Computational and experimental study of dental resin composites with high filler content

Journal of Materials Science - Nanocomposites have been used in various industries due to their excellent properties. For some of them, high filler content (over 50 wt%) is beneficial to improving...     

Optimization of room-temperature TCR of polycrystalline La0.9-xSrxK0.1MnO3 ceramics by Sr adjustment

High-density La_0.9-xSr_xK_0.1MnO₃ ceramics (LSKMO, A-site = La, Sr and K, 0 ≤ x ≤ 0.25) are successfully fabricated by using facile sol-gel method. Electrical properties are performed by using combination of phenomenological percolation (PP) model, double exchange (DE) mechanism, and Jahn-Teller (JT) effect. Moreover, X-ray diffraction and scanning electron microscopy are employed to analyze the structure and morphology of LSKMO ceramics. Valence states and ionic stoichiometry are assessed by using X-ray photoemission spectrometry. Results reveal that Sr²⁺ ions, substituting La³⁺ ions, significantly influenced DE mechanism and JT effect. In addition, Sr-doping plays essential role in improving electrical properties of LSKMO ceramics. At optimal doping content of x = 0.09, peak temperature coefficient of resistance (TCR) of the resistivity is found to be 11.56% K^?1 at 297.15 K, which is optimal TCR for A-site K-occupied perovskite manganese oxides. These results confirm that polycrystalline LSKMO ceramics render high room-temperature TCR values due to Sr-doping.     

Colossal dielectric response and relaxation behavior in novel system of Zr4+ and Nb5+ co-substituted CaCu3Ti4O12 ceramics

In this work, we developed a novel system of isovalent Zr⁴⁺ and donor Nb⁵⁺ co-doped CaCu₃Ti₄O₁₂ (CCTO) ceramics to enhance dielectric response. The influences of Zr⁴⁺ and Nb⁵⁺ co-substituting on the colossal dielectric response and relaxation behavior of the CCTO ceramics fabricated by a conventional solid-phase synthesis method were investigated methodically. Co-doping of Zr⁴⁺ and Nb⁵⁺ ions leads to a significant reduction in grain size for the CCTO ceramics sintered at 1060 °C for 10 h. XRD and Raman results of the CaCu₃Ti_3.8-xZr_xNb_0.2O₁₂ (CCTZNO) ceramics show a cubic perovskite structure with space group Im-3. The first principle calculation result exhibits a better thermodynamic stability of the CCTO structure co-doped with Zr⁴⁺ and Nb⁵⁺ ions than that of single-doped with Zr⁴⁺ or Nb⁵⁺ ion. Interestingly, the CCTZNO ceramics exhibit greatly improved dielectric constant (~10⁵) at a frequency range of 10²–10⁵ Hz and at a temperature range of 20–210 °C, indicating a giant dielectric response within broader frequency and temperature ranges. The dielectric properties of CCTZNO ceramics were analyzed from the viewpoints of defect-dipole effect and internal barrier layer capacitance (IBLC) model. Accordingly, the immensely enhanced dielectric response is primarily ascribed to the complex defect dipoles associated with oxygen vacancies by co-doping Zr⁴⁺ and Nb⁵⁺ ions into CCTO structure. In addition, the obvious dielectric relaxation behavior has been found in CCTZNO ceramics, and the relaxation process in middle frequency regions is attributed to the grain boundary response confirmed by complex impedance spectroscopy and electric modulus.     

贯筋藤凝乳剂对小鼠急性毒性与遗传毒性研究

目的探究贯筋藤作为凝乳剂的安全性。方法以贯筋藤凝乳剂为受试物,采用限量法评价贯筋藤凝乳剂对小鼠的急性毒性,观察小鼠体重及解剖后心脏、脾脏、肝脏、肾脏是否发生病变;采用Ames实验评价其遗传毒性,设20、100、500、2500、12500μg/皿剂量组进行遗传毒性实验。结果急性毒性实验未出现小鼠死亡情况。研究发现小鼠的精神亢奋,有较强攻击欲望,根据小鼠的生理状况对小鼠进行脑组织中MAO-A和5-HT含量检测发现空白组和实验组差异极显著(P0.01)。通过Ames试验检测贯筋藤凝乳剂的遗传毒性,根据结果发现在12500μg/皿的情况下出现抑制微生物生长的情况,而在2500μg/皿的剂量下统计每组菌落数差异不著性(P0.05)。结论贯筋藤凝乳剂的LD50剂量大于10000 mg/kg,并根据Ames试验确定贯筋藤凝乳剂在最高2500μg/皿不具有致突变作用。     

Fabrication and Characterization of Highly Oriented Composite Nanofibers with Excellent Mechanical Strength and Thermal Stability

Here, highly‐oriented poly(m‐phenylene isophthalamide)/polyacrylonitrile multi‐walled carbon nanotube (PMIA/PAN‐MWCNT) composite nanofiber membranes with excellent mechanical strength and thermal stability are successfully produced using electrospinning. It is demonstrated that the cooperation of multi‐walled carbon nanotubes (MWCNT) and high‐speed rotating collection is beneficial to the acquisition of highly oriented fibers and effectively improves the mechanical strength of the membrane along the orientation direction. Specifically, the tensile stress of poly(m‐phenylene isophthalamide)/polyacrylonitrile (PMIA/PAN) membrane is enhanced significantly from 10.6 to 20.7 MPa, benefiting from the highly oriented alignment of the fibers as well as the reinforcing effect of MWCNTs on the fibers. Furthermore, the stressing process of single fiber and fiber aggregates is carefully simulated, and the influence of MWCNTs on the mechanical properties of PMIA/PAN‐MWCNT membranes is analyzed comprehensively, providing a meaningful auxiliary means for the study of mechanical properties. In addition, the composite nanofiber membrane has the advantages of both PMIA and PAN, possessing high temperature resistance, flame‐retardancy, and chemical stability, for an ideal high‐temperature material. In short, the as‐prepared PMIA/PAN‐MWCNT composite membrane with excellent comprehensive property emerges a promising application in many fields, especially in high‐tech.     

Low-complexity transmit antenna selection algorithm formassive MIMO

Massive multiple input multiple output (MIMO) systems can increase capacity and reliability greatly. However,extremely high hardware costs and computational complexity lead to the demand for reasonable antenna selection.Aiming at the problem that the traditional antenna selection algorithm based on maximizing sum capacity has largecomplexity and worse bit error rate (BER) performance, a two-step selection algorithm is proposed, which selectsa part of the antennas based on the norm-based antenna selection (NBS) firstly, and then selects the antenna basedon maximizing capacity via convex optimization. The simulation results show that the improved algorithm has betterBER performance than the traditional algorithms. At the same time, it reduces computational complexity greatly.     

Correction to: GPU-accelerated scanning path optimization in particle cancer therapy

Free electron lasers provide high-power and ultrashort pulses with extreme brightness. In order to improve a facility's capabilities and explore the possibility of performing high-resolution time-resolved experiments, a beam arrival time resolution under 100 fs is required. In this article, a novel beam arrival time monitor(BAM)equipped with two cavities has been designed and a beam flight time measurement scheme based on the BAM prototype has been proposed to estimate phase jitter in the signal measurement system. The two BAM cavities work at different frequencies and the frequency difference is designed to be 35 MHz. Therefore, a self-mixing intermediate frequency signal can be generated using the two cavities. The measured beam flight time shows a temporal deviation of 37 fs(rms).     

电磁搅拌对大圆坯结晶器冶金行为影响的探讨

 为了探究结晶器电磁搅拌(M EMS)对大圆坯结晶器内综合冶金行为的影响。以大断面圆坯连铸结晶器冶金行为为研究对象，基于电磁热流体与凝固传输理论建立三维耦合数值模型。揭示大圆坯连铸常用五孔水口浇注条件下结晶器内电磁场、流场、传热与凝固等综合冶金行为，提出电磁搅拌对结晶器冶金性能影响的多参量评价方法。以中碳铬钼齿轮钢650 mm大圆坯连铸为例，指出结晶器电磁搅拌存在最佳搅拌电流，可获得相对较好的综合冶金效果。具体表现为弯月面保持一定的切向速度和过热度，有利于保护渣的熔化和夹杂物的上浮去除；液面波动幅度在控制范围内，可避免卷渣、改善表面质量；结晶器内钢液过热得到有效耗散，有利于等轴晶形核改善铸坯内部质量；侧孔出流钢液速度得到有效控制，可抑制注流对初凝坯壳的冲刷，提高了初生坯壳生长的均匀性。此外，电磁搅拌产生的水平旋流强度也可得到有效控制，有利于避免常见的皮下白亮带现象。