Chemical & Biomolecular Engineering
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Formerly known as the Department of Chemical Engineering.
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Item 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.Item 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.Item 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.Item 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.Item RNA Interference mediated knockdown of genes in order to increase protein production using the baculovirus expression system(Springer Nature, 2006-10-10) Hebert, Colin; Kim, Eun Jeong; Kramer, Shannon F; Valdes, James J; Bentley, William EItem Microbial nar-GFP cell sensors reveal oxygen limitations in highly agitated and aerated laboratory-scale fermentors(Springer Nature, 2009-01-15) Garcia, Jose R; Cha, Hyung J; Rao, Govind; Marten, Mark R; Bentley, William ESmall-scale microbial fermentations are often assumed to be homogeneous, and oxygen limitation due to inadequate micromixing is often overlooked as a potential problem. To assess the relative degree of micromixing, and hence propensity for oxygen limitation, a new cellular oxygen sensor has been developed. The oxygen responsive E. coli nitrate reductase (nar) promoter was used to construct an oxygen reporter plasmid (pNar-GFPuv) which allows cell-based reporting of oxygen limitation. Because there are greater than 109 cells in a fermentor, one can outfit a vessel with more than 109 sensors. Our concept was tested in high density, lab-scale (5 L), fed-batch, E. coli fermentations operated with varied mixing efficiency – one verses four impellers. In both cases, bioreactors were maintained identically at greater than 80% dissolved oxygen (DO) during batch phase and at approximately 20% DO during fed-batch phase. Trends for glucose consumption, biomass and DO showed nearly identical behavior. However, fermentations with only one impeller showed significantly higher GFPuv expression than those with four, indicating a higher degree of fluid segregation sufficient for cellular oxygen deprivation. As the characteristic time for GFPuv expression (approx 90 min.) is much larger than that for mixing (approx 10 s), increased specific fluorescence represents an averaged effect of oxygen limitation over time and by natural extension, over space. Thus, the pNar-GFPuv plasmid enabled bioreactor-wide oxygen sensing in that bacterial cells served as individual recirculating sensors integrating their responses over space and time. We envision cell-based oxygen sensors may find utility in a wide variety of bioprocessing applications.Item 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.Item 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.Item 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.Item 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.