Seller strategies on eBay: Does size matter?

We examine seller strategies in 1177 Internet auctions on eBay, to understand the diversity of strategies used, and their impacts. Dimensions of strategic choice include the use of a ‘Buy it Now’ option, the level of the starting price, and the use of a secret reserve price. A major focus of our analysis is on differences across sellers with different volumes of sales. The largest volume sellers (termed “retailers”) in our sample employ uniform selling strategies, but lower volume sellers exhibit a wide variety of strategic choices. While some components of sellers’ strategies appear important in raising seller revenue, including starting the auction with a ‘Buy it Now’ offer, the overall impact of seller strategy choices on the outcome appears to be quite small. We interpret this as evidence for the competitiveness of the online auction market for frequently traded items with conventional retail alternatives. An exception is provided by the use of a secret reserve price, which raises the winning bid conditional on a sale, but reduces the probability of a sale. Depending on sellers’ risk aversion and impatience, this may also be an efficient outcome

Equilibrium Vengeance

The efficiency-enhancing role of the vengeance motive is illustrated in a simple social dilemma game in extensive form. Incorporating behavioral noise and observational noise in random interactions in large groups leads to seven continuous families of (short run) Perfect Bayesian equilibria (PBE) that involve both vengeful and non-vengeful types. A new long run evolutionary equilibrium concept, Evolutionary Perfect Bayesian Equilibrium (EPBE), shrinks the equilibrium set to two points. In one EPBE, only the non-vengeful type survives and there are no mutual gains. In the other EPBE, both types survive and reap mutual gains.reciprocity; vengeance; evolutionary perfect Bayesian equilibrium; social dilemmas

Equilibrium Vengeance

This paper introduces two ideas, emotional state dependent utility components (ESDUCs), and evolutionary perfect Bayesian equilibrium (EPBE). Using a simple extensive form game, we illustrate the efficiency-enhancing role of a powerful ESDUC, the vengeance motive. Incorporating behavioral noise and observational noise leads to a range of (short run) Perfect Bayesian equilibria (PBE) involving both vengeful and non-vengeful types. We then derive two (long run) EPBE, one where both types survive and reap mutual gains, and a second where only the non-vengeful type survives and there are no mutual gains.negative reciprocity, perfect Bayesian equilibrium, evolutionary perfect Bayesian equilibrium, emotional state dependent utility

Vengefulness Evolves in Small Groups

We discuss how small group interactions overcome evolutionary problems that might otherwise erode vengefulness as a preference trait. The basic viability problem is that the fitness benefits of vengeance often do not cover its personal cost. Even when a sufficiently high level of vengefulness brings increased fitness, at lower levels, vengefulness has a negative fitness gradient. This leads to the threshold problem: how can vengefulness become established in the first place? If it somehow becomes established at a high level, vengefulness creates an attractive niche for cheap imitators, those who look like highly vengeful types but do not bear the costs. This is the mimicry problem, and unchecked it could eliminate vengeful traits. We show how within-group social norms can solve these problems even when encounters with outsiders are also important.

If I Ruled the World: Putting Hip Hop on the Atlas

“If I Ruled the World: Putting Hip Hop on the Atlas” contends for a third wave of Global Hip Hop Studies that builds on the work of the first two waves, identifies Hip Hop as an African diasporic phenomenon, and aligns with Hip Hop where there are no boundaries between Hip Hop inside and outside of the United States. Joanna Daguirane Da Sylva adds to the cipha with her examination of Didier Awadi. Da Sylva\u27s excellent work reveals the ways in which Hip Hoppa Didier Awadi elevates Pan-Africanism and uses Hip Hop as a tool to decolonize the minds of African peoples. The interview by Tasha Iglesias and myself of members of Generation Hip Hop and the Universal Hip Hop Museum provides a primary source and highlights two Hip Hop organizations with chapters around the world. Mich Yonah Nyawalo’s Negotiating French Muslim Identities through Hip Hop details Hip Hop artists Médine and Diam’s, who are both French and Muslim, and whose self-identification can be understood as political strategies in response to the French Republic’s marginalization of Muslims. In “Configurations of Space and Identity in Hip Hop: Performing ’Global South’,” Igor Johannsen adds to this special issue an examination of the spatiality of the Global South and how Hip Hoppas in the Global South oppose global hegemony. The final essay, “‘I Got the Mics On, My People Speak’: On the Rise of Aboriginal Australian Hip Hop,” by Benjamin Kelly and Rhyan Clapham, provides a thorough analysis of Aboriginal Hip Hop and situates it within postcolonialism. Overall, the collection of these essays points to the multiple identities, political economies, cultures, and scholarly fields and disciplines that Hip Hop interacts with around the world

Evaluating force field accuracy with long-time simulations of a tryptophan zipper peptide

We have combined a custom implementation of the fast multiple-time-stepping LN integrator with parallel tempering to explore folding properties of small peptides in implicit solvent on the time scale of microseconds. We applied this algorithm to the synthetic {\beta}-hairpin trpzip2 and one of its sequence variants W2W9. Each simulation consisted of over 12 {\mu}s of aggregated virtual time. Several measures of folding behavior showed convergence, allowing comparison with experimental equilibrium properties. Our simulations suggest that the electrostatic interaction of tryptophan sidechains is responsible for much of the stability of the native fold. We conclude that the ff99 force field combined with ff96 {\phi} and {\psi} dihedral energies and implicit solvent can reproduce plausible folding behavior in both trpzip2 and W2W9.Comment: 10 pages, 11 figures, submitted to the Journal of Chemical Physics on June 28, 201