A Graphical Model Formulation of Collaborative Filtering Neighbourhood Methods with Fast Maximum Entropy Training

Item neighbourhood methods for collaborative filtering learn a weighted graph over the set of items, where each item is connected to those it is most similar to. The prediction of a user's rating on an item is then given by that rating of neighbouring items, weighted by their similarity. This paper presents a new neighbourhood approach which we call item fields, whereby an undirected graphical model is formed over the item graph. The resulting prediction rule is a simple generalization of the classical approaches, which takes into account non-local information in the graph, allowing its best results to be obtained when using drastically fewer edges than other neighbourhood approaches. A fast approximate maximum entropy training method based on the Bethe approximation is presented, which uses a simple gradient ascent procedure. When using precomputed sufficient statistics on the Movielens datasets, our method is faster than maximum likelihood approaches by two orders of magnitude.Comment: ICML201

Three-Point Functions and su(1|1) Spin Chains

We compute three-point functions of general operators in the su(1|1) sector of planar N = 4 SYM in the weak coupling regime, both at tree-level and one-loop. Each operator is represented by a closed spin chain Bethe state characterized by a set of momenta parameterizing the fermionic excitations. At one-loop, we calculate both the two-loop Bethe eigenstates and the relevant Feynman diagrams for the three-point functions within our setup. The final expression for the structure constants is surprisingly simple and hints at a possible form factor based approach yet to be unveiled.Comment: 36 page

Trends in Alcohol Services Utilization from 1991–1992 to 2001–2002: Ethnic Group Differences in the U.S. Population

Background:  During the early 1990s in the United States, changes to the provision and financing of alcohol treatment services included reductions in inpatient treatment services and in private sector spending for treatment. We investigated trends in alcohol services utilization over the 10‐year period from 1991–1992 to 2001–2002 among U.S. whites, blacks, and Hispanics. Methods:  Data come from 2 household surveys of the U.S. adult population. The 1991 to 1992 National Longitudinal Alcohol Epidemiologic Survey and the 2001 to 2002 National Epidemiologic Survey on Alcohol and Related Conditions conducted face‐to‐face interviews with a multistage cluster sample of individuals 18 years of age and older in the continental United States. Treatment utilization represented both total utilization and the use of alcohol services. Data analyses were prevalence rates and multivariate logistic regressions for lifetime utilization with drinkers and individuals with alcohol use disorders (AUDs). Results:  From 1991–1992 to 2001–2002, drinking‐related emergency room and human services use increased for drinkers, while total utilization and the use of private health professional services and mutual aid decreased for individuals with AUDs. In drinkers and individuals with AUDs, blacks and Hispanics were less likely than whites to use private health professional care. Hispanics with AUDs were less likely than whites with AUDs to use alcohol or drug programs. Ethnicity interacted with alcohol severity to predict alcohol services utilization. At higher levels of alcohol severity, blacks and Hispanics were less likely than whites to ever use treatment and to use alcohol services (i.e., human services for Hispanic drinkers, mental health services for blacks with AUDs, and mutual aid for Hispanics with AUDs). Conclusions:  Our findings showed increases from 1991–1992 to 2001–2002 in alcohol services utilization for drinkers, but reductions in utilization for individuals with AUDs. Blacks and Hispanics, particularly those at higher levels of alcohol severity, underutilized treatment services compared to whites. These utilization trends for blacks and Hispanics may reflect underlying disparities in healthcare access for minority groups, and language and logistical barriers to utilizing services

An Analysis of Actual and Potential Trade between the EU Countries and the Eastern European Countries

The Eastern Enlargement represents an opportunity for trade growth for all the European Union (EU) countries. In fact, trade between the EU and the Central and Eastern European countries (CEEC) has increased considerably in the nineties. However, both benefits and losses from trade expansion do not equally affect all countries and regions inside the EU. This paper focus on the analysis of the potential bilateral trade flows between the EU and the CEEC and in special between the CEEC and the Southern European countries. The analysis is based on the gravity model approach using panel data from 1993 to 1999. It is possible to conclude that there is still scope for further expansion of the trade flows between some CEEC and some of the EU countries, in particular of some Southern countries