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(1 - 8 of 8)
- Title
- DETERMINING EMISSIONS FROM LANDFILLS AND CREATING ODOR BUFFER DISTANCES.
- Creator
-
Guarrieloo, Nicholas, Cooper, David, University of Central Florida
- Abstract / Description
-
With population growing every year, more and more people are looking for places to live. This can lead to construction of houses near and around landfills. As homes get closer to landfills, the odors these landfills produce become more of a problem, and lead to an increase in odor complaints. Modeling these odors and recommending odor buffer distances will help determine limits on how close to landfills new homes should be allowed. This should help reduce future odor complaints. To solve this...
Show moreWith population growing every year, more and more people are looking for places to live. This can lead to construction of houses near and around landfills. As homes get closer to landfills, the odors these landfills produce become more of a problem, and lead to an increase in odor complaints. Modeling these odors and recommending odor buffer distances will help determine limits on how close to landfills new homes should be allowed. This should help reduce future odor complaints. To solve this problem one must accurately estimate odorous gas emissions from the landfill. Often odors can be indicated by methane emissions. A new technique using hundreds of ambient VOC concentrations, which are taken from landfills on a quarterly basis, was used to invert and solve the Gaussian dispersion equation for methane emissions. In this technique, Voronoi diagram theory was used to automatically locate numerous point sources for optimal positioning relative to receptors. The newly solved methane emission rates can now be input into a dispersion model, and the resulting methane concentrations used as surrogates for odors around the landfill. One of the most important steps in the analysis is to determine which model is best to use for odor modeling. There are many considerations that go into this decision, such as how much time it takes to run the model, how accurate the model is, and how easy the model is to use. Two current models CALPUFF and AERMOD were compared. In the modeling, methane was used as a surrogate for the odors. Since landfills handle many different combinations of waste, the type of odor may vary from landfill to landfill. In this test case, H2S was assumed to be the main contributor to the odor emitted from the landfill, and the H2S-to-methane ratio was used to estimate downwind H2S concentrations from the modeled methane concentrations. Once an air dispersion model is selected, it can be used to model odors and to develop a graphical screening method to show where these odors are most likely to occur and how strong they will be. This can be used to determine how close to a landfill homes can be built without having significant odor impacts bothering these new residents. Also, this tool can be used for improving landfill gas management. Several example scenarios include the possibility of not enough soil cover placed on the waste, leaks from an aging collection system, or cracks in the collection piping created by the settling of waste.
Show less - Date Issued
- 2009
- Identifier
- CFE0002527, ucf:47646
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002527
- Title
- RESOURCE BANKING: AN ENERGY-EFFICIENT, RUN-TIME ADAPTIVE PROCESSOR DESIGN TECHNIQUE.
- Creator
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Staples, Jacob, Heinrich, Mark, University of Central Florida
- Abstract / Description
-
From the earliest and simplest scalar computation engines to modern superscalar out-of-order processors, the evolution of computational machinery during the past century has largely been driven by a single goal: performance. In today's world of cheap, billion-plus transistor count processors and with an exploding market in mobile computing, a design landscape has emerged where energy efficiency, arguably more than any other single metric, determines the viability of a processor for a given...
Show moreFrom the earliest and simplest scalar computation engines to modern superscalar out-of-order processors, the evolution of computational machinery during the past century has largely been driven by a single goal: performance. In today's world of cheap, billion-plus transistor count processors and with an exploding market in mobile computing, a design landscape has emerged where energy efficiency, arguably more than any other single metric, determines the viability of a processor for a given application. The historical emphasis on performance has left modern processors bloated and over provisioned for everyday tasks in the hope that during computationally intensive periods some performance improvement will be observed. This work explores an energy-efficient processor design technique that ensures even a highly over provisioned out-of-order processor has only as many of its computational resources active as it requires for efficient computation at any given time. Specifically, this paper examines the feasibility of a dynamically banked register file and reorder buffer with variable banking policies that enable unused rename registers or reorder buffer entries to be voltage gated (turned off) during execution to save power. The impact of bank placement, turn-off and turn-on policies as well as rail stabilization latencies for this approach are explored for high-performance desktop and server designs as well as low-power mobile processors.
Show less - Date Issued
- 2011
- Identifier
- CFE0003991, ucf:48675
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003991
- Title
- STOCHASTIC RESOURCE CONSTRAINED PROJECT SCHEDULING WITH STOCHASTIC TASK INSERTION PROBLEMS.
- Creator
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Archer, Sandra, Armacost, Robert, University of Central Florida
- Abstract / Description
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The area of focus for this research is the Stochastic Resource Constrained Project Scheduling Problem (SRCPSP) with Stochastic Task Insertion (STI). The STI problem is a specific form of the SRCPSP, which may be considered to be a cross between two types of problems in the general form: the Stochastic Project Scheduling Problem, and the Resource Constrained Project Scheduling Problem. The stochastic nature of this problem is in the occurrence/non-occurrence of tasks with deterministic...
Show moreThe area of focus for this research is the Stochastic Resource Constrained Project Scheduling Problem (SRCPSP) with Stochastic Task Insertion (STI). The STI problem is a specific form of the SRCPSP, which may be considered to be a cross between two types of problems in the general form: the Stochastic Project Scheduling Problem, and the Resource Constrained Project Scheduling Problem. The stochastic nature of this problem is in the occurrence/non-occurrence of tasks with deterministic duration. Researchers Selim (2002) and Grey (2007) laid the groundwork for the research on this problem. Selim (2002) developed a set of robustness metrics and used these to evaluate two initial baseline (predictive) scheduling techniques, optimistic (0% buffer) and pessimistic (100% buffer), where none or all of the stochastic tasks were scheduled, respectively. Grey (2007) expanded the research by developing a new partial buffering strategy for the initial baseline predictive schedule for this problem and found the partial buffering strategy to be superior to Selim's "extreme" buffering approach. The current research continues this work by focusing on resource aspects of the problem, new buffering approaches, and a new rescheduling method. If resource usage is important to project managers, then a set of metrics that describes changes to the resource flow would be important to measure between the initial baseline predictive schedule and the final "as-run" schedule. Two new sets of resource metrics were constructed regarding resource utilization and resource flow. Using these new metrics, as well as the Selim/Grey metrics, a new buffering approach was developed that used resource information to size the buffers. The resource-sized buffers did not show to have significant improvement over Grey's 50% buffer used as a benchmark. The new resource metrics were used to validate that the 50% buffering strategy is superior to the 0% or 100% buffering by Selim. Recognizing that partial buffers appear to be the most promising initial baseline development approach for STI problems, and understanding that experienced project managers may be able to predict stochastic probabilities based on prior projects, the next phase of the research developed a new set of buffering strategies where buffers are inserted that are proportional to the probability of occurrence. The results of this proportional buffering strategy were very positive, with the majority of the metrics (both robustness and resource), except for stability metrics, improved by using the proportional buffer. Finally, it was recognized that all research thus far for the SRCPSP with STI focused solely on the development of predictive schedules. Therefore, the final phase of this research developed a new reactive strategy that tested three different rescheduling points during schedule eventuation when a complete rescheduling of the latter portion of the schedule would occur. The results of this new reactive technique indicate that rescheduling improves the schedule performance in only a few metrics under very specific network characteristics (those networks with the least restrictive parameters). This research was conducted with extensive use of Base SAS v9.2 combined with SAS/OR procedures to solve project networks, solve resource flow problems, and implement reactive scheduling heuristics. Additionally, Base SAS code was paired with Visual Basic for Applications in Excel 2003 to implement an automated Gantt chart generator that provided visual inspection for validation of the repair heuristics. The results of this research when combined with the results of Selim and Grey provide strong guidance for project managers regarding how to develop baseline predictive schedules and how to reschedule the project as stochastic tasks (e.g. unplanned work) do or do not occur. Specifically, the results and recommendations are provided in a summary tabular format that describes the recommended initial baseline development approach if a project manager has a good idea of the level and location of the stochasticity for the network, highlights two cases where rescheduling during schedule eventuation may be beneficial, and shows when buffering proportional to the probability of occurrence is recommended, or not recommended, or the cases where the evidence is inconclusive.
Show less - Date Issued
- 2008
- Identifier
- CFE0002491, ucf:47673
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002491
- Title
- DETERMINING FLORIDA LANDFILL ODOR BUFFER DISTANCES USING AERMOD.
- Creator
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Figueroa, Veronica, Cooper, C. David, University of Central Florida
- Abstract / Description
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As U.S. landfills continue to grow in size, concerns about odorous gas emissions from landfills are increasing. For states that are expanding in population, such as Florida, odors from landfills are a major concern because new housing developments, needed to accommodate the rapid population growth, are creeping closer and closer to the existing landfills. As homes get closer to landfills, odor complaints are likely to become more frequent, causing landfill managers increased problems with...
Show moreAs U.S. landfills continue to grow in size, concerns about odorous gas emissions from landfills are increasing. For states that are expanding in population, such as Florida, odors from landfills are a major concern because new housing developments, needed to accommodate the rapid population growth, are creeping closer and closer to the existing landfills. As homes get closer to landfills, odor complaints are likely to become more frequent, causing landfill managers increased problems with public interactions. Odor buffer zones around landfills need to be established to give municipalities tools to help prevent the building of future homes too close to landfills. Using the latest air dispersion model, AERMOD, research predicted downwind odor concentrations from a Central Florida landfill. Accurate estimates of methane emissions throughout a Central Florida landfill were determined using a new technique developed as part of this research that uses hundreds of ambient air VOC measurements taken within a landfill, as receptors. Hundreds of point sources were placed on the landfill, and the standard Gaussian dispersion equations were solved by matrix inversion methods. The methane emission rates were then used as surrogates for odor emissions to predict downwind odor concentrations via AERMOD. By determining a critical zone around a landfill with regards to odor, stakeholders will be able to meet regulatory issues and assist their communities. Other beneficial uses from this research include: determination of existing gas collection system efficiencies, calculation of fugitive greenhouse gas emissions from municipal solid waste (MSW) landfills, and improved landfill gas management.
Show less - Date Issued
- 2008
- Identifier
- CFE0002200, ucf:47910
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002200
- Title
- BUFFER TECHNIQUES FOR STOCHASTIC RESOURCE CONSTRAINED PROJECT SCHEDULING WITH STOCHASTIC TASK INSERTIONS PROBLEMS.
- Creator
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Grey, Jennifer, Armacost, Robert, University of Central Florida
- Abstract / Description
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Project managers are faced with the challenging task of managing an environment filled with uncertainties that may lead to multiple disruptions during project execution. In particular, they are frequently confronted with planning for routine and non-routine unplanned work: known, identified, tasks that may or may not occur depending upon various, often unpredictable, factors. This problem is known as the stochastic task insertion problem, where tasks of deterministic duration occur...
Show moreProject managers are faced with the challenging task of managing an environment filled with uncertainties that may lead to multiple disruptions during project execution. In particular, they are frequently confronted with planning for routine and non-routine unplanned work: known, identified, tasks that may or may not occur depending upon various, often unpredictable, factors. This problem is known as the stochastic task insertion problem, where tasks of deterministic duration occur stochastically. Traditionally, project managers may include an extra margin within deterministic task times or an extra time buffer may be allotted at the end of the project schedule to protect the final project completion milestone. Little scientific guidance is available to better integrate buffers strategically into the project schedule. Motivated by the Critical Chain and Buffer Management approach of Goldratt, this research identifies, defines, and demonstrates new buffer sizing techniques to improve project duration and stability metrics associated with the stochastic resource constrained project scheduling problem with stochastic task insertions. Specifically, this research defines and compares partial buffer sizing strategies for projects with varying levels of resource and network complexity factors as well as the level and location of the stochastically occurring tasks. Several project metrics may be impacted by the stochastic occurrence or non-occurrence of a task such as the project makespan and the project stability. New duration and stability metrics are developed in this research and are used to evaluate the effectiveness of the proposed buffer sizing techniques. These "robustness measures" are computed through the comparison of the characteristics of the initial schedule (termed the infeasible base schedule), a modified base schedule (or as-run schedule) and an optimized version of the base schedule (or perfect knowledge schedule). Seven new buffer sizing techniques are introduced in this research. Three are based on a fixed percentage of task duration and the remaining four provide variable buffer sizes based upon the location of the stochastic task in the schedule and knowledge of the task stochasticity characteristic. Experimental analysis shows that partial buffering produces improvements in the project stability and duration metrics when compared to other baseline scheduling approaches. Three of the new partial buffering techniques produced improvements in project metrics. One of these partial buffers was based on a fixed percentage of task duration and the other two used a variable buffer size based on knowledge of the location of the task in the project network. This research provides project schedulers with new partial buffering techniques and recommendations for the type of partial buffering technique that should be utilized when project duration and stability performance improvements are desired. When a project scheduler can identify potential unplanned work and where it might occur, the use of these partial buffer techniques will yield a better estimated makespan. Furthermore, it will result in less disruption to the planned schedule and minimize the amount of time that specific tasks will have to move to accommodate the unplanned tasks.
Show less - Date Issued
- 2007
- Identifier
- CFE0001584, ucf:52850
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001584
- Title
- Monitoring and Modeling to Estimate Hydrogen Sulfide Emissions and Dispersion from Florida Construction and Demolition Landfills to Construct Odor Buffering Distances.
- Creator
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Bolyard, Steven, Cooper, Charles, Mackie, Kevin, Randall, Andrew, Zhang, Husen, University of Central Florida
- Abstract / Description
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Emissions of hydrogen sulfide (H2S) from construction and demolition (C & D) landfills can result in odors that are a significant nuisance to nearby neighborhoods and businesses. As Florida's population continues to grow and create development pressures, housing is built closer to existing landfills. Additionally, new landfills will be created in the future. This research project was undertaken to develop a detailed modeling methodology for use by counties and other landfill owners to provide...
Show moreEmissions of hydrogen sulfide (H2S) from construction and demolition (C & D) landfills can result in odors that are a significant nuisance to nearby neighborhoods and businesses. As Florida's population continues to grow and create development pressures, housing is built closer to existing landfills. Additionally, new landfills will be created in the future. This research project was undertaken to develop a detailed modeling methodology for use by counties and other landfill owners to provide them with an objective and scientifically defensible means to establish odor buffer zones around C & D landfills. A technique for estimating methane (and odorous gas) emissions from municipal solid waste (MSW) landfills was recently developed by researchers at the University of Central Florida. This technique was based on measuring hundreds of ambient methane concentrations near the surface of the landfill, and combining that data with matrix inversion mathematics to back-solve the dispersion equations. The technique was fully documented in two peer-reviewed journal articles. This project extends that methodology. In this work the author measured ambient H2S concentrations at various locations in a C & D landfill, and applied those same matrix inversion techniques to determine the H2S emission rates from the landfill. The emission rates were then input into the AERMOD dispersion model to determine H2S odor buffer distances around the landfill.Three sampling trips to one C & D landfill were undertaken, data were taken, and the modeling techniques were applied. One problem encountered was that H2S emissions from C & D landfills are typically about 1000 times smaller than methane emissions (from MSW landfills). Thus, H2S ambient concentrations often are near the detection limits of the instruments, and the data may not be as reliable. However, this approach could be used for any particular C & D landfill if the appropriate amount of data were available to characterize its emissions with some certainty. The graphical tool developed in this work shows isopleths of (")H2S(") concentrations at various distances, and color codes the isopleths into a (")green-yellow-red(") scheme (analogous to a traffic signal) that depicts zones where private landowners likely will not detect odors, where they may experience some odors, or where they likely will experience odors. The (")likelihood(") can be quantified by selecting the Nth highest hourly concentrations in one year to form the plot. In this study, N was conservatively selected as 8. Requiring that concentrations be at or below the 8th highest concentration in a year corresponds to a 99.9% probability of not exceeding that concentration at that distance in any future year. The graphical tool can be applied to any C & D landfill but each landfill is different. So this technique depends on having a fairly good estimate of the rate of emissions of H2S from the landfill in question, and at least one year's worth of hourly meteorological data (wind speed, direction, and stability class) that is representative of the landfill location. The meteorological data can be obtained with relative ease for most locations in Florida; however, the emission data must be obtained from on-site measurements for any given landfill.
Show less - Date Issued
- 2012
- Identifier
- CFE0004272, ucf:52879
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004272
- Title
- ZINC CADMIUM SULPHIDE AND ZINC SULPHIDE AS ALTERNATIVE HETEROJUNCTION PARTNERS FOR CIGS2 SOLAR CELLS.
- Creator
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Kumar, Bhaskar, Dhere, Neelkanth G, University of Central Florida
- Abstract / Description
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Devices with ZnCdS/ZnS heterojunction partner layer have shown better blue photon response due to higher band gap of these compounds as compared to devices with CdS heterojunction partner layer. CdS heterojunction partner layer has shown high photovoltaic conversion efficiencies with CIGS absorber layer while efficiencies are lower with CuIn1-xGaxS2 (CIGS2). A negative conduction band offset has been observed for CdS/CIGS2 as compared to near flat conduction band alignment in case of CdS/CIGS...
Show moreDevices with ZnCdS/ZnS heterojunction partner layer have shown better blue photon response due to higher band gap of these compounds as compared to devices with CdS heterojunction partner layer. CdS heterojunction partner layer has shown high photovoltaic conversion efficiencies with CIGS absorber layer while efficiencies are lower with CuIn1-xGaxS2 (CIGS2). A negative conduction band offset has been observed for CdS/CIGS2 as compared to near flat conduction band alignment in case of CdS/CIGS devices, which results in higher interface dominated recombination. Moreover, it has been predicted that optimum band offsets for higher efficiency solar cells may be achieved for cells with alternative heterojunction partner such as ZnS. With varying ratio of Zn/ (Zn+Cd) in ZnxCd1-xS a range of bandgap energies can be obtained and thus an optimum band offset can be engineered. For reducing interface dominated recombination better lattice match between absorber and heterojunction partners is desirable. Although CdS has better lattice match with CuIn1-xGaxS2 absorber layer, same is not true for CuIn1-xGaxS2 absorber layers. Utilizing ZnxCd1-xS as heterojunction partner provides a range of lattice constant (between aZnS= ~5.4 Ǻ and aCdS= ~5.7 Ǻ) depending on Zn/(Zn+Cd). Therefore better lattice match can be obtained between heterojunction partner and absorber layer. Better lattice match will lead to lower interface dominated recombination, hence higher open circuit voltages. In the present study chemical bath deposition parameters are near optimized for high efficiency CIGS2 Solar cells. Effect of various chemical bath deposition parameters on device performance was studied and attempts were made to optimize the deposition parameters in order to improve the device performance.In/(In+Ga) ratio in absorber layer is varied to obtain good lattice match and optimum band alignment. Solar cells with conversion efficiencies comparable to conventional CdS/CIGS2 has been obtained with ZnxCd1-xS /CIGS2. High short current as well as higher open circuit voltages were obtained with ZnxCd1-xS as alternative heterojunction partner for CIGS2 solar cells as compared to SLG/Mo/CIGS2/ CdS / i-ZnO/ZnO:Al.
Show less - Date Issued
- 2007
- Identifier
- CFE0001936, ucf:47469
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001936
- Title
- ARCHITECTURAL SUPPORT FOR IMPROVING COMPUTER SECURITY.
- Creator
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Kong, Jingfei, Zhou, Huiyang, University of Central Florida
- Abstract / Description
-
Computer security and privacy are becoming extremely important nowadays. The task of protecting computer systems from malicious attacks and potential subsequent catastrophic losses is, however, challenged by the ever increasing complexity and size of modern hardware and software design. We propose several methods to improve computer security and privacy from architectural point of view. They provide strong protection as well as performance efficiency. In our first approach, we propose a new...
Show moreComputer security and privacy are becoming extremely important nowadays. The task of protecting computer systems from malicious attacks and potential subsequent catastrophic losses is, however, challenged by the ever increasing complexity and size of modern hardware and software design. We propose several methods to improve computer security and privacy from architectural point of view. They provide strong protection as well as performance efficiency. In our first approach, we propose a new dynamic information flow method to protect systems from popular software attacks such as buffer overflow and format string attacks. In our second approach, we propose to deploy encryption schemes to protect the privacy of an emerging non-volatile main memory technology – phase change memory (PCM). The negative impact of the encryption schemes on PCM lifetime is evaluated and new methods including a new encryption counter scheme and an efficient error correct code (ECC) management are proposed to improve PCM lifetime. In our third approach, we deconstruct two previously proposed secure cache designs against software data-cache-based side channel attacks and demonstrate their weaknesses. We propose three hardware-software integrated approaches as secure protections against those data cache attacks. Also we propose to apply them to protect instruction caches from similar threats. Furthermore, we propose a simple change to the update policy of Branch Target Buffer (BTB) to defend against BTB attacks. Our experiments show that our proposed schemes are both security effective and performance efficient.
Show less - Date Issued
- 2010
- Identifier
- CFE0003211, ucf:48589
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003211
