124 research outputs found
Crowdfunding: Geography, Social Networks, and the Timing of Investment Decisions
We examine a crowdfunding platform that connects artists with funders. Although the Internet reduces many distance-related frictions, local and distant funders exhibit different funding patterns. Local funders appear less responsive to information about the cumulative funds raised by an artist. However, this distance effect appears to proxy for a social effect: it is largely explained by funders who likely have an offline social relationship with the artist (“friends and family”). Yet, this social effect does not persist past the first investment, suggesting that it may be driven by an activity like search but not monitoring. Thus, although the platform seems to diminish many distance-sensitive costs, it does not eliminate all of them. These findings provide a deeper understanding of the abilities and limitations of online markets to facilitate transactions and convey information between buyers and sellers with varying degrees of social connectedness
Zero-range process with open boundaries
We calculate the exact stationary distribution of the one-dimensional
zero-range process with open boundaries for arbitrary bulk and boundary hopping
rates. When such a distribution exists, the steady state has no correlations
between sites and is uniquely characterized by a space-dependent fugacity which
is a function of the boundary rates and the hopping asymmetry. For strong
boundary drive the system has no stationary distribution. In systems which on a
ring geometry allow for a condensation transition, a condensate develops at one
or both boundary sites. On all other sites the particle distribution approaches
a product measure with the finite critical density \rho_c. In systems which do
not support condensation on a ring, strong boundary drive leads to a condensate
at the boundary. However, in this case the local particle density in the
interior exhibits a complex algebraic growth in time. We calculate the bulk and
boundary growth exponents as a function of the system parameters
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
Dynamically Driven Renormalization Group Applied to Sandpile Models
The general framework for the renormalization group analysis of
self-organized critical sandpile models is formulated. The usual real space
renormalization scheme for lattice models when applied to nonequilibrium
dynamical models must be supplemented by feedback relations coming from the
stationarity conditions. On the basis of these ideas the Dynamically Driven
Renormalization Group is applied to describe the boundary and bulk critical
behavior of sandpile models. A detailed description of the branching nature of
sandpile avalanches is given in terms of the generating functions of the
underlying branching process.Comment: 18 RevTeX pages, 5 figure
Minimal half-spaces and external representation of tropical polyhedra
We give a characterization of the minimal tropical half-spaces containing a
given tropical polyhedron, from which we derive a counter example showing that
the number of such minimal half-spaces can be infinite, contradicting some
statements which appeared in the tropical literature, and disproving a
conjecture of F. Block and J. Yu. We also establish an analogue of the
Minkowski-Weyl theorem, showing that a tropical polyhedron can be equivalently
represented internally (in terms of extreme points and rays) or externally (in
terms of half-spaces containing it). A canonical external representation of a
polyhedron turns out to be provided by the extreme elements of its tropical
polar. We characterize these extreme elements, showing in particular that they
are determined by support vectors.Comment: 19 pages, 4 figures, example added with a new figure, figures
improved, references update
Motion of a driven tracer particle in a one-dimensional symmetric lattice gas
We study the dynamics of a tracer particle subject to a constant driving
force in a one-dimensional lattice gas of hard-core particles whose
transition rates are symmetric. We show that the mean displacement of the
driven tracer grows in time, , as , rather than the linear
time dependence found for driven diffusion in the bath of non-interacting
(ghost) particles. The prefactor is determined implicitly, as the
solution of a transcendental equation, for an arbitrary magnitude of the
driving force and an arbitrary concentration of the lattice gas particles. In
limiting cases the prefactor is obtained explicitly. Analytical predictions are
seen to be in a good agreement with the results of numerical simulations.Comment: 21 pages, LaTeX, 4 Postscript fugures, to be published in Phys. Rev.
E, (01Sep, 1996
Predicting Missing Links via Local Information
Missing link prediction of networks is of both theoretical interest and
practical significance in modern science. In this paper, we empirically
investigate a simple framework of link prediction on the basis of node
similarity. We compare nine well-known local similarity measures on six real
networks. The results indicate that the simplest measure, namely common
neighbors, has the best overall performance, and the Adamic-Adar index performs
the second best. A new similarity measure, motivated by the resource allocation
process taking place on networks, is proposed and shown to have higher
prediction accuracy than common neighbors. It is found that many links are
assigned same scores if only the information of the nearest neighbors is used.
We therefore design another new measure exploited information of the next
nearest neighbors, which can remarkably enhance the prediction accuracy.Comment: For International Workshop: "The Physics Approach To Risk:
Agent-Based Models and Networks", http://intern.sg.ethz.ch/cost-p10
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