Interesting Magnetic and Optical Properties of ZnO Co-doped with Transition Metal and Carbon

Magnetic and optical properties of ZnO co-doped with transition metal and carbon have been investigated using density functional theory based on first-principles ultrasoft pseudopoten-tial method. Upon co-doping with transition metal (TM) and carbon, the calculated results show a shift in the Fermi level and a remarkable change in the covalency of ZnO. Such cases energetically favor ferromagnetic semiconductor with high Curie temperature due to p-d exchange interaction between TM ions and holes induced by C doping. The total en-ergy difference between the ferromagnetic and the antiferromagnetic configurations, spatial charge and spin density, which determine the magnetic ordering, were calculated in co-doped systems for further analysis of magnetic properties. It was also discovered that optical prop-erties in the higher energy region remain relatively unchanged while those at the low energyregion are changed after the co-doping. These changes of optical properties are qualitatively explained based on the calculated electronic structure. The validity of our calculation in comparison with other theoretical predictions will further motivate the experimental inves-tigation of (TM, C) co-doped ZnO diluted magnetic semiconductors.     

The Global Optimization of Pt<Subscript>13</Subscript> Cluster Using the First-Principle Molecular Dynamics with the Quenching Technique

The high-temperature first-principle molecular dynamics method used to obtain the low energy configurations of clusters [L. L. Wang and D. D. Johnson, PRB 75, 235405 (2007)] is extended to a considerably large temperature range by combination with the quenching technique. Our results show that there are strong correlations between the possibilities for obtaining the ground-state structure and the temperatures. Larger possibilities can be obtained at relatively low temperatures (as corresponds to the pre-melting temperature range). Details of the structural correlation with the temperature are investigated by taking the Pt₁₃ cluster as an example, which suggests a quite efficient method to obtain the lowest-energy geometries of metal clusters.     

Mesoporous silica nanorods toward efficient loading and intracellular delivery of siRNA

The technology of RNA interference (RNAi) that uses small interfering RNA (siRNA) to silence the gene expression with complementary messenger RNA (mRNA) sequence has great potential for the treatment of cancer in which certain genes were usually found overexpressed. However, the carry and delivery of siRNA to the target site in the human body can be challenging for this technology to be used clinically to silence the cancer-related gene expression. In this work, rod shaped mesoporous silica nanoparticles (MSNs) were developed as siRNA delivery system for specific intracellular delivery. The rod MSNs with an aspect ratio of 1.5 had a high surface area of 934.28 m²/g and achieved a siRNA loading of more than 80 mg/g. With the epidermal growth factor (EGF) grafted on the surface of the MSNs, siRNA can be delivered to the epidermal growth factor receptor (EGFR) overexpressed colorectal cancer cells with high intracellular concentration compared to MSNs without EGF and lead to survivin gene knocking down to less than 30%.     

Bayesian Modeling of NMR Data: Quantifying Longitudinal Relaxation in Vivo,and in Vitro with a Tissue-Water-Relaxation Mimic (Crosslinked Bovine Serum Albumin)

Recently, a number of magnetic resonance imaging protocols have been reported that seek to exploit the effect of dissolved oxygen (O₂, paramagnetic) on the longitudinal ¹H relaxation of tissue water, thus providing image contrast related to tissue oxygen content. However, tissue water relaxation is dependent on a number of mechanisms and this raises the issue of how best to model the relaxation data. This problem, the model selection problem, occurs in many branches of science and is optimally addressed by Bayesian probability theory. High signal-to-noise, densely sampled, longitudinal ¹H relaxation data were acquired from rat brain in vivo and from a cross-linked bovine serum albumin (xBSA) phantom, a sample that recapitulates the relaxation characteristics of tissue water in vivo. Bayesian-based model selection was applied to a cohort of five competing relaxation models: (1) monoexponential, (2) stretched-exponential, (3) biexponential, (4) Gaussian (normal) R ₁-distribution, and (5) gamma R ₁-distribution. Bayesian joint analysis of multiple replicate datasets revealed that water relaxation of both the xBSA phantom and in vivo rat brain was best described by a biexponential model, while xBSA relaxation datasets truncated to remove evidence of the fast relaxation component were best modeled as a stretched exponential. In all cases, estimated model parameters were compared to the commonly used monoexponential model. Reducing the sampling density of the relaxation data and adding Gaussian-distributed noise served to simulate cases in which the data are acquisition-time or signal-to-noise restricted, respectively. As expected, reducing either the number of data points or the signal-to-noise increases the uncertainty in estimated parameters and, ultimately, reduces support for more complex relaxation models.     

Characterization of the globular oxide inclusion ratings in steel using laser-induced breakdown spectroscopy

Grade assessment of steel is generally performed via the metallographic method, which is timeconsuming and is not able to provide the elemental distribution information. In this paper, we present a method to measure the globular oxide inclusion ratings in steel using laser-induced breakdown spectroscopy (LIBS). The measurement is performed in two basic steps: steel samples are polished using metallographic sand paper and the Al₂O₃ inclusion number and size distribution in a marked area are observed using scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDS) for further LIBS scanning analysis. The threshold intensity that distinguishes soluble aluminum and insoluble aluminum inclusions is determined using LIBS combined with the SEM/EDS statistical data. Carbon steel (the sample number is S9256) and bearing steel (the sample number is GCr15) are analyzed in scanning mode, and the number of Al₂O₃ inclusions in different size ranges is obtained from the statistical information derived from the Al₂O₃ size calibration curve. According to heavy and thin series for globular oxide inclusions grade assessment, the method we propose is comparable to the traditional metallographic method in terms of accuracy; however, the process is simplified and the measurement speed is significantly improved.     

Carbon-based single atom catalyst: Synthesis,characterization, DFT calculations

Carbon-based single-atom catalysts(SACs) with atomic sizes of active sites have become the promising candidates for a variety of catalytic systems because of their high atom utilization, and unique electronic structures. Different types of single-atom sites can be fabricated via multiple preparation strategies, which would demonstrate distinct different coordination configurations and electronic features, and ultimately affected the structure-catalysis relationship of SACs in targeted reactions....     

Investigation of carbon-supported Ni@Ag core-shell nanoparticles as electrocatalyst for electrooxidation of sodium borohydride

Carbon-supported Ni@Ag core-shell nanoparticles were synthesized and used as the anode electrocatalyst for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The morphology, structure, and composition of the as-prepared electrocatalysts are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). Electrochemical characterizations are performed by cyclic voltammetry (CV), chronoamperometry (CA), linear scan voltammetry with rotating disk electrode (LSV RDE), and fuel cell test. The catalytic behaviors and main kinetic parameters (e.g., Tafel slope, number of electrons exchanged, exchange current density, and apparent activation energy) toward BH ₄ ^‐ oxidation on Ag/C and Ni@Ag/C electrocatalysts are determined. Results show that the as-prepared nanoparticles have a core-shell structure with the average size approximately 13 nm. The kinetics of NaBH₄ oxidation is faster for Ni@Ag/C than that for Ag/C. Among the as-prepared catalysts, the highest transition electron value and the lowest apparent activation energy are obtained on Ni₁@Ag₁/C; the values are 4.8 and 20.23 kJ mol^?1, respectively. The DBHFC using Ni₁@Ag₁/C as anode electrocatalyst and Pt mesh (1 cm²) as cathode electrode obtains the maximum anodic power density as high as 8.54 mW cm^?2 at a discharge current density of 8.42 mA cm^?2 at 25 °C.     

Finite element method for viscoelastic medium with damage and the application to structural analysis of solid rocket motor grain

This paper studies the damage-viscoelastic behavior of composite solid propellants of solid rocket motors(SRM).Based on viscoelastic theories and strain equivalent hypothesis in damage mechanics,a three-dimensional(3-D)nonlinear viscoelastic constitutive model incorporating with damage is developed.The resulting viscoelastic constitutive equations are numerically discretized by integration algorithm,and a stress-updating method is presented by solving nonlinear equations according to the Newton-Raphson method.A material subroutine of stress-updating is made up and embedded into commercial code of Abaqus.The material subroutine is validated through typical examples.Our results indicate that the finite element results are in good agreement with the analytical ones and have high accuracy,and the suggested method and designed subroutine are efficient and can be further applied to damage-coupling structural analysis of practical SRM grain.     

Thermo-Associative and Salt-Associative Graft Copolymers of Surfactant Macromonomers and Acrylamide: Synthesis and Solution Properties in Dilute Aqueous Solutions

Three new surfactant macromonomers (SMM) with different ethylene oxide (EO)/propylene oxide (PO) ratios (for SMM1, SMM2, and SMM3, the EO/PO ratios were 1:0.5, 1:0.9, and 1:1.25, respectively) were synthesized by the reaction between PEO-PPO di-block polymers having terminal tertiary amine groups and chloropropene. Graft copolymers of acrylamide and SMM (PAM-g-SMM) were prepared with different SMMs and grafting densities in water, and the products were confirmed by FTIR and elemental analysis. Owing to the strong hydrophobicity of the graft, the PAM-g-SMM3 was not water soluble. However, PAM-g-SMM1 and PAM-g-SMM2 aqueous solutions had good surface activity and their surface tensions were 44.26 and 37.63 mN/m at a concentration of 1000 mg/L, respectively. In general, in diluted graft PAM solutions, the copolymer predominantly formed intrapolymeric associates. The PAM-g-SMM2 was both thermo-associative and salt-associative in dilute solution. For PAM-g-SMM2, when the temperature and salt concentration increased, interpolymeric aggregations were formed.     

水下通信中的异常声压监控网络系统设计

传统水下通信声压异常监控网络存在无法自主完成节点的投放和回收,存储监控盲区并且无法进行动态组网,不能对异常声压进行准确的监控等较大的缺陷;为此,设计并实现了一种新的水下异常声压监控系统,系统中的通信协议基于节点间的深度信息完成数据的转发,给出了系统中监控器、CC2430 处理器、终端节点以及协调器节点的硬件设计原理并给出了系统采集数据的软件流程;系统中实现了对链路层的AODV 路由协议进行改进,增强系统对异常声压的监控性能;测试结果说明,该系统获取的声压监测星座图明显优于传统系统,在不同的干扰类型下,发射信号使用PSK调制,载波中心频率是10 kHz,采样率是50 kHz,码率是2 000 bit/s;实验结果表明:该种系统具有较低异常声压信号监控误差率,可对异常声压信道的传输特性进行较好的校正和补偿,具有较强稳定性。