An Estimation and Analysis Framework for the Rasch Model

The Rasch model is widely used for item response analysis in applications ranging from recommender systems to psychology, education, and finance. While a number of estimators have been proposed for the Rasch model over the last decades, the available analytical performance guarantees are mostly asymptotic. This paper provides a framework that relies on a novel linear minimum mean-squared error (L-MMSE) estimator which enables an exact, nonasymptotic, and closed-form analysis of the parameter estimation error under the Rasch model. The proposed framework provides guidelines on the number of items and responses required to attain low estimation errors in tests or surveys. We furthermore demonstrate its efficacy on a number of real-world collaborative filtering datasets, which reveals that the proposed L-MMSE estimator performs on par with state-of-the-art nonlinear estimators in terms of predictive performance.Comment: To be presented at ICML 201

Magnetohydrodynamic simulations of black hole accretion

We discuss the results of three-dimensional magnetohydrodynamic simulations, using a pseudo-Newtonian potential, of thin disk (h/r ~ 0.1) accretion onto black holes. We find (i) that magnetic stresses persist within the marginally stable orbit, and (ii) that the importance of those stresses for the dynamics of the flow depends upon the strength of magnetic fields in the disk outside the last stable orbit. Strong disk magnetic fields (alpha > 0.1) lead to a gross violation of the zero-torque boundary condition at the last stable orbit, while weaker fields (alpha ~ 0.01) produce results more akin to traditional models for thin disk accretion onto black holes. Fluctuations in the magnetic field strength in the disk could lead to changes in the radiative efficiency of the flow on short timescales.Comment: 6 pages, to appear in proceedings, 20th Texas Symposium on Relativistic Astrophysics, eds J.C. Wheeler and H. Marte

Flavor SU(3) analysis of charmless B->PP decays

We perform a global fits to charmless $B \to PP$ decays which independently constrain the $(\bar\rho,\bar\eta)$ vertex of the unitarity triangle. The fitted amplitudes and phase are used to predict the branching ratios and CP asymmetries of all decay modes, including those of the $B_s$ system. Different schemes of SU(3) breaking in decay amplitude sizes are analyzed. The possibility of having a new physics contribution to $K \pi$ decays is also discussed.Comment: 3 pages, 2 figs. Talk given at EPS-HEP07 To appear in the proceedings, Reference adde

Role of aggressivity on reactivity and craving before and after cue exposure in recently detoxified alcoholics: Results from an experimental study

The role of aggressivity and cue exposure in induction of craving were investigated in a clinical setting. Thirty abstinent alcoholic patients were divided into a low and a high aggressive group based on scores on the physical aggression subscale of the Buss-Durkee Hostility Inventory and exposed to alcohol cues. Craving was measured by means of the Alcohol Craving Questionnaire (ACQ) and Visual Analogue Scales (VAS). Important findings are: (1) main effects of aggressivity on `emotionality', `purposefulness' and `expectancy' of ACQ were very significant; (2) on `drinking intention' and `craving for alcohol' of VAS, aggressivity and cue exposure showed a significant interaction; (3) the main effect of cue exposure on heart rate also reached a significance level of 0.007. The results were discussed in the context of the Classical, Operant Conditioning Theory, the Cognitive Craving Theory of Tiffany, Gilbert's STAR Model, and the Self-Medication Hypothesis Copyright (C) 2001 S. Karger AG, Basel

Effects of irritability on craving before and after cue exposure in abstinent alcoholic inpatients: Experimental data on subjective response and heart rate

Objective: Irritability is often linked with problem drinking. The aim of this study is to examine the possible influence of irritability on craving induced by a cue-exposure paradigm. Methods: 30 male abstinent alcoholic inpatients of the Psychiatric Hospital of Munich University, Germany gave answers to a series of personality questionnaires. Results of this study concerning the impact of aggressivity on craving for alcohol has recently been published. In this study, the subjects were subdivided into a low- and a high-irritable group based on their scores on the irritability subscale of the Buss-Durkee Hostility Inventory and were exposed to alcohol cues. Craving was measured by means of the Alcohol Craving Questionnaire (ACQ) and Visual Analogue Scales (VAS). The heart rate was also assessed throughout the whole process. ANCOVA for repeated measurement was employed to evaluate the data - irritability disposition as the between-subject factor and the experimental manipulation (absence vs. presence of alcohol cues) as the within-subject factor. Results: Major findings are: (1) main effects of irritability on `emotionality', `purposefulness', and `expectancy' of the ACQ as well as on `craving for alcohol' of the VAS were significant; (2) cue exposure also exerted a significant main effect on I craving for alcohol' of the VAS and on the heart rate after the presentation of alcohol cues; (3) on `compulsivity' of the ACQ and `intention to alcohol intake' of the VAS; there was a significant interaction between irritability and cue exposure. The high-irritable alcoholics, compared with their statements in the baseline, tended to report a higher control over alcohol intake and a lower intention to alcohol use after cue exposure. However, after confrontation with alcohol stimuli, their low-irritable counterparts reported a much lower control and a slightly higher intention than they did in the baseline. Conclusions: The results of this study indicate that induced craving in hospitalized alcohol addicts probably varies with the magnitude of their irritability; it might make patients more aware of their vulnerability to alcohol, help them develop more differential coping strategies and improve medical therapy against alcohol craving. Copyright (C) 2002 S. Karger AG, Basel

Food Security and the Federal Minimum Wage

This working paper, by William M. Rodgers III, Hanley S. Chiang, and Bruce W. Klein, estimates the extent to which increases in the U.S. federal minimum wage in October 1996 and September 1997 improved the ability of households to be food secure -- that is, to purchase for their members an adequate supply of nutritional and safe foods. First, the authors show that the two increases significantly altered the hourly wage distribution of householders (principal person in a household). The shifts were greatest among household heads that are minority, single parents, and household heads with no more than a high school diploma. Even after controlling for the link between the 1990s economic expansion and food security, the October 1996 and September 1997 increases in the federal minimum wage raised food security and reduced hunger, particularly in low-income households where householders had completed no more than a high school degree or were a single parent

Towards a Management Paradigm with a Constrained Benchmark for Autonomic Communications

This paper describes a management paradigm to give effect to autonomic activation, monitoring and control of services or products in the future converged telecommunications networks. It suggests an architecture that places the various management functions into a structure that can then be used to select those functions which may yield to autonomic management, as well as guiding the design of the algorithms. The validation of this architecture, with particular focus on service configuration, is done via a genetic algorithm -- Population Based Incremental Learning (PBIL). Even with this centralized adaptation strategy, the simulation results show that the proposed architecture and benchmark can be applied to this constrained benchmark, produces effective convergence performance in terms of finding nearly optimal configurations under multiple constraints