The Economics of Internet Search

This lecture provides an introduction to the economics of Internet search engines. After a brief review of the historical development of the technology and the industry, I describe some of the economic features of the auction system used for displaying ads. It turns out that some relatively simple economic models provide significant insight into the operation of these auctions. In particular, the classical theory of two-sided matching markets turns out to be very useful in this context.

Economic FAQs About the Internet

This is a set of Frequently Asked Questions (and answers) about the economic, institutional, and technological structure of the Internet. We describe the history and current state of the Internet, discuss some of the pressing economic and regulatory problems, and speculate about future developments.Internet, telecommunications, congestion pricing, National Information Infrastructure

Are there Psychological Barriers in the Dow-Jones Index?

The popular press attaches particular significance to certain numerical values of the Dow-Jones index. These magic numbers are referred to as `resistance levels' or `psychological barriers.' We examine 38 years of closing values of this index to see if it is of any help in predicting future stock market returns.Dow-Jones index, psychological barriers, resistance levels, market efficiency

Contidioning Prices on Purchase History

Many transactions are now computer mediated, making it possible for sellers to condition their pricing on the history of interactions with individual consumers. This paper investigates conditions under which price conditioning will or will not be used. Our simplest model involves rational consumers with constant valuations for the good being sold and a monopoly seller who can commit to a pricing policy. In this framework, the seller will not find it profitable to condition pricing on past behavior. We consider various generalizations of this model, such as allowing the seller to offer enhanced services to previous customers, making the seller unable to commit to a pricing policy, and allowing competition in the marketplace. All of these generalizations have equilibria with price conditioning.Price discrimination, Price conditioning, Privacy, Ecommerce

Flow visualization and flow field measurements of a 1/12 scale tilt rotor aircraft in hover

The results are given of flow visualization studies and inflow velocity field measurements performed on a 1/12 scale model of the XV-15 tilt rotor aircraft in the hover mode. The complex recirculating flow due to the rotor-wake-body interactions characteristic of tilt rotors was studied visually using neutrally buoyant soap bubbles and quantitatively using hot wire anemometry. Still and video photography were used to record the flow patterns. Analysis of the photos and video provided information on the physical dimensions of the recirculating fountain flow and on details of the flow including the relative unsteadiness and turbulence characteristics of the flow. Recirculating flows were also observed along the length of the fuselage. Hot wire anemometry results indicate that the wing under the rotor acts to obstruct the inflow causing a deficit in the inflow velocities over the inboard region of the model. Hot wire anemometry also shows that the turbulence intensities in the inflow are much higher in the recirculating fountain reingestion zone

Taxation of Asset Income in the Presence of a World Securites Market

This paper shows, using a standard CAPM model of security prices in a world market, that even small countries can affect the price of domestically issued risky securities, while large countries can affect the prices of all securities. As a result, countries have the incentive to set tax rates such that in equilibrium investors specialize in domestic securities, and net capital flows between countries are restricted. Each country does this to increase the utility of domestic residents, taking as given the tax policies of other governments, but the net outcome is a reduction in world efficiency and likely a reduction in the utility of all individuals.

PSpectRe: A Pseudo-Spectral Code for (P)reheating

PSpectRe is a C++ program that uses Fourier-space pseudo-spectral methods to evolve interacting scalar fields in an expanding universe. PSpectRe is optimized for the analysis of parametric resonance in the post-inflationary universe, and provides an alternative to finite differencing codes, such as Defrost and LatticeEasy. PSpectRe has both second- (Velocity-Verlet) and fourth-order (Runge-Kutta) time integrators. Given the same number of spatial points and/or momentum modes, PSpectRe is not significantly slower than finite differencing codes, despite the need for multiple Fourier transforms at each timestep, and exhibits excellent energy conservation. Further, by computing the post-resonance equation of state, we show that in some circumstances PSpectRe obtains reliable results while using substantially fewer points than a finite differencing code. PSpectRe is designed to be easily extended to other problems in early-universe cosmology, including the generation of gravitational waves during phase transitions and pre-inflationary bubble collisions. Specific applications of this code will be pursued in future work.Comment: 22 pages; source code for PSpectRe available: http://easther.physics.yale.edu v2 Typos fixed, minor improvements to wording; v3 updated as per referee comment

Beoordeling criteria GMT-1 "biologische diversiteit"

In het kader van de Kaderrichtlijn Mariene Strategie (KRM) streeft Nederland (in internationale Noordzee-context) naar een “Goede Milieu Toestand” (GMT, of GES Good Environmental Status) van het mariene milieu. Een element van deze GMT is “biologische diversiteit”. De invulling van dit element is onlangs geformuleerd door een taskgroep onder regie van het Joint Research Centre (JRC) van de Europese Commissie en het International Council for Exploration of the Sea (ICES). Binnen het project ‘Aanvullende beschermde gebieden op de Noordzee’ heeft IMARES een interne workshop georganiseerd, welke tot doel had een oordeel te vormen over de bruikbaarheid en toepasbaarheid van resultaten van de JRC/ICES task-groep ten aanzien van het GMT element 1 “biologische diversiteit”, ten behoeve van het aanwijzen van aanvullend te beschermen gebieden in de Nederlandse Exclusieve Economische Zone (EEZ)

Review of the spatial and temporal distribution by life stage for 19 North Sea fish species

Considering the increase in human activity in the North Sea, particularly cargo shipping and the rapidly expanding construction and operation of oil platforms and wind farms, as well as the continued use of the area for military purposes, fisheries and sand extraction, there is a growing concern about the potentially harmful impacts of such anthropogenic activities on marine life. Particular concerns have been raised about the effect of loud impulse sounds and high noise levels, which may affect marine animal life in different ways: habitat use, such as feeding and migration, and reproduction patterns may be disturbed. In the extreme case animals may suffer from sub-lethal or lethal physical damage such as hearing loss and disrupted swim ladders. Knowledge of the spatial distribution and seasonal patterns in the presence of different life stages of marine species is therefore critical for assessing to what extent the dispersion of marine life overlaps with the distribution of human activities and for estimating how potentially harmful impacts can be mitigated both spatially and temporally. The aim of this desk study is consequently to provide a concise overview of existing information on seasonal patterns in the dispersion of fish species in the North Sea, in particular by highlighting the knowledge gaps