Evaluation of primary water stress corrosion cracking growth rates by using the extended finite element method

AbstractBackgroundMitigation of primary water stress corrosion cracking (PWSCC) is a significant issue in the nuclear industry. Advanced nickel-based alloys with lower susceptibility have been adopted, although they do not seem to be entirely immune from PWSCC during normal operation. With regard to structural integrity assessments of the relevant components, an accurate evaluation of crack growth rate (CGR) is important.MethodsFor the present study, the extended finite element method was adopted from among diverse meshless methods because of its advantages in arbitrary crack analysis. A user-subroutine based on the strain rate damage model was developed and incorporated into the crack growth evaluation.ResultsThe proposed method was verified by using the well-known Alloy 600 material with a reference CGR curve. The analyzed CGR curve of the alternative Alloy 690 material was then newly estimated by applying the proven method over a practical range of stress intensity factors.ConclusionReliable CGR curves were obtained without complex environmental facilities or a high degree of experimental effort. The proposed method may be used to assess the PWSCC resistance of nuclear components subjected to high residual stresses such as those resulting from dissimilar metal welding parts

Advances in AFM Imaging Applications for Characterizing the Biophysical Properties of Amyloid Fibrils

Although the formation mechanism of amyloid fibrils in bodies is still debated, it has recently been reported how amyloid fibrils can be formed in vitro. Accordingly, we have gained a better understanding of the self-assembly mechanism and intrinsic properties of amyloid fibrils. Because the structure of amyloid fibrils consists of nanoscaled insoluble strands (a few nanometers in diameter and micrometers long), a special tool is needed to study amyloid fibrils at length. Atomic force microscopy (AFM) is supposed to be a versatile toolkit to probe such a tiny biomolecule. The physical/chemical properties of amyloid fibrils have been explored by AFM. In particular, AFM enables the visualization of amyloid fibrillation with different incubation times as well as the concentrations of the formed amyloid fibrils as affected by fibril diameters and lengths. Very recently, the minute structural changes and/or electrical properties of amyloid fibrils have been made by using advanced AFM techniques including dynamic liquid AFM, PeakForce QNM (quantitative nanomechanical mapping), and Kelvin probe force microscopy (KPFM). Herein, we summarize the biophysical properties of amyloid fibrils that are newly discovered with the help of those advanced AFM techniques and suggest our perspectives and future directions for the study of amyloid fibrils

Optimal Schedules in Multitask Motor Learning

Although scheduling multiple tasks in motor learning to maximize long-term retention of performance is of great practical importance in sports training and motor rehabilitation after brain injury, it is unclear how to do so. We propose here a novel theoretical approach that uses optimal control theory and computational models of motor adaptation to determine schedules that maximize long-term retention predictively. Using Pontryagin’s maximum principle, we derived a control law that determines the trial-by-trial task choice that maximizes overall delayed retention for all tasks, as predicted by the state-space model. Simulations of a single session of adaptation with two tasks show that when task interference is high, there exists a threshold in relative task difficulty below which the alternating schedule is optimal. Only for large differences in task difficulties do optimal schedules assign more trials to the harder task. However, over the parameter range tested, alternating schedules yield long-term retention performance that is only slightly inferior to performance given by the true optimal schedules. Our results thus predict that in a large number of learning situations wherein tasks interfere, intermixing tasks with an equal number of trials is an effective strategy in enhancing long-term retention

Application of Red Cell Membrane in Nanobiotechnology

Red cells are full of unique biological properties such as immune evasion and molecular-specific permeability. These properties originate from various membrane proteins on the surface of the cell membrane. For this reason, red cell membrane is coated on nanomaterials or sensors to bestow the functionalities of the membrane proteins. In this chapter, various types of membrane proteins of red cell and its functions are described. Also, the following two experimental procedures are summarized: (I) the extraction of red cell membrane containing membrane proteins and (II) coating of the extracted cell membrane onto the nanoparticles and solid surface of sensors. Finally, the applications of red cell membrane in drug delivery system and biosensor are discussed