Numerous studies on zinc and zinc alloy coated steel sheets have appeared since corrosion problems were widely recognized in the automotive industry in the 1970s. In general, accelerated corrosion ...tests including the Salt Spray Test and Cyclic Corrosion Tests have been applied to evaluate the corrosion resistance of coated steels in the laboratory in order to shorten the product development period. However, the reproducibility of corrosion in actual use conditions by corrosion tests is always a controversial issue. In this paper, author’s previous studies regarding corrosion of coated steel sheets in automobiles and corrosion tests are reviewed. The perforation corrosion behaviors of coated steels at lapped parts in snowy and tropical regions were clarified on the basis of an analysis of corroded vehicles. Several types of accelerated corrosion tests used in the automotive industry were conducted for comparison with the corrosion observed in the actual vehicles. The Perforation Corrosion Index (PCI), which is the corrosion rate ratio of steel and zinc coating, was introduced as an index for comparing the correlation of corrosion behaviors. Coating weight is the major factor determining the perforation corrosion resistance of existing coated materials in automobile use environments. Corrosion tests that have a PCI value close to that in the use environment can simulate similar corrosion tendencies. The influence of the specimen configuration is also a key factor for adequate evaluation of corrosion resistance. Specimens without an intentional large clearance and bare metal surface in the lapped portion are recommended for perforation corrosion tests.
Nature is full of power-law interactions, e.g., gravity, electrostatics, and hydrodynamics. When sources of such fields are randomly distributed in space, the superposed interaction, which is what we ...observe, is naively expected to follow a Gauss or Lévy distribution. Here, we present an analytic expression for the actual distributions that converge to novel limits that are in between these already-known limit distributions, depending on physical parameters, such as the concentration of field sources and the size of the probe used to measure the interactions. By comparing with numerical simulations, the origin of non-Gauss and non-Lévy distributions are theoretically articulated.
•Atmospheric Corrosion Monitor (ACM) sensor is applicable to automotive environment.•The cause of corrosion of respective parts is identified by ACM monitoring.•Corrosion rate of materials is ...estimated from the correlation with ACM outputs.•We demonstrate corrosion life prediction for respective parts in use environments.
Severity of corrosion damage in automobiles depends on use environments and parts. Corrosion life prediction is a key technology for the optimum selection of materials. The Fe–Ag type Atmospheric Corrosion Monitor (ACM) sensor has been the object of many studies from this viewpoint. In the present study, ACMs were installed on various parts of a monitoring test vehicle and the corrosivity of the environments of those parts was evaluated. To simulate different use environments, pure water and salt water were sprayed on the right and left halves of the vehicle body. The corrosion behavior in each part was characterized by the output of the ACM sensor against atmospheric parameters and driving history. Corrosion of test coupons (cold-rolled steel, Zn-coated steel) was also measured at the same positions. The corrosion rates of these exposure test specimens showed a good correlation with the average daily charge calculated from the sensor output. These results demonstrated the possibility of corrosion life prediction and materials selection based on ACM monitoring results. It was concluded that ACM monitoring is applicable to corrosivity evaluation of automotive environments, including both specific parts of automobiles and automobile use environments.
Physiological processes in cells are performed efficiently without getting jammed although cytoplasm is highly crowded with various macromolecules. Elucidating the physical machinery is challenging ...because the interior of a cell is so complex and driven far from equilibrium by metabolic activities. Here, we studied the mechanics of in vitro and living cytoplasm using the particle-tracking and manipulation technique. The molecular crowding effect on cytoplasmic mechanics was selectively studied by preparing simple in vitro models of cytoplasm from which both the metabolism and cytoskeletons were removed. We obtained direct evidence of the cytoplasmic glass transition; a dramatic increase in viscosity upon crowding quantitatively conformed to the super-Arrhenius formula, which is typical for fragile colloidal suspensions close to jamming. Furthermore, the glass-forming behaviors were found to be universally conserved in all the cytoplasm samples that originated from different species and developmental stages; they showed the same tendency for diverging at the macromolecule concentrations relevant for living cells. Notably, such fragile behavior disappeared in metabolically active living cells whose viscosity showed a genuine Arrhenius increase as in typical strong glass formers. Being actively driven by metabolism, the living cytoplasm forms glass that is fundamentally different from that of its non-living counterpart.
Nonequilibrium Mechanics of Active Cytoskeletal Networks Mizuno, Daisuke; Tardin, Catherine; Schmidt, C.F ...
Science (American Association for the Advancement of Science),
01/2007, Letnik:
315, Številka:
5810
Journal Article
Recenzirano
Cells both actively generate and sensitively react to forces through their mechanical framework, the cytoskeleton, which is a nonequilibrium composite material including polymers and motor proteins. ...We measured the dynamics and mechanical properties of a simple three-component model system consisting of myosin II, actin filaments, and cross-linkers. In this system, stresses arising from motor activity controlled the cytoskeletal network mechanics, increasing stiffness by a factor of nearly 100 and qualitatively changing the viscoelastic response of the network in an adenosine triphosphate-dependent manner. We present a quantitative theoretical model connecting the large-scale properties of this active gel to molecular force generation.
Molecular motors are nonequilibrium open systems that convert chemical energy to mechanical work. Their energetics are essential for various dynamic processes in cells, but largely remain unknown ...because fluctuations typically arising in small systems prevent investigation of the nonequilibrium behavior of the motors in terms of thermodynamics. Recently, Harada and Sasa proposed a novel equality to measure the dissipation of nonequilibrium small systems. By utilizing this equality, we have investigated the nonequilibrium energetics of the single-molecule walking motor kinesin-1. The dissipation from kinesin movement was measured through the motion of an attached probe particle and its response to external forces, indicating that large hidden dissipation exists. In this short review, aiming to readers who are not familiar with nonequilibrium physics, we briefly introduce the theoretical basis of the dissipation measurement as well as our recent experimental results and mathematical model analysis and discuss the physiological implications of the hidden dissipation in kinesin. In addition, further perspectives on the efficiency of motors are added by considering their actual working environment:
living cells
.
Green tea polyphenol (–)-epigallocatechin-3-gallate (EGCG) has various beneficial properties including chemopreventive, anticarcinogenic, and antioxidant actions. The interaction with proteins known ...as EGCG-binding targets may be related to the anticancer effects. However, the binding mechanisms for this activity remain poorly understood. Using mass spectrometry and chemical detection methods, we found that EGCG forms covalent adducts with cysteinyl thiol residues in proteins through autoxidation. To investigate the functional modulation caused by binding of EGCG, we examined the interaction between EGCG and a thiol enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Concentration-dependent covalent binding of EGCG to GAPDH was found to be coupled to the irreversible inhibition of GAPDH activity. Mutation experiments revealed that EGCG is primarily bound to the cysteinyl thiol group of the active center, indicating that the irreversible inhibition of GAPDH is due to the covalent attachment of EGCG to the active-center cysteine. Moreover, using EGCG-treated cancer cells, we identified GAPDH as a target of EGCG covalent binding through specific interactions between catechols and aminophenyl boronate agarose resin. Based on these findings, we propose that the covalent modification of proteins by EGCG may be a novel pathway related to the biological activity of EGCG.
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