Seismic detection of sonic booms

The pressure signals from a sonic boom will produce a small, but detectable, ground motion. The extensive seismic network in southern California, consisting of over 200 sites covering over 50 000 square kilometers, is used to map primary and secondary sonic boom carpets. Data from the network is used to analyze three supersonic overflights in the western United States. The results are compared to ray-tracing computations using a realistic model of the stratified atmospheric at the time of the measurements. The results show sonic boom ground exposure under the real atmosphere is much larger than previously expected or predicted by ray tracing alone. Finally, seismic observations are used to draw some inferences on the origin of a set of "mystery booms" recorded in 1992–1993 in southern California

E-Learning Works - Exactly How Well Depends on its Unique Features and Barriers

Key Findings: E-learning is comparable to traditional teacher-led classroom instruction in terms of effectiveness. E-learning has specific features that may influence learning: content, immersion, interactivity, and communication. Barriers to e-learning adoption include fraud and cheating, digital divides and their impact on low income and underprepared students, and cost issues

E-Learning in Postsecondary Education

Over the past decade postsecondary education has been moving increasingly from the class room to online. During the fall 2010 term 31 percent of U.S. college students took at least one online course. The primary reasons for the growth of e-learning in the nation\u27s colleges and universities include the desire of those institutions to generate new revenue streams, improve access, and offer students greater scheduling flexibility. Yet the growth of e-learning has been accompanied by a continuing debate about its effectiveness and by the recognition that a number of barriers impede its widespread adoption in higher education

Self-Assessments of Knowledge: Where Do We Go From Here?

[Excerpt] In this paper, we argue that there remain several unanswered questions surrounding self-assessments of knowledge that must be addressed before we can reach a more definitive conclusion on the viability of these measures. The answers to these questions may provide further evidence that self-assessments should not be used as an indicator of learning or they may serve to qualify the conditions under which self-assessments can be used with reasonable confidence. In either case, addressing these issues is critical if work in this area is to influence how researchers and practitioners evaluate trainees’ learning

An investigation of shock strengthening in a conical convergent channel

The behaviour of an initially plane, strong shock wave propagating into a conical convergence is investigated experimentally and theoretically. In the experiment a 10° half-angle cone is mounted on the end of a pressure-driven shock tube. Shock waves with initial Mach numbers varying from 6.0 to 10·2 are generated in argon a t a pressure of 1·5 Torr. During each run local shock velocities a t several positions along the cone axis are measured using a thin multi-crystal piezoelectric probe inserted from the vertex. This technique produces accurate velocity data for both the incident and reflected shock waves. In the corresponding analysis, a simplified characteristics method is used to obtain an approximate solution of the axisymmetric diffraction equations derived by Whitham (1959). Both the shock velocity measurements and the axisymmetric diffraction solution confirm that the incident shock behaviour is dominated by cyclic diffraction processes which originate at the entrance of the cone. Each diffraction cycle is characterized by Mach reflexion on the cone wall followed by Mach reflexion on the axis, These cycles evidently persist until the shock reaches the cone vertex, where the measured velocity has increased by as much as a factor of three. Real-gas effects, enhanced in the experiment by increasing the initial Mach number and decreasing the pressure, apparently alter the shock wave behaviour only in the region near the vertex. Velocity measurements for the reflected shock within the cone show that the shock velocity is nearly constant throughout most of the convergence length

AN ANALYSIS OF ALTERNATIVE NET PRESENT VALUE CAPITAL INVESTMENT DECISION MODELS

We have found that the disagreement between Returns-to-Assets (RTA) and Returns-to-Equity (RTE) proponents is not confined to agricultural economics. Depending on the course they are taking and the accompanying text, students are likely to learn that there is a "right" way to calculate Net Present Values (NPVs), either by the RTA method or the RTE method. In most cases, only one of the two methods is discussed and illustrated with numerical examples. Less common are texts that compare the two methods, discuss their underlying assumptions, or show how the NPVs from the two methods can be reconciled. The paper is organized as follows. The first section of the main body of the paper provides a comparative overview of the RTA and RTE methods; the second section discusses our textbook survey; the final section offers our conclusions. Appendix A contains a brief history of the theoretical development of discounted cash flow (DCF) concepts. Appendix B contains additional details on defining components of NPV models. Finally, Appendix C is a listing of some additional references.Research Methods/ Statistical Methods,

UNDERSTANDING THE RURAL - URBAN DIGITAL DIVIDE

This paper explains the current "digital divide" in internet use between rural and urban areas using a Logit adoption model with data collected from the August 2000 Current Population Survey. A non-linear decomposition shows that rural urban household attribute differences account for 66 percent of the digital divide, while place based differences account for the remaining 34 percent of the divide.Research and Development/Tech Change/Emerging Technologies,

The Role of Infrastructure in the Rural - Urban Digital Divide

A significant gap exists in the percentage of rural and urban households that connect to the Internet. Furthermore, this "digital divide" has been increasing with respect to high-speed connections. The primary course of action to address this emerging high-speed digital divide has been to subsidize digital communications technology (DCT) infrastructure. This paper explores the diffusion of DCT infrastructure in both rural and urban areas over the period 2000 - 2003, and estimates its contribution to the emerging divide in high-speed access. The findings suggest that the rural - urban high-speed divide is more strongly associated with differences in household characteristics like education and income than differences in infrastructure.Research and Development/Tech Change/Emerging Technologies,