An expert system for checking the correctness of memory systems using simulation and metamorphic testing

During the last few years, computer performance has reached a turning point where computing power is no longer the only important concern. This way, the emphasis is shifting from an exclusive focus on the optimisation of the computing system to optimising other systems, like the memory system. Broadly speaking, testing memory systems entails two main challenges: the oracle problem and the reliable test set problem. The former consists in deciding if the outputs of a test suite are correct. The latter refers to providing an appropriate test suite for determining the correctness of the system under test. In this paper we propose an expert system for checking the correctness of memory systems. In order to face these challenges, our proposed system combines two orthogonal techniques – simulation and metamorphic testing – enabling the automatic generation of appropriate test cases and deciding if their outputs are correct. In contrast to conventional expert systems, our system includes a factual database containing the results of previous simulations, and a simulation platform for computing the behaviour of memory systems. The knowledge of the expert is represented in the form of metamorphic relations, which are properties of the analysed system involving multiple inputs and their outputs. Thus, the main contribution of this work is two-fold: a method to automatise the testing process of memory systems, and a novel expert system design focusing on increasing the overall performance of the testing process. To show the applicability of our system, we have performed a thorough evaluation using 500 memory configurations and 4 di erent memory management algorithms, which entailed the execution of more than one million of simulations. The evaluation used mutation testing, injecting faults in the memory management algorithms. The developed expert system was able to detect over 99% of the critical injected faults, hence obtaining very promising results, and outperforming other standard techniques like random testingThis work was supported by the Spanish Ministerio de Economía, Industria y Competitividad, Gobierno de España/FEDER (grant numbers DArDOS, TIN2015-65845-C3-1-R and FAME, RTI2018-093608-B-C31) and the Comunidad de Madrid project FORTE under Grant S2018/TCS-4314. The first author is also supported by the Universidad Complutense de Madrid - Santander Universidades grant (CT17/17-CT18/17

Validating communication network configurations in cloud and HPC systems using Metamorphic Testing

Funding: This work was supported by the Madrid Government (Comunidad de Madrid-Spain) under the Multiannual Agreement with the Complutense University as part of the Program to Stimulate Research for Young Doctors in the context of the V PRICIT (Regional Programme of Research and Technological Innovation) under grant PR65/19-22452, the Spanish MINECO/FEDER project MASSIVE under Grant RTI2018-095255-B-I00, the Comunidad de Madrid project FORTE-CM under grant S2018/TCS-4314, and project S2018/TCS-4339 (BLOQUES-CM) co-funded by EIE Funds of the European Union and Comunidad de Madrid.During the last years, the fast evolution of computers and networks has led to the creation of a wide variety of services that have changed the way we live, like video streaming, on-line gaming and online shopping. These services are supported by complex systems, which require not only high computational power but high-speed and low-latency networks to fulfil the expected quality requirements. However, a misleading configuration in one of the thousand components that compose these systems may cause performance bottlenecks and functioning disruptions. Unfortunately, conventional testing methods are not adequate for checking these systems since, on many occasions, there does not exist a mechanism to determine if the behaviour of a system is the expected one. Fortunately, Metamorphic Testing is a valuable and promising testing technique that alleviates the two fundamental problems of testing: the oracle problem and the reliable test set problem. In this paper, we combine Metamorphic Testing and simulation techniques for validating communication network con- figurations in HPC systems. For this, we rely on a catalogue of Metamorphic Relations, based on network communications knowledge, for checking its correctness. In addition, we have conducted an experimental study for analysing the communica- tion network of HPC systems. The results show that Metamorphic Testing is appropriate for checking the correctness of communication networks supported by complex topologies in HPC systems.Postprin

Parallel mutation testing for large scale systems

Mutation testing is a valuable technique for measuring the quality of test suites in terms of detecting faults. However, one of its main drawbacks is its high computational cost. For this purpose, several approaches have been recently proposed to speed-up the mutation testing process by exploiting computational resources in distributed systems. However, bottlenecks have been detected when those techniques are applied in large-scale systems. This work improves the performance of mutation testing using large-scale systems by proposing a new load distribution algorithm, and parallelising different steps of the process. To demonstrate the benefits of our approach, we report on a thorough empirical evaluation, which analyses and compares our proposal with existing solutions executed in large-scale systems. The results show that our proposal outperforms the state-of-the-art distribution algorithms up to 35% in three different scenarios, reaching a reduction of the execution time of—at best—up to 99.66%This work was supported by the Spanish MINECO/FEDER project under Grants PID2021- 122270OB-I00, TED2021-129381B-C21 and PID2019-108528RBC22, the Comunidad de Madrid project FORTE-CM under Grant S2018/TCS-4314, Project S2018/TCS-4339 (BLOQUES-CM) cofunded by EIE Funds of the European Union and Comunidad de Madrid and the Project HPC-EUROPA3 (INFRAIA-2016-1-730897), with the support of the EC Research Innovation Action under the H2020 Programm

Optimization of a combined electrocoagulation-electroflotation reactor

This work studies the efficiency of an electroflotation process for the separation of the solids produced during the electrocoagulation treatment of three different types of wastewater: kaolin suspension, coloured organic solution and oil-in-water emulsion. Additionally, a combined electrocoagulation-electroflotation reactor is designed and optimized taking into account the effect of current density, residence time, pollutant concentration and the ratio floated/settled solids. To do this, an experimental design with response surface methodology (RSM) has been used. Results show that electroflotation is a good alternative to the removal of oil microdrops and dyes, but it is not recommended for the separation of solids formed during electrocoagulation of colloid suspensions due to its high density. It has been found that the use of aluminium leads to better results than the use of iron in the treatment of oil-in-water emulsions and coloured solutions. In these cases, the use of a combined electrocoagulation-electroflotation reactor is recommended and the effect of the main inputs has been studied.Este trabajo estudia la eficiencia de un proceso de electroflotación para la separación de los sólidos producidos durante el tratamiento de electrocoagulación de tres tipos diferentes de aguas residuales: suspensión de caolín, solución orgánica coloreada y emulsión de aceite en agua. Además, se diseña y optimiza un reactor combinado de electrocoagulación-electroflotación teniendo en cuenta el efecto de la densidad de corriente, el tiempo de residencia, la concentración de contaminantes y la relación sólidos flotantes / sedimentados. Para ello, se ha utilizado un diseño experimental con metodología de superficie de respuesta (RSM). Los resultados muestran que la electroflotación es una buena alternativa a la eliminación de microgotas de aceite y tintes, pero no se recomienda para la separación de sólidos formados durante la electrocoagulación de suspensiones coloidales debido a su alta densidad. Se ha encontrado que el uso de aluminio conduce a mejores resultados que el uso de hierro en el tratamiento de emulsiones de aceite en agua y soluciones coloreadas. En estos casos se recomienda el uso de un reactor combinado de electrocoagulación-electroflotación y se ha estudiado el efecto de los insumos principales

Improving the degradation of low concentration of microcystin-LR with PEM 2 electrolyzers and photo-electrolyzers

In this work, the performances of two electrochemical cells, a conventional liquid-electrolyte electrolyzer (LEE) and a solid-electrolyte electrolyzer (SEE) were compared for the treatment of two real water matrixes polluted with microcystin-LR at trace concentrations. The first consists of single-compartment flow cell, while the second consists of membrane-electrode assembly flow cell. Both cells can attain the removal of the microcystin, although the toxin degradation was more efficient in the SEE, for both water matrixes assessed, decreasing the initial concentration by 3-logs and achieving in short treatment times concentrations below the guidelines of the World Health Organization (WHO) for drinking water. Irradiation of UVC improves results reached by the electrochemical technologies, although in lower extension than initially expected. The great performance of SEE reactor is attributed to a more suitable production of oxidants and a lower operation-dependence with respect to the water matrix conductivity. This cell can remove pollutants also faster than the single photolysis and, in comparing its performance with the other technologies assessed in this work, it is the best choice requiring the less time and energy to meet the WHO standards, without being necessary the coupling with photolysis

A new electrochemically-based process for the removal of perchloroethylene from gaseous effluents

Removal of perchloroethylene using combined granular active carbon (GAC) adsorption and electrolysis is evaluated in this research. There is an interest in the regeneration of GAC using methanol solutions, because this process can obtain the almost complete desorption of the pollutant retained during the treatment of gaseous flows. In this work, the electrolysis of perchloroethylene (used not only as a hazardous pollutant but also as a model of organic pollutant) in methanol media containing sodium chloride and sodium hydroxide is evaluated and results are compared to those obtained during the electrolysis of this pollutant in aqueous media. Results demonstrate the feasibility of this treatment technology, which does not only remove the raw molecule but it is also capable to remove all the intermediates detected by GC-ECD, allowing the possibility of the reuse of the methanol solution for further regeneration steps

Enhanced electrolytic treatment for the removal of clopyralid and lindane

In this work, it is evaluated the more critical point of a new electrochemical technology for the removal of organic pollutants based on the regeneration of granular active carbon (GAC) (that can be used efficiently to concentrate aqueous wastes) with methanol and in the electrochemical treatment of methanol with conductive diamond electrochemical oxidation (CDEO). The system proposed was studied with lindane and clopyralid. Results show that it is possible the complete removal of the raw pesticides and intermediates formed by electrolyzing these species in methanol media and that both sodium chloride and sodium hydroxide can be used as supporting electrolyte to increase the conductivity of methanol. The cell voltages obtained are quite similar to those obtained during the electrolysis of aqueous wastes. The electrolysis of these dilute solutions does not generate significant concentrations of intermediates and the depletion of the raw pollutant fits well to a pseudo-first order kinetic model. Oxidants capable to oxidize iodide to iodine are produced during the electrolysis in methanol media and they have an important influence on the degradation of the pollutants. The new technology, based on the concentration of the pollutant before electrolysis, allows to remove completely pollutants from soil and soil washing fluids in a more efficient way, although the concentration of pollutant attained and, hence, the efficiency of the overall removal process depends on the adsorption equilibria of the pollutant in aqueous and methanol media

Reversible electrokinetic adsorption barriers for the removal of organochlorine herbicide from spiked soils

This work aims to describe the removal of clopyralid from clay soils using electrokinetically assisted soil flushing (EKSF) coupled with a permeable reactive barrier (PRB), consisting of beds of Granulated Activated Carbon (GAC). To do this, two strategies have been evaluated on bench-scale electroremediation facilities (175 dm3): electrokinetic adsorption barrier (EKAB) and reversible electrokinetic adsorption barrier (REKAB). Likewise, to clarify the contribution of the different mechanisms to remediation process results are compared to those obtained in a reference test (without applying an electric field) and to results obtained in the EKSF of soils polluted with compounds with different polarity and vapour pressure. Results show that during EKAB and REKAB tests, clopyralid is removed from the soil by adsorption in PRB, electrokinetic transport and, very less decisively, by evaporation. The application of polarity reversion attains a higher retention of clopyralid in the activated carbon-PRB and a better regulation of pH because of the neutralization of H+ and OH− generated in the electrolyte wells. After 30 days of operation, the removal of clopyralid by EKAB is 45% while it reaches 57% in the case of REKAB

Competitive Anodic Oxidation of Methyl Paraben and Propylene Glycol: Keys to Understand the Process

This work focuses on the competitive oxidation of two very different molecules, when they underwent electrochemical oxidation with diamond electrodes. To shed light on the mechanisms of this competitive oxidation, solutions containing methyl paraben and propylene glycol at different ratios are electrolyzed (using sulfate or chloride supporting electrolytes). Results obtained pointed out that removal of both species can be easily attained by the electrochemical process, being promoted the mineralization by the action of the sulfate derivative products and the formation of chlorinated hydrocarbons by the action of chlorine oxidants, although the mechanisms of the oxidation do not depend on the primary anion contained in the waste. The higher the concentration of species to be oxidized, the higher is the amount of intermediates and the slower is the mineralization the ratio influences. An important outcome is that there is a limit concentration in each one organic compound interferes on the degradation of a pollutant. Thus, the interference effect of PG on MeP oxidation was only observed for low MeP/PG ratios

Effects of ultrasound irradiation on the electrochemical treatment of wastes containing micelles

This work focuses on the effect of the irradiation of ultrasound during the electrolysis of wastes polluted with micelles. To do this, synthetic wastewater (emulating the ones produced in cosmetic industry) was formulated and it underwent several electrochemical and sono-electrochemical, at low and high frequencies, oxidation assays. Processes were monitored paying attention not only to the changes observed in the organic soluble intermediates and final products, but also to the size of the micelles. Results demonstrate that the presence of surfactant in wastes may interfere on the degradation of pollutants due to the formation of micelles. Nevertheless, 90% of mineralization was achieved by the coupled process of electrolysis and low frequency ultrasound. Furthermore, ultrasound irradiation can contribute to faster turbidity and foam depletion and to retard the formation of perchlorates. Regarding the micelles, it was found that application of ultrasound directly affects the changes on particles size during their destruction which, in turn, influences on the performance of the electrochemical process. A simple phenomenological model is proposed to explain the influence of this irradiation