New Analyses of Double-Bang Events in the Atmosphere

We use CORSIKA+Herwig simulation code to produce ultra-high energy neutrino interactions in the atmosphere. Our aim is to reproduce extensive air showers originated by extragalactic tau-neutrinos. For charged current tau-neutrino interactions in the atmosphere, beside the air shower originated from the neutrino interaction, it is expected that a tau is created and may decay before reaching the ground. That phenomenon makes possible the generation of two related extensive air showers, the so called Double-Bang event. We make an analysis of the main characteristics of Double-Bang events in the atmosphere for mean values of the parameters involved in such phenomenon, like the inelasticity and tau decay length. We discuss what may happen for the ``out of the average'' cases and conclude that it may be possible to observe this kind of event in ultra-high energy cosmic ray observatories such as Pierre Auger or Telescope Array.Comment: 17 pages, 5 figures, final version to appear in BJ

Adaptive Multicast of Multi-Layered Video: Rate-Based and Credit-Based Approaches

Network architectures that can efficiently transport high quality, multicast video are rapidly becoming a basic requirement of emerging multimedia applications. The main problem complicating multicast video transport is variation in network bandwidth constraints. An attractive solution to this problem is to use an adaptive, multi-layered video encoding mechanism. In this paper, we consider two such mechanisms for the support of video multicast; one is a rate-based mechanism that relies on explicit rate congestion feedback from the network, and the other is a credit-based mechanism that relies on hop-by-hop congestion feedback. The responsiveness, bandwidth utilization, scalability and fairness of the two mechanisms are evaluated through simulations. Results suggest that while the two mechanisms exhibit performance trade-offs, both are capable of providing a high quality video service in the presence of varying bandwidth constraints.Comment: 11 page

The influence of capital origin on Brazilian foreign trade patterns

This article aims to determine whether the geographical pattern of the external trade of foreign-owned enterprises in Brazil differs from that of domestic enterprises and whether, in the case of foreign enterprises, the region of origin of their capital is an important factor in determining that pattern, both in terms of the origin and destination of their imports and exports and with regard to the technological content. The methodology employed was panel analysis, applied to a representative set of enterprises, using trade data broken down by region for 1989, 1997 and 2000.Multinational Firm Intra-Firm Trade

An Impossible Job? The View From the Urban Superintendent's Chair

Presents the results of a survey of superintendents of the 100 largest urban and ex-urban districts in the U.S. Examines how school leaders define their challenges and potential solutions

A Matter of Definition: Is There Truly a Shortage of School Principals?

Analyzes the shortage of principals in basic economic terms of supply and demand. Examines the supply of candidates, and the realities of the demand for principals. Offers recommendations that address distinct elements of principal supply and demand