Recommendation Subgraphs for Web Discovery

Recommendations are central to the utility of many websites including YouTube, Quora as well as popular e-commerce stores. Such sites typically contain a set of recommendations on every product page that enables visitors to easily navigate the website. Choosing an appropriate set of recommendations at each page is one of the key features of backend engines that have been deployed at several e-commerce sites. Specifically at BloomReach, an engine consisting of several independent components analyzes and optimizes its clients' websites. This paper focuses on the structure optimizer component which improves the website navigation experience that enables the discovery of novel content. We begin by formalizing the concept of recommendations used for discovery. We formulate this as a natural graph optimization problem which in its simplest case, reduces to a bipartite matching problem. In practice, solving these matching problems requires superlinear time and is not scalable. Also, implementing simple algorithms is critical in practice because they are significantly easier to maintain in production. This motivated us to analyze three methods for solving the problem in increasing order of sophistication: a sampling algorithm, a greedy algorithm and a more involved partitioning based algorithm. We first theoretically analyze the performance of these three methods on random graph models characterizing when each method will yield a solution of sufficient quality and the parameter ranges when more sophistication is needed. We complement this by providing an empirical analysis of these algorithms on simulated and real-world production data. Our results confirm that it is not always necessary to implement complicated algorithms in the real-world and that very good practical results can be obtained by using heuristics that are backed by the confidence of concrete theoretical guarantees

Analytical solution of a one-dimensional Ising model with zero temperature dynamics

The one-dimensional Ising model with nearest neighbour interactions and the zero-temperature dynamics recently considered by Lefevre and Dean -J. Phys. A: Math. Gen. {\bf 34}, L213 (2001)- is investigated. By introducing a particle-hole description, in which the holes are associated to the domain walls of the Ising model, an analytical solution is obtained. The result for the asymptotic energy agrees with that found in the mean field approximation.Comment: 6 pages, no figures; accepted in J. Phys. A: Math. Gen. (Letter to the Editor

A Model for the Propagation of Sound in Granular Materials

This paper presents a simple ball-and-spring model for the propagation of small amplitude vibrations in a granular material. In this model, the positional disorder in the sample is ignored and the particles are placed on the vertices of a square lattice. The inter-particle forces are modeled as linear springs, with the only disorder in the system coming from a random distribution of spring constants. Despite its apparent simplicity, this model is able to reproduce the complex frequency response seen in measurements of sound propagation in a granular system. In order to understand this behavior, the role of the resonance modes of the system is investigated. Finally, this simple model is generalized to include relaxation behavior in the force network -- a behavior which is also seen in real granular materials. This model gives quantitative agreement with experimental observations of relaxation.Comment: 21 pages, requires Harvard macros (9/91), 12 postscript figures not included, HLRZ preprint 6/93, (replacement has proper references included

Quitting patient care and career break intentions among general practitioners in South West England: findings of a census survey of general practitioners

Objective: Given recent concerns regarding general practitioner (GP) workforce capacity, we aimed to describe GPs’ career intentions, especially those which might impact on GP workforce availability over the next 5 years. Design: Census survey, conducted between April and June 2016 using postal and online responses , of all GPs on the National Health Service performers list and eligible to practise in primary care. Two reminders were used as necessary. Setting: South West England (population 3.5  million), a region with low overall socioeconomic deprivation. Participants: Eligible GPs were 2248 out of 3370 (67 % response rate). Main outcome measures: Reported likelihood of permanently leaving or reducing hours spent in direct patient care or of taking a career break within the next 5 years and present morale weighted for non-response. Results: Responders included 217 7 GPs engaged in patient care. Of these, 863 (37% weighted, 95%  CI 35 % to 39 %) reported a high likelihood of quitting direct patient care within the next 5 years. Overall, 1535 (70% weighted, 95%  CI 68 % to 72 %) respondents reported a career intention that would negatively impact GP workforce capacity over the next 5 years, through permanently leaving or reducing hours spent in direct patient care, or through taking a career break. GP age was an important predictor of career intentions; sharp increases in the proportion of GPs intending to quit patient care were evident from 52 years. Only 305 (14% weighted, 95%  CI 13 % to 16 %) reported high morale, while 1195 ( 54 % weighted, 95%  CI 52 % to 56 %) reported low morale. Low morale was particularly common among GP partners. Current morale strongly predicted GPs’ career intentions; those with very low morale were particularly likely to report intentions to quit patient care or to take a career break. Conclusions: A substantial majority of GPs in South West England report low morale. Many are considering career intentions which, if implemented, would adversely impact GP workforce capacity within a short time period. Study registration: NIHR HS&DR - 14/196/02, UKCRN ID 20700

An analysis of Australia's carbon pollution reduction scheme

The authors review the decision-making since the Labour Government came into office (November 2007). The Australian Government’s ‘Carbon Pollution Reduction Scheme’ White Paper (15 December 2008) proposes that an Australian Emissions Trading Scheme (AETS) be implemented in mid-2010. Acknowledging that the scheme is comprehensive, the paper finds that in many cases, Australia will take a softer approach to climate change through the AETS than the European Union ETS(EUETS). The paper assesses key issues in the White Paper such as emissions reduction targets, GHG coverage, sectoral coverage, inclusion of unlimited quantities of offsets from Kyoto international markets and exclusion of deforestation activities

Spectral Energy Distributions and Multiwavelength Selection of Type 1 Quasars

We present an analysis of the mid-infrared (MIR) and optical properties of type 1 (broad-line) quasars detected by the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z ~ 3, with predictions to z = 7. We demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei (AGNs) than MIR or optical colors alone. Composite spectral energy distributions (SEDs) are constructed for 259 quasars with both Sloan Digital Sky Survey and Spitzer photometry, supplemented by near-IR, GALEX, VLA, and ROSAT data, where available. We discuss how the spectral diversity of quasars influences the determination of bolometric luminosities and accretion rates; assuming the mean SED can lead to errors as large as 50% for individual quasars when inferring a bolometric luminosity from an optical luminosity. Finally, we show that careful consideration of the shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened/obscured AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio

Molecular Epidemiology of Adenovirus Type 7 in the United States, 1966–20001

Genetic variation among 166 isolates of human adenovirus 7 (Ad7) obtained from 1966 to 2000 from the United States and Eastern Ontario, Canada, was determined by genome restriction analysis. Most (65%) isolates were identified as Ad7b. Two genome types previously undocumented in North America were also identified: Ad7d2 (28%), which first appeared in 1993 and was later identified throughout the Midwest and Northeast of the United States and in Canada; and Ad7h (2%), which was identified only in the U.S. Southwest in 1998 and 2000. Since 1996, Ad7d2 has been responsible for several civilian outbreaks of Ad7 disease and was the primary cause of a large outbreak of respiratory illness at a military recruit training center. The appearance of Ad7d2 and Ad7h in North America represents recent introduction of these viruses from previously geographically restricted areas and may herald a shift in predominant genome type circulating in the United States

Characterization of human metapneumoviruses isolated from patients in North America.

Human metapneumovirus (HMPV) was recently identified in The Netherlands and was linked to acute respiratory tract illness. In this study, 11 isolates from 10 patients with respiratory disease from Quebec, Canada, were tested by a reverse-transcriptase polymerase chain reaction based on the fusion protein gene. Identified sequences were consistent with HMPV. The patients were 2 months to 87 years of age (median age, 58 years) and presented with acute respiratory tract illness during the winter season. Sequence studies of the nucleocapsid, fusion, and polymerase genes identified 2 main lineages of HMPV and cocirculation of both lineages during the same year. These findings support a previous finding that HMPV is a human respiratory pathogen that merits further study

China and the crisis : global power, domestic caution and local initiative

Even though the global crisis had a quick and dramatic impact on Chinese exports, the Chinese government responded with a range of policy responses that have helped maintain high rates of growth. This success has helped propel China to the centre of global politics, accelerating what many perceive to be a power shift from the West to China. But these gains were achieved by reversing policy in previous years designed to make a fundamental shift in China‟s mode of development, and have highlighted the problems associated with making such a transition. At the moment that many are looking at the Chinese "model" as a potential alternative to the Washington Consensus, one of the consequences of the crisis is to further question the long term efficacy of this "model" in China itself