Regulated changes in material properties underlie centrosome disassembly during mitotic exit

Centrosomes must resist microtubule-mediated forces for mitotic chromosome segregation. During mitotic exit, however, centrosomes are deformed and fractured by those same forces, which is a key step in centrosome disassembly. How the functional material properties of centrosomes change throughout the cell cycle, and how they are molecularly tuned, remain unknown. Here, we used optically induced flow perturbations to determine the molecular basis of centrosome strength and ductility in C. elegans embryos. We found that both properties declined sharply at anaphase onset, long before natural disassembly. This mechanical transition required PP2A phosphatase and correlated with inactivation of PLK-1 (Polo kinase) and SPD-2 (Cep192). In vitro, PLK-1 and SPD-2 directly protected centrosome scaffolds from force-induced disassembly. Our results suggest that, before anaphase, PLK-1 and SPD-2 respectively confer strength and ductility to the centrosome scaffold so that it can resist microtubule-pulling forces. In anaphase, centrosomes lose PLK-1 and SPD-2 and transition to a weak, brittle state that enables force-mediated centrosome disassembly.

Investigation of the dispersion processes of composite colloidal capillary-porous materials

The technology of drying colloidal capillary-porous materials to a final humidity of 6-8%, developed at the Institute of Technical Thermophysics of the NAS of Ukraine, allowed to obtain a brittle state, in which it is possible to grind this product to small particles. The most suitable for industrial grinding of the dried composite colloidal capillary-porous materials is the impact method, because when wiping and crushing the material has accumulated, stuck to the working surface. Powders are characterized by one pronounced maximum corresponding to the particle size of the powder of 0,16 mm. As the rotation speed of the shredder rotor changes, the particle size distribution of 0,16 mm increases by reducing the larger particles. The amount of powder thus obtained is directly proportional to the speed of rotation of the rotor. The study of the dispersion and classification of functional powders showed that all powders have the largest particle size of 0,16 mm. The maximum yield of this fraction is 70% and the lowest is 40%. The structural-mechanical characteristics of powders from composite colloidal capillary-porous materials were investigated for the first time. Characteristics of different fractions were determined by such parameters as bulk density, vibration density, angle of natural slope, speed of material flow through the funnel and others. Studies to determine the structural and mechanical properties of functional powders have shown that they can be attributed to more bulk powders, as opposed to highly bound monopowders. Creating compositions improves their structural and mechanical properties.

Material aging causes centrosome weakening and disassembly during mitotic exit

ABSTRACTCentrosomes must resist microtubule-mediated forces for mitotic chromosome segregation. During mitotic exit, however, centrosomes are deformed and fractured by those same forces, which is a key step in centrosome disassembly. How the functional material properties of centrosomes change throughout the cell cycle, and how they are molecularly tuned remain unknown. Here, we used optically-induced flow perturbations to determine the molecular basis of centrosome strength and ductility in C. elegans embryos. We found that both properties declined sharply at anaphase onset, long before natural disassembly. This mechanical transition required PP2A phosphatase and correlated with inactivation of PLK-1 (Polo Kinase) and SPD-2 (Cep192). In vitro, PLK-1 and SPD-2 directly protected centrosome scaffolds from force-induced disassembly. Our results suggest that, prior to anaphase, PLK-1 and SPD-2 confer strength and ductility to the centrosome scaffold so that it can resist microtubule-pulling forces. In anaphase, centrosomes lose PLK-1 and SPD-2 and transition to a weak, brittle state that enables force-mediated centrosome disassembly.

Durability of metal structures under quasi-static load

Failure of materials and structures is one of unresolved problems of mechanics. This paper offers an approximate approach to assessing durability of products on the basis of a mechanical experiment. The experiment represents the fatigue process as a transition of a plastic material into its brittle state. A simplified physical model – which could be used to build a mathematical model of fatigue process – hangs on a local transition of a plastic material into its brittle state. The calculation methodology includes both an original part on cyclic degradation of material strength and correlations based on experiments and checked by design routines. Two approaches to calculating the durability of a randomly-loaded object are compared: using the equation of cyclic degradation of strength and the rule of linear summation of fatigue damages. The results obtained are useful for improving methodologies of calculating service life or durability of structures.

Deterioration in Strength of Brittle-State Porous Bodies

A theory is presented to predict the deterioration in strength for a structure composed of a brittle-state porous material which has been subjected to a damaging tension field. Based on the theory, a degradation factor can be formulated as a means of evaluating the residual strength numerically. A proposed material function for a brittle-state porous medium was evaluated experimentally and was found to be satisfactory for an alumina material. The modulus of elasticity at room temperature of the same material has been found to increase with the density ratio in semi-logarithmic form.

Dynamic Vitrification and the Activation Energy of Rubbery Polymers

1. The resistance to brittleness of a wide variety of rubbers was studied by the method of periodic deformation. 2. Dynamic glassing, during which transition from the highly elastic into the brittle state is observed, always occurs in the liquid state of aggregation of a polymer, where the activation energy of molecular rearrangement changes with temperature according to an exponential law. 3. In a small temperature interval the change of the activation energy can be approximated by a linear law; consequently, Equations (1) and (4) expressing the dependence of the temperature of transition of the rubber into the brittle state on the frequency of deformations are satisfied approximately. The constants entering into these equations and their relationship to the activation energy are determined. 4. The activation energy of dynamic glassing is directly proportional to the glass temperature of the polymer and is greater than the activation energy of static glassing by approximately 5–10%, consequently the rate of establishment of the equilibrium structure is greater than the rate of stress relaxation or the rate of development of elastomeric deformation. 5. The relatively high activation energy of dynamic in comparison with static glassing is caused, apparently, by the larger size of the segments of the polymer chain during mechanical action compared to the size during free thermal motion.