Study of nanocrystalline Fe－Al－N soft magnetic thin films

Fe－Al－N films were fabricated by reactive sputtering using a radio-frequency magnetron sputtering system. The effects of Al and N content and annealing temperature on microstructure and magnetic properties were investigated. The Fe－Al－N films, which have good soft magnetic properties, consist of nanocrystalline α-Fe grains and a small amount of other phases in the boundaries of α-Fe grains. The average α-Fe grain size is about 10－15nm. A slight amount of Fe－N and Al－N compounds precipitate in the boundaries of α-Fe grains and suppress their growth. Annealing improves the soft magnetic properties slightly by releasing the residual stress and reducing defects.     

射频溅射FeTaN纳米晶软磁薄膜结构和磁性

用射频反应溅射制备了FeTaN纳米晶软磁薄膜.研究了薄膜结构和磁性与制备条件的依赖关系.研究发现,当Ta的含量较高时,在N2+Ar混合气氛中易形成沉积态薄膜的非晶结构.适当的热处理后,αFe纳米晶从中晶化生成.薄膜显示出优良的软磁特性 关键词： 纳米晶 软磁性 非晶态     

探索加密货币波动率预测中的模型不确定性问题:log转换、时区采样以及模型设定

文章全面地比较了一系列模型在预测加密货币波动率时的表现.结果发现,粗糙波动率模型在预测多期样本外的波动率时表现更加稳健和可靠,而异质自回归(HAR)模型相对较弱,但经过log转换后的HAR模型在预测上则表现更优.此外,考虑到加密货币的特点,选取合适的时区划分依据也非常重要,因为不同的时区可能对加密货币市场的波动率产生影响.研究还引入了最小二乘模型平均法来应对波动率建模中的模型不确定性.结果表明,模型平均方法在加密货币市场波动率预测中相比其他方法具有优越性,能够平衡不同模型之间的优缺点,提高预测的可信度和稳定性,对于预测市场的波动性是非常有效的.文章研究指出,在选择合适的波动率模型时需要综合考虑加密货币波动率的特性和历史表现,并且在应用模型时需要注意其在不同数据集和预测目标下的表现,避免盲目使用导致预测效果的不确定性.     

CuO-CeO2-MnOx/γ-Al2O3催化剂选择性催化脱除NO机理研究

利用溶胶凝胶法制备CuO-CeO2-MnOx/γ-Al2O3催化剂颗粒,在固定床上测试其催化脱硝活性.CuO-CeO2-MnOx/γ-Al2O3催化剂在200～450℃范围内脱硝效率保持在70%以上.利用程序升温方法研究了催化剂对NH3的氧化性能,活性组分负载量增多,加强了催化剂对NH3氧化性能.红外表征显示NH3被吸附在催化剂的L酸位和B酸位.NO以多种硝酸盐物种在催化剂表面吸附.吸附态NH3参与SCR反应,但吸附态NO物种仅部分参加SCR反应.     

运用最小二乘模型平均法预测外汇实际波动率（英文）

金融风险管理的重中之重在于对金融资产实际波动率的预测.因为汇率市场的复杂性以及多变性,汇率波动率数据具有极强的异方差性.文章着重研究在异方差环境下,如何正确地使用最小二乘模型平均法来提高实际波动率的预测精度.文章以异质自回归(HAR)模型为基础,以不同的滞后项构建出多个候选模型.最终模型是所有候选模型的加权平均.而通过为每个候选模型配给不同的权重,模型平均法可以灵活动态地调节最终模型的结构.文章首先证明了所提出的最小二乘模型平均法具有渐近最优性.在随后大量实证中,发现所提出的方法在汇率实际波动率的预测精度方面优于很多同类方法.     

Synthesis of thermally stable HfO_xN_y as gate dielectric for AlGaN/GaN heterostructure field-effect transistors

In this paper, we adopted thermally stable HfO_xN_y as gate dielectric for TiN/HfO_xN_y/AlGaN/GaN heterostructure field-effect transistors(HFETs) application. It demonstrated that the surface morphologies, composition, and optical properties of the HfO_xN_y films were dependent on oxygen flow rate in the O_2/N_2/Ar mixture sputtering ambient. The obtained metal–oxide–semiconductor heterostructure field-effect transistors by depositing HfO_2 and HfO_xN_y dielectric at different oxygen flow rates possessed a small hysteresis and a low leakage current. After post deposition annealing at 900℃, the device using HfO_xN_y dielectric operated normally with good pinch-off characteristics, while obvious degradation are observed for the HfO_2 gated one at 600℃. This result shows that the HfO_xN_y dielectric is a promising candidate for the self-aligned gate process.