Level Of Refinement Research Articles

Effect of process parameters on surface composite fabrication of newly commercialized Mg-ZE41 alloy by friction stir processing (FSP): microstructural development and microhardness

PurposeAltering the microstructure and developing the surface metal matrix composites (MMCs) in a solid-state by friction stir processing (FSP) has been on trend for the past decade. The microstructural modification increases the material properties, which are structure sensitive. The microstructural evolution is highly influenced by the selection of process parameters in FSP. In this study, the effect of process parameters on the microstructure evolution and microhardness of the fabrication of surface MMCs of newly commercialized Mg-ZE41 alloy by the incorporation of different reinforcement particles such as ZrO2, CeO2 and Al2O3 is investigated.Design/methodology/approachBy making use of Taguchi’s design of experimentation, which recognizes the crucial factors and ascertain their effect on the properties of the material, the optimization of process parameters for this study was done using MATLAB-14 software. The parameters were adopted along with the levels throughout the FSP for the fabrication of different surface MMCs. For each reinforcement particle, two factors at three levels each had L9 factorial design were used to analyse the effect of these factors on the processing result (microstructure, grain refinement and hardness). The two different factors used in this study are tool rotational speed (TRS) and tool traverse speed (TTS) as a part of the full factorial design matrix for different surface MMCs.FindingsAmong all combinations, TRS of 1500 rpm and TTS of 20 mm/min. for ZE41-ZrO2 MMCs and ZE41-CeO2 MMCs were observed as optimum to produce defect-free processed zone along with the high level of grain refinement and hardness, whereas for ZE41-Al2O3 the same was obtained at 1500 rpm TRS and 10 mm/min TTS.Originality/valueIn this paper, the role of process parameters in the development of surface MMCs on newly commercialized Mg-ZE41 alloy by FSP is investigated. The effect of TRS and TTS on microstructure evolution, grain refinement and microhardness is analysed. Hence, in this study, the optimum parameters for the fabrication of surface MMCs of Mg-ZE41 alloy have thus been established.

On the analysis of plasticity induced crack closure in welded specimens: A mechanism controlled by the stress intensity factor resulting from residual stresses

The aim of this paper is to clarify how and to what extent varied welding residual stresses (WRSes) affect the plane stress plasticity induced crack closure (PICC) simulation. A well-characterized, representative WRS field with tensile and compressive reversals was imported and the predicted PICC results were evaluated against the relevant WRS-free ones. It turned out that instead of WRS typically reported in the literature, there is actually a Kres (stress intensity factor resulting from residual stresses) controlled crack closure mechanism when investigating the PICC behavior in the presence of a WRS field, i.e., WRS influences PICC in the form of Kres. Four major categories where the crack tip was located in different Kres zones were defined using MT (middle tension) and SENT (single edge notch tension) specimens to investigate the mechanism in detail. In summary, the Kres value determined the general steady-state PICC level in the WRS field, i.e., a diminished steady-state opening stress level was predicted in the WRS field with a positive Kres regardless of whether the crack is located in a tensile or a compressive WRS zone, and an elevated value was estimated when the Kres was negative. Besides, the initial transient period was scrutinized that occurred in some WRS scenarios and the concept of primary and secondary plastic wake evolution was proposed to explain its formation. It was found that the transient behavior could be eradicated by tailoring the secondary plastic wake employing appropriate constitutive models and mesh refinement levels. The results attained in the present work provide some guidelines for the WRS-PICC modeling and simulation in the fracture mechanics community.

Concurrent model for sharp and progressive columnar to equiaxed transitions validated by directional solidification experiments processed in microgravity conditions

Columnar and equiaxed structures, which occur during solidification of metallic alloys, influence the texture and properties of castings, welded joints and additively manufactured components. During transient solidification, where grain refiner particles provide the predominant nucleation mechanism, a Columnar to Equiaxed Transition (CET) occurs when conditions that had originally favoured directional columnar growth change to those favouring equiaxed. Constitutional undercooling ahead of the columnar front can permit equiaxed nucleation and growth. By carrying out experiments in microgravity conditions, liquid flows due to thermal and solutal buoyancy effects are suppressed. In these diffusion-controlled conditions, we have observed examples of both sharp (clear) and progressive (gradual) CET. The experimental outcomes, especially the observation of a progressive CET, has highlighted the need for a continuum model that allows for competitive columnar and equiaxed structure development; hence, the Concurrent Columnar to Equiaxed Transition (C2ET) model is proposed. The C2ET is thermally transient and relies on the well-known concept of extended growth for impingement mechanics; thereby, greatly reducing numerical complexity. Importantly, the proposed approach removes the need for a specific equiaxed-blocking criterion, which is often proposed as an essential requirement in other CET models. The C2ET model is validated by four experimental solidification scenarios: two velocity jumps and two thermal-gradient decreases. The velocity jumps induced sharp CETs; whereas, thermal-gradient decreases gave progressive CETs. The C2ET model gave good agreement for the columnar and equiaxed transition zones for both sharp and progressive CET. Results are compared with the classic Hunt model. Unlike Hunt’s model, the C2ET model predicted all macrostructure transitions faithfully using a single (or consistent) set of nucleation input parameters across all four scenarios. Since, the same level of grain refinement was used in each experiment, a consistent set of nucleation parameters was expected. The validated approach can enable effective simulation at lower computational cost for industrial processes that rely on a solidification processing step.

A unified diffuse interface method for the interaction of rigid bodies with elastoplastic solids and multi-phase mixtures

This work outlines a new multi-physics-compatible immersed rigid body method for Eulerian finite-volume simulations. To achieve this, rigid bodies are represented as a diffuse scalar field, and an interface seeding method is employed to mediate the interface boundary conditions. The method is based on an existing multi-material diffuse interface method that is capable of handling an arbitrary mixture of fluids and elastoplastic solids. The underlying method is general and can be extended to a range of different applications including high-strain rate deformation in elastoplastic solids and reactive fluid mixtures. As such, the new method presented here is thoroughly tested through a variety of problems, including fluid–rigid body interaction, elastoplastic–rigid body interaction, and detonation–structure interaction. Comparison is drawn between both experimental work and previous numerical results, with excellent agreement in both cases. The new method is straightforward to implement, highly local, and parallelizable. This allows the method to be employed in three dimensions with multiple levels of adaptive mesh refinement using complex immersed geometries. The rigid body field can be static or dynamic, with the tangent of hyperbola interface capturing reconstruction method being used to keep the interface sharp in the dynamic case.

Formal verification and validation of run-to-completion style state charts using Event-B

State chart notations with ‘run to completion’ semantics are popular with engineers for designing controllers that react to environment events with a sequence of state transitions but lack formal refinement and rigorous verification methods. State chart models are typically used to design complex control systems that respond to environmental triggers with a sequential process. The model is usually constructed at a concrete level and verified and validated using animation techniques relying on human judgement. Event-B, on the other hand, is based on refinement from an initial abstraction and is designed to make formal verification by automatic theorem provers feasible. ion and formal verification provide greater assurance that critical (e.g. safety or security) properties are not violated by the control system. In this paper, we introduce a notion of refinement into a ‘run to completion’ state chart modelling notation and leverage Event-B’s tool support for theorem proving. We describe the difficulties in translating ‘run to completion’ semantics into Event-B refinements and suggest a solution. We illustrate our approach and show how models can be validated at different refinement levels using our scenario checker animation tools. We show how critical invariant properties can be verified by proof despite the reactive nature of the system and how behavioural aspects of the system can be verified by testing the expected reactions using a temporal logic, model checking approach. To verify liveness, we outline a proof that the run to completion is deadlock-free and converges to complete the run.

A refinement development approach for enhancing the safety of PLC programs with Event-B

Programmable Logic Controllers (PLC) are widely used in Industrial Control Systems (ICS) with strict safety assurance requirements. Unfortunately, traditional techniques for debugging prefer to use post-development approaches, such as simulation and black-box testing, rather than enhancing safety before programing. In this paper, we propose a refinement-based approach to model and verify PLC systems, aiming to assure safety properties by construction. It uses the Event-B formalism and focuses on the levels of requirement analysis, specification refinement, and system development. This approach takes a three-layer framework stepwise to specify the behaviors and properties of PLC programs, thereby reducing the modeling complexity. The basic firmware layer models the general mechanisms of PLC firmware, such as periodical instruction execution and centralized I/O scanning, which are application-independent models with fundamental safety properties at an abstract level. The middle layer establishes configuration models. These models correspond to the PLC settings and interactive environments of a specific system, such as I/O addresses and peripheral devices. The business layer models business logic with more specific system-level safety requirements. With our approach, the safety properties of PLC systems can be verified throughout the modeling and refinement process. In addition, rules are proposed to convert the most concrete Event-B model into PLC code satisfying the IEC 61131-3 standard. We demonstrate this approach with a real-world running example of a pump control system for gas transmission. • A refinement-based approach for modeling PLC systems using Event-B. • Defining PLC features are modeled with a 3-layer framework. • It decomposes the complexity of modeling and verification by stepwise refinement. • The safety requirements of PLC systems can be verified during the development. • It generates PLC program code compatible with IEC 61131-3 standard from the model.

An efficient geometry-adaptive mesh refinement framework and its application in the immersed boundary lattice Boltzmann method

This work presents an adaptive mesh refinement (AMR) method. This AMR is based on a pointless representation of octrees, i.e. hash table. An individual hash table is used for each level of refinement to avoid conflicts of key values. Cases for two complex geometries are presented to analyse the performance of the AMR framework with different data structures and strategies. Then, the immersed boundary-lattice Boltzmann method (IB-LBM) is implemented as an example to evaluate the performance of the proposed AMR framework in computational fluid dynamics (CFD) applications. The integrated solver is validated and its performance is analysed through several cases. Considerable reductions of more than 65% in computational time are achieved when the hash table is adopted instead of the binary tree. Moreover, hash table offers more benefits to 3D cases with larger numbers of nodes. The AMR framework presented in this study is simple to implement with the standard C++ libraries and time-efficient for computational fluid dynamics (CFD) applications, which is released as open-source software and can be used by researchers with their CFD solvers.

The Deformation Characteristics and Effect of Processing Parameters on the Microstructure of 7075 Al Shell Part Manufactured by Rotating Backward Extrusion

Rotating backward extrusion (RBE) is known as a new severe plastic deformation technology that effectively combines the features of conventional backward extrusion (CBE) and torsion deformation. In this study, 7075 Al alloy shell parts were successfully prepared by CBE and RBE with a different number of revolutions (N = 5, 10, 15, 25, 50) at 410 °C. The effects of the RBE process on the grain refinement, precipitates and properties of extruded parts were revealed, and the deformation characteristics were compared with CBE. The results showed that the RBE process could greatly eliminate the dead deformation zone at the bottom of the CBE section and significantly improved the comprehensive strain level of the material due to the addition of severe torsional deformation via an open punch. The grain refinement feature of RBE parts showed a gradient distribution that continuously weakened from the inner wall to the outer wall with decreasing compressive and torsional stress. Increasing the number of revolutions significantly promoted the level of grain refinement, the grain refinement range, and effectively broke down and refined the coarse insoluble Fe-rich phases of the extruded parts. It was revealed that the finest grain size of approximately 1.3 μm could be obtained in the inner wall region when N was increased to 25, which was linked to the comprehensive effects of continuous dynamic recrystallization and geometric dynamic recrystallization. RBE greatly promoted an improvement in properties of the extruded parts. After T6 treatment, the microhardness of the fine-grained region of the RBE (25 N) part increased to ~192–197 HV, compared with ~180 HV in the initial T6-extruded state.

Numerical Study of Natural Convection of Power Law Fluid in a Square Cavity Fitted with a Uniformly Heated T-Fin

Flow of a liquid in an enclosure with heat transfer has drawn special focus of researchers due to the abundant thermal engineering applications. So, the aim of present communication is to explore thermal characteristics of natural convective power-law liquid flow in a square enclosure rooted with a T-shaped fin. The formulation of the problem is executed in the form of partial differential expressions by incorporating the rheological relation of the power-law fluid. The lower wall of the enclosure along with the fin is uniformly heated and vertical walls are prescribed with cold temperature. For effective heat transfer within the cavity the upper boundary is considered thermally insulated. A finite element based commercial software known as COMSOL is used for simulations and discretization of differential equations and is executed incorporating a weak formulation. Domain discretization is performed by dividing it into triangular and rectangular elements at different refinement levels. A grid independence test is accomplished for quantities of engineering interest like local and average Nusselt numbers to attain accuracy and validity in results. Variation in the momentum and thermal distributions against pertinent parameters is analyzed through stream lines and isothermal contour plots. Measurement of the heat flux coefficient along with the calculation of kinetic energy against involved parameters is displayed through graphs and tables. After the comprehensive overview of attained results it is deduced that kinetic energy elevates against the upsurging magnitude of the Rayleigh number, whereas contrary behavior is encapsulated versus power-law index n. Elevation in the Nusselt number for the shear thinning case i.e., n=0.5 adheres as compared to Newtonian i.e., n=1 and shear thickening cases i.e., n=1.5. It is perceived that by the upsurging power-law index viscosity augmentations and circulation zones increases. Heat is transferred quickly against Rayleigh number (Ra) due to production of temperature difference in flow domain.

"A chiare lettere - Confronti” • A proposito di guerra o pace ai tribunali ecclesiastici esistenti in Italia. Quale cultura di riforme organiche sta dietro l’attuale pontificato?

SOMMARIO. 1. Preambolo: perseverare diabolicum? - 2. (segue) I tribunali regionali nella attuazione del regime concordatario, in Italia - 3. Ancora in tema di competenza matrimoniale dell’ordinario diocesano. Intermezzo - 4. Corollari di principio in tema di giurisdizione penale e/o amministrativa - 5. Problematicità di una transizione contraddittoria, a ogni livello - 6. (segue) Dalla frammentazione feudale all’armonia di un moderno ordinamento giudiziario.
 Regarding peace of war to the italian ecclesiastical courts. Which is the methodical reform background of pope Francis?
 ABSTRACT: The accentuated tendency of the part of the Vatican (MP Mitis judex) to express a preference for the pastoral attributions of the diocesan bishop in terms of judgment of nullity of canonical marriage, in competition with those of the interdiocesan ecclesiastical tribunals created for the implementation of the concordat regime in Italy (MP Qua cura), could propose in this matter, after the Gospodinoff case (Constitutional Court, dec. N. 1/77) and the Pellegrini case (European Court of Human Rights, sentence 20 July 2001), the risk of a further vulnus to the principles of due process, on the other hand recently renforced in the Italian constitutional order. In dwelling on this inconvenience, the Author observes that the Catholic Church expresses with this, once again, its serious cultural and political delay in relation to the modern systems with which interacts ; and wonders why the Holy See has not decided by now to abandon the institutes and doctrines of ecclesiastical public law with which, starting from the 16th-17th centuries, with intransigence worthy of the better cause is has too often continued to feed the claim to keep on regulate relations with the political authorities on the models , now obsolete and perishable, of the Christian regime. The Author takes the opportunity to indicate how, conversely, the model of the interdiocesan tribunals, even if imperfect, can and should be generalized, in order to begin to solve the set of problems that the lack of modernization of the canonical system proposes, on the subject of the judicial system, in comparison with the level of refinement reached by legislative policy and the science of law (at the state and interstate level), in terms of protection of human rights, in the field of administrative and criminal procedural law.

An entropy–stable discontinuous Galerkin approximation of the Spalart–Allmaras turbulence model for the compressible Reynolds Averaged Navier–Stokes equations

We present an entropy–stable formulation for the compressible Reynolds Averaged Navier–Stokes (RANS) Discontinuous Galerkin (DG) equations and the Spalart–Allmaras one–equation closure. The model is designed to satisfy an entropy law, which includes free– and no–slip wall boundary conditions. We then construct a high–order DG approximation of the model that satisfies the summation–by–parts simultaneous–approximation–term (SBP-SAT) property. With the help of a discrete stability analysis, we construct two approximations: a kinetic energy preserving scheme based on Pirozzoli's two–point flux and a thermodynamic entropy conserving one based on Chandrashekar's split–form. The schemes are applicable to, and the stability proofs hold for, three–dimensional unstructured meshes with curvilinear hexahedral elements. We test the convergence of the schemes on a manufactured solution for increasing polynomial orders and mesh refinement levels, to then assess their numerical stability by propagating a flow from a random initial condition, and finally solve the flow around a two–dimensional flat plate and a NACA 0012 airfoil, comparing numerical results with those available in the literature. The proposed schemes are entropy–stable, and provide accurate solutions for the selected test cases.

Multilevel T-spline Approximation for Scattered Observations with Application to Land Remote Sensing

In this contribution, we introduce a multilevel approximation method with T-splines for fitting scattered point clouds iteratively, with an application to land remote sensing. This new procedure provides a local surface approximation by an explicit computation of the control points and is called a multilevel T-splines approximation (MTA). It is computationally efficient compared with the traditional global least-squares (LS) approach, which may fail when there is an unfavourable point density from a given refinement level. We validate our approach within a simulated framework and apply it to two real datasets: (i) a surface with holes scanned with a terrestrial laser scanner (ii) a patch on a sand-dune in the Netherlands. Both examples highlight the potential of the MTA for rapidly fitting large and noisy point clouds with variable point density and with similar results compared to the global LS approximation.

Analysis-suitable unstructured T-splines: Multiple extraordinary points per face

Analysis-suitable T-splines (AST-splines) are a promising candidate to achieve a seamless integration between the design and the analysis of thin-walled structures in industrial settings. In this work, we allow multiple extraordinary points per face, i.e., we remove the restriction of preceding works that required extraordinary points to be at least four rings apart from each other. We do so by mathematically showing that AST-splines with multiple extraordinary points per face are linearly independent and their polynomial basis functions form a non-negative partition of unity. This extension of the subset of AST-splines drastically increases the flexibility to build geometries using AST-splines; e.g., much coarser meshes can be constructed around small holes. The AST-spline spaces detailed in this work have C1 inter-element continuity near extraordinary points and C2 inter-element continuity elsewhere. For the convergence studies performed in this paper involving second- and fourth-order linear elliptic problems with manufactured solutions, we have not found any drawback caused by allowing multiple EPs per face in either the first refinement levels or the asymptotic behavior. To illustrate a possible isogeometric framework that is already available, we design the B-pillar and the side outer panel of a car using T-splines with the commercial software Autodesk Fusion360, import the control nets into our in-house code to build AST-splines, and import the Bézier extraction information into the commercial software LS-DYNA to solve eigenvalue problems. The results are compared with conventional finite elements and good agreement is found between AST-splines and conventional finite elements.

Development and Transformation of Inclusive Finance in my Country's Commercial Banks

Different degrees of financial exclusion will exist in the process of financial development. Vulnerable groups such as low-income groups are often excluded from formal financial services and cannot obtain normal financial services. The concept of inclusive finance is based on such a reality. The realization of financial inclusion aims to enable economic entities at different levels of society to obtain the necessary and reasonable financial services and financial support. As the main body of my country's financial institution system, commercial banks are not only providers of inclusive financial services, but also play the role of leaders in inclusive financial innovation. Therefore, it is necessary to strengthen the capacity building of commercial banks' inclusive financial services and improve their inclusive financial services. The quality and efficiency of financial inclusion are related to the development level and sustainability of inclusive finance in the whole society. At present, my country's commercial banks are actively exploring and practicing digital transformation. Through the empowerment of financial technologies such as big data and artificial intelligence, they have developed inclusive financial services and product models to solve the problems of difficult and expensive financing for the private economy. This paper first introduces the dilemma of developing inclusive finance under the traditional model of commercial banks, mainly including information asymmetry, low level of management refinement, and insufficient customer coverage. The use of digitization can solve many problems in traditional models; finally, the article proposes inclusive finance for my country's commercial banks from the aspects of accelerating data application transformation, enriching customer acquisition scenarios, promoting digital process transformation, innovating risk control technology, and cultivating digital transformation professionals. Policy recommendations for digital transformation development.

Nivel de madurez en la gestión del conocimiento en la clínica de una escuela de salud: un estudio de caso desde la perspectiva de los administradores

Knowledge management (KM) consists of generating, storing, distributing and using knowledge. Therefore, this study aimed to verify the perception of health managers about the degree of maturity in knowledge management in a clinical school of a community university in the south of Santa Catarina. A qualitative research was carried out through the application of a questionnaire of the CG measurement model by Batista (2012) with all managers of the school clinic, eight in total, with a general coordinator and a manager for each area: nursing, pharmacy, physiotherapy, medicine, nutrition, dentistry and psychology. As a result, it was found that most services are still in the initiation stage, in which the institution begins to recognize the importance of KM initiatives. One manager pointed out that it is in the initiation phase (expansion), in which there are KM practices in some areas of the institution, one manager has a perception of the level of refinement, in which KM implementation is constantly evaluated and improved, and another manager has the perception that your clinic is on the fifth level – maturity – in which CG is institutionalized. Thus, it is suggested that services that have KM in their initiation and expansion that they implement a KM model, using the singular and collective knowledge and creativity to improve the initiatives of creation, storage, dissemination and application of knowledge. For services in refinement and maturity, it is suggested to maintain and improve existing practices.

Replacing Mineral Fertilisers for Bio-Based Fertilisers in Potato Growing on Sandy Soil: A Case Study

The refinement level of bio-based fertilisers (BBFs) can influence environmental and agronomic performance. This study analyses the environmental and agronomic effect of different BBFs on potato growing in sandy soil. A less refined product (liquid fraction of digestate (LFD)), two refined products (ammonium sulphate (AS) and potassium concentrate (KC)), and mineral fertilizer (MF) are compared by conducting: (i) a nitrogen (N) incubation experiment where the N release rate of the BBFs is determined, (ii) a greenhouse gas emission experiment where N2O, CO2, and CH4 emissions after BBF application are measured, (iii) a pot experiment where the nutrient fertiliser replacement value (NFRV) of the BBF is calculated, and (iv) a full-scale field trial where the potato quality and quantity and the remaining N residues in the soil after harvest are assessed. The N release rate and the NFRV of AS (142 ± 19% and 1.13, respectively) was higher compared with the LFD (113 ± 24% and 1.04) and MF (105 ± 16% and 1.00). Lowest N2O emissions were observed after the application of the less refined product (0.02 ± 0.01 per 100 g N applied) and highest for MF urea (0.11 ± 0.02 per 100 g N applied). In the full-scale field trial, no significant difference in potato yield was observed in the plots that received manure in combination with BBF or MF. This study showed that all three BBFs can safely be used in potato growing on sandy soils. However, the adoption of BBFs can be stimulated by (i) solving the practical issues that occurred during the application of LFD, (ii) making sure BBFs are on the list of RENURE materials so they can legally replace mineral fertiliser, and (iii) reducing the surplus of slurry manure to stimulate the use and fair pricing of BBF products.

Achieving high strength and ductility in selective laser melting Ti-6Al-4V alloy by laser shock peening

In this work, the influences of laser shock peening (LSP) on the residual stress state, microstructures and mechanical properties of Ti-6Al-4V alloy fabricated by selective laser melting (SLM) were researched. Particularly, the microstructural evolution before and after LSP was clarified using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) observations. The results showed that the residual stress was adjusted from tensile to compressive state. Furthermore, high-density dislocations and a great number of parallel nano mechanical twins (nano-MTs) were promoted in the coarse lamellar α' structures, contributing to the grain refinement. The ultimate tensile strength and elongation of the SLM-manufactured (SLMed) Ti-6Al-4V alloy increased by approximately 14.3% and 18.3% after LSP treatment, respectively. Finally, the dominant mechanism of tensile property enhancement by LSP was revealed. High levels of compressive residual stress and grain refinement of the α' structures induced by LSP realized the excellent combination of strength and ductility.

Using Computational Modelling to Study Extensional Rheometry Tests for Inelastic Fluids

The present work focuses on the extensional rheometry test, performed with the Sentmanat extensional rheometer (SER) device, and its main objectives are: (i) to establish the modelling requirements, such as the geometry of the computational domain, initial and boundary conditions, appropriate case setup, and (ii) to investigate the effect of self-induced errors, namely on the sample dimensions and test temperature, on the extensional viscosity obtained through the extensional rheometry tests. The definition of the modelling setup also comprised the selection of the appropriate mesh refinement level to model the process and the conclusion that gravity can be neglected without affecting the numerical predictions. The subsequent study allowed us to conclude that the errors on the sample dimensions have similar effects, originating differences on the extensional viscosity proportional to the induced variations. On the other hand, errors of a similar order of magnitude on the test temperature promote a significant difference in the predicted extensional viscosity.

Developing a Prototype of a Mechanical Ventilator Controller from Requirements to Code with ASMETA

Rigorous development processes aim to be effective in developing critical systems, especially if failures can have catastrophic consequences for humans and the environment. Such processes generally rely on formal methods, which can guarantee, thanks to their mathematical foundation, model preciseness, and properties assurance. However, they are rarely adopted in practice. In this paper, we report our experience in using the Abstract State Machine formal method and the ASMETA framework in developing a prototype of the control software of the MVM (Mechanical Ventilator Milano), a mechanical lung ventilator that has been designed, successfully certified, and deployed during the COVID-19 pandemic. Due to time constraints and lack of skills, no formal method was applied for the MVM project. However, we here want to assess the feasibility of developing (part of) the ventilator by using a formal method-based approach. Our development process starts from a high-level formal specification of the system to describe the MVM main operation modes. Then, through a sequence of refined models, all the other requirements are captured, up to a level in which a C++ implementation of a prototype of the MVM controller is automatically generated from the model, and tested. Along the process, at each refinement level, different model validation and verification activities are performed, and each refined model is proved to be a correct refinement of the previous level. By means of the MVM case study, we evaluate the effectiveness and usability of our formal approach.

Visualizing adverse events in clinical trials using correspondence analysis with R-package visae

BackgroundGraphical displays and data visualization are essential components of statistical analysis that can lead to improved understanding of clinical trial adverse event (AE) data. Correspondence analysis (CA) has been introduced decades ago as a multivariate technique that can communicate AE contingency tables using two-dimensional plots, while quantifying the loss of information as other dimension reduction techniques such as principal components and factor analysis.MethodsWe propose the application of stacked CA using contribution biplots as a tool to explore differences in AE data among treatments in clinical trials. We defined five levels of refinement for the analysis based on data derived from the Common Terminology Criteria for Adverse Events (CTCAE) grades, domains, terms and their combinations. In addition, we developed a Shiny app built in an R-package, visae, publicly available on Comprehensive R Archive Network (CRAN), to interactively investigate CA configurations based on the contribution to the explained variance and relative frequency of AEs. Data from two randomized controlled trials (RCT) were used to illustrate the proposed methods: NSABP R-04, a neoadjuvant rectal 2 × 2 factorial trial comparing radiation therapy with either capecitabine (Cape) or 5-fluorouracil (5-FU) alone with or without oxaliplatin (Oxa), and NSABP B-35, a double-blind RCT comparing tamoxifen to anastrozole in postmenopausal women with hormone-positive ductal carcinoma in situ.ResultsIn the R04 trial (n = 1308), CA biplots displayed the discrepancies between single agent treatments and their combinations with Oxa at all levels of AE classes, such that these discrepancies were responsible for the largest portion of the explained variability among treatments. In addition, an interaction effect when adding Oxa to Cape/5-FU was identified when the distance between Cape+Oxa and 5-FU + Oxa was observed to be larger than the distance between 5-FU and Cape, with Cape+Oxa and 5-FU + Oxa in different quadrants of the CA biplots. In the B35 trial (n = 3009), CA biplots showed different patterns for non-adherent Anastrozole and Tamoxifen compared with their adherent counterparts.ConclusionCA with contribution biplot is an effective tool that can be used to summarize AE data in a two-dimensional display while minimizing the loss of information and interpretation.