Intermediate Solution Research Articles

Conservative and Adaptive Penalty for Model-Based Safe Reinforcement Learning

Reinforcement Learning (RL) agents in the real world must satisfy safety constraints in addition to maximizing a reward objective. Model-based RL algorithms hold promise for reducing unsafe real-world actions: they may synthesize policies that obey all constraints using simulated samples from a learned model. However, imperfect models can result in real-world constraint violations even for actions that are predicted to satisfy all constraints. We propose Conservative and Adaptive Penalty (CAP), a model-based safe RL framework that accounts for potential modeling errors by capturing model uncertainty and adaptively exploiting it to balance the reward and the cost objectives. First, CAP inflates predicted costs using an uncertainty-based penalty. Theoretically, we show that policies that satisfy this conservative cost constraint are guaranteed to also be feasible in the true environment. We further show that this guarantees the safety of all intermediate solutions during RL training. Further, CAP adaptively tunes this penalty during training using true cost feedback from the environment. We evaluate this conservative and adaptive penalty-based approach for model-based safe RL extensively on state and image-based environments. Our results demonstrate substantial gains in sample-efficiency while incurring fewer violations than prior safe RL algorithms. Code is available at: https://github.com/Redrew/CAP

Search Strategies for Topological Network Optimization

We consider an application of combinatorial search to the optimization of topologies in series-parallel networks. We propose a recursive search over the space of decomposition trees, in which partial solutions are obtained by exploring k-way partitionings of expandable nodes. We present two complementary pruning techniques that bound the value of intermediate solutions from above and below, applying monotonic operations to the contents of unresolved leaves. We also develop a means to exploit the convexity of our objective function, so as to prevent the redundant recomputation of subcircuit configurations. Finally, we evaluate our approach on a parameterized benchmark suite of electrical circuits, demonstrating over an order of magnitude improvement in performance as compared to a baseline implementation.

Self-assembly in escin-nonionic surfactant mixtures: From micelles to vesicles

Hypothesis: Saponins are a class of plant derived surfactants which are widely used in food related foams and emulsions, aerated drinks, and in pharmaceuticals and cosmetics. As a potential biosourced and renewable ingredient in a wider range of surfactant based formulations their potential is intimately associated with their mixing with synthetic surfactants. As such the nature of the mixed saponin-surfactant self-assembly is an important characteristic to investigate and understand. The unconventional structure of the saponins compared to the conventional synthetic surfactants poses some interesting constraints on the structures of the mixed aggregates.Experiments: Small angle neutron scattering, SANS, is used to investigate the structure of the saponin, escin, mixed with a range of nonionic surfactants with different ethylene oxide groups, from triethylene glycol monododecyl ether, C12E3, to dodecaethylene glycol monododecyl ether, C12E12.Findings: The scattering data reveal a complex evolution in the solution self-assembled structure with varying escin / nonionic composition and ethylene oxide chain length. The rich structural development comprises of the evolution from the elongated micelle structure of escin to the micelle structure of the nonionic surfactant. At the intermediate solution compositions the structure is predominantly planar, comprising mostly of planar / micellar mixed phases. The nature of the planar structures depend upon the ethylene oxide chain length and the solution composition, and include lamellar, bilamellar vesicle, multilamellar vesicle, and nanovesicle structures, in common with what is observed in other surfactant mixtures.

Evolution of the Tepeoba porphyry-skarn Cu-Mo-Au deposit, NW Turkey: New mineralogical and geochemical findings

This study recently investigates the evolution of the Tepeoba porphyry Cu-Mo-Au deposit (Cu ∼ 3 wt%, Mo ∼ 0.16 wt%, Au ∼ 10 ppm) with associated skarn prospects in the Biga Peninsula (NW Turkey) using the geochemical and mineralogical data. Ore-related alteration types which include biotite (±muscovite)-K-feldspar at the center of the mineralization zone, actinolite-albite alteration, and outer chlorite-epidote-calcite mineral facies, are observed in the Tepeoba mine area along the southern contact between the Karakaya Complex (mainly hornfels at the mine area) and porphyry Eybek intrusion. Porphyry style alteration pattern has been detected recognized in the porphyritic microgranite host rock. On the other hand, the calcareous and carbonate as well as the mineralized hornfels refer to the skarn style alteration pattern associated with a porphyritic felsic stock. Sulfide-rich stockwork and mineralized brittle brecciated, and fracture zones are associated with these hydrothermally altered wallrocks. Ore mineralogy includes chalcopyrite, molybdenite, pyrrhotite, pyrite, subordinate cubanite and native gold. These minerals are replaced by marcasite, hematite, and goethite in the oxidized cap rocks. EPMA data of the alteration and sulfide minerals revealed that Cu-, Fe-, Mo-sulfides partially replace biotite ± muscovite-K-feldspar/actinolite-albite and chlorite-epidote-calcite alteration facies. The estimated ore formation conditions returned wide range of temperatures of 546–471 °C (biotite thermometry) to 340–264 °C (chlorite thermometry), at which sulfides had most likely precipitated while the oxygen fugacity of the magmatic-hydrothermal ore fluids was gradually lowered and developed during the stage of retrograde metasomatic reactions. Chalcopyrite and cubanite was likely to have formed via un-mixing of intermediate solid solution (iss) under oxidizing hydrothermal conditions. Under these conditions, thiosulfide complexes could have been responsible for the transport and deposition of gold. This also refers to native gold, which could have been liberated from sulfide ores (i.e., pyrite) in the oxidation zone due to the processes of supergene enrichment.

Magnetite geochemistry and iron isotope signature of disseminated and massive mineralization in the Kalatongke magmatic Cu[sbnd]Ni sulfide deposit, northwest China

Magnetite is a common accessory mineral and an indicator to magma evolution and sulfide fractional crystallization in magmatic NiCu sulfide deposits. The Kalatongke magmatic sulfide deposit at the southern margin of the Central Asian Orogenic Belt is composed of 11 mafic intrusions. The sulfide orebodies (Y1, Y1 deep, and Y2) are hosted by three small mafic intrusions, and magnetite is common in all mineralized samples. Based on ilmenite exsolution texture, composition, and type of mineralization, three types of magnetite are identified, (1) primary Fe-rich magma-related magnetite (type 1), (2) sulfide liquid-related magnetite (type 2), and (3) hydrothermal magnetite (type 3). We speculate that Fe isotope equilibrium fractionation between early or co-crystallized light 54Fe-enriched sulfide and magnetite may account for the ultra-high magnetite δ56Fe value (0.70‰ to 1.35 ‰) in the magmatic magnetite (types 1 and 2). Enriched compatible elements in type 1 magnetite (TiO2 = 1.52 wt% to 7.89 wt%, V = 775 ppm to 2420 ppm, Cr = 2697 ppm to 14,658 ppm, and Ni contents = 478 ppm to 1256 ppm), reflect the characteristics of primary Fe-rich magmatic magnetite crystallized at relatively high temperature and low oxygen fugacity. Type 2 magnetite in massive ores has Ni (762 ppm to 1769 ppm) and δ56Fe (0.89 ‰ to 1.10 ‰) values similar to type 1 magnetite, but significantly lower TiO2, V and Cr contents (TiO2 = 0.07 to 3.72 wt%, V = 61 to 2314 ppm, Cr = 5 to 2937 ppm), indicating co-crystallization with an evolved sulfide liquid across a wide span of temperature and oxygen fugacity. Type 3 magnetite is of hydrothermal fluid origin, with low δ56Fe (0.29 ‰ to 0.41 ‰) and Ni (177 ppm to 377 ppm).Magnetite composition and Fe isotope signatures at the Kalatongke magmatic sulfide deposit can reveal the genesis of magnetite and the evolution of the melt and sulfide. The Y1 orebody was completely crystallized over a short period of time, while the Y1 deep and Y2 east orebodies underwent a protracted evolution during which magnetite co-crystallized from primitive Fe-rich melt, Fe-rich evolved melt and Cu-rich intermediate sulfide solution. Magnetite and sulfide in the Y2 west massive orebody likely formed last. The compatibility of both lithophile and chalcophile elements, combined with Fe isotopes in magnetite, makes magnetite a good indicator of silicate and sulfide melt evolution.

Symmetry relationships between the crystal structures of chalcopyrite and its derivatives – a systematic approach to inform XRD analysis of Cu−Fe−S phases

AbstractChalcopyrite is the most important mineral for copper production and a detailed understanding regarding its chemical behaviour is essential for the development of Cu‐winning processes. However, previous literature describing chalcopyrite synthesis and phase behaviour are inconsistent and sometimes contradictive. Here, we discuss the symmetry relationships between chalcopyrite and other phases in the Cu−Fe−S system, namely isocubanite, talnakhite, mooihoekite, haycockite, and the so‐called intermediate solid solution. We show how these closely related crystal structures result in similar X‐ray diffraction patterns, which can easily result in false conclusions when studying chalcopyrite synthesis and phase behaviour. By discussing previous literature results in light of our findings, we hope to resolve key contradictions and uncertainties in this field and inform future research into the chemical behaviour of this technologically important mineral.

Acetamiprid in several binary aqueous solutions: Solubility, intermolecular interactions and solvation behavior

This study focused on the solubility profile, dissolving characteristics, computational methods, and solvation behavior of acetamiprid in aqueous solutions of isopropanol/acetone/methanol/EG (1). The quantitative analysis of molecular surface, as well as Hirshfeld surface analysis, were used herein to explain the electrostatic features of basicity of acetamiprid molecule. The primary and second electrophilic sites are the CN and N groups, respectively. All solubility tests were carried out in a shake-flask technique at p = 101.2 kPa and temperatures ranging from 278.15 to 318.15 K. The solubility parameter and dipolarity-polarizability of solutions played a significant role in solubility variation. To investigate solubility performance, the three-dimensional Hansen solubility parameter was used. Several common relationships, such as the modified van't Hoff Jouyban–Acree model, the mixture response surface model, and the Jouyban–Acree model, provided acceptable correlation results for the solubility magnitudes with relative average deviations of < 4.98 percent. The preferred solvation of acetamiprid was further investigated by quantification using the inverse Kirkwood–Buff integrals method. Positive preferential solvation values in isopropanol/ethanol/acetone/methanol-rich and -intermediate composition solutions suggest that isopropanol/ethanol/acetone/methanol preferentially solvates acetamiprid. Nonetheless, EG in the EG + water solution didn’t preferentially solvate acetamiprid. Moreover, the dissolution and transfer properties as well as enthalpy–entropy compensation were discussed.

The European Union as a Security Community Against the Backdrop of Challenges Caused by the Global Pandemic

The European Union, the most advanced integrational arrangement of its kind today, and a model for other regional integration projects, is a relatively new actor on the international scene. It constitutes a community of values, a normative power, a cultural and political community, but, above all else, a security community. And it is to this fi nal dimension that Europe owes the longest period of peace in its modern history. However, today, faced with a new reality forged by global changes and the emergence of new threats, the theoretical construct of the security community, developed by Karl W. Deutsch, requires new insights and adjustments, including in relation to the European Union. The aim of this study is to establish whether, despite the current crisis, the European Union still meets the criteria of a security community. And considering the changes that have taken place over the years, the research problem amounts to the question of whether the concept of security itself, and thus of the security community, shouldn’t be revised so as to better reflect the present reality. In turn, the research thesis is as follows: despite all the difficulties and more or less unprecedented events, especially those of recent times, the EU meets the criteria of a security community, wherein it presents an intermediate (halfway-house) solution between a pluralistic and an amalgamated community. In support of the presented arguments, primary and secondary sources will be used, and research methods such as a description, interpretation, comparison, and critical assessment of the literature will be applied. Considerations will start with theoretical issues, followed by a discussion of the EU as a new actor on the international scene, after which security factors and their manifestations in the EU will be addressed.

Critical Phenomena in Dynamical Scalarization of Charged Black Holes.

We report a new black hole (BH) scalarization mechanism and disclose novel dynamical critical phenomena in the process of the nonlinear accretion of the scalar field into BHs. The accretion process can transform a seed BH into a final scalarized or bald BH, depending on the initial parameter of the scalar field p. There is a critical parameter p_{*} and near it all intermediate solutions are attracted to a critical solution (CS) and stay there for a time scaling as T∝-γln|p-p_{*}|. At late times, the solutions evolve into scalarized black holes (BHs) if p>p_{*}, or bald BHs if p<p_{*}. The final masses of the resulting scalarized-bald BHs satisfy power laws M_{p}-M_{±}∝|p-p_{*}|^{γ_{±}}, where M_{±} are the masses of the scalarized and bald BHs, respectively, when p→p_{*} from above or below, and γ_{±} the corresponding exponents.

A Model for Assessing the Causality of Factors in the Development of Voluntary Pension Insurance in the Republic of Kazakhstan

Many countries have been experiencing a crisis in their pension systems for fiscal and demographic reasons. Voluntary pension funds are a way out of the crisis. The depth of the problem lies in the study of social and economic-mathematical aspects in making economic decisions on implementing voluntary contributions. The authors studied sustainable development, considering the assessment of the causal relationship between factors in the development of voluntary pension insurance in the Republic of Kazakhstan. The article analyzes pension system models and studies the experience of the OECD countries. The results of the analysis highlight the most important factors affecting the development of pension systems with an emphasis on voluntary pension insurance mechanisms. The authors propose a conservative, economic, extended economic, and extended intermediate solution for building a set of cause-and-effect models for the development of voluntary pension insurance in the Republic of Kazakhstan based on a survey of a representative sample of citizens in the Republic of Kazakhstan using the QCA method.

A review on decentralized wastewater treatment systems in India

Pollution of water resources and a lack of potable water are two important issues that city dwellers in India encounter. The passage of untreated sewage down municipal drains is one of the most significant sources of water resource pollution. In densely populated areas, effective sanitation and wastewater management is becoming increasingly difficult. In many developing nations, centralized sewage and wastewater treatment facilities serve only a section of big cities, and on-site sanitation is frequently insufficient in heavily populated areas. There is a demand for complementary and intermediate solutions. DEWATS (community-managed anaerobic decentralized wastewater treatment systems) is a good option for the possibility of relatively fast sanitation improvements in high-priority neighbourhoods where the local authority is not providing a full sanitation service. The following technical treatment modules are typically seen in DEWATS. The primary treatment consists of sedimentation ponds, settlers, septic tanks or bio digester, secondary treatment consists of anaerobic baffled reactors, anaerobic filters or anaerobic and facultative pond systems, secondary aerobic/facultative treatment consists of horizontal gravel filters and post-treatment consists of aerobic polishing ponds. The experience of India in establishing community-managed DEWATS on a large scale is examined in this review.

A Dynamic Structural Equation Approach to Estimate the Short-Term Effects of Air Pollution on Human Health

Abstract Detailed knowledge on the effects of air pollutants on human health is a prerequisite for the development of effective policies to reduce the adverse impact of ambient air pollution. However, measuring the effect of exposure on health outcomes is an extremely difficult task as the health impact of air pollution is known to vary over space and over different exposure periods. In general, standard approaches aggregate the information over space or time to simplify the study but this strategy fails to recognize important regional differences and runs into the well-known risk of confounding the effects. However, modelling directly with the original, disaggregated data requires a highly dimensional model with the curse of dimensionality making inferences unstable; in these cases, the models tend to retain many irrelevant components and most relevant effects tend to be attenuated. The situation clearly calls for an intermediate solution that does not blindly aggregate data while preserving important regional features. We propose a dimension-reduction approach based on latent factors driven by the data. These factors naturally absorb the relevant features provided by the data and establish the link between pollutants and health outcomes, instead of forcing a necessarily high-dimensional link at the observational level. The dynamic structural equation approach is particularly suited for this task. The latent factor approach also provides a simple solution to the spatial misalignment caused by using variables with different spatial resolutions and the state-space representation of the model favours the application of impulse response analysis. Our approach is discussed through the analysis of the short-term effects of air pollution on hospitalization data from Lombardia and Piemonte regions (Italy).

Three-Dimensional Distribution of Platinum Group Minerals in Natural MSS-ISS Ores From the Norilsk One Deposit, Russia

The Mt. Rudnaya MSS-ISS (monosulfide and intermediate solid solution) fine-grained ores from a NE termination of Norilsk 1 deposit were analyzed using a combination of X-ray computed micro tomography, spectral X-ray computed micro tomography and scanning electron microscopy to achieve both, 2D and 3D data. The ores consist of ISS composed of tiny lamellar intergrowths of cubanite and chalcopyrite solid solutions, which form up to 4-mm distinct globules surrounded by an ISS-MSS matrix. Our X-ray computed micro tomography results may provide 3D textural evidence of a possible natural sulfide-sulfide liquid immiscibility between Cu-rich and Cu-poor sulfide liquids that occurred before MSS and ISS were crystallized. The platinum group minerals (PGM) distribution shows that 20.6 vol% of all PGM occur in the ISS-MSS matrix and 79.4 vol% in the ISS globules. We suggest that this distributional behavior is due to the fact that the platinum group elements (PGE) cannot be dissolved in ISS, which led to the formation of the large PGM grains, which are up to 120 μm on their longest axis. The initial enrichment of ISS in PGE was controlled by differences in the partition coefficients of platinum and palladium between Cu-poor and Cu-rich liquids.

Three-dimensional volume reconstruction from multi-slice data using a shape transformation

We present a computational method for the 3D volume reconstruction from cross-sectional data. The proposed method is based on the Allen–Cahn (AC) equation with a source term. The source term is related to shape transformation from a source object to a target object. Using the operator splitting method, the governing equation is solved by splitting it into three steps. The numerical solution is obtained explicitly using the Euler's methods and the separation of variables. To reconstruct the 3D object from two slice data, we set one slice as the target data and the other data as the initial data. We solve the governing equation and stack intermediate solutions based on the relative fraction of the symmetric difference of two regions occupied by the target and source data. To demonstrate that the proposed method can reconstruct a 3D model through extracted intermediate slice data during shape transformation, we perform several computational tests. Furthermore, the proposed method is applied to a 3D volume reconstruction from multi-slice data of human vertebra.

Flexibility, choice, and labour law: The challenge of on-demand platforms

Working through platforms is a recent but fast-growing phenomenon, with obvious implications for workers’ rights. Discussions have so far focused on the status of platform-based workers, but, recently, a growing consensus is emerging by courts around the world that workers for platforms such as Uber are in fact employees. As a result, legal disputes are likely to shift, to a large extent, from status questions to working-time questions. This might seem like a very specific issue, but, in fact, it has crucial implications for the entire model of platform work, and addressing this question requires us to rethink some of the fundamental pillars of labour law, notably whether more room should be opened for flexibility and individual choice within this system. We argue that one aspect of the platform model – ‘work on demand,’ which allows workers to log into the app whenever they wish to do so – poses a difficulty. Workers should be compensated for the time they are ‘on call’ and available to work. But platforms can be expected to respond by assigning workers to pre-set shifts to avoid paying for an unknown amount of working hours, thereby dismantling the ‘on-demand’ model. Such a change would be welcomed by many employees, who will gain more security, but others can be expected to object to losing the flexibility which they value. We consider possible solutions that could allow workers to choose the ‘on-demand’ model. While rejecting the possibility of allowing employees to waive on-call compensation rights, we consider several intermediate solutions that ensure partial payments for this time or exempt employees with another full-time job. The proposed solutions are based on the understanding that more choice is preferable in labour law as long as we can protect the interests of the affected employees and eliminate the externalities that some choices might generate for other workers.

Bi-objective optimization of transcritical CO2 heat pump systems

For the transcritical CO2 heat pump cycle, the gas cooler (GC) pressure can be controlled independently and it can be optimized for optimum COP. Control correlations can be developed offline either based on simulations or experiments or optimization can be done online in real time with continuous pressure and temperature measurements at different locations. The online methods provide more accurate results than the offline correlations, however, they have a long convergence time to the optimum value, especially if the initial GC pressure condition is far away from the optimum. In this paper, we investigate the transcritical cycle as a bi-objective optimization problem where COP and cooling/heating capacity are conflicting objectives with primarily optimizing the GC pressure for maximum cycle COP and maximum cooling or heating capacity which can be useful for transient conditions. The Non-Dominated Sorting Genetic Algorithm (NSGA-II) is used, which generates for different operating conditions the best non-dominated solutions i.e. the Pareto Front that includes the maximum COP, max cooling capacity, and also the intermediate optimum trade-off solutions. The effect on the Pareto Front of each optimization variable; GC outlet temperature, evaporation temperature, evaporator useful superheat, and compressor speed is shown separately, where all except superheat have a significant effect on the Pareto Front. A control methodology is proposed where according to a pre-defined preference, steady-state or transient operation, an optimization parameter is set to either maximize cooling or heating capacity (e.g. obtaining comfort as soon as possible in transient operation), maximize COP (for minimum energy consumption) or operate at a trade-off point as desired. The proposed approach can be applied as an offline control method and it can also be integrated as a hybrid solution with any online optimization method. In both, whenever a new condition is imposed, the offline based bi-objective algorithm will provide a very close estimate of the optimum GC pressure. In a hybrid solution, the online optimizer will then start searching for the true optimum from this very close value and hence reach much faster to the true optimum value. Thus, yielding enhanced capabilities (bi-objective optimization of COP and Q˙c), and in a hybrid solution, additionally further enhanced accuracy (vs offline) with reduced convergence time to the optimum COP and Q˙c (vs online only). A gain to loss ratio in terms of the conflicting objectives (COP and capacity) is presented that can be used as a criteria for deciding whether to move from one solution to another on the Pareto Front.

Anatase/Rutile homojunction quantum dots anchored on g-C3N4 nanosheets for antibiotics degradation in seawater matrice via coupled adsorption-photocatalysis: Mechanism insight and toxicity evaluation

• Anatase/rutile homojunction QDs anchored on g-C 3 N 4 is obtained by template method. • A formation process of A-R QDs/g-C 3 N 4 (TCN-150) is performed. • TCN-150 shows coupled adsorption-photocatalysis activity to OTC removal in seawater. • Toxicity of OTC and its photocatalytic intermediates are evaluated. • Adsorption-photocatalysis synergistic mechanism of TCN-150 is proposed. In this work, a facile two-step approach involving a templated solvothermal reaction and post-pyrolysis was developed for fabrication of ternary heterojunctions of anatase/rutile quantum dots (QDs)/g-C 3 N 4 (TCN-150), which shows well coupled adsorption and photocatalytic activity. The encapsulation of hydrolyzed titanium precursors by P123 polymer on the surface of exfoliated g-C 3 N 4 nanosheets produced anatase/rutile homojunction QDs (7–8 nm)/g-C 3 N 4 heterostructural lamellas, while the subsequent pyrolysis resulted in amorphous carbon layers stacking on g-C 3 N 4 . The adsorption occurs on the carbon layers, while the photocatalysis proceeds on the conduction band of g-C 3 N 4 and valence band of anatase, which gave free radicals of ∙O 2 − and ∙OH for antibiotics decomposition, respectively. Formation of mixed anatase/rutile phases and amorphous carbon in the composite promoted the oxytetracycline (OTC) removal in dynamic flow conditions, with efficiencies about 46.8 and 3.8 times than that of g-C 3 N 4 and TiO 2 respectively, owing to facilitated photogenerated charge separation and transfer, as well as the synergy between adsorption and photocatalysis. The toxicity evaluation of detected final intermediates in the proposed OTC degradation pathways showed decreased acute toxicity of LD 50 and reduced mutagenicity, confirming weaken toxicities of intermediate solutions after visible-light irradiation for 120 min, and this demonstrated a huge potential of TCN-150 as an eco-friendly photocatalyst for practical applications.

Exploring factors influencing bicycle-sharing adoption in India: a UTAUT 2 based mixed-method approach

PurposeBicycle sharing offers a novel way to create smart and sustainable mobility solutions for the future. The purpose of this study is to draw on the Unified Theory of Acceptance and Use of Technology 2 (UTAUT 2) framework for identifying the factors necessary to predict bike-sharing intention among users in India.Design/methodology/approachData were collected through a questionnaire distributed across four major cities in India, and 515 responses were analyzed. A sequential approach was employed to analyze the data using Partial Least Square–Structural Equation Modeling (PLS-SEM) and Fuzzy-set Qualitative Comparative Analysis (fsQCA).FindingsThe findings from PLS analysis revealed that performance expectancy, effort expectancy, facilitating conditions, hedonic motivation and price value are the salient variables that affect users' intentions to participate in bike sharing. In addition, based on fsQCA, six configurations of causal conditions are presented as intermediate solutions that produce the same results. Although antecedent conditions, such as habit and social influence, had an insignificant effect on individuals' BSI, they create conditions sufficient to encourage users' participation in bike sharing in combination with other variables.Research limitations/implicationsA few limitations of this research and the implications of the findings in terms of theory and policy implications are also discussed.Originality/valueThe reported study is one of the earliest to explain bike-sharing adoption in India using the UTAUT 2 model.

Heuristics for constrained role mining in the post-processing framework

Role mining techniques are frequently used to derive a set of roles representing the current organization of a company following the RBAC model and simplifying the definition and the implementation of security policies. Constraints on the resulting roles can be defined to have valid roles, that can be efficiently managed, limiting for example the number of permissions included in a role or the users a role can be assigned to. Since the associated problems are NP hard, several heuristics have been developed to find sub-optimal solutions adopting the concurrent or the post-processing approach. In the first case, assignment matrices are obtained satisfying the given constraints during the computation, while in the second case, the intermediate solutions are obtained without considering the constraints, that are enforced successively. In this paper we present two heuristics for the Permission Usage and Role Usage Cardinality Constraints in the post-processing approach: we consider constraints limiting the number of permissions that can be included in a role in the first case, and the number of roles that can include a permission in the second case, refining the roles produced by some other technique (not considering any constraint). For both heuristics we analyze their performance after their application to some standard datasets, showing the improved results obtained w.r.t. state of the art solutions.

Relevant, Irrelevant, or Ambiguous? Toward a New Interpretation of QCA’s Solution Types

The field of qualitative comparative analysis (QCA) is witnessing a heated debate on which one of the QCA’s main solution types should be at the center of substantive interpretation. This article argues that the different QCA solutions have complementary strengths. Therefore, researchers should interpret the three solution types in an integrated way, in order to get as much information as possible on the causal structure behind the phenomenon under investigation. The parsimonious solution is capable of identifying causally relevant conditions, the conservative solution of identifying contextually irrelevant conditions. In addition to conditions for which the data provide evidence that they are causally relevant or contextually irrelevant, there will be conditions for which the data neither suggest that they are relevant nor contextually irrelevant. In line with the procedure for crafting the intermediate solution, it is possible to make clear for which of these ambiguous conditions it is not plausible that they are relevant in the context of the research.