3D microscopic reconstruction of pearls using combined optical microscopy and photogrammetry

Theory: Formulation of thermomechanical problems in 3D and its numerical implementation. Numerical methods for solving temperature, Poisson, momentum and continuity equations in 3D. Exercises: Programming of numerical methods for temperature and Poisson equations and coupled solving of momentum and continuity equations in 3D. Why simply not always 3D? We know very well that the Earth is a 3D, nearly spherical object and, therefore, all the dynamic processes inside our planet are inherently three dimensional. Therefore, it is very logical to assume that realistic geodynamic modelling should always be done in 3D. Also, if you talk to geoscientists studying various natural geological objects, you are frequently told that such objects can only be modelled in 3D. This is a normal expectation since they are perfectly aware of the spatial 2D variability of geological structures on the Earth's surface and they thus know that a similar variability also exists in depth. Therefore, 3D modelling appears to be the natural choice for ‘observers’. What about ‘modellers’? Why don't they always use 3D modelling? What's wrong with it? The ‘uncensored’ truth about 3D modelling is the following: 3D thermomechanical modelling is quite easy from a methodological point of view – it is fairly straightforward to formulate and discretise the governing equations in a 3D Cartesian geometry for both simple viscous and more realistic visco-elasto-plastic rheologies (especially by using the same relatively simple finite-differences and marker-in-cell techniques that we extensively discussed in this book). […]

The purpose of this work is to study the problem of uniform grip at the points of contact of a round or spherical object (fruits and vegetables) with the grip. The research methodology uses pressure sensors mounted on the “fingers” of the handle. At a certain force value in the contact zone, the “fingers” of the handle stop. The grip must create equal forces at the points of contact of all “fingers” for an even grip. To explore these issues, phalangeal graspers adapting to the fetal surface are analyzed here. The flat model shows the general patterns of the relationship between the forces of the “fingers” of the grip and the round object to be grasped. The flat model shows the general patterns of the relationship between the forces of the “fingers” of the grip and the round object to be grasped. We examined the 3D model of this gripper and calculated the parameters of the 3D model. Conclusions and practical consequences are the values of stresses and elastic displacements at the points of the contact lines of the teeth of the 3D models of the gripper and the object being grabbed. The distribution of forces on a flat diagram and the values of von Mises stresses in the 3D model demonstrate a certain similarity in the uniformity of distribution of these parameters. Color scales with the values of the corresponding parameters are also presented; the calculation was carried out using the finite element modeling method in inventor.

1 - Mechanism of fatigue in the absence of defects and inclusions

An improved technique for characterizing the fracture toughness via scratch test experiments

Automatic segmentation of the pharyngeal airway space with convolutional neural network

Cement paste degradation under external sulfate attack: An experimental and numerical research

Magnetorheological (MR) gels consist of micron sized magnetic particles inside a gel matrix. Before physical cross-linking, the suspension is subjected to a small magnetic field which creates a particle string structure. After cross-linking, the string is kept within the gel at room temperature. Under an external homogeneous magnetic field and mechanical deformation, the soft swollen gel matrix allows the string to largely rearrange at microscopic scales. With the help of two homemade magneto cells mounted on an optical microscope, we were able to follow the conformational change and instabilities of a single magnetic particle string under the combined influence of shear (or stretch) and the magnetic field. In the absence of mechanical deformation, an external magnetic field, applied in the perpendicular direction to the string, breaks it into small pieces generating periodic structures like sawteeth. When an external magnetic field is applied parallel to the pre-aligned string, it exhibits a length contraction. However, under shear strain perpendicular to the original pre-structured string (and magnetic field), the string breaks and short string segments tilt, making an angle with the original direction that is smaller than that of the applied shear (non-affine). The difference in tilt angle scales with the inverse length of the small segments L-1 and the magnetic flux density B, reflecting the ability of the gel matrix to expel solvents under local stress.

Swollen physical magneto-responsive gels were obtained by self-assembly of triblock copolymers containing dispersed soft magnetic particles. When subject to simple shear cyclic loading–unloading cycles in the presence of a magnetic field, magnetorheological (MR) gels show a stress hardening behavior. The stress-hardening was characterized by the increase of the maximum stress against the number of cycles. Most of the stress increases are achieved in the first and second cycles and only minor effects take place in the subsequent ones. The cyclic behaviour of MR gels with dilute particle volume fraction is also studied with the help of a homemade shear cell mounted on an optical microscope. Despite the difference of particle volume fraction, we are able to relate cyclic stress hardening to the change in particle–particle distribution observed directly at the microscopic scale. While anisotropic particle strings created by a pre-structuring process (original sample alignment) still has many defects, the history of simple shear in the presence of the magnetic field gradually removes the defects of the particle strings and helps them to relax towards a zipped cluster. We show here the first directly observed example of the shear-annealing effect in MR gels. The shear induced rearrangement of the particle network serves as the microscopic origins of the above mentioned cyclic stress hardening behavior of MR gels and seems to be fully reversible after the removal of the magnetic field. Results show that a slow quiescent process also takes place and it is suggested to be related to solvent flow outwards of the clusters, while they get more compact. Interestingly, all directly observed rearrangements including string breaking seem to be fully reversible after removal of the magnetic field.

Viscoelastic properties of complex fluids in the microscopic scale can be studied by measuring the transport properties of small, embedded probe particles. We have measured the complex electrophoretic mobility micro*(omega) of nanometer-sized particles dispersed in a lyotropic lamellar phase, which shows two relaxation processes at approximately 1 kHz (high frequency relaxation, HF) and 1 Hz (low frequency relaxation, LF). It is shown quantitatively that these processes are caused by the trapping of particles within two local structures of characteristic size in the lamellar phase: the interbilayer distance and the persistence length. The origin of observed relaxations is further investigated and augmented in this study with data obtained by two other complementary methods, dielectric spectroscopy and the direct observation of fluorescently labelled probe particles under an optical microscope. It is shown that the local distortion field of the lamellar phase is induced by the extra steric interaction involving the collision of a colloidal particle with the membrane. The resulting distortion field hinders the Brownian motion of colloidal particles parallel to the membranes (not vertical), and causes the observed HF relaxation. On the other hand, the origin of LF relaxation is presumably a result of the defects in the lamellar structure. Since the results of this study show that the transport property is strongly influenced by microscopic environments, this method is referred to as electrophoretic microrheology.

Visual sensing based three dimensional (3D) particle localization in an optical microscope is important for both fundamental studies and practical applications. Compared with the lateral (X and Y) localization, it is more challenging to achieve a high resolution measurement of axial particle location. In this study, we aim to investigate the effect of different factors on axial measurement resolution through an analytical approach. Analytical models were developed to simulate 3D particle imaging in an optical microscope. A radius vector projection method was applied to convert the simulated particle images into radius vectors. With the obtained radius vectors, a term of axial changing rate was proposed to evaluate the measurement resolution of axial particle localization. Experiments were also conducted for comparison with that obtained through simulation. Moreover, with the proposed method, the effects of particle size on measurement resolution were discussed. The results show that the method provides an efficient approach to investigate the resolution of axial particle localization.

In this paper the influences on the dimension accuracy and the roughness of pulsed laser caved shapes in alumina ceramic have been studied. The experiments were performed on the experimental setup shown in figure 1. As a laser source pulsed LP-3000 Nd:YAG laser was used. A single lens, mounted on the z translation stage, with focusing length of 100 mm was used to focus the laser light onto the target surface which was mounted on the x-y computer controlled translation stages. The movement resolution was 10 μm. The samples used were Al2O3 ceramic plates. After treatment ceramic samples were examined by an optical microscope and the surface profile measurement were performed with a stylus apparatus.

A method for rapid measurement of laser ablation rate of hard dental tissue

The present paper refers to an innovative SOFC concept named EVOLVE after a running FP7 project which integrates advanced materials and an inventive anode current collector made from a NiCrAl preoxidized foam impregnated with a conductive perovskite. Even if the concept is the beneficial combination of Metal supported cell (MSC) and Anode supported cell (ASC) technologies, strong improvements in terms of reliability and durability are expected. In order to enhance anode efficiency, the 3D microstructure needs to be precisely described at the microscopic scale. ISTEC has produced LST-GDC active anode layers using screen printing process. Back-scattered electrons (BSE) SEM images that contain relevant microstructure information have been realized by Centre des Matériaux. All the original images have been enhanced by Centre de Morphologie Mathématique using a series of morphological operators to remove artefacts. Finally, a 3D pluri-Gaussian model has been generated from 2D images, and then computed to predict volume fraction of the 3 phases, 3D tortuosity, gas permeation and ionic conductivities.

Grain breakage in rockfill in civil engineering structures is the major cause responsible for settlement and collapse. It is inherently due to large grain size and angular shape of the grains. To model these features, a three-dimensional discrete element model of a breakable grain is presented hereafter. The model is able to reproduce grain breakage into rigid irregular fragments with conservation of the mass of the initial grain. Polyhedral shapes are chosen to represent the grains, and are divided into irregular tetrahedral fragments joined together by a cohesive law to enable breakage. This model is implemented in a Non-Smooth Contact Dynamics code. Single grain crushing tests are first conducted to capture the influence of mechanical and geometrical parameters of the model. The intra-granular cohesion defines the grain strength. The grain size and the size and geometrical disposition of subgrains can act in a competitive way, thus contributing to the definition of the grain strength, and in the validation of the scale of effect observed in this type of material: the bigger the grain, the lower its strength. The same grain model is then used to generate multi granular samples subjected to oedometric compression, where grains interact via contact and friction processes, with a uniform initial grain size distribution. The effects of grain breakage are investigated through the analysis on the macroscopic and microscopic scales, with a comparison with unbreakable grains samples. The ability of the model to reproduce physical laboratory tests is confirmed through the simulations.

Melt-grown, highly crystalline CsPbBr3 has been intensely investigated as a semiconductor for direct hard radiation detection. While the phase purity and crystallinity of the CsPbBr3 ingots are assessed by X-ray diffraction and optical microscopy, the overall quality of the material is ultimately judged by the performance of the final device. The iterative evaluation of crystal quality would greatly benefit from broadening readily accessible structural methods. In this work, we establish nuclear quadrupole resonance (NQR) spectroscopy as a versatile, noninvasive technique for evaluating the quality of melt-grown CsPbBr3 ingots. We show that in addition to its inherent utility for probing the local environment around a quadrupolar nucleus, NQR spectroscopy is highly sensitive to crystal orientation and crystallinity, as further supported by ab initio calculations. The key spectroscopic descriptors (linewidth and integrals) can thus be correlated with both macroscopic and microscopic structural features, thereby establishing a robust and rapid method for evaluating crystal quality. Customized resonators can accommodate large ingots and enable measurements directly in the quartz ampule used for melt growth, as well as semiautomated spatial mapping of spectroscopic features across the ingots. For instance, we show that removing the impurities collected near the top of the ingot and subsequent recrystallization improve the homogeneity and overall crystallinity of the samples, highlighting the need for multiple purification steps. We also observe that different crystallographic orientations of crystal domains along the ingot are obtained and preserved in cut crystal disks. These findings pave the way for integrating NQR spectroscopy as a practical, noninvasive tool for in-line or in-situ crystal quality control and guided sample selection.