High strength-to-weight ratio, directional strength and stiffness are the significant factors, forcing polymer composites into the aerospace, marine and automotive industries. Due to these major factors fuel efficiency and crashworthiness properties are the significant outcomes from use of these advanced materials. This present thesis work deals with experimental study of the in-plane tensile properties of polymer matrix composite materials reinforced by high modulus fibers under Quasi-Static and Hiagh Strain Rate tensile tests. Behavior of Glass fiber-reinforced (GFRP) and Carbon fiber reinforced (CFRP) composite materials is studied. The test coupons are balanced and symmetric in fiber orientation with respect to the test direction. The related experiments are performed with a MTS 810 high rate test machine to determine the mechanical properties of tension test coupons. The specimens were tested separately under quasistatic and high-speed conditions with stroke rates of up to 500 in/s. All specimens were tested to failure in order to characterize the effect of high strain rate on failure strength of the material. In this work, a new method to obtain stress-strain curves for the tensile tests is proposed. The strain rate nature of composite laminates in tensile loadings clearly show that unlike in metals these materials do not exhibit the constant strain rate behavior in case of high strain rate tests. Throughout the test, the strain rate values change due to the dynamics of the system and directional stiffness of the composite laminates. In case of 0° fiber oriented specimens, the fiber properties dominate the matrix properties as fiber strength is much higher than that of matrix materials. For different fiber orientations of the laminates the strain rate varies for the same stroke rate tests as the matrix material starts playing role in case of higher fiber angles. The results show that high strain rates have a significant effect on the properties of the composites coupons. The increment of the ultimate strength with high strain rate is proportional to the strain rate. In the future developments the stress-strain curves obtained from these various tensile tests can be used to insert in a finite element code to develop a material model for computational simulations. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering / Includes bibliographic references (leaves 52-56)

Converged IP networks seek to incorporate voice, data, and video on the same infrastructure. However, the integration of all types of traffic onto a single IP network has several advantages as well as disadvantages. While reducing cost and increasing mobility and functionality, VoIP may lead to reliability concerns, degraded voice quality, incompatibility, and end-user complaints due to changing network characteristics. Voice quality degrades considerably due to low bandwidth, high packet loss rates, high jitter, or if total end-to-end delay is greater than the ITU-T suggested 150ms. In order to ensure these strict requirements are met, the underlying network must deploy various schemes to ensure resource availability. This research proposes an adaptive codec selection mechanism which changes the voice encoding scheme in the middle of an active call based on the network conditions. The mechanism is mainly proposed for H.323 based systems and is intended to cause little to no effect on voice quality. The proposed mechanism involves establishing a three-way handshake process in mid-call to renegotiate station capabilities, making the switch at a determined sequence number in an RTP packet. The proposed mechanism ensures the voice continuity while switching codecs by filling the play out buffers appropriately. The effect of these changes on voice quality is determined using the objective E-model. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical and Computer Engineering.

Thesis (M.A.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of English

Ecosystem processes drive biogeochemical cycles that influence input and losses of nutrients in the biosphere. Through human activities the environment has been highly enriched with nutrients, especially nitrogen. In most ecosystems, nitrogen availability should be limited, but soils and aquatic ecosystems have been anthropogenically impacted. In streams, availability of nutrients, geochemical characteristics, hydrodynamics, and human activities influence the metabolic activities and structure of microbial communities. The aim of the current study is to contrast gene abundance and metabolic responses of N2-fixing guilds exposed to chronic nitrogen loading in three different types of Kansas prairie streams: urban, agricultural, and pristine. Nitrogen-fixation activity was expected to be negatively correlated to the level of fixed nitrogen, while nifH (nitrogenase gene) abundance would be unchanged. A combination of process-level and molecular techniques were applied to study nitrogen fixation in these small prairie streams. Nitrogen fixation activity was measured with acetylene reduction assays. Rates of acetylene reduction for urban, agricultural, and pristine prairie streams were 1.5 to 93.5, 2.1 to 112.8, and 2.9 to 81.9 fmol N2/g soil/h, respectively. The highest rates were found in leaf litter, sediments and algal bio films. Samples of sediments and leaf litter were field-frozen for molecular analyses of the nitrogen-fixing microbial guild. Direct DNA extracts were examined by SYBR real-time PCR to determine the abundance of nifH, given a detection limit of 2 x 102 nifH gene copies/g sample. The abundance of bacterial 16S rRNA was between 1.0 x 106 to 1.0 x 1012 gene copies per gram to 1.0 x 10gene copies per gram sample. The abundance of nifH genes ranged between 1.0 x 10to 1.0 x 10gene copies per gram in all streams. The assay was quantitative over at least 8 orders of magnitude, from 1 ng to 0.1 pg of nifH target. This study provides a link between the abundance of nifH genes and nitrogen-fixation activity. An understanding of the effects of nitrogen pollution on nitrogen cycling guilds in small streams will increase our ability to overcome the challenges of nutrient pollution. This work was supported by Kansas NSF EPSCoR Ecological Genomics. / Thesis (M.S.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Biological Sciences

Analysis of crashworthy structures has been a primary area of interest for many researchers for quite a few years now. The quest for a better energy absorbing structure ora better crashworthy structure has led researchers to carry out various analysis procedures experimentally and also by simulating the characteristics. E-glass fiber reinforced epoxy wrapped over aluminum tube has proven to possess better energy absorbing capabilities. This study attempts to analyze certain characteristics of such hybrid structures. This thesis examines the properties with respect to energy absorption of the abovementioned tubes when certain parameters such as ply orientation, angle of impact, speed of impact for different aspect ratios, are varied. The axial crushing behavior and the energy absorption capability of aluminum composite hybrid tube under quasi-static loading is studied using LS-Dyna finite element solver. A aluminum tube, externally wrapped with E-glass epoxy composite material with two layers and ply orientation of +/- 30o, +/- 45o and 0/90o, are used for finite element analysis. The speeds considered are 8mph, 15mph and 30mph. The angles of impact considered are 0o, 15o, and 30o. The analysis is carried out for various permutations and combinations of the above mentioned Parameters, and the results obtained are studied and aims at optimum set of parameters for making the energy absorption of such hybrid structures. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.

Accidents with heavy vehicles, especially in underride crashes, be it rear, side or frontal, are responsible for thousands of deaths all over the world. In many cases, these tragedies are consequences of not having effective underride guards mounted to the rear, side and front of the heavy vehicles. Lack of effective underride guards brings less compatibility making heavy vehicles more aggressive on roads. Several designs have been designed for energy absorbing underride guards. A new underride guard is developed based on the mechanical principle of simple pliers tool was conceived by Louis Otto Faber Schmutzler, SAE BRAZIL 1995. This research work describes nature of underrides, the design and analysis of two new guards for rear and side, vehicle behavior at different speeds and prevention of passenger compartment intrusion. With the advance in computer simulations, full finite element validated vehicle models are being analyzed for different impact scenarios. The main purpose of building the simulation models is to reduce the real time tests which are associated with significant cost. In this thesis, two new guards for rear and side are modeled using MSC-Patran and the performance of the guard in preventing passenger compartment intrusion is analyzed using LS- Dyna. A zero passenger compartment intrusion is achieved with the employment of the newly designed underride guards for rear and side of the trucks. The newly designed guard models are validated using FMVSS 223/224 regulations. The results are in good correlation with the experimental data for rear and the passenger compartment intrusions are reduced in the case of rear and side underride. The performance of the guard is studied at 30, 40 and 50 miles per hour. / "December 2006."

This thesis is aimed at studying the tribology of sliding contacts subject to high current densities. A flat-ended Copper tip sliding on a flat Copper plate was the test configuration and current densities of the order of 10, 500 and 1000 A/mm2 were used. The friction coefficient, contact resistance and material transfer were studied for clean metal-to-metal contacts and compared with those for the case where a solid lubricant interface conditioner (SLIC) was used. Three types of tests were carried out. Static tests were done with and without pre-application of conditioner to evaluate the repeatability of contact resistance measurement and to study the effect of applied load and conditioner on the conductivity of the interface. It was found that pre-application of a thick layer of SLIC increases the contact resistance by 20 %. Circular tests, with the pin repeatedly traversing a circle, were done to evaluate the effect of sliding distance on the frictional coefficient and contact resistance with and without pre-application of solid conditioner. It was found that the conditioner reduces the friction coefficient in half and increases the time to failure many-fold. However, there was a small increase in contact resistance with conditioner. The wear rate of the tip increased with increase in contact pressure and current density. Spiral tests, where the tip was moved outward from the center of the plate, were done to study the transfer of material between the pin and the plate and the effect of change in surface velocity. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering / "December 2006."

Distributed coding is a new paradigm for video transmission, based on the Wyner-Ziv theorem. In this thesis, a new Wyner-Ziv codec was proposed using non-binary Low-Density Parity-Check (LDPC) codes. Non-binary LDPC codes, developed for use in channel coding, have been extended for source coding to compress correlated non-binary sources, such as video. The approach is based on considering the correlation as a virtual q-ary symmetric channel and applying the syndrome concept. The system considered focused on the compression of a equiprobable memoryless non-binary source with side information at the decoder. Results obtained through simulations demonstrated that for rates 1/2 and 3/4, the non-binary compression scheme performed better than the equivalent binary compression scheme. The nonbinary scheme, when extended for distributed video coding, produced the original frame with negligible error. / "December 2006." / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical and Computer Engineering.

The composite scarf joint configuration was utilized to simulate scarf-patch-repaired composite panels. An adhesive bonded scarf (tapered) joint was selected due to less peeling and shear stress over the bondline than with a single-lap or butt joint. The rubber-toughened epoxy film adhesive used had been characterized using ASTM D5656 Standard test (single-lap) incorporated with 2-D plane strain finite element analysis to verify its elastic and plastic properties. In addition to physical test, the ultimate shear strength of the adhesive was predicted using the von Mises and Drucker-Prager plasticity models in conjunction with dynamic shear failure criterion in the commercial finite element software ABAQUS. The numerical analysis provided satisfactory results when compared with experimental data under the relative displacement versus ultimate load level. The revised 4-pinned method more accurately predicted relative displacement than did the 3-pinned method in ASTM D5656 Standard. For composite scarf joint analysis, the 3-D stress analysis with transversely isotropic material properties of composites gave better results than the 2-D plane strain analysis. Regarding the tensile strength of repaired laminates, the finite element dynamic analysis based on the adhesive failure incorporated with the 90-degree ply failure provided the best results, which matched the experimental ultimate loads and the surface strain distributions within the overlap. As expected, the edge effects and longitudinal strain variations across the width of the repaired specimens were only observed in 3-D models and were verified by experimental data. Moreover, the 3-D static and dynamic simulations revealed the relations between laminate strength and the edge effects caused by different stacking sequences. Based on the similar geometry, it was also demostrated in this study that the balanced and symmetric stacking sequence about mid-plane of the repaired composite panel exhibits higher tensile strength. / "December 2006." / Thesis (M.S.)-- Wichita State University, College of Engineering, Dept. of Aerospace Engineering

Source coding and channel coding are two important parts of a communications system. Source coding deals with the compression of source data, while channel coding adds some redundancy to circumvent the channel errors. Source coding and channel coding can be done either jointly or separately depending on the design issues like complexity of the system, rate, power, distortion tradeoffs. For optimal performance, all the parameters should be carefully chosen and optimized. This thesis looks at the scenarios of multi-terminal communications model where source and channel separation will not degrade the performance of the system in terms of rate power and distortion tradeoffs. Specifically, we investigate the transmission of data from correlated sources over an orthogonal multiple access channel under a total power constraint. It is observed that source-channel separation in this particular scenario is possible without any loss in the performance of the system. For the correlated sources case of the multiterminal communications, we provide an alternate approach for achieving source-channel separation. / "December 2006."