In this paper, we present a model of a trust-based recommendation system on a social network. The idea of the model is that agents use their social network to reach information and their trust relationships to filter it. We investigate how the dynamics of trust among agents affect the performance of the system by comparing it to a frequencybased recommendation system. Furthermore, we identify the impact of network density, preference heterogeneity among agents, and knowledge sparseness to be crucial factors for the performance of the system. The system self-organises in a state with performance near to the optimum; the performance on the global level is an emergent property of the system, achieved without explicit coordination from the local interactions of agents.

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The increasing diversity of consumers' demand, as documented by the debate on the long tail of the distribution of sales volume across products, represents a challenge for retail stores. Recommender systems offer a tool to cope with this challenge. The recent developments in information technology and ubiquitous computing makes it feasible to move recommender systems from the on-line commerce, where they are widely used, to retail stores. In this paper, we aim to bridge the management literature and the computer science literature by analysing a number of issues that arise when applying recommender systems to retail stores: these range from the format of the stores that would benefit most from recommender systems to the impact of coverage and control of recommender systems on customer loyalty and competition among retail stores.

To minimize relapse rates in cases of severe crowding, we recommend that the canines and second molars be included in the appliance.

Despite the fact that social networks are ubiquitous on the Internet, only few websites exploit the potential of combining user communities and online marketplaces. Not many platforms allow users to engage in a phenomenon called "group buying" — buyers joining groups, or coalitions, to bundle their purchasing power towards sellers. We argue that this may be due to a lack of face-to-face interaction on the Internet; often, users do not know which other users to trust, which makes them suspicious of engaging in online business, in particular if many unknown other parties are involved. This situation, however, can be alleviated by leveraging the social networks of users: based on who a user knows and is connected to, a trust metric — for example, the TrustWebRank metric developed by us — can be computed to assess who else may be considered trustworthy to that user. In this paper, we build a simple agent-based model of coalition formation among agents in the setting of group buying in an electronic marketplace. In this model, agents use their trust relationships in order to determine who to form coalitions with. We show that this leads agents to experience high utility and that agents are able to learn who is trustworthy and who is not, even when they have no initial knowledge about the trustworthiness of other agents. This work may provide the foundation for a real-world application of an online coalition formation platform for e-commerce built on a social networking platform such as Facebook.

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The introduction within the past few years of a large number of surface-active agents has stimulated numerous explorations into the properties of these compounds. In the field of bacteriology investigations of their inhibitory and stimulatory effects have been made on a variety of organisms. The work of Dubos (1) on Mycobacterium tuberculosis and work in this institution on Staphylococcus aureus and Escherichia coli and other organisms (2) have prompted the present study. It was originally intended to seek a method to produce more rapid, homogenous growth of Lactobacilli in liquid media. The work has since evolved into several phases.The object of this paper is to report 1. the effects of minute amounts of various types of wetting agents on stimulation of growth of Lactobacilli in both liquid and solid media, and 2. the inhibitory activity of some of these agents.Methods. Strains of recently isolated oral Lactobacilli were used throughout the study. Cultures were transferred in broth every 24-48 hours and to solid media once each week. In testing surface-active agents for inhibition and stimulation the Oxford cup method was used. Two ml. of a 48 hour culture of oral Lactobacilli, previously diluted 1: 1000, was used to seed 1 liter of tomato juice agar.3 After the shake cultures were poured into sterile petri dishes, the agar surfaces were allowed to dry for 30 minutes.Sterile porcelain cylinders were placed on the surface of the agar and filled with sterile dilutions of the surface-active agents and controls of the diluting fluids. The plates were incubated at 370 C. for 24, 48, and 72 hours. Zones of partial or complete inhibition and stimulation of growth of the organism were measured in millimeters. Dilution series were prepared of the surface-active agents to ascertain their stimulatory characteristics in liquid media. Lactose, nutrient, nutrient with 2% dextrose, and bacto-dextrose special4 (pH 5.2) broths were used. With the exception of the last-named medium, these were made up with sterile distilled water and also in a buffer solution: potassium acid phthalate-sodium hydroxide, with a pH after autoclaving of 5.2. All media were 1 Read at the 25th General Meeting of the International