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- Title
- CONGESTION AVOIDANCE AND FAIRNESS IN WIRELESS SENSOR NETWORKS.
- Creator
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Ahmad, Mohammad, Turgut, Damla, University of Central Florida
- Abstract / Description
-
Sensor network congestion avoidance and control primarily aims to reduce packet drops while maintaining fair bandwidth allocation to existing network flows. The design of a congestion control algorithm suited for all types of applications in sensor networks is a challenging task due to the application-specific nature of these networks. With numerous sensors transmitting data simultaneously to one or more base stations (also called sinks), sensor nodes located near the base station will most...
Show moreSensor network congestion avoidance and control primarily aims to reduce packet drops while maintaining fair bandwidth allocation to existing network flows. The design of a congestion control algorithm suited for all types of applications in sensor networks is a challenging task due to the application-specific nature of these networks. With numerous sensors transmitting data simultaneously to one or more base stations (also called sinks), sensor nodes located near the base station will most likely experience congestion and packet loss. In this thesis, we propose a novel distributed congestion avoidance algorithm which calculates the ratio of the number of downstream and upstream nodes. This ratio value (named Characteristic ratio) is used to take a routing decision and incorporate load balancing while also serving as a pointer to the congestion state of the network. Available queue sizes of the downstream nodes are used to detect incipient congestion. Queue characteristics of candidate downstream nodes are used collectively to implement both congestion avoidance and fairness by adjusting the node's forwarding rate and next hop destination. Such an approach helps to minimize packet drops, improve energy efficiency and load balancing. In cases of severe congestion, the source is signaled to reduce its sending rate and enable the network recovery process. This is essentially a transport layer algorithm and would work best with a multi-path routing protocol and almost any MAC layer standard. We present the design and implementation of the proposed protocol and compare it with the existing avoidance protocols like Global rate control and Lightweight buffering. Our simulation results show a higher packet delivery ratio with greater node buffer utilization for our protocol in comparison with the conventional mechanisms.
Show less - Date Issued
- 2007
- Identifier
- CFE0001755, ucf:47255
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001755
- Title
- Measuring the evolving Internet ecosystem with exchange points.
- Creator
-
Ahmad, Mohammad Zubair, Guha, Ratan, Bassiouni, Mostafa, Chatterjee, Mainak, Jha, Sumit, Goldiez, Brian, University of Central Florida
- Abstract / Description
-
The Internet ecosystem comprising of thousands of Autonomous Systems (ASes) now include Internet eXchange Points (IXPs) as another critical component in the infrastructure. Peering plays a significant part in driving the economic growth of ASes and is contributing to a variety of structural changes in the Internet. IXPs are a primary component of this peering ecosystem and are playing an increasing role not only in the topology evolution of the Internet but also inter-domain path routing. In...
Show moreThe Internet ecosystem comprising of thousands of Autonomous Systems (ASes) now include Internet eXchange Points (IXPs) as another critical component in the infrastructure. Peering plays a significant part in driving the economic growth of ASes and is contributing to a variety of structural changes in the Internet. IXPs are a primary component of this peering ecosystem and are playing an increasing role not only in the topology evolution of the Internet but also inter-domain path routing. In this dissertation we study and analyze the overall affects of peering and IXP infrastructure on the Internet. We observe IXP peering is enabling a quicker flattening of the Internet topology and leading to over-utilization of popular inter-AS links. Indiscriminate peering at these locations is leading to higher end-to-end path latencies for ASes peering at an exchange point, an effect magnified at the most popular worldwide IXPs. We first study the effects of recently discovered IXP links on the inter-AS routes using graph based approaches and find that it points towards the changing and flattening landscape in the evolution of the Internet's topology. We then study more IXP effects by using measurements to investigate the networks benefits of peering. We propose and implement a measurement framework which identifies default paths through IXPs and compares them with alternate paths isolating the IXP hop. Our system is running and recording default and alternate path latencies and made publicly available. We model the probability of an alternate path performing better than a default path through an IXP by identifying the underlying factors influencing the end-to end path latency. Our first-of-its-kind modeling study, which uses a combination of statistical and machine learning approaches, shows that path latencies depend on the popularity of the particular IXP, the size of the provider ASes of the networks peering at common locations and the relative position of the IXP hop along the path. An in-depth comparison of end-to-end path latencies reveal a significant percentage of alternate paths outperforming the default route through an IXP. This characteristic of higher path latencies is magnified in the popular continental exchanges as measured by us in a case study looking at the largest regional IXPs. We continue by studying another effect of peering which has numerous applications in overlay routing, Triangle Inequality Violations (TIVs). These TIVs in the Internet delay space are created due to peering and we compare their essential characteristics with overlay paths such as detour routes. They are identified and analyzed from existing measurement datasets but on a scale not carried out earlier. This implementation exhibits the effectiveness of GPUs in analyzing big data sets while the TIVs studied show that the a set of common inter-AS links create these TIVs. This result provides a new insight about the development of TIVs by analyzing a very large data set using GPGPUs.Overall our work presents numerous insights into the inner workings of the Internet's peering ecosystem. Our measurements show the effects of exchange points on the evolving Internet and exhibits their importance to Internet routing.
Show less - Date Issued
- 2013
- Identifier
- CFE0004802, ucf:49744
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004802
- Title
- Quantum Algorithms for: Quantum Phase Estimation, Approximation of the Tutte Polynomial and Black-box Structures.
- Creator
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Ahmadi Abhari, Seyed Hamed, Brennan, Joseph, Mucciolo, Eduardo, Li, Xin, Marinescu, Dan, University of Central Florida
- Abstract / Description
-
In this dissertation, we investigate three different problems in the field of Quantum computation. First, we discuss the quantum complexity of evaluating the Tutte polynomial of a planar graph. Furthermore, we devise a new quantum algorithm for approximating the phase of a unitary matrix. Finally, we provide quantum tools that can be utilized to extract the structure of black-box modules and algebras. While quantum phase estimation (QPE) is at the core of many quantum algorithms known to date...
Show moreIn this dissertation, we investigate three different problems in the field of Quantum computation. First, we discuss the quantum complexity of evaluating the Tutte polynomial of a planar graph. Furthermore, we devise a new quantum algorithm for approximating the phase of a unitary matrix. Finally, we provide quantum tools that can be utilized to extract the structure of black-box modules and algebras. While quantum phase estimation (QPE) is at the core of many quantum algorithms known to date, its physical implementation (algorithms based on quantum Fourier transform (QFT)) is highly constrained by the requirement of high-precision controlled phase shift operators, which remain difficult to realize. In the second part of this dissertation, we introduce an alternative approach to approximately implement QPE with arbitrary constant-precision controlled phase shift operators.The new quantum algorithm bridges the gap between QPE algorithms based on QFT and Kitaev's original approach. For approximating the eigenphase precise to the nth bit, Kitaev's original approach does not require any controlled phase shift operator. In contrast, QPE algorithms based on QFT or approximate QFT require controlled phase shift operators with precision of at least Pi/2n. The new approach fills the gap and requires only arbitrary constant-precision controlled phase shift operators. From a physical implementation viewpoint, the new algorithm outperforms Kitaev's approach.The other problem we investigate relates to approximating the Tutte polynomial. We show that the problem of approximately evaluating the Tutte polynomial of triangular graphs at the points (q,1/q) of the Tutte plane is BQP-complete for (most) roots of unity q. We also consider circular graphs and show that the problem of approximately evaluating the Tutte polynomial of these graphs at a point is DQC1-complete and at some points is in BQP.To show that these problems can be solved by a quantum computer, we rely on the relation of the Tutte polynomial of a planar G graph with the Jones and HOMFLY polynomial of the alternating link D(G) given by the medial graph of G. In the case of our graphs the corresponding links are equal to the plat and trace closures of braids. It is known how to evaluate the Jones and HOMFLY polynomial for closures of braids.To establish the hardness results, we use the property that the images of the generators of the braid group under the irreducible Jones-Wenzl representations of the Hecke algebra have finite order. We show that for each braid we can efficiently construct a braid such that the evaluation of the Jones and HOMFLY polynomials of their closures at a fixed root of unity leads to the same value and that the closures of the resulting braid are alternating links.The final part of the dissertation focuses on finding the structure of a black-box module or algebra. Suppose we are given black-box access to a finite module M or algebra over a finite ring R and a list of generators for M and R. We show how to find a linear basis and structure constants for M in quantum poly (log|M|) time. This generalizes a recent quantum algorithm of Arvind et al. which finds a basis representation for rings. We then show that our algorithm is a useful primitive allowing quantum computer to determine the structure of a finite associative algebra as a direct sum of simple algebras. Moreover, it solves a wide variety of problems regarding finite modules and rings. Although our quantum algorithm is based on Abelian Fourier transforms, it solves problems regarding the multiplicative structure of modules and algebras, which need not be commutative. Examples include finding the intersection and quotient of two modules, finding the additive and multiplicative identities in a module, computing the order of an module, solving linear equations over modules, deciding whether an ideal is maximal, finding annihilators, and testing the injectivity and surjectivity of ring homomorphisms. These problems appear to be exponentially hard classically.
Show less - Date Issued
- 2012
- Identifier
- CFE0004239, ucf:49526
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004239
- Title
- Charge and Spin Transport in Low-Dimensional Materials.
- Creator
-
Ahmadi, Amin, Mucciolo, Eduardo, Del Barco, Enrique, Ishigami, Masa, Guo, Jing, University of Central Florida
- Abstract / Description
-
My research has been focused on two main areas. First, electronic transports in chiral carbonnanotubes in the presence of charged adatoms. To study such systems we employed recursiveGreens function technique to evaluate the conductance using the Landauer formula. Comparingwith the experimental data, we determined the effective amplitude and the range of scatteringpotentials. In addition, using a similar approach we explained qualitatively an unusual conductancefeature in a metallic carbon...
Show moreMy research has been focused on two main areas. First, electronic transports in chiral carbonnanotubes in the presence of charged adatoms. To study such systems we employed recursiveGreens function technique to evaluate the conductance using the Landauer formula. Comparingwith the experimental data, we determined the effective amplitude and the range of scatteringpotentials. In addition, using a similar approach we explained qualitatively an unusual conductancefeature in a metallic carbon nanotube. The second part of my study was concerned to the dynamicalspin injection and spin currents in low-dimensional materials. We have developed an atomisticmodel to express the injected spin current in terms of the systems Greens function. The newformulation provides a framework to study the spin injection and relaxation of a system with anarbitrary structure.
Show less - Date Issued
- 2017
- Identifier
- CFE0006550, ucf:51343
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006550
- Title
- Size, Shape, Composition and Chemical state effects in nanocatalysis.
- Creator
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Ahmadi, Mahdi, Roldan Cuenya, Beatriz, Rahman, Talat, Kara, Abdelkader, Coffey, Kevin, University of Central Florida
- Abstract / Description
-
The field of nanocatalysis has gained significant attention in the last decades due to the numerous industrial applications of nanosized catalysts. Size, shape, structure, and composition of the nanoparticles (NPs) are the parameters that can affect the reactivity, selectivity and stability of nanocatalysts. Therefore, understanding how these parameters affect the catalytic properties of these systems is required in order to engineer them with a given desired performance. It is also important...
Show moreThe field of nanocatalysis has gained significant attention in the last decades due to the numerous industrial applications of nanosized catalysts. Size, shape, structure, and composition of the nanoparticles (NPs) are the parameters that can affect the reactivity, selectivity and stability of nanocatalysts. Therefore, understanding how these parameters affect the catalytic properties of these systems is required in order to engineer them with a given desired performance. It is also important to gain insight into the structural evolution of the NP catalysts under different reaction conditions to design catalysts with long durability under reaction condition. In this dissertation a synergistic combination of in situ, ex situ and operando state-of-the art techniques have allowed me to explore a variety of parameters and phenomena relevant to nanocatalysts by systematically tuning the NP size, chemical state, composition and chemical environment.
Show less - Date Issued
- 2016
- Identifier
- CFE0006243, ucf:51084
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006243
- Title
- On the security of NoSQL cloud database services.
- Creator
-
Ahmadian, Mohammad, Marinescu, Dan, Wocjan, Pawel, Heinrich, Mark, Brennan, Joseph, University of Central Florida
- Abstract / Description
-
Processing a vast volume of data generated by web, mobile and Internet-enabled devices, necessitates a scalable and flexible data management system. Database-as-a-Service (DBaaS) is a new cloud computing paradigm, promising a cost-effective and scalable, fully-managed database functionality meeting the requirements of online data processing. Although DBaaS offers many benefits it also introduces new threats and vulnerabilities. While many traditional data processing threats remain, DBaaS...
Show moreProcessing a vast volume of data generated by web, mobile and Internet-enabled devices, necessitates a scalable and flexible data management system. Database-as-a-Service (DBaaS) is a new cloud computing paradigm, promising a cost-effective and scalable, fully-managed database functionality meeting the requirements of online data processing. Although DBaaS offers many benefits it also introduces new threats and vulnerabilities. While many traditional data processing threats remain, DBaaS introduces new challenges such as confidentiality violation and information leakage in the presence of privileged malicious insiders and adds new dimension to the data security. We address the problem of building a secure DBaaS for a public cloud infrastructure where, the Cloud Service Provider (CSP) is not completely trusted by the data owner. We present a high level description of several architectures combining modern cryptographic primitives for achieving this goal. A novel searchable security scheme is proposed to leverage secure query processing in presence of a malicious cloud insider without disclosing sensitive information. A holistic database security scheme comprised of data confidentiality and information leakage prevention is proposed in this dissertation. The main contributions of our work are:(i) A searchable security scheme for non-relational databases of the cloud DBaaS; (ii) Leakage minimization in the untrusted cloud.The analysis of experiments that employ a set of established cryptographic techniques to protect databases and minimize information leakage, proves that the performance of the proposed solution is bounded by communication cost rather than by the cryptographic computational effort.
Show less - Date Issued
- 2017
- Identifier
- CFE0006848, ucf:51777
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006848
- Title
- Differential Expression Of Proteins Involved In VLDL Trafficking Causes Reduced VLDL Secretion In Male Ames Dwarf Mice.
- Creator
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Ahmed Moinuddin, Faisal, Siddiqi, Shadab, Masternak, Michal, Naser, Saleh, University of Central Florida
- Abstract / Description
-
Cardiovascular diseases (CVDs) have been recorded as the number one cause of death worldwide, accounting for 32% of total deaths annually. More than two-thirds of all CVD cases are associated with atherosclerosis, which is the accumulation of fats and other substances causing plaque formation in the interior walls of major arteries. This leads to narrowing of the lumen and hardening of the arteries, ultimately resulting in angina, heart attack and/or stroke. Studies have shown that the...
Show moreCardiovascular diseases (CVDs) have been recorded as the number one cause of death worldwide, accounting for 32% of total deaths annually. More than two-thirds of all CVD cases are associated with atherosclerosis, which is the accumulation of fats and other substances causing plaque formation in the interior walls of major arteries. This leads to narrowing of the lumen and hardening of the arteries, ultimately resulting in angina, heart attack and/or stroke. Studies have shown that the pathogenesis of atherosclerosis and associated CVDs is strongly linked to elevated secretion of liver-specific lipoproteins called very-low-density-lipoprotein (VLDL). VLDLs are crucial lipoproteins responsible for transportation of triacylglycerides (TAGs), chemically inert particles that are physiologically significant for their energy storing capacity, from the liver to peripheral tissues. These VLDL particles are synthesized in the lumen of the endoplasmic reticulum (ER) of hepatocytes, transported from the ER to the cis-Golgi in special transport vesicles called VLDL-transport-vesicles (VTVs) and secreted into plasma through a highly regulated secretory pathway. Previous studies from our laboratory have shown that VTV-mediated ER-to-Golgi VLDL trafficking is the rate-limiting step in overall VLDL secretion from hepatocytes into plasma. In this project, we investigated intracellular VLDL trafficking and VLDL secretion in Ames dwarf (Prop1df, df/df) mice, a mutant mouse model homozygous for a recessive mutation at Prop1 gene locus (Prop1df) having deficiency of growth hormone (GH), thyroid stimulating hormone (TSH) and prolactin (PRL). This model is characteristic of prolonged longevity (~50% longer) and improved insulin sensitivity in comparison to their wild-type (N) counterparts. Ames dwarf (df/df) mice have recently been shown to have highly reduced plasma TAG levels, associating them with reduced susceptibility to atherosclerosis and associated CVDs. The underlying mechanism responsible for reduced VLDL secretion in Ames dwarf mice is yet to be characterized. We hypothesize that VTV-mediated trafficking of VLDL is reduced in Ames dwarf mice because of reduced expression of proteins regulating VLDL and VTV formation. To test our hypothesis, we first performed VTV-budding assay using cellular fractions isolated separately from Ames dwarf (df/df) and wild-type (N) mice livers. Our results show a significant (45%) reduction in VTV-budding process in Ames dwarf (df/df) mice compared to wild-type (N). Next we performed 2-dimensional differential gel electrophoresis (2-DIGE) on VTV and whole cell lysate (WCL) samples in order to examine the differences in protein expression and to have highly specific protein separation. ExPASy database was used to analyze protein spots that allowed us in identifying proteins specifically expressed in each of the mouse groups. Employing western blotting, samples (ER, cytosol, VTV and WCL) from both sets of mice were tested for expression levels of VLDL and VTV associated proteins (ApoB100, Sec22b, CideB, MTP, Apo-A1 and Apo-AIV) with ?-actin as the loading control. Significant differences in expression level of these proteins were observed which strongly suggest that the formation of VTV from ER in male Ames dwarf (df/df) mice is reduced compared to wild-type (N). Overall, we conclude that the differential expression of proteins required for VLDL transport causes reduced VLDL secretion in male Ames dwarf (df/df) mice.
Show less - Date Issued
- 2015
- Identifier
- CFE0005916, ucf:50829
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005916
- Title
- Detailed Understanding of Flow, Heat Transfer, and Pressure Drop Behavior in a Square Channel With 45 Deg Ribs.
- Creator
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Ahmed, Lumaya, Kapat, Jayanta, Gordon, Ali, Ahmed, Kareem, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
-
Internal Duct Cooling (IDC) with rib turbulators is one of the common cooling techniques applied inside the turbine airfoils. It is very important for the gas turbine industry to design and develop an optimized cooling channel that maximizes the amount of heat removed, while simultaneously minimizing the pressure drop for a target overall cooling effectiveness. Angled ribs perform superior to the transverse ribs due to additional secondary flow associated with them. However, they result in a...
Show moreInternal Duct Cooling (IDC) with rib turbulators is one of the common cooling techniques applied inside the turbine airfoils. It is very important for the gas turbine industry to design and develop an optimized cooling channel that maximizes the amount of heat removed, while simultaneously minimizing the pressure drop for a target overall cooling effectiveness. Angled ribs perform superior to the transverse ribs due to additional secondary flow associated with them. However, they result in a highly non-homogenous heat transfer distribution, which is a manifestation of the complex, turbulent flow field inside the channel. It is very important to comprehend the secondary flow physics to characterize the heat transfer distribution in such angled ribbed channels. Additionally, due to the manufacturing constraint, the gas turbine industry encounters a challenge to make ribs edge sharp and results in ribs with rounded edges. The one of the main objectives of the present study is to provide a fundamental understanding of the flow physics on the heat transfer and pressure drop behavior in 45(&)deg; ribbed channels both with sharp and rounded-edge ribs. It is found that the secondary flow has a significant effect on the heat transfer behavior for both types of ribs. There is a great need of high-fidelity PIV flow field data in the inter-rib space for an angled ribbed channel which can be used for CFD validation, especially for LES. The current study provides benchmarking flow field data in the inter-rib space in a square channel with 45(&)deg; ribs using stereoscopic PIV technique. Besides the experiments, numerical studies were also conducted by using LES and different RANS models. The LES results show an excellent prediction capability for aerothermal behavior in such channels. However, the prediction capability of RANS models is found to be inconsistent for different rib configurations and flow conditions.
Show less - Date Issued
- 2018
- Identifier
- CFE0007302, ucf:52171
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007302
- Title
- Multi-Level Safety Performance Functions for High Speed Facilities.
- Creator
-
Ahmed, Mohamed, Abdel-Aty, Mohamed, Radwan, Ahmed, Al-Deek, Haitham, Mackie, Kevin, Pande, Anurag, Uddin, Nizam, University of Central Florida
- Abstract / Description
-
High speed facilities are considered the backbone of any successful transportation system; Interstates, freeways, and expressways carry the majority of daily trips on the transportation network. Although these types of roads are relatively considered the safest among other types of roads, they still experience many crashes, many of which are severe, which not only affect human lives but also can have tremendous economical and social impacts. These facts signify the necessity of enhancing the...
Show moreHigh speed facilities are considered the backbone of any successful transportation system; Interstates, freeways, and expressways carry the majority of daily trips on the transportation network. Although these types of roads are relatively considered the safest among other types of roads, they still experience many crashes, many of which are severe, which not only affect human lives but also can have tremendous economical and social impacts. These facts signify the necessity of enhancing the safety of these high speed facilities to ensure better and efficient operation. Safety problems could be assessed through several approaches that can help in mitigating the crash risk on long and short term basis. Therefore, the main focus of the research in this dissertation is to provide a framework of risk assessment to promote safety and enhance mobility on freeways and expressways. Multi-level Safety Performance Functions (SPFs) were developed at the aggregate level using historical crash data and the corresponding exposure and risk factors to identify and rank sites with promise (hot-spots). Additionally, SPFs were developed at the disaggregate level utilizing real-time weather data collected from meteorological stations located at the freeway section as well as traffic flow parameters collected from different detection systems such as Automatic Vehicle Identification (AVI) and Remote Traffic Microwave Sensors (RTMS). These disaggregate SPFs can identify real-time risks due to turbulent traffic conditions and their interactions with other risk factors.In this study, two main datasets were obtained from two different regions. Those datasets comprise historical crash data, roadway geometrical characteristics, aggregate weather and traffic parameters as well as real-time weather and traffic data.At the aggregate level, Bayesian hierarchical models with spatial and random effects were compared to Poisson models to examine the safety effects of roadway geometrics on crash occurrence along freeway sections that feature mountainous terrain and adverse weather. At the disaggregate level; a main framework of a proactive safety management system using traffic data collected from AVI and RTMS, real-time weather and geometrical characteristics was provided. Different statistical techniques were implemented. These techniques ranged from classical frequentist classification approaches to explain the relationship between an event (crash) occurring at a given time and a set of risk factors in real time to other more advanced models. Bayesian statistics with updating approach to update beliefs about the behavior of the parameter with prior knowledge in order to achieve more reliable estimation was implemented. Also a relatively recent and promising Machine Learning technique (Stochastic Gradient Boosting) was utilized to calibrate several models utilizing different datasets collected from mixed detection systems as well as real-time meteorological stations. The results from this study suggest that both levels of analyses are important, the aggregate level helps in providing good understanding of different safety problems, and developing policies and countermeasures to reduce the number of crashes in total. At the disaggregate level, real-time safety functions help toward more proactive traffic management system that will not only enhance the performance of the high speed facilities and the whole traffic network but also provide safer mobility for people and goods. In general, the proposed multi-level analyses are useful in providing roadway authorities with detailed information on where countermeasures must be implemented and when resources should be devoted. The study also proves that traffic data collected from different detection systems could be a useful asset that should be utilized appropriately not only to alleviate traffic congestion but also to mitigate increased safety risks. The overall proposed framework can maximize the benefit of the existing archived data for freeway authorities as well as for road users.
Show less - Date Issued
- 2012
- Identifier
- CFE0004508, ucf:49274
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004508
- Title
- Corrosion behaviour of AISI 304 stainless steel in contact with eutectic salt for concentrated solar power plant applications.
- Creator
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Ahmed, Omar, Sohn, Yongho, Mohajeri, Nahid, Coffey, Kevin, Fang, Jiyu, University of Central Florida
- Abstract / Description
-
In response to the extensive energy demands on national and global levels, concentrated solar power (CSP) plants are designed to harness and convert solar energy to electricity. For such green energy application, robust, reliable and durable materials for CSP constructions are required. The corrosion resistance is among many parameters to consider in these thermal-electrical stations such as for pipes and storage tanks in CSP. In this investigation, the corrosion behavior of AISI 304...
Show moreIn response to the extensive energy demands on national and global levels, concentrated solar power (CSP) plants are designed to harness and convert solar energy to electricity. For such green energy application, robust, reliable and durable materials for CSP constructions are required. The corrosion resistance is among many parameters to consider in these thermal-electrical stations such as for pipes and storage tanks in CSP. In this investigation, the corrosion behavior of AISI 304 stainless steel (18 wt. % Cr, 8 wt. % Ni) with the heat transfer fluid, also known as solar salt, has been examined. The ternary eutectic salt mixture with the composition, 53 wt. % KNO3, 40 wt. % NaNO2, and 7 wt. % NaNO3, that melts at 142(&)deg;C, has a potential use in CSP as a heat transfer fluid. The solar salt was prepared for this corrosion study from reagent grades of high purity nitrites and nitrates. Samples of AISI 304 stainless steel were sectioned from a sheet stock of the alloy and exposed to solar salt at 530(&)deg;C in air at 1 atmospheric pressure. After test intervals of 250, 500, and 750 hours in total immersion condition, AISI 304 stainless steel samples have developed a scale of corrosion products made up of multiple oxides. X-ray diffraction and scanning electron microscopy with X-ray energy-dispersive spectroscopy were employed to examine the extent of corrosion and identify the corrosion products. Transmission electron microscopy was used to verify the corrosion products identity via electron diffraction patterns. Oxides of iron were found to be the primary corrosion products in the presence of the molten alkali nitrates-nitrite salt mixture because of the dissolution of the protective chromium oxide (Cr2O3) scale formed on AISI 304 stainless steel coupons. The corrosion scale was uniform in thickness and made up of sodium iron oxide (NaFeO2), iron oxide, hematite (Fe2O3), and chromium-iron oxide (Cr,Fe)2O3 solid solution. The latter was found near the AISI 304 stainless steel. This indicates that the scale formed, particularly on the upper layers with presence of sodium iron oxide and iron oxide, hematite, is protective, and forms an effective barrier against penetration of fused solar salt. At the alloy interface with the bulk corrosion scale, the corrosion process induced a compositional modification in the grains located at the interface. There are iron rich and iron depleted grains at the interface if compared to the nominal iron content of the alloy. The mode of attack is identified as uniform at the test temperature of 530(&)deg;C, showing a parabolic behavior with a parabolic rate constant (Kp) equals to 1.08(&)#215;10^(-17)(m2/sec). By extrapolation, annual corrosion rate is estimated to reach 0.784 mils per year. Corrosion behavior of AISI 304 stainless steel is discussed in terms of thermodynamics and reaction paths.
Show less - Date Issued
- 2013
- Identifier
- CFE0004969, ucf:49587
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004969
- Title
- An analysis of the preparedness of educational institutions to ensure the security of their institutional information.
- Creator
-
Ahmed, Vikram, Johnson, Jerry, Murray, Kenneth, Baldwin, Lee, Amiri, Shahram, University of Central Florida
- Abstract / Description
-
The purpose of this exploratory study was to analyze and examine the differences in the preparedness of educational institutions toward ensuring the security of their data by comparing their self-reported perceptions of security risks and their assessments of the corresponding risk-mitigating practices. Factors that were studied with reference to securing institutional data were aligned with the five components of information systems: hardware, software, data, procedures and people. The study...
Show moreThe purpose of this exploratory study was to analyze and examine the differences in the preparedness of educational institutions toward ensuring the security of their data by comparing their self-reported perceptions of security risks and their assessments of the corresponding risk-mitigating practices. Factors that were studied with reference to securing institutional data were aligned with the five components of information systems: hardware, software, data, procedures and people. The study examined the perceptions of security threats associated with these factors and explored the perceptions of the effectiveness of critical measures with respect to these factors within the constraints applicable to educational institutions. Given the dynamic nature of the threats to information security, this study further explored mechanisms and frequencies with which the different types of educational institutions conduct key security practices and stay up-to-date in their information security policies and procedures. The population of interest for this study consisted of a cross-sectional representation of the following types of educational institutions in the state of Florida: public and private PK-12 institutions, public and private universities, and virtual schools. At every stage of this exploratory study, comparative analyses were conducted. The researcher found no statistically significant differences between the types of educational institutions in their perceptions of security risks. However, in terms of their perceptions of the effectiveness of security measures, frequencies of key security practices and policy updates, budget allocations, and overall assessment of security preparedness, the educational institutions showed statistically significant differences.
Show less - Date Issued
- 2018
- Identifier
- CFE0007145, ucf:52293
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007145
- Title
- SELF-ASSEMBLY AND PHOTOPHYSICS OF SELECTED ORGANIC MATERIALS AND TWO-PHOTON BIOIMAGING WITH PROFLUORESCENT NITROXIDES, POLYELECTROLYTE NANOPARTICLES, AND SQUARAINE PROBES.
- Creator
-
Ahn, Hyo-Yang, Belfield, Kevin, University of Central Florida
- Abstract / Description
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Two-photon absorption and upconverted fluorescence has been utilized in a variety of applications in pure science and engineering. Multiphoton-based techniques were used in this research in order to understand photophysical and chemical characteristics of several fluorescent dyes and to demonstrate some of their key applications. Two-photon fluorescence microscopy (2PFM) has become a powerful technique in bio-photonics for non-invasive imaging in the near-infrared (NIR) region (700~1000 nm)...
Show moreTwo-photon absorption and upconverted fluorescence has been utilized in a variety of applications in pure science and engineering. Multiphoton-based techniques were used in this research in order to understand photophysical and chemical characteristics of several fluorescent dyes and to demonstrate some of their key applications. Two-photon fluorescence microscopy (2PFM) has become a powerful technique in bio-photonics for non-invasive imaging in the near-infrared (NIR) region (700~1000 nm) that often results in less photobleaching. In Chapter 1, there is a brief introduction to fluorescence, examples of fluorescence materials, and a discussion of the advantages of two-photon absorption. 2PFM imaging was utilized in Chapters 2 to 4 for various applications. In Chapter 2, a new squaraine dye is introduced and its linear and nonlinear photophysical properties are characterized. This compound has very high two-photon absorption (2PA) cross sections and high photostability both in an organic solvent and when encapsulated in micelles. Based on these properties, this dye was demonstrated as a near-infrared (NIR) probe in in vitro 2PFM imaging with excitation over 800 nm wavelength. In Chapter 3, new profluorescent nitroxides are introduced. Nitroxide radicals are utilized for electron paramagnetic resonance (EPR) spectroscopy and in biological systems as some are known, in some manner, to mimic the behavior of superoxide dismutase (SOD) that detoxifies or mitigates oxidative stress by trapping free radicals. Here, two profluorescent nitroxides investigated for use as a two-photon fluorescent oxidative stress indicator in in vitro two-photon fluorescence microscopy (2PFM) imaging. In Chapter 4, two-photon excited (2PE) fluorescence of a conjugated polyelectrolyte (CPE), PPESO3, was studied in methanol and in water. The results of CPE quenching studies were comparable under both one-photon excitation conditions and two-photon excitation. CPE coated silica nanoparticles were incubated in HeLa cells and 2PFM imaging was demonstrated for this new class of fluorescent probe. Supramolecular structures based on organized assemblies/aggregation of chromophores have attracted widespread interest as molecular devices with potential applications in molecular electronics, artificial light harvesting, and pharmacology. In Chapter 5, J-aggregate formation was investigated for two porphyrin-based dyes, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS, 4) and an amino tris-sulfonate analog (5) in water via UV-vis, fluorescence, and lifetime decay studies. The effect of aggregation on two-photon absorption properties was also investigated. A functionalized norbornene-based homopolymer, synthesized by the ring opening metathesis polymerization technique was used as a J-aggregation enhancement template and had a role of polymer-templating to facilitate porphyrin aggregation and modulate 2PA. In Chapter 6, squaraine dye aggregates templated with single wall carbon nanotubes (SWCNTs) that were atomically clean were studied by using optical absorption spectroscopy, atomic force microscopy (AFM), and photoconductivity measurements. SWCNTs selectively promote the formation of squaraine dye aggregates with a head-to-head stacking arrangement, and these dye aggregates effectively photosensitize SWCNTs, demonstrating that this novel approach can yield highly photosensitized devices.
Show less - Date Issued
- 2011
- Identifier
- CFE0003978, ucf:48665
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003978
- Title
- INFORMATION RETRIEVAL PERFORMANCE ENHANCEMENT USING THE AVERAGE STANDARD ESTIMATOR AND THE MULTI-CRITERIA DECISION WEIGHTED SET OF PERFORMANCE MEASURES.
- Creator
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AHRAM, TAREQ, McCauley-Bush, Pamela, University of Central Florida
- Abstract / Description
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Information retrieval is much more challenging than traditional small document collection retrieval. The main difference is the importance of correlations between related concepts in complex data structures. These structures have been studied by several information retrieval systems. This research began by performing a comprehensive review and comparison of several techniques of matrix dimensionality estimation and their respective effects on enhancing retrieval performance using singular...
Show moreInformation retrieval is much more challenging than traditional small document collection retrieval. The main difference is the importance of correlations between related concepts in complex data structures. These structures have been studied by several information retrieval systems. This research began by performing a comprehensive review and comparison of several techniques of matrix dimensionality estimation and their respective effects on enhancing retrieval performance using singular value decomposition and latent semantic analysis. Two novel techniques have been introduced in this research to enhance intrinsic dimensionality estimation, the Multi-criteria Decision Weighted model to estimate matrix intrinsic dimensionality for large document collections and the Average Standard Estimator (ASE) for estimating data intrinsic dimensionality based on the singular value decomposition (SVD). ASE estimates the level of significance for singular values resulting from the singular value decomposition. ASE assumes that those variables with deep relations have sufficient correlation and that only those relationships with high singular values are significant and should be maintained. Experimental results over all possible dimensions indicated that ASE improved matrix intrinsic dimensionality estimation by including the effect of both singular values magnitude of decrease and random noise distracters. Analysis based on selected performance measures indicates that for each document collection there is a region of lower dimensionalities associated with improved retrieval performance. However, there was clear disagreement between the various performance measures on the model associated with best performance. The introduction of the multi-weighted model and Analytical Hierarchy Processing (AHP) analysis helped in ranking dimensionality estimation techniques and facilitates satisfying overall model goals by leveraging contradicting constrains and satisfying information retrieval priorities. ASE provided the best estimate for MEDLINE intrinsic dimensionality among all other dimensionality estimation techniques, and further, ASE improved precision and relative relevance by 10.2% and 7.4% respectively. AHP analysis indicates that ASE and the weighted model ranked the best among other methods with 30.3% and 20.3% in satisfying overall model goals in MEDLINE and 22.6% and 25.1% for CRANFIELD. The weighted model improved MEDLINE relative relevance by 4.4%, while the scree plot, weighted model, and ASE provided better estimation of data intrinsic dimensionality for CRANFIELD collection than Kaiser-Guttman and Percentage of variance. ASE dimensionality estimation technique provided a better estimation of CISI intrinsic dimensionality than all other tested methods since all methods except ASE tend to underestimate CISI document collection intrinsic dimensionality. ASE improved CISI average relative relevance and average search length by 28.4% and 22.0% respectively. This research provided evidence supporting a system using a weighted multi-criteria performance evaluation technique resulting in better overall performance than a single criteria ranking model. Thus, the weighted multi-criteria model with dimensionality reduction provides a more efficient implementation for information retrieval than using a full rank model.
Show less - Date Issued
- 2008
- Identifier
- CFE0002426, ucf:47747
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002426
- Title
- TOP MANAGEMENT'S PERCEPTIONS OF SERVICE EXCELLENCE AND HOSPITALITY: THE CASE OF DR. P. PHILLIPS HOSPITAL.
- Creator
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Aiello, Taryn, Severt, Denver, University of Central Florida
- Abstract / Description
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This study investigated service excellence and hospitality in a healthcare setting. It is unique from other hospitality research in that it considers hospitality and service excellence as separate concepts, applicable across industries. Part of the premise of this study explores how hospitality extends past service excellence to create a comfortable and welcoming environment to combat patient anxiety and stress. Furthermore, this is one of the first qualitative studies on the importance of...
Show moreThis study investigated service excellence and hospitality in a healthcare setting. It is unique from other hospitality research in that it considers hospitality and service excellence as separate concepts, applicable across industries. Part of the premise of this study explores how hospitality extends past service excellence to create a comfortable and welcoming environment to combat patient anxiety and stress. Furthermore, this is one of the first qualitative studies on the importance of service excellence and hospitality in the healthcare industry. This case study measured top management's perceptions of service excellence and hospitality within one community-based hospital located in Orlando, Florida. The researcher conducted one-hour interviews with twelve leading managers to gain their opinions of service excellence and hospitality within their organization. Consistent with a thorough review of literature, three conclusions were revealed: 1) there is a strong, but mixed, top management commitment to service excellence and hospitality throughout organization; 2) the terms "service excellence" and "hospitality", when used, were discussed interchangeably as if the two theories were equivalent; and 3) External barriers to the patient experience that were identified included improvement of technology, increased consumerism, quality regulations, and workforce deficits. Internal barriers to the patient experience include communication and inconsistency. The research provided implications to healthcare organizations that are looking to implement practices of hospitality and service management to improve service delivery. Additionally, the study of hospitality outside the industry offers ideas of improvement for hospitality management and organizational researchers. It can also be used as a foundation to formulate additional studies in the area of service excellence and hospitality within the healthcare field, as this research is limited to only top management's views.
Show less - Date Issued
- 2008
- Identifier
- CFE0002311, ucf:47837
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002311
- Title
- An Exploratory Study of Customer Vulnerability: A Cross-Segment Approach.
- Creator
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Aiello, Taryn, Severt, Denver, Rompf, Paul, Breiter, Deborah, University of Central Florida
- Abstract / Description
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The purpose of this study is to explore the concept of customer vulnerability across varying service industries. While the concept of customer vulnerability has been debated in business, marketing, sociology, and psychology scholarly literature, there has been little research conducted that specifically investigates consumers' perceptions of vulnerability during the service exchange. Specific to this research, customer vulnerability is defined as experiences in which consumers participate in...
Show moreThe purpose of this study is to explore the concept of customer vulnerability across varying service industries. While the concept of customer vulnerability has been debated in business, marketing, sociology, and psychology scholarly literature, there has been little research conducted that specifically investigates consumers' perceptions of vulnerability during the service exchange. Specific to this research, customer vulnerability is defined as experiences in which consumers participate in a service exchange with a firm during a time of individual or shared medical, physical, emotional, or spiritual necessity, whether the vulnerability is experienced during the course of the transaction or whether consumers arrive to the firm already immersed in that state. Customer vulnerability is an important concept for research, as the exchanges between service providers and consumers during a time of vulnerability are heightened in emotion and memory. As a result, these exchanges lend themselves to be more likely to become transformative experiences, in that the provider and recipient may be left emotionally, intellectually, and spiritually changed as a result. Therefore, additional focus is needed in this area to understand transformative experiences in service as a result of exchanges between service providers and customers.The explorative study first conducts a critical literature review across disciplines regarding scales that have been used and are considered by the researcher to be important constructs of analysis when exploring vulnerable service encounters. Next, a qualitative investigation of consumer forums is conducted in the air travel, banking, and assisted living industries, which resulted in the finding that similar behavioral attributes within industry, but different behavioral attributes between industries, were needed to cater to consumers experiencing vulnerability. The study is followed by a quantitative investigation of vulnerable service experiences through an application of the identified scales combined with the results of the qualitative investigation across the same three industries. Exploratory factor analysis revealed that two industries' results loaded onto two factors; however, each industry's factors differed due to the nature of that industry. The air travel factors were entitled task humanism and task functionality. The banking factors were entitled maintenance functionality and maintenance humanism. A third factor was revealed within the assisted living facility segment entitled hospitable humanism, along with factors of personal humanism and personal functionality. The study concludes by presenting a discussion of the findings and practical implications for service industry managers, a presentation of the study limitations, and suggestions for future research.
Show less - Date Issued
- 2013
- Identifier
- CFE0005291, ucf:50542
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005291
- Title
- A REINFORCEMENT LEARNING TECHNIQUE FOR ENHANCING HUMAN BEHAVIOR MODELS IN A CONTEXT-BASED ARCHITECTURE.
- Creator
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Aihe, David, Gonzalez, Avelino, University of Central Florida
- Abstract / Description
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A reinforcement-learning technique for enhancing human behavior models in a context-based learning architecture is presented. Prior to the introduction of this technique, human models built and developed in a Context-Based reasoning framework lacked learning capabilities. As such, their performance and quality of behavior was always limited by what the subject matter expert whose knowledge is modeled was able to articulate or demonstrate. Results from experiments performed show that subject...
Show moreA reinforcement-learning technique for enhancing human behavior models in a context-based learning architecture is presented. Prior to the introduction of this technique, human models built and developed in a Context-Based reasoning framework lacked learning capabilities. As such, their performance and quality of behavior was always limited by what the subject matter expert whose knowledge is modeled was able to articulate or demonstrate. Results from experiments performed show that subject matter experts are prone to making errors and at times they lack information on situations that are inherently necessary for the human models to behave appropriately and optimally in those situations. The benefits of the technique presented is two fold; 1) It shows how human models built in a context-based framework can be modified to correctly reflect the knowledge learnt in a simulator; and 2) It presents a way for subject matter experts to verify and validate the knowledge they share. The results obtained from this research show that behavior models built in a context-based framework can be enhanced by learning and reflecting the constraints in the environment. From the results obtained, it was shown that after the models are enhanced, the agents performed better based on the metrics evaluated. Furthermore, after learning, the agent was shown to recognize unknown situations and behave appropriately in previously unknown situations. The overall performance and quality of behavior of the agent improved significantly.
Show less - Date Issued
- 2008
- Identifier
- CFE0002466, ucf:47715
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002466
- Title
- Dialectics of Microbudget Cinema.
- Creator
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Ajdinovic, Milos, Stoeckl, Ula, Watson, Keri, Peters, Philip, Danker, Elizabeth, Perez, Jonathan, University of Central Florida
- Abstract / Description
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Magic Kingdom is a feature-length, microbudget motion picture, produced, (")written("), directed, and edited by Milos Ajdinovic as a part of the University of Central Florida's Masters in Fine Arts program in Digital Entrepreneurial Cinema. Its narrative is a product of the collective improvisation between a group of collaborators (-) Chealsea Anagnoson, Henry Gibson, Mikaela Duffy and Marcus Nieves (-) moderated by Milos Ajdinovic. This written dissertation is an attempt to document the...
Show moreMagic Kingdom is a feature-length, microbudget motion picture, produced, (")written("), directed, and edited by Milos Ajdinovic as a part of the University of Central Florida's Masters in Fine Arts program in Digital Entrepreneurial Cinema. Its narrative is a product of the collective improvisation between a group of collaborators (-) Chealsea Anagnoson, Henry Gibson, Mikaela Duffy and Marcus Nieves (-) moderated by Milos Ajdinovic. This written dissertation is an attempt to document the concepts and processes that surrounded the production of this film.
Show less - Date Issued
- 2017
- Identifier
- CFE0006849, ucf:51787
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006849
- Title
- Routing, Localization and Positioning Protocols for Wireless Sensor and Actor Networks.
- Creator
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Akbas, Mustafa, Turgut, Damla, Boloni, Ladislau, Georgiopoulos, Michael, Brust, Matthias, Bassiouni, Mostafa, Zhao, Yue, University of Central Florida
- Abstract / Description
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Wireless sensor and actor networks (WSANs) are distributed systems of sensor nodes and actors that are interconnected over the wireless medium. Sensor nodes collect information about the physical world and transmit the data to actors by using one-hop or multi-hop communications. Actors collect information from the sensor nodes, process the information, take decisions and react to the events.This dissertation presents contributions to the methods of routing, localization and positioning in...
Show moreWireless sensor and actor networks (WSANs) are distributed systems of sensor nodes and actors that are interconnected over the wireless medium. Sensor nodes collect information about the physical world and transmit the data to actors by using one-hop or multi-hop communications. Actors collect information from the sensor nodes, process the information, take decisions and react to the events.This dissertation presents contributions to the methods of routing, localization and positioning in WSANs for practical applications. We first propose a routing protocol with service differentiation for WSANs with stationary nodes. In this setting, we also adapt a sports ranking algorithm to dynamically prioritize the events in the environment depending on the collected data. We extend this routing protocol for an application, in which sensor nodes float in a river to gather observations and actors are deployed at accessible points on the coastline. We develop a method with locally acting adaptive overlay network formation to organize the network with actor areas and to collect data by using locality-preserving communication.We also present a multi-hop localization approach for enriching the information collected from the river with the estimated locations of mobile sensor nodes without using positioning adapters. As an extension to this application, we model the movements of sensor nodes by a subsurface meandering current mobility model with random surface motion. Then we adapt the introduced routing and network organization methods to model a complete primate monitoring system. A novel spatial cut-off preferential attachment model and center of mass concept are developed according to the characteristics of the primate groups. We also present a role determination algorithm for primates, which uses the collection of spatial-temporal relationships. We apply a similar approach to human social networks to tackle the problem of automatic generation and organization of social networks by analyzing and assessing interaction data. The introduced routing and localization protocols in this dissertation are also extended with a novel three dimensional actor positioning strategy inspired by the molecular geometry. Extensive simulations are conducted in OPNET simulation tool for the performance evaluation of the proposed protocols.
Show less - Date Issued
- 2013
- Identifier
- CFE0005292, ucf:50564
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005292
- Title
- PREDICTING COMPENSATION AND RECIPROCITY OF BIDS FOR SEXUAL AND/OR ROMANTIC ESCALATION IN CROSS-SEX FRIENDSHIPS.
- Creator
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Akbulut, Valerie, Weger, Harry, University of Central Florida
- Abstract / Description
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With more opportunities available to men and women to interact, both professionally and personally (i.e., the workplace, educational setting, community), friendships with members of the opposite sex are becoming more common. Increasingly, researchers have noted that one facet that makes cross-sex friendships unique compared to other types of relationships (i.e. romantic love, same-sex friendships, familial relationships), is that there is the possibility and opportunity for a romantic or...
Show moreWith more opportunities available to men and women to interact, both professionally and personally (i.e., the workplace, educational setting, community), friendships with members of the opposite sex are becoming more common. Increasingly, researchers have noted that one facet that makes cross-sex friendships unique compared to other types of relationships (i.e. romantic love, same-sex friendships, familial relationships), is that there is the possibility and opportunity for a romantic or sexual relationship to manifest. Communication research has yet to investigate how one decides whether to begin a romantic or sexual relationship or choose to remain platonic with their cross-sex friend. Given that cross-sex friendships deal with a lot of ambiguity regarding the nature of the friendship, this researcher sought to uncover what factors determine whether parties reciprocate romantic or sexual interest or opt to remain platonic through the theoretical lens of interaction adaptation theory. Specifically, the researcher sought to determine what expectations and desires predict compensation or reciprocity of romantic or sexual desires. At a large Southeastern university, quantitative data were collected from 307 participants. The results indicated that of the variables, Not Attracted, Incompatibility, and closeness were significant predictors of romantic reciprocation. In the case of 'friends with benefit' relationships, the results indicated that of the variables, Not Attracted, Sexual/Romantic Potential, sex, and sexual attitudes were significant predictors of sexual reciprocity. Further explanations of results, limitations, and future directions for research are discussed.
Show less - Date Issued
- 2009
- Identifier
- CFE0002531, ucf:47668
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002531
- Title
- SYSTEM DESIGN AND OPTIMIZATION OF OPTICAL COHERENCE TOMOGRAPHY.
- Creator
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Akcay, Avni, Rolland, Jannick, University of Central Florida
- Abstract / Description
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Optical coherence imaging, including tomography (OCT) and microscopy (OCM), has been a growing research field in biomedical optical imaging in the last decade. In this imaging modality, a broadband light source, thus of short temporal coherence length, is used to perform imaging via interferometry. A challenge in optical coherence imaging, as in any imaging system towards biomedical diagnosis, is the quantification of image quality and optimization of the system components, both a primary...
Show moreOptical coherence imaging, including tomography (OCT) and microscopy (OCM), has been a growing research field in biomedical optical imaging in the last decade. In this imaging modality, a broadband light source, thus of short temporal coherence length, is used to perform imaging via interferometry. A challenge in optical coherence imaging, as in any imaging system towards biomedical diagnosis, is the quantification of image quality and optimization of the system components, both a primary focus of this research. We concentrated our efforts on the optimization of the imaging system from two main standpoints: axial point spread function (PSF) and practical steps towards compact low-cost solutions. Up to recently, the criteria for the quality of a system was based on speed of imaging, sensitivity, and particularly axial resolution estimated solely from the full-width at half-maximum (FWHM) of the axial PSF with the common practice of assuming a Gaussian source power spectrum. As part of our work to quantify axial resolution we first brought forth two more metrics unlike FWHM, which accounted for side lobes in the axial PSF caused by irregularities in the shape of the source power spectrum, such as spectral dips. Subsequently, we presented a method where the axial PSF was significantly optimized by suppressing the side lobes occurring because of the irregular shape of the source power spectrum. The optimization was performed through optically shaping the source power spectrum via a programmable spectral shaper, which consequentially led to suppression of spurious structures in the images of a layered specimen. The superiority of the demonstrated approach was in performing reshaping before imaging, thus eliminating the need for post-data acquisition digital signal processing. Importantly, towards the optimization and objective image quality assessment in optical coherence imaging, the impact of source spectral shaping was further analyzed in a task-based assessment method based on statistical decision theory. Two classification tasks, a signal-detection task and a resolution task, were investigated. Results showed that reshaping the source power spectrum was a benefit essentially to the resolution task, as opposed to both the detection and resolution tasks, and the importance of the specimen local variations in index of refraction on the resolution task was demonstrated. Finally, towards the optimization of OCT and OCM for use in clinical settings, we analyzed the detection electronics stage, which is a crucial component of the system that is designed to capture extremely weak interferometric signals in biomedical and biological imaging applications. We designed and tested detection electronics to achieve a compact and low-cost solution for portable imaging units and demonstrated that the design provided an equivalent performance to the commercial lock-in amplifier considering the system sensitivity obtained with both detection schemes.
Show less - Date Issued
- 2005
- Identifier
- CFE0000651, ucf:46527
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000651