Large-Scale Simulations of Reionization

We use cosmological simulations to explore the large-scale effects of reionization. Since reionization is a process that involves a large dynamic range - from galaxies to rare bright quasars - we need to be able to cover a significant volume of the universe in our simulation without losing hte important small scale effects from galaxies. Here we have taken an approach that uses clumping factors derived from small scale simulations to approximate the radiative transfer on the sub-cell scales. Using this technique, we can cover a simulation size up to $1280 h^{-1} Mpc$ with $10 h^{-1} Mpc$ cells. This allows us to construct synthetic spectra of quasars similar to observed spectra of SDSS quasars at high reshifts and compare them to the observational data. These spectra can then be analyzed for HII region sizes, the presence of the Gunn-Peterson trough and the Lyman-$\alpha$ forest.Comment: 25 page

A Model for Emergency Service of VoIP Through Certification and Labeling

Voice over Internet Protocol (VoIP) will transform many aspects of traditional telephony service including technology, the business models and the regulatory constructs that govern such service. This transformation is generating a host of technical, business, social and policy problems. The Federal Communications Commission (FCC) could attempt to mandate obligations or specific solutions to the policy issues around VoIP, but is instead looking first to industry initiatives focused on key functionality that users have come to expect of telecommunications services. High among these desired functionalities is access to emergency services that allow a user to summon fire, medical or law enforcement agencies. Such services were traditionally required (and subsequently implemented) through state and federal regulations. Reproducing emergency services in the VoIP space has proven to be a considerable task, if for no other reason then the wide and diverse variety of VoIP implementations and implementers. Regardless of this difficulty, emergency service capability is a critical social concern, making it is particularly important for the industry to propose viable solutions for promoting VoIP emergency services before regulators are compelled to mandate a solution, an outcome that often suffers compromises both through demands on expertise that may be better represented in industry and through the mechanisms of political influence and regulatory capture. While technical and business communities have, in fact, made considerable progress in this area, significant uncertainty and deployment problems still exist. The question we ask is: can an industry based certification and labeling process credibly address social and policy expectations regarding emergency services and VoIP, thus avoiding the need for government regulation at this critical time?1 We hypothesize that it can. To establish this, we developed just such a model for VoIP emergency service compliance through industry certification and device labeling. The intent of this model is to support a wide range of emergency service implementations while providing the user some validation that the service will operate as anticipated. To do this we first examine possible technical implementations for emergency services for VoIP. Next, we summarize the theory of certification as self-regulation and examine several relevant examples. Finally, we synthesize a specific model for certification of VoIP emergency services. We believe that the model we describe provides both short term and long-term opportunities. In the short term, an industry driven effort to solve the important current problem of emergency services in VoIP, if properly structured and overseen as we suggest, should be both effective and efficient. In the long term, such a process can serve as a model for the application of self-regulation to social policy goals in telecommunications, an attractive tool to have as telecommunications becomes increasingly diverse and heterogeneous

The Effects Of Competition On The Price For Cable Modem Internet Access

An important issue in economics is how market structure affects prices. While the standard view is that competition lowers prices, Chen and Riordan (2006) argued that with product differentiation it is not exceptional for prices to be higher under duopoly than monopoly. This paper empirically investigates one implication from Chen and Riordan, namely, that prices are lower under duopoly when consumer preferences for the two products are similar, and they are more likely to be higher under duopoly if consumer preferences for the two products are more diverse. Focusing on the price for cable modem Internet access, with or without competition from a DSL provider, and using education dispersion and ethnic diversity as proxies for consumer preference diversity, we find empirical support for this implication. In markets where preference diversity is low, competition reduces prices. As preference becomes more diverse, the negative effect of competition on prices diminishes; and when preference diversity is high enough, competition increases prices

Paid Placement: Advertising and Search on the Internet

Paid placement, where advertisers bid payments to a search engine to have their products appear next to keyword search results, has emerged as a predominant form of advertising on the Internet. This paper studies a product-di¤erentiation model where consumers are initially uncertain about the desirability of and valuation for di¤erent sellers products, and can learn about a seller s product through a costly search. In equilibrium, a seller bids more for placement when his product is more relevant for a given keyword, and the paid placement of sellers by the search engine reveals information about the relevance of their products. This results in e¢ cient (sequential) search by consumers and increases total output

The Effects of International Simple Resale on Prices in International Telecommunications Markets

This paper empirically investigates the effect of international simple resale (ISR) authorization on the prices for international message telephone service (IMTS). We compile a firm-level panel data set for over 200 United States-foreign country bilateral markets from 1995 to 2004. These data provide detailed information on prices, variable costs, fixed costs and market shares for 75 firms for each bilateral market, as well as the timing of ISR authorization by the Federal Communications Commission for each bilateral market. Estimates from a difference-in-differences model show that ISR authorization, and the associated lowering of barriers to entry, almost always results in lower prices for all markets. Additionally, we find evidence that ISR authorization alters the relationship between market concentration and price. Prior to ISR authorization more concentrated markets have higher prices. ISR authorization dampens this effect and in some cases reverses the relationship so that market concentration is negatively correlated with IMTS prices set by incumbent firms

Boulder Revised Code 1981

https://scholar.law.colorado.edu/colorado-municipal-codes/1036/thumbnail.jp

Charter of the City of Boulder State of Colorado

https://scholar.law.colorado.edu/colorado-municipal-codes/1030/thumbnail.jp