Viscoelastic properties of epithelial cells

Epithelial cells form tight barriers that line both the outer and inner surfaces of organs and cavities and therefore face diverse environmental challenges. The response to these challenges relies on the cells’ dynamic viscoelastic properties, playing a pivotal role in many biological processes such as adhesion, growth, differentiation, and motility. Therefore, the cells usually adapt their viscoelastic properties to mirror the environment that determines their fate and vitality. Albeit not a high-throughput method, atomic force microscopy is still among the dominating methods to study the mechanical properties of adherent cells since it offers a broad range of forces from Piconewtons to Micronewtons at biologically significant time scales. Here, some recent work of deformation studies on epithelial cells is reviewed with a focus on viscoelastic models suitable to describe force cycle measurements congruent with the architecture of the actin cytoskeleton. The prominent role of the cortex in the cell’s response to external forces is discussed also in the context of isolated cortex extracts on porous surfaces.

МОДЕЛЮВАННЯ ПРОЦЕСУ ВЗАЄМОДІЇ ІМПУЛЬСНОГО СТРУМЕНЯ ІЗ ЗАГОТОВКОЮ ПРИ ЕЛЕКТРОГІДРАВЛІЧНОМУ НА-ВАНТАЖЕННІ

The eg-stamping of thin-leaf-sized parts has shown its technical and economic efficiency, including the ability to receive parts of ultrahon-thread accuracy. At the same time, the workpieces are loaded on the eg-presses of large intensive energy (up to 500 kJ), which have the possibility of space-time loading control. Such management is carried out using multi-terminated discharge blocks in which dozens of discharge cavities are combined into one. The controlled parameters can be the electrical parameters of tens of discharge circuits of the current pulse generator, the volume and step of the arrangement of the discharge cavities, their height to the workpiece, as well as the sequence of discharges in time (simultaneous or with a shift in the time of EG-discharges in adjacent discharge cavities). The choice of rational ranges of these parameters is impossible without numerical simulation of processes occurring in the discharge volume of the entire block.In the simulation, the processes of heat power is comprehensively considered with the EG-discharge, the formation and propagation of the vapor-gas bubble, which generates a flooded stream of liquid, and deforming the supple billet when exposed to such a jet.The results of numerical experiments in the LS-DYNA environment using the ALE method with the EG-discharge in a single bit (submersible) chamber, in two and three neighboring conditions with different variable conditions are set: the distance from the discharge zone to the workpiece (discharge distance) and the displacement of the time of two and three discharges in the adjacent discharges. As compared parameters were selected: movement of the billet and their speed, the distribution of deformations on the surface of the workpiece and the work of deformation. The adequacy of the model of the real process is shown. An energy-efficient energy-generating cell is proposed for generating EG-discharges from a multi-mounted pulse current generator.

A DISCRETE ELEMENT FORMALISM FOR MODELLING WEAR PARTICLE FORMATION IN CONTACT BETWEEN SLIDING METALS

The paper describes an advanced discrete-element based mechanical model, which allows modelling contact interaction of ductile materials with taking into account fracture and surface adhesion by the cold welding mechanism. The model describes these competitive processes from a unified standpoint and uses plastic work of deformation as a criterion of both local fracture and chemical bonding of surfaces in contact spots. Using this model, we carried out a preliminary study of the formation of wear particles and wedges during the friction of rough metal surfaces and the influence of the type of forming third body (interfacial) elements on the dynamics of the friction coefficient. The qualitative difference of friction dynamics in the areas of the contact zone characterized by different degrees of mechanical confinement is shown.

The justification of interaction of fruits with the rolling-in device of a combine-harvester for harvesting cucurbit crops

The role of cucurbit crops in the life of man has been studied and presented. The process of interaction between the rolling-in device of a combine-harvester and a fruit, as well as the process of hitting water-melons into different surfaces, have been considered. The diagram of the distribution of velocities when the rolling-in device interacts with a fruit, as well as the area of expansion of plastic deformation as a result of the impact of a fruit, have been presented. The equation of work, which arises when a fruit hits into the rolling-in device, has been considered, the work being decomposed into plastic work of deformation and elastic work of deformation. The work of plastic deformation, which arises when fruits come into collision with a surface, is considered in more detail, the work being decomposed into plastic work of deformation in the volume, which is limited by a spherical segment and a cone. The absolute and allowable velocities after the impact have been theoretically determined and substantiated. The parameters of allowable velocities for the varieties "Crimson sweet" and "Kholodok" have been theoretically found and the confirmation of the theoretical analysis was carried out in experimental research, which was conducted on a laboratory installation for determining the critical speed of impact on fruits of cucurbit crops. The comparison of the theoretical and experimental values of the terminal velocities confirms the credibility of the research.

Study of the applicability of porous pressings of aluminum and aluminum alloys as energy-absorbing elements

This work reports the results of experimental studies on the applicability of porous pressings of aluminum alloys to passive safety systems. The porous pressings were made from aluminum and aluminum alloy powders with a particle size up to 200 ?m using a hydraulic press. The porosity was varied by varying the pressure in the press hydrosystem and the pressing force. The specimens were not sintered, and no plasticizer was added. To determine which specimen characteristic, the mass or the porosity, is more important, specimens of the same mass (0.01 kg) were used [the deviation did not exceed (2.7 ? 2.8) % ]. To determine the impact absorption ability of the porous pressings of aluminum and aluminum alloy powders, a vertical impact testing machine was used. The ram mass was 22.5 kg (weight 220 N), the fall speed was 5 m/s, and the fall energy was 300 J. The impact absorption ability of the porous pressings was determined by comparing the accelerations and rebound height of the ram in the presence of a porous pressing with their calculated free-fall values. The experiments showed that the use of specimens of maximum porosity decreases the impact energy by the value of the plastic work of deformation and the fracture energy. A comparison of the performance of different specimens showed that the energy absorption ability increases with porosity. As demonstrated by the experiments, porous pressings of aluminum and aluminum alloys can be used as energy -absorbing elements of passive safety systems for commercial and armored combat vehicles, and the impact absorption ability of porous fillers, in particular porous pressings of aluminum and aluminum alloys, can be determined using vertical impact testing machines. Using porous pressings of aluminum and aluminum alloys as an energy-absorbing material decreases the impact acceleration by a factor of 30 to 85 at an impact speed up to 5 m/s. The ability of a pressing to reduce the impact acceleration depends on its dimensions and porosity to a greater extent than on its mass. The greatest decrease in impact acceleration is provided by porous pressings of maximum porosity, in which the impact energy is converted to the plastic work of deformation and the fracture energy.

Impact of Almond Variety on “Amaretti” Cookies as Assessed through Image Features Modeling, Physical Chemical Measures and Sensory Analyses

In the present study, the influence of almond variety on color, chemical, physical and sensory characteristics of “amaretti” cookies during the shelf life, was assessed. Four varieties were chosen for the study, two of which were local (Cossu, Arrubia) and two widely cultivated (Tuono, Texas). Almonds have been characterized in the content of proteins, crude fat, amygdalin and fatty acids profile. The evolution of the characteristics during the shelf life hasbeen measured through image data modeling, texture, physical chemical and sensory analyses. Data were then treated with a multivariate approach performing a PCA. Image analysis and fitting on log normal and powerlaw functions highlighted the influence of the variety on the total area affected by surface breakages, and on the distribution of the cracking surfaces dimension classes. Texture parameters (crust hardness, thickness and work of deformation) were negatively correlated to moisture content. Sensory profile confirmed the differences in tactile features measured through instrumental texture, while slight to no differences were found in odor profile. Consumer test showed an higher acceptability for Arrubia, Texas and Tuono samples throughout the shelf life, while Cossu samples were less accepted. Overall, the choice of almond variety influences product features and liking of almond products, therefore it represents an important phase to direct the choice of both farmers and confectionery manufacturers.

Linking interfacial work of deformation from deconvoluted macro-rheological spectrum to early stage healing in selected polyurethanes

The interfacial work of deformation obtained by decovolution of the relaxation spectra acquired via macrorheology is linked and is able to predict interfacial healing in polyurethanes.

Evaluation of metals deformability

The laws of the deformation behavior of metals, determined by carrying out standardized uniaxial tensile tests are studied. The distribution of various strength class metals by strain resistance is analyzed. It is taken into account that in the thermodynamic aspect the deformation process is dissipative effect, therefore, the deformation work, determined by the area of the tension diagram, serves as basis for assessing of the metals deformability criteria. It is found that the normalized specific work of deformation increases linearly with increasing strength. In the applied aspect, the numerical values of the compliance criterion can be used to predict the behavior of various strength class materials during mechanical processing (metal forming and cutting) or operation.

Estimates of Metal Deformability

This paper is devoted to the study of the laws of the deformation behavior of metals, determined by carrying out standardized uniaxial tensile tests. The distribution of various strength grade metals by strain resistance was analyzed. It was taken into account that in the thermodynamic aspect the deformation process is a dissipative effect. In that regard, the magnitude of deformation work, determined by the area of the tension diagram, serves as a basis for assessing the deformability criteria of metals. It was found, that the normalized specific work of deformation linearly increases with strength. As well as it was established that localization of plastic flow is related directly to the characteristics of the tension diagram under solid deformation. In the applied aspect, the numerical values of the compliance criterion can be used to predict the materials behavior of different strength grade during mechanical processing (metal forming and cutting) or operation.

Shape Indexes for Dieless Forming of the Elongated Forgings with Sharpened End by Tensile Drawing with Rupture

The criteria for the assessment of the form change in the process of direct profiling of workpieces , applying the stretching method with a rupture are developed, methods for their calculation are proposed with allowance for the volume of the redistributed metal and energy costs for deformation. The nature of the functional connection of these criteria of shape change assessment with the work of deformation is determined.