Finite Element Modelling of TRIP Steels

A constitutive model that describes the mechanical behaviour of steels exhibiting “Transformation Induced Plasticity” (TRIP) during martensitic transformation is presented. Multiphase TRIP steels are considered as composite materials with a ferritic matrix containing bainite and retained austenite, which gradually transforms into martensite. The effective properties and overall behaviour of TRIP steels are determined by using homogenization techniques for non‐linear composites. The developed constitutive model considers the different hardening behaviour of the individual phases and estimates the apportionment of plastic strain and stress between the individual phases of the composite. A methodology for the numerical integration of the resulting elastoplastic constitutive equations in the context of the finite element method is developed and the constitutive model is implemented in a general‐purpose finite element program. The prediction of the model in uniaxial tension agrees well with the experimental data. The problem of necking of a bar in uniaxial tension is studied in detail.     

Quality Indices for Aluminum Alloy Castings: A Critical Review

Several indices are available in the literature to assess the structural quality of cast Al alloys, especially Al-7 pct Si-Mg alloys that are based on tensile test results. Some of these indices, most notably the one developed by Drouzy et al., provide a number that necessarily does not have a physical meaning, whereas the others are a measure of what fraction of the expected tensile performance is achieved. These indices are analyzed in depth, their similarities and shortcomings are discussed in detail, and recommendations are made.     

Mobile tele-echography: user interface design.

Ultrasound imaging allows the evaluation of the degree of emergency of a patient. However, in some instances, a well-trained sonographer is unavailable to perform such echography. To cope with this issue, the Mobile Tele-Echography Using an Ultralight Robot (OTELO) project aims to develop a fully integrated end-to-end mobile tele-echography system using an ultralight remote-controlled robot for population groups that are not served locally by medical experts. This paper focuses on the user interface of the OTELO system, consisting of the following parts: an ultrasound video transmission system providing real-time images of the scanned area, an audio/video conference to communicate with the paramedical assistant and with the patient, and a virtual-reality environment, providing visual and haptic feedback to the expert, while capturing the expert's hand movements. These movements are reproduced by the robot at the patient site while holding the ultrasound probe against the patient skin. In addition, the user interface includes an image processing facility for enhancing the received images and the possibility to include them into a database.     

Study of the solubility,antioxidant activity and structure of inclusion complex of vanillin with β-cyclodextrin

In the present study, complexes of vanillin with β-cyclodextrin (β-CD) were prepared by the freeze-drying method. The formation of the inclusion complex was confirmed by differential scanning calorimetry (DSC). DSC thermograms indicated that the endothermic peak of vanillin and the physical mixture of vanillin with β-CD, due to the melting of vanillin crystals, were absent in DSC thermograms obtained for the freeze-dried inclusion complex. Moreover, the DSC studies under oxidation conditions indicate that the complex of vanillin with β-CD is protected towards oxidation since it remains intact at temperatures where the free vanillin is oxidising. The structure of the complex in aqueous solutions was established by nuclear magnetic resonance (NMR) studies and specifically by two-dimensional rotational frame NOE spectra. NMR studies showed inclusion of the entire vanillin molecule in the β-CD in a tilted manner and with the aldehyde group in the primary side. The stoichiometry of the complex was 1:1. A phase solubility study was performed by mixing an excess amount of vanillin with aqueous solutions containing increasing amounts of β-CD. The results indicated that the complex of a vanillin/β-CD inclusion is more soluble in water than vanillin alone.     

Correction to: Classifying MOOC forum posts using corpora semantic similarities: a study on transferability across different courses

Neural Computing and Applications - A correction to this paper has been published: https://doi.org/10.1007/s00521-021-05904-z     

Microbiological quality of tomatoes and peppers produced under the good agricultural practices protocol AGRO 2-1 & 2-2 in Crete, Greece

The efficiency of the good agricultural practices (GAP) protocol AGRO 2-1 & 2-2, in advancing microbiological-quality of tomatoes and peppers, was studied in greenhouses at Ierapetra, Crete, Greece. The 240 tested vegetables-samples, produced under AGRO 2-1 & 2-2, showed satisfactory quality: Listeria monocytogenes absent per 25 g; Escherichia coli < 20 Colony Forming Units per gram (CFU/g); total coliforms 4.37–4.68 log CFU/g; aerobic plate counts 5.78–5.92 log CFU/g. Based on actual results and practices evaluation, we conclude that AGRO 2-1 & 2-2 can reduce microbial hazards for consumers and furthermore can establish practices in compliance to basic Euro-Retailer-Produce GAP (EUREPGAP) requirements.     

Autonomous stair-climbing with miniature jumping robots.

The problem of vision-guided control of miniature mobile robots is investigated. Untethered mobile robots with small physical dimensions of around 10 cm or less do not permit powerful onboard computers because of size and power constraints. These challenges have, in the past, reduced the functionality of such devices to that of a complex remote control vehicle with fancy sensors. With the help of a computationally more powerful entity such as a larger companion robot, the control loop can be closed. Using the miniature robot's video transmission or that of an observer to localize it in the world, control commands can be computed and relayed to the inept robot. The result is a system that exhibits autonomous capabilities. The framework presented here solves the problem of climbing stairs with the miniature Scout robot. The robot's unique locomotion mode, the jump, is employed to hop one step at a time. Methods for externally tracking the Scout are developed. A large number of real-world experiments are conducted and the results discussed.     

Variational stability of infinite-dimensional optimal control problems

In this paper we examine the variational stability of infinite-dimensional optimal control problems governed by nonlinear evolution equations. Our tools are the Kuratowski—Mosco convergence of sets and the corresponding τ-convergence of functions. We prove the τ-convergence of cost functional and the convergence of the values of the problems, and we examine the variational stability of the solution and reachable sets. These results are then applied to a sequence of nonlinear parabolic distributed-parameter optimal control problems     

Molecular simulation studies of adsorption of hydrogen cyanide and methyl ethyl ketone on zeolite NaX and activated carbon

In the present research study the primary aim is to understand and characterize the physical adsorption of polar molecules namely, hydrogen cyanide and methyl ethyl ketone (MEK) in zeolite NaX, and activated carbon through detailed Monte-Carlo simulations and computational quantum chemistry techniques. The sorption capacity and affinity of the zeolite is compared with activated carbon with different acid site concentrations, type of acid site, and pore sizes by simulating single component isotherms and Henry's constant at 25 degrees C. The role/contribution of certain types of electrostatic interactions namely charge-dipole, charge-induced dipole with zeolite NaX and activated carbon, as well as dipole-dipole interactions among polar molecules is analyzed and discussed.