杂质浓度对Zr替位掺杂γ-TiAl合金的结构延性和电子性质的影响

以Zr替代Ti(或Al)掺杂γ-TiAl体系为研究对象, 掺杂浓度(摩尔比)分别为1/54, 1/36, 1/24和1/16. 采用基于密度泛函理论的第一性原理方法, 计算研究了Zr掺杂γ-TiAl体系的晶体结构及其稳定性、延性和电子性质等. 结果显示, Zr替位掺杂, 可以改变γ-TiAl基合金的结构对称性. 计算的形成能表明, Zr替代Ti原子会使体系的形成能降低, 而Zr替代Al原子会使体系的形成能增加. 因而, 在掺入γ-TiAl时, Zr更倾向于替代Ti 原子, 但是Zr替代Al原子也具有一定的可能性, 从而会产生多样的掺杂体系, 对于改善合金的性质具有重要意义. 对各个体系轴比的计算与分析表明, 当掺杂浓度为1.85 at%–6.25 at% 时, Zr替代Al原子会使体系的轴比减小、接近于1, 从而改善合金的延性效果明显. 能带结构显示各个Zr掺杂γ-TiAl体系均具有金属导电性. 对电子态密度和布居数的分析表明, Zr替代Al原子后, Zr与其邻近Ti原子的共价键结合强度大为降低, 导致合金体系中的Ti-Al(Zr)键的平均强度明显减弱, 金属键增强, 这是改善γ-TiAl合金延性的重要因素.     

Two near-infrared highly sensitive cyanine fluorescent probes for pH monitoring

Two near-infrared(NIR) p H-activated heptamethine indocyanine probes with quaternary ammonium unit were designed and synthesized. The absorption and emission titrations indicate that cationic structure improves the cyanine dye's aqueous solubility and these two probes exhibit highly sensitive response to p H in acid condition. Their fluorescence intensities both gradually increase about 25-fold from p H 7.60 to 3.00 with p Ka values of 4.72 and 4.45 respectively, which are suitable for studying acidic organelles in living cells. Moreover, their fluorescence intensities are linearly proportional to p H values in the range of 5.50–4.00. These results are probably attributed to the protonation of the indole nitrogen atoms, which are verified by 1H NMR spectra. Furthermore, these two probes can achieve real-time imaging of cellular p H and detection of p H in situ in living He La cells due to their excellent properties,including good reversibility, desirable photostability, high selectivity, low cytotoxicity and remarkable membrane permeability.     

Morphologies of a spherical bimodal polyelectrolyte brush induced by polydispersity and solvent selectivity

It is commonly realized that polydispersity may significantly affect the surface modification properties of polymer brush systems. In light of this, we systematically study morphologies of bidisperse polyelectrolyte brush grafted onto a spherical nanocolloid in the presence of trivalent counterions using molecular dynamics simulations. Via varying polydispersity, grafting density, and solvent selectivity, the effects of electrostatic correlation and excluded volume are focused, and rich phase behaviors of binary mixed polyelectrolyte brush are predicted, including a variety of pinned-patch morphologies at low grafting density and micelle-like structures at high grafting density. To pinpoint the mechanism of surface structure formation, the shape factor of two species of polyelectrolyte chains and the pair correlation function between monomers from different polyelectrolyte ligands are analyzed carefully. Also, electrostatic correlations, manifested as the bridging through trivalent counterions, are examined by identifying four states of trivalent counterions. Our simulation results may be useful for designing smart stimuli-responsive materials based on mixed polyelectrolyte coated surfaces.     

Generalized Igusa–Todorov function and finitistic dimensions

We introduce a new function from the bounded derived category of a finite dimensional algebra over a field to the set of all natural numbers, which is a generalized version of the Igusa–Todorov function. Then we extend the results corresponding to the Igusa–Todorov function. As an application, we give a new proof of the finiteness of the finitistic dimension of special biserial algebras.     

Hypercyclic composition operators on the $$S^p $$ S p space with automorphism symbols

Archiv der Mathematik - Let $$S^p$$ be the space of holomorphic functions whose derivative lies in the classical Hardy space $$H^p$$ over the unit disk. We prove in this paper that the composition...     

素数立方阶群局部传递的图

目的是研究局部传递图的性质和分类.运用置换群和陪集图的理论,获得了关于素数立方阶群局部传递图的完全分类,证明了这些图是一些互不相交的关于素数立方阶群边传递图的并.     

Investigation of Infrared Photonic Crystal Slab with Defect Waveguides

This paper deals with the two dimensional (2-D) infrared photonic crystal slab with an air-bridge structure featuring defect waveguides in which the optical propagation properties were obtained by measurements of transmission spectra. 3-D finite-difference time-domain (FDTD) simulations have revealed the appearance of four defect propagation modes for the band structure and transmission spectra in the air-bridge slab. These defect modes were experimentally identified in the measured transmission spectra.     

Synthesis and electrochemical characteristics of Ta-N thin films fabricated by cathodic arc deposition

Ta-N thin films were deposited on AISI 317L stainless steel (SS) substrates by cathodic arc deposition (CAD) at substrate biases of −50 and −200 V. The as-deposited films were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX). The results show that stoichiometric TaN with hexagonal lattice (3 0 0) preferred orientation was achieved at the bias of −200 V. On the other hand, Ta-rich Ta-N thin film deposited at −50 V shows amorphous nature. According to the XPS result, Ta element in the films surface exist in bonded state, including the Ta-N bonds characterized by the doublet (Ta 4f_7/2 = 23.7 eV and Ta 4f_5/2 = 25.7 eV). Electrochemical properties of the Ta-N coated stainless steel systems were investigated using potentiodynamic polarization and electrochemical impedance spectroscope (EIS) in Hank's solution at 37 °C. For the Ta-N coated samples, the corrosion current (i_corr) is two or three orders of magnitude lower than that of the uncoated ones, indicating a significantly improved corrosion resistance. Growth defects in the Ta-N thin films produced by CAD, however, play a key role in the corrosion process, especially the localised corrosion. Using the polarization fitting and the EIS modelling, we compared the polarization resistance (R_p) and the porosity (P) of the Ta-N coatings deposited at different biases. It seems that Ta-N film with comparatively lower bias (−50 V) shows better corrosion behavior in artifical physiological solution. That may be attributed to the effect of ion bombarding, which can be modulated by the substrate bias.     

Cr-doping induced ferromagnetic behavior in antiferromagnetic EuTiO3 nanoparticles

We have synthesized a series of high quality EuTi_1−xCr_xO₃ (x = 0.0, 0.02, and 0.04) nanoparticles by simple sol-gel technique. The averaged grain size of these obtained nanoparticles displays no obvious change with Cr-doping and is about 100 nm. The structural and magnetic properties of EuTi_1−xCr_xO₃ (x = 0.0, 0.02, and 0.04) samples were detailedly investigated. It is found that the G-antiferromagnetic (G-AFM) ordering of pure EuTiO₃ can be significantly modified with slight Cr-doping, and finally the ferromagnetic behavior is enhanced for EuTi_1−xCr_xO₃ system with Cr-doping.