Product Variety, Across-Market Demand Heterogeneity, and the Value of Online Retail

Online retail gives consumers access to an astonishing variety of products. However, the additional value created by this variety depends on the extent to which local retailers already satisfy local demand. To quantify the gains and account for local demand, we use detailed data from an online retailer and propose methodology to address a common issue in such data - sparsity of local sales due to sampling and a significant number of local zeros. Our estimates indicate products face substantial demand heterogeneity across markets; as a result, we find gains from online variety that are 30% lower than previous studies

Product Variety, Across-Market Demand Heterogeneity, and the Value of Online Retail

Online retail gives consumers access to an astonishing variety of products. However, the additional value created by this variety depends on the extent to which local retailers already satisfy local demand. To quantify the gains and account for local demand, we use detailed data from an online retailer and propose methodology to address a common issue in such data - sparsity of local sales due to sampling and a significant number of local zeros. Our estimates indicate products face substantial demand heterogeneity across markets; as a result, we find gains from online variety that are 30% lower than previous studies

Product Variety, Across-Market Demand Heterogeneity, and the Value of Online Retail

Online retail gives consumers access to an astonishing variety of products. However, the additional value created by this variety depends on the extent to which local retailers already satisfy local demand. To quantify the gains and account for local demand, we use detailed data from an online retailer and propose methodology to address a common issue in such data-sparsity of local sales due to sampling and a significant number of local zeros. Our estimates indicate products face substantial demand heterogeneity across markets; as a result, we find gains from online variety that are 45% lower than previous studies

Product Variety, Across-Market Demand Heterogeneity, and the Value of Online Retail

Online retail gives consumers access to an astonishing variety of products. However, the additional value created by this variety depends on the extent to which local retailers already satisfy local demand. To quantify the gains and account for local demand, we use detailed data from an online retailer and propose methodology to address a common issue in such data-sparsity of local sales due to sampling and a significant number of local zeros. Our estimates indicate products face substantial demand heterogeneity across markets; as a result, we find gains from online variety that are 45% lower than previous studies

Which anthropometric and lower body power variables are predictive of professional and amateur playing status in male rugby union players?

The purpose of this study was to compare anthropometric and lower body power measurements between current professional and amateur male rugby union players. The present study also sought to determine which anthropometric and physical performance variables were predictive of playing standard. Thirty professional and 30 amateur RU players performed Wattbike 6 s maximal effort (WB6S) and countermovement (CMJ) and squat jump (SJ) assessments, anthropometric measures were also taken. Dependant variables recorded and analysed including: body mass, stature, Σ8 site skinfolds, WB6S absolute and relative peak power, CMJ and SJ average concentric force, jump height, peak velocity, time to peak force, rate of force development (RFD) and absolute and relative peak force and power. Professional players were heavier, taller and leaner than their amateur counterparts (p < 0.05). Professional players performed significantly better in all physical performance measures except CMJ and SJ time to peak force, CMJ RFD and SJ relative peak force. Variables which were predictive of playing standard were: Σ8 skinfolds, CMJ peak velocity and WB6S absolute and relative peak power (p < 0.05). These findings indicate that the current body of male professional RU players is anthropometrically and physically superior to their amateur counterparts, although not all variables assessed here were predictive of playing standard. Data presented here indicate that Σ8 skinfolds, WB6S absolute and relative power and CMJ peak velocity are predictive of playing standard, whereas other anthropometric and strength and power variables are not

Proudman resonance with tides, bathymetry and variable atmospheric forcings

Proudman resonance is a primary amplification mechanism for meteotsunamis, which are shallow-water waves generated by atmospheric forcings. The effect of tides, sloping bathymetry and the speed, amplitude and aspect ratio of the atmospheric forcing on Proudman resonant wave growth are investigated using analytical approximations and numerical models. With tides included, maximum wave growth through Proudman resonance occurred when the atmospheric-forcing speed matched the tidal-wave speed. Growth greater than Proudman resonance occurred with a positive tidal elevation together with a tidal current in the opposite direction to wave propagation, due to linear growth combined with further amplification from wave-flux conservation. Near-Proudman resonant growth occurred when the forced-wave speed or free-wave speed varied by either a small amount, or varied rapidly, around a speed appropriate for Proudman resonance. For a forcing moving at Proudman resonant speed, resultant wave growth was proportional to the total, time-integrated forcing amplitude. Finally, Proudman resonant wave growth was lower for forcings with lower aspect ratios (AP), partly because forced-wave heights are proportional to 1 + A 2P , but also because free waves could spread in two dimensions. Whilst the assumptions of strict Proudman resonance are never met, near-Proudman resonant growth may occur over hundreds of kilometres if the effective Froude number is near 1 and the resultant wave propagates predominantly in one dimension

CFD Code Validation of Wall Heat Fluxes for a G02/GH2 Single Element Combustor

This paper puts forth the case for the need for improved injector design tools to meet NASA s Vision for Space Exploration goals. Requirements for this improved tool are outlined and discussed. The potential for Computational Fluid Dynamics (CFD) to meet these requirements is noted along with its current shortcomings, especially relative to demonstrated solution accuracy. The concept of verification and validation is introduced as the primary process for building and quantifying the confidence necessary for CFD to be useful as an injector design tool. The verification and validation process is considered in the context of the Marshall Space Flight Center (MSFC) Combustion Devices CFD Simulation Capability Roadmap via the Simulation Readiness Level (SRL) concept. The portion of the validation process which demonstrates the ability of a CFD code to simulate heat fluxes to a rocket engine combustor wall is the focus of the current effort. The FDNS and Loci-CHEM codes are used to simulate a shear coaxial single element G02/GH2 injector experiment. The experiment was conducted a t a chamber pressure of 750 psia using hot propellants from preburners. A measured wall temperature profile is used as a boundary condition to facilitate the calculations. Converged solutions, obtained from both codes by using wall functions with the K-E turbulence model and integrating to the wall using Mentor s baseline turbulence model, are compared to the experimental data. The initial solutions from both codes revealed significant issues with the wall function implementation associated with the recirculation zone between the shear coaxial jet and the chamber wall. The FDNS solution with a corrected implementation shows marked improvement in overall character and level of comparison to the data. With the FDNS code, integrating to the wall with Mentor s baseline turbulence model actually produce a degraded solution when compared to the wall function solution with the K--E model. The Loci-CHEM solution, produced by integrating to the wall with Mentor s baseline turbulence model, matches both the heat flux rise rate in the near injector region and the peak heat flux level very well. However, it moderately over predicts the heat fluxes downstream of the reattachment point. The Loci-CHEM solution achieved by integrating to the wall with Mentor s baseline turbulence model was clearly superior to the other solutions produced in this effort

OSIRIS-REx Touch-And-Go (TAG) Mission Design and Analysis

The Origins Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-REx) mission is a NASA New Frontiers mission launching in 2016 to rendezvous with the near-Earth asteroid (101955) 1999 RQ36 in late 2018. After several months in formation with and orbit about the asteroid, OSIRIS-REx will fly a Touch-And-Go (TAG) trajectory to the asteroid s surface to obtain a regolith sample. This paper describes the mission design of the TAG sequence and the propulsive maneuvers required to achieve the trajectory. This paper also shows preliminary results of orbit covariance analysis and Monte-Carlo analysis that demonstrate the ability to arrive at a targeted location on the surface of RQ36 within a 25 meter radius with 98.3% confidence