Diversifying Top-K Results

Top-k query processing finds a list of k results that have largest scores w.r.t the user given query, with the assumption that all the k results are independent to each other. In practice, some of the top-k results returned can be very similar to each other. As a result some of the top-k results returned are redundant. In the literature, diversified top-k search has been studied to return k results that take both score and diversity into consideration. Most existing solutions on diversified top-k search assume that scores of all the search results are given, and some works solve the diversity problem on a specific problem and can hardly be extended to general cases. In this paper, we study the diversified top-k search problem. We define a general diversified top-k search problem that only considers the similarity of the search results themselves. We propose a framework, such that most existing solutions for top-k query processing can be extended easily to handle diversified top-k search, by simply applying three new functions, a sufficient stop condition sufficient(), a necessary stop condition necessary(), and an algorithm for diversified top-k search on the current set of generated results, div-search-current(). We propose three new algorithms, namely, div-astar, div-dp, and div-cut to solve the div-search-current() problem. div-astar is an A* based algorithm, div-dp is an algorithm that decomposes the results into components which are searched using div-astar independently and combined using dynamic programming. div-cut further decomposes the current set of generated results using cut points and combines the results using sophisticated operations. We conducted extensive performance studies using two real datasets, enwiki and reuters. Our div-cut algorithm finds the optimal solution for diversified top-k search problem in seconds even for k as large as 2,000.Comment: VLDB201

Determinants of Crop Choices by Bangladeshi Farmers: A Bivariate Probit Analysis

Using a bivariate probit model, the study jointly determines the factors underlying the probability of Bangladeshi farmers adopting a diversified cropping system and/or modern rice technology. Results reveal that the availability of irrigation is the single most important determinant of the decision to adopt modern rice technology, and adoption is higher among the tenant farmers. The exact opposite is true for the likelihood of adopting a diversified cropping system, which is significantly higher in areas with no irrigation as well as among the owner- operators. Furthermore, the diversified cropping system has a significantly higher rate of adoption in regions with developed infrastructure. Farmers' education, farming experience, farm asset ownership, and non-agricultural income all positively influence crop diversification. Also, small farmers are more likely to adopt a diversified cropping system. Significant regional variation exists in the level of crop diversification as well. The decision to adopt a diversified cropping system and/or modern rice technology is significantly correlated, implying that a univariate analysis of such decision is biased. Crop diversification can be promoted by investing in farmers' education as well as rural infrastructure development. Also, land reform policies focusing on delegating land ownership to landless and marginal farmers, and tenurial reforms are noteworthy.

Combination of Spatial and Temporal Diversification in European Cropping Systems

There is a lack of results on the advantages and limitations of combining different crop diversification strategies both in time and space, which makes it difficult for famers and advisers to find relevant information for the transition towards more diversified cropping systems. A network of ten field experiments (diverIMPACTS project) was built across seven European countries, covering a range of pedo-climatic conditions and different farming systems: arable and vegetable systems under both conventional and organic management. Each field experiment tests one or several diversified cropping systems, which combine three diversification strategies with low input practices. These diversified cropping systems are compared to reference systems, which are less diversified and more dependent on external inputs. The three strategies of crop diversification are rotation, multiple cropping (growing different crop species on the same land within one growing season) and intercropping (growing different species in proximity on the same field). A diversified system includes, for example, the addition of cover crops or cash crops, such as legumes, for their expected ecosystem services, or crops for new markets (e.g hemp, lentil), the use of multiple cropping to increase productivity per year (e.g. winter barley with soybean) and intercropping (e.g. barley/pea,wheat/faba bean, oat/lupin) to increase productivity per unit of area and reduce external inputs. Expected impacts include: higher arable land productivity, diversification and increased farmer revenues through access to new markets and reduced economic risk, lower environmental impact through reduced use of pesticides, chemical fertilisers, energy and water, and improved delivery of ecosystem services, including biodiversity. The diversified cropping systems will be assessed using standardized measurements across the network and multi-criteria assessment tools. Decisions regarding the design and management of the diversified cropping systems will be recorded to support other diversification initiatives. The year 2018 is the first year of the network. This paper presents the original approach, the strategies designed in the network, and the assumptions concerning the interests to combine temporal and spatial diversification in order to improve the delivery of multiple services. This network will be a source of inspiration for other initiatives of crop diversification in Europe. The ultimate goal is to guide farmers in their transition towards more diversified cropping systems and to promote innovations by various actors at different scales (e.g. innovations regarding machinery for sowing or harvesting new sole or mixed crops, value-chains through the consolidation of new markets, new process of transformation, or adaptation of value-chains to intercropping)

Diversified Portfolios with Jumps in a Benchmark Framework

This paper considers diversifed portfolios in a sequence of jump diffusion market models. Conditions for the approximation of the growth optimal portfolio (GOP) by diversified portfolios are provided. Under realistic assumptions, it is shown that diversified portfolios approximate the GOP without requiring any major model specifications. This provides a basis for systematic use of diversified stock indices as proxies for the GOP in derivative pricing, risk management and portfolio optimization.benchmark model; growth optimal portfolio; diversi¯ed portfolio

Persistence of outstanding performance and shareholder value among diversified firms: The impact of past performance, efficient internal capital market, and relatedness of business segments

The research domain that attempts to study the relationship between diversification and performance has not yet reached definitive and interpretable findings, and recent studies challenge the existence of a "diversification discount" and explain it partially by a data artefact. None of these studies centred their research on the question: does there exist a specific performance pattern among diversified firms? This research aims to identify persistence in performance heterogeneity by measuring the shareholder value creation of diversified firms using alternative indicators other than the excess value methodology. It also aims to measure the impact on the performance according to the degree of efficiency of the internal capital market and the degree of relatedness among business segments. A sample of 164 diversified firms with turnover higher than 1$ billion during the period 1999-2006 is examined. Because of the presence of the firm's specific effect and the length of the time series, the persistence performance is tested through the instrumental variables (IV) system generalized method of moments (GMM) dynamic panel data and the persistence of shareholder value creation and destruction is estimated according to different estimators from top tercile and lower tercile portfolios of diversified firms. Some diversified firms persistently create value as well as beat the market index while others persistently underperform. Finally, if the efficiency of the internal capital market gives certain explanatory power of the performance pattern, but limited compared to the past performance, important insights might be drawn from the findings that diversified firms with segments in many unrelated industries perform better than others in few industries or with a high number of segments; hence the inverted-U curvilinear relationship between diversification and performance is here not confirmed.diversification; performance persistence; internal capital market; relatedness obusiness segments;

RISK AND RETURNS OF DIVERSIFIED CROPPING SYSTEMS UNDER NONNORMAL, CROSS-, AND AUTOCORRELATED COMMODITY PRICE STRUCTURES

This study analyzes the risks of diversified tropical cropping systems that combine cocoa, plantain, and tree-crop components in different proportions versus traditional monocultures. A technique for modeling the expected values, variances, and covariances of correlated time-series variables that are autocorrelated and nonnormal (right or left skewed and kurtotic) is applied to simulate commodity prices. The importance of using simulated cumulative density functions (cdf's) which reflect the most important characteristics of the stochastic behavior of prices for analyzing risk and returns of diversified agricultural systems is demonstrated. The analysis priovides evidence in favor of diversified cocoa-plantain-Cordia agroforestry system technologies versus the traditional monocultures.Demand and Price Analysis,

Modeling the Volatility and Expected Value of a Diversified World Index

This paper considers a diversified world stock index in a continuous financial market with the growth optimal portfolio (GOP) as the reference unit or benchmark. Diversified broadly based portfolios, which include major world stock market indices, are shown to approximate the GOP. It is demonstrated that a key financial quantity is the drift of the discounted GOP, which can be expressed explicitly using a certain quadratic variation term. Using real market approximations for the discounted GOP it is shown that its drift does not vary greatly in the long term. For a diversified world index this leads to a natural model where the discounted index is a time transformed squared Bessel process of dimension four. The inverse of the squared GOP volatility then follows a square root process of dimension four.world index; volatility; benchmark model; growth optimal portfolio; bessel process; square root process

Designing a flexible support system in dialogue with students to meet their needs

A more stringent financial climate, alongside technological and lifestyle changes, have diversified student needs and promoted the use of inclusive learning and support strategies. This paper reports on the development and evaluation of academic skills centres at an English Higher Education Institution and considers ways in which the service is able to benefit users and providers, it goes on to argue that, by fostering a dialogue with students and using a range of delivery models, the provision has been made flexible, diversified and student centred and thereby addresses issues of current significance within the institution and sector more broadly