Critical behaviors of bond and crystal field dilution Blume–Emery–Griffiths model

The critical behavior of the spin-1 bond and crystal field dilution Blume–Emery–Griffiths model have been investigated on simple-cubic lattice within the framework of the effective field theory. In particular, both bond dilution and random crystal field are considered at the same time. The interplay between bond and crystal field dilution constructs rich and interesting phase diagrams. Significant distinctions are exhibited. When positive ratio α changes in a certain range, there exist double tricritical points in phase-transition lines in T–D plane. Moreover, this first-order phase transition is enlarged with increasing of ratio α at a fixed crystal field dilution concentration, while this first-order phase transition will shrink when bond dilution concentration is fixed. In addition, we observe that there exist two bond percolation thresholds for negative crystal field and α>0 in T–P plane.     

Optical properties of Dy ions in sodium gadolinium tungstates crystal

Dy³⁺-doped NaGd(WO₄)₂ crystal with sizes of about Φ20×40 mm² was grown by the Czochralski technique along the (0 0 1) orientation. Polarized absorption spectra, fluorescence spectra, and fluorescence decay curve of Dy³⁺-doped NaGd(WO₄)₂ have been recorded at room temperature. Based on the Judd-Ofelt (J-O) theory, the intensity parameters from the measured line strengths were evaluated. The J-O parameters were used to predict radiative transition probabilities, radiative lifetimes and branching ratios for various excited levels of Dy³⁺-doped NaGd(WO₄)₂ crystal. The luminescent quantum efficiency of the ⁴F_9/2 level was determined to be approximately 63% for this material. The emission cross-section of the ⁴F_9/2→⁶H_13/2 transition was estimated by using the Füchtbauer-Ladengurg method.     

光学外差探测信噪比研究

对于光学外差探测系统而言,为了有效利用回波信号,需要对信噪比这一表征系统性能的重要指标进行研究。从理论分析了信噪比,给出了计算信噪比的一般公式。理论分析表明,当探测器光敏面上本振光与信号光的振幅、相位、偏振都满足严格的匹配时,外差效率最大。对场分布为艾里函数的光外差信噪比进行研究和数值模拟。结果表明,当艾里斑尺寸的比例系数控制在0.8~1.2内,并使信号光斑主轴偏移量x0控制在0.5以下,探测器的尺寸在(0.6~0.8)λf/d内时,可获得大于0.7ηPs/hνB的信噪比。     

Seed-mediated synthesis of acanthosphere-like gold microstructures with tunable LSPR in the NIR region using gemini surfactants as directing agents for SERS applications

Acanthosphere-like gold microstructures (AGMs) were synthesized using a facile, two-step, seed-mediated method and butanediyl-1,4-bis(dimethylhexadecylammonium bromide) (16-4-16) as a structure-directing agent. The morphologies and sizes of the products were controlled during the synthesis process by adjusting the concentrations of 16-4-16, the AgNO₃ feed, HAuCl₄, ascorbic acid, the amount of Ag seeds and the types of gemini surfactants used through systematic inquiry; particle sizes ranging from 130 to 800 nm were well prepared. Correspondingly, the morphology of the products changed between regular and irregular AGMs, and the products presented a number of new morphologies, such as open-mouthed submicrostructures and ribbon nanowires. In particular, with the increase in the 16-4-16 concentration, the structural morphology of the thorns clearly changed from a tip to a lamellar structure. A UV-vis spectroscopic analysis indicated that the localized surface plasmon resonance (LSPR) peak of the AGMs could be adjusted by changing the above factors, which extended from 500 to 1350 nm in the near-infrared (NIR) region, enabling a tremendous potential for using the AGMs as platforms for various biomedical applications. Based on the intermediate products, we propose a two-stage growth mechanism for the AGMs in which their solid cores and tips are generated successively. Surface-enhanced Raman scattering (SERS) measurements indicate that the AGMs can serve as sensitive SERS substrates; a SERS detection limit of 5 × 10^?7 M is presented for rhodamine B molecules.

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Structural and electronic properties of potassium-doped 1,2;8,9-dibenzopentacene superconductor: comparing with doped [7]phenacenes

Polycyclic aromatic hydrocarbons doped by metal have exhibited the potential of high temperature superconductivity. Understanding the basic properties of materials is the key to reveal the superconductivity. Here, a systemically theoretical study has been done to explore crystal structures and electronic properties of pristine and potassium-doped 1,2;8,9-dibenzopentacene, compared with [7]phenacenes case. We determined that vdW-DF2 functional is more suitable to describe the non-local interaction in a molecular crystal. Based on this functional, we predicted the crystal structures and investigated in detail the K atomic positions in a system. It was found that the intralayer doping leads to lower total energy. From the calculated formation energy, for each 1,2;8,9-dibenzopentacene molecule, the doping of two electrons is more stable under the relatively K-poor condition while the doping of four electrons is more stable under the K-rich condition. Between these two phases, the three-electron doping phase stabilises in a narrow region of K chemical potential. Combining with the electronic states at Fermi level, we analysed the reasons of superconductivity enhancement in doped 1,2;8,9-dibenzopentacene. This work further deepens the understanding of 1,2;8,9-dibenzopentacene superconductor.     

金溶胶中邻羟基苯甲酸吸附行为的密度泛函理论与实验研究

研究了邻羟基苯甲酸(OHBA)的常规拉曼散射(NRS)光谱以及其吸附在Au纳米颗粒上的表面增强拉曼散射(SERS)光谱。以氯金酸为原料,柠檬酸三钠为还原剂,用化学还原法制备了球形的金纳米粒子溶胶,采用激光显微拉曼光谱仪(激发波长为785 nm),测定OHBA分子的NRS光谱及其吸附在Au纳米颗粒上的SERS光谱。同时,应用密度泛函理论(DFT),在B3LYP/6-31+G**(C,H,O)/LANL2DZ(Au)水平上,对OHBA分子进行了结构优化,在此基础上计算了OHBA分子的NRS光谱以及其吸附在Au纳米颗粒上两种不同吸附构型下的SERS光谱,并和实验值进行比较。结果表明,OHBA分子通过羧基吸附构型的计算值比通过羟基吸附构型的计算值与实验值符合的更好。最后,利用GaussView可视化软件对其振动模式进行了全面归属。通过对邻羟基苯甲酸分子拉曼谱峰的详细指认能够得出：Au溶胶中的邻羟基苯甲酸分子,是通过羧基倾斜地吸附在Au纳米颗粒表面的。可视化软件直观形象地展示出了该分子的结构特征和分子基团振动情况,对其振动峰位的归属提供了重要依据。本文工作对推进邻羟基苯甲酸在生物医药等领域进一步的应用具有重要作用。     

Synthesis of RGO/Cu8S5/PPy Composite Nanosheets with Enhanced Peroxidase‐Like Activity for Sensitive Colorimetric Detection of H2O2 and Phenol

In this paper, a novel strategy for the fabrication of reduced graphene oxide (rGO)/Cu₈S₅/polypyrrole (PPy) composite nanosheets with Cu₈S₅ nanoparticles and PPy layer anchored on the surface of rGO as peroxidase‐like nanocatalyst is reported. During the synthesis, graphene oxide (GO)/CuO composite nanosheets are prepared first and used as templates, then the sulfuration of CuO and polymerization of pyrrole are accompanied with the reduction of GO, resulting in ternary rGO/Cu₈S₅/PPy composite nanosheets. The synthesized Cu₈S₅ nanoparticles with a diameter in the range from tens to hundreds of nanometers are dispersed within PPy decorated rGO nanosheets. The resultant ternary rGO/Cu₈S₅/PPy composite nanosheets exhibit a higher peroxidase‐like catalytic activity toward the oxidation of 3,3′,5,5′‐tetramethylbenzidine in the presence of H₂O₂ than GO/CuO and rGO/CuS composite nanosheets, revealing a synergistic effect on their activity. The as‐prepared rGO/Cu₈S₅/PPy platform provides a simple colorimetric approach for the detection of H₂O₂ and phenol with a high sensitivity. This work offers a new way for the fabrication of rGO‐based nanocomposite with superior enzyme‐like activity, which displays great potential applications in biocatalysis and environmental monitoring.     

Binary linear codes with few weights from Boolean functions

Boolean functions have very nice applications in coding theory and cryptography. In coding theory, Boolean functions have been used to construct linear codes in different ways. The objective of this paper is to construct binary linear codes with few weights using the defining-set approach. The defining sets of the codes presented in this paper are defined by some special Boolean functions and some additional restrictions. First, two families of binary linear codes with at most three or four weights from Boolean functions with at most three Walsh transform values are constructed and the parameters of their duals are also determined. Then several classes of binary linear codes with explicit weight enumerators are produced. Some of the binary linear codes are optimal or almost optimal according to the tables of best codes known maintained at http://www.codetables.de, and the duals of some of them are distance-optimal with respect to the sphere packing bound.