Abstract This paper empirically analyses the price of diamonds from different perspectives. The sample data contains detailed information on more than 165,000 diamonds certified by Gemological Institute of America, which can be purchased since July 2016 from a large online diamond supplier. Our empirical analysis allows to extend the classic 4Cs model in several directions as follows: (a) the classical 4Cs model is insufficient in order to explain the price, so that other attributes, such as polishing, symmetry, and fluorescence, must be incorporated to accurately estimate the price of a particular piece; (b) the large sample size allows us to analyse specific price ranges characterized by high market activity; (3) a very detailed analysis has been conducted for round diamonds, incorporating interactions between attributes within the regression model and studying the marginal rates of substitution between diamond weight and alternative characteristics given a certain price. Our model is able to detect diamonds that could constitute a clear market opportunity for buyers. This model can help to select efficient demand options taking advantage of the information available on the website, improving the overall efficiency of exchange in this sector.

Efficient, resilient, and sustainable electricity delivery is a key cornerstone in increasingly large and complex urban environments, where citizens expect to keep or rise their living standards. In this context, cost-effective and ubiquitous digital technologies are driving the transformation of existing electrical infrastructures into truly smart systems capable of better providing the services a low-carbon society is demanding. The goal of this paper is twofold: 1) to review the dramatically evolving landscape of power systems, from the old framework based on centralized generation and control, aimed at serving inelastic customers through alternating current (ac) transmission networks and one-way distribution feeders, to a new paradigm centered mainly around two main axes: renewable generation, both centralized and distributed, and active customers (prosumers), interacting with each other through hybrid ac/dc smart grids; 2) to illustrate, through featured success stories, how several smart grid concepts and technologies have been put into practice in Spain over the last few years to optimize the performance of urban electrical assets.