Sensor networks consist of a set of wireless sensor nodes which sense the environment and route the sensed information to a sink node. Data gathering is one of the important applications in sensor networks. In this thesis, using multiple channels, we consider TDMA schedule algorithm focusing on many-to-one communication which is called convergecast. In convergecast, a packet generated in each sensor node is delivered to a sink node without any data aggregation in the intermediate node. In large network environment with many hops, we found that usage of multiple channels significantly improves delay efficiency comparing to usage of a single channel. We formulate this problem and propose heuristic algorithms for proper channel assignment and convergecast in different topologies. In general topology, with 2 channels, we present the convergecast algorithm requiring timeslot at most 2N−1+d where N is the number of sensor nodes and d is the delay to avoid interference among sensor nodes. We also found that, for general topology, usage of 4 channels contributes to even more delay efficiency which can achieve d=0. Furthermore, unlike using 3 or fewer channels, using 4 channels is also memory efficient without creating an extra internal memory table in a sensor node to avoid interference among nodes. Additionally, such delay efficiency can result in energy efficiency which is also another important issue in sensor networks. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science.

One of the main causes for degrade in the performance of a production line is bottleneck machine. To improve system performance, bottleneck (BN) is one of the critical factors that need to be addressed. Most of the researchers focus on long term bottlenecks in the system. From other researches, it is evident that detection and elimination of short term BNs is more efficient than long term BNs. Till now, there is no generic method to identify bottlenecks in production lines with and without buffer. Proposed inactive duration method for identification of BNs detects both short term and long term bottlenecks. In production lines, bottlenecks can be classified into buffer bottlenecks and machine bottlenecks. Machine BNs are mainly due to variability in the system. There is always strong relationship between variability and machine BN. Due to dynamic nature of manufacturing lines, there will be frequent shifting of BN between different machines. In this research, BN characteristics are proposed to analyze the critical nature of BN and BN shifting. In production lines with buffer, buffer bottlenecks are eliminated by placing optimal buffer size before each machine. This thesis presents a two step heuristic procedure for optimal buffer size determination. Case studies were conducted for both production lines with optimal buffer and without buffer. Results from case studies proved that increase in variability increases BN time and BN shifting between different machines. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering.

In a single model manual assembly line, product flows through series of workstations arranged in a sequential manner. Each workstation has a finite number of tasks and each task has probabilistic processing time. Due to the probabilistic nature of task time, the task times can exceed the expected standard task time at some instance. If a series of tasks exceeds in a particular station, then there is a risk that the product may exceed the cycle time. As a result, a small variability in task time can lead to large delays in the delivery lead time of the product. Most of the line balancing approaches assume deterministic task times thereby ignoring the impact of task time variability on the system performance measures. The larger the variability of task time, the higher the risk associated with the station. In this paper, the impact of variability in task time is quantified in terms of risk. Risk is defined as potential loss caused when the product fails to complete within the specified station time. For line balancing, in addition to cycle time balancing, the risk should be balanced in order to improve the performance of the assembly line. In this research, a risk based assembly line balancing technique for highly variable task times is presented. The results from the case study show that the method increases the performance of the assembly line while balancing the risk of delays at each station. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering.

With a rise in demand for electricity and depletion of fossil fuel levels, researchers are looking for an alternative resource to generate power, one which is more environmentally friendly. Fuel cells are one of the best alternatives presently available and are considered by many to be the most promising energy sources with efficiencies of up to 60%. Presently, the cost associated with the usage of fuel cells available in the market is quite high. Researchers are trying to bring down costs associated with their usage and improve efficiency. PEM fuel cells are one of the most promising types of fuel cells. Researchers are currently trying to improve its efficiency by improving its electrolyte. Nafion® is one of the main electrolyte used in PEM fuel cells as it acts as proton conductor. Graphene has an exceptionally high surface area to volume ratio and excellent strength. Current research is focused on integrating graphene in PEM fuel cell electrolytes to improve performance. In this study, graphene is added to Nafion® in varying weight percentages to study the performance of the fuel cell given these changes. The graphene weight percentage is varied by 1, 2, 3, and 4. The fuel cell was operated and it was observed that with the addition of graphene there is an improvement in voltage, proton conductivity, and electron conductivity of the PEM fuel cell. The improvement of proton conductivity and electron conductivity followed a linear path with the increase in graphene weight percentage in the Nafion®. Physical properties of the Nafion® membrane with additional graphene were measured and found out that dielectric constant and thermal conductivity also improved linearly with an increase in graphene weight percentage. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.

Radio-Frequency Identification (RFID) has made a revolutionary mark in identifying and tracking number of different industry objects, which has reduced the manual tracking to much higher extent. The key problem which is associated with the reading of RFID tags is the collision between tag responses, which makes the reading more difficult and hence requires more time to complete identifying all tags. Collisions also reduce the accuracy of the reader to read tags at any given instant of time. With many RFID readers being portable these days, limited battery power can be an issue, and hence, energy is another metric of interest. The purpose of this thesis was to design a protocol which would be helpful to read RFID tags in more efficient manner in terms of time and energy. A new RFID anti-collision protocol Intelligent ALOHA (I-ALOHA) is proposed that is a combination of two existing approaches: Intelligent Query Tree (IQT) protocol and Abramson’s Logic of Hiring Access (ALOHA) method. I-ALOHA, like IQT, divides the tag IDs into two parts and reads only postfix parts of the tags when the prefixes are common. It uses the basic features of ALOHA time slots to reduce collisions among tag responses. Simulations done on MATLAB indicated that I-ALOHA performs very well in number of different scenarios in terms of energy and time consumption compared to existing anti-collision protocols. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science

This research attempts to investigate an important and common phenomenon in aerodynamics called shock interaction in a turbulent flow’s boundary layer. Due to advancements in current computational units, more complex geometries could be simulated with providing more accurate results. The tools used in this investigation are computational turbulent model of hybrid RANS/LES, called detached eddy simulation (DES). DES and its variant delayed detached eddy simulation (DDES) were the two computational schemes used for numerical simulation. Two protrusions were focused on in this work: a symmetrical bump and a proposed aircraft UHF antenna. Computation where performed with commercial software Cobalt and FLUENT in the High Performance Computing Center (HiPeCC) in Wichita State University. Computational simulation is costly in terms of energy consumption and time usage. Even so with the advanced computational units of HiPeCC, using in average of 18 processors, total simulation for this research took over 2 months of simulation. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering

In this thesis, the achievable rate at low SNR is established for Amplify-and-Forward (AF) cooperative system with a source node, a destination node and a relay node. To characterize the effect of relay locations, an aggregate channel model which consists of both long-term path loss and short-term path loss fading is used. To consider the effect of channel information at the relay, average and instantaneous power constraints are applied respectively when evaluating the achievable rate. As analytic solutions to the achievable rate seem difficult to obtain, approximations for the achievable rate, the optimal power loadings, the optimal amplification coefficients for both types of power constraints are derived in this thesis. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science

New media developed in the 21st century allows for conversations and interactions among people and organizations online. This capacity is referred to as social media (Safko & Brake, 2009). Twitter is the most active social media tool and influences the use of other social networks (Webster, 2010). Companies are entering Twitter to engage in conversations with their publics and modifying their branding strategies to work within this new medium (Jansen et al., 2009). This study attempts to understand how news media companies that use traditional media, are integrating social media branding strategies into their efforts to engage consumers. The main research question posed in this study is: How are news media companies using branding strategies to create a relationship with their target audiences through social media? To answer this research question, a literature review was developed, which presented definitions and theories of media, social media and branding. Additionally, data were analyzed from six news media companies present on Twitter through a thematic analysis. Specifically, tweets posted by three national and three local news media organizations collected over a two month period from February 1 – April 1, 2011 were analyzed considering premises and theories from McLuhan and Powers (1989); McLuhan (1994; 2002), Ong (2002), Poster (1995), Lévy, Li and Bernoff (2008), Jansen, Zhang, Sobel, and Chowdury (2009), Kotler and Keller (2006), Hatch & Schultz (2002), and others. The results showed that news media companies are communicating to their audience in three manners: spreading information, promoting marketing strategies, and generating conversations. This study also presents the potential that companies have to develop an organizational identity on Twitter and social media / Thesis (M.A.)--Wichita State University, College of Liberal Arts and Sciences,Elliot School of Communication

With the increase of wireless devices, the wireless spectrum is becoming overloaded causing users to experience delays and performance degradation. Typically, a device will start transmitting data on a frequency and continue transmitting on that frequency regardless of the channel being overloaded or not. Some smarter devices such as routers are able to sense when their channel is becoming overloaded by observing delays and amount of devices transmitting on that frequency. Spectrum analyzers are usually very expensive and usually do not provide many functionalities other than analysis. Utilizing newer alternatives for sensing the spectrum such as Software Defined Radios (SDR) can address frequency allocation problems and allow users to decide the best frequency to use for communication. A promising SDR such as GNU Radio will be covered in this thesis, as well as the hardware components needed for its functionality. In this thesis, a cognitive radio approach is taken in designing a channel selection algorithm by scanning and monitoring the wireless spectrum on IEEE 802.11 b/g through the use of GNU Radio and USRP. Tests are performed as a proof of concept and to help future research with the use of cognitive radios. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering.

Medium Access Control (MAC) delays increase the frame inter-arrival time on the destination node in saturated ad hoc networks. With the increase in the network size more and more nodes contend for the medium which increases the collisions and drops affecting the frame inter-arrival time. High frame inter-arrival rates result in a queue overflow at the destination node and low frame inter-arrival rates increase the packet end-to-end delay. The variable parameters in the simulations are the network size and the data rates for the transmission. It is observed with simulations that the average frame inter-arrival time increases with the increase in the number of contending nodes in a saturated ad hoc network. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science.