Probing the nature of defects in graphene by Raman spectroscopy

Raman spectroscopy is able to probe disorder in graphene through defect-activated peaks. It is of great interest to link these features to the nature of disorder. Here we present a detailed analysis of the Raman spectra of graphene containing different type of defects. We found that the intensity ratio of the D and D' peak is maximum (～13) for sp(3)-defects, it decreases for vacancy-like defects (～7), and it reaches a minimum for boundaries in graphite (～3.5). This makes Raman Spectroscopy a powerful tool to fully characterize graphene.     

Characterisation of friction properties between a laminated carbon fibres reinforced polymer and a monocrystalline diamond under dry or lubricated conditions

The machining of carbon fibre reinforced polymer (CFRP) is a hot topic for the aircraft industry. Such materials are considered as difficult to cut materials due to their heterogeneity and presence of hard fibres. In this context, a lot of finite element models have been developed in order to understand their material removal mechanisms. Among the scientific issues faced by these works, the identification of friction coefficients between CFRP and cutting tool materials remains unanswered. So, this paper aims to characterize the friction properties between composite and cutting tool materials. For instance, the paper focuses on the context of a laminated CFRP machined with a monocrystalline diamond tool under dry or under lubricated conditions. The specific tribological conditions during machining of such heterogeneous materials are discussed in the paper, especially the configuration of the tribosystem (‘opened tribosystem’) and the orientation of laminates and fibres during sliding. The great lack of friction coefficient is mainly due to the absence of relevant tribometers simulating the tribological conditions occurring in cutting. This paper presents the development of a new tribometer designed to simulate conditions corresponding to machining of CFRP materials. It provides quantitative values of friction coefficient depending on several key parameters. A range of sliding velocities and contact pressures has been tested. The influence of layers orientation and cutting fluids has also been investigated. It has been shown that friction coefficients are very low (∼0.06) in dry regime. Friction coefficient is not sensitive to contact pressure nor to sliding velocity. Additionally this works has revealed that a cutting fluid leads to a significant decrease in friction coefficients (∼0.02), which corresponds to a friction less situation.     

HOLZ lines splitting on SiGe/Si relaxed samples: Analytical solutions for the kinematical equation

Sample thinning for TEM observation introduces large changes with respect to the initial strain state of the bulk sample and particularly relaxation via the free surfaces which leads to HOLZ lines splitting in the CBED pattern. This phenomenon has been simulated owing to extensive calculations either in the kinematical or the dynamical framework of electron diffraction mainly using displacement fields resulting from finite element modelling of the sample relaxation. HOLZ line splitting is well reproduced and numerical fits can be used to compare experimental and calculated curves. This paper proposes new analytical solutions for the kinematical equation of electron diffraction. Simple mathematical functions are used to approximate the deformation profiles. We showed that, under certain conditions, the rocking curve profile can be analytically calculated, thus providing some clue to separate different contributions to the rocking curves against deformation profile. These simplified analytical expressions are used to extract the maximum amplitude displacement within the sample with about 10% accuracy. This accuracy can even be improved to 1% with a short adjustement routine. The influence of the shape of the displacement profile on the rocking curves is demonstrated.     

Mechanistic approach to predict real machining time for milling free-form geometries applying high feed rate

An accurate estimate of machining time is very important for predicting delivery time, manufacturing costs, and also to help production process planning. Most commercial CAM software systems estimate the machining time in milling operations simply by dividing the entire tool path length by the programmed feed rate. This time estimate differs drastically from the real process time because the feed rate is not always constant due to machine and computer numerical controlled (CNC) limitations. This study presents a practical mechanistic method for milling time estimation when machining free-form geometries. The method considers a variable called machine response time (MRT) which characterizes the real CNC machine’s capacity to move in high feed rates in free-form geometries. MRT is a global performance feature which can be obtained for any type of CNC machine configuration by carrying out a simple test. For validating the methodology, a workpiece was used to generate NC programs for five different types of CNC machines. A practical industrial case study was also carried out to validate the method. The results indicated that MRT, and consequently, the real machining time, depends on the CNC machine’s potential: furthermore, the greater MRT, the larger the difference between predicted milling time and real milling time. The proposed method achieved an error range from 0.3% to 12% of the real machining time, whereas the CAM estimation achieved from 211% to 1244% error. The MRT-based process is also suggested as an instrument for helping in machine tool benchmarking.     

(−)Geosmin sorption by enological yeasts in model wine and FTIR spectroscopy characterization of the sorbent

For the first time, we report that enological yeasts or yeast cell walls can sorb (−)geosmin, an undesirable molecule that causes critical organoleptic defects in wine at low concentrations (around 50 ng l⁻¹). The wine is described as “earthy” or “mouldy”. The influence of various post-harvesting processes on yeast (−)geosmin sorption capacity was studied. The dried yeast biomass obtained by the different processes was analysed by FTIR spectroscopy in ATR mode: structural differences were detected between the samples depending on the strain and the treatment used. Surface proteins and mainly phospholipids from the plasma membrane appeared to induce significantly different signals which may explain the different sorption capacities. The possible involvement of phospholipids in (−)geosmin sorption by yeasts highlights the complexity of this phenomenon.     

A real-time low-cost marker-based multiple camera tracking solution for virtual reality applications

One of the reasons of how virtual reality applications penetrate industrial production chains slowly is because of significant investment costs to purchase adequate supporting hardware. As a consequence such applications are only available to major companies and fail to benefit the production processes of small and medium enterprises. In this article, we introduce PTrack, a real-time, low-cost, marker-based multiple camera tracking solution for virtual reality providing the accuracy and scalability usually found in much more expensive tracking systems. PTrack is composed of single camera tracking PTrack Units. Each unit is connected to a video camera equipped with infrared strobes and features a novel iterative geometric pose estimation algorithm which does marker-based single camera tracking and is therefore completely autonomous. Multiple PTrack units successively extend the tracking range of the system. For a smooth transition of tracked labels from one camera to another, camera range areas must overlap to form a contiguous tracking space. A PTrack Sensor Fusion Module then computes the pose of a certain label within tracking space and forwards it to interested applications. A universal test setup for optical tracking systems has been built allowing to measure translational and rotational accuracy of PTrack as well as of competing systems.     

Kombinierte Fließ- und Grenzbedingungen

A careful study of the models for isotropic material behaviour (e.g. von Mises, Tresca, Mohr–Coulomb, Drucker–Prager etc.) demonstrates, that they seldom coincide with the experimental data. Incompressible models usually deliver wrong estimations of material behaviour at multi-axial loadings. Models, which take compressibility into account lead to forbidden values of the plastic Poisson’s ratio at compression. From experience we know, it is hard to model the multi-dimensional material behaviour in a proper way due to the lack of experimental information. A large number of models provide acceptable results in certain regions of the stress space only. This observation results in the idea of building combinations of “well-tried” models. In the paper the well-known limit surfaces are described and systemized on the basis of symmetry in the π-plane. This systemstisation allows to fill in some gaps in the combined models. In order to allow the choice of the model to be made in a unique way new plausibility conditions, which reduce the number of possible combinations are introduced. For instance in combinations of continuous models (Tresca, Mohr–Coulomb, Schmidt–Ishlinsky–Hill etc.) the C⁰- and C¹-transitions can be used, however for continuously differentiable models only a C¹-transition makes sense. The singularities of the modells (e.g. maximum strain hypothesis, Mohr–Coulomb, Tresca etc.) have no physical justification. Furthemore the models with hexagonal symmetry (e.g. Tresca, Schmidt–Ishlinsky–Hill etc.) are of theoretical interest only, they oversimplify the material behaviour. So after taking such models out of consideration only the cubic, the triquadratic, and “geo-mechanical” models can be recommended for applications. In order to provide an overview on how the models of isotropic material behaviour were developed, numerous references to well-known applications were provided.     

On the performance of binomial and beta-binomial models of demand forecasting for multiple slow-moving inventory items

The paper deals with the lead-time demand forecasting for inventory management of multiple slow-moving items in the case when the available demand history is very short. Two stochastic models of demand are compared: (i) the first based on the “population-averaged” binomial distribution of requests (the traditional approach); and (ii) the second based on the beta-binomial probability distribution that assumes that the demand probabilities for the inventory items follow the beta distribution, and employs the Bayesian framework to forecast the lead-time demand (longitudinal statistical approach). The conducted simulation study shows that using the latter model leads to the significant decrease of the holding cost and higher inventory system reliability. Besides, as follows from the simulation results, the beta-binomial demand model is especially useful when the demand probabilities are low and have the U-shaped distribution.     

Using a game engine for VR simulations in evacuation planning.

Researchers who want to use virtual reality-based simulations in their work must address some important requirements. Simulations require a good 3D graphical rendering capability. For realistic results, they must also consider the effects of physical laws, such as gravity and collision forces. A software platform that meets these requirements can serve a broad range of science and technology applications, but developing an entire platform is hard work itself. In this article, we present our use of a game engine for virtual simulations of building evacuations in emergency situations. We have modeled a real IEN building in 3D to perform preliminary evacuation tests, prior to real ones, and thus support evacuation planning. Nuclear plants represent just one of many environments where virtual simulations might be the best or only means of evaluating situations that are too dangerous to simulate in real environments-for example, in the presence of fire and smoke or radioactive or chemical contamination.