The BARISTA: A model for bid arrivals in online auctions

The arrival process of bidders and bids in online auctions is important for studying and modeling supply and demand in the online marketplace. A popular assumption in the online auction literature is that a Poisson bidder arrival process is a reasonable approximation. This approximation underlies theoretical derivations, statistical models and simulations used in field studies. However, when it comes to the bid arrivals, empirical research has shown that the process is far from Poisson, with early bidding and last-moment bids taking place. An additional feature that has been reported by various authors is an apparent self-similarity in the bid arrival process. Despite the wide evidence for the changing bidding intensities and the self-similarity, there has been no rigorous attempt at developing a model that adequately approximates bid arrivals and accounts for these features. The goal of this paper is to introduce a family of distributions that well-approximate the bid time distribution in hard-close auctions. We call this the BARISTA process (Bid ARrivals In STAges) because of its ability to generate different intensities at different stages. We describe the properties of this model, show how to simulate bid arrivals from it, and how to use it for estimation and inference. We illustrate its power and usefulness by fitting simulated and real data from eBay.com. Finally, we show how a Poisson bidder arrival process relates to a BARISTA bid arrival process.Comment: Published in at http://dx.doi.org/10.1214/07-AOAS117 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Effects of Selection on Morphological Characteristics in \u3ci\u3eSetaria sphacelata\u3c/i\u3e (Schumach.) Moss

Cattle production in Florida is limited by the lack of available warm-season forages adapted to the cool winters of the region. Setaria (S. sphacelata) has demonstrated green growth during cool conditions in subtropical climates around the world, and has the potential to fill this niche in cattle production in Florida. Four populations were selected in Gainesville and Ona, Florida: two cycles of selection for increased head number, one cycle for increased leaf width and one cycle for grazing tolerance. The objectives of this research were to compare these populations morphologically to determine changes due to selection. Selection for leaf width increased this trait while maintaining other morphological characteristics constant. Selection for head number decreased plant height and increased head number in each cycle, and decreased leaf width and inflorescence length in the second cycle. Selection for grazing regrowth resulted in reduced plant height and inflorescence length. Concern regarding susceptibility of Setaria to chinch bug and possible winter killing in Florida remain to be resolved before this species may be commercialized in Florida

Existence of Open Loop Equilibria for Disturbed Stackelberg Games

In this work, we derive necessary and sufficient conditions for the existence of an hierarchic equilibrium of a disturbed two player linear quadratic game with open loop information structure. A convexity condition guarantees the existence of a unique Stackelberg equilibria; this solution is first obtained in terms of a pair of symmetric Riccati equations and also in terms of a coupled of system of Riccati equations. In this latter case, the obtained equilibrium controls are of feedback type

Seleção de genótipos de Panicum maximum Jacq. para tolerância ao frio.

Com o objetivo de avaliar a tolerância de genótipos de P. maximum sob estresse térmico por baixas temperaturas, foi conduzido um experimento com dois genótipos e três cultivares (Mombaça, Massai e Tanzânia), no laboratório de fisiologia vegetal na Embrapa Gado de Corte, em três câmaras climáticas, durante 30 dias. O delineamento experimental foi de blocos casualizados com três repetições em esquema fatorial 5x3, com cinco genótipos e três temperaturas noturnas (12°C, 4°C e 0°C)

Approaches to calculate the dielectric function of ZnO around the band gap

Being one of the most sensitive methods for optical thin film metrology ellipsometry is widely used for the characterization of zinc oxide (ZnO), a key material for optoelectronics, photovoltaics, and printable electronics and in a range of critical applications. The dielectric function of ZnO has a special feature around the band gap dominated by a relatively sharp absorption feature and an excitonic peak. In this work we summarize and compare direct (point-by-point) and parametric approaches for the description of the dielectric function. We also investigate how the choice of the wavelength range influences the result, the fit quality and the sensitivity. Results on ZnO layers prepared by sputtering are presented

Selection of morphological traits to improve forage characteristics of Setaria sphacelata grown in Florida.

A genetically diverse population of Setaria sphacelata was developed at Gainesville, Florida by intercrossing the cultivars ?Narok?, ?Kazungula? and ?Solander? and a local persistent population. To determine heritability of traits that may improve setaria as a forage plant in Florida, progeny of the intercrossed population underwent two cycles of selection for inflorescence number and one cycle for leaf width. The selected populations, together with cultivars and introductions, were evaluated for morphological characters, yield and forage quality in field experiments with close- and wide-spaced plants. Increase of inflorescence number was not obtained by selection but resulted in decreased plant height, inflorescence length, yield, leaf width, and leafiness. Leaf width was increased by selection and was associated with increased leafiness and whole-plant crude protein content. The results suggest good prospects for selection of setaria cultivars suited to Florida with improved yield and quality providing they tolerate winter cold and reliably produce seed