It is well known that time and temperature are not direct measurements of either material state during cure or mechanical properties after cure in polymer composites. Rather, in current practice, the viscoelastic properties and mechanical properties during cure are merely assumed based on an extensive statistical data of time and temperature history of the material. This practice is time-consuming and costly. In this study, an ex-situ estimation of the actual material states using advanced analytical instruments has been proposed and validated. An encapsulated sample rheometer was used as the main ex-situ instrument capable of measuring with high repeatability and robustness necessary for the validation of viscoelastic curing models of composites (especially prepregs) at production level. This rheometer was coupled with Differential Scanning Calorimetry (DSC) to obtain a correlation of the key variables of curing and the actual material states. Experimental and analytical modeling studies of the viscoelastic properties and thermal properties of four commercial prepregs were conducted using these instruments. These key cure variables were directly correlated with the viscoelastic states of the material during cure. The viscoelastic properties such as storage modulus, loss modulus, and tanδ and the glass transition temperature of the Advanced Composite Group (ACG) MTM45 and MTM45-1 prepregs and Cytec 977-2 PW and 977-2 UD prepregs were measured using the rheometer during different isothermal cure cycles below the final glass transition temperature (g∞ T). Thermal analysis of 977-2 PW and 977-2 UD prepregs was obtained using the DSC and these thermal results were correlated to the rheometry measurements. Glass transition temperatures (g T) of the cure cycles were measured using both rheometry and DSC techniques. A semi-empirical curing model, based on the viscoelastic properties of prepregs, was developed and compared with the experimental data collected at a constant frequency. A process engineer could use this curing model to monitor, control, and optimize a cure process, and to aid in the curing of parts that have time and temperature history discrepancies. This model can be statistically correlated to critical composite properties and can be validated with time and temperature feedback. Therefore, temperature sensors, such as thermocouples, would remain as the primary in-situ sensors and there would be no need for material state sensors inside the autoclave or other processing units. / Thesis (M.S)-- Wichita State University, College of Engineering, Dept. of Mechanical Engineering / "December 2007."

Design by emulation has been widely used in the field of control systems. Design by emulation is a process where initially a continuous time controller is designed to achieve desired closed loop specifications. This continuous time controller is then mapped to a digital equivalent using a suitable mapping technique. Methods traditionally used for this mapping include forward rectangular rule, bilinear rule and zero-pole matching. We are presenting a new approach for mapping a continuous time controller to a discrete time controller. This approach, unlike any of the traditional mapping method, produces a discrete time transfer function with a magnitude response or phase response nearly the same as its analog prototype. To achieve this objective we are using the Magnitude Invariance Method (MIM) and Phase Invariance Method (PIM) that were recently developed in the field of signal processing. The frequency responses and the step responses of the closed loop systems obtained using this approach are systematically investigated to evaluate the effectiveness of these mapping techniques / Thesis (M.S)-- Wichita State University, College of Engineering, Dept. of Electrical and Computer Engineering. / "December 2007."

This study was aimed at improving the thermal modeling of the orthogonal machining process. The first goal was to improve the prediction of the heat partition coefficient (β) and the second was to improve the prediction of the temperature distribution in the tool. The fraction of heat generated in the primary shear zone that is conducted into the workpiece is termed as the heat partition coefficient (β). β is a key factor in the calculation of the shear plane temperature and in calculating the cutting forces based on material flow stress. The aim of this study was to identify models for accurate estimation of the heat partition coefficient. This study utilized a new approach to obtain the heat partition coefficient for the primary shear zone using the steady state heat transfer analysis capability in ABAQUS/Standard. 2D heat transfer elements that include mass convection were used to model the flow of material through the workpiece and chip. Heat was applied along the shear plane and the resulting steady state temperature fields were obtained. The heat partition coefficients obtained from these analyses were compared with those predicted by the available analytical models as well as with the coefficients obtained from the thermomechanical analyses carried out using ABAQUS/Explicit. It was found that β is a unique function of the thermal number Nt, above the value Nt= 2.0. It was also found that the βs obtained from FEA were closest to the predictions of Wiener’s model. Transient FEA results show that the time constant of the thermomechanical coupling determining the tool temperature is of the order of 940 μs, carrying the temperature to not reach steady state over the 3600 μs typically used in our analysis. To obtain the steady state temperature distribution in the tool, two different approaches were utilized. The first was a multi step analysis approach in which the thermomechanical and the steady state thermal analysis capabilities of ABAQUS were employed sequentially. The power dissipation and the stable chip geometry obtained from the first thermomechanical step were used as inputs for the second step of the analysis, which was a steady state heat transfer analysis. A third analysis step, a thermomechanical analysis, was carried out, with the steady state temperatures from the second step and the stable chip geometry from the first step as initial conditions. It was observed that the temperature decreased in the third step, implying that the steady state analysis overpredicted the steady state temperatures. This may be attributed to the fact that the decrease in plastic and frictional power with increase in temperature is not accounted for in the steady state analysis. The second approach involved scaling the specific heat of the tool by a factor of 1/50 and carrying out a one step thermomechanical analysis. For a linear thermal analysis, this is expected to reduce the thermal time constant by a factor of 50. The actual thermal time constant decreases to 185 μs. It is found that the temperature distribution in the tool converges to within 10° C (1%) of the steady state temperatures. The rake face temperature distribution is used to evaluate the tool wear based on Usui’s tool wear model. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering.

The cure kinetics of a high performance epoxy adhesive system based on TGDDM/DGEBA/DDS/DICY and toughened with carboxy terminated poly(acrylonitrile-co-butadiene) rubber with aluminum filler was investigated using differential scanning calorimetry. Three different sets of experiments were performed to follow the cure kinetics of the adhesive in a multi-step cure cycle. Three-dimensional plots of data entered into a surface-fitting software allowed for the interpolation of the degree and rate of cure as functions of heating rate and temperature, time and temperature, or time and initial degree of cure. Isothermal cure was modeled successfully using the kinetic model of Kamal. The gel point of the adhesive was measured using dynamic shear rheometry under isothermal conditions. Methods were developed to combine ramp and soak segments so that both the conversion (α) and rate of cure (dα/dt) can be followed through a two-step cure cycle of the type used to cure composite prepreg and adhesive in an industrial setting. / Thesis (M.S.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Chemistry. / "July 2006."

Large ice particles shed from an airframe can cause damage to downstream aerodynamic surfaces and aft mounted engines. A simulation tool was developed to compute the trajectories of shed ice particles and determine the probability of these particles passing through a particular downstream location. The flowfield into which the ice particles shed was determined using CFD. The aerodynamic forces and moments acting on the ice particles were obtained from published literature and experimental data. Three, four and six degree of freedom trajectory simulation models were developed to compute the trajectories of shed ice particles. Monte Carlo simulations were performed by varying the aerodynamic and geometric properties of the ice particles to obtain a probability map depicting the regions where the ice particles were most likely to strike. / Includes bibliographical references (p.117-120)

Broadband aircraft communications have come long way from web surfing to the very recent live TV channels by the Qatar airways. This thesis has gone one step further by analyzing the possibility of video on demand and live TV channels using single antenna for IFE options provided by the aircraft. With TVOD (true video on demand), passengers have the option to select a movie or TV channel from content which are hosted in the ground server at any time with the start, pause and stop functionality. As opposed to the prescheduled programs which are already in place. The research work defines the challenges, complete architecture, products and the emerging technological solutions in implementing the VOD and live TV channels through Ku band satellite IP communication. In addition, cost analysis and ways to efficiently use the bandwidth is also discussed. The proposed architecture’s performance is analyzed with the help of frequency sharing introduced in this thesis. The channel capacity and throughput for various parameters are calculated using the mathematical model. / Thesis (M.S): Wichita State University, College of Engineering, Dept. of Electrical and Computer Engineering

This study examines the effects of focused fluency practice on reading fluency, motivation, and interest in reading using a variety of research based strategies designed to improve fluency in struggling students. The twelve-week study looks at six third grade students with low achievement in reading. Multiple assessments and an assortment of methods included: repeated reading strategies, Reader’s Theatre, Quick Reads, humorous literature, and reading for a reason. Rationale for each strategy is given and individual student progress is profiled to show the effectiveness of using a variety of methods to improve reading fluency. Results found repeated readings of independent and instructional level texts to improve reading rates, error and self-correction rates in students with slow reading acquisition. The importance of reading motivation is highlighted using information from pre and post reading surveys. / Thesis (M.Ed.) - Wichita State University, College of Education, Dept. of Curriculum and Instruction

Carbon nanomaterials have recently been discovered which possess many unique physical properties. Multiple attempts have been made to integrate these materials into new technologies, including carbon nanocomposites with the goal of vastly improving the performance of these products. This thesis focuses on the incorporation of carbon nanofibers (CNF), multi-walled carbon nanotubes (MWNT), and buckminsterfullerene’s (buckyballs) into Cytec’s Corfil 625-1, an existing one-part potting compound. The goal was to improve the compressive strength of the material while maintaining the lap shear strength and keeping the density under that of a commercially available two-part potting compound, 3M’s EC-3500. The use of surfactants from BYK-Chemie led to an improvement in compressive strength of 45% when 5 wt% CNF was added. Carboxylic acid functionalization also showed improvement, however, CNF could not be added at a wt% as high as with the surfactant and a compressive strength enhancement of 11.5% was obtained. It was determined from SEM micrographs that preliminary mixing methods were breaking the glass balloons that were present in the 625-1 as provided by Cytec. As a result, the material was obtained without the microballoons and curing agent and new mixing methods were developed. The new compound allowed for greater flexibility in the mixing process, including higher shear and heating. It was also necessary to investigate the use of glass microballoons in order to replace what was not provided by Cytec. The use of S15 glass microballoons from 3M allowed for production of a potting compound similar to that of the 625-1 originally provided by Cytec. S38HS microballoons produced a one-part compound that was similar to the goal compound EC-3500. Sonication for 5 hours produced better results than the hand mixing that was initially performed, increasing the compressive strength of the potting compound by 21.7% when 1 wt% functionalized CNF was added to the compound. MWNT of various sizes were investigated, with the smallest diameter nanotube (8 nm) providing the best improvement. A three roll mill was utilized as a new mixing method that would reduce complications and allow for the process to be scaled up producing larger batches of carbon nanocomposite. The number of times the material was run through the mill was an important parameter and a 30.9% improvement was acquired when the composite went through 7 times. / Thesis (M.S) - Wichita State University, College of Engineering, Dept. of Mechanical Engineering

This essay considers Willa Cather’s use of fairy tale, musical, and mythological references within The Song of the Lark to rewrite cultural paradigms of patriarchal oppression and create a female-empowered narrative of an artist’s life. Through a complex network of allusions, Cather creates a successful künstlerroman by conveying the complicated realities of her female protagonist’s struggle to become an artist. Only by examining the full context of the novel’s allusions can we clearly understand the author’s characterization of her main character, Thea Kronberg. / Thesis (M.A.) - Wichita State University, College of Liberal Arts and Science, Dept. of English

This thesis proposes a scheme of obtaining an estimate of channel coefficients and noise power spectral density (PSD) using iterative expectation maximization based on a turbo-coded code-division multiple-access (CDMA) receiver under different communication scenarios such as time-varying interference and pulse-band jamming. At the receiver, an initial estimate is obtained with the aid of pilot symbols. The subsequent values of channel coefficient and noise PSD are updated by soft feedback from the turbo decoder. The updated channel coefficient and noise PSD are iteratively passed to the turbo decoder, which results in improved decoding accuracy. The proposed systems are verified through simulations using a structure similar to the Third Generation Partnership Project Long-Term Evolution (3GPP LTE) system under Jakes and Rayleigh fading environments. In addition, this thesis also proposes the scheme of obtaining an estimate of channel coefficients and noise PSD without sending any pilots under a single-user environment. At the receiver, the initial estimate of channel coefficient and noise PSD are obtained without pilots using blind estimation, and then the further estimations are done using expectation maximization. The estimated values are updated iteratively by feedback from the turbo decoder. The updated channel coefficient and noise PSD are iteratively passed to the turbo decoder, which yields improved decoding results. The elimination of pilot symbols sacrifices performance but allows increased energy per transmitted symbol, increased information throughput, or the inclusion of additional parity bits. / Thesis (M.S) - Wichita State University, College of Engineering, Dept. of Electrical and Computer Engineering