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To mitigate the cost of manually producing and maintaining models capturing software specifications,specification miningtechniques can be exploited to automatically derive up-to-date models that faithfully represent the behavior of software systems. So far,specification mining solutions focused on extracting information about the functional behavior of the system, especially in the form ofmodels that represent the ordering of the operations. Well-known examples are finite state models capturing the usage protocol ofsoftware interfaces and temporal rules specifying relations among system events.Although the functional behavior of a software system is a primary aspect of concern, there are several other non-functionalcharacteristics that must be typically addressed jointly with the functional behavior of a software system. Efficiency is one of the most relevant characteristics. Indeed, an application that delivers the right functionalities with an inefficient implementation may fail to satisfy the expectations of its users.Interestingly, the timing behavioris strongly dependent on the functional behavior of a software system. For instance, the timing of an operation depends on the functional complexity and size of the computation that is performed. Consequently, models that combine the functional and timing behaviors, as well as their dependencies, are extremely important to precisely reason on the behavior of software systems.In this paper, we address the challenge of generating models that capture both the functional and timing behavior of a software system from execution traces. The result is the Timed k-Tail (TkT) specification mining technique, which can mine finite state models that capture such an interplay: the functional behavior is represented by the possible order of the events accepted by the transitions, while the timing behavior is represented through clocks and clock constraints of different nature associated with transitions.Our empirical evaluation with several libraries and applications shows that TkT can generate accurate models, capable of supporting the identification of timing anomalies due to overloaded environment and performance faults. Furthermore, our study shows that TkT outperforms state-of-the-art techniques in terms of scalability and accuracy of the mined models.

The detection of performance issues in Java-based applications is not trivial since many factors concur to poor performance, and software engineers are not sufficiently supported for this task. The goal of this manuscript is the automated detection of performance problems in running systems to guarantee that no quality-based hinders prevent their successful usage. Starting from software performance antipatterns, i.e., bad practices (e.g., extensive interaction between software methods) expressing both the problem and the solution with the purpose of identifying shortcomings and promptly fixing them, we develop a framework that automatically detects seven software antipatterns capturing a variety of performance issues in Java-based applications. Our approach is applied to real-world case studies from different domains, and it captures four real-life performance issues of Hadoop and Cassandra that were not predicted by state-of-the-art approaches. As empirical evidence, we calculate the accuracy of the proposed detection rules, we show that code commits inducing and fixing real-life performance issues present interesting variations in the number of detected antipattern instances, and solving one of the detected antipatterns improves the system performance up to 50%.

Architectural anomalies, also known as architectural smells, represent the violation of design principles or decisions that impact internal software qualities with significant negative effects on maintenance, evolution costs and technical debt. Architectural smells, if early removed, have an overall impact on reducing a possible progressive architectural erosion and architectural debt. Some tools have been proposed for their detection, exploiting different methods, usually based only on static analysis. This work analyzes how dynamic analysis can be exploited to detect architectural smells. We focus on two smells, Hub-Like Dependency and Cyclic Dependency, and we extend an existing tool integrating dynamic analysis. We conduct an empirical study on ten projects. We compare the results obtained comparing a method featuring dynamic analysis and the original version of Arcan based only on static analysis to understand if dynamic analysis can be successfully used. The results show that dynamic analysis helps identify missing architectural smells instances, although its usage is hindered by the lack of test suites suitable for this scope.

Due to their open nature and popularity, Android-based devices represent one of the main targets for malware attacks that may adversely affect the privacy of their users. Considering the huge Android market share, it is necessary to build effective tools able to reliably detect zero-day malware on these platforms. Therefore, several static and dynamic analysis methods based on Neural Networks and Deep Learning have been proposed in the literature. Despite machine learning can be considered the most promising approach for classifying applications into malware or legitimate ones, its success strongly depends on the choice of the right features used for building the detection model. This is definitely not an easy task that requires a systematic solution. Accordingly, this work represents the sequences of API calls invoked by apps during their execution as sparse matrices looking like images (API-images), which can be used as fingerprints of the apps’ behavior over time. We also used autoencoders to autonomously extract the most representative and discriminating features from these matrices, that, once provided to an artificial neural network-based classifier have shown to be effective in detecting malware, also when the network is trained on a reduced number of samples. Experimental results show that the resulting framework is able to outperform more complex and sophisticated machine learning approaches in malware classification.

This paper proposes a new simple approach for assessing dynamic soil-structure interaction effects on structures supported by embedded massive foundations. The classical substructure method was revisited by proposing an exact decomposition approach which allows performing the inertial interaction analysis of the superstructure without modeling foundation and soil, which are replaced by properly defined impedances. The proposed approach requires redefinition of simplified formulas for both the dynamic stiffnesses and the kinematic interaction factors, which are referred to the top of the massive foundation. Accurate expressions for the complex impedances were derived based on rigorous finite-element results. The same formulas were used to calibrate a four-spring model for the analysis of the kinematic interaction problem, resulting in different expressions for the kinematic interaction factors depending on the adopted assumptions. The proposed approach, in conjunction with the novel formulas for impedances and kinematic factors, was applied to the case of bridge piers on caisson foundations, and the results were more accurate than those of the existing simplified procedures.

Volcanic pyroclastic deposits generally have a metastable and collapsible structure, which may lead to their liquefaction under monotonic, cyclic, and dynamic loading. Their structure could be partly attributed to the nature of the pyroclastic particles, especially their lightweight, fragile and porous features. In comparing the results of monotonic and cyclic undrained triaxial tests performed on Cervinara soil, the steady-state concept is used to define the occurrence of liquefaction. A significant part of the experimental program on Rangiriri soil is carried out to highlight the role of the fragility of pyroclastic particles on the occurrence of liquefaction. The comparison between the results obtained on the two types of pyroclastic soils shows the possibility of explaining the undrained mechanism of pore pressure buildup using the state parameter ψ. The parameter ψ seems to be useful also in comparing the results obtained on pyroclastic soils with those on ordinary sands. The state parameter has a clear physical significance that could be used to define a more reliable model of undrained pore pressure buildup for soils of different natures. © 2021 American Society of Civil Engineers.

Background The assessment of the force exerted during a gesture in human motion analysis can provide direct and indirect information regarding the expended energy, especially during the execution of a sport gesture. In this field, assessment and improvement of the performance can be supported by instrumented devices able to measure and process mechanical quantities. In cycling, strain gauges-based instrumented pedals represent one of the last innovations in the sector, because they can provide data about the power exerted (produced) during training and the pedal efficiency. Optimization of the strain-gauges positioning is thus required to improve accuracy in the exerted force estimation. Methods A new technique to give a support for evaluating the best compromise between maximum sensitivity and ease of assembly was developed in the present work, based on a Finite Element Model (FEM) and a parametric analysis of the strain field at different sensor placements. Optimal positions were identified as those combining high sensitivity and low dependence from positioning inaccuracies. Results Parametric strain-load trends obtained from the developed model show a linear behavior of strain gauges pairs and confirm that there is a good sensitivity of the adopted sensors if they are mounted in handy positions of the developed load cell. Discussion The conducted analysis enables to calculate the sensitivity of the load cell to the exerted forces, and evaluates its dependence to the positioning of strain gauges, and makes it possible to appropriately choose strain gauges positioning in areas where border effects are minimized. The strain distributions obtained by the FEM analysis in the presented load cells gives useful indications for all the situations where small strain gauges are requested to be mounted on a reduced offered area.

Field monitoring techniques can collect data about the behavior of software applications while running in the field, with real users and real data. Developers can exploit the information extracted from the field to timely improve, tune, and fix their systems, anticipating feedback by users. It is, however, challenging to extract a relevant amount of information from field executions without introducing significant overhead. This paper addresses this challenge by studying how to inexpensively trace data in-memory while postponing save operations to idle time, so that the operations requested by users are exposed to a negligible overhead only. In particular, this paper presents delayed saving, a technique that efficiently traces references to objects, opportunistically saving information only when the monitored application is not serving any user request. Storing references and postponing save operations may introduce inaccuracy in the collected data, that is, a lately saved object might be in a different state compared to the state of the object at the time it was traced. Our evaluation shows that the level of inaccuracy introduced by delayed saving is limited compared to its efficiency and low intrusiveness.

The seismic assessment of archaeological heritages is studied by means of 2D numerical analysis with Discrete Element Method (DEM). The proposed approach is based on a refined discretization that reproduces the effective block masonry pattern and on a routine for carrying out seismic analysis according to either quasi-static or dynamic approaches. The applicability of the DEM for the analysis of archaeological heritages is discussed referring to the case studies of the south-east edge of the external wall of the Colosseum that was restored by Stern in 1807, and the arcades of the Claudio Aqueduct in Rome. The analyses based on DEM provide a reliable estimate of the seismic capacity and a refined representation of the expected failure mode, while also contributing to the design of appropriate strengthening measures. The approach is finally validated through comparison between the outcome of the numerical simulation and the survey of the existing crack pattern of the monuments.

Offshore structures are mainly associated with the oil and gas industry given that globally, nearly one-third of the oil and gas extracted worldwide comes from offshore sources. This situation is likely to continue to rise over the coming decades because of abundant deposits of oil and gas still present in the oceans and society's dependency on hydrocarbon fuels. Regardless, offshore wind shows promise and continues to rise at an exponential rate because it provides means for decarbonization while contributing to economic growth in many countries. As such, wind continuos to be a leading solution against climate change globally. To ensure that a structure will fulfill its function, fatigue design is crucial to ensure an adequate service life because it is responsible for more than 80% of structural failures, most of them catastrophic and without warning. This work aims to evaluate environmental loads and fatigue analysis in a jacket-type platform located in the North Sea. Wave data scatter has been provided, and using Morison's formula, the loads on the structure were used to achieve an applicable normal loading force. Then, a static and a dynamic fatigue analysis for the offshore jacket-type structure under consideration are evaluated and compared.

The production of “green hydrogen” is currently one of the hottest topics in the field of renewable energy systems research. Hydrogen storage is also becoming more and more attractive as a flexible solution to mitigate the power fluctuations of solar energy systems. The most promising technology for electricity-to-hydrogen conversion, and vice versa, is the reversible solid-oxide cell (SOC). This device is still very expensive, but it exhibits excellent performance under dynamic operating conditions compared to the competing devices. This work presents the dynamic simulation of a prototypal renewable plant combining a 50 kW photovoltaic (PV) field with a 50 kW solid-oxide electrolyzer cell (SOEC) and a compressed hydrogen tank. The electricity is used to meet the energy demand of a dwelling located in the area of Campi Flegrei (Naples). The SOC efficiency is simulated by developing a mathematical model in MATLAB®. The model also calculates the cell operating temperature as a function of the input current. Once the optimal values of the operating parameters of the SOC are calculated, the model is integrated in the transient system simulation tool (TRNSYS) for dynamic analysis. Furthermore, this work presents a parametric analysis of the hydrogen storage system (HSS). The results of the energy and environmental analyses show that the proposed system can reach a primary energy saving by 70% and an amount of saved CO2 of 28 tons/year. Some possible future market scenarios are considered for the economic analysis. In the most realistic case, the optimal configuration shows a simple pay back lower than 10 years and a profit index of 46%.

Video observation is gaining popularity as a data collection technique to study eating behavior. Traditional approaches to data analysis of video observations are based on static counts reporting the number of times an action occurs, disregarding the dynamic aspects captured in the video. In this paper, we investigate French consumers’ bread consumption patterns during a restaurant meal. We propose a novel approach, the Temporal Dominance of Behavior (TDB), to visualise the dynamic information contained in video material in terms of frequency, duration, sequence and simultaneity of actions based on standard data analysis principles from temporal methods such as Temporal Dominance of Sensations (TDS) and Temporal Check-All-That-Apply (T-CATA). TDB allows reporting hours of videos across several subjects in a single graphical output, providing an efficient summary overview suitable for results interpretation and communication. Regarding bread consumption patterns during a restaurant meal in French consumers, three groups of consumers are drawn: the No-breaders (43%), the Bread-as-a-tool group (48%) and the Bread lovers (9%). Eating behavior varies in the consumed quantity of bread as well as in consumption dynamics throughout the meal, and it is related to both the type of dish that is consumed and to consumer characteristics. The Temporal Observation Curves approach provides a graphical synthesis of the dynamic information. We discuss the added-value of the TDB method compared to single-point analysis, provide recommendations for future developments and suggest potential applications in the consumer and food domain.

The wind resource offshore is often excellent due to a higher average wind speed and lower turbulence intensity. Jacket structures are the most common offshore platforms for extraction of oil and natural gas in relative low water depths. When the offshore resources run out, these structures must be displaced to another area containing underground resources or removed in the case of reaching their design life. Therefore, one possible procedure to reduce the carbon footprint on the planet, allowing society to rely on promising sources of ’clean’ energy while salvaging these oil and gas platforms, is to consider the transformation of these oil and gas platforms into offshore wind turbine support structures. The present research focus on the possibility of converting such structures for gas extraction into offshore platforms for wind turbines. In this study, a comparison between the behavior of horizontal and vertical axis wind turbines on the same offshore platform is presented. In this comparison, two different software programs are used: MATLAB and SAP2000. The model proposed is a new simplified tool used to study the structural analysis of the jacket structures, developed and summarized in 10 steps, adopted to evaluate the behavior of the platform with the wind tower configurations.

This study investigates the effects of converter-interfaced generation integration on the dynamic response of the power system of Continental Europe. The system is analysed with a large-scale dynamic model of the entire synchronous area, considering different instantaneous integration percentages of converter-interfaced generation across the system. The study focuses on the reduction of the overall available kinetic energy and the impact on frequency dynamics and system oscillations. The dynamic model of the system originally provided by ENTSO-E is further developed according to a specific methodology, replacing a determined amount of synchronous generation and introducing a corresponding amount of converter-controlled current sources. The reference incident of a generation loss in Western Europe specified by ENTSO-E is considered in the analysis. The results of time-domain simulations and modal analysis show how the integration of non-synchronous generation affects the frequency dynamics of Western, Central and Eastern Europe, bringing to attention some relevant effects of the spatial distribution of different generation sources within an extensive system as the Continental Europe synchronous area.

This paper aims to investigate the crashworthiness capability of a commercial aircraft metallic sandwich leading edge, subjected to bird strike events. A sensitivity analysis is presented, aimed to assess the influence of the skin parameters (inner and outer faces and core thicknesses) on the leading-edge crashworthiness and to determine, among the configurations able to withstand a bird strike event, the best compromise in terms of weight and structural performances. In order to easily manage the design parameters and the output data, the ModeFrontier code was used in conjunction with the FE code Abaqus/Explicit. A dedicated python routine was developed to define a fully parametric simplified leading-edge model. To fulfill the aerodynamic requirements, the external surfaces were considered fixed during the sensitivity analysis, and, thus, only the internal leading edge&rsquo, s components were modified to study their influence on the structural response. The total mass of the model, the maximum deformation and the energy dissipated due to material failure and the plastic deformations were monitored and used to compare and assess the behavior of each configuration.

The overall kinetic energy reduction due to increasing share of converter-interfaced generation (CIG) has been investigated so far by several works for systems of different types and sizes. The so called synthetic inertia is one of the most common and reviewed solutions to the issue of system inertia reduction. The paper investigates the effects of synthetic inertia as frequency service provided by the CIG sources for the Continental Europe (CE) synchronous area using a detailed large scale dynamic model. The model - provided in the basic form by the System Protection & Dynamics (SP&D) group of the ENTSOE - is properly developed substituting a determined amount of synchronous machines with CIG sources. The CIG sources implemented the typical current vector control and the inclusion of synthetic inertia schemes. The system is then analyzed through combined time-domain simulations and modal analysis computations, exploring the effects of CIG sources participation to the frequency response of the CE system when delivering synthetic inertia against power unbalances. The specific impact on the inter-area oscillations of the system is recognized and discussed.

Collecting data about the sequences of function calls executed by an application while running in the field can be useful to a number of applications, including failure reproduction, profiling, and debugging. Unfortunately, collecting data from the field may introduce annoying slowdowns that negatively affect the quality of the user experience. So far, the impact of monitoring has been mainly studied in terms of the overhead that it may introduce in the monitored applications, rather than considering if the introduced overhead can be really recognized by users. In this paper we take a different perspective studying to what extent collecting data about sequences of function calls may impact the quality of the user experience, producing recognizable effects. Interestingly we found that, depending on the nature of the executed operation and its execution context, users may tolerate a non-trivial overhead. This information can be potentially exploited to collect significant amount of data without annoying users.

This paper presents the experimental application of a new method for seismic vulnerability assessment of buildings recently introduced in literature, the SMAV (Seismic Model Ambient Vibration) methodology with reference to their operational limit state. The importance of this kind of evaluation arises from the civil protection necessity that some buildings, considered strategic for seismic emergency management, should retain their functionality also after a destructive earthquake. They do not suffer such damage as to compromise the operation within a framework of assessment of the overall capacity of the urban system. To this end, for the characterization of their operational vulnerability, a Structural Operational Index (IOPS) has been considered. In particular, the dynamic environmental vibrations of the two considered strategic buildings, the fire station and the town hall building of a small town in the South of Italy, have been monitored by positioning accelerometers in well-defined points. These measurements were processed through modern Operational Modal Analysis techniques (OMA) in order to identify natural frequencies and modal shapes. Once these parameters have been determined, the structural operational efficiency index of the buildings has been determined evaluating the seismic vulnerability of the strategic structures analyzed. his study aimed to develop a model to accurately predict the acceleration of structural systems during an earthquake.

The increase of converter-interfaced generation (CIG) typically related to renewable energy sources is progressively causing a significant change of power systems operation. The curtailment of synchronous generation with the consequent reduction of the overall kinetic energy is one of the related issues, currently under investigation in academia and industry. The work considers the problem of overall inertia reduction from a large-scale point of view, analyzing the impact of different CIG integration levels to the frequency response of the power system of Continental Europe. The kinetic energy is evaluated for each country of the synchronous area, and the system is modified substituting conventional synchronous generation with converter-interfaced generation. The models of power converters and corresponding controls follow typical representation for stability studies: they are modeled as controlled current sources with active and reactive power control loops, implemented as user-written equations within the overall mathematical model of Continental Europe power system. Comprehensive time-domain simulations are performed for each scenario, assuming the system subjected to a power plant outage: the obtained frequencies for Western, Central and Eastern Europe are reported, and typical frequency metrics are used to evaluate the response of the system across the different scenarios. Results show how the penetration of CIG affects the frequency response of the system, in terms of instantaneous frequency deviation and maximum frequency rate. A significant change in the inter-area oscillations is also observed, with a progressive increase of the oscillation frequency of the East-West mode, as confirmed by the modal analysis of the system.

Le tecniche di monitoraggio possono estrarre dati accurati sul comportamento dei sistemi software. Se utilizzati nel campo, possono rivelare come le applicazioni si comportano in contesti del mondo reale e come i programmi sono effettivamente esercitati dai loro utenti. Tuttavia, la raccolta, l'elaborazione e la distribuzione dei dati sul campo devono essere eseguiti senza interruzioni e in modo non invasivo mentre gli utenti interagiscono con le loro applicazioni. Per limitare l'intrusività del monitoraggio sul campo, un approccio comune consiste nel ridurre la quantità di dati raccolti (ad esempio, in pochi eventi e in crash dump), che tuttavia possono influire gravemente sull'efficacia delle tecniche che sfruttano i dati sul campo. Questa tesi di dottorato indaga il trade-off tra il monitoraggio sul campo e il degrado dell'esperienza utente nelle applicazioni interattive, cioè le applicazioni che richiedono input dell'utente per continuare le sue operazioni. In particolare, abbiamo identificato due grandi sfide: capire come l'utente percepisce il sovraccarico del monitoraggio e studiare come raccogliere dati in modo non intrusivo senza perdere troppe informazioni. In breve, forniamo tre contributi principali. In primo luogo, presentiamo uno studio empirico volto a quantificare se e in che misura il sovraccarico di monitoraggio introdotto in un'applicazione interattiva è percepito dagli utenti. I risultati riportati possono essere sfruttati per progettare attentamente le procedure di analisi in esecuzione sul campo. In particolare, abbiamo scoperto che gli utenti non percepivano differenze significative per un overhead dell'80% e raramente percepivano un overhead del 140%. In secondo luogo, introduciamo un framework di monitoraggio per ricavare dati a runtime completi senza influire sulla qualità dell'esperienza utente. La tecnica produce un automa a stati finiti che mostra i possibili usi dell'applicazione dagli eventi osservati sul campo. Dal modello, è anche possibile estrarre tracce accurate e complete che potrebbero essere utilizzate per supportare varie attività, come il debugging, la riproduzione e la profilazione di errori di campo. Infine, presentiamo una strategia per ridurre ulteriormente l'impatto del monitoraggio limitando l'attività svolta in parallelo con le operazioni degli utenti: la strategia ritarda il salvataggio di eventi da archiviare in fasi di inattività dell'applicazione per ridurre l'impatto sull'esperienza utente. L'approccio riduce considerevolmente l'impatto del monitoraggio sulle operazioni degli utenti producendo tracce estremamente accurate. I risultati ottenuti in questo dottorato la tesi può abilitare una serie di soluzioni di test e analisi che sfruttano in modo estensivo i dati sul campo. Monitoring techniques can extract accurate data about the behavior of software systems. When used in the field, they can reveal how applications behave in real-world contexts and how programs are actually exercised by their users. However, the collection, processing, and distribution of field data must be done seamlessly and unobtrusively while users interact with their applications. To limit the intrusiveness of field monitoring a common approach is to reduce the amount of collected data (e.g., to rare events and to crash dumps), which, however, may severely affect the effectiveness of the techniques that exploit field data. This Ph.D. thesis investigates the trade-off between field monitoring and the degradation of the user experience in interactive applications, that is, applications that require user inputs to continue its operations. In particular, we identified two big challenges: to understand how the user perceives monitoring overhead and, to study how to collect data in a non-intrusive way without losing too much information. In brief, we provide three main contributions. In the first place, we present an empirical study aimed at quantifying if and to what extent the monitoring overhead introduced in an interactive application is perceived by users. The reported results can be exploited to carefully design analysis procedures running in the field. In particular, we realized that users do not perceive significant differences for an overhead of 80\% and seldom perceived an overhead of 140\%. Secondly, we introduce a monitoring framework for deriving comprehensive runtime data without affecting the quality of the user experience. The technique produces a finite state automaton that shows possible usages of the application from the events observed in the field. From the model, it is also possible to extract accurate and comprehensive traces that could be used to support various tasks, such as debugging, field failures reproduction and profiling. Finally, we present a strategy to further reduce the impact of monitoring by limiting the activity performed in parallel with users' operations: the strategy delays the saving of events to file to idle phases of the application to reduce the impact on the user experience. The approach considerably decreases the impact of monitoring on user operations producing highly accurate traces. The results obtained in this Ph.D. thesis can enable a range of testing and analysis solutions that extensively exploit field data.

In irregular and asymmetric structures dynamic actions may induce overloading effects on the peripheral columns of the resisting structural frames and eventually lead to a weaker and more brittle behavior of the overall structure. In the present research work the dynamic assessment of irregular and asymmetric multi-storey structures is investigated. In order to reduce the structural vulnerability related to dynamic loadings we analyze a traditional retrofitting strategy for fixed base structures by the inclusion of shear walls in the structural frames and a base isolated strategy by the adoption of a base isolation system for the passive control of structures. A base isolation system is designed and verified by adopting a solution realized by elastomeric isolators placed in parallel with friction sliders. A comparative analysis of the dynamic performance of asymmetric structures is reported for a traditional fixed base strategy retrofitted by the inclusion of shear walls and for a base isolated strategy. The analysis gives clarifications on the advantages and the drawbacks of the base isolation technique with respect to more traditional solutions when they are adopted for regularizing the dynamic behavior of asymmetric structures characterized by irregularities in plan. A comparative analysis is reported for the retrofitted fixed base structure and the base isolated structure together with a comprehensive evaluation of the structural behavior of the two considered strategies for the regularization of the dynamic behavior of structures under dynamic loadings.

The paper presents the study of the 500-kV Vietnamese power system. The oscillatory response of the system is analyzed both with a modal analysis and a time domain analysis. The 500-kV system of Vietnam is modeled in details, including all the power plants with the corresponding regulators. The model is developed in collaboration with the Institute of Energy Science IES-VAST of Vietnam and it is validated with the data provided by the National Load Dispatch Centre (NLDC) of Vietnam. The simulation results reveal a clear identification of potential inter-area oscillations between North and South of the Country. A worsening of the observed phenomenon should be considered as possible, especially in the perspective of the new installation of a significant amount of power from renewable sources into the Vietnamese system.

Context Automated GUI Exploration Techniques have been widely adopted in the context of mobile apps for supporting critical engineering tasks such as reverse engineering, testing, and network traffic signature generation. Although several techniques have been proposed in the literature, most of them fail to guarantee the exploration of relevant parts of the applications when GUIs require to be exercised with particular and complex input event sequences. We refer to these GUIs as Gate GUIs and to the sequences required to effectively exercise them as Unlocking GUI Input Event Sequences. Objective In this paper, we aim at proposing a GUI exploration approach that exploits the human involvement in the automated process to solve the limitations introduced by Gate GUIs, without requiring the preliminary configuration of the technique or the user involvement for the entire duration of the exploration process. Method We propose juGULAR, a Hybrid GUI Exploration Technique combining Automated GUI Exploration with Capture and Replay. Our approach is able to automatically detect Gate GUIs during the app exploration by exploiting a Machine Learning approach and to unlock them by leveraging input event sequences provided by the user. We implement juGULAR in a modular software architecture that targets the Android mobile platform. We evaluate the performance of juGULAR by an experiment involving 14 real Android apps. Results The experiment shows that the hybridization introduced by juGULAR allows to improve the exploration capabilities in terms of Covered Activities, Covered Lines of Code, and generated Network Traffic Bytes at a reasonable manual intervention cost. The experimental results also prove that juGULAR is able to outperform the state-of-the-practice tool Monkey. Conclusion We conclude that the combination of Automated GUI Exploration approaches with Capture and Replay techniques is promising to achieve a thorough app exploration. Machine Learning approaches aid to pragmatically integrate these two techniques.

Stringent environmental constraints make the construction of new transmission overhead lines more and more difficult. Alternatively, today it is possible to use cable lines for high (HV) and extra-high (EHV) voltage systems. The configuration of the so-called mixed lines can create some problems in the operation of the electrical system, both during steady-state and transient conditions. In particular, the system stability is one of the main concerns when analyzing the dynamic response of power systems. In this paper, the study of angular stability of a system containing a mixed line is presented: a specific control logic applied to the shunt reactors of the mixed line is proposed as improvement of the overall system stability. The proposed switching logic is first discussed from a theoretical point of view and validated with two different testing systems. Then, the existing overhead-cable lines connecting Sicily to the rest of continental Europe 400 kV power system are taken as case study for the application of the proposed switching strategy. Several simulations are performed in the power system analysis software NEPLAN360: the results show the fundamental role of the timing of the control actions applied on the shunt reactors in helping the system to keep the stability. The proposed control proves to be an effective support to the system subjected to critical contingencies, contributing decisively to avoid the angular separation between areas and therefore to preserve the stability of the system.

Seismic design criteria allow enhancing the structural ductility and controlling the damage distribution. Therefore, detailing rules and design requirements given by current seismic codes might be also beneficial to improve the structural robustness. In this paper a comprehensive parametric study devoted to quantifying the effectiveness of seismic detailing for steel Moment Resisting Frames (MRF) in limiting the progressive collapse under column loss scenarios is presented and discussed. The overall structural performance was analysed through nonlinear static and dynamic analyses. With this regard the following cases were examined: (i) MRF structures designed for wind actions according to Eurocode 1; (ii) MRF structures designed for seismic actions according to Eurocode 8. The investigated parameters were (i) the number of storeys; (ii) the interstorey height; (iii) the span length; (iv) the building plan layout; and (v) the column loss scenario. Results show that structures designed according to capacity design principles are less robust than wind designed ones, provided that the connections have the same capacity threshold in both cases. In addition, the numerical outcomes show that both the number of elements above the removed column and stiffness of beams are the key parameters in arresting progressive collapse.

In this paper, Nodal dynamic method is introduced to model the TRIGA Mark II reactor of the University of Pavia as a dynamic system for the total operative power range (i.e. 0–250 kW) using a zero dimensional thermal hydraulic method. Neutronic and thermal hydraulic models are coupled in order to demonstrate reactor dynamic behavior. The reactor is divided into bi-dimensional zones and simulated in Serpent 2 to obtain two group cross sections for each specified zone as well as kinetic parameters. And they are applied in nodal method for the analysis of reactor dynamic behavior. Point kinetic and nodal dynamic methods are utilized for the second core configuration as the neutronic model. Different reactivities (i.e. 190, 104, 78, 40 pcm) are inserted by control rods in different power levels (i.e. 1, 50, 100, 150 kW) for the reactor dynamic analysis. A program is written in MATLAB to couple neutronic and thermal hydraulic models. A system of ordinary differential equations are produced and solved in space state model. The calculated and experimental power excursion results are in good agreement with less than 1% difference. The results between nodal method and point kinetic method are very consistent with less than 0.05% of difference.

Summary The primary objective of the “performance-based seismic design” is to provide stipulated seismic performances for building structures. However, a certain degree of design freedom is needed for matching a specific seismic response. This design freedom is not obtainable by the conventional lateral resisting systems because their stiffness and strength are coupled. Here, we put emphasis on the role of the unconventional lateral resisting systems in adding more flexibility to the design. In this paper, we seek to explore the seismic design of moment-resisting frame structures equipped with an innovative hysteretic device, known as “crescent-shaped brace.” One conspicuous feature of this device is its distinctive geometrical configuration, which is responsible for the enhanced nonlinear force-displacement behavior exhibited by the device. A new performance-based approach for the seismic design of the crescent-shaped brace is proposed. The performance of the device is evaluated, and its application in multistory shear-type structures is investigated. Two case studies were established to illustrate the design methodology. The first is a new two-story RC structure, and the second is an existing three-story RC structure. Nonlinear time history and pushover analyses are performed to evaluate the behavior of the controlled structures. The analyses show that for each of the two case studies, the acceleration–displacement capacity spectrum conforms to the performance objectives curve. This finding confirms the validity of the proposed design approach and the effectiveness of the new hysteretic device in resisting lateral forces.

Fully assessing the robustness of a software application in-house is infeasible, especially considering the huge variety of hardly predictable stimuli, environments, and configurations that applications must handle in the field. For this reason, modern testing and analysis techniques can often process data extracted from the field, such as crash reports and profile data, or can even be executed directly in the field, for instance to diagnose and correct problems. In all these cases, collection, processing, and distribution of field data must be done seamlessly and unobstrusively while users interact with their applications. To limit the intrusiveness of in-the-field monitoring a common approach is to reduce the amount of collected data (e.g., to rare events and to crash dumps), which, however, may severely affect the effectiveness of the techniques that exploit field data. The objective of this Ph.D. thesis is to define solutions for collecting field data in a cost effective way without affecting the quality of the user experience. This result can enable a new range of testing and analysis solutions that extensively exploit field data., 2 pages, no figures, conference article

The seismic vulnerability analysis of a strategic building is presented in this paper. A refined finite-element model was set up on the basis of available experimental results, and updated on the basis of new experimental analyses on materials and structure. As demonstrated by an experimental vibration analysis, the structural behavior is influenced very much by the irregularity of the building and the presence of an adjacent building with no seismic joint. The results indicate a high vulnerability of the building to seismic actions, and the inadequacy of the pile foundation - for which a specific nonlinear analysis was performed - to support horizontal seismic loads. A retrofit intervention, based on the insertion of a seismic isolation system and the realization of a seismic joint with the adjacent building, was proposed, which allows the reduction of horizontal forces in the piles and the torsional movements of the structure. © 2016 American Society of Civil Engineers.

With the increase in terrorist attacks in recent years, the effects of explosions on building become highly topical. In this regard, the paper deals with the analysis of blast loaded steel structures. When a blast loaded structure is analysed, as known, two major design issues and scientific challenges have to be approached and solved. The first issue derives from the analysis and description of the input dynamic load (time-pressure wave), being dependent on the type of explosion and explosive, while the second issue is related to the analysis of the actual dynamic response of the structure under impact. As such, real field blast tests using the so called ANFO explosives are first presented. The examined constructional system consists of steel rolled beams with two different type of cross sections (HEB100 and IPE120). The actual experimental observations are then assessed and compared with both SDOF and FE models carried out in ABAQUS. In doing so, the actual shape (i.e. decaying path for the pressure load) of the experimental blast wave is used, together with two further approximations for its description. The comparative calculations are then proposed for selected control points, in terms of mechanical and kinematic quantities (i.e. displacements, accelerations and strains). A critical discussion of the so collected comparative results is hence proposed.

Gas explosions frequently occur in residential buildings inducing the out-of-plane collapse of single structural components which may trigger the progressive collapse of the structure. In this study, the out-of-plane collapse capacity of load-bearing tuff stone masonry (TSM) walls subjected to blast loading is investigated. A finite element macro-modelling strategy was adopted and dynamic analysis was carried out through LS-DYNA software to derive pressure–impulse diagrams for blast resistant design and assessment. Different modelling assumptions were considered. A sensitivity analysis allowed the evaluation of the influence of vertical pre-compression level and aspect ratio of TSM walls on blast collapse capacity. Numerical predictions of blast capacity were then compared to those provided by simplified analytical models, design code pressures and peak pressures estimated after real incidents.

This paper presents the vulnerability of public buildings in Sabah which are subjected to earthquakes from Sumatra and the Philippines. Tremors in Peninsular Malaysia and East Malaysia due to Sumatra and Philippine earthquakes have been reported several times. Engineers are concerned of the seismic vulnerability of public buildings due to lack of earthquake consideration in Malaysia‟s building design procedure. 8 (eight) reinforced concrete buildings which are mostly categorized as moment resisting frames has been selected for vulnerability study. A case study has been conducted on low rise, medium rise, and high rise buildings. The buildings are analyzed using Finite Element Modeling (FEM) under different types of analyses including Time History Analysis (THA) considering low to medium earthquake intensities. Different intensities of earthquake load, 0.05g, 0.10g, 0.15g and 0.20g are applied to the structures to know the maximum allowable earthquake load intensities for the buildings. In the non-linear analysis of modal frames, it indicates that most of the buildings are categorised in the moderate damage level where there is no structural damage but some non-structural damage are expected. The performances of the structure are shown by the yield point at beam-column connections where the internal forces at beam elements exceed the design capacity of the beams. The Labuan Airport building was performed the early yielding point at 3.85 sec for column element at intensity 0.05g. The study indicates that the plastic hinge initially formed on the column at the lower storey level for both low and high rise building frames.

In the last years, non-destructive techniques based on ambient vibration data have been developed in order to estimate the modal parameters (natural frequencies and mode shapes) of buildings. They have been performed mainly by using the accelerometers data of slender buildings. The present paper illustrates an assessment of identification techniques, applied to the numerical results of a finite element (FE) model obtained for a reinforced concrete frame building. The frame, with a four storey configuration, has been designed in accordance with the actual Italian seismic guidelines which respect the provisions of the Eurocodes. Several tests have been conducted in order to determine a suitable procedure that can permit to identify, from the data of virtual accelerometers placed on the building model, the relevant correct modal parameters. This procedure may permit to identify the correct number of accelerometers and their position within the structure, in order to guarantee a good frequency identification in real conditions in terms of external excitement.

SUMMARY The paper investigates the dynamic behaviour of hybrid systems made of partially restrained (PR) steel– concrete composite frames coupled with viscoelastic dissipative bracings. A numerical model that accounts for both the resisting mechanisms of the joint and the viscoelastic contribution of the dissipative bracing is introduced and briefly discussed. The model is first validated against experimental outcomes obtained on a one-storey two-bay composite frame with partial strength semi-rigid joints subjected to free vibrations. A number of time-history analyses under different earthquake ground motions and peak ground accelerations are then carried out on the same type of frame. The purpose is to investigate the influence of the type of beam-to-column connection and property of the viscoelastic bracing on the performance of the hybrid system. The inherent stiffness of the bare PR frame and the plastic hysteresis of the beam-to-column joints, which always lead to only limited damage in the joint, are found to provide a significant contribution to the overall structural performance even under destructive earthquakes. This remark leads to the conclusion that the viscoelastic bracing can be effectively used within the hybrid system. Copyright q 2008 John Wiley & Sons, Ltd.

The characterization of the joint behaviour under physiological loading condition is a necessary step to come to the definition of significant joint models, which open the way to the identification of better treatments and prosthesis and orthosis designs. A test rig has been recently developed, capable to replicate a generic loading condition while measuring the relative motion of the bones participating to the articulation and estimating the associated muscular forces. In this paper, the rig architecture and functioning will be briefly recalled. Then, the result of its application on a knee joint will be presented.

The increasing diffusion of smart devices, along with the dynamism of the mobile applications ecosystem, are boosting the production of malware for the Android platform. So far, many different methods have been developed for detecting Android malware, based on either static or dynamic analysis. The main limitations of existing methods include: low accuracy, proneness to evasion techniques, and weak validation, often limited to emulators or modified kernels. We propose an Android malware detection method, based on sequences of system calls, that overcomes these limitations. The assumption is that malicious behaviors (e.g., sending high premium rate SMS, cyphering data for ransom, botnet capabilities, and so on) are implemented by specific system calls sequences: yet, no apriori knowledge is available about which sequences are associated with which malicious behaviors, in particular in the mobile applications ecosystem where new malware and non-malware applications continuously arise. Hence, we use Machine Learning to automatically learn these associations (a sort of "fingerprint" of the malware); then we exploit them to actually detect malware. Experimentation on 20000 execution traces of 2000 applications (1000 of them being malware belonging to different malware families), performed on a real device, shows promising results: we obtain a detection accuracy of 97%. Moreover, we show that the proposed method can cope with the dynamism of the mobile apps ecosystem, since it can detect unknown malware.

Among the design activities of the in vessel components for DEMO promoted by European Fusion Development Agreement (EFDA) organization, this work deals with the gap required at the supporting keys of the blanket. Due to its higher operating temperatures compared to the vacuum vessel (VV) ones, this gap will increase during operation. The electro magnetic (EM) loads due to fast disruptions occur on a short time and might accelerate the blanket significantly before it touches the supporting keys, causing an impact of the blanket itself onto the keys. Depending on their stiffness, the EM loads with their short time scale could excite the structure's natural frequencies, causing dynamic amplification. Both phenomena (impact and dynamic amplification) can cause stresses in the structure significantly higher than the static ones. This work develops a finite element model of DEMO blanket to study its non-linear transient dynamic behavior under impact loadings. A VV sector, the ribs between the inner and outer VV, the backward manifolds and the supporting keys of the blanket have been modeled. The analyses have been performed with Abaqus [1] and Ansys [2] FEM codes focused on the displacements of the keys in their housing on the blanket. The dynamic amplification factor has been evaluated as the ratio of dynamic to static displacements in meaningful points of the structure for a growing gap till 5 mm. © 2015 Elsevier B.V. All rights reserved.

Structures involving uncertainties in material and/or in geometrical parameters are referred to as uncertain structures. Reliability analysis of such structures strongly depends on variation of parameters and probabilistic approach is often used to characterize structural uncertainties. In this paper dynamic analysis of linearly elastic system in presence of random parameter variations will be performed. In detail parameter fluctuations have been considered as inelastic, stress and parameter dependent superimposed strains. Analysis is then carried out via superposition principle accounting for response to external agencies and parameter dependent strains. Proposed method yields asymptotic solution which may be applied to whatever coefficient of variation of random structural parameter showing fast convergence increasing number of terms in the asymptotic expansion. Numerical examples illustrate the application of the proposed method to linear elastic truss under dynamic load contrasted with Monte-Carlo solution.

The evaluation of the knee joint behavior is fundamental in many applications, such as joint modeling, prosthesis and orthosis design. A new test rig for in vitro analysis of the knee joint behavior is presented in this paper. Based on a cable-driven parallel manipulator loading system, the rig can simulate general knee loading conditions, such as clinical tests and common daily activities like walking and sit to stand, in a wide range of flexion angles. The joint natural response in terms of movement is measured by an optoelectronic system. Furthermore, the new rig allows the estimation of the contribution of the principal leg muscles in guaranteeing the equilibrium of the joint. Despite its simplicity and low cost, the rig presents good accuracy, repeatability and versatility that allows its application on a wide range of specimen sizes. It represents an advanced application of cable-driven parallel robots for in vitro motion analysis of the knee subjected to general loads.