Understanding the complexity of #SAT using knowledge compilation

Two main techniques have been used so far to solve the #P-hard problem #SAT. The first one, used in practice, is based on an extension of DPLL for model counting called exhaustive DPLL. The second approach, more theoretical, exploits the structure of the input to compute the number of satisfying assignments by usually using a dynamic programming scheme on a decomposition of the formula. In this paper, we make a first step toward the separation of these two techniques by exhibiting a family of formulas that can be solved in polynomial time with the first technique but needs an exponential time with the second one. We show this by observing that both techniques implicitely construct a very specific boolean circuit equivalent to the input formula. We then show that every beta-acyclic formula can be represented by a polynomial size circuit corresponding to the first method and exhibit a family of beta-acyclic formulas which cannot be represented by polynomial size circuits corresponding to the second method. This result shed a new light on the complexity of #SAT and related problems on beta-acyclic formulas. As a byproduct, we give new handy tools to design algorithms on beta-acyclic hypergraphs

Exhaustive Search of Ligand Binding Pathways via Volume-based Metadynamics

Determining the complete set of ligands' binding/unbinding pathways is important for drug discovery and to rationally interpret mutation data. Here we have developed a metadynamics-based technique that addressed this issue and allows estimating affinities in the presence of multiple escape pathways. Our approach is shown on a Lysozyme T4 variant in complex with the benzene molecule. The calculated binding free energy is in agreement with experimental data. Remarkably, not only we were able to find all the previously identified ligand binding pathways, but also we uncovered 3 new ones. This results were obtained at a small computational cost, making this approach valuable for practical applications, such as screening of small compounds libraries

The resilient character of PDO/PGI products in dynamic food markets

The European and Italian food system is experiencing a change in the relationship with the consumer and with the distribution. In fact, customers are increasingly demanding, and are attracted, by products that have high quality content and a strong link with the territory. The brands with the price are the two factors affecting the strategic policies of the food producer firms. At the same time, the retail system has proven to be very sensitive to consumer demands by providing quality products at competitive prices and using their brand as an element of loyalty. In the European context, the Italian agri-food system has the higher number of products with the Protected Designation of Origin (PDO) and Protected Geographical Indication (PGI) recognition. However, 90% of PDO products are represented by only 15 Designations. This figure shows how different types of products find a much diversified business position in relation to the firm’s characteristics, to the markets characteristics, to the reputation of the Designation and to the consortium strategies in relation to their commercialization. The objective of this research, based on observed data collected through the survey of QUALIVITA Association, is to provide an exhaustive picture of the economic characteristics of the Italian PDO, PGI Designations and define a typology of such Designation according different set of variables as production system, reputation level, role of the territory and distribution channel. The ultimate goal is to determine the strategic levers taken at the marketing stage and to identify which factors clarify their potentiality on the market. The methodology adopted for the quantitative analysis is based on non-hierarchical cluster analysis by the method of k-mean in order to identify clusters of similar designations which explain what variables act on the various strategies adopted and on the related development processes.PDO/PGI, quality, modern distribution, cluster analysis, marketing strategies, development processes, Agricultural and Food Policy, Marketing,

New wine in new bottles: Visualizing the progression over time of the epidemics of tobacco smoking and obesity through the use of modified population pyramids

Tobacco smoking and obesity greatly contribute to premature death and disease in developed countries. In order to measure the extent to which these risk factors affect a population, as well as to describe the progression of these epidemics over time, routine surveillance of the prevalence of obesity and smoking is carried out by international organizations, national departments of health, and statistical offices. To this end, summary measures—like age-standardized rates, and tabular and graphical representations, such as maps—are used. In this study, we argue that population pyramids, a widely used demographic tool, may be easily adapted to provide relevant visual information for public health purposes. By means of two juxtaposed histograms, one for each gender, population pyramids show either the proportion or the actual number of subjects in each age and gender subgroup. We suggest that stratifying each bar of the two histograms according to ordinal categories of the health condition or risk factor examined may provide useful details on the relationship between this condition or factor and key demographic variables like age and gender. In addition, the actual number of exposed subjects can be immediately read from the graph. We therefore built a statistical routine with Stata to create modified population-pyramid plots separately for overweight/obese and current/former smoker. Data were derived from five National Health Interview Surveys carried out in Italy between 1983 and 2005. For each survey, data on age, gender, smoking status, height, and weight were extracted for subjects aged 20–99. Age and gender-specific prevalence rates of overweight/obese, and of current/former/never smoker were computed and applied to population estimates performed by the Italian national statistical institute (ISTAT). The resulting estimated numbers of underweight/normal weight/overweight/obese individuals and of former/current/never smokers were used to create the modified population pyramids. In conclusion, modified population pyramids may contribute to assessing the impact of risk factors on a population in absolute terms, to evaluating how these risk factors are distributed by age and gender, and to assessing how the age and gender distribution of these risk factors changes over time.