Online Reciprocal Recommendation with Theoretical Performance Guarantees

A reciprocal recommendation problem is one where the goal of learning is not just to predict a user's preference towards a passive item (e.g., a book), but to recommend the targeted user on one side another user from the other side such that a mutual interest between the two exists. The problem thus is sharply different from the more traditional items-to-users recommendation, since a good match requires meeting the preferences of both users. We initiate a rigorous theoretical investigation of the reciprocal recommendation task in a specific framework of sequential learning. We point out general limitations, formulate reasonable assumptions enabling effective learning and, under these assumptions, we design and analyze a computationally efficient algorithm that uncovers mutual likes at a pace comparable to those achieved by a clearvoyant algorithm knowing all user preferences in advance. Finally, we validate our algorithm against synthetic and real-world datasets, showing improved empirical performance over simple baselines

On similarity prediction and pairwise clustering

We consider the problem of clustering a finite set of items from pairwise similarity information. Unlike what is done in the literature on this subject, we do so in a passive learning setting, and with no specific constraints on the cluster shapes other than their size. We investigate the problem in different settings: i. an online setting, where we provide a tight characterization of the prediction complexity in the mistake bound model, and ii. a standard stochastic batch setting, where we give tight upper and lower bounds on the achievable generalization error. Prediction performance is measured both in terms of the ability to recover the similarity function encoding the hidden clustering and in terms of how well we classify each item within the set. The proposed algorithms are time efficient

On the Troll-Trust Model for Edge Sign Prediction in Social Networks

In the problem of edge sign prediction, we are given a directed graph (representing a social network), and our task is to predict the binary labels of the edges (i.e., the positive or negative nature of the social relationships). Many successful heuristics for this problem are based on the troll-trust features, estimating at each node the fraction of outgoing and incoming positive/negative edges. We show that these heuristics can be understood, and rigorously analyzed, as approximators to the Bayes optimal classifier for a simple probabilistic model of the edge labels. We then show that the maximum likelihood estimator for this model approximately corresponds to the predictions of a Label Propagation algorithm run on a transformed version of the original social graph. Extensive experiments on a number of real-world datasets show that this algorithm is competitive against state-of-the-art classifiers in terms of both accuracy and scalability. Finally, we show that troll-trust features can also be used to derive online learning algorithms which have theoretical guarantees even when edges are adversarially labeled.Comment: v5: accepted to AISTATS 201

Entanglement Generation and Dynamics for a Bose-Hubbard model in a Double-Well Potential

The study of entanglement between bosonic systems is of primary importance for establishing feasible resources needed for implementing quantum information protocols, both in their interacting atomic or photonic realizations. Atomic systems are particularly efficient in the production of large amounts of entanglement, providing higher information density than conventional qubit entangled states. Such increased quantum resources pave the way to novel fundamental tests of nature and efficient applications in quantum information, metrology and sensing. We consider a basic setup made up of two parties A and B, each one populated by a single level bosonic variable. The bosons are interacting and can hop between A and B, thus describing a two-site Bose-Hubbard Hamiltonian. We consider the generation of quantum states in several situations that cover the majority of physical realizations: ground state, finite temperature, unitary dynamics, dissipation through dephasing and loss of particles. The system is analyzed through truncated exact diagonalization, as a function of the microscopic parameters. The non separability of the obtained quantum states is estimated by means of the negativity, which has recently been proven to be a suitable measure of entanglement. Finally, we calculate lower bounds of the entanglement of formation, an indicator that quantifies the minimal amount of entanglement resources needed to build up such states.Comment: 17 pages, 9 figure

Air Cooling and Dehumidification with a zeolite coated heat exchanger regenerated by Solar thermal energy

This paper presents some experimental results of a new device for low energy/low exergy air conditioning system. The device can realize both dehumidification and sensible cooling of external air, and it is designed for very low pressure drops, drastically reducing the electricity consumption for the driving fans. It is composed by a finned coil heat exchanger, coated with a SAPO-34 zeolite layer, that handles both heat and mass transfer in a single component. During the adsorption a cold water flow at 20 °C circulates through the coil, cooling the air and realizing in a single step a complete air-treatment. Hot water produced with evacuated solar collector is then used to regenerate the zeolite

Populismo e ciências sociais brasileiras:: desafios teóricos e metodológicos

Along the way to obtaining the most significant results in the relevant debate, this article provides an analytical, historico-critical, and methodological, though not exhaustive, overview of the uses (as well as the abuses) of the concept of populism in the Brazilian social sciences – given that the latter constitute a true laboratory for the Latin American appropriation of populism. If, on the one hand, the Brazilian debate incorporates all the strengths and weaknesses of the European and North American debates on populism, the adoption of this concept in Brazilian politico-social thinking, on the other hand, must meet some specific needs, starting from the early theories about the ‘amorphous’ people, between the second half of the 19th century and the beginning of the 20th century, going through the analysis of the national-developmental cycle in the ‘Vargas Era’ (within the period from 1930 to 1964), until reaching the resumption of this concept in the last decades, in order to define the phenomenon named as ‘Lulism’ and, above all, the so-called ‘Bolsonarism,’ in the very 21st century.Ao longo do caminho trilhado para obter os resultados mais significativos no debate pertinente, este artigo proporciona um panorama analítico, histórico-crítico e metodológico, embora não exaustivo, dos usos (e também dos abusos) do conceito de populismo nas ciências sociais brasileiras – tendo em vista que estas constituem um verdadeiro laboratório da apropriação latino-americana do populismo. Se, por um lado, o debate brasileiro incorpora todos os pontos fortes e fracos do debate europeu e norte-americano sobre o populismo, a adoção desse conceito no pensamento político-social brasileiro, por outro lado, deve atender a algumas necessidades específicas, a partir das primeiras teorias sobre o povo “amorfo”, entre a segunda metade do século XIX e o início do século XX, passando pela análise do ciclo nacional-desenvolvimentista da “Era Vargas” (no período de 1930 a 1964), até chegar à recuperação desse conceito nas últimas décadas, para definir o fenômeno do “lulismo” e, sobretudo, o chamado “bolsonarismo”, já no século XXI