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A Nobel Prize in Economics was given to the psychologist Daniel Kahneman for his joint research with the late psychologist Amos Tversky on decision making under uncertainty and on subjective judgments of uncertainty. The two proposed Prospect Theory as a descriptive alternative to Utility Theory, the reigning normative theory of choice under uncertainty. Kahneman and Tversky argued that human psychology prevents people from being rational in the sense required by Utility Theory – consistency – for two main reasons. First, people are more sensitive to changes in position (economic or otherwise) than to final positions, a fact ignored by Utility Theory. Thus, they value a 50% discount on a 100NIS item more than a 5% discount on a 1000 NIS item. Moreover, they are more sensitive to changes for the worse than to changes for the better. Second, we are sensitive not just to outcomes, but to outcomes-under-a-description, which makes us inconsistent from a consequentialist veiwpoint (e.g., we don't feel the same about losing 100 NIS on our way to the theater boxoffice, vs. losing a 100 NIS ticket on our way to the theater). The article describes some of the empirical observations that led to the development of Prospect Theory, and some of its basic tenets.

Models have been put forward recently that seem to be successful in explaining apparently anomalous experimental results in the Ultimatum Game, where responders reject positive offers. While imparting fixed preference orders to fully rational agents, these models depart from traditional models by assuming preferences that take account not only of the material payoff to oneself, but also of that which is given to others. However, they leave open the question of how an agent's economic survival is helped by a preference order that advises him to leave money on the table. Our answer is that, indeed, doing so does not help. But that the same envious preference order that ill advises in some circumstances to reject an "insultingly" small offer, advises well in other circumstances, when it helps the same agent to overcome his risk- aversion and to offer a risky, tough offer that yields him a higher expected dollar gain. We show the existence of population distributions where the two effects exactly balance out across different preference types. These distributions are stable, stationary, and inefficient, in which different preferences asymptotically are represented, and where, as commonly observed in an Ultimatum Game, positive offers are made, of which some are rejected with positive probability. Our theory yields new testable hypotheses.

This study examined the effects of negative group stereotypes on adolescents' reasoning about peer retribution. The sample of adolescents was drawn from central and northern Israel and consisted of 2,604 Arab and Jewish students (ages 13-17; grades 7-11). A quasi-experimental, between-subject design was used, in which the students in each grade were assigned randomly to 1 of 4 peer retribution scenarios. The findings provide evidence that Arab and Jewish students have stereotypes about one another and that in-group bias affected their approval and reasoning about peer retribution only in specific situations. This inquiry provides evidence that it was the number of justifications endorsed within a specific domain that distinguished Arab and Jewish respondents. Theoretical and practical implications are discussed.

We propose two sequential mechanisms for efficient production of public goods. Our analysis differs from the existing literature in allowing for the presence of multiple public goods and in also being simple.  While both mechanisms ensure efficiency, the payoffs in the first mechanism are asymmetric, being sensitive to the order in which agents move. The second mechanism corrects for this through a two-stage game where the order of moves in the second stage are randomly determined. The payoffs from the second mechanism correspond to the Shapley value of a well-defined game which summarizes the production opportunities available to coalitions in the economy.

We find the key behind the existence traits of asymptotic saturated nonlinear optical solitons in the emergence of linear wave segments. These traits, produced by the progressive relegation of nonlinear dynamics to wave tails, allow a direct and versatile analytical prediction of self-trapping existence conditions and simple soliton scaling laws, which we confirm experimentally in saturated-Kerr self-trapping observed in photorefractives. This approach provides the means to correctly evaluate beam tails in the saturated regime, which is instrumental in the prediction of soliton interaction forces. (C) 2003 Optical Society of America.

Book Review

Book Review

Book Review

Book Review

This paper estimates the substitability brtween public and private consumption. The main finding is that such substitability exists, but is limited. According to our main estimate it amounts to 20 percent.

Book Review

Book Review

Book Review

We present a theoretical study of the energetics, equilibrium size, and size distribution of membrane pores composed of electrically charged amphipathic peptides. The peptides are modeled as cylinders (mimicking alpha-helices) carrying different amounts of charge, with the charge being uniformly distributed over a hydrophilic face, defined by the angle subtended by polar amino acid residues. The free energy of a pore of a given radius, R, and a given number of peptides, s, is expressed as a sum of the peptides’ electrostatic charging energy (calculated using Poisson-Boltzmann theory), and the lipid-perturbation energy associated with the formation of a membrane rim (which we model as being semitoroidal) in the gap between neighboring peptides. A simple phenomenological model is used to calculate the membrane perturbation energy. The balance between the opposing forces (namely, the radial free energy derivatives) associated with the electrostatic free energy that favors large R, and the membrane perturbation term that favors small R, dictates the equilibrium properties of the pore. Systematic calculations are reported for circular pores composed of various numbers of peptides, carrying different amounts of charge (1-6 elementary, positive charges) and characterized by different polar angles. We find that the optimal R’s, for all (except, possibly, very weakly) charged peptides conform to the ‘‘toroidal’’ pore model, whereby a membrane rim larger than similar to1 nm intervenes between neighboring peptides. Only weakly charged peptides are likely to form ‘‘barrel-stave’’ pores where the peptides essentially touch one another. Treating pore formation as a two-dimensional self-assembly phenomenon, a simple statistical thermodynamic model is formulated and used to calculate pore size distributions. We find that the average pore size and size polydispersity increase with peptide charge and with the amphipathic polar angle. We also argue that the transition of peptides from the adsorbed to the inserted (membrane pore) state is cooperative and thus occurs rather abruptly upon a change in ambient conditions.

Animal conflicts are often characterized by time dependent strategy sets. This paper considers the following type of animal conflicts: a member of a group is at risk and needs the assistance of another member to be saved. As long as assistance is not provided, the individual which is at risk has a positive, time dependent rate of dying. Each of the other group members is a potential helper. Assisting this individual accrues a cost, but losing him decreases the inclusive fitness of each group member. A potential helper s interval between the moment an individual finds itself at risk and the moment it assists is a random variable, hence its strategy is to choose the probability distribution for this random variable. Assuming that each of the potential helpers knows the others strategies, we show that the ability to observe their realizations influences the Evolutionarily Stable Strategies (ESS) of the game. According to our results, where the realizations can be observed ESS always exist: immediate assistance, no assistance and delayed assistance. Where the realizations cannot be observed ESS do not always exist, immediate assistance and no assistance are possible ESS, while delayed assistance cannot be an ESS. We apply our model to the n brothers problem and to the parental investment conflict.

To date experimental in vivo pheochromocytoma (PC) models have not been available. A major in vitro PC model consists of PC12 cells that respond to nerve growth factor (NGF) by differentiation, mediated by the trkA receptor. We report the establishment of PC12 tumor models expressing low and high levels of trkA receptor in CD1 nude mice. The tumors are characterized by their responsiveness to NGF, karyotype, presence of enolase, and chromaffin granules, as well as dopamine release. These novel PC models facilitate research on the role of the trkA receptor in cancer and the development of trkA-selective anti-cancer agents.