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The IEEE 802.11 wireless local area network (WLAN) standard supports multiple transmission modes. However, the higher mandatory data rate mode does not necessarily yield higher throughput. This research started from the relationship between the link throughput and the channel's carrier-to-noise (C/N) ratio. Two algorithms are proposed, a throughput optimization and transmitter power saving (TOTPS) algorithm and an extended throughput optimization and transmitter power saving (ETOTPS) algorithm, based on the knowledge of the C/N ratio at the receiver. In particular, we take the approach of adjusting link parameters like transmitter power and transmission mode to achieve the maximum throughput at different C/N values. Since the TOTPS algorithm tends to reduce the transmitter power without degrading the link throughput, transmitter power can be saved. This not only prolongs battery life, which is critical in ad hoc wireless networks, but also reduces the potential interference to neighboring wireless network systems. The ETOTPS algorithm, on the other hand, aims for higher throughput by trading in more transmitter power. This is particularly desired for high-speed data transfer in an emergency situation. Both algorithms are developed to be applied to IEEE 802.11b, IEEE 802.11a and IEEE 802.11g links. / Ph. D.

<p dir="ltr">Link slabs offer a cost-effective solution for eliminating deck expansion joints in multi-span bridges. A link slab is the cast-in-place concrete portion that makes only the deck slab continuous while the girders remain simply supported between two adjacent deck spans. By closing the expansion-joint opening, link slabs can reduce the costs of repairing and rehabilitating leaking joints and improving the bridge riding surface. Link slabs are designed to resist the bending moments imposed by girder end rotation due to live load plus impact, assuming the bridge spans are simply supported at the joints. The continuity provided by the link slab under live load is neglected, based on the assumption that its stiffness is lower than that of the girders. Furthermore, structural elements capable of load transfer (e.g., stirrups and shear stud connectors) within the limits of the deck joint elimination are often removed to reduce induced stresses in the link slab. A bond breaker is placed between the top of the girders and the bottom of the link slab to mitigate stresses. The debonded length, typically set at 5% of each span length, defines the total length of the link slab. Practices may vary among states, such as Indiana, where a composite action between the link slab and supporting girders is maintained. </p><p dir="ltr">However, increased cracking observed in the field is the primary concern about debonded link slabs. Once the cracks form, they allow the entrance of corrosive chemicals and debris, causing deterioration of concrete bridge components. The causes of the increased cracking and resulting leakage at the link slabs have been associated with the limitations of the existing design approaches in considering the effects of thermal loads and support conditions. This study presents a comprehensive finite element analysis to evaluate the behavior of bridge deck link slabs under the combined effect of traffic loads and vertical temperature gradients. The link slabs are subjected to HL-93 loading and temperature gradients following AASHTO LFRD Bridge Design Specifications. A finite element model of the Plott Creek Bridge in Haywood country in North Carolina, instrumented by Wing & Kowalksy (2005), is developed using ABAQUS/Standard software. The numerical model is validated against test data from previous studies available in the literature.</p><p dir="ltr">The results of the numerical investigation reveal that vehicular traffic loading is the primary factor contributing to the cracking of the link slabs. However, vertical temperature gradients are also identified as significant factors inducing stresses within the link slabs. Specifically, the combination of live load and a negative temperature gradient is the most influential loading condition contributing to cracking at the top surface of the link slabs. It is important to note that the rotation of the girder ends due to live load induces a negative moment (tension at the top) on the link slab. A negative temperature gradient, where the temperature on the top deck surface is lower than that on the web of the beams, results in an additional negative moment on the link slab due to its addition to the rotation from the live load. The temperature gradients are observed to increase the girder end rotation obtained from live load analysis for simply supported beams by approximately 20% in the range of parameters considered in the present study. This finding underscores the importance of considering temperature effects in link slab design to ensure structural integrity. </p><p dir="ltr">Furthermore, parametric studies are conducted to assess the impact of various factors such as girder support conditions, span length, debonded zone length, and material properties on crack initiation in link slabs. The analyses show that the primary factors affecting the tensile stress developed in the link slabs are the span length and the girder support conditions. This highlights the importance of considering these factors when designing link slabs. Based on the findings, design recommendations are proposed to enhance the current practices for link slab design. These recommendations include considering temperature gradients alongside live loads, adopting distributed bar spacing for crack control, and incorporating an allowable stress limit of 0.60fy for steel reinforcement following AASHTO LFRD Bridge Design Specifications. Given that link slabs exhibit cracking under service conditions, it is advisable to determine the amount of longitudinal tension reinforcement based on cracked section analysis rather than simply providing the minimum reinforcement. Furthermore, incorporating a debonded zone within 5% to 7.5% of the span length at each side of the link slab is recommended to reduce stresses. The use of roller support is not recommended for link slab applications, while hinge supports can be effective if the span length is less than 15~m (50~ft.). </p>

The design of the most commonly-used Internet and Local Area Network protocols provide no way of verifying the sender of a packet is who it claims to be. Protocols and applications exist that provide authentication but these are generally for special use cases. A malicious host can easily launch an attack while pretending to be another host to avoid being discovered. At worst, the behavior may implicate a legitimate host causing it and the user to be kicked off the network. A malicious host may further conceal its location by sending the attack packets from one or more remotely-controlled hosts. Current research has provided techniques to support traceback, the process of determining the complete attack path from the victim back to the attack coordinator. Most of this research focuses on IP traceback, from the victim through the Internet to the edge of the network containing the attack packet source, and Stepping-Stone traceback, from source to the host controlling the attack. However, little research has been conducted on the problem of Data-Link Layer Traceback (DLT), the process of tracing frames from the network edge to the attack source, across what is usually a layer-2 network. We propose a scheme called Tagged-fRAme tracebaCK (TRACK) that provides a secure, reliable DLT technique for Ethernet networks. TRACK defines processes for Ethernet switches and a centralized storage and lookup host. As a frame enters a TRACK-enabled network, a tag is added indicating the switch and port on which the frame entered the network. This tag is collected at the network edge for later use in the traceback operation. An authentication method is defined to prevent unauthorized entities from generating or modifying tag data. Simulation results indicate that TRACK provides accurate DLT operation while causing minimal impact on network and application performance. / Master of Science

Wood beam-column connections have traditionally been designed as simple shear connections, ignoring their potential moment capacity. A major reason for not utilizing such moment connections is linked to the brittle limit states that wood components exhibit. The purpose of this research was to develop and test a ductile and high-strength wood moment frame connection. A design procedure for such a connection is presented herein. The proposed glulam beam-column connection utilizes an embedded steel knife plate with a reduced section that acts as a ductile yield link, thus limiting the moment that can be transferred through the connection. This configuration is intended to fail through yielding of the ductile link, thus preventing non-ductile failure mechanisms of wood from occurring. In addition, the connection provides more wood cover over the embedded steel plate, which potentially may increase the connection's fire rating as compared to typical connections. Two specimens, based on a baseline connection developed using the design procedure presented, were monotonically loaded until failure. Unlike the first specimen, the second was reinforced in the perpendicular-to-grain direction using self-tapping screws. Failure mechanisms were analyzed, and performance characteristics related to the connection's strength, stiffness, and ductility were evaluated. Results indicated that the reinforced specimen exhibited higher strength, stiffness, and ductility compared to the unreinforced specimen. The reinforced specimen showed improvements of 9.49% and 42.2% in yielding and ultimate moment, respectively, compared to the unreinforced specimen. Moreover, an improvement of 31.3% in ductility was obtained using perpendicular-to-grain reinforcement. / Master of Science / Due to the variability of wood properties and its brittle behavior, the joints of wood buildings have traditionally been designed to resist gravity loads only. These types of loads result in predictable behavior of structural wood members at the joints, which helps in simplifying the design process. However, when wood structures are subjected to lateral loads, such as earthquake and wind loads, their joints are likely to fail abruptly as the building sways, resulting in sudden, unpredictable collapse. The purpose of this research was to develop and test a high-strength wood structural joint that can fail gradually and predictably. A design procedure for such a joint is presented herein. The proposed glue-laminated wood joint utilizes an embedded steel plate with a reduced section that acts as a ductile link. This configuration is intended to fail through gradual deformation of the ductile link, thus preventing brittle wood failure at the joint. In addition, this joint provides more wood cover over the embedded steel plate, which potentially may increase the fire resistance of the joint compared to typical configurations. Two specimens, based on a baseline joint developed using the design procedure presented, were subjected to slowly-increasing loads until failure. Unlike the first specimen, the second specimen was reinforced in the direction perpendicular to wood grain using long screws to prevent separation of wood layers. Failure mechanisms were analyzed, and the performance characteristics of the two specimens were evaluated and compared. Results indicated that the reinforced specimen exhibited higher strength and improved ductility at failure.

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / Space Link Extension (SLE) is a set of Consultative Committee for Space Data Systems (CCSDS) recommended standards for extending the space link from ground stations to other spaceflight mission ground facilities over a ground network, allowing distributed access to space link telecommand and telemetry services. The currently defined and implemented SLE recommendations are oriented around a traditional CCSDS telecommand and telemetry protocol set, which uses discrete telecommand frames that are encapsulated in Communication Link Transmission Units (CLTUs) for transport over the ground segment, and telemetry data encapsulated in Transfer Frames at the spacecraft. This paper discusses several non-traditional uses of the SLE services. The applications addressed within lie outside the discrete packet telecommand/telemetry subset of the SLE recommendations that are fully defined by CCSDS. This paper will focus on the use of the currently implemented SLE model to enable the transport of other forms of data, which may be subject to various transmission constraints, across the ground segment.