DE-PACRR: Exploring Layers Inside the PACRR Model

Recent neural IR models have demonstrated deep learning's utility in ad-hoc information retrieval. However, deep models have a reputation for being black boxes, and the roles of a neural IR model's components may not be obvious at first glance. In this work, we attempt to shed light on the inner workings of a recently proposed neural IR model, namely the PACRR model, by visualizing the output of intermediate layers and by investigating the relationship between intermediate weights and the ultimate relevance score produced. We highlight several insights, hoping that such insights will be generally applicable.Comment: Neu-IR 2017 SIGIR Workshop on Neural Information Retrieva

Product Variety under Brand Influence: An Empirical Investigation of Personal Computer Demand

Prior research suggests that brand may influence consumer preference for differentiated products. However, the extant literature does not measure how brand value affects product similarity and consumer choice. This paper examines demand response to the proliferation of personal computers (PCs). Using both the central processing unit (CPU) and brand as segmentation variables, I construct a two-level nested generalized extreme value (GEV) discrete choice model to estimate the brand values and product similarities of a set of PC vendors. With these estimates, I infer the relative efficacy of product variety for firms which possess different degrees of brand values. My results suggest that consumers treat PCs from the same firm as close substitutes, and the proximity of the PCs correlates positively with the firms?brand values. This finding suggests that there is decreasing demand returns to product variety for branded multiproduct firms. I discuss a few possible drivers of brand value, and explore the significance of product line extension in building long-term brand reputation.product variety, brand value, discrete choice, similarity, cannibalization

Technology Timing and Pricing In the Presence of an Installed Base

This paper studies a vendor.s timing and pricing strategies to tackle its own installed base when selling a newly improved product. We characterize the market with either a partly- or fully- covered installed base, consumers. relative willingness to pay for the newly improved version of the product, and their relative payoffs from delayed purchase. Instead of using the conventional assumption of constant consumer reservation price, we propose that if consumers already own an existing (old) version of a durable product, their willingness to purchase the newly improved version would increase over time. This effect, interweaving with consumer heterogeneity on valuation of quality and purchase history, may enable perfect intertemporal price discrimination (Salant 1989). We find that upgrade pricing may not be able to differentiate consumers with different purchase history when consumer heterogeneity is sufficiently high. Instead, the vendor would maximize its profit through intertemporal price discrimination, delayed product introduction, or pooling pricing. By overcoming the intractability of studying delayed product introduction in a market with heterogeneous consumers, this study analytically confirms Fishman and Rob.s conjecture (2000) that heterogeneity in consumers. valuation of quality may discourage a vendor to launch a new product. Particularly, consumers. anticipation of future price reduction can lead to delayed product introduction even when the extent of quality improvement embodied in the new product is high.New product introduction, intertemporal price discrimination, delayed product introduction, installed base, upgrade policy

The Economics of Privacy

This chapter reviews economic analyses of privacy. We begin by scrutinizing the “free market” critique of privacy regulation. Welfare may be non-monotone in the quantity of information, hence there may be excessive incentive to collect information. This result applies to both non-productive and productive information. Over-investment is exacerbated to the extent that personal information is exploited across markets. Further, the “free market” critique does not apply to overt and covert collection of information that directly causes harm. We then review research on property rights and challenges in determining their optimal allocation. We conclude with insights from recent empirical research and directions for future research.

Quantum Antiferromagnetism of Fermions in Optical Lattices with Half-filled p-band

We study Fermi gases in a three-dimensional optical lattice with five fermions per site, i.e. the s-band is completely filled and the p-band with three-fold degeneracy is half filled. We show that, for repulsive interaction between fermions, the system will exhibit spin-3/2 antiferromagnetic order at low temperature. This conclusion is obtained in strong interaction regime by strong coupling expansion which yields an isotropic spin-3/2 Heisenberg model, and also in weak interaction regime by Hatree-Fock mean-field theory and analysis of Fermi surface nesting. We show that the critical temperature for this antiferromagnetism of a p-band Mott insulator is about two orders of magnitudes higher than that of an $s$-band Mott insulator, which is close to the lowest temperature attainable nowadays

A Deterministic Equivalent for the Analysis of Non-Gaussian Correlated MIMO Multiple Access Channels

Large dimensional random matrix theory (RMT) has provided an efficient analytical tool to understand multiple-input multiple-output (MIMO) channels and to aid the design of MIMO wireless communication systems. However, previous studies based on large dimensional RMT rely on the assumption that the transmit correlation matrix is diagonal or the propagation channel matrix is Gaussian. There is an increasing interest in the channels where the transmit correlation matrices are generally nonnegative definite and the channel entries are non-Gaussian. This class of channel models appears in several applications in MIMO multiple access systems, such as small cell networks (SCNs). To address these problems, we use the generalized Lindeberg principle to show that the Stieltjes transforms of this class of random matrices with Gaussian or non-Gaussian independent entries coincide in the large dimensional regime. This result permits to derive the deterministic equivalents (e.g., the Stieltjes transform and the ergodic mutual information) for non-Gaussian MIMO channels from the known results developed for Gaussian MIMO channels, and is of great importance in characterizing the spectral efficiency of SCNs.Comment: This paper is the revision of the original manuscript titled "A Deterministic Equivalent for the Analysis of Small Cell Networks". We have revised the original manuscript and reworked on the organization to improve the presentation as well as readabilit