This study is part of a project aimed at investigating the reasons for the noise generation and sound propagation in the hermetically sealed H25A air conditioner compressor manufactured by Bristol Compressor Co. This study aims to investigate the pressure fluctuations inside the compressor cavity and their effect on the forces generated by the impact of valves on valve seats and valve stops. In order to achieve this objective a computer program, which mathematically simulates the operation of the compressor, was written. The simulation program is capable of predicting the pressure fluctuations inside the cylinders as well as the various Cavities inside the compressor. The pressure driven forces on the suction and discharge valves can then be computed and their effect on the forces transmitted to the compressor shell be studied. The results from an earlier experimental study were used in order to verify the results generated by the simulation program. The results from the simulation program were comparable to the experimental values. / Master of Science

Vibration testing and analysis is becoming increasingly important in the electronics industry. It is used as a workmanship screen, as well as a way to duplicate the deployed environment in both the military and commercial avionics worlds. To minimize the effects of the vibration from testing and what will be encountered in service, the mechanical analyst must be able to accurately predict mode shapes and frequencies of in-situ PC board. This thesis will investigate modeling the wedge locks as non-uniform translational and rotational springs. The first eight natural frequencies of a rectangular circuit board (with no components soldered to it, and with wedge locks along two edges) will be empirically determined. Eight frequencies will be used to solve for four unknowns: continuously distributed translational and rotational spring stiffnesses along the segments of board that are in contact (two unknowns) with the wedge lock, and those that are not in contact (two unknowns). A finite element model will be developed of the physical system. The translational and rotational spring stiffnesses will be optimized to minimize an error function involving the difference between the empirical and analytically predicted natural frequencies. / Master of Science

A literature review was performed to investigate the current status of two-cycle gasoline engines from the standpoint of design, performance, benefits, lubrication and emissions. The two-stroke engine offers several significant advantages over its four-stroke counterpart, which include: simple design, low production cost, higher power to weight ratio, smaller size, lower peak operating temperatures, and lower NO𝗑 emissions. The main drawbacks of two-stroke engines are the high unburned hydrocarbon and particulate exhaust emissions which are attributed to the lubricating oil and the scavenge process. Technologies to reduce exhaust emissions from two-stroke engines are strongly contingent on the ability to develop improved, environmentally friendly, lubricants which can be used at high fuel:oil ratios. An experimental study of lubrication of an air-cooled, two-stroke, gasoline engine by tribopolymerization is presented. Tribopolymerization is defined as the planned or intentional formation of protective polymeric films directly and continuously on rubbing surfaces to reduce damage and wear by the use of minor concentrations of selected compounds capable of forming polymeric films in situ[12]. Two monomers were investigated as potential anti-wear compounds, namely (a) Cas dimer acid/ethylene glycol monoester, a condensation monomer, and (b) diallyl phthalate, an addition monomer. The condensation monomer was found to provide sufficient wear protection under a range of unloaded test conditions. Under loaded test conditions, however, piston scuffing occurred well before the planned test period of 20 hours had expired with all of the lubricants tested. Photomacrograph and SEM photographs reveal rather thick deposits on the monoester lubricated piston using a mass concentration of 0.5% monoester in gasoline. The heavy deposits were not noted using a mass concentration of 0.5% diallyl phthalate or with a 0.1% mass concentration of the monoester in bis (2-ethylhexyl) sebacate, a synthetic base oil. As a secondary topic which parallels this study, other existing and rising fuel lubricity problems have been investigated. The poor friction and wear characteristics of diesel, jet, and alcohol fuels have led to tribological problems in various engine fuel system components. The outstanding anti-wear performance of monomer additives in several similar tribological systems in the past shows good potential for the solution to a variety of current fuel lubricity problems. / Master of Science

The purpose of this study was to investigate the effects of keyboard height, the presence or absence of a wrist support, and keying time on different risk factors associated with musculoskeletal disorders experienced by VDT operators. Measurements of wrist posture, activity of the trapezius muscles, shoulder abduction and typing performance were recorded at fixed intervals during a controlled 40 minute keying task. Ratings of musculoskeletal comfort were recorded before and after each keying task. Six subjects performed the keying tasks on six different days. A different keyboard height and wrist support condition was tested on each day. For wrist extension, ANOVA showed that the effects of Keyboard Height, Wrist Support, and Height x Keying Time were significant. For ulnar deviation, the main effects of Keyboard Height and Keying Time were significant. For forearm pronation, only the effect of Wrist Support was significant. Mean shoulder abduction ranged between 0 and 2 degrees. Mean EMG activity for all keying tasks was 5.3 %MVC. Subjects made an average of 26.5 errors during each keying task (.6 errors/min.), and an average of 1.64 errors for each time interval (.8 errors/min.). For the reported change in musculoskeletal comfort of the back, neck, left and right shoulders, left and right upper arms, left and right forearms, left wrist, and left hand, the main effect of Wrist Support was significant. In all cases the decrease in musculoskeletal comfort was greater when the wrist support was absent. Subjects preferred wrist supports, and heights at or greater than seated elbow height. The keying condition that was preferred most by subjects was when the keyboard was positioned at elbow height and when the wrist support present. The condition preferred least was when the keyboard was positioned 5 cm below elbow height and when the wrist support was absent. These results indicate that the use of wrist supports can decrease wrist extension and musculoskeletal discomfort during keying tasks. Keyboard heights at or above seated elbow height may help decrease wrist extension but keyboard heights above elbow height may increase ulnar deviation. / Master of Science

The objective of this study is to design a composite that mimics the mechanical performance of a tendon. The biomimetic composite structure was composed of an elastomeric matrix reinforced with continuous polymer fibers. The matrix material was a thermoplastic polyurethane, Estane 5714 F5P. A polyamide (Nylon 6-6), a polyethylene terephthalate (Dacron) and a block copolymer of polyethylene oxide and aromatic polyurethane (Lycra) were used as the straight fiber reinforcement A crimped Nylon 6 fiber was obtained in order to simulate the crimp in natural tendon. The composites were manufactured with the polymer matrix in solution form. A solution of the polyurethane and tetrahydrofuran was used to coat the fibers using a single-tow coating device. The effect of structure of the composite on the mechanical properties was examined by manufacturing composites with three different structures: straight fiber reinforced, crimped fiber reinforced and braided composites. The composites were then examined for physical and mechanical properties. All of the composites exceeded the natural tendon's breaking strength and elongation to failure. Through biomimicking, a composite was manufactured with a higher initial stiffness and strength than the crimped nylon fiber. The shape of the stress-strain curves of tendon and the synthetic composites were also compared. The scale of the structure of the composites was compared to that of tendon. A non-dimensional ratio of the periodicity of the crimp to filament size (R) revealed a much larger level of structure in the synthetic composites than in the tendon. This ratio was found to have a correlation to the mechanical properties of the composites. / Master of Science

The cellular slime mold Dictyostelium discoideum is a simple eukaryote that has been used as a model organism for the investigation of eukaryotic cell signaling, regulation of gene expression, and development. Transcription of the gp-2 gene is induced during development and is regulated by extracellular morphogens such as cyclic AMP (cAMP; Sucic et al., 1993) and differentiation induction factor (DIF; Yin et al., 1994a). These morphogens are known to be involved in regulating cellular differentiation and pattern formation in the multicellular development of Dictyostelium. This makes the gp-2 gene a good candidate for the investigation of the mechanisms of regulation of gene expression during cellular differentiation. The gp-2 gene has been cloned and previous analyses of the promoter with 5' deletions have revealed the presence of several regulatory regions which contain repeated sequence elements; TA-boxes, the TAG-boxes, and C-boxes (Sucic et al., 1993; Rutherford et al., submitted). The C-rich regulatory region contains two C-box repeats and is the most proximal of the regulatory regions. The aims of this investigation are the precise definition of regulatory elements within the C-rich regulatory region and identification of the role played by these sequences in the transcriptional regulation of the gp-2 gene. The effects of disrupting regulatory sequences within the C-rich region with upstream regulatory elements intact were investigated using internal deletions and site-directed mutations. Using the luciferase reporter gene system it was shown that site-directed mutation of the downstream C-box (CB-2) and adjacent bases results in a 50-fold decrease in the developmentally induced luciferase levels compared to a wild-type promoter construct (OS). An internal deletion of this mutant construct that deletes the upstream Cbox (CB-1) and intervening sequences has no further effect on levels of expression induced during development. These data suggest that CB-2 and adjacent sequences are the regulatory sequences within the C-rich region that are involved in the transcriptional regulation of gp-2. The mutant promoter constructs regulate gene expression during development with the same temporal profile as the wild-type construct indicating that these sequences are not involved with the timing of induction of expression of the gp-2 gene. The induction of the gp-2 promoter constructs by extracellular cAMP was analyzed. The wild-type construct was induced approximately 10-20-fold by extracellular cAMP. However, the site-directed mutated promoter construct was not induced by cAMP under the same conditions. This suggests that CB-2 and adjacent sequences are involved with the induction of gp-2 expression by extracellular cAMP. Previously, 5' deletion analyses have shown that upstream regulatory elements are involved in cAMP-responsive expression of the gp-2 gene (Sucic et al., 1993). The data presented here indicate that the regulation of expression of the gp-2 gene by extracellular cAMP also requires sequences in and around CB-2. / Master of Science

Three genes encode identical calmodulin proteins in mammals. One possible reason for this unique situation is that it allows differential regulation of calmodulin gene expression. In order to study the promoter regions of the different genes, the 5’ ends of three mouse calmodulin cDNAs were isolated using a modified 5’ Rapid Amplification of cDNA Ends (RACE) method. Using these cDNAs as probes, the promoter regions of the Cam I and Cam III genes as well as a Cam II pseudogene were isolated from a 129SVJ mouse genomic library. When the Cam II cDNA was used to determine the chromosomal location of the Cam II gene, the results indicated that at least two likely pseudogenes exist in addition to the functional gene. Using a probe that contained only sequence from the promoter region and first intron of the Cam II gene, the chromosomal location of the bona fide Cam II gene was identified. Evidence indicates that conflicting growth signals in cells can lead to apoptosis. To determine if calmodulin, a proliferation signal, would induce apoptosis in cells cultured in differentiation conditions, C2C12 myoblasts were transiently transfected with a calmodulin expression vector. Half of the transfected cells were treated with calcium ionophore to determine if the calcium levels would have an effect. Overexpression of calmodulin did not lead to apoptosis, and the calcium ionophore caused death of the control- and calmodulin-transfected cells. / Master of Science

This work investigates power flow and energy transfer in controlled structures. If the goal of control is to stop an initially vibrating structure, energy must be forced out through dissipating components. The analysis performed here quantifies energy being transferred internally and externally to dissipative mechanisms in the primitives of a spring-mass-damper system and a beam-piezoelectrics-electronics system over the transient period of the systems’ response to initial conditions. The systems studied were broken down into capacitive, inertial, resistive and sourcing primitives. All systems containing primitives from all domains can be modeled this way. The analysis started from first principles and investigated energy flow in general. Energy flowing from the mechanical primitives to the electrical primitives is especially important because controlled structures often integrate primitives from these two domains. Computer simulations showed that power seemingly flows into sources used to control the structures. This work also laid the groundwork for the development of control design methods based on energy flow. / Master of Science

This study investigated the peak shaving and pollutant removal performance of an underground stormwater detention facility. The facility was located beneath the parking lot of a retail shopping mall in Prince William County, Virginia. The study methodology incorporated automatic inflow and outflow monitoring stations containing flow metering and automatic sampling equipment. The flow metering equipment continuously monitored flow rates, thereby making it possible to describe the inflow and outflow hydrographs. The automatic sampling equipment collected equal volume - variable time composite samples of runoff, making it possible to determine the inflow and outflow event mean concentrations of various pollutant constituents. Twenty runoff events were monitored between April, 1993 and January, 1994. The inflow and outflow hydrographs were compared to determine peak shaving performance. Due to the large volume of groundwater infiltration into the facility, which altered the inflow and outflow behavior, only 15 events were used in the peak shaving analysis. The inflow peak discharges for the 15 events were substantially less than the two year design storm used for the facility. To determine peak shaving performance at higher flow rates, design storms with greater peak flow rates were routed though the facility using the inventory method. The resultant peak shaving performance was similar to performance estimates in the facility design specifications. In fact, the facility actually reduced peak flows somewhat more than anticipated due to an outlet orifice that was constructed smaller than the design specified. To determine pollutant removal performance at the facility, inflow and outflow event mean concentrations for the various pollutant constituents were compared. A subset of 10 events was used in this analysis because of sampling equipment failures that resulted in insufficient distribution of sample aliquats over a runoff event. Seven different methods of quantification were used to estimate pollutant removal performance. Results indicated that, generally, the facility design and operational protocol provided little or no pollutant removal for most constituents monitored. The trace metals lead and copper were removed more consistently than any other constituents. Zinc was removed somewhat less than either lead or copper, probably because the storage pipe, being made of galvanized steel, was a source of zinc. / Master of Science

Experimental spatial dynamics modeling is a new method used to obtain a dynamic model of a harmonically excited vibrating structure. The continuous three-dimensional, complexed-valued velocity field of the structure is solved from a weighted least-squares finite element formulation, making use of high spatial density data obtained from a scanning laser Doppler vibrometer. Analytical expressions for the first- and second-order error sensitivity of the obtained model with respect to model parameters of the finite element model are developed. A frequency response analysis, resulting in a pseudo-dynamic stiffness matrix and the direct method of differentiation are used to obtain the required sensitivities. These sensitivities may be used to update the parameters to obtain a more accurate model, and also to yield a signal-to-noise level for which the data must be obtained. Analytical expressions are also developed for the first-order error sensitivity of the obtained model with respect to the spatial variables (position and orientation) of the laser. A parametric representation of both the laser beam as well as the surface of the structure is used. A variation in the spatial variables of the laser leads to a shift in the measured velocity, compared to the analytical model. The influence of changes in the spatial variables on the accuracy of the model is thus crucial. Once again, the results obtained may also be used to yield a signal-to-noise level for which the data must be obtained. The formulations developed are examined by making use of a theoretical model of a beam structure with out-of-plane harmonic excitation. / Master of Science