Preferred Extension Research Articles

Bioenergy Production on Degraded Land: Landowner Perceptions in Central Kalimantan, Indonesia

Bioenergy production from degraded land provides an opportunity to secure a new renewable energy source to meet the rapid growth of energy demand in Indonesia while turning degraded land into productive landscape. However, bioenergy production would not be feasible without landowner participation. This study investigates factors affecting landowners’ preferences for bioenergy production by analyzing 150 landowners with fire experience in Buntoi village in Central Kalimantan using Firth’s logistic regression model. Results indicated that 76% of landowners preferred well-known species that have a readily available market such as sengon (Albizia chinensis (Osb.) Merr.) and rubber tree (Hevea brasiliensis Müll.Arg.) for restoration on degraded land. Only 8% of preferred nyamplung (Calophyllum inophyllum L.) for bioenergy production; these particular landowners revealed a capacity to handle the uncertainty of the bioenergy market because they had additional jobs and income, had migrated from Java where nyamplung is prevalent, and preferred agricultural extension to improve their technical capacity. These results contribute to identifying key conditions for a bottom-up approach to bioenergy production from degraded land in Indonesia: a stable bioenergy market for landowners, application of familiar bioenergy species, and agricultural extension support for capacity building.

Predictive models and abstract argumentation: the case of high-complexity semantics

AbstractIn this paper, we describe how predictive models can be positively exploited in abstract argumentation. In particular, we present two main sets of results. On one side, we show that predictive models are effective for performing algorithm selection in order to determine which approach is better to enumerate the preferred extensions of a given argumentation framework. On the other side, we show that predictive models predict significant aspects of the solution to the preferred extensions enumeration problem. By exploiting an extensive set of argumentation framework features—that is, values that summarize a potentially important property of a framework—the proposed approach is able to provide an accurate prediction about which algorithm would be faster on a given problem instance, as well as of the structure of the solution, where the complete knowledge of such structure would require a computationally hard problem to be solved. Improving the ability of existing argumentation-based systems to support human sense-making and decision processes is just one of the possible exploitations of such knowledge obtained in an inexpensive way.

Manipulability in a group activity selection problem

We consider the aspect of strategic manipulation in a group activity selection problem. Given a set of activities in which they might participate, the agents have preferences over the activities themselves and over the number of participants in the activities; the goal is to assign agents to activities on basis of their preferences. In this paper, we consider the possibility of strategic manipulation involved in providing solutions in such a setting, for the solution concepts of maximum individual rationality, core stability, and Pareto optimality respectively. For three different preference extensions (Gärdenfors extension, maxi–min extension and maxi–max extension) we analyze strategic manipulability with respect to the number of activities available. In general, the considered solution concepts turn out to be prone to strategic manipulation; in some natural special cases, however, strategyproofness is provided by such an aggregation.

On the tradeoff between efficiency and strategyproofness

We study social decision schemes (SDSs), i.e., functions that map a collection of individual preferences over alternatives to a lottery over the alternatives. Depending on how preferences over alternatives are extended to preferences over lotteries, there are varying degrees of efficiency and strategyproofness. In this paper, we consider four such preference extensions: stochastic dominance (SD), a strengthening of SD based on pairwise comparisons (PC), a weakening of SD called bilinear dominance (BD), and an even weaker extension based on Savage's sure-thing principle (ST). While random serial dictatorships are PC-strategyproof, they only satisfy ex post efficiency. On the other hand, we show that strict maximal lotteries are PC-efficient and ST-strategyproof. We also prove the incompatibility of (i)PC-efficiency and PC-strategyproofness for anonymous and neutral SDSs, (ii) ex post efficiency and BD-strategyproofness for pairwise SDSs, and (iii) ex post efficiency and BD-group-strategyproofness for anonymous and neutral SDSs.

Characteristics of free-range chicken production in Ogun State, Nigeria

The study investigated personal characteristics of respondents, habits and practices, numbers of chickens and other animals cared for, causes of chicken loss, chickens’ diseases and health care awareness by respondents, and preferred extension capability to provide linkage services. Fifty farmers were selected using multi-stage sampling procedure. Data were collected with the administration of structured questionnaire and analyzed with frequency counts and percentages. Results showed that 70% of respondents were female and 42% were within 18 to 45 age bracket. Adult female (48%) spend the most time caring for the chickens while, 30% and 24% keep chickens for sales and consumption respectively. 76% provide housing, 74% provided feed-supplement and 80% give medication to support their flocks like intensive system. Predators (40%) and diseases (36%) were the main causes of poultry loss. Continuous sensitization on basic information about chicken care (100%) and market accessibility (76.51%) were some of the preferred extension capability by farmers. Continuous training and provision of linkage services in terms of simple housing, feed-supplement, vaccination against Newcastle-Disease and deworming of birds) are recommended extension capability to develop FPP business. Keywords: Free-Range Chickens

The Impact of Farm Visits on Farmers’ Satisfaction with Extension: Examining the Dependence on Individual Methods in the Caribbean

This research sought to investigate the dependence on farm visits in selected Caribbean islands, and estimate the impact of such visits on farmers’ satisfaction with extension. The study utilized a causal-comparative design using a convenience sample from six major farming countries in the Eastern Caribbean. Descriptive frequencies, ANOVA, principal factor analysis, and hierarchical OLS regression models were presented. It appears the low use of alternate approaches to disseminate information to eastern Caribbean farmers has led to a dependency on farm visits. This is unsustainable primarily because of its high cost, given the financial constraints of countries. Results indicated that while farmers were fairly satisfied with extension, there was a significant difference in satisfaction based on country of residence, and frequency of farm visits was a significant moderator of satisfaction. Countries’ GDP per capita were consistent with satisfaction levels. Proactive initiatives by extension that focus on alternative education approaches are needed; farmers can be clustered into commodity groups and extension can also make use of the good ICT infrastructure in these countries. Extension can influence farmers’ expectations if it capitalizes on other approaches such as ICTs and group visits. Effective use of alternative lower-cost approaches can result in greater ability to deliver each dimension of quality and match farmers’ expectations. Farm visits have become entrenched as the preferred extension method in the Caribbean. This first-time study, which looks at the issue from an extension and economic perspective, shows the urgent need to revisit the farm visit approach to extension.

On the impact of configuration on abstract argumentation automated reasoning

In this paper we consider the impact of configuration of abstract argumentation reasoners both when using a single solver and choosing combinations of framework representation–solver options; and also when composing portfolios of algorithms.To exemplify the impact of the framework–solver configuration we consider one of the most configurable solvers, namely ArgSemSAT—runner-up of the last competition on computational models of argumentation (ICCMA-15)—for enumerating preferred extensions. We discuss how to configure the representation of the argumentation framework in the input file and show how this coupled framework–solver configuration can have a remarkable impact on performance.As to the impact of configuring differently structured portfolios of abstract argumentation solvers, we consider the solvers submitted to ICCMA-15, which provided the community with a heterogeneous panorama of approaches for handling abstract argumentation frameworks. A superficial reading of the results of ICCMA-15 is that reduction-based systems (either SAT-based or ASP-based) are always the most efficient. Our investigation, concerning the enumeration of stable and preferred extensions, shows that this is not true in full generality and suggests the areas where the relatively under-developed non-reduction-based systems should focus more to improve their performance. Moreover, it also highlights that the state-of-the-art solvers are very complementary and can be successfully combined in portfolios.

Coincidence of Condorcet committees

The Condorcet Committee a la Gehrlein (CCG) is a fixed-size subset of candidates such that each of its members defeats in a pairwise contest any candidate outside. The Condorcet Committee a la Fishburn (CCF) is a fixed-size subset of candidates that is preferred to all other subsets of the same size by a majority of voters. In general, these two types of Condorcet committees may not always exist. Kaymak and Sanver (Soc Choice Welf 20:477–494, 2003) studied the conditions under which the CCF exists under a large class of extensions of preferences. We focus here on the most important members of their class, the lexicographic extension of preferences, and we define more precisely, the conditions under which these committees coincide when they exist. Our results depart from the rather optimistic conclusions of Kaymak and Sanver (Soc Choice Welf 20:477–494, 2003) on the coincidence between the CCG and the CCF. We exhibit profiles for which the CCF is empty while the CCG exists and the preferences are all of lexicographic type. Furthermore, we obtain the same conclusion when we derive preferences on candidates from those on sets of candidates using the separability assumption.

Impossibilities for probabilistic assignment

We consider the problem of assigning objects probabilistically among a group of agents who may have multi-unit demands. Each agent has linear preferences over the (set of) objects. The most commonly used extension of preferences to compare probabilistic assignments is by means of stochastic dominance, which leads to corresponding notions of envy-freeness, efficiency, and strategy-proofness. We show that equal treatment of equals, efficiency, and strategy-proofness are incompatible. Moreover, anonymity, neutrality, efficiency, and weak strategy-proofness are incompatible. If we strengthen weak strategy-proofness to weak group strategy-proofness, then when agents have single-unit demands, anonymity, neutrality, efficiency, and weak group strategy-proofness become incompatible.

Deformation twinning in rolled WE43-T5 rare earth magnesium alloy: Influence on strain hardening and texture evolution

Insights from a detailed investigation into the anisotropic strain hardening, tension/compression yield asymmetry, and evolution of crystallographic texture of rolled WE43 rare earth magnesium alloy during quasi-static tension and compression at room temperature are presented in this paper. It is seen that WE43 exhibits monotonically falling normalized strain hardening rates during both tension and compression in multiple loading directions, which is unusual for Mg alloys. Moreover, the difference in strain hardening in tension and compression subsequent to initial yield is observed to be very small and, as a result, the tension/compression asymmetry is not pronounced. Nevertheless, crystallographic texture evolves substantially, where crystals before deformation oriented with their crystallographic c-axis parallel with the normal direction (ND) and slightly tilted towards the rolling direction (RD) of the plate reorient their c-axis nearly parallel to the compression direction for every testing direction. Amount of deformation twinning in WE43 with plastic strain is quantified here for the first time and correlated with the above-described aspects of plastic deformation and texture evolution. In doing so, we confirm that the 101¯21¯011 twin is the preferred extension twin in WE43 just like in many Mg alloys. Besides, we find a substantial activity of another c-axis extension twinning mode 112¯11¯1¯26 in WE43, which is another unusual observation for Mg alloys. Activity of the c-axis contraction twins was found to be negligible. The falling strain hardening rates in WE43 are rationalized here to be a consequence of: (1) modest texture hardening because the activation stress for pyramidal slip systems is similar in magnitude to those of basal and prismatic slip systems, (2) small Hall-Petch-like hardening effect due to extension twinning because of their transmissivity to slip and rapid growth, and (3) negligible Hall-Petch-like hardening effect due to contraction twinning because of their small activity.

Canonical utility functions and continuous preference extensions

I define canonical utility functions via an explicit formula that inherits semicontinuity, continuity, Cauchy continuity, and uniform continuity from preferences. This construction is used to (i)show Rader’s and Debreu’s theorems in a fast and transparent way,(ii)refine these results for Cauchy and uniformly continuous preferences on a metric space X,(iii)extend such preferences from X to any larger metric domain Y⊃X, while preserving Cauchy and uniform continuity respectively. By contrast, regular continuity does not guarantee that continuous preference extensions should exist even in standard decision theoretic frameworks. For example, continuous preferences over simple lotteries or finite menus need not have continuous extensions to Borel distributions or compact menus respectively.

Power set extensions of dichotomous preferences

In this paper we assume that a set X is partitioned into two indifference classes and study several ways in which this dichotomous information can be extended, so as to obtain an ordering of the power set of X. The axioms that we introduce enable such a partition of X to be interpreted as being made out of “good” and “bad” objects. We define a family of rules that naturally take into account the number of good objects and the number of bad objects, and provide axiomatic characterizations of different rules in the family that fit into a variety of decisional situations.

Operational challenges faced by smallholder farmers: a case of Ethekwini Metropolitan in South Africa

The study is aimed at establishing the impact of access to capital, access to markets, access to information and access to technology on competitiveness of smallholder farmers on the market in Ethekwini Metropolitan in South Africa. A questionnaire is used as a research instrument. A total of 100 participants was sampled from a population of 485 smallholder farmers in Ethekwini Metropolitan. From the sample, 21% were male and 79% were female. All respondents were all from the African race. The study reveales that access to funding, access to markets, access to information and access to technology not only influenced viability of the smallholder farmers in Ethekwini Metropolitan, but also that the smallholder farmers were not getting enough access to all four stated variables. Of the 100 farmers, 66% of the smallholder farmers had plots with less than 0.5 acres under cultivation. Another finding was that even though the farmers had basic tools to work with, they required funding to acquire irrigation, water storage facilities, transport and tractors. As far as passing information to farmers is concerned, the farmers mostly preferred extension visits.The study recommends that well equipped agricultural resource centres be established in all the agricultural hubs. It is also recommended that the government employs an asset based community development approach when funding smallholder farmers and that the smallholder farmers and other stakeholders be conscientized on the concept of sustainable farming

Gender perspectives in use of extension services in Maharashtra

Present investigation was carried out in six agro-climatic zones of Maharashtra viz., South Konkan Coastal, North Konkan Coastal, Western Ghat, Sub montane, Western Maharashtra Plain and Eastern Vidarbha. From each zone one district, from each district two blocks and from each block five villages were randomly selected. From each village 30 households (30 male and 30 female) were selected randomly. Hence, from each zone 150 households (150 male and 150 female = 300) were randomly selected. The total households selected from six zones were 900 and the total respondents selected were 1800. The results indicated that VLEW, NGO personnel and Bank personnel were known to rural men and women. Frequency of contact was meagre. Demonstration was found to be mostly preferred extension method. Shortage of time, personnel involved are men were the reasons given by the rural women and venue of the programme was not convenient and the programmes were organized without prior notice were the reasons given by the rural men for not availing extension services.

Manipulability in a Group Activity Selection Problem

We consider the aspect of strategic manipulation in the group activity selection problem GASP. In that problem, the goal is to assign agents to activities when the agents have preferences over the activities themselves and over the number of participants in the activities, that is preferences over pairs “(activity, group size)”, including the possibility “do nothing”. In such a setting the main, natural solution concept studied in Darmann et al. (2012) to aggregate the agents’ preferences into a group solution is maximum individual rationality: the aim is to assign the maximum number of agents to activities in a way such that no agent prefers doing nothing to the actual choice. In this paper, we consider the possibility of strategic manipulation involved in providing such solutions. We adapt and analyze well-known preference extensions such as the Kelly extension and the Gardenfors extension in our setting. In addition, for some special cases inherent in the model of GASP we show that strategyproofness is provided by such an aggregation, while for others this is not the case.

Finding Strategyproof Social Choice Functions via SAT Solving

A promising direction in computational social choice is to address research problems using computer-aided proving techniques. In particular with SAT solvers, this approach has been shown to be viable not only for proving classic impossibility theorems such as Arrow's Theorem but also for finding new impossibilities in the context of preference extensions. In this paper, we demonstrate that these computer-aided techniques can also be applied to improve our understanding of strategyproof irresolute social choice functions. These functions, however, requires a more evolved encoding as otherwise the search space rapidly becomes much too large. Our contribution is two-fold: We present an efficient encoding for translating such problems to SAT and leverage this encoding to prove new results about strategyproofness with respect to Kelly's and Fishburn's preference extensions. For example, we show that no Pareto-optimal majoritarian social choice function satisfies Fishburn-strategyproofness. Furthermore, we explain how human-readable proofs of such results can be extracted from minimal unsatisfiable cores of the corresponding SAT formulas.

Value-based argumentation framework built from prioritized qualitative choice logic

Abstract The notion of preference is crucial in many fields. This justifies the development of many formalisms for preferences representation such as CP-nets, qualitative choice logic and its extensions. Preferences help to choose the best option in decision making, to compare between arguments in argumentation theory, etc. In this paper, we establish a link between a preference formalism, called Prioritized Qualitative Choice Logic (PQCL) and argumentation theory. We show that for any set of preferences expressed using PQCL (called PQCL theory), a Value-based Argumentation Framework (VAF) can be built. However, we point out some problems related to the evaluation of arguments which does not guarantee the correspondence between elements of PQCL theory and those of its associated VAF. We show that the major problem is due to the evaluation of arguments defined in existing argumentation frameworks, where an absolute status is assigned to each argument: objectively (or skeptically) accepted if it belongs to every extension, subjectively (or credulously) accepted if it is in some extensions and not in others and rejected if it does not belong to any extension. To deal with this problem, we propose to revise the evaluation of arguments in the corresponding VAF. As a result, there is a direct relationship between preferred extensions of the corresponding VAF and preferred models of a set of preferences expressed using PQCL. In addition, rank ordering the set of arguments is possible. The relationship between the two formalisms is interesting since on the one hand, it points out that one should be careful in using argumentation theory for decision making purposes or in formalizing a given problem as an argumentation framework and on the other hand, it makes it possible to use an argumentation framework for preference elicitation.

Exploiting Parallelism for Hard Problems in Abstract Argumentation

Abstract argumentation framework (AF) is a unifying framework able to encompass a variety of nonmonotonic reasoning approaches, logic programming and computational argumentation. Yet, efficient approaches for most of the decision and enumeration problems associated to AFs are missing, thus limiting the efficacy of argumentation-based approaches in real domains. In this paper, we present an algorithm for enumerating the preferred extensions of abstract argumentation frameworks which exploits parallel computation. To this purpose, the SCC-recursive semantics definition schema is adopted, where extensions are defined at the level of specific sub-frameworks. The algorithm shows significant performance improvements in large frameworks, in terms of number of solutions found and speedup.

Set-monotonicity implies Kelly-strategyproofness

This paper studies the strategic manipulation of set-valued social choice functions according to Kelly’s preference extension, which prescribes that one set of alternatives is preferred to another if and only if all elements of the former are preferred to all elements of the latter. It is shown that set-monotonicity—a new variant of Maskin-monotonicity—implies Kelly-strategyproofness in comprehensive subdomains of the linear domain. Interestingly, there are a handful of appealing Condorcet extensions—such as the top cycle, the minimal covering set, and the bipartisan set—that satisfy set-monotonicity even in the unrestricted linear domain, thereby answering questions raised independently by Barbera (J Econ Theory 15(2):266–278(1977a)) and Kelly (Econometrica 45(2):439–446 (1977)).

Ranking sets of interacting objects via semivalues

In this paper, we address the problem of how to extend a ranking over single objects to another ranking over all possible collections of objects, taking into account the fact that objects grouped together can have mutual interaction. An answer to this issue is provided using game theory and, specifically, the fact that an extension (i.e. a total preorder on the set of all subsets of objects) must be aligned with some probabilistic value, in the sense that the ranking of the objects (according to some probabilistic value computed on a numerical representation of the extension) must also preserve the primitive preorder on the singletons, no matter which utility function is used to represent the extension. We characterize families of aligned extensions, we focus on their geometric properties and we provide algorithms to verify their alignments. We also show that the framework introduced in this paper may be used to study a new class of extension problems, which integrate some features dealing with risk and complete uncertainty within the class of preference extension problems known in the literature with the name of sets as final outcomes.