基于直接积分矩方法的纳米颗粒动力学研究

本文介绍了直接积分矩方法的理论模型,并用其研究颗粒凝并问题。研究发现,自由剪切流场形成的涡将对温度场起耗散作用,强烈影响对颗粒生成,导致涡心颗粒浓度增加,进而导致凝并作用也会大大增强。

Effect of second-phase particle size and presence of vibration on AZ91/SiC surface composite layer produced by FSP

An improved method of friction stir processing(FSP)was introduced for the processing of AZ91 magnesium alloy specimens.This novel process was called“friction stir vibration processing(FSVP)”.FSP and FSVP were utilized to develop surface composites on the studied alloy while SiC nanoparticles were applied as second-phase particles.The effect of reinforcing SiC particles with different sizes(30 and 300 nm)on different characteristics of the composite surface was studied.The results indicated that the microstructure was refined and mechanical properties such as hardness,ductility,and strength were enhanced as FSVP was applied.Furthermore,it was concluded that the effect of reinforcing particles with a size of 30 nm on the microstructure and mechanical properties of the surface composite was more obvious than that of particles with a size of 300 nm.It was also found that mechanical properties and microstructure of FSV-processed specimens were improved as vibration frequency increased.The hardness value in the stir zone was about 157 MPa for the FSV-processed specimen at a vibration frequency of 50 Hz,while this value was around 116 MPa for the FSV-processed specimen at a vibration frequency of 25 Hz.

Combined effects of local curvature and elasticity of an isothermal wall for jet impingement cooling under magnetic field effects

The aim of this study is to examine the effects of local curvature and elastic wall effects of an isothermal hot wall for the purpose of jet impingement cooling performance.Finite element method was used with ALE.Different important parametric effects such as Re number(between 100 and 700),Ha number(between 0 and 20),elasticity(between 104 and 109),curvature of the surface(elliptic,radius ratio between 1 and 0.25) and nanoparticle volume fraction(between 0 and 0.05) on the cooling performance were investigated numerically.The results showed that the average Nu number enhances for higher Hartmann number,higher values of elastic modulus of partly flexible wall and higher nanoparticle volume fraction.When the magnetic field is imposed at the highest strength,there is an increase of3.85% in the average Nu for the curved elastic wall whereas it is 89.22% for the hot part above it,which is due to the vortex suppression effects.Nanoparticle inclusion in the base fluid improves the heat transfer rate by about 27.6% in the absence of magnetic field whereas it is 20.5% under the effects of magnetic field at Ha=20.Curvature effects become important for higher Re numbers and at Re=700,there is 14.11% variation in the average Nu between the cases with the lowest and highest radius ratio.The elastic wall effects on the heat transfer are reduced with the increased curvature of the bottom wall.

Synthesis and size control of copper nanoparticles and their catalytic application

The synthesis and catalytic properties of copper nanoparticles（Cunps） were reported using L-ascorbic acid as reducing and capping agent in aqueous medium. The effect of different concentrations of L-ascorbic acid on the particle size of Cunps was investigated. The synthesized Cunps were characterized by UV-Visible spectrophotometer, scanning electron microscopy（SEM）, transmission electron microscopy（TEM） and Fourier transform infrared（FTIR） spectrophotometer. The result indicates that the size of copper nanoparticles decreases with the increase in concentration of L-ascorbic acid. L-Ascorbic acid plays an important role to protect the copper nanoparticles from oxidation and agglomeration which helps nanoparticles to get better stability for the application. The synthesized Cunps show excellent catalytic activity in the oxidation of serine（Ser） by peroxomonosulphate（PMS）. The catalytic activity of Cunps increases with the decrease in size of Cunps. The Cunps are expected to be suitable alternative and play an imperative role in the fields of catalysis and environmental remediation.

Reaction pathway and kinetics of CdO nanoparticles prepared from CdCO_3 precursor using thermal decomposition method

The non-isothermal kinetics of CdO nanoparticles prepared from CdCO3 precursor using thermal decomposition method was investigated. A model-fitting Malek approach and a model-free advanced isoconversional method of Vyazovkin were applied to the analysis of the DSC and TGA data. The results showed that CdO nanoparticles prepared from CdCO3 followed an autocatalytic reaction. Sestak–Berggren model could favorably describe the studied reaction process. Moreover, the apparent activation energy of CdCO3 decomposition was calculated to be (119.19±9.97) kJ/mol and the explicit rate equation form of CdCO3 decomposition was established.

Gold nanoparticle/ZnO nanorod hybrids for enhanced reactive oxygen species generation and photodynamic therapy

Gold nanoparticle （Au NP）@ZnO nanorod （NR） （Au@ZnO） hybrids with various ZnO：Au molar ratios were developed to enhance the generation of reactive oxygen species （ROS） in photodynamic therapy （PDT） applications. Introducing a metal/semiconductor heterostructure interface between Au NPs and ZnO NRs modulated electron transfer under ultraviolet （UV） irradiation, which dramatically suppressed the electron-hole recombination in ZnO and simultaneously increased the amount of excited electrons with high energy at Au NP surfaces. Hence, the ROS yield of the nanohybrid was considerably improved over those of pristine Au NPs or ZnO NRs alone and demonstrated a ＂1 ＋ 1 〉 2 effect.＂ This enhancement was strengthened with increases in the proportion of Au in the hybrid. The results showed that the Au@ZnO nanohybrids with a ZnO：Au ratio of 20：1 generated the highest ROS yield because they had the largest interface area between Au and ZnO, which in turn led to the lowest cell viability for HeLa and C2C12 cells during PDT. Furthermore, both ROS generation and cell destruction were positively correlated with nanohybrid dosage. The Au@ZnO hybrid （20：1, 100 μg/mL） resulted in HeLa cell viability as low as 28% after UV exposure for 2 min, which indicated its promising potential to improve the therapeutic efficacy of PDT.

Effects of nanoparticles on devitrification and recrystallization of aqueous glycerol and PEG-600 solutions

Nanoparticles in solution offer unique electrical, mechanical and thermal properties due to their physical presence and interac- tion with the state of dispersion. This work is aimed to study the effects of hydroxyapatite （HA） nanoparticles on the behavior of devitrification and recrystallization of glycerol （60% w/w） and PEG-600 （50% w/w） solutions during warming. HA nano- particles of different sizes （20, 40, 60 nm） and concentrations （0.1%, 0.5%, w/w） were incorporated into solutions, and were studied by calorimetric analysis coupled with cryomicroscopy. The presence of HA nanoparticles has little effect on the devit- rification end temperatures, but affects the devitrification onset temperatures of glycerol and PEG-600 solutions. The investi- gation with the cryomicroscope observed that the ice morphologies of glycerol and PEG-600 solutions are dendritic and spher- ic respectively. The ice fraction of glycerol solution containing 0.1% HA with the size of 60 nm decreased to 2/5 of that of the solution without nanoparticles at -45℃. The ice fractions of PEG-600 solutions increased signifcantly between -64℃ and -54℃, and the ice fraction of PEG-600 solution without nanoparticles increased by 92% within the temperature range. The findings have significant implications for biomaterial cryopreservation, cryosurgery, and food manufacturing. The complexity of ice crystal growth kinetics in nanoparticle-containing solutions awaits further study.