Swelling Behavior of Physically Cross-Linked Gelatin Gels in Varied Salt Solutions

A series of physically cross-linked gelatin networks were prepared and the effects of salt concentration and chemical valence of the salt ions on the swelling properties of the gelatin gels were studied in detail. It was found that the swelling behaviors as polyelectrolytic or polyampholytic gels depended on the charge distribution on the gelatin chains. The swelling capacity of polyelectrolytic gels with excess positive charges decreased with an increase in salt concentrations. However, the swelling capacity of polyelectrolytic gels with excess negative charges showed a nonmonotonic change with salt concentration. For polyampholytic gels, the equilibrium swelling ratio increased monotonously with the concentration of NaCl and CaCl₂ solutions_. On the other hand, the swelling capacities of the polymer networks increased first and were then followed by a decrease with an increase in the concentration of AlCl₃ solution. Moreover, the swelling kinetics of the gelatin gels in varied salt solutions with different concentrations was also investigated.     

二维过渡金属硫族化合物中的缺陷和相关载流子动力学的研究进展

原子级厚度的单层或者少层二维过渡金属硫族化合物因其独特的物理特性而被寄希望成为下一代光电子器件的重要组成部分。然而,二维材料的缺陷在很大程度上影响着材料的性质。一方面,缺陷的存在降低了材料的荧光量子效率、载流子迁移率等重要参数,影响了器件的性能。另一方面,合理地调控和利用缺陷催生了单光子源等新的应用,因此,表征、理解、处理和调控二维材料中的缺陷至关重要。本文综述了二维过渡金属硫族化合物中的缺陷以及缺陷相关的载流子动力学研究进展,旨在梳理二维材料中的缺陷及其超快动力学与材料性能之间的关系,为二维过渡金属硫族化合物材料特性和高性能光电子器件的相关研究提供支持。     

Surface segregation and radiation hardening of 16Cr12MoWSiVNbB steel after irradiation with Ni++ and He+ ions

Irradiation of EP-823 (16Cr12MoWsiVNbB) ferritic-martensitic steel with 7-MeV Ni⁺⁺ ions and with 30- and 70-keV He⁺ ions at a temperature of 500°C was followed by an increase in the microhardness, which was due to both radiation point defects and changes in the phase composition and the dislocation structure of the steel. It was found that the dependence of the largest relative increase in the microhardness on the concentration of radiation-induced point defects in the near-surface region of the steel under irradiation with different ions correlated with an analogous dependence of the surface segregation of silicon and chromium.     

Free-radical cross-linking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate in the presence of trimethoxyvinylsilane

Free-radical cross-linking copolymerization of methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), and trimethoxyvinylsilane (TMVS) has been investigated in toluene at a total monomer concentration of 4 mol L⁻¹ and at 70 °C. Conversion of monomer, volume swelling ratio, weight fraction, and gel point were measured as a function of the reaction time, TMVS concentration, toluene content, temperature, and chain transfer agents up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in toluene, gel fraction, and Fourier transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by scanning electron microscopy (SEM).

Based on the obtained results, it was concluded that the FTIR data did not have the capacity to show the presence of the TMVS moiety in these kinds of copolymers. On the other hand, the variation of weight fraction of gel, W_g, and its equilibrium volume swelling ratio in toluene, q_v, exhibited the same behaviors as that of MMA/EGDM copolymers. Also, the dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percent of conversion and gel fraction. Finally, TMVS is a suitable silicone co-monomer for this system and it has been proved useful.     

The study of native defects in as-grown GaAs by positron annihilation

A mono-energetic positron beam was applied for a study of native defects in GaAs. From measurements of Doppler broadening profiles and lifetime spectra of positrons, it was found that Ga-vacancies were introduced by Si-doping. On the other hand, for p-type GaAs, interstitial clusters were found to be introduced by Zn-doping. The observed species of defects are in agreement with those expected from the Fermi level.     

Defect studies of hydrogen-loaded thin Nb films

Hydrogen interaction with defects in thin niobium (Nb) films was investigated using slow positron implantation spectroscopy (SPIS) combined with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thin Nb films on Si substrates were prepared using cathode beam sputtering at room temperature. Initially, the microstructure of the virgin (hydrogen-free) films was characterized. Subsequently, the films were step-by-step electrochemically charged with hydrogen and the evolution of the microstructure with increasing hydrogen concentration was monitored. Hydrogen loading leads to a significant lattice expansion which was measured by XRD. Contrary to free-standing bulk metals, thin films are highly anisotropic. The in-plane expansion is prevented because the films are clamped on the elastically hard substrate. On the other hand, the out-of-plane expansion is substantially higher than in the bulk samples. Moreover, an enhanced hydrogen solubility in the α-phase was found in nanocrystalline Nb films. It was found that most of positrons in the films are trapped at open-volume defects at grain boundaries (GBs). These defects represent trapping sites also for hydrogen atoms. Hydrogen trapping at vacancy-like defects like GBs leads to a local increase of the electron density and is reflected by a pronounced decrease of the S parameter in the hydrogen-loaded samples. In addition, it was found that new defects are introduced at higher concentrations of hydrogen due to the formation of NbH (β-phase) particles.     

Investigation of the swelling of human skin cells in liquid media by tapping mode scanning force microscopy

The swelling of individual human skin cells (so-called corneocytes) was studied in distilled water and hexadecene, respectively, by tapping mode scanning force microscopy. The area, the mean height, and the volume were recorded and compared to data of the same cell, which has been obtained under ambient conditions. In distilled water, we found an average swelling in height and volume of about (-)%5010, but no significant increase of the area. Additionally, phase-contrast images suggest a significant change of the viscoelastic properties of the corneocytes. On the other hand, the corneocytes behaved inertly when exposed to hexadecene as an example of a non-polar solvent.     

Interactions between grain boundary and compositional domain boundary during spinodal decomposition in nanocrystalline alloys

Due to the large grain boundary (GB) volume fraction in nanocrystalline materials, interactions between GB and compositional domain boundary (CDB) play an important role in determining the nanoscale-modulated domain structures during spinodal decomposition. In the present paper, the phase field crystal model is employed to investigate the interactions between GB and CDB. Simulation results show that CDB coarsening can drive the GB migration and bring the impingement of particles with different orientations; the large volume fraction of GB can increase the dislocation volume fraction in CDBs but does not change its proportion in the whole defects number; the crossover point of the coarsening dynamic comes from the block effect of GB with large volume fraction.     

X-rays absorption study on medieval corrosion layers for the understanding of very long-term indoor atmospheric iron corrosion

The study and prediction of very long-term atmospheric corrosion behaviour of ferrous alloys is of great importance in different fields. First the conservation of metallic artefacts in museum and the corrosion diagnosis on ferrous reinforcement used in ancient monuments since medieval times needs reliable data to understand the mechanisms. Second, in the frame of the interim storage of nuclear waste in France, it is necessary to model the long-term corrosion of low alloy steel overcontainer. The nature of phases and elements constituting the corrosion layers can greatly influence the corrosion mechanisms. On the one hand, it is crucial to precisely determine the nature of microscopic phases that can be highly reactive. On the other hand, some elements as P and S could modify this reactivity. To clarify this point and complementary to other studies using Raman micro spectroscopy technique, X-rays Absorption Spectroscopy (XAS) under synchrotron radiation plays a crucial role. It allows one to precisely identify the reactive phases in the corrosion layers. Micro-XAS was required in order to refine the spatial variation, at micrometer scale, of the predominant Fe oxidation state and to characterise the corresponding corrosion products. Moreover, the role of minor elements on phase’s stability and the chemical form of these elements in the rust layer, especially phosphorus and sulphur, was investigated.     

Fractal Dimensions of κ-Carrageenan Gels during Gelation and Swelling

A photon scattering technique for research on the sol-gel and gel-sol transitions in κ-carrageenan-water systems with various carrageenan contents (CC) was utilized for characterizing the fractal dimensions during gelation and swelling. It was observed that the scattered photon intensity, I_sc, increased at all temperatures with an increase in the CC when I_sc was monitored against temperature. Additionally, the sol-gel transition temperatures were found to be much lower than the gel-sol transition temperatures, causing hysteresis of the phase transition loops. I_sc increased with an increase in CC at all test temperatures, which is attributed to the formation of a fractal-like carrageenan gel. After drying, the gels were used in swelling experiments where the gels were immersed in water at room temperature, reswelling to the original structure. It was observed that I_sc from the carrageenan gels increased as the CC was increased. The fractal dimension, d, during gelation was found to increase as the gelation temperature was increased. On the other hand, the d values during swelling decreased as the swelling time was increased.     

各向异性焊缝中超声相控阵瞬态声场仿真及缺陷定位方法

针对多层各向异性奥氏体不锈钢焊缝中超声相控阵瞬态声场的仿真问题,提出应用高斯声束等效点源模型计算宽带离散化的多个单频稳态声场,通过傅里叶变换将其拓展为瞬态声场,并分析了声场转换过程的主要影响参数。该方法可快速计算焊缝内部超声相控阵聚焦声场的瞬态能量分布和任意一点的时域波形信号。在此基础上针对多层奥氏体不锈钢焊缝内部缺陷的超声相控阵成像检测问题,提出利用上述时域高斯声束法对多通道缺陷散射信号进行时间反转计算,并根据时域声场焦点确定缺陷位置。最后通过实验,验证使用此方法检测实际奥氏体不锈钢焊缝试块内部缺陷的效果。结果表明,提出的方法能够确定缺陷位置,且计算速度快、运算量小,适合作为多层介质内部缺陷实时成像的声场仿真模型。      

Effect of magnon–phonon interaction on transverse acoustic phonon excitation at finite temperature

A magnon–phonon interaction model is developed on the basis of two-dimensional square Heisenberg ferromagnetic system. By using Matsubara Green function theory transverse acoustic phonon excitation is studied and transverse acoustic phonon excitation dispersion curves is calculated on the main symmetric point and line in the first Brillouin zone. On line Σ it is found that there is hardening for transverse acoustic phonon on small wave vector zone (nearby point Γ), there is softening for transverse acoustic phonon on the softening zone and there is hardening for transverse acoustic phonon near point M. On line Δ it is found there is no softening and hardening for transverse acoustic phonon. On line Z it is found that there is softening for transverse acoustic phonon on small wave vector zone (nearby point X) and there is hardening for transverse acoustic phonon nearby point M. The influences of various parameters on transverse acoustic phonon excitation are also explored and it is found that the coupling of the magnon–phonon and the spin wave stiffness constant play an important role for the softening of transverse acoustic phonon.     

典型放电气体的击穿场强阈值研究

为了研究等离子体产生时的气体击穿特性,利用低气压条件下气体击穿场强阈值模型,分析了He、Ne、Ar、Kr、Xe和Hg蒸汽等6种典型放电气体的击穿阈值随入射波频率、电子温度、气体压强以及气体温度的变化规律。结果表明:气体击穿阈值随气体压强的增大而减小,随气体温度、电子温度和入射脉冲频率的增大而增大。气体压强和入射频率对击穿阈值的影响大于气体温度和电子温度,在所考虑的范围内,气体压强对击穿场强的影响约为100 V/m,入射脉冲频率对击穿场强的影响为50~300 V/m,气体温度和电子温度对击穿场强的影响为20~30 V/m。当考虑气体压强、气体温度以及电子温度等因素的影响时,各种气体的击穿场强阈值产生的变化规律相类似;但考虑入射频率的影响时,不同气体的击穿场强阈值差异很大。在所考虑的典型放电气体中,Xe具有最低的击穿场强阈值,He的击穿阈值最大。     

Size and compositionally controlled manganese ferrite nanoparticles with enhanced magnetization

The effects of solvents on the anatase crystallite size prepared by sol–gel microwave-assisted solvothermal method were investigated in this study. Eight different alcohol solvents classified into two groups, i.e. primary and secondary/ternary alcohols, were used as reaction media and the effects of solvent properties, such as dielectric constant, boiling point, and internal pressure during the solvothermal process, on the crystallite size and shape were analyzed. According to the experimental results, selecting the solvent type allowed not only the alteration of the crystallite size but also the crystallite shape without the need of any additives. The boiling point of solvent was determined as the major factor influencing the crystallite size. Among the solvents with similar boiling points, the solvent with a higher carbon number produced the smaller crystallite size because of steric hindrance effect. In addition, the carboxyl groups dissociated from the alcohol solvent can play a role as a structural capping agent to retard the anatase crystal growth along the [001] direction and led to a rectangular crystallite shape with preferred development in {001} facets. On the other hand, the alcoholysis reaction was found easily occurred between the primary alcohol and isopropoxide that effectively limited the hydrolysis and condensation processes but also suppressed the structural capping effect. Therefore, the anatase crystals prepared in the primary alcohols became exceptionally small and showed spherical shape. Finally, the anatase crystals prepared using isopropanol demonstrated the highest photocatalytic activity due to its evident preferred crystallization in the {001} facets.     

多晶硅薄膜低温生长中晶粒大小的控制

以SiCl4H2为气源,用等离子体增强化学气相沉积(PECVD)方法低温快速沉积多晶硅薄膜.实验发现,在多晶硅薄膜的生长过程中,气相空间各种活性基团的相对浓度是影响晶粒大小的重要因素,随功率、H2/SiCl4流量比的减小和反应室气压的增加,晶粒增大.而各种活性基团的相对浓度依赖于PECVD工艺参数,通过工艺参数的改变,分析生长过程中空间各种活性基团相对浓度的变化,指出“气相结晶”过程是晶粒长大的一个重要因素. 关键词： 气相结晶 多晶硅薄膜 晶粒生长 SiCl4     

Isothermal-isobaric computer simulations of melting and crystallization of a Lennard-Jones system

Constant-pressure, constant-temperature molecular dynamics simulations are carried out to study the behaviour of the microscopic atomic structure via the melting and crystallization processes of a model system composed of 864 Lennard-Jones (LJ) particles with periodic boundary conditions. On heating an fcc crystal of LJ particles, it is ascertained that melting takes place. On the other hand, a LJ liquid, when quenched slowly, crystallizes into a stacking of layers with stacking faults where each layer forms a close-packed structure with occasional point defects. A large hysteresis in the volume-temperature curve is observed.     

Impurities and the static central peak in lead germanate

The static central peak in the Raman spectrum of lead germanate (Pb₅Ge₃O₁₁) has been studied as a function of barium-doping and oxygen concentration. It is found that the substitution of barium for lead dramatically increases the intensity and temperature spread of the central peak while also shifting it and the Curie point to much lower temperatures. On the other hand, variations in the observed central peak intensity in nominally pure samples cannot be correlated with variation in oxygen content and must be attributed to some as yet unidentified impurities or defects.     

Effects of defects on heat conduction of graphene/hexagonal boron nitride heterointerface

We investigate the effects of point defects on the Interface Thermal Resistance (ITR) of graphene/hexagonal boron nitride (G/h-BN) heterointerface with various stacking forms by ultrafast thermal pulse method. The results reveal that the ITR of different stacking forms presents a significant downward trend with the existence of point defects. This counterintuitive behavior is attributed to the defects increase the vibration intensity of out-of-plane phonons of graphene in low-frequency region, thus enhancing the phonons coupling between graphene and h-BN layer. ITR of G/h-BN is further reduced by 50% with the defect rate increases from 0% to 5% and that is reduced by 65% with the temperature rises from 200 K to 700 K. Besides, it is found that the defective G/h-BN has thermal rectification characteristic and that is positively related to temperature and defect rate. Our study provides a practical way for the application of defects in graphene and a new approach for the design of thermal rectifier devices.     

Effects of molybdenum on precipitation behaviours in aged cast stainless steels

The effects of Mo on precipitation behaviours in aged cast stainless steels have been investigated. Mo-free CF3 steel and Mo-bearing CF3M steel, both of which consisted of a duplex structure of ferrite and austenite phases, were prepared. Microstructural evolution in the ferrite phase during ageing at 723 K has been observed by transmission electron microscopy (TEM). Precipitates in CF3 steel were identified to belong to the G-phase and possess lattice coherency with the ferrite phase at interphase boundaries. On the other hand, precipitates in CF3M steel were found to be nanodomains of not only to the G-phase but also to another phase enriched in Mo. Some of the nanodomains containing Mo exhibited diffraction patterns having pseudo five-fold symmetry, but others exhibited regular periodicity in high-resolution TEM images. The atomic structure of the Mo-related nanodomains is proposed to be a distorted χ-phase that retains coherency with the matrix.     

Boundary Mobility and Energy Anisotropy Effects on Microstructural Evolution During Grain Growth

We have performed mesoscopic simulations of microstructural evolution during curvature driven grain growth in two-dimensions using anisotropic grain boundary properties obtained from atomistic simulations. Molecular dynamics simulations were employed to determine the energies and mobilities of grain boundaries as a function of boundary misorientation. The mesoscopic simulations were performed both with the Monte Carlo Potts model and the phase field model. The Monte Carlo Potts model and phase field model simulation predictions are in excellent agreement. While the atomistic simulations demonstrate strong anisotropies in both the boundary energy and mobility, both types of microstructural evolution simulations demonstrate that anisotropy in boundary mobility plays little role in the stochastic evolution of the microstructure (other than perhaps setting the overall rate of the evolution. On the other hand, anisotropy in the grain boundary energy strongly modifies both the topology of the polycrystalline microstructure the kinetic law that describes the temporal evolution of the mean grain size. The underlying reasons behind the strongly differing effects of the two types of anisotropy considered here can be understood based largely on geometric and topological arguments.