A Theoretical Analysis of Two-Stage Recommendation for Cold-Start Collaborative Filtering

In this paper, we present a theoretical framework for tackling the cold-start collaborative filtering problem, where unknown targets (items or users) keep coming to the system, and there is a limited number of resources (users or items) that can be allocated and related to them. The solution requires a trade-off between exploitation and exploration as with the limited recommendation opportunities, we need to, on one hand, allocate the most relevant resources right away, but, on the other hand, it is also necessary to allocate resources that are useful for learning the target's properties in order to recommend more relevant ones in the future. In this paper, we study a simple two-stage recommendation combining a sequential and a batch solution together. We first model the problem with the partially observable Markov decision process (POMDP) and provide an exact solution. Then, through an in-depth analysis over the POMDP value iteration solution, we identify that an exact solution can be abstracted as selecting resources that are not only highly relevant to the target according to the initial-stage information, but also highly correlated, either positively or negatively, with other potential resources for the next stage. With this finding, we propose an approximate solution to ease the intractability of the exact solution. Our initial results on synthetic data and the Movie Lens 100K dataset confirm the performance gains of our theoretical development and analysis

Cationic vacancy induced room-temperature ferromagnetism in transparent conducting anatase Ti_{1-x}Ta_xO_2 (x~0.05) thin films

We report room-temperature ferromagnetism in highly conducting transparent anatase Ti1-xTaxO2 (x~0.05) thin films grown by pulsed laser deposition on LaAlO3 substrates. Rutherford backscattering spectrometry (RBS), x-ray diffraction (XRD), proton induced x-ray emission (PIXE), x-ray absorption spectroscopy (XAS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) indicated negligible magnetic contaminants in the films. The presence of ferromagnetism with concomitant large carrier densities was determined by a combination of superconducting quantum interference device (SQUID) magnetometry, electrical transport measurements, soft x-ray magnetic circular dichroism (SXMCD), XAS, and optical magnetic circular dichroism (OMCD) and was supported by first-principle calculations. SXMCD and XAS measurements revealed a 90% contribution to ferromagnetism from the Ti ions and a 10% contribution from the O ions. RBS/channelling measurements show complete Ta substitution in the Ti sites though carrier activation was only 50% at 5% Ta concentration implying compensation by cationic defects. The role of Ti vacancy and Ti3+ was studied via XAS and x-ray photoemission spectroscopy (XPS) respectively. It was found that in films with strong ferromagnetism, the Ti vacancy signal was strong while Ti3+ signal was absent. We propose (in the absence of any obvious exchange mechanisms) that the localised magnetic moments, Ti vacancy sites, are ferromagnetically ordered by itinerant carriers. Cationic-defect-induced magnetism is an alternative route to ferromagnetism in wide-band-gap semiconducting oxides without any magnetic elements.Comment: 21 pages, 10 figures, to appear in Philosophical Transaction - Royal Soc.

Interactions between TRH and ethanol in the medial septum

When rats were pretreated with ethanol (3.0 g/kg, IP), subsequent microinjection of thyrotropin-releasing hormone (TRH) (500 or 1000 ng) into the medial septum, 30 minutes later, significantly shortened the time necessary for the rats to regain their righting reflex. Conversely, microinjection of TRH into the nucleus accumbens (1000 ng/side) or the area of the raphe obscurus (1000 ng) had no effect on ethanol-induced depression, although both of these structures mediate specific TRH effects in the CNS. In order to determine if this antagonism was due to a specific TRH interaction, TRH Fab fragments were microinjected into the medial septum just prior to the microinjection of TRH. Under these conditions, TRH did not alter ethanol’s depressant actions. Finally, this TRH antagonism of ethanol-induced depression appears attributable to a net increase in neuronal activity, because electrical stimulation (160 μA, 120 Hz, 1.5 msec duration) of the medial septum antagonized ethanol’s impairment of the righting reflex. These results are discussed in relationship to a potential CNS site for the action of ethanol

Enhancing topology adaptation in information-sharing social networks

The advent of Internet and World Wide Web has led to unprecedent growth of the information available. People usually face the information overload by following a limited number of sources which best fit their interests. It has thus become important to address issues like who gets followed and how to allow people to discover new and better information sources. In this paper we conduct an empirical analysis on different on-line social networking sites, and draw inspiration from its results to present different source selection strategies in an adaptive model for social recommendation. We show that local search rules which enhance the typical topological features of real social communities give rise to network configurations that are globally optimal. These rules create networks which are effective in information diffusion and resemble structures resulting from real social systems

A 5-HT1A agonist and a 5-HT2c antagonist reduce social interaction deficit induced by multiple ethanol withdrawals in rats

Repeated withdrawals from chronic forced ethanol exposure sensitize animals to withdrawal-induced deficits in social interaction behavior. The deficits in social interaction behavior following withdrawal from continuous ethanol exposure can be reduced following acute treatments with 5-HT2C antagonists or 5-HT1A agonists

SB242084, flumazenil, and CRA1000 block ethanol withdrawal–induced anxiety in rats

Anxiety-like behaviors are integral features of withdrawal from chronic ethanol exposure. In the experiments in the current study, we tested the hypothesis that anxiety can be regulated independently of other withdrawal signs and thus may be responsive to selective pharmacological agents. For 17 days, rats were fed ethanol (8–12 g/kg/day) in a liquid diet. Between 5 and 6 h after cessation of ethanol treatment, rats were tested in either the social interaction or plus-maze test of anxiety-like behavior after treatment with drugs hypothesized to have anxiolytic action. SB242084, flumazenil, and CRA1000—antagonists for 5-hydroxytryptamine (serotonin) (5-HT) 2C (5-HT2C), benzodiazepine, and corticotropin-releasing factor type 1 (CRF1) receptors, respectively—attenuated decreased social interaction without concomitant effects on activity measures. In contrast, ifenprodil, MDL 72222, and zolpidem—antagonists for N-methyl-d-aspartate (NMDA) and 5-HT3 receptors, and agonist for benzodiazepine type 1 receptors, respectively—did not share this effect. Results for SB242084, flumazenil, and ifenprodil in the elevated plus-maze test were comparable to those in the social interaction test. These results support the suggestion that multiple neuronal systems (CRF1, 5-HT2C, and benzodiazepine receptors) contribute to the ethanol withdrawal sign of decreased social interaction. Furthermore, the selective effects of pharmacological agents on social interaction seem to indicate that this behavior can be dissociated from other signs. Because anxiety may be a complicating factor in alcohol withdrawal and relapse, future studies of this type are needed to provide focus for the effort to define selective and novel antianxiety agents for these disorders

Mapping quantitative trait Loci for resistance to downy mildew in pearl millet: field and glasshouse screens detect the same QTL

Downy mildew, caused by the pathogen Sclerospora graminicola (Sacc.) J. Schrot, can cause devastating yield losses in pearl millet [Pennisetum glaucum (L.) R. Br.]. Breeding for resistance to downy mildew is facilitated by an artificial glasshouse screening method that can be used worldwide. Quantitative trait loci (QTLs) mapping was used to determine whether resistance QTLs identified under field conditions in India were also detected in glasshouse screens carried out in India and the UK. Quantitative trait loci were mapped using 114 individual pearl millet progeny derived from a resistant x susceptible cross: molecular marker mapping was carried out in an F2 population with restriction fragment length polymorphisms (RFLPs), and disease incidence was assessed on F4 families. Composite interval mapping (CIM) was used to detect associations between F4 family means and marker genotypes. Despite key environmental and methodological differences between the disease screens, the same two QTLs were detected in each screening environment. One QTL had a major effect and explained up to 60% of the phenotypic variation, while the other had a minor effect and explained up to 16% of the phenotypic variation. Two additional QTLs were also consistently detected across screens by examining pair-wise marker interactions. Multiple-trait interval mapping detected all of the QTLs that had been detected in individual screens, including the QTLs that had only been detected by examining pair-wise marker interactions, demonstrating its increased power over single trait mapping. Quantitative trait locus x environment interactions were significant at each QTL due to differences in the magnitude, rather than direction, of QTL effects. The differences in magnitude appeared to be a consequence of the degree of normality of the disease distribution, rather than any differences between screening methods