Bronchodilator response following methacholine-induced bronchoconstriction predicts acute asthma exacerbations.

Methacholine bronchial provocation test provides the concentration of methacholine causing a 20% decrease in forced expiratory volume in 1 s (FEV1) from baseline (PC20). The dose-response slope (DRS), and other continuous indices of responsiveness (CIR; the percentage decline from the post-diluent baseline FEV1 after the last dose of methacholine), and per cent recovery index (PRI; the percentage increase from the maximally reduced FEV1 after bronchodilator inhalation) are alternative measures. The clinical relevance of these indices in predicting acute asthma exacerbations has not been fully evaluated.In two prospective cohorts of childhood and elderly asthmatics, baseline PC20, DRS, CIR and PRI were measured and evaluated as predictors of acute asthma exacerbations.We found that PRI was significantly related to the presence of asthma exacerbations during the first year of follow-up in both cohorts of childhood (p=0.025) and elderly asthmatics (p=0.003). In addition, PRI showed a significant association with the total number of steroid bursts during 4.3 years of follow-up in the cohort of childhood asthmatics (p=0.04).We demonstrated that PRI, an index of reversibility following methacholine-induced bronchoconstriction, was a good clinical predictor of acute exacerbations of asthma in both childhood and elderly asthmatics.

Effects of mechanical deformation on energy conversion efficiency of piezoelectric nanogenerators.

Piezoelectric nanogenerators (PNGs) are capable of converting energy from various mechanical sources into electric energy and have many attractive features such as continuous operation, replenishment and low cost. However, many researchers still have studied novel material synthesis and interfacial controls to improve the power production from PNGs. In this study, we report the energy conversion efficiency (ECE) of PNGs dependent on mechanical deformations such as bending and twisting. Since the output power of PNGs is caused by the mechanical strain of the piezoelectric material, the power production and their ECE is critically dependent on the types of external mechanical deformations. Thus, we examine the output power from PNGs according to bending and twisting. In order to clearly understand the ECE of PNGs in the presence of those external mechanical deformations, we determine the ECE of PNGs by the ratio of output electrical energy and input mechanical energy, where we suggest that the input energy is based only on the strain energy of the piezoelectric layer. We calculate the strain energy of the piezoelectric layer using numerical simulation of bending and twisting of the PNG. Finally, we demonstrate that the ECE of the PNG caused by twisting is much higher than that caused by bending due to the multiple effects of normal and lateral piezoelectric coefficients. Our results thus provide a design direction for PNG systems as high-performance power generators.

A statistical study on nanoparticle movements in a microfluidic channel.

Microfluidic channels have received much attention because they can be used to control and transport nanoscale objects such as nanoparticles, nanowires, carbon nanotubes, DNA and cells. However, so far, practical channels have not been easy to design because they require very expensive fabrication and sensitive experiments. Numerical approaches can be alternatives or supplementary measures to predict the performance of new channels because they efficiently explain nanoscale multi-physics phenomena and successfully solve nanowire alignment and cell adhesion problems. In this paper, a newly updated immersed finite element method that accounts for collision force and Brownian motion as well as fluid-solid interaction is proposed, and is applied to simulate nanoparticle movements in a microfluidic channel. As part of the simulation, Brownian motion effects in a single nanoparticle focusing lens system are examined under different temperature conditions, and the resulting transport efficiencies are discussed. Furthermore, nanoparticle movements in a double focusing lens system are predicted to show the enhancement of focusing efficiency.

Prediction of anisotropic behavior of nano/micro composite based on damage mechanics with cell modeling.

New advanced composite materials have recently been of great interest. Especially, many researchers have studied on nano/micro composites based on matrix filled with nano-particles, nano-tubes, nano-wires and so forth, which have outstanding characteristics on thermal, electrical, optical, chemical and mechanical properties. Therefore, the need of numerical approach for design and development of the advanced materials has been recognized. In this paper, finite element analysis based on multi-resolution continuum theory is carried out to predict the anisotropic behavior of nano/micro composites based on damage mechanics with a cell modeling. The cell modeling systematically evaluates constitutive relationships from microstructure of the composite material. Effects of plastic anisotropy on deformation behavior and damage evolution of nano/micro composite are investigated by using Hill's 48 yield function and also compared with those obtained from Gurson-Tvergaard-Needleman isotropic damage model based on von Mises yield function.

Numerical simulation of a nanoparticle focusing lens in a microfluidic channel by using immersed finite element method.

Lap-on-a-chip system is one of challenging parts in nano and bio engineering fields, for instance, microfluidic channels on the chip are useful for selecting a target particle and mass transferring of boiomolecules in fluid. However, since experimental approach is highly expensive both in time and cost, alternative reliable methods are required to conceive optimized channels. The purpose of this research is to simulate a nanoparticle focusing lens in a microfluidic channel from nanoparticle control point of view. A promising immersed finite element method is expanded to estimate the path of randomly moving nanoparticles through a focusing lens. The channel flow is assumed as incompressible viscous fluid and Brownian motion effects as well as initial position of particle are quantitatively examined. As a representative result, while the nanoparticles with/without Brownian motion were focused along the center of the channel, the concentration factor representing focusing efficiency was calculated. Therefore, it is expected that the newly proposed numerical method considering Brownian motion will be efficiently applicable to design the microfluidic channel containing various particles, molecules and so forth in the near future.