Arlington Memorial Bridge Spans the Decades as a Study in Long-Term Price Change

[Excerpt] The Arlington Memorial Bridge is one of seven existing bridges that carry automobile traffic across the Potomac River to and from Washington, DC. Though there have been bridges crossing the Potomac in the area since the first bridge constructed at the site of the Chain Bridge in 1797, these early bridges were often damaged by environmental factors, and others were replaced over time. Thus, the Arlington Memorial Bridge, opened for use on January 18, 1932, is the second-oldest of the bridges currently in use, after the Francis Scott Key Bridge (completed in 1923.) This article examines the history of the Arlington Memorial Bridge and compares the original construction with a contemporary proposed rebuilding of it, which provides an interesting illustration of long-term price change in the United States, with the help of Bureau of Labor Statistics (BLS) data

Security in Cognitive Radio Networks

In this paper, we investigate the information-theoretic security by modeling a cognitive radio wiretap channel under quality-of-service (QoS) constraints and interference power limitations inflicted on primary users (PUs). We initially define four different transmission scenarios regarding channel sensing results and their correctness. We provide effective secure transmission rates at which a secondary eavesdropper is refrained from listening to a secondary transmitter (ST). Then, we construct a channel state transition diagram that characterizes this channel model. We obtain the effective secure capacity which describes the maximum constant buffer arrival rate under given QoS constraints. We find out the optimal transmission power policies that maximize the effective secure capacity, and then, we propose an algorithm that, in general, converges quickly to these optimal policy values. Finally, we show the performance levels and gains obtained under different channel conditions and scenarios. And, we emphasize, in particular, the significant effect of hidden-terminal problem on information-theoretic security in cognitive radios.Comment: Submitted to CISS 201