A Density-Based Approach to the Retrieval of Top-K Spatial Textual Clusters

Keyword-based web queries with local intent retrieve web content that is relevant to supplied keywords and that represent points of interest that are near the query location. Two broad categories of such queries exist. The first encompasses queries that retrieve single spatial web objects that each satisfy the query arguments. Most proposals belong to this category. The second category, to which this paper's proposal belongs, encompasses queries that support exploratory user behavior and retrieve sets of objects that represent regions of space that may be of interest to the user. Specifically, the paper proposes a new type of query, namely the top-k spatial textual clusters (k-STC) query that returns the top-k clusters that (i) are located the closest to a given query location, (ii) contain the most relevant objects with regard to given query keywords, and (iii) have an object density that exceeds a given threshold. To compute this query, we propose a basic algorithm that relies on on-line density-based clustering and exploits an early stop condition. To improve the response time, we design an advanced approach that includes three techniques: (i) an object skipping rule, (ii) spatially gridded posting lists, and (iii) a fast range query algorithm. An empirical study on real data demonstrates that the paper's proposals offer scalability and are capable of excellent performance

Do spatial constraints affect the job search efficiency?

Theoretical and empirical works on job search often neglect the role of unemployed environment like spatial constraints meets while searching for a job. This paper proposes a job search model where both the spatial search area and the reservation wage are assumed to be endogenous. We exploit data from a French survey conducted by Research Direction of Employment Ministry (DARES) to estimate the structural parameters of the model. First we estimate the choice of the search area, i.e. the choice between passive (receiving job offers through the local public employment agencies) and active strategies (extending the job search area using others search channels). Using a bivariate probit model, we highlight that this choice depends significantly on individual attributes and spatial constraints and that it affects job quality. Besides, the independence of irrelevant alternatives is not rejected. Secondly, using Gamma duration model we treat both individual and unobservable heterogeneity and the multiple destinations after unemployment (long-term jobs, short-term jobs and subsidised jobs). Moreover, estimations are made on sub-samples in which individuals are homogenous according to their level of diploma and their situation towards the unemployment insurance. Controlling for unobservable heterogeneity and selection bias, the econometric results show that the passive strategy is more efficient for lowgraduated people accessing a subsidised job. However, the active strategy is more efficient for high-graduated individuals accessing a full-term or a short-term job.job search, spatial constraints

Landscape heterogeneity influences on sheep habits under extensive grazing management in Southern Patagonia

In Southern Patagonia, continuous grazing with fixed stocking rates in large paddocks prevails over grazing systems subjected to regular evaluations and rotational rests. Because of this, sheep extensive systems need technologies to improve their production levels under sustainable management. In this context, the aim of this work was to provide knowledge of sheep habits (diet, daily activity and spatial distribution patterns) in seven paddocks at a production scale throughout the year in Southern Patagonia. The area is an extensive ecotone between forest and steppe, characterized by a rugged landscape with valleys and mountains. Three vegetation types were distinguished in each paddock: forest, steppe and wetland. After a two years trial, sheep showed an important array of strategies for facing restrictions imposed by climate and low forage availability. A strong dietary selectivity, a high percentage of time allocated to grazing, large explored areas and opportunistic selection of vegetation types explained the capacity for reproduction under Southern Patagonia harsh conditions. The application of an intensified management involving paddock subdivision and separation of vegetation types should consider how sheep grazing strategies are limited.Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria; Argentina. Universidad Nacional de la Patagonia Austral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

A grid-based infrastructure for distributed retrieval

In large-scale distributed retrieval, challenges of latency, heterogeneity, and dynamicity emphasise the importance of infrastructural support in reducing the development costs of state-of-the-art solutions. We present a service-based infrastructure for distributed retrieval which blends middleware facilities and a design framework to ‘lift’ the resource sharing approach and the computational services of a European Grid platform into the domain of e-Science applications. In this paper, we give an overview of the DILIGENT Search Framework and illustrate its exploitation in the field of Earth Science