expected, non-steady behavior was observed.
Interface Broadening and Radiation Enhanced Diffusion During Sputter Depth Profiling
(1988) Chambers, George Paul; Rousch, Marvin; Chemical and Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The process of ion bombardment of solids has been investigated using Monte Carlo Computer Code simulation in conjunction with ultra-high vacuum experimental techniques. The computer code EVOLVE has been used to study the shape of the resultant collision cascade as well as the origins of sputtered particles while experimental studies of interface regions have been performed to elucidate the physical processes occurring during sputtering. The EVOLVE code models the target as an amorphous multicomponent semi-infinite solid. The target composition during ion bombardment is simulated. The study concludes that recoil activity grows in size and tends to move away from the target surface with increasing time. It is further concluded that the majority of sputtered atoms originate from early generations and are produced from sites near the entry point of the bombarding ion. Low energy noble gas ion bombardment of thin-film Cr/Ni multilayered structures has been performed in conjunction with Auger electron spectroscopy under UHV conditions. An accurate, reliable, and systematic parameterization of the interface region between metallic layers is presented. It is concluded from this study that the extent of the distortion of the interface region due to ion induced broadening is dependent not only on the material system used but on the experimental conditions employed as well. Lastly, radiation enhanced diffusion (RED) has been studied using Ag/Ni thin-film multilayered structures. A physical mathematical model of the radiation broadened Ag layer, capable of successfully deconvoluting the contributions to interface broadening due to RED from those due to cascade mixing and microstructure development, is presented and shown to be an accurate characterization of the interface region. It is concluded from the application of this model that RED can contribute substantially to interface broadening in multicomponent systems with low activation energies of diffusion. It is further concluded from this study that elevated temperatures, sustained during the depth profiling process, can cause the effects of RED to subside dramatically. This phenomenon is most probably due to the dispersion of complex defects responsible for the RED process.
Measurements of the Size Distribution and Aerodynamic Properties of Soot
(1989) Cleary, Thomas George; Gentry, James W.; Chemical and Biomolecular Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The particle size distribution and aerodynamic properties of soot agglomerates formed by the combustion of acetylene is studied. A positive pressure soot generator was constructed which allowed for the characterization of the soot aerosol. Nearly monodisperse particles (10 to 20 nm in diameter) have been observed at low acetylene flow rates. The mean size and width of the distribution are confirmed with a diffusion battery and a differential mobility analyzer. Size distribution measurements of soot agglomerates have been obtained from optical and electron microscopy for a range of acetylene flow rates. The electron microscopy results are compared to model predictions of the cluster size distribution. Friction coefficient measurements from electrical mobility classified agglomerates have been made and are compared to fractal models for clusters. Aerodynamic diameters of impacted agglomerates are related to the geometric mean size form optical microscopy. These results suggest that the geometric mean size can replace the spherical diameter if a particle density of 0.1 g/cc is assumed.
ENGINEERING THE B1 DOMAIN OF STREPTOCOCCAL PROTEIN G: STRUCTURAL INVESTIGATIONS BY MULTlDIMENSIONAL HETERONUCLEAR NMR
(2000) Frank, Mary Kirsten; Thirumalai, Devarajan; Institute for Physical Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
The B1 domain of streptococcal protein G provides a well-characterized system for structural investigations of proteins. In this thesis, the urea-unfolded state has been characterized, the tolerance towards hydrophobic substitutions in the core has been surveyed, the hydrogen exchange behavior of the backbone amides has been elucidated, and structural information on a tetrameric mutant of this domain has been gathered. The chemical shifts of the urea-unfolded state were assigned. The secondary chemical shifts, the 3JHNa coupling constants and the short-range NOEs gave no indication of residual structure. Measurement of the backbone 15N relaxation parameters revealed a region of restricted motion in the β3- β4 turn of the native protein. Motion in the rest of the protein was uniform, with the exception of 3-4 residues at either end of the chain. A series of hydrophobic substitutions were made in the hydrophobic core. The resulting mutants were assayed for stability and overall fold . The core of the protein is particularly sensitive to substitutions at position 26. One of the mutants was unable to adopt the GB1 fold and optimized its stability by adopting a homotetrameric form. Hydrogen exchange in the backbone amides was measured at 25 °C. Rates of hydrogen exchange were inversely correlated with burial of the amide nitrogen. The slow-exchanging backbone amides did not correlate with the hydrogen bonds formed early in protein folding. Hydrogen exchange rates from NH to ND and from ND to NH were similar. The ratio between these two rates does not correlate with any obvious physical parameters of the hydrogen bonds. Chemical shifts for the tetrameric mutant (HS#124) were determined using three-dimensional heteronuclear NMR techniques. Measurement of the backbone dynamics revealed a highly flexible region between positions 8 and 22. The secondary structure and β-sheet interactions of this mutant were characterized. The β-sheet interactions were intermolecular and only one of the three β-strand pairings was similar to the β-strand pairings found in wild type GB1 . The novel pairing is between β1 of one monomer and β1 of another monomer and a shift in register is observed for the β3-β4 pairing.
SLIDING MESH COMPUTATIONAL FLUID DYNAMICS SIMULATION OF A WIDE AND NARROW GAP INLINE ROTOR-STATOR MIXER
(2001) Kevala, Karl Rustom; Calabrese, Richard V.; Chemical and Biomolecular Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The FLUENT™ Computational Fluid Dynamics code was used to simulate the flow of water within an inline rotor-stator mixer. Two devices were simulated. Both had identical dimensions, except for the width of the shear gap: 4 mm for the 'wide gap' model and 0.5 mm for the 'standard gap' model. A two-dimensional approximation was used in conjunction with a RANS turbulence model and sliding mesh technique. Simulated turbulence intensities and mass flow rates are more evenly distributed in the standard gap model. Further, turbulence and mean shear levels within the gap are minimal and probably not important for the production of dispersions. The most intense turbulence is near the downstream stator slot wall, and it is due to fluid impingement. For the standard gap model, this region is more focused and of higher intensity. It is concluded that a narrow gap clearance is needed to produce high intensity stagnation flows on the stator teeth. Simulation results are also compared with previously reported measurements acquired via Laser Doppler Anemometry. With respect to mean velocity, qualitative agreement is good. Quantitatively, neither the mean velocities nor turbulence values are well predicted. This discrepancy is believed to be due in large part to leakage flow over the top of the rotor and stator teeth and to the three-dimensional nature of the flow. Future simulations should be carried out in three dimensions using more sophisticated turbulence models. Additionally, algorithms should be developed to decrease computation time by exploiting the periodic nature of rotor-stator flows.
FINELY-DISCRETIZED LATTICE MODELS FOR THERMODYNAMIC PROPERTIES OF FLUIDS
(2003-11-21) moghaddam, sarvin; Anisimov, Mikhail; Panagiotopoulos, Athanassios Z; Chemical Engineering
The demand for exploring thermodynamic and structural properties of complex fluids and their mixtures using molecular simulation methods sparks the need for efficient computational techniques. One such method is the fine-lattice discretization technique, for which these calculations can run up to two orders of magnitude faster than the off-lattice calculations. Generally, a major obstacle to simulating real systemsis the computational time required for evaluating the potential energy. In fine-lattice discretization techniques, the potentials of intermolecular interactions are calculated once at the beginning of thesimulation and are used repeatedly during the simulation. In this thesis, this technique is used along with grand canonical histogram reweighting Monte Carlo calculations to obtain the coexistence properties of various non-polar and polar real and model fluids. Moreover, mixed-field finite size scaling methods have been used to determine critical parameters of the systems studied. New intermolecular potential models have been developed for diatomic molecules using off-lattice calculations to reproduce experimentally observed coexistence densities, vapor pressures, and critical parameters. The goal was to investigate an important problem in fine-lattice discretization technique, namely, how to build fine-lattice models reproducing properties of diatomic molecules and other systems of interest. The results reported indicate that it is possible to obtain a good description of the phase behavior of models of real systems such as nitrogen, carbon dioxide, and water over a broad range of temperatures. It has been observed that the structural properties of lattice models depend heavily on the lattice discretization parameter, which controls how closely the lattice system approaches the continuum behavior. We have found that deviations of the critical temperatures are stronger by a factor of 5 for dipolar dumbbell model, compared to non-polar fluid models, ``monomers'' and ``dimers'' with one and two Buckingham exponential-6 sites, respectively. For the trimer model with quadrupolar interactions, the critical temperatures are less sensitive to the lattice discretization parameter. The observed effect of the lattice discretization parameter on estimates for the thermodynamic and structural properties of fluids raises the need for a theoretical investigation. We have studied the subject analytically in one-dimensional space for a hard-core potential model and numerically for a hard-core with a square-well and a variety of logarithmic repulsive potentials. We have found that the smoothness of the repulsive part of the function is largely responsible for the speed of convergence of critical parameters to their continuum counterparts. A numerical study of the two- and three-dimensional cases is presented and the dependence of the lattice discretization parameter on the number of lattice points contained within a hard-core sphere has been investigated. The distribution of the lattice points oscillates around a limiting form for the lattice discretization parameter.
Simplified Protein Purification Using Protein-Polysaccharide Conjugation
(2003-12-05) Small, David Andrew; Bentley, William E; Ehrman, Sheryl H; Raghavan, Srinivasa R; Weigand, William A; Chemical Engineering
The purification step of protein production and isolation is the most time consuming and complex step in processing. Optimization of the purification process requires rapid, economical, and cost-effective methods to purify proteins at both the small-scale and the large-scale. Instead of using complicated chromatographic techniques and dialysis, a more simplified method is proposed utilizing only a centrifuge. A tyrosine tag with an enterokinase enzymatic cleavage site was added to the C-terminus of green fluorescent protein (GFP). The tyrosine tagged protein was expressed in E. coli cells. The cells were harvested and lysed. The lysate containing the tyrosine tagged GFP was covalently coupled to a polysaccharide (chitosan) using tyrosinase enzyme. The GFP in the protein-polysaccharide conjugate was then liberated using the enzyme, enterokinase. This method was effective in conjugating and purifying the protein using a centrifuge with a limited number of processing steps.
USING ANTISENSE MESSENGER RNA TO DOWNREGULATE LON MEDIATED PROTEOLYSIS IN ESCHERICHIA COLI
(2003-12-18) Carter, Karen; Bentley, William E; Chemical Engineering
The advent of metabolic engineering has instigated the introduction of foreign heterologous proteins into host cells, such as Escherichia coli. However, the metabolic burden incurred by the host cell to produce the desired recombinant protein elicits a cellular stress response that can result in reduced yields and degradation of the desired protein. In, lon is one of the major proteases responsible for this abnormal protein degradation, including recombinant proteins. Consequently, a variety of antisense strategies have been examined and shown to effectively control endogenous gene expression and function in E. coli. For this investigation we explored using a 300 base pair sequence of the 5' coding region of E. coli lon gene, including the start codon, cloned into both the pSE420 and pTO plasmids in the antisense (reverse) orientation. We examined the ability of lon antisense RNA to inhibit the production of endogenous lon protease and increase the protein yield and activity of a model recombinant protein, organophosphorus hydrolase (OPH). Results indicate that the overproduction of lon antisense did effectively downregulate the production of endogenous lon. In addition, cultures induced for lon antisense also revealed higher OPH protein levels in the first hour of production and a 7-fold higher activity.
Protein Production Development with Recombinant Vaccinia Virus
(2004-04-29) Bleckwenn, Nicole Aleece; Bentley, William E; Chemical Engineering
The vaccinia virus expression system was developed into a scaleable recombinant protein production process in perfused mammalian cell culture. Growth of anchorage dependent HeLa cells on microcarriers and the suspension adapted HeLa S3 cell line were studied in bioreactor cultures utilizing the ATF System or hollow fiber filter, respectively, for perfusion. Recombinant vaccinia virus expressing enhanced green fluorescent protein (EGFP) as a model protein was used to study the effects of several process parameters on expression. These included multiplicity of infection (MOI), volume during infection, serum concentration during infection, inducer concentration, timing of inducer addition relative to infection, and dissolved oxygen and temperature during the protein production phase. Increases in protein yield were made as each of these parameters was studied. The microcarrier based system reached 20 mg/l EGFP while the suspension based system achieved 27 mg/l under the conditions found through experiment. A second virus containing the gene for gp120, an HIV envelope coat protein with complex post-translational modifications, was produced in microcarrier based bioreactor culture with HeLa cells. The protein produced was purified and analyzed for post-translational modifications which found that half of the molecular weight was contributed through N-linked glycans. The reactor culture produced 10.5 mg/l gp120 at 96 hours post infection with an ID(50) of 3.1 µg/ml. A survey of expression, using both EGFP and gp120 expressing viruses, was conducted on several mammalian cell lines which may be more appropriate for commercial manufacturing processes. Results varied, depending on the protein produced, with HeLa cells producing the most EGFP and BS-C-1 the most gp120. 293 cells performed fairly well in both cases and their use in other manufacturing processes and ability to grow in serum-free suspension culture lead to a recommendation that they be considered for further process development. These studies have provided insight into the vaccinia virus expression system as a potentially large-scale production method for complex human proteins. Further optimization of the process could continue to increase the yields and potentially bring this viral process into the arena of available technologies for production.
FLUID AND PARTICLE DYNAMICS IN AN AEROSOL VIRTUAL IMPACTOR
(2004-05-03) Charrouf, Marwan; Calabrese, Richard V; Chemical Engineering
The collection and characterization of chemical and biological aerosols is essential to many areas of particle research such as toxicological studies, pollutant sampling, and biohazard assessment. This work presents the simulation of a low cutpoint, high volume aerosol sampling device known as the "virtual impactor". A steady state, three dimensional RANS type calculation is done using the FLUENT(TM) computational fluid dynamics code to predict the turbulent flow field inside the device. Particle collection efficiency and wall losses are then obtained by solving the particle equation of motion governed by drag for mono-dispersed samples of spherical particles in the 0.1-0.4 micro-meter diameter range. Predictions of the mean fluid velocity field with the incompressible Reynolds stress model and the compressible k-epsilon turbulence model are relied upon for conducting particle tracking calculations. FORTRAN 90 computer code is developed to solve the particle equation of motion using an implicit second order accurate time integration scheme. In addition, a multi-variate, scattered point interpolation method is implemented to obtain the fluid velocity at a position away from an Eulerian mesh point. It is found that "adaptive" drag law models are necessary to correctly account for slip and compressibility. The results indicate the trends observed in the experiments, and a 50% cutpoint diameter between 0.250 and 0.275 micro-meter. Recommendations for improved modeling in future work are made.
Study of ocular transport of drugs released from a sustained release device
(2004-05-03) Kim, Hyuncheol; Wang, Nam Sun; Chemical Engineering
Delivering ocular therapeutics to a target site with minimal side effects requires detailed information about the distribution and elimination pathways. This knowledge can guide the development of new drug delivery devices. In this study, we investigated the movement of two drug surrogates, H-110, which is lipophilic, and Gd-DTPA, which is hydrophilic, released from polymer-based implants using a fluorescein technique and magnetic resonance imaging (MRI). We also studied the pharmacokinetics of intravitreally injected triamcinolone acetonide, a low water soluble drug used for treating sight-threatening diseases such as diabetic retinopathy and choroidal neovascularization associated with age-related macular degeneration (AMD). At 24 hour post implantation, H-110 released from an intravitreal implant was detected in the subretinal space. However, following a subconjunctival implant, very little H-110 fluorescence was detected in the subretinal region. H-110 most likely reached the subretinal space from an intravitreal implant by diffusion through the vitreous and retina. However, most of the H-110 released from a subconjunctival implant is thought to dissipate through the choroidal blood flow. Concentration profiles of Gd-DTPA, which was released from an intravitreal implant in a New Zealand white rabbit, approached pseudo-steady state within 7 to 8 hours and showed gradients at the rabbit's vitreous-retina border suggesting that diffusion was occurring into the retinal-choroidal-scleral membrane. Parametric analysis with a finite element mathematical model of the rabbit eye yielded for Gd-DTPA a diffusion coefficient of 2.8 × 10-6 cm2/sec in the vitreous and a permeability of 1.0 × 10-5 cm/sec in the composite retina-choroid-sclera membrane. Gd-DTPA concentration decreased away from the implant. Such regional concentration variations throughout the vitreous may have clinical significance when the ubiquitous eye diseases are treated using a single positional implant. Subconjunctival implants in vivo delivered a mean total of 2.7 µg of Gd-DTPA over 8 hours into the vitreous representing only 0.12% of the total amount of compound released from the implant in vitro. No Gd-DTPA was detected in the posterior segment of the eye. Ex vivo, the Gd-DTPA concentration in the vitreous was 30 fold higher suggesting the elimination of significant in vivo barriers to the movement of drugs from the subconjunctival space into the vitreous. We developed a new preservative-free formulation for intravitreal injections of triamcinolone acetonide for the treatment of diabetic macular edema, and choroidal neovascularization associated with AMD in human clinical trials at the National Institutes of Health. A pharmacokinetic study in rabbits was done to estimate elimination rate of two injection amounts of triamcinolone acetonide, 4 mg and 16 mg, from the vitreous. From our pharmacokinetic model, we found the half-lives for 4 mg and 16 mg injection in the vitreous to be 18.6 days and 37.6 days, respectively. We subsequently estimated the half-lives of 1 mg and 8 mg triamcinolone acetonide injection in order to predict therapeutic exposure in human. There are three components in this thesis: the study of lipophilic H-110 transport with fluorescence, the study of hydrophilic transport of Gd-DTPA with MRI, and the pharmacokinetic analysis of triamcinolone acetonide. They have each contributed to further insights into our fundamental understanding of drug movement in the eye and the implication on optimal therapeutic delivery.
Substrate Specificity and Molecular Characterization of PAH-Degrading Anaerobic Enrichment Cultures Under Methanogenic Conditions
(2004-05-06) Baldwin, Brandi; Holoman, Tracey R. P.; Chemical Engineering
Over the past several years, this lab has cultivated enriched anaerobic mixed cultures capable of degrading the low-molecular-weight polycyclic aromatic hydrocarbons (PAHs), naphthalene or phenanthrene, as a sole carbon source. Characterization of the enrichment cultures by 16S rDNA analysis revealed two unique populations, though they were initiated from the same sediment source. This study set out to determine the ability of these highly enriched communities to utilize a new carbon source, and to identify the effect of this shift on the population profile. The phenanthrene-degrading culture demonstrated significant naphthalene-degrading activity; however, the naphthalene-degrading culture was unable to degrade phenanthrene. Molecular characterization of these cultures showed a single species common to both original enrichment cultures and dominating in the population able to degrade both substrates. These results suggest that very few members of the mixed cultures participate in the degradation of PAHs, whereas the remaining members live off the metabolic byproducts.
Production of High Surface Area Silica Particles by Acoustodispersion Precipitation
(2004-07-28) Matthews, Jermey Norman Augustus; Harris, Michael T; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
A continuous Acoustodispersion Precipitation Reaction (APR) flow process was applied to the production of high surface area silica particles. An ultrasonic reactor was used to atomize and disperse silica gel into a drying chamber for further solidification. Upon particle synthesis, the resulting powder was analyzed The effect of sodium silicate concentration, volumetric flow rate through the ultrasonic nozzle, and drying temperature on particle diameter and specific surface area (Asp) was observed. A mathematical equation was derived using the Box-Behnken statistical design. SEM imaging was employed in measuring the particle size and observing the morphology, and BET theory was exploited in collecting surface area data. SEM images showed porous and spherical silica particles. The number average diameter of the particles ranged from 13 - 55 microns. Most of the Asp values ranged from 100 300 m2/g. The highest Asp achieved was 342 m2/g and the lowest was 19.9 m2/g.
Coil-to-Helix Transition of Poly(ethylene oxide) in Solution
(2004-07-30) Alessi, Michael Louis; Greer, Sandra C.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Poly(ethylene oxide) (PEO) is a simple polymer with repeating units [- C - C - O -] soluble in organic and aqueous solvents. The carbon atoms are hydrophobic; the oxygen atoms are hydrophilic and participate in hydrogen bonding. In all solvents in which PEO has previously been studied, PEO forms a coil in solution. Neutron scattering studies of PEO in isobutyric acid show that PEO undergoes a coil-to-rod transition in a solution of isobutyric acid (IBA). The stiffening is seen to progress smoothly with the addition of IBA, from a coil in D2O to a rod in pure deuterated-IBA. In addition to a solvent driven transition, a reversible rod-to-coil transition was seen to occur as a function of temperature, between 55 and 60 oC. Polarimetry experiments show that the rod formed by the PEO in solution is actually a helix, the conformation that PEO has in the solid state. It is also shown that, through the use of chiral impurities and temperature, the direction of the helix can be affected, allowing polymer folding to be influenced on a molecular level.
A STUDY OF GROUND-LEVEL OZONE OVER THE BALTIMORE/WASHINGTON OZONE NONATTAINMENT AREA
(2004-08-04) Choi, Yu-Jin; Ehrman, Sheryl H; Calabrese, Richard V; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Surface ozone is a persistent problem in U.S.A. and Europe as well as developing countries. A key prerequisite to identifying effective approaches to meeting an ozone air quality standard is to understand the relationship between VOC and NOx, the significance of biogenic emissions, and the contribution of long-range transport. The Baltimore/Washington area is an EPA-designated severe ozone non-attainment area. In this study, the characteristics of ozone events over this area were investigated to develop a possible control strategy. Both observational and computational modeling approaches were employed, and it was divided into three parts. The first part was to investigate sources of VOC emissions in the Baltimore area using highly time resolved measurements, and to investigate possible relationships between each VOC source category and episodes of elevated ozone concentrations. The results showed that biogenic emissions contribute significantly to local ozone production in this area. The second part was emissions inventory evaluation, focused on VOC emissions inventory because VOC estimates are commonly assumed to be more uncertain than NOx estimates. The results indicated a possibility of overestimation of solvent VOC emissions. Photochemical simulations with reduction of solvent VOC emissions did not affect ozone prediction, but affected significantly secondary organic aerosol prediction. Lastly, photochemical ozone simulations were performed to find an effective control strategy for this area. The simulation results showed that long-range transport of ozone was responsible for 20-90 ppb of ozone concentration in the state of Maryland, Northern Virginia, and D.C. area, displaying a decreasing contribution as it approached to the Baltimore/Washington area. Local emissions contributed considerably to high ozone occurrences in this area. Moreover, the contribution of biogenic VOC emissions in this region was responsible for much of the local ozone production, which was a consistent result from the part one. Accordingly, the results indicated that NOx emissions reductions would probably mitigate high ozone occurrences in this area, and this was confirmed through several simulations with emissions reductions. However, our results suggested that control of only local NOx emissions might not be sufficient to comply with the 8 hr ozone standard because of the importance of long-range transported ozone.
Suface-Modified Magnetic Nanoparticles for Cellular Interactions and Improved Biological Applications
(2004-08-17) Williams, Darryl Nathaniel; Pulliam Holoman, Tracey R; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
In order to enhance the utilization of magnetic nanoparticles in biological systems, it is important to develop a fundamental understanding of the interactions that take place between the two systems. Magnetic nanoparticles are of particular interest for applications such as transfection, biodetection, and targeted drug delivery to name a few. The goal of this research was to study the effect iron oxide nanoparticles have on cellular growth and function, as well as to improve the particles' stability and biocompatibility in aqueous and biological media. Particle synthesis consisted of producing magnetite using the Massart method. Composite iron oxide nanoparticles produced under combustion synthesis were also studied. Previous results indicated that the inorganic nanoparticles formed small aggregates in microbial growth media, thus influencing particle stability. To mitigate this problem, a stabilizing polymer known as gum arabic was tested to control particle size and prevent further agglomeration in aqueous and growth media. Results showed that gum arabic greatly improved particle stability. Growth studies measured the influence of the nanoparticles on cell proliferation using both M9 and Luria Bertani media to track growth of Escherichia coli (E. coli) in minimal and rich growth conditions. In addition to E. coli, prostate carcinoma cells (cell line DU145) were cultured in the presence of the treated nanoparticles to determine whether gum arabic improved the uptake of the particles in mammalian cells. Fluorescent microscopy was incorporated to detect the location of the nanoparticles in or about the cells by labeling the gum arabic with fluorescein isothiocyanate (FITC). The results illustrate the potential use of gum arabic as a surface-modifying agent to improve magnetic particle stability, as well as to promote nanoparticle uptake by mammalian cell cultures.