Model-based Purchase Predictions for Large Assortments

Being able to accurately predict what a customer will purchase next is of paramount importance to successful online retailing. In practice, customer purchase history data is readily available to make such predictions, sometimes complemented with customer characteristics. Given the large assortments maintained by online retail- ers, scalability of the prediction method is just as important as its accuracy. We study two classes of models that use such data to predict what a customer will buy next: A novel approach that uses latent Dirichlet allocation (LDA), and mixtures of Dirichlet-Multinomials (MDM). A key benefit of a model-based approach is the potential to accommodate observed customer heterogeneity through the inclusion of predictor variables. We show that LDA can be extended in this direction while retaining its scalability. We apply the models to purchase data from an online re- tailer and contrast their predictive performance with that of a collaborative filter and a discrete choice model. Both LDA and MDM outperform the other meth- ods. Moreover, LDA attains performance similar to that of MDM while being far more scalable, rendering it a promising approach to purchase prediction in large assortments

Studies on helminthiasis in the pig

When this project was initiated in 1964, there was no comprehensive information available on the helminth fauna of British pigs. In order to establish a base for epidemiological studies, post-mortem material from 3,800 pigs was examined. Twelve helminth species were identified, including five not previously recorded from pigs in the United Kingdom, The incidence of Ascaris suum and Trichur is suis was found to decline with the increasing age of the host, whilst Oesophagostomum spp. and Hyostrongylus rubidus were encountered most frequently in the adult stock. The latter genera occurred in the greatest numbers in the spring and early summer. The significance of these observations, including the prominent role of the sow in the epidemiology of oesophagostomiasis, is discussed. Data collected from field studies showed that the number of Oesophagostomum ova shed in the faeces of sows is greatest when the piglets are suckling. After weaning, there is a sudden drop in values caused by the expulsion of adult worms. The periparturient rise in egg-counts does not take place if the progeny are taken away at birth. Smaller, regular peaks in the Oesophagostomum egg output of one non-pregnant sow coincided with oestrus. The administration of certain hormones (FSH and LH; progesterone; ACTH) modified this pattern. The periparturient egg-rise appears to enhance the opportunities for the transmission of infection to successive generations of pigs. In addition, biological pathways exist for the dispersion of larvae from the dung-pat. Third stage Oesophagostomum juveniles will, for example, coil around the abdomen of certain manure breeding flies (Psychoda spp.), which then function as transport hosts. Under laboratory conditions, porcine oesophagostome larvae can invade the intestinal mucosa of rats where they become encapsulated. If the rat tissues are fed to pigs they are able to resume their development and grow to maturity, A single dose of a broad spectrum anthelmintic given to gilts or sows one to two weeks before the expected date of farrowing was shown to eliminate the periparturient egg- rise. A new anthelmintic, 0,0-dimethyl-2,2-dichlorovinyl phosphate, was evaluated for the first time in adult pigs. It proved to be highly effective and well tolerated. Litters from sows treated with this compound were approximately 4% heavier at weaning than those from control dams. Other workers have demonstrated that one sequel of oesophagostomiasis in ruminants is an accelerated rate of plasma protein catabolism. It seemed possible therefore that the reduced growth-rate of infected piglets may be associated with a similar dysfunction. Serum samples from experimentally infected pigs did not, however, reveal any marked hypoalbuminaemia. When albumin catabolism was measured by studying the fate of injected 125l-albumin in parasitized and worm-free animals, no difference could be demonstrated. This result was confirmed by observing the rate of passage of 131l-polyvinylpyrrolidone into the gastro-intestinal tract following intravenous injection. Again, identical values were obtained for test and control animals. Finally, the use of the guinea-pig as a possible substitute for the pig in experimental Oesophagostomum infections was examined. It was discovered that larvae would invade the intestinal mucosa and that those remaining at this site formed the nucleus for nodule formation. Others migrated further to the mesenteric lymph nodes, peritoneum and liver. The worms neither grew nor moulted even though many remained alive for 48 days. The behaviour of Oesophagostomum in the guinea-pig thus differs from that normally displayed in the natural host

Engine system assessment study using Martian propellants

A top-level feasibility study was conducted that identified and characterized promising chemical propulsion system designs which use two or more of the following propellant combinations: LOX/H2, LOX/CH4, and LOX/CO. The engine systems examined emphasized the usage of common subsystem/component hardware where possible. In support of this study, numerous mission scenarios were characterized that used various combinations of Earth, lunar, and Mars propellants to establish engine system requirements to assess the promising engine system design concept examined, and to determine overall exploration leverage of such systems compared to state-of-the-art cryogenic (LOX/H2) propulsion systems. Initially in the study, critical propulsion system technologies were assessed. Candidate expander and gas generator cycle LOX/H2/CO, LOX/H2/CH4, and LOX/CO/CH4 engine system designs were parametrically evaluated. From this evaluation baseline, tripropellant Mars Transfer Vehicle (MTV) LOX cooled and bipropellant Lunar Excursion Vehicle (LEV) and Mars Excursion Vehicle (MEV) engine systems were identified. Representative tankage designs for a MTV were also investigated. Re-evaluation of the missions using the baseline engine design showed that in general the slightly lower performance, smaller, lower weight gas generator cycle-based engines required less overall mission Mars and in situ propellant production (ISPP) infrastructure support compared to the larger, heavier, higher performing expander cycle engine systems

Map of Athabasca River Basin within Alberta

Map of the Athabasca River Basin in green; lakes and rivers in blue; tan shaded Province of Alberta; names of surrounding provinces, etc.37