Local orthogonal polynomial expansion for density estimation

A local orthogonal polynomial expansion (LOrPE) of the empirical density function is proposed as a novel method to estimate the underlying density. The estimate is constructed by matching localised expectation values of orthogonal polynomials to the values observed in the sample. LOrPE is related to several existing methods, and generalises straightforwardly to multivariate settings. By manner of construction, it is similar to local likelihood density estimation (LLDE). In the limit of small bandwidths, LOrPE functions as kernel density estimation (KDE) with high-order (effective) kernels inherently free of boundary bias, a natural consequence of kernel reshaping to accommodate endpoints. Consistency and faster asymptotic convergence rates follow. In the limit of large bandwidths LOrPE is equivalent to orthogonal series density estimation (OSDE) with Legendre polynomials, thereby inheriting its consistency. We compare the performance of LOrPE to KDE, LLDE, and OSDE, in a number of simulation studies. In terms of mean integrated squared error, the results suggest that with a proper balance of the two tuning parameters, bandwidth and degree, LOrPE generally outperforms these competitors when estimating densities with sharply truncated supports.     

Network construction/restoration problems: cycles and complexity

Journal of Combinatorial Optimization - In network construction/restoration problems introduced in Averbakh and Pereira (IIE Trans 44(8):681–694, 2012; Eur J Oper Res 244:715–729,...     

Penta-Extensions of Hereditary Classes of Graphs

Penta is the configuration shown in figure 1(a), where continuous lines represent edges and dotted lines represent non-edges. The vertex u in figure 1(a) is called the center of Penta. A graph G is called a pentagraph if every induced subgraph H of G has a vertex v which is not a center of induced Penta in H. The class of pentagraphs is a common generalization of chordal [triangulated] graphs and Mahadev graphs. We construct a polynomial-time algorithm that either find a maximum stable set of G or concludes that G is not a pentagraph. We propose a method for extending α-polynomial hereditary classes based on induced Pentas.     

Endothelial progenitor cell therapy for atherosclerosis: the philosopher's stone for an aging population?

Much of the increased risk for atherosclerosis progression with age may be a result of age-related declines in the capacity of precursor cells to repair damage in the arterial endothelium. To estimate the impact of progenitor cell therapy for atherosclerosis on cardiovascular disease (CVD) mortality, life expectancy, and survival, as compared with the lifetime control of conventional risk factors, we modeled the health effects of bone marrow-derived endothelial progenitor cell therapy using data from the 1950 to 1996 follow-up of the Framingham Heart Study. To model cardiovascular disease mortality, we assumed that progenitor cell therapy was applied at age 30, with the effect assumed to be a 10-year delay in atherosclerosis progression. Age projections were constructed analytically using the stochastic process model for risk factor dynamics and mortality and microsimulation techniques. We considered three types of interventions: (i) keeping risk factors within selected limits to model current clinical recommendations; (ii) an age shift of 10 years to model the effects of progenitor cell therapy; and (iii) elimination of a competing risk (such as cancer). Our study suggests that progenitor cell therapy might increase life expectancy in the population as much as the complete elimination of cancer (in females, an additional 3.67 versus 3.37 years; in males, an additional 5.94 versus 2.86 years, respectively).     

A Numerical Study of Small Parameter Behavior of Some Families of Distributions

Limiting distributions play an important role in approximating the exact distributions, especially when they have a rather cumbersome analytic form, or simply when they do not have a closed from. The question that naturally arises is how good the approximation is. In this article, we propose a procedure for the numerical assessment of the “goodness” of some easy-to-calculate limiting distributions, originally proposed in Bar-Lev and Enis, in various cases of the underlying distributions, some of which are inherently computationally challenging. The details of the procedure are provided in three examples. The first example deals with the gamma distributions; the second deals with Bessel distributions related to a symmetric random walk, and the third example deals with positive stable distributions. The details of two additional variations of these examples are also discussed. These examples illustrate the ease with which the limiting approximations could be applied in the various cases, well-demonstrating their computational simplicity and attractiveness.     

The occurrence of happy and traumatic events in the life of common people

Until recent times, psychology and the social sciences have paid only limited attention to the positive aspects of human life. The present article aims to review psychological and epidemiological studies about the occurrence of happy and traumatic events in the life of common people, critically discussing their findings and suggesting new research directions. Overall, it has emerged that most people report having experienced at least one traumatic event in their lives; on the other hand, moderate happy experiences may occur with a daily frequency. Unfortunately, the studies conducted thus far suffer from methodological limitations as they did not consider extremely happy events and collected data about happy and traumatic events separately. The author emphasizes the necessity to jointly investigate the prevalence of both happy and traumatic events. Hopefully, this will permit to achieve more reliable indicators of quality of life, thus contributing to increase researchers’ understanding of what makes human existence joyful and sorrowful.     

Mobilities

This paper reconstructs the emergence of a student mobilization that occupied a central place in the Mexican political scenario in May and June of 2012. Within the framework of a formally democratic regime with an authoritarian functioning logic, the #YoSoy132 (#IAm132) movement was launched within social networks and quickly became an agent of dissatisfaction with the role played by the media as an interested party in a flawed electoral process. The shift from spontaneous protest to organic mobilization involved extending the proposal beyond the private university to which its first members belonged. It also meant that the initial reactive position gave rise to a collective movement of a proactive nature. Although the future of this movement is still uncertain, spaces for struggle have opened up around it, which have been described as the Mexican Spring.     

Correlated equilibrium in a nutshell

We analyze the concept of correlated equilibrium in the framework of two-player two-strategy games. This simple framework makes it possible to clearly demonstrate the characteristic features of this concept. We develop an intuitive and easily memorizable test for equilibrium conditions and provide a complete classification of symmetric correlated equilibria in symmetric games.