Essays in platform economics

In this thesis we present three papers which investigate informative content generated by consumers, aiming to improve the usefulness for matching high quality products at lower prices. Following a general perspective, we explore platform product listing, searchable through a decision making mechanism. In a more specialized perspective, we take into account a dropping price modality service, differentiating the consumer benefit in the case of high or low quality product matching. Chapter 1 Product quality on platform markets. Abstract Many studies have questioned the meaning of \u201cproduct quality\u201d, hanging between a characteristic interpretation of a product for improving consumer satisfaction, and scientific approach to measure its benefits. Starting from the historical quality setting as mirror image of the price, we investigate the adoption of new signals, developed over the years to adjust the original relationship. Recently, bootstrapping by emperor of e-commerce platforms, the rating system has emerged as a reference contribute for product quality informativeness. We study this tendency, to show its failure in the presence of low price market and new brands. For this purpose, we collect User Generated Contents from a well-known online retailing platform. We capture and distill meaningful features in order to adjust the rating assigned by reviewers, and propose a novel quality formula able to increase the accuracy of the information provided to the consumer. We suggest that our formula better captures product quality, and, when adopted by a platform for sorting the products, it increases the products variety and, consequently the satisfaction of the consumer. Our proposal suggests a way to facilitate the consumer search (as we will show in the second chapter). Moreover, it can be used as a measure of market efficiency in the case of voluntary opacity of the platform in exposing product quality signals.Chapter 2 Optimizing Product Quality in Online Search Abstract Exploiting an original definition of product quality, based on the information we can get from the User Generated Content, and driven by a statistical learning algorithm, we propose a new ordering mechanism for product search on platforms. This product quality formula is imported in a decision making mechanism which adopts an optimal Stopping Rule, in order to set the optimal time to terminate the search process and choose a good to purchase. We show how the consumer can benefit from the implementation of such a mechanism, demonstrating an improvement in terms of consumer utility at different levels of price, with respect to other sorting traditionally adopted by platforms. We propose a utility function fitted to a Gumbel distribution, and we demonstrate a stochastic dominance of our model. Experimental evidences on the camera market category put in relevance the efficiency of our quality index for ranking the effective quality compared to the more traditional rating system. This is particularly true for the low-price accessory market segment of products, in which we show higher utility dominance and slightly higher elasticity of demand.Chapter 3 Price Matching and Platform Pricing Abstract In this study we investigate the effects of Price Matching Guarantees (PMG) commercial policies on U.S. online consumer electronics daily prices. By applying a Diff-in-Diff identification strategy we find evidence in favor of price reductions occurring after the PMG policy is repealed. We further investigate if such effect is heterogeneous according to products characteristics, by exploiting User Generated Contents (products popularity and quality) and online search visibility measures (Google Search Rank). Estimates suggest that for high quality (visibility) products PMG policies harms competition by keeping prices high, while for low quality (visibility) products, prices decrease during the policy validity period

A spectroscopic study of a large sample of L/T transition brown dwarfs

In this thesis I present the spectroscopic analysis of a large sample of L and T dwarfs, in order to constrain the sub-stellar initial mass function and formation history. The main points I tried to address are the development of a better spectral type to distance calibration and of a better spectral type to effective temperature calibration, and the identification of a statistically complete sample of brown dwarf to be used to measure the luminosity function, and therefore to constrain the initial mass function and formation history. To achieve the first goal I conducted the spectroscopic follow-up of brown dwarfs from the PARallaxes of Southern Extremely Cool objects (PARSEC) program. This is a large astrometric campaign to measure the parallaxes and proper motions of 120 L and T dwarfs in the southern hemisphere. I combined the astrometric results with the near infra-red spectra I obtained using the Ohio State Infra-Red Imager/Spectrometer (OSIRIS) on the Southern Astrophysical Research telescope (SOAR). That allowed me to investigate the nature of some unresolved binaries and common proper motion companion in the sample, as well as sub-dwarfs candidates, and potential members of young moving groups. Combining the spectra with the astrometric information and the available photometry I derived the bolometric luminosity and effective temperature for the targets, and determined a new polynomial conversion between spectral type and effective temperature of a brown dwarfs. This is a fundamental step to compare the results of empirical observations to numerical simulations of the sub-stellar luminosity function. Once refined the type to temperature calibration, I measured the luminosity function. In order to do so my collaborators and I have selected a sample of 250 brown dwarfs candidates from the United Kingdom Deep Infra-red Sky Survey (UKIDSS) Large Area Survey (LAS) and followed them up with the echelle spectrograph X-shooter on the Very Large Telescope. I present in this thesis the results of the observations of 196 of the brown dwarfs candidates. Using the X-shooter spectra I determined their spectral types, and I identified a number of unresolved binary candidates and peculiar objects. One of the peculiar objects in the sample, ULAS J222711004547, turned out to be the reddest brown dwarf observed so far, and I therefore proceeded to analyse further its spectrum. Applying a de-reddening technique to its spectrum suggests that the most likely reason for its redness is an excess of dust in its photosphere, and that can account for the differences seen between objects of similar spectral type. By comparing the results of the spectroscopic campaign to numerical simulations, I found that it is currently impossible to constrain robustly the initial mass function and formation history of sub-stellar objects, because of our limited knowledge of the binary fraction among brown dwarfs. The sample of binary candidates identified in this thesis can be used to place a better constraint on the binary fraction, but in order to do that the candidates need to be followed-up via high resolution imaging or radial velocity monitoring to confirm their binary nature

When Will It Finally End: The Effectiveness of the Rule 10b-5 Private Action as a Fraud-Deterrence Mechanism Post-Janus

The article discusses the Rule 10b-5 as a private method to limit the fraud-deterrence in the security for sales or purchase under the U.S. Securities Exchange Act. It mentions that the U.S. Supreme Court rejected the rule 10b-5 private actions liability for aiding and abetting. It states that the mutual fund company Janus Distribution LLC is responsible for the limitation of prevention of fraud because of escaping liability to the corporate officers for their unattributed misstatements

Linhas paralelas: os negros e os jornais na fotografia do século XIX

Existe uma coleção de fotografias que ocupa a contracorrente do discurso jornalístico sobre o cotidiano dos negros que viviam em Porto Alegre (Brasil). As cenas organizadas pelos Irmãos Ferrari, Virgílio Calegari e Lunara, entre o final do século XIX e meados do século XX, evidenciam elementos da pobreza em que os negros viviam e que se seguiu ao regime escravocrata: o traje descomposto e gasto que cobria os corpos, os pés invariavelmente descalços, o trabalho infantil ambulante e o ambiente doméstico dos lugares sem urbanização, em que se instalavam irregularmente. Nos jornais a Gazetinha, o Jornal da Tarde e O Independente, de Porto Alegre, os negros são associados à vagabundagem e bem localizados nos lugares “perigosos” da cidade. Há um ponto de tensão entre o que era dito na imprensa e o que foi visibilizado nas fotografias. Os elementos organizados na cena fotográfica possibilitam que se inicie um jogo de visibilidade/invisibilidade entre essas fotografias e os jornais, que produz certa descontinuidade no grande arquivo da época, voltado em sua quase totalidade às paisagens e retratos da burguesia. Antes que houvesse condições técnicas para a reprodução fotográfica na imprensa, os Irmãos Ferrari, Virgílio Calegari e Lunara demonstram uma prática, que se desvia da fotografia documental, em que o fotógrafo se ocupa do reconhecimento do presente que lhe corresponde. Palavras-chave: negros, jornalismo, fotografia, século XIX, Porto Alegre Abstract A collection of photographs taken between the end of the 19th century and the mid-20th century serves as a counterpoint to the journalistic discourse of the period on the daily life of black people in Porto Alegre (Brazil). The scenes photographed by the Ferrari Brothers, Virgilio Calegari and Lunara, show aspects of the poverty in which blacks lived following the end of slavery: they invariably appear shoeless, wearing worn and untidy clothes and living in squalid domestic environments in squatter settlements; there are children working at odd jobs. In the discursive space of the local newspapers Gazetinha, Jornal da Tarde and O Independente, blacks were represented as vagrants and associated with “dangerous” parts of the city. Their visibility in the photographs and invisibility in the press produces a discontinuity in the huge photographic archive of this period, which consists almost exclusively of landscapes and portraits of the bourgeoisie. It is argued that the Ferrari Brothers did not limit themselves to photography as a documentary practice, but deployed it as a way of recognizing the social realities of their time. Key words: blacks, journalism, photography, 19th century, Porto Alegr

Identifying the ejected population from disintegrating multiple systems

Kinematic studies of the Hipparcos catalogue have revealed associations that are best explained as disintegrating multiple systems, presumably resulting from a dynamical encounter between single/multiple systems in the field (Li et al. 2009). In this work we explore the possibility that known ultra-cool dwarfs may be components of disintegrating multiple systems, and consider the implications for the properties of these objects. We will present here the methods/techniques that can be used to search for and identify disintegrating benchmark systems in three database/catalogues: Dwarf Archive, the Hipparcos Main Catalogue, and the Gliese-Jahrei{\ss} Catalogue. Placing distance constraints on objects with parallax or colour-magnitude information from spectrophotometry allowed us to identify common distance associations. Proper motion measurements allowed us to separate common proper motion multiples from our sample of disintegrating candidates. Moreover, proper motion and positional information allowed us to select candidate systems based on relative component positions that were tracked back and projected forward through time. Using this method we identified one candidate disintegrating quadruple association, and two candidate disintegrating binaries, all of them containing one ultra-cool dwarf.Comment: 5 pages, 1 figure, proceeding of The 19th Cambridge Workshop on Cool Stars, Stellar Systems, and the Su