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Title: Selecting a Compensation Strategy to Control Project Duration: Empirical Comparison of Lump Sum and Reimbursable Strategies (Working Paper)
Creator: Chen, Juan, Menches, Cindy L.
Date: 2012-05-01, 2012-05-01
Description: Reducing project duration is a significant concern for many industries in the speed-to-market era. Numerous studies have examined the effects...
Show moreReducing project duration is a significant concern for many industries in the speed-to-market era. Numerous studies have examined the effects of project delivery methods on speeding up the process of construction. However, no study has quantitatively compared the effect of using different compensation strategies on schedule duration and schedule reduction. Using the data obtained from 175 international construction projects, this paper focuses on examining the influence of compensation strategy (lump sum versus reimbursable) on project duration while specifically taking into account the industry sector (heavy industrial versus light industrial). The results of the study provide empirical evidence that using a reimbursable compensation strategy can potentially shorten the procurement duration, construction duration, and overall project duration of heavy industrial projects. However, reimbursable contracting did not appear to reduce the project duration on light industrial projects.
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Title: Power Measurement for Road Bicycles: Towards a Universal Solution (sequence unknown), IPRO 324 - Deliverables: IPRO 324 IPRO Day Presentation F09
Creator: Adrianzen, Luis, Allen, Ross, Antonio, Chris, Callan, Mark, Claxton, Sara, Diesse, Patrick, Gaylord, Matthew, Herbert, Greg, Shaffer, Dan, Wegrzyn, Celeste
Date: 2009-12
Description: The goal of the IPRO is to try to find an inexpensive, but accurate way of measuring the power output of a rider on a bicycle. Problems with...
Show moreThe goal of the IPRO is to try to find an inexpensive, but accurate way of measuring the power output of a rider on a bicycle. Problems with systems currently available are: some products are not compatible with all bike systems causing the need to purchase new parts, the cost of the available products is expensive, and some of the available measuring systems are not very accurate.
Deliverables for IPRO 324: Power Measurement for Road Bicycles: Towards a Universal Solution for the fall 2009 semester
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Title: Green Building Design Concept & Integration (sequence unknown), IPRO 335 - Deliverables: IPRO 335 Midterm Presentation F09
Creator: Avanessian, Aris, Banda, Justine, Bergerson, Joshua, Burke, Jeffrey, Christo, Robert, Dexter, Eric, Kim, Kibum, Mey, Andrew, Okunaga, Jonathan, Razeq, Ali, Schaefer, Jacqueline, Thovar Leon, Adrian, Um, Hye
Date: 2009-12
Description: The scope of this IPRO project spans structural, architectural, foundation, HVAC, lighting and electric system designs, as well as building...
Show moreThe scope of this IPRO project spans structural, architectural, foundation, HVAC, lighting and electric system designs, as well as building cost estimating and professional ethics. The IPRO team will become informed about and apply principles associated with green design concepts, energy sustainability, post occupancy comfort, acoustic design issues, smart building concepts, health issues (abatement of mold- and allergy-causing agents), and safety considerations.
Deliverables for IPRO 335: Green Building Design Concept & Integration for the fall 2009 semester
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Title: TRACK on Devon Avenue
Creator: Kohn, Adi
Date: 2011, 2011-05
Description: This project encourages innovative design and planning concepts that further the development of a better, healthier and more active lifestyle...
Show moreThis project encourages innovative design and planning concepts that further the development of a better, healthier and more active lifestyle through the infusion of activities into everyday practices in a space inhabited daily. It is not about encouraging us to go to the gym and workingout more. It’s about giving citizens a workout through their interactions with this environment on a daily basis.
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Title: Improving Efficiency Through Advanced Technology for Electrical Construction (sequence unknown), IPRO 338 - Project Plan: IPRO 338 Project Plan F09
Creator: Kyung Cho, Bum, Crites, Sarah, Czapla, Sarah, Guerrero, Jose, Kim, Yoosuk, Malawski, Frank, Maloney, Michael, Pedrina, Kaleo, Qiu, Li, Yi, Jennifer
Date: 2009-12
Description: The team is to improve the efficiency of electrical contracting projects through new software and technology, communications, and project...
Show moreThe team is to improve the efficiency of electrical contracting projects through new software and technology, communications, and project management techniques, especially through Building Information Modeling (BIM) utilization.
Sponsorship: Electrical Contractor's Association
Project Plan for IPRO 338: Improving Efficiency Through Advanced Technology for Electrical Construction for the fall 2009 semester
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Title: DEVELOPMENT AND ANALYSIS OF A SECURE AND EFFICIENT VEHICULAR AD HOC NETWORK
Creator: Hao, Yong
Date: 2012-07-06, 2012-07
Description: Vehicular ad hoc networks (VANETs) enable vehicles to communicate with each other by equipping every vehicle with an on board unit (OBU). Many...
Show moreVehicular ad hoc networks (VANETs) enable vehicles to communicate with each other by equipping every vehicle with an on board unit (OBU). Many interesting and promising functionalities can be achieved in the VANETs, such as safety related application and data downloading application. In this thesis, we focus on the security and privacy provision as well as efficiency improvement of above two applications in the VANETs. In the safety related application, each vehicle periodically broadcasts messages including its current position, direction and velocity (which can be generated by a global positioning system (GPS) device) to inform its geographic data to its neighbors. Privacy is an important issue in VANETs. Meanwhile, some important security functionalities such as message authentication, integrity and non-repudiation should be integrated into the VANETs. In this thesis, we propose a distributed key management protocol based on group signature to provide security and privacy for vehicles. Distributed key management is expected to facilitate the revocation of malicious vehicles, verification efficiency, maintenance of the system and heterogeneous security policies, compared with the centralized key management assumed by the existing group signature schemes. In our framework, each road side unit (RSU) acts as the key distributor for the group, where a new issue incurred is that the semi-trust RSUs may be compromised. Therefore, we develop security protocols which are able to detect compromised RSUs and their malicious accomplices. Moreover, we address the issue of large computation overhead due to the group signature implementation. A practical cooperative message authentication protocol (CMAP) is thus proposed to alleviate the verification burden for vehicles. In the CMAP, on average, each vehicle just needs to verify a very small amount of received geographic messages. Compared with the existing probabilistic verification protocol, CMAP can save at least 40 % computation resource for vehicles. In the data downloading application, we propose a secure cooperative data downx loading framework for payment services in VANETs. In our framework, vehicles download data when they pass by an RSU and then share the data after they travel out of the RSU’s coverage. A fundamental issue of our framework is how vehicles share data with each other. Thus, we develop an application layer data sharing protocol (DSP) in which vehicles share their downloaded data one by one in sequence according to their positions. A better performance can be achieved by the proposed protocol because it is able to avoid medium access control (MAC) layer collisions and the hidden terminal effect. Analytical models are derived to quantitatively evaluate the impact of the distance between RSUs on the amount of data that vehicles can download in a drive through. The simulation results show that our protocol can download 87.4% more data for vehicles than the existing scheme “VC-MAC” when the distance between two consecutive RSUs reaches 10 kilometers. Moreover, we also address security and privacy issues in the process of data downloading and sharing. Both applicants’ exclusive access to the applied data and vehicles’ privacy are ensured by our framework. Compared with the communication overhead in the intuitive method, the communication overhead in our framework will be reduced to 50%. We also propose a security protocol to detect sybil attacks in privacy preserved VANETs. In the above two applications, vehicles’ location information is utilized to facilitate the efficiency. However, if malicious vehicles launch the sybil attack by forging several fake entities and claim they are at some certain positions. The overall performance of the applications will be compromised greatly. So, we propose a security protocol to detect sybil attacks by examining the rationality of vehicles’ positions. The attack detection utilizes the characteristics of communication. No extra hardware and little communication and computation overhead will be introduced to vehicles. Moreover, a smart attacker scenario in which a malicious vehicle may adjust its communication range to avoid detection and the malicious vehicles’ collusion scenario are also considered.
Ph.D. in Computer Engineering, July 2012
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Title: STUDIES ON RING OPENING REACTIONS AND SYNTHETIC APPLICATIONS OF AZIRIDINIUM IONS
Creator: Sun, Xiang
Date: 2013, 2013-12
Description: Aziridinium ions are valuable and important intermediates to prepare complex nitrogen containing compounds. Various enantiomerically enriched ...
Show moreAziridinium ions are valuable and important intermediates to prepare complex nitrogen containing compounds. Various enantiomerically enriched -haloamines were synthesized as precursors to generate aziridinium ions in situ. Optically active aziridinium perchlorates or triflates were prepared and characterized using 1H and 13C NMR. Regioselective and enantioselective ring opening reactions of aziridinium ions with diverse nucleophilies including cyanide, azide, amines, hydride and water were extensively studied. An efficient one-pot synthetic route to enantiomerically enriched alcohols and amine precursors was developed. Development of the adequate bifunctional chelators is a critical step for radioimmunotherapy (RIT) of cancer. The practical and scalable regiospecific ring opening reactions of aziridinium ions with macrocyclic amines were utilized for synthesis of a series of bifunctional ligands including 3p-C-NETA, C-NE3TA, 3p-C-NE3TA, 3p-C-DECA, 3p-C-DE4TA, an optically active (S)-C-NE3TA, and bifunctional DTPA analogues for RIT using 90Y and 177Lu. Preparation of bifunctional chelators that can rapidly form 64Cu complexes with high stability is an imminent goal for effective PET imaging. A series of NOTA and NE3TA-based chelators were prepared. NE3TA-based bile acid conjugates and NE3TA- based dual receptor-targeted conjugates were synthesized and possess potential for application of targeted PET imaging with 64Cu.
PH.D in Chemistry, December 2013
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Title: Teacher Knowledge Share (Semester Unknown) IPRO 320: Teacher Knowledge Share IPRO 320 Abstract F08
Creator: Bern, David, Bochantin, Marike, Hartline, Julian, Mccall, Ian, Mick, Emily, Peake, Andrew, Pierce, Alison, Pindrik, Dmitriy, Quinn, Michael, Stanford, Carly, Tilatti, Michael
Date: 2008, 2008-12
Description: The goal of IPRO 320 is to create an online professional network for school teachers at the kindergarten through twelfth grade level to allow...
Show moreThe goal of IPRO 320 is to create an online professional network for school teachers at the kindergarten through twelfth grade level to allow for the sharing of ideas, lesson plans and other professionally relevant information. This is a continuing project which saw limited success in the previous semester in that a functioning web site was constructed based on surveys of public school teachers but it saw very little use. This semester, the planned approach is to build on the research generated last semester by performing additional market research with teachers. Following that, IPRO 320 will rework much of the previous web site by refining some of the features, adding additional ones as the research indicates and improving the website in general, both functionally and aesthetically.
Deliverables
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Title: Overlap Overlay
Creator: Wankel, Jordan
Date: 5/4/2011, 2011-05
Description: The purpose of this overlay is to provide the proper mechanics which allows a new type of home ownership while addressing current urban...
Show moreThe purpose of this overlay is to provide the proper mechanics which allows a new type of home ownership while addressing current urban vacancy. The overlay attempts to be democratic. It establishes basic rules based on the existing block requirements, while also providing flexibility within. Residents voluntarily participate in the system, benefiting from the whole. Social interactions, block orientated activities, and housing arrangements expand and contract over time.
Sponsorship: Goodman, David
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Title: Our Energy Future: Lessons in Sustainability AND IPRO Teams for K-12: The Education Outreach Service Learning Cluster (sequence unknown), IPRO 332 - Deliverables: IPRO%20332%20Final%20Report%20F09_redacted
Creator: Chavez, Jorge, Johnson, Ross, Chin, Jason, Grande, Gina, Lay, Livia, Mccloat, Declain, Nguyen, Nam, Olechno, Patrick, Randle, Jennifer, Tyler Ii, Micheal, Vega, Mayra, Weiner, Andrew, Zajac, Gregory
Date: 2009-12
Description: The mission of the IPRO is to educate the community, focusing mainly on elementary and high school students, on the issues of sustainability...
Show moreThe mission of the IPRO is to educate the community, focusing mainly on elementary and high school students, on the issues of sustainability and energy conservation. The group looks to expand on the work that has been completed in previous semesters, by adding multi-media presentations to enhance the current teaching modules. Previous modules have presented to classrooms simply with information, and the team looks to add upon this by adding interactive and entertaining materials to intrigue the audience.
Deliverables for IPRO 332: IOur Energy Future: Lessons in Sustainability AND IPRO Teams for K-12: The Education Outreach Service Learning Cluster for the fall 2009 semester
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Title: Innovative Mapping (sequence unknown), IPRO 303 - Deliverables: IPRO 303 Project Plan F09
Creator: Komoroski, Aaron, Mora, Andres, Sarraf, Basel, Kemp, Brandon, Duong, Cindy, Woodward, Frank, Suwada, Jerry, Michael, Mark, Sinha, Piyush, Glover, Richard, Mandrekar, Urba
Date: 2009-12
Description: The team worked to target the majority of mobile device users and give them an outlet to report any changes, mistakes or developments that...
Show moreThe team worked to target the majority of mobile device users and give them an outlet to report any changes, mistakes or developments that have been overlooked by NAVTEQ in the company's mobile mapping solutions. The team also worked to develop a solution that enables the average map user – men and women ages 18-35, students and tourists – to address these alterations in a simple, hassle-free way.
Sponsorship: NAVTEQ
Deliverables for IPRO 303: Innovative Mapping for the fall 2009 semester.
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Title: Protecting the Artists' Social Construct in a Mutually Beneficial Developer Environment: DSheen_ProtectingArtistSocialConstruct_Board
Creator: Sheen, Daniel
Date: 2011, 2011-05
Description: This project is a mixed-use high rise which will incorporate the program of the newly constructed high rise buildings of retail, hotel, and...
Show moreThis project is a mixed-use high rise which will incorporate the program of the newly constructed high rise buildings of retail, hotel, and condominiums with the program of the existing Powerhouse Arts District, art gallery, auction house, art work spaces, and artist lofts. In order for this combination of program to occur and to retain developer interest in this high rise tower, relationships between the program were investigated. Typical “inefficient” or unleasable spaces in a traditional high rise were used as opportunities to incorporate these art district programs into the site. Artist lofts were design on the perimeter of the mechanical floors to take advantage of double height spaces as well as privacy. Art galleries, and an auction house was incorporated on the lower service level in order to take advantage of loading/unloading access. Art work spaces were designed around program which required column free spacing and a sunken art plaza was designed to add additional frontage to different retail and art programs located below grade. The design of both the high rise and its program intends to restore the deteriorating identity of the Powerhouse Arts District in Jersey City, NJ.
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Title: Teacher Knowledge Share (Semester Unknown) IPRO 320: Teacher Knowledge Share IPRO 320 Project Plan F08
Creator: Bern, David, Bochantin, Marike, Hartline, Julian, Mccall, Ian, Mick, Emily, Peake, Andrew, Pierce, Alison, Pindrik, Dmitriy, Quinn, Michael, Stanford, Carly, Tilatti, Michael
Date: 2008, 2008-12
Description: The goal of IPRO 320 is to create an online professional network for school teachers at the kindergarten through twelfth grade level to allow...
Show moreThe goal of IPRO 320 is to create an online professional network for school teachers at the kindergarten through twelfth grade level to allow for the sharing of ideas, lesson plans and other professionally relevant information. This is a continuing project which saw limited success in the previous semester in that a functioning web site was constructed based on surveys of public school teachers but it saw very little use. This semester, the planned approach is to build on the research generated last semester by performing additional market research with teachers. Following that, IPRO 320 will rework much of the previous web site by refining some of the features, adding additional ones as the research indicates and improving the website in general, both functionally and aesthetically.
Deliverables
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Title: Innovative Mapping (sequence unknown), IPRO 303 - Deliverables
Creator: Komoroski, Aaron, Mora, Andres, Sarraf, Basel, Kemp, Brandon, Duong, Cindy, Woodward, Frank, Suwada, Jerry, Michael, Mark, Sinha, Piyush, Glover, Richard, Mandrekar, Urba
Date: 2009-12
Description: The team worked to target the majority of mobile device users and give them an outlet to report any changes, mistakes or developments that...
Show moreThe team worked to target the majority of mobile device users and give them an outlet to report any changes, mistakes or developments that have been overlooked by NAVTEQ in the company's mobile mapping solutions. The team also worked to develop a solution that enables the average map user – men and women ages 18-35, students and tourists – to address these alterations in a simple, hassle-free way.
Sponsorship: NAVTEQ
Deliverables for IPRO 303: Innovative Mapping for the fall 2009 semester.
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Title: FACTORS ASSOCIATED WITH COGNITIVE IMPAIRMENT IN WELLMOTIVATED CHRONIC NON-MALIGNANT PAIN PATIENTS EVALUATED FOR SPINAL CORD STIMULATION
Creator: Zalizniak, Kevin C.
Date: 2016, 2016-12
Description: Cognitive impairment in individuals with chronic pain is frequently observed and clinically significant (McCracken, & Iverson, 2001). It has...
Show moreCognitive impairment in individuals with chronic pain is frequently observed and clinically significant (McCracken, & Iverson, 2001). It has long been recognized that emotional factors contribute to both patient perception of impaired cognition and verifiable cognitive impairment on testing (Burt, Zembar, & Niederehe, 1995). However, scientific consensus is lacking regarding how specific emotions, such as depression, anxiety, and pain catastrophizing impact cognition in chronic pain patients. Research seeking to clarify such relationships has been hampered by methodological shortcomings, which include limited sample sizes, non-objective measures, and failure to examine multiple emotional dimensions in unique samples (McCracken and Vowels, 2014; Moriarty, McGuire, & Finn, 2011). The present study examined factors that might contribute to cognitive impairment in this population using a sample of 78 chronic pain patients evaluated for surgical candidacy for spinal cord stimulator (SCS) implantation at the University of Illinois at Chicago. Use of such a sample ensured patients were wellmotivated to perform to the best of their ability, so as to increase their chance of being cleared for such a highly desirable procedure. Additionally, the vast majority of participants passed well-validated objective measures of effort. Hypothesized associations between attentional function as measured objectively by the RBANS attention index and a number of predictor variables: depression and anxiety, subjective pain experience, pain catastrophizing, somatization, and engagement in pain behaviors were not found, and subsequent analyses of proposed mediating relationships could not be performed. However, fully a third (35.9 percent) of our well-motivated sample did not show clinically significant impairment (below 85, or 1 SD below the mean), as was expected. Thus, it is possible that a well-motivated sample may have been less likely than samples used in previous investigations to show cognitive impairment overall. Strengths and limitations of the study are discussed, as well as clinical and research implications.
Ph.D. in Psychology, December 2016
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Title: Measuring complexity in reactor networks with cubic autocatalytic reactions
Creator: Tatara, E., Birol, I., Cinar, A., Teymour, F.
Date: 2005-04-13
Publisher: AMER CHEMICAL SOC
Description: Systems with high steady-state multiplicity and rich dynamic behavior are difficult to investigate using conventional reductionist methods. A...
Show moreSystems with high steady-state multiplicity and rich dynamic behavior are difficult to investigate using conventional reductionist methods. A network of more than five reactors hosting cubic autocatalytic reactions may potentially have more than 101 steady states and many distinct dynamic regimes, all for the same parameter set. This paper discusses how the static complexity of such systems can be measured to give a holistic picture. To achieve this, stochastic simulations were performed to statistically determine the bifurcation structure of the system, and the gathered information is summarized using a measure akin to fractal dimension. With this measure, the growth of static complexity is investigated as a function of the network size.
Endnote format citation for DOI:10.1021/ie049246t
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Title: Innovative Uses of Native CAD Files
Creator: Menches, Cindy L., Kleps, Stephen M.
Date: 2012-08-31, 2011-08-31
Description: This technical report describes the outcomes resulting from conducting interviews with professional estimators within the electrical...
Show moreThis technical report describes the outcomes resulting from conducting interviews with professional estimators within the electrical construction industry. The purpose of the interviews was to identify whether native files are shared, why sharing does not occur more frequently, how file sharing might benefit the estimating process, and barriers to sharing native CAD files for the purpose of estimating from CAD drawings.
Sponsorship: Electri International
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Title: SIZE AND VALUE RISK IN FINANCIAL FIRMS
Creator: Baek, Seungho
Date: 2013, 2013-12
Description: Although the Fama and French’s three factor model is now the most popular replacement for CAPM in corporate finance and investment management,...
Show moreAlthough the Fama and French’s three factor model is now the most popular replacement for CAPM in corporate finance and investment management, the exclusion of financial firms can be questioned on both theoretical and empirical grounds. Financial firms are around 19 percent of the value of the U.S. stock market. The financial service industry is the major industry in many large U.S. cities including New York, Chicago, Los Angeles and Miami in that their GDPs of financial services for each city are more than 23 percent. Also, there is no theoretical reason for excluding financial firms. Modigliani and Miller [31] [32] suggest that leverage affects beta, but it does not invalidate the capital asset pricing model. It would therefore be more satisfying if the pricing model applied generally, rather than being restricted to nonfinancial corporations. From this consideration, this paper assesses the validity of size and value risk as common risk factors to measure of expected equity returns in financial companies based on the fact that Fama and French [11] [12] excluded financial firms in their study of the cross-section of expected stock returns. The findings from empirical asset pricing tests suggest that size and value risk premia commonly exist in both nonfinancial and financial firms even if two factors are less explicable in financial firms, that an interest rate risk premium (ΔL/L) which defined as a financial firm specific risk factor only appears in financial companies.
PH.D in Management Science, December 2012
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Title: NON-GAUSSIAN STOCHASTIC DYNAMICS: MODELING, SIMULATION, QUANTIFICATION AND ASSIMILATION
Creator: Gao, Ting
Date: 2015, 2015-05
Description: Motivated by real world applications, three topics - deterministic quantities, uncertainty quantification and data assimilation, are...
Show moreMotivated by real world applications, three topics - deterministic quantities, uncertainty quantification and data assimilation, are considered for non-Gaussian stochastic dynamics. More specifically, three problems are formulated to investigate non-Gaussian dynamics: (i) exit problem and time-dependent probability density; (ii) parameter and function estimation for stochastic differential equations driven by L´evy motion; and (iii) nonlinear data assimilation to infer transition phenomena. First, numerical algorithms are developed to study important metrics: mean exit time, escape probability and time-dependent probability density, which can be utilized to quantify dynamical behaviors of stochastic differential equations with non- Gaussian -stable L´evy motion. Moreover, detailed numerical analysis work is done to ensure the algorithms accurate, fast and stable considering the singular nature of the L´evy jump measure. Second, new approaches on parameter and function estimation in stochastic dynamical systems are devised. Taking advantage of observations on mean exit time, escape probability or probability density, model uncertainty can be quantified by some optimization methods. These methods are beneficial to systems for which mean exit time, escape probability or probability density are feasible to observe. Finally, nonlinear data assimilation on non-Gaussian models is studied. For continuous-discrete filtering, a recursive Bayesian approach is used, and for continuous filtering, Zakai equation is solved to provide the system state estimation. In both cases, time-dependent transition probability between metastable states are investigated. xiMotivated by real world applications, three topics - deterministic quantities, uncertainty quantification and data assimilation, are considered for non-Gaussian stochastic dynamics. More specifically, three problems are formulated to investigate non-Gaussian dynamics: (i) exit problem and time-dependent probability density; (ii) parameter and function estimation for stochastic differential equations driven by L´evy motion; and (iii) nonlinear data assimilation to infer transition phenomena. First, numerical algorithms are developed to study important metrics: mean exit time, escape probability and time-dependent probability density, which can be utilized to quantify dynamical behaviors of stochastic differential equations with non- Gaussian -stable L´evy motion. Moreover, detailed numerical analysis work is done to ensure the algorithms accurate, fast and stable considering the singular nature of the L´evy jump measure. Second, new approaches on parameter and function estimation in stochastic dynamical systems are devised. Taking advantage of observations on mean exit time, escape probability or probability density, model uncertainty can be quantified by some optimization methods. These methods are beneficial to systems for which mean exit time, escape probability or probability density are feasible to observe. Finally, nonlinear data assimilation on non-Gaussian models is studied. For continuous-discrete filtering, a recursive Bayesian approach is used, and for continuous filtering, Zakai equation is solved to provide the system state estimation. In both cases, time-dependent transition probability between metastable states are investigated.
Ph.D. in Applied Mathematics, May 2015
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Title: Coupling of Twin Rectangular Supersonic Jets
Creator: Raman, G., Taghavi, R.
Date: 1998-01-10
Publisher: Cambridge Univ Press
Description: Twin jet plumes on aircraft can couple, producing dynamic pressures significant enough to cause structural fatigue. For closely spaced jets...
Show moreTwin jet plumes on aircraft can couple, producing dynamic pressures significant enough to cause structural fatigue. For closely spaced jets with a moderate aspect ratio (e.g. 5), previous work has established that two coupling modes (antisymmetric and symmetric) are kinematically permissible. However, the dynamics of twin-jet coupling have remained unexplored. In this paper a more fundamental assessment of the steady and unsteady aspects of twin-jet coupling is attempted. While we document and discuss the nozzle spacings and Mach numbers over which phase-locked coupling occurs, our concentration is much more on answering the following questions: (a) What mechanism causes the jets to couple in one mode or the other? (b) Why do the jets switch from one mode to another? (c) Are the two modes mutually exclusive or do they overlap at the transition point? Our results reveal, among many things, the following. (i) For very closely spaced twin jets in the side-by-side configuration phased feedback based on source to nozzle exit distance of adjacent jets does not fully explain the coupling modes. However, the 'null' phase regions surrounding the jets where the phase of an acoustic wavefront (arriving from downstream) does not vary appears to correlate well with the existence of the symmetric mode. When the 'null' regions of adjacent jets do not overlap antisymmetric coupling occurs and when they do overlap the jets couple symmetrically. We provide a simple correlation using a parameter (a) that can be used as a simple test to determine the mode of coupling. (ii) The switch from the antisymmetric to the symmetric mode of coupling appears to occur because of an abrupt shift in the effective screech source from the third to the fourth shock, which in turn causes the 'null' phase region surrounding the jets to grow abruptly and overlap. (iii) The two modes are mutually exclusive. Our results provide considerable insight into the twin-jet coupling problem and offer hope for designing twin-jet configurations that minimize damage to aircraft components.
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