User's Length Research Articles

Collaborative Filtering Recommendation on Users' Interest Sequences.

As an important factor for improving recommendations, time information has been introduced to model users’ dynamic preferences in many papers. However, the sequence of users’ behaviour is rarely studied in recommender systems. Due to the users’ unique behavior evolution patterns and personalized interest transitions among items, users’ similarity in sequential dimension should be introduced to further distinguish users’ preferences and interests. In this paper, we propose a new collaborative filtering recommendation method based on users’ interest sequences (IS) that rank users’ ratings or other online behaviors according to the timestamps when they occurred. This method extracts the semantics hidden in the interest sequences by the length of users’ longest common sub-IS (LCSIS) and the count of users’ total common sub-IS (ACSIS). Then, these semantics are utilized to obtain users’ IS-based similarities and, further, to refine the similarities acquired from traditional collaborative filtering approaches. With these updated similarities, transition characteristics and dynamic evolution patterns of users’ preferences are considered. Our new proposed method was compared with state-of-the-art time-aware collaborative filtering algorithms on datasets MovieLens, Flixster and Ciao. The experimental results validate that the proposed recommendation method is effective and outperforms several existing algorithms in the accuracy of rating prediction.

Groundwater use in developing cities: policy issues arising from current trends

Growing importance of urban groundwater use The objective of this essay is to promote dialogue on important policy issues for urban planning and development arising from increased dependence on groundwater for water-supply provision in developing cities. There is much indirect evidence (although no comprehensive data) to substantiate this trend, which is occurring in response to population growth, increasing per capita water use, higher ambient temperatures and reduced security of river intakes (due to quality degradation and climate change) having been facilitated by the modest cost of water wells and the fact that ‘aquifers lie within a well’s length of users’! (Foster et al. 1998). Where urban centres are underlain and/or surrounded by high-yielding aquifers, this has allowed water utilities to expand mains water-supply incrementally at modest capital cost—usually resulting in better mains water-service levels, lower water-supply prices and less private in-situ use. However, there are rarely sufficient groundwater resources within urban areas themselves to satisfy municipal water-supply demands and resource sustainability (both quantity and quality) will often become an issue. Growth in urban groundwater use is not restricted to cities with ready access to high-yielding aquifers but also widely occurs where the utility water supply is imported from considerable distance from a major surface water source. Here, private in-situ water-well construction has often increased rapidly as a result of poor (present or historic) municipal water-service levels and/or high water-supply prices. For example (Foster et al. 2010): In Peninsular India, water well use for urban residential self-supply is ubiquitous in the face of very poor utility water services (often 1-in-24 hours or less) and greatly reduces dependence on expensive tankered water supplies. In Brazil many cities experienced major private water-well drilling 15–20 years ago, in response to water-supply crises during extended drought, but such water wells continue because they provide a lower-cost water supply. In Sub-Saharan Africa, despite much higher unit costs of drilling, water wells (for direct water collection or reticulation to standposts) are widely the fastest growing source of urban water supply in the struggle to meet burgeoning demand. Appraisal of groundwater: sanitation nexus Urban groundwater quality is widely threatened by inadequately controlled pollution pressures, especially given the close connection between wastewater handling, disposal or reuse and underlying phreatic groundwater (Howard 2007). In-situ sanitation of urban areas presents a significant groundwater quality hazard, which must be recognised and managed. The hazard is further accentuated because self-supply from groundwater is generally more intensive where access is easiest—namely in the presence of shallow unconfined aquifers, which are the more vulnerable to pollution from the land surface. In most aquifer types, except the extremely vulnerable, there will be sufficient natural groundwater protection to eliminate faecal pathogens in percolating wastewater from in-situ urban sanitation although the hazard can increase markedly with sub-standard water-well construction and/or certain types of informal or illegal sanitation. However, elevated concentrations of N compounds (usually nitrate) and dissolved organic carbon (DOC) in groundwater will also be present to varying degrees according to the population density served by in-situ sanitation (Reynolds et al. 2002), and will persist (although generally to lesser degree) at depth in the aquifer. Such groundwater pollution widely persists for years after the source is removed, for example, by installation of main sewerage or another alternative sanitation system. Groundwater contamination can be much reduced by dry or eco-sanitation units, in which urine is separated from faeces and not discharged to the ground. The deployment of such units is highly recommended for new urbanisation overlying a shallow aquifer, but has limitations as a universal solution to urban groundwater contamination since it is difficult to imagine retro-installation in large numbers of existing properties given the current capital cost of US$ 900/unit and they will be unsuitable for certain cultural groups who use water for anal cleansing.