The Permeability of Network Boundaries: Strategic Alliances in the Japanese Electronics Industry in the 1990s

This paper looks at the choice of strategic partners for alliance formation in the Japanese electronics industry during the post-bubble economic period 1992-97. Results from a dyad analysis of 128 companies suggest that firms tend to look for partners within their existing vertical keiretsu networks of organizations for alliances that target the creation of resources that build on existing knowledge (production or distribution) but that this common keiretsu effect disappears for alliances that involve new knowledge creation (new product or technology development). The role of corporate networks, environmental uncertainty and their implications for our understanding of strategic alliance formation and the dynamics of social networks are discussed.

Confidence regions for the multinomial parameter with small sample size

Consider the observation of n iid realizations of an experiment with d>1 possible outcomes, which corresponds to a single observation of a multinomial distribution M(n,p) where p is an unknown discrete distribution on {1,...,d}. In many applications, the construction of a confidence region for p when n is small is crucial. This concrete challenging problem has a long history. It is well known that the confidence regions built from asymptotic statistics do not have good coverage when n is small. On the other hand, most available methods providing non-asymptotic regions with controlled coverage are limited to the binomial case d=2. In the present work, we propose a new method valid for any d>1. This method provides confidence regions with controlled coverage and small volume, and consists of the inversion of the "covering collection"' associated with level-sets of the likelihood. The behavior when d/n tends to infinity remains an interesting open problem beyond the scope of this work.Comment: Accepted for publication in Journal of the American Statistical Association (JASA

mixtools: An R Package for Analyzing Mixture Models

The mixtools package for R provides a set of functions for analyzing a variety of finite mixture models. These functions include both traditional methods, such as EM algorithms for univariate and multivariate normal mixtures, and newer methods that reflect some recent research in finite mixture models. In the latter category, mixtools provides algorithms for estimating parameters in a wide range of different mixture-of-regression contexts, in multinomial mixtures such as those arising from discretizing continuous multivariate data, in nonparametric situations where the multivariate component densities are completely unspecified, and in semiparametric situations such as a univariate location mixture of symmetric but otherwise unspecified densities. Many of the algorithms of the mixtools package are EM algorithms or are based on EM-like ideas, so this article includes an overview of EM algorithms for finite mixture models.

Noise-induced volatility of collective dynamics

"Noise-induced volatility" refers to a phenomenon of increased level of fluctuations in the collective dynamics of bistable units in the presence of a rapidly varying external signal, and intermediate noise levels. The archetypical signature of this phenomenon is that --beyond the increase in the level of fluctuations-- the response of the system becomes uncorrelated with the external driving force, making it different from stochastic resonance. Numerical simulations and an analytical theory of a stochastic dynamical version of the Ising model on regular and random networks demonstrate the ubiquity and robustness of this phenomenon, which is argued to be a possible cause of excess volatility in financial markets, of enhanced effective temperatures in a variety of out-of-equilibrium systems and of strong selective responses of immune systems of complex biological organisms. Extensive numerical simulations are compared with a mean-field theory for different network topologies

Synthesis and proton conduction properties of lanthanide amino-sulfophosphonates

Crystalline acid-functionalized metal phosphonates are potential candidates as proton conducting electrolytes. Their frameworks can be chemically modified to contain proton carriers such as acidic groups (P-OH; -SO3H, -COOH,…) and guest molecules (H2O, NH3,…) that generates hydrogen bond networks stable in a wide range of temperature [1,2]. In this work, focus is laid on properties derived from the combination of lanthanide ions with the amino-sulfophosphonate ligand (H2O3PCH2)2-N-(CH2)2-SO3H. Hightrough-put screening was followed to reach the optimal synthesis conditions under solvothermal conditions at 140 ºC. Isolated polycrystalline solids, Ln[(O3PCH2)2-NH-(CH2)2-SO3H].2H2O (Ln= La, Pr and Sm), crystallize in the monoclinic (La) and orthorhombic (Pr and Sm) systems with unit cell volume of ~2548 Å3. Preliminary proton conductivity measurements for Sm derivative have been carried out between 25º and 80 ºC at relative humidity (RH) values of 70 % and 95 %. The sample exhibits enhanced conductivity at high RH and T (Figure 1) and constant activation energies of 0.4 eV, typical of a Grothuss mechanism of proton.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. FQM-1656; MAT2013-41836-

Effect of temperature on the growth and development of quinoa plants (Chenopodium quinoa Willd.): A review on a global scale

The increase in temperature and constant changes in climate negatively affects the development of the plants, which has resulted in an alarming situation for many of the different crops of agricultural and food interest. In the specific case of quinoa, the investigation points to a significant loss in the productivity of the grain crop indicating differences depending on the altitudes of the areas of agriculture production and the availability of water. A current informed description of the responses regarding phonological development under stressful conditions could help us develop appropriate strategies to improve the conditions for the production of quinoa and allow us to propose cultivation of the product under environmental conditions where other products cannot survive. The main discoveries regarding this study were framed within the effect of caloric stress on the germination of quinoa seeds, their phenology, their response to different evaluated cultivars and their effects on their growth as well as their physiological and productive levels. Thus, the analysis is described based on a review of the available scientific documents available in the Scopus database and doctoral work thesis, allowing for the consolidation of the most recent investigations regarding the quinoa and their relationship with temperature

Quinoa crop biodiversity in Chile: an ancient plant cultivated with sustainable agricultural practices and producing grains of outstanding and diverse nutritional values

Quinoa crop (Chenopodium quinoa) has been cultivated since the last seven thousand years in Latin America. However the nutritional and functional properties have been diffused only since the last decade. The exportation market to Northern countries is increasing at levels not seen previously for an organic product. Its ancient cultivation practices were normally sustainable even in Chile. However strong isolation of today' small farmers in Chile has provoked less access to international markets and also great genetic distances among cultivars from the long latitudinal and ecological gradient where this crop is cultivated (4000 m.a.s.l. at 19ºS to coastal areas at sea level between 18ºS to 40ºS). The nutritional diversity along this gradient has not been previously studied. This study focuses on the nutritional properties of five distinctive local land races found along Chile, belonging to different genetic pools, but collected from farmers that have not developed formal crop improvement, with the exemption of a single hybrid variety, also included in this study. Results showed that genetic variability of quinoa ecotypes plus the environmental diversity allow an also great nutritional diversity. Protein content had significant lower levels (12%) for northern ecotypes while higher values (16%) were found among the less known southern seed origins, cultivated by Mapuche people. While other properties like Vitamin B2 showed higher values in northern ecotypes, supporting the idea that genetic richness or diversity of quinoa ecotypes hide an also rich nutritional diversity. All the cultivars are managed under sustainable ecological practices, unique possibility among small-scale farmers. (Résumé d'auteur