563 research outputs found
Exploration and exploitation in the presence of network externalities
This paper examines the conditions under which exploration of a new, incompatible technologyis
conducive to firm growth in the presence of network externalities. In particular,
this studyis motivated bythe divergent evolutions of the PC and the workstation markets in
response to a new technology: reduced instruction set computing (RISC). In the PC market,
Intel has developed new microprocessors bymaintaining compatibilitywith the established
architecture, whereas it was radicallyr eplaced byRISC in the workstation market. History
indicates that unlike the PC market, the workstation market consisted of a large number
of power users, who are less sensitive to compatibilitythan ordinaryusers. Our numerical
analysis indicates that the exploration of a new, incompatible technologyis more likelyto
increase the chance of firm growth when there are a substantial number of power users or
when a new technologyis introduced before an established technologytakes off.
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Entanglement between Demand and Supply in Markets with Bandwagon Goods
Whenever customers' choices (e.g. to buy or not a given good) depend on
others choices (cases coined 'positive externalities' or 'bandwagon effect' in
the economic literature), the demand may be multiply valued: for a same posted
price, there is either a small number of buyers, or a large one -- in which
case one says that the customers coordinate. This leads to a dilemma for the
seller: should he sell at a high price, targeting a small number of buyers, or
at low price targeting a large number of buyers? In this paper we show that the
interaction between demand and supply is even more complex than expected,
leading to what we call the curse of coordination: the pricing strategy for the
seller which aimed at maximizing his profit corresponds to posting a price
which, not only assumes that the customers will coordinate, but also lies very
near the critical price value at which such high demand no more exists. This is
obtained by the detailed mathematical analysis of a particular model formally
related to the Random Field Ising Model and to a model introduced in social
sciences by T C Schelling in the 70's.Comment: Updated version, accepted for publication, Journal of Statistical
Physics, online Dec 201
Global Jacquet-Langlands correspondence, multiplicity one and classification of automorphic representations
In this paper we show a local Jacquet-Langlands correspondence for all
unitary irreducible representations. We prove the global Jacquet-Langlands
correspondence in characteristic zero. As consequences we obtain the
multiplicity one and strong multiplicity one theorems for inner forms of GL(n)
as well as a classification of the residual spectrum and automorphic
representations in analogy with results proved by Moeglin-Waldspurger and
Jacquet-Shalika for GL(n).Comment: 49 pages; Appendix by N. Grba
Dynamical HII Region Evolution in Turbulent Molecular Clouds
We present numerical radiation-hydrodynamic simulations of the evolution of
HII regions formed in an inhomogeneous medium resulting from turbulence
simulations. We find that the filamentary structure of the underlying density
distribution produces a highly irregular shape for the ionized region, in which
the ionization front escapes to large distances in some directions within
80,000 years. In other directions, on the other hand, neutral gas in the form
of dense globules persists within 1 parsec of the central star for the full
duration of our simulation (400,000 years). Divergent photoablation flows from
these globules maintain a root-mean-squared velocity in the ionized gas that is
close to the ionized sound speed. Simulated images in optical emission lines
show morphologies that are in strikingly detailed agreement with those observed
in real HII regions.Comment: Minor changes to sync with accepted version. 7 pages, ApJ in press.
Accompanying video available at
http://ifront.org/wiki/Turbulent_Hii_Regions/Paper
Al Qaeda at the bar: coordinating ideologues and mercenaries in terrorist organizations
Most terrorist groups have limited lifespans. A number of scholars and casual observers have noted that terrorist organizations often are comprised of two types of participants: ideologues or "true believers" dedicated to the group's cause, and mercenaries, who are adept at raising money through illegal means. The latter are interested primarily in their personal gains and have relatively little ideological commitment. Terrorist groups need both participants in order to function effectively. The purpose of the study is to understand the impact of communication on the compositions of terrorist groups. Three experimental treatments consider a coordination problem, and focus on the behavior of the mercenaries. Participants choose whether or not to participate in a terrorist attack. Payoffs are U-shaped in the number of participants, and increase with the number of successful attacks. The treatments allow communication between a leader and frontline fighters ("leader" treatment) or among the frontline fighters themselves ("communication" treatment). In the first treatment, a group leader can post messages to the members, which has a 19 % coordination success rate. For the communication treatment, all participants can post messages anonymously to each other, which yields a 27 % coordination success rate. By contrast, the baseline ("no communication" treatment) shows a success rate of 11 %. We conclude from our experimental evidence that disrupting communications among the frontline fighters is more effective in terminating terrorist organizations
A First- and Second-Order Motion Energy Analysis of Peripheral Motion Illusions Leads to Further Evidence of “Feature Blur” in Peripheral Vision
Anatomical and physiological differences between the central and peripheral visual systems are well documented. Recent findings have suggested that vision in the periphery is not just a scaled version of foveal vision, but rather is relatively poor at representing spatial and temporal phase and other visual features. Shapiro, Lu, Huang, Knight, and Ennis (2010) have recently examined a motion stimulus (the “curveball illusion”) in which the shift from foveal to peripheral viewing results in a dramatic spatial/temporal discontinuity. Here, we apply a similar analysis to a range of other spatial/temporal configurations that create perceptual conflict between foveal and peripheral vision.To elucidate how the differences between foveal and peripheral vision affect super-threshold vision, we created a series of complex visual displays that contain opposing sources of motion information. The displays (referred to as the peripheral escalator illusion, peripheral acceleration and deceleration illusions, rotating reversals illusion, and disappearing squares illusion) create dramatically different perceptions when viewed foveally versus peripherally. We compute the first-order and second-order directional motion energy available in the displays using a three-dimensional Fourier analysis in the (x, y, t) space. The peripheral escalator, acceleration and deceleration illusions and rotating reversals illusion all show a similar trend: in the fovea, the first-order motion energy and second-order motion energy can be perceptually separated from each other; in the periphery, the perception seems to correspond to a combination of the multiple sources of motion information. The disappearing squares illusion shows that the ability to assemble the features of Kanisza squares becomes slower in the periphery.The results lead us to hypothesize “feature blur” in the periphery (i.e., the peripheral visual system combines features that the foveal visual system can separate). Feature blur is of general importance because humans are frequently bringing the information in the periphery to the fovea and vice versa
Why Blu-Ray vs. HD-DVD is not VHS vs. Betamax: The Co-Evolution of Standard-Setting Consortia
The \u3cem\u3eChlamydomonas\u3c/em\u3e Genome Reveals the Evolution of Key Animal and Plant Functions
Chlamydomonas reinhardtii is a unicellular green alga whose lineage diverged from land plants over 1 billion years ago. It is a model system for studying chloroplast-based photosynthesis, as well as the structure, assembly, and function of eukaryotic flagella (cilia), which were inherited from the common ancestor of plants and animals, but lost in land plants. We sequenced the ∼120-megabase nuclear genome of Chlamydomonas and performed comparative phylogenomic analyses, identifying genes encoding uncharacterized proteins that are likely associated with the function and biogenesis of chloroplasts or eukaryotic flagella. Analyses of the Chlamydomonas genome advance our understanding of the ancestral eukaryotic cell, reveal previously unknown genes associated with photosynthetic and flagellar functions, and establish links between ciliopathy and the composition and function of flagella
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