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We revise the procedure proposed by Balassa to infer comparative advantage, which is a standard tool in Economics to analyze specialization (of countries, regions, etc). Balassa’s approach compares a country’s export of a given product with what would be expected from a benchmark based on the total volumes of countries and product flows. Based on results in the literature, we show that implementing Balassa’s idea leads to conditions for estimating parameters conflicting with the information content of the model itself. Moreover, Balassa’s approach does not implement any statistical validation. Hence, we propose an alternative procedure to overcome such a limitation, based upon the framework of entropy maximization and implementing a proper test of hypothesis: the ‘key products’ of a country are, now, the ones whose production is significantly larger than expected, under a null-model constraining the same amount of information defining Balassa’s approach. What we found is that country diversification is always observed, regardless of the strictness of the validation procedure. Besides, the ranking of countries’ fitnesses is only partially affected by the details of the validation scheme employed for the analysis while large differences are found to affect the rankings of product complexities. The routine for implementing the entropy-based filtering procedures employed here is freely available through the official Python Package Index PyPI .

In order to improve device performance, recent trends in microelectronics are to explore nanowire gate-all-around structures and alternative channel materials with superior properties. In this paper, we investigate the electrical transport properties, at room and low temperature, in as-grown three-dimensional (3D) vertically stacked germanium (Ge)-enriched nanowires. Measurements using the Pseudo-MOSFET (ψ-MOSFET) concept show that the transport in gateless nanowires is controlled by the voltage applied on the substrate, as in a MOS transistor. Interestingly, the substrate bias effect depends on the designed geometry of the nanowire. In nanowires with high width/length aspect ratio, we show the possibility of turning on both electron and hole channels. For nanowires with small width/length ratio, only the hole channel is visible. The impact of series resistance on the drain current level is reported. Transport modification with the concentration of germanium in the nanostructures is also discussed. Low-temperature measurements show the variation of electrical parameters such as threshold voltage, flatband voltage, subthreshold swing and mobility. The transport properties in multi-parallel stacked nanowire are addressed. [ABSTRACT FROM AUTHOR]

Bipartite networks are currently regarded as providing a major insight into the organization of many real-world systems, unveiling the mechanisms driving the interactions occurring between distinct groups of nodes. One of the most important issues encountered when modeling bipartite networks is devising a way to obtain a (monopartite) projection on the layer of interest, which preserves as much as possible the information encoded into the original bipartite structure. In the present paper we propose an algorithm to obtain statistically-validated projections of bipartite networks, according to which any two nodes sharing a statistically-significant number of neighbors are linked. Since assessing the statistical significance of nodes similarity requires a proper statistical benchmark, here we consider a set of four null models, defined within the exponential random graph framework. Our algorithm outputs a matrix of link-specific p -values, from which a validated projection is straightforwardly obtainable, upon running a multiple hypothesis testing procedure. Finally, we test our method on an economic network (i.e. the countries-products World Trade Web representation) and a social network (i.e. MovieLens, collecting the users’ ratings of a list of movies). In both cases non-trivial communities are detected: while projecting the World Trade Web on the countries layer reveals modules of similarly-industrialized nations, projecting it on the products layer allows communities characterized by an increasing level of complexity to be detected; in the second case, projecting MovieLens on the films layer allows clusters of movies whose affinity cannot be fully accounted for by genre similarity to be individuated.