View All Items
(1 - 20 of 171)
Pages
- Title
- ASCERTAINING THE GROWTH OF A COMPANYA SYSTEM DYNAMICS APPRAOCH.
- Creator
-
Noor Mohideen, Fakir Mohideen, Rabelo, Luis, University of Central Florida
- Abstract / Description
-
Business is often about creating change for other businesses. At times, these changes affect only the company and at other times they affect the entire industry. There is a time in the life of a business when its fundamental way of functioning is questioned and is subjected to change. That change can mean an opportunity to rise to new heights, or it might even signal the beginning of the end. This fundamental change in any business is known as an inflection point. Understanding the nature of...
Show moreBusiness is often about creating change for other businesses. At times, these changes affect only the company and at other times they affect the entire industry. There is a time in the life of a business when its fundamental way of functioning is questioned and is subjected to change. That change can mean an opportunity to rise to new heights, or it might even signal the beginning of the end. This fundamental change in any business is known as an inflection point. Understanding the nature of its inflection point and responding to that point suitably will help to safeguard a company's growth. So today's managers, when faced with such changes, have to be equipped with the adequate tools to guide the company out of troubles and to place it in a position where it can prosper. The fundamental changes can be scrutinized by studying the internal dynamic behavior of the system. Therefore, the managers are required to be systems thinkers so that they can study the internal dynamic behavior of the company and maneuver the inflection point successfully. System dynamics is an effective tool, which helps the managers to understand the structure and internal dynamic behaviors of a large and complex system. System dynamics models are developed to assist the management to navigate its way through the inflection point. This thesis focuses on how system dynamics model-analysis and model based policy development process can help a company to overcome an inflection point. Further enhancements and calibrations can be done to the model to provide industry specific solutions.
Show less - Date Issued
- 2005
- Identifier
- CFE0000335, ucf:46300
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000335
- Title
- Controlled Bubble Dynamics Inside Micropillar Arrays.
- Creator
-
Khalil Arya, Faraz, Peles, Yoav, Gou, Jihua, Kassab, Alain, Abdolvand, Reza, University of Central Florida
- Abstract / Description
-
Bubble dynamics inside micro domains was manipulated and used to pump liquid. Micropillars were formed inside two 1.5 mm wide and 220 (&)#181;m high microchannels with a length of 23 mm. One microchannel had three arrays of micropillars with diameters of 40 (&)#181;m and the other had a single array of micropillars with diameters of 30 (&)#181;m. An array of five 200 (&)#181;m by 200 (&)#181;m heaters was deposited inside these micropillar arrays and was used to control bubble size and...
Show moreBubble dynamics inside micro domains was manipulated and used to pump liquid. Micropillars were formed inside two 1.5 mm wide and 220 (&)#181;m high microchannels with a length of 23 mm. One microchannel had three arrays of micropillars with diameters of 40 (&)#181;m and the other had a single array of micropillars with diameters of 30 (&)#181;m. An array of five 200 (&)#181;m by 200 (&)#181;m heaters was deposited inside these micropillar arrays and was used to control bubble size and trajectory. A sequential power switching of the heaters was used to pump liquid in a desired direction with a flow rate of up to 133 (&)#181;l/min for the three arrays micropillars microchannel and up to 44.4 (&)#181;l/min for the single array micropillars device.
Show less - Date Issued
- 2018
- Identifier
- CFE0007757, ucf:52381
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007757
- Title
- Analysis and Design Optimization of Multiphase Converter.
- Creator
-
Zhang, Kejiu, Wu, Xinzhang, Batarseh, Issa, Yuan, Jiann-Shiun, Sundaram, Kalpathy, Chow, Louis, University of Central Florida
- Abstract / Description
-
Future microprocessors pose many challenges to the power conversion techniques. Multiphase synchronous buck converters have been widely used in high current low voltage microprocessor application. Design optimization needs to be carefully carried out with pushing the envelope specification and ever increasing concentration towards power saving features. In this work, attention has been focused on dynamic aspects of multiphase synchronous buck design. The power related issues and optimizations...
Show moreFuture microprocessors pose many challenges to the power conversion techniques. Multiphase synchronous buck converters have been widely used in high current low voltage microprocessor application. Design optimization needs to be carefully carried out with pushing the envelope specification and ever increasing concentration towards power saving features. In this work, attention has been focused on dynamic aspects of multiphase synchronous buck design. The power related issues and optimizations have been comprehensively investigated in this paper. In the first chapter, multiphase DC-DC conversion is presented with background application. Adaptive voltage positioning and various nonlinear control schemes are evaluated. Design optimization are presented to achieve best static efficiency over the entire load range. Power loss analysis from various operation modes and driver IC definition are studied thoroughly to better understand the loss terms and minimize the power loss. Load adaptive control is then proposed together with parametric optimization to achieve optimum efficiency figure.New nonlinear control schemes are proposed to improve the transient response, i.e. load engage and load release responses, of the multiphase VR in low frequency repetitive transient. Drop phase optimization and PWM transition from long tri-state phase are presented to improve the smoothness and robustness of the VR in mode transition. During high frequency repetitive transient, the control loop should be optimized and nonlinear loop should be turned off. Dynamic current sharing are thoroughly studied in chapter 4. The output impedance of the multiphase synchronous buck are derived to assist the analysis. Beat frequency is studied and mitigated by proposing load frequency detection scheme by turning OFF the nonlinear loop and introducing current protection in the control loop.Dynamic voltage scaling (DVS) is now used in modern Multi-Core processor (MCP) and multiprocessor System-on-Chip (MPSoC) to reduce operational voltage under light load condition. With the aggressive motivation to boost dynamic power efficiency, the design specification of voltage transition (dv/dt) for the DVS is pushing the physical limitation of the multiphase converter design and the component stress as well. In this paper, the operation modes and modes transition during dynamic voltage transition are illustrated. Critical dead-times of driver IC design and system dynamics are first studied and then optimized. The excessive stress on the control MOSFET which increases the reliability concern is captured in boost mode operation. Feasible solutions are also proposed and verified by both simulation and experiment results. CdV/dt compensation for removing the AVP effect and novel nonlinear control scheme for smooth transition are proposed for dealing with fast voltage positioning. Optimum phase number control during dynamic voltage transition is also proposed and triggered by voltage identification (VID) delta to further reduce the dynamic loss. The proposed schemes are experimentally verified in a 200 W six phase synchronous buck converter.Finally, the work is concluded. The references are listed.
Show less - Date Issued
- 2013
- Identifier
- CFE0005079, ucf:50742
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005079
- Title
- Conformations and Dynamics of Semi-Flexible Polymers.
- Creator
-
Huang, Aiqun, Bhattacharya, Aniket, Kokoouline, Viatcheslav, Tatulian, Suren, Campiglia, Andres, University of Central Florida
- Abstract / Description
-
In this dissertation, we investigate the conformations, transverse fluctuations and dynamics of two-dimensional (2D) semi-flexible polymers both in the bulk and under channel confinement. We present unified scaling relations in regard to various quantities of interest for a broad range of combinations of chain length and chain stiffness using Langevin dynamics simulation. We also present a three-dimensional (3D) heterogeneous semi-flexible chain model for a double stranded DNA (dsDNA). Our...
Show moreIn this dissertation, we investigate the conformations, transverse fluctuations and dynamics of two-dimensional (2D) semi-flexible polymers both in the bulk and under channel confinement. We present unified scaling relations in regard to various quantities of interest for a broad range of combinations of chain length and chain stiffness using Langevin dynamics simulation. We also present a three-dimensional (3D) heterogeneous semi-flexible chain model for a double stranded DNA (dsDNA). Our model not only confirms the established findings for homogeneous dsDNA, but also predicts new physical phenomenon for heterogeneous dsDNA. The problems studied in this dissertation are relevant to analysis of the conformations and dynamics of biopolymers (such as DNA) in living organisms, and also offer insights for developing devices which operate on the single-molecule level.In particular, we present a unified description for the dynamics of building-blocks (monomers) of a semi-flexible chain. We consider the full range of flexibility from the case where the chain is fully flexible (no stiffness at all) to the case where the chain behaves like a rod (infinite stiffness). Our theory predicts qualitatively different sub-diffusive regimes for the monomer dynamics originating from the chain stiffness by studying the mean square displacement (MSD) of the monomers before the chain dynamics become purely diffusive.For the conformations in the bulk, we present results confirmed and agreed by two completely different models of semi-flexible polymers, with one of which is the bead-spring model (studied by Langevin dynamics) in the continuum space, the other (studied by Monte Carlo) is a self-avoiding walk chain on the square lattice, where only discrete bond angles are possible. We point out the universal features of chain conformations and fluctuations which are independent of the models.For the conformations under channel confinement, we discover qualitatively different conformations and dynamics of the chain as a function of the channel width and chain stiffness, and show how globule like shapes ((")de Gennes blobs(")) for more flexible chains continuously go over to shapes in the form of deflections from the wall ((")Odijk limit(")) for more stiff chains. We provide theoretical arguments how these regimes occur and interpolate among each other as one varies different parameters of the model. We also demonstrate the effect of physical dimensions (either 2D or 3D) on these regimes and argue that since in 2D the excluded volume (EV) effect is more severe compared to 3D, certain regimes do not exist in 2D.Finally, we study a model of a dsDNA , where both base-pairing and base-stacking interactions are accounted for albeit at a low computational cost compared to the other existing models. Our model correctly recovers the stiffness for dsDNA and ssDNA at different temperatures. Under most conditions of interest, a dsDNA can locally denature and form bubbles due to thermal fluctuations. At a critical temperature, a dsDNA undergoes a phase transition, in which the two strands of dsDNA completely melt to two single strands (two ssDNA). By considering EV interactions and calculating the bubble size distribution, recent studies have shown that this denaturation process is a first order transition. We show that for a homogeneous dsDNA made of only AT or GC pairs, our simulation results agree with the previous conclusion of first order transition, however, for sequences of periodic AT and GC regions, when the periodic size is relatively large compared to the sequence length, we show that the bubble size distribution exhibits peaks expressing the sequence pattern, and more importantly, the denaturation is no longer a first order transition.All these studies reported in the dissertation are relevant to the physics of living systems.
Show less - Date Issued
- 2016
- Identifier
- CFE0006464, ucf:51429
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006464
- Title
- DYNAMIC SPEED MONITORING SYSTEM EFFECTIVENESS ON SHARP CURVES.
- Creator
-
Persaud, Vasu, Oloufa, Amr, University of Central Florida
- Abstract / Description
-
The design of rural interchanges is of critical concern due to the need for the safe transition of vehicles from one high speed roadways to another and vice versa. This transition is accomplished by entry and exit ramps of various forms. The southbound entry loop ramp at the US 27/ US 192 trumpet interchange in Polk County, Florida does not provide such safe transition since historically there has been a high incidence of vehicular off-tracking. The geometry of the southbound entry ramp...
Show moreThe design of rural interchanges is of critical concern due to the need for the safe transition of vehicles from one high speed roadways to another and vice versa. This transition is accomplished by entry and exit ramps of various forms. The southbound entry loop ramp at the US 27/ US 192 trumpet interchange in Polk County, Florida does not provide such safe transition since historically there has been a high incidence of vehicular off-tracking. The geometry of the southbound entry ramp coupled with high approach speeds are two of the contributing factors. Due to the high cost of interchange modification and ramp realignment, one approach to increasing safety at the interchange is to decrease approach speeds (assumes that speed is a surrogate measure of safety) utilizing a Dynamic Speed Monitoring (DSM) system. The objective of this thesis was to test the effectiveness of such a DSM system at reducing vehicle speeds at the rural US 27/ US 192 trumpet interchange in Polk County, Florida. The system tested was a solar powered, radar based, wireless speed warning system which potentially could be used at traffic locations where it is difficult to secure power and to extended wires. The Measures of Effectiveness (MOEs) for the system were the reduction in mean and variance of speed along with the proportion of vehicles in the higher speed ranges after system implementation. This thesis describes the testing of the DSM effectiveness and involves the documentation of the experiments conducted, the data collected and the analysis of the results. Speed data was collected Before and After installation of the DSM system at two points preceding the southbound entry ramp. Approach speeds were collected at a point 250 feet in advance of the southbound entry ramp curve (also the detection zone of the DSM system radar) and PC speeds were collected at the Point of Curve of southbound entry ramp. Various data sets were analyzed in order to ascertain the systems effectiveness during the day and night, weekdays and weekends, various time periods during the day, and within various speed ranges. The Approach and PC data analysis indicated that the DSM system significantly (at the 95% confidence level) reduced speed mean and variance and increased speed limit/ advisory speed compliance. The Approach mean speed was reduced by 3.58 mph and the PC mean speed was reduced by 1.57 mph. The Approach speed variance was reduced by 3.34 and the PC speed variance was reduced by 0.70 mph. Approach speed limit compliance was increased by 22.27% and PC advisory speed (35 mph) + 5 mph compliance was increased by 11.56% (it was apparent that motorist were utilizing speeds above the advisory speed to navigate the curve). In general, the effectiveness of the DSM system was diminished on weekends as well as during the late night and early morning (12 AM to 7 AM) time periods. This suggested that when there were lower volumes and when motorists' perceived that speed limit enforcement was not as likely, the DSM system effectiveness was reduced. The DSM system resulted in a reduction in the percentage of vehicles utilizing the higher speed ranges (> 45 mph). There was a 62% average reduction in the vehicles that utilized the speed ranges above 57 mph for the Approach data and there was a 36% average reduction in the vehicles that utilized the speed ranges above 45 mph for the PC data. The DSM system resulted in a shift in the distribution of speeds from the higher speed bins to the lower speed bins Before and After installation.
Show less - Date Issued
- 2007
- Identifier
- CFE0001864, ucf:47388
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001864
- Title
- THE EFFECTS OF STIMULUS MOTION ON CONTRAST SENSITIVITY: DYNAMIC SENSITIVITY FUNCTIONS.
- Creator
-
Zavod, Merrill, Rinalducci, Edward, University of Central Florida
- Abstract / Description
-
Static Visual Acuity (SVA) has been called into question for some time as a measure of overall visual system function and as a predictor of performance on real-life tasks requiring vision (i.e., operating an automobile). Specifically, it has been pointed out that the targets employed in most SVA testing (high contrast, stationary letters) are an insufficient analog to actual targets encountered in everyday activities, which are often in motion and/or of less-than-perfect contrast. In addition...
Show moreStatic Visual Acuity (SVA) has been called into question for some time as a measure of overall visual system function and as a predictor of performance on real-life tasks requiring vision (i.e., operating an automobile). Specifically, it has been pointed out that the targets employed in most SVA testing (high contrast, stationary letters) are an insufficient analog to actual targets encountered in everyday activities, which are often in motion and/or of less-than-perfect contrast. In addition, the size-threshold methodology typically used to measure SVA is incongruent with current theories of a multi-channel visual system. Dynamic Visual Acuity (DVA) and Contrast Sensitivity have been suggested as alternatives to SVA, but while each mitigates specific weaknesses of the SVA measure, neither addresses the shortcomings completely. Traditional DVA measures employ moving targets, but these targets are usually of perfect contrast and a size-threshold methodology is used to specify acuity levels. Contrast Sensitivity employs a contrast-threshold methodology and allows measurement of specific visual channels, but stationary targets are utilized. The present study combined the DVA and Contrast Sensitivity measures in an effort to retain the unique qualities of each while addressing their shortcomings, resulting in a more detailed picture of the human visual system and functioning than has yet been possible. By measuring contrast sensitivity to targets at a set of spatial frequencies spanning the human "window of visibility" and under conditions of motion representative of that encountered in everyday activities, it was hoped that a more powerful predictor of actual visual performance would be created. In addition, normative data was established for two separate age populations, in the hopes of learning more about specific changes that occur to the visual system during the aging process. Indeed, several effects and interactions among the three main variables (spatial frequency, velocity, age) were uncovered, which appears to indicate that the new test may provide more information about the visual system than DVA or contrast sensitivity by themselves. The ramifications of this effort to human factors and visual performance research are discussed along with recommendations for the continuation and application of this line of research.
Show less - Date Issued
- 2004
- Identifier
- CFE0000293, ucf:46210
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000293
- Title
- A PHENOMENOLOGICAL DESCRIPTION OF THE LIVED EXPERIENCE OF CREATING ART FOR WOMEN WITH BREAST CANCER.
- Creator
-
Stark, Laurie, Bushy, Angeline, University of Central Florida
- Abstract / Description
-
Conventional approaches to cancer treatment typically do not address the personal experiences of the women with breast cancer. The aim of this study was to develop a structural description of the lived experience of women with breast cancer who create art, specifically through painting, sketching or drawing. A phenomenological approach was employed to explore the meaning of creating art for four women with a diagnosis of breast cancer. The philosophical underpinnings for this study were based...
Show moreConventional approaches to cancer treatment typically do not address the personal experiences of the women with breast cancer. The aim of this study was to develop a structural description of the lived experience of women with breast cancer who create art, specifically through painting, sketching or drawing. A phenomenological approach was employed to explore the meaning of creating art for four women with a diagnosis of breast cancer. The philosophical underpinnings for this study were based on the phenomenological method of bracketing which allows the researcher and subjects to focus on lived experience. This qualitative methodology provided a means to examine the phenomenon of interest in depth from the participantsÂÂÂÂÂÂ' subjective perspective. Data were collected through face-to-face interviews and follow up telephone conversations. GiorgiÂÂÂÂÂÂ's method for analyzing phenomenological data was used to elicit an invariant description of the meaning that creating art had for the participants. Three predominate themes emerged from the analysis. Contextual constituents of the phenomenon were identified as that of giving back and time to create. Dynamic components consisted of creative space and creative expression. Enduring factors consisted of the creative experience and sense of self. Nurses are in a unique position to facilitate the creative art process which holds the potential for self-healing and self-responsibility for their patients. Included are limitations of the study and recommendations for future research.
Show less - Date Issued
- 2010
- Identifier
- CFE0003208, ucf:48583
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003208
- Title
- COMMISSIONING OF A DYNAMIC MECHANICAL ANALYZERFOR THE CHARACTERIZATION OF LOW TEMPERATURE NITIFE SHAPE MEMORY ALLOYS.
- Creator
-
Nandiraju, Maruthi Diwakar, Vaidyanathan, Raj, University of Central Florida
- Abstract / Description
-
NiTiFe shape memory alloys can undergo transformations between cubic, trigonal and monoclinic phases at low temperatures. The low hysteresis associated with the trigonal R-phase transformation make them candidates for actuator applications at low temperatures. However, the literature available on these alloys is limited and there is a need to establish processing-structure-property correlations. This study was undertaken with the objective of determining and understanding such correlations in...
Show moreNiTiFe shape memory alloys can undergo transformations between cubic, trigonal and monoclinic phases at low temperatures. The low hysteresis associated with the trigonal R-phase transformation make them candidates for actuator applications at low temperatures. However, the literature available on these alloys is limited and there is a need to establish processing-structure-property correlations. This study was undertaken with the objective of determining and understanding such correlations in a Ni46.8Ti50Fe3.2 alloy. First, a dynamic mechanical analyzer (DMA) was successfully commissioned to facilitate mechanical testing between -150 and 600ºC. The experiments performed over selected ranges of stress and temperature probed a range of deformation phenomena in these materials. In addition to conventional elastic and dislocation based plastic deformation, also probed were stress-induced formation of the R- and martensite (B19') phases, and twinning in the R- and martensite (B19') phases. Constrained recovery experiments, wherein phase transformations were thermally induced against external loads, were also performed to assess the performance of these alloys in actuator applications. In addition to a DMA, a differential scanning calorimeter, liquid helium dilatometer and a transmission electron microscope were also used. The samples tested were subjected to different thermo-mechanical processing parameters (i.e., percentage of cold work, solutionizing, aging, and annealing time/temperature). Selected combinations of cold work and annealing temperature/times were found to result in narrower transformations (in temperature space), making such alloys of value in cyclic actuator applications. Thus this work contributed to further understand the processing-structure-property relationship in NiTiFe alloys that exhibit the R-phase transformation and in lowering the operating temperature range of shape-memory alloys in order for them to be used in hydrogen related technologies. The immediate benefit to NASA Kennedy Space Center is the development of a shape-memory thermal conduction switch for application in cryogenic liquefaction, densification and zero boil-off systems. This is being extended to include the potential use of shape-memory alloy actuator elements for cryogenic seals, valves, fluid-line repair, self-healing gaskets, and even to ambient debris-less separation and latch/release mechanisms. The financial support of NASA through grant NAG3-2751 is gratefully acknowledged.
Show less - Date Issued
- 2006
- Identifier
- CFE0001409, ucf:47041
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001409
- Title
- OPTICAL SOLITONS IN PERIODIC STRUCTURES.
- Creator
-
Makris, Konstantinos, Christodoulides, Demetrios, University of Central Florida
- Abstract / Description
-
By nature discrete solitons represent self-trapped wavepackets in nonlinear periodic structures and result from the interplay between lattice diffraction (or dispersion) and material nonlinearity. In optics, this class of self-localized states has been successfully observed in both one-and two-dimensional nonlinear waveguide arrays. In recent years such lattice structures have been implemented or induced in a variety of material systems including those with cubic (Kerr), quadratic,...
Show moreBy nature discrete solitons represent self-trapped wavepackets in nonlinear periodic structures and result from the interplay between lattice diffraction (or dispersion) and material nonlinearity. In optics, this class of self-localized states has been successfully observed in both one-and two-dimensional nonlinear waveguide arrays. In recent years such lattice structures have been implemented or induced in a variety of material systems including those with cubic (Kerr), quadratic, photorefractive, and liquid-crystal nonlinearities. In all cases the underlying periodicity or discreteness leads to new families of optical solitons that have no counterpart whatsoever in continuous systems. In the first part of this dissertation, a theoretical investigation of linear and nonlinear optical wave propagation in semi-infinite waveguide arrays is presented. In particular, the properties and the stability of surface solitons at the edge of Kerr (AlGaAs) and quadratic (LiNbO3) lattices are examined. Hetero-structures of two dissimilar semi-infinite arrays are also considered. The existence of hybrid solitons in these latter types of structures is demonstrated. Rabi-type optical transitions in z-modulated waveguide arrays are theoretically demonstrated. The corresponding coupled mode equations, that govern the energy oscillations between two different transmission bands, are derived. The results are compared with direct beam propagation simulations and are found to be in excellent agreement with coupled mode theory formulations. In the second part of this thesis, the concept of parity-time-symmetry is introduced in the context of optics. More specifically, periodic potentials associated with PT-symmetric Hamiltonians are numerically explored. These new optical structures are found to exhibit surprising characteristics. These include the possibility of abrupt phase transitions, band merging, non-orthogonality, non-reciprocity, double refraction, secondary emissions, as well as power oscillations. Even though gain/loss is present in this class of periodic potentials, the propagation eigenvalues are entirely real. This is a direct outcome of the PT-symmetry. Finally, discrete solitons in PT-symmetric optical lattices are examined in detail.
Show less - Date Issued
- 2008
- Identifier
- CFE0002013, ucf:47610
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002013
- Title
- A METHODOLOGY FOR MINIMIZING THE OSCILLATIONS IN SUPPLY CHAINS USING SYSTEM DYNAMICS AND GENETIC ALGORITHMS.
- Creator
-
LAKKOJU, RAMAMOORTHY, RABELO, LUIS, University of Central Florida
- Abstract / Description
-
Supply Chain Management (SCM) is a critically significant strategy that enterprises depend on to meet challenges that they face because of highly competitive and dynamic business environments of today. Supply chain management involves the entire network of processes from procurement of raw materials/services/technologies to manufacturing or servicing intermediate products/services to converting them into final products or services and then distributing and retailing them till they reach final...
Show moreSupply Chain Management (SCM) is a critically significant strategy that enterprises depend on to meet challenges that they face because of highly competitive and dynamic business environments of today. Supply chain management involves the entire network of processes from procurement of raw materials/services/technologies to manufacturing or servicing intermediate products/services to converting them into final products or services and then distributing and retailing them till they reach final customers. A supply chain network by nature is a large and complex, engineering and management system. Oscillations occurring in a supply chain because of internal and/or external influences and measures to be taken to mitigate/minimize those oscillations are a core concern in managing the supply chain and driving an organization towards a competitive advantage. The objective of this thesis is to develop a methodology to minimize the oscillations occurring in a supply chain by making use of the techniques of System Dynamics (SD) and Genetic Algorithms (GAs). System dynamics is a very efficient tool to model large and complex systems in order to understand their complex, non-linear dynamic behavior. GAs are stochastic search algorithms, based on the mechanics of natural selection and natural genetics, used to search complex and non-linear search spaces where traditional techniques may be unsuitable.
Show less - Date Issued
- 2005
- Identifier
- CFE0000683, ucf:46489
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000683
- Title
- ESTIMATION OF TANGENTIAL MOMENTUM ACCOMMODATION COEFFICIENT USING MOLECULAR DYNAMICS SIMULATION.
- Creator
-
Finger, George, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
The Tangential Momentum Accommodation Coefficient (TMAC) is used to improve the accuracy of fluid flow calculations in the slip flow regime. Under such conditions (indicated by Knudsen number greater than 0.001), the continuum assumption that a fluid velocity at a solid surface is equal to the surface velocity is inaccurate because relatively significant fluid "slip" occurs at the surface. Prior work has not led to a method to quickly estimate a value for TMAC - it is frequently assumed. In...
Show moreThe Tangential Momentum Accommodation Coefficient (TMAC) is used to improve the accuracy of fluid flow calculations in the slip flow regime. Under such conditions (indicated by Knudsen number greater than 0.001), the continuum assumption that a fluid velocity at a solid surface is equal to the surface velocity is inaccurate because relatively significant fluid "slip" occurs at the surface. Prior work has not led to a method to quickly estimate a value for TMAC - it is frequently assumed. In this work, Molecular Dynamics techniques are used to study the impacts of individual gas atoms upon solid surfaces to understand how approach velocity, crystal geometry and interatomic forces affect the scattering of the gas atoms, specifically from the perspective of tangential momentum. It is a logical step in the development of a comprehensive technique to estimate total coefficient values to be used by those investigating flows in micro- and nano-channels or on orbit spacecraft where slip flow occurs. TMAC can also help analysis in transitional or free molecular regimes of flow. The gas – solid impacts were modeled using Lennard Jones potentials. Solid surfaces were modeled with approximately 3 atoms wide by 3 atoms deep by 40 or more atoms long. The crystal surface was modeled as a Face Centered Cubic (100). The gas was modeled as individual free gas atoms. Gas approach angles were varied from 10° to 70° from normal. Gas speed was either specified directly or by way of a ratio relationship with the Lennard-Jones energy potential (Energy Ratio). In order to adequately model the trajectories and maintain conservation of energy, very small time steps (on the order of 0.0005 ô , where ô is the natural time unit) were used. For each impact the initial and final tangential momenta were determined and after a series of many impacts, a value of TMAC was calculated for those conditions. The modeling was validated with available experimental data for He gas atoms at 1770 m/s impacting Cu over angles ranging from 10° to 70°. The model agreed within 3% of the experimental values and correctly predicted that the coefficient changes with angle of approach. Molecular Dynamics results estimate TMAC values from a high of 1.2 to a low of 0.25, generally estimating a higher coefficient at the smaller angles. TMAC values above 1.0 indicate backscattering, which has been experimentally observed in numerous instances. The ratio of final to initial momenta, when plotted for a given sequence of gas atoms spaced across a lattice cycle typically follows a discontinuous curve, with continuous portions indicating forward and back scattering and discontinuous portions indicating multiple bounces. Increasing the Energy Ratio above a value of 5 tends to decrease the coefficient at all angles. Adsorbed layers atop a surface influence the coefficient similar to their Energy Ratio. The results provide encouragement to develop the model further, so as to be able in the future to evaluate TMAC for gas flows with Maxwell temperature distributions involving numerous impact angles simultaneously.
Show less - Date Issued
- 2005
- Identifier
- CFE0000760, ucf:46567
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000760
- Title
- ANALYSIS AND MODELING OF THE EDS MAGLEV SYSTEM BASED ON THE HALBACH PERMANENT MAGNET ARRAY.
- Creator
-
Han, Qinghua, Phillips, Ronald, University of Central Florida
- Abstract / Description
-
Electro-dynamic suspension (EDS) Magnetic levitation (Maglev) with its advantage in maintenance, safety, efficiency, speed, and noise is regarded as a leading candidate for the next generation transportation / space launch assist system. The Halbach array due to its unique magnetic field feature has been widely used in various applications. The EDS system using Halbach arrays leads to the potential EDS system without super-conductor (SC) technology. In this thesis, the Halbach array magnetic...
Show moreElectro-dynamic suspension (EDS) Magnetic levitation (Maglev) with its advantage in maintenance, safety, efficiency, speed, and noise is regarded as a leading candidate for the next generation transportation / space launch assist system. The Halbach array due to its unique magnetic field feature has been widely used in various applications. The EDS system using Halbach arrays leads to the potential EDS system without super-conductor (SC) technology. In this thesis, the Halbach array magnetic field and the dynamics of a novel Halbach array EDS Maglev system were considered. The practical Halbach array magnetic field was analyzed using both a Fourier series approach and the finite element method (FEM). In addition, the optimal Halbach array geometry was derived and analyzed. A novel active magnetic array was introduced and used in the Halbach array EDS Maglev configuration. Further more, since the system is self-regulated in lateral, roll, pitch, and yaw directions, the control was simplified and can be implemented electronically. The dynamic stability analysis and simulation results showed that the system is marginally stable and a control mechanism is needed for stability and ride comfort control. The six degree of freedom (DOF) dynamics, and the vehicle's mass center offset effects on those dynamics were investigated with multiple passive and active magnetic forces. The results indicated that the vehicle's mass center offset has a strong effect on the dynamics of the Maglev system due to the uniqueness of the magnetic force and also that the mass center offset can cause Maglev oscillations at the take off stage. In order to guarantee the dynamic stability and ride comfort of the Maglev system, an optimized active damping and a linear quadratic regulator (LQR) control were developed. Finally, the simulation confirmed the effectiveness of the proposed multi-input and multi-output (MIMO) control designs.
Show less - Date Issued
- 2004
- Identifier
- CFE0000072, ucf:46145
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000072
- Title
- DESIGN OF A DYNAMIC FOCUSING MICROSCOPE OBJECTIVE FOR OCT IMAGING.
- Creator
-
Murali, Supraja, Rolland, Jannick, University of Central Florida
- Abstract / Description
-
Optical Coherence Tomography (OCT) is a novel optical imaging technique that has assumed significant importance in bio-medical imaging in the last two decades because it is non-invasive and provides accurate, high resolution images of three dimensional cross-sections of body tissue, exceeding the capabilities of the current predominant imaging technique –ultrasound. In this thesis, high resolution OCT is investigated for in vivo detection of abnormal skin pathology for the early...
Show moreOptical Coherence Tomography (OCT) is a novel optical imaging technique that has assumed significant importance in bio-medical imaging in the last two decades because it is non-invasive and provides accurate, high resolution images of three dimensional cross-sections of body tissue, exceeding the capabilities of the current predominant imaging technique –ultrasound. In this thesis, high resolution OCT is investigated for in vivo detection of abnormal skin pathology for the early diagnosis of cancer. The technology presented is based on a dynamic focusing microscopic imaging probe conceived for skin imaging and the detection of abnormalities in the epithelium. A novel method for dynamic focusing in the biological sample using liquid crystal (LC) lens technology to obtain three dimensional images with invariant resolution throughout the cross-section and depth of the sample is presented and discussed. Two different skin probe configurations that incorporate dynamic focusing with LC lenses, one involving a reflective microscope objective sub-system, and the other involving an all-refractive immersion microscope objective sub-system are investigated. In order to ensure high resolution imaging, a low coherence broadband source, namely a femtosecond mode-locked Ti: sapphire laser centered at a wavelength of approximately 800nm is used to illuminate the sample. An in-depth description and analysis of the optical design and predicted performance of the two microscope objectives designed for dynamic three dimensional imaging at 5ìm resolution for the chosen broadband spectrum is presented.
Show less - Date Issued
- 2005
- Identifier
- CFE0000869, ucf:46665
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000869
- Title
- LATTICE VIBRATION STUDY OF SILICA NANOPARTICLE IN SUSPENSION.
- Creator
-
Sachdeva, Parveen, Kumar, Ranganathan, University of Central Florida
- Abstract / Description
-
In recent years considerable research has been done in the area of "nanofluids". Nanofluids are colloidal suspensions of nanometer size metallic or oxide particles in a base fluid such as water, ethylene glycol. Nanofluids show enhanced heat transfer characteristics compared to the base fluid. The thermal transport properties of nanofluids depend on various parameters e.g. interfacial resistance, Brownian motion of particles, liquid layering at the solid-liquid interface and clustering of...
Show moreIn recent years considerable research has been done in the area of "nanofluids". Nanofluids are colloidal suspensions of nanometer size metallic or oxide particles in a base fluid such as water, ethylene glycol. Nanofluids show enhanced heat transfer characteristics compared to the base fluid. The thermal transport properties of nanofluids depend on various parameters e.g. interfacial resistance, Brownian motion of particles, liquid layering at the solid-liquid interface and clustering of nanoparticles. In this work atomic scale simulation has been used to study possible mechanisms affecting the heat transfer characteristics of nanofluids. Molecular dynamics simulation for a single silica nanoparticle surrounded by water molecules has been performed. Periodic boundary condition has been used in all three directions. The effect of nanoparticle size and temperature of system on the thermal conductivity of nanofluids has been studied. It was found that as the size of nanoparticle decreases thermal conductivity of nanofluid increases. This is partially due to the fact that as the diameter of nanoparticle decreases from micrometer to nanometer its surface area to volume ratio increases by a factor of 103. Since heat transfer between the fluid and the nanoparticle takes place at the surface this enhanced surface area gives higher thermal conductivity for smaller particles. Thermal conductivity enhancement is also due to the accumulation of water molecules near the particle surface and the lattice vibration of the nanoparticle. The phonon transfer through the second layer allows the nanofluid thermal conductivity to increase by 23%-27% compared to the base fluid water for 2% concentration of nanosilica.
Show less - Date Issued
- 2006
- Identifier
- CFE0001278, ucf:46897
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001278
- Title
- DYNAMIC ENTREPRENEURIAL NETWORKS: AN INVESTIGATION OF ENTREPRENEURS, NEW VENTURES AND THEIR NETWORKS.
- Creator
-
Sullivan, Diane, Ford, Cameron, University of Central Florida
- Abstract / Description
-
Entrepreneurs need resources to organize new venture offerings into marketplace-acceptable forms. Entrepreneurs use others' assistance via networks to obtain these resources. Research indicates that firms face resource dependencies, that likely change over time, where they must respond to those controlling resources. Although some work has investigated implications of new ventures' networks at one time period, little work has investigated the dynamic nature and associated outcomes of networks...
Show moreEntrepreneurs need resources to organize new venture offerings into marketplace-acceptable forms. Entrepreneurs use others' assistance via networks to obtain these resources. Research indicates that firms face resource dependencies, that likely change over time, where they must respond to those controlling resources. Although some work has investigated implications of new ventures' networks at one time period, little work has investigated the dynamic nature and associated outcomes of networks as they change due to different resource requirements as the venture develops. This research examines the dynamic nature of networks, due different resource requirements over time, and how these changes impact entrepreneurial outcomes via interactions with entrepreneurs' existing networks. In order to account for the dynamic nature of entrepreneurial new ventures and their networks of resource providers, a model is presented that investigates antecedents to subsequent entrepreneurial network characteristics. The model also anticipates changes eminent to the founder as a consequence of interactions with their networks due to experiences associated with the new venture development process. This work relies on network theory integrated with resource dependence theory arguments, work that examines founder attributes as associated with entrepreneurial outcomes and research that investigates the stages of new venture development. Predictions developed from the model were tested in two studies. The first study utilized the Panel Study of Entrepreneurial Dynamics, an existing panel database containing information about nascent entrepreneurs, as its data source to test predictions examining the dynamics of entrepreneurs' networks across two time frames. The second study used a cross-sectional mass mail survey design to investigate all of the model's predictions on a random sample of newly incorporated firms in the state of Florida. The results of the studies provided support for about one third of the predictions and there were a few contrasting findings across studies. Overall, the results of the studies suggest that some conceptualizations presented in the theoretical model should be reevaluated and that the applicability of some constructs when studying firms in the organizing stages of development should be reconsidered.
Show less - Date Issued
- 2006
- Identifier
- CFE0001173, ucf:46863
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001173
- Title
- Investigation of a Self-powered Fontan Concept Using a Multiscale Computational Fluid-Structure Interaction Model.
- Creator
-
Beggs, Kyle, Kassab, Alain, Steward, Robert, Mansy, Hansen, DeCampli, William, University of Central Florida
- Abstract / Description
-
Congenital Heart Disease (CHD) occurs in about 1\% (40,000) of newborn babies each year in the United States alone. About 10.9\% (960) of whom suffer from Hypoplastic Left Heart Syndrome (HLHS) - a subset of CHD where children are born with a single-ventricle (SV). A series of three surgeries are carried out to correct HLHS culminating in the Fontan procedure where venous flow returns passively to the lungs. The current configuration for the Fontan results in elevated Central Venous Pressure ...
Show moreCongenital Heart Disease (CHD) occurs in about 1\% (40,000) of newborn babies each year in the United States alone. About 10.9\% (960) of whom suffer from Hypoplastic Left Heart Syndrome (HLHS) - a subset of CHD where children are born with a single-ventricle (SV). A series of three surgeries are carried out to correct HLHS culminating in the Fontan procedure where venous flow returns passively to the lungs. The current configuration for the Fontan results in elevated Central Venous Pressure (CVP), inadequate ventricular preload, and elevated Pulmonary Vascular Resistance (PVR) leading to a barrage of disease. To alleviate these complications, a `self-powered' Fontan is suggested where an Injection Jet Shunt (IJS) emanating from the aorta is anastomosed to each pulmonary artery. The IJS attempts to reduce the central venous pressure, increase preload, and aid in pulmonary arterial growth by entraining the flow with a high energy source provided by the aorta. Previous computational studies on this concept with rigid vessel walls show mild success, but not enough to be clinically relevant. It is hypothesized that vessel wall deformation may play an important role in enhancing the jet effect to provide a larger exit area for the flow to diffuse while also being more physiologically accurate. A multiscale 0D-3D tightly coupled Computational Fluid Dynamics (CFD) with Fluid-Structure Interaction (FSI) model is developed to investigate the efficacy of the proposed `self-powered' Fontan modification. Several runs are made varying the PVR to investigate the sensitivity of IVC pressure on PVR. IVC pressure decreased by 2.41 mmHg while the rigid wall study decreased the IVC pressure by 2.88 mmHg. It is shown that IVC pressure is highly sensitive to changes in PVR and modifications to the Fontan procedure should target aiding pulmonary arterial growth as it is the main indicator of Fontan success.
Show less - Date Issued
- 2018
- Identifier
- CFE0007311, ucf:52107
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007311
- Title
- COMPUTATIONAL HURRICANE HAZARD ANALYSIS-A PERFORMANCE BASED ENGINEERING VIEW.
- Creator
-
Vanek, Christopher, Mackie, Kevin, University of Central Florida
- Abstract / Description
-
Widespread structural damage to critical facilities such as levees, buildings, dams and bridges during hurricanes has exemplified the need to consider multiple hazards associated with hurricanes as well as the potential for unacceptable levels of performance even if failure is not observed. These inadequate standards warrant the use of more accurate methods to describe the anticipated structural response, and damage for extreme events often termed performance based engineering (PBE)....
Show moreWidespread structural damage to critical facilities such as levees, buildings, dams and bridges during hurricanes has exemplified the need to consider multiple hazards associated with hurricanes as well as the potential for unacceptable levels of performance even if failure is not observed. These inadequate standards warrant the use of more accurate methods to describe the anticipated structural response, and damage for extreme events often termed performance based engineering (PBE). Therefore PBE was extended into the field of hurricane engineering in this study. Application of performance-based principles involves collection of the numerous hazards data from sources such as historical records, laboratory experiments or stochastic simulations. However, the hazards associated with a hurricane typically include spatial and temporal variation therefore, more detailed collection of data from each hazard of this loading spectrum is required. At the same time, computational power and computer-aided design have advanced and potentially allows for collection of the structure-specific hazard data. This novel technique, known as computational fluid dynamics (CFD), was applied to the wind and wave hazards associated with hurricanes to accurately quantify the spectrum of dynamic loads in this study. Numerical simulation results are presented on verification of this technique with laboratory experimental studies and further application to a typical Florida building and bridge prototype. Both the time and frequency domain content of random process signals were analyzed and compared through basic properties including the spectral density, autocorrelation, and mean. Following quantification of the dynamic loads on each structure, a detailed structural FEM was constructed of each structure and response curves were created for various levels of hurricane categories. Results show that both the time and frequency content of the dynamic signal could be accurately captured through CFD simulations in a much more cost effective manner than laboratory experimentation. Structural FEM models showed the poor performance of two coastal structures designed using deterministic principles, as serviceability and strength limit states were exceeded. Additionally, the response curves created for the prototype structure could be further developed for multiple wind directions and wave periods. Thus CFD is a viable option to wind and wave laboratory studies and a key tool for the development of PBE in the field of hurricane engineering.
Show less - Date Issued
- 2010
- Identifier
- CFE0003491, ucf:48963
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003491
- Title
- On Hall Magnetohydrodynamics: X-type Neutral Point and Parker Problem.
- Creator
-
Reger, Kyle, Shivamoggi, Bhimsen, Rollins, David, Eastes, Richard, University of Central Florida
- Abstract / Description
-
The framework for the Hall magnetohydrodynamic (MHD) model for plasma physics is built up from kinetic theory and used to analytically solve problems of interest in the field. The Hall MHD model describes fast magnetic reconnection processes in space and laboratory plasmas. Specifically, the magnetic reconnection process at an X-type neutral point, where current sheets form and store enormous amounts of magnetic energy which is later released as magnetic storms when the sheets break up, is...
Show moreThe framework for the Hall magnetohydrodynamic (MHD) model for plasma physics is built up from kinetic theory and used to analytically solve problems of interest in the field. The Hall MHD model describes fast magnetic reconnection processes in space and laboratory plasmas. Specifically, the magnetic reconnection process at an X-type neutral point, where current sheets form and store enormous amounts of magnetic energy which is later released as magnetic storms when the sheets break up, is investigated. The phenomena of magnetic flux pile-up driving the merging of antiparallel magnetic fields at an ion stagnation-point flow in a thin current sheet, called the Parker problem, also receives rigorous mathematical analysis.
Show less - Date Issued
- 2012
- Identifier
- CFE0004428, ucf:49345
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004428
- Title
- BIT-RATE AWARE RECONFIGURABLE ARCHITECTURE FOR H.264/AVC DEBLOCKING FILTER.
- Creator
-
Khraisha, Rakan, Lee, Jooheung, University of Central Florida
- Abstract / Description
-
In H.264/AVC, DeBlocking Filter (DBF) achieves bit rate savings and it is used to improve visual quality by reducing the presence of blocking artifacts. However, these advantages come at the expense of increasing computational complexity of the DBF due to highly adaptive mode decision and small 4x4 block size. The DBF easily accounts for one third of the computational complexity of the decoder. The computational complexity required for various target applications from mobile to high...
Show moreIn H.264/AVC, DeBlocking Filter (DBF) achieves bit rate savings and it is used to improve visual quality by reducing the presence of blocking artifacts. However, these advantages come at the expense of increasing computational complexity of the DBF due to highly adaptive mode decision and small 4x4 block size. The DBF easily accounts for one third of the computational complexity of the decoder. The computational complexity required for various target applications from mobile to high definition video applications varies significantly. Therefore, it becomes apparent to design efficient architecture to adapt to different requirements. In this work, we exploit the scalability on both the hardware level and the algorithmic level to synergize the performance and to reduce computational complexity. First, we propose a modular DBF architecture which can be scaled to adapt to the required computing capability for various bit-rates, resolutions, and frame rates of video sequences. The scalable architecture is based on FPGA using dynamic partial reconfiguration. This desirable feature of FPGAs makes it possible for different hardware configurations to be implemented during run-time. The proposed design can be scaled to filter up to four different edges simultaneously, resulting in significant reduction of total processing time. Secondly, our experiments show by lowering the bit rate of video sequences, significant reduction in computational complexity can be achieved by the increased presence of skipped macroblocks, thus, avoiding redundant filtering operations. The implemented architecture has been evaluated using Xilinx Virtex-4 ML410 FPGA board. The design can operate at a maximum frequency of 103 MHz. The reconfiguration is done through Internal Configuration Access Port (ICAP) to achieve maximum performance needed by real time applications.
Show less - Date Issued
- 2010
- Identifier
- CFE0003247, ucf:48542
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003247
- Title
- Dynamic Modeling Approach to Quantify Change Orders Impact on Labor Productivity.
- Creator
-
Al-Kofahi, Zain, Oloufa, Amr, Tatari, Omer, Uddin, Nizam, Xanthopoulos, Petros, University of Central Florida
- Abstract / Description
-
In construction projects, change orders are commonly faced. These change orders, which are issued by the owner, may cause interruption to the contractor's work, resulting in damages such as loss of labor productivity, delay damages, and cost overruns which may lead to claims. The relationship between change orders and loss of labor productivity is not well understood because of the difficulty in linking the cause of the productivity loss to the change order. So, to receive compensation, the...
Show moreIn construction projects, change orders are commonly faced. These change orders, which are issued by the owner, may cause interruption to the contractor's work, resulting in damages such as loss of labor productivity, delay damages, and cost overruns which may lead to claims. The relationship between change orders and loss of labor productivity is not well understood because of the difficulty in linking the cause of the productivity loss to the change order. So, to receive compensation, the contractor needs to prove with a credible calculation that the productivity loss was a result of the change order issued by the owner. Compared to all available productivity loss quantification methods, the (")Measured Mile(") approach is considered the most acceptable and popular approach in litigation. In this study, loss of labor productivity due to change orders is studied using a system dynamics method. A system dynamics model is developed using Vensim Software, validated, and utilized to quantitatively measure the impact of the change in the project scope on labor productivity. Different road construction projects were analyzed using both methods: measured mile analysis and system dynamics model; then, the results from those two approaches were compared
Show less - Date Issued
- 2016
- Identifier
- CFE0006430, ucf:51448
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006430
