Mechanism Design via Dantzig-Wolfe Decomposition

In random allocation rules, typically first an optimal fractional point is calculated via solving a linear program. The calculated point represents a fractional assignment of objects or more generally packages of objects to agents. In order to implement an expected assignment, the mechanism designer must decompose the fractional point into integer solutions, each satisfying underlying constraints. The resulting convex combination can then be viewed as a probability distribution over feasible assignments out of which a random assignment can be sampled. This approach has been successfully employed in combinatorial optimization as well as mechanism design with or without money. In this paper, we show that both finding the optimal fractional point as well as its decomposition into integer solutions can be done at once. We propose an appropriate linear program which provides the desired solution. We show that the linear program can be solved via Dantzig-Wolfe decomposition. Dantzig-Wolfe decomposition is a direct implementation of the revised simplex method which is well known to be highly efficient in practice. We also show how to use the Benders decomposition as an alternative method to solve the problem. The proposed method can also find a decomposition into integer solutions when the fractional point is readily present perhaps as an outcome of other algorithms rather than linear programming. The resulting convex decomposition in this case is tight in terms of the number of integer points according to the Carath{\'e}odory's theorem

A Truthful Mechanism for the Generalized Assignment Problem

We propose a truthful-in-expectation, $(1-1/e)$-approximation mechanism for a strategic variant of the generalized assignment problem (GAP). In GAP, a set of items has to be optimally assigned to a set of bins without exceeding the capacity of any singular bin. In the strategic variant of the problem we study, values for assigning items to bins are the private information of bidders and the mechanism should provide bidders with incentives to truthfully report their values. The approximation ratio of the mechanism is a significant improvement over the approximation ratio of the existing truthful mechanism for GAP. The proposed mechanism comprises a novel convex optimization program as the allocation rule as well as an appropriate payment rule. To implement the convex program in polynomial time, we propose a fractional local search algorithm which approximates the optimal solution within an arbitrarily small error leading to an approximately truthful-in-expectation mechanism. The presented algorithm improves upon the existing optimization algorithms for GAP in terms of simplicity and runtime while the approximation ratio closely matches the best approximation ratio given for GAP when all inputs are publicly known.Comment: 18 pages, Earlier version accepted at WINE 201

Removal of malathion from various waters by advanced oxidation processes

Summary: The degradation of malathion was investigated under various conditions, including ultrasound (US) irradiation, ultraviolet (UV) irradiation, and the combination of US/UV, UV/ZnO, UV/H2O2, and US/UV/ZnO/H2O2. In addition, the effect of the operational parameters, such as the initial concentration of the catalyst, the initial malathion concentration, the initial salt concentration (NaHCO3 and Na2SO4), and pH, were studied. Analyses were performed by a gas chromatography-mass spectroscopy instrument. The k values were in the following order: US/UV/H2O2/ZnO > US/UV > UV/ZnO > UV/H2O2 > UV > US. ZnO concentration of 100 mg/l, malathion initial concentration of 200 μg/l, H2O2 concentration of 30 mg/l, pH of 9, and irradiation time of 105 min were the optimum conditions for degrading malathion by the US/UV/H2O2/ZnO system. Additionally, the optimized parameters were also tested for the treatment of an actual water sample containing the pesticide. As a result, the efficiency of the US/UV/H2O2/ZnO system was higher in the distilled water sample than in the actual water sample. © 2015, Chemical Society of Pakistan. All rights reserved

Fast Convex Decomposition for Truthful Social Welfare Approximation

Approximating the optimal social welfare while preserving truthfulness is a well studied problem in algorithmic mechanism design. Assuming that the social welfare of a given mechanism design problem can be optimized by an integer program whose integrality gap is at most $\alpha$, Lavi and Swamy~\cite{Lavi11} propose a general approach to designing a randomized $\alpha$-approximation mechanism which is truthful in expectation. Their method is based on decomposing an optimal solution for the relaxed linear program into a convex combination of integer solutions. Unfortunately, Lavi and Swamy's decomposition technique relies heavily on the ellipsoid method, which is notorious for its poor practical performance. To overcome this problem, we present an alternative decomposition technique which yields an $\alpha(1 + \epsilon)$ approximation and only requires a quadratic number of calls to an integrality gap verifier

Comparison of environmental health indices of private clinics in Chramahal and Bakhtiari province, Iran

A clinic is a site in which patients have high potential risks. Therefore, inspecting the environmental health conditions of clinics is very important for community health and preventing infection. This research was carried to investigate the environmental indices of clinics in Chramahal and Bakhtiari province. A cross sectional study was done in 2013 in 342 clinics using a checklist comprising the following items: Ventilation, heating and light, solid waste management, disinfection equipment, physical space, welfare facilities, environmental sanitation, water and wastewater management, and safety and protection. The checklist consisted of 42 items. Data were analyzed using SPSS software version 13. The results showed that the highest mean (0.97±0.86) was observed for physical space and the least mean (0.45±0.12) was observed for disinfection equipment. Results also indicated that that 96.5 of the clinics had ventilation, heating and light, 29.2 had solid waste management, 33.6 had disinfection equipment, 91.2 had physical space, 86.3 had welfare facilities, 26.3 had environmental sanitation, 50.3 had water and wastewater management, and 31.9 had safety and protection schemes. It can be concluded from the results of the present study that the best small province regarding the environmental health criteria in clinics was Boroujen and the worst was Cohrang. The findings could serve as a reference for the design and management of privacy clinic. © 2014 AENSI Publisher All rights reserved

Fluoride content of mineral water and tap water in Chaharmahal and Bakhtiari province, Iran

Poor quality of drinking water in many countries, people have recently changed to bottled water consumption. This study wanted to measure the fluoride (F) concentration of drinking water in comparison with commercial brands of mineral bottled water available in Chaharmahal and Bakhtiari province, Iran. 11 different brands of bottled mineral water and 90 samples of tap water were evaluated for fluoride concentration. The standard SPADNS method was used for analysis of Fluoride in the water (DR/5000s Spectrophotometer). The highest concentration of fluoride in a bottled water brand was found to be 0.41 mg/L. There was a significant difference between the average fluoride value of tap water (municipal) (0.20 ± 0.03 mg/L), tap water (rural) (0.13 ± 0.02 mg/L), and bottled water (0.24 ± 0.02 mg/L) (P < 0.05). The measured fluoride concentrations of bottled water were lower than those displayed on the labels. Results showed that the average fluoride value of both mineral bottled water and tap water samples contain fluoride below the maximum allowable level. © 2014 RASĀYAN. All rights reserved

Bacteriological quality of raw cow milk in Shahrekord, Iran

Aim: The aim of this study was to evaluate the rate of contamination with Escherichia coli, coliforms, and Staphylococcus aureus in raw milk from Shahrekord city, Iran. Materials and Methods: In this study, 300 raw milk samples were collected randomly from five regions, namely northeast, east, southeast, south, and southwest regions of Shahrekord city according to stratified random sampling design. Samples were analyzed for Total plate count (TPC), Staphylococcus aureus, coliform, and E. coli. Results: Out of 300 samples of raw milk, contamination with coliforms, E. coli, and S. aureus was observed in 237 (79), 207 (69) and 125 (41.66) samples, respectively. The highest rate of contamination was in the samples from southwest region with coliforms, E. coli, and S. aureus were present in 30 (100), 29 (96.66), and19 (63.33) samples, respectively (p<0.05). Conclusions: Considering the high rate of raw milk contamination with S. aureus, E. Coli, and coliforms, sanitary practice during collecting, transporting, and storage especially in the summer season is recommended. © The authors

Electrodermal activity and expressive writing: looking at skin conductance level, individual differences and emotions.

Eventos traumáticos são acompanhados por emoções desconhecidas. Escrever sobre traumas pode liberar essas emoções e ajudar a regulá-las. Apesar do conhecimento disponível sobre o efeito da escrita expressiva na saúde e na regulação emocional, a principal influência autonómica da escrita expressiva nas emoções, mudanças físicas e diferenças individuais ainda não são claras. Ao analisar a atividade eletrodérmica (EDA) ao longo da escrita, estudamos estes tópicos de investigação. Para estudar as correlações entre escrita expressiva, mudanças corporais e diferenças individuais, 57 estudantes universitários do primeiro ano foram aleatoriamente distribuídos por um grupo de controlo ou expressivo, completando uma tarefa de escrita neutra ou emocional, respectivamente. Os dados psicofisiológicos em tempo real foram registrados durante a escrita (5 min. Linha de base; 15 min. Tarefa de escrita; 5 min. Pós-escrita), para examinar as mudanças psicofisiológicas e emocionais. Os resultados mostraram que os participantes do grupo expressivo tiveram maior afeto negativos em relação ao grupo controlo após terminar a tarefa. Além disso, ao iniciar a tarefa de escrita e ao finalizá- la (pós-escrita), independentemente do tópico, o EDA aumentou. A busca de recompensas é uma possível razão para o aumento pós-escrita do EDA em ambos os grupos. Adicionalmente, os resultados revelaram que os extrovertidos apresentaram menor EDA em comparação aos introvertidos 5 minutos após o início da tarefa de escrita, provavelmente devido ao efeito de habituação. Essas descobertas aumentam o conhecimento sobre as influências do sistema nervoso autónomo durante a escrita e seu efeito nas emoções, e também, como estes podem ser influenciadas por diferenças individuais na personalidade