Fast Quaternion Log-Polar Radial Harmonic Fourier Moments for Color Image Zero-Watermarking

Journal of Mathematical Imaging and Vision - As a copyright protection technology, zero-watermarking has received widespread attention in recent years. The zero-watermarking algorithm based on...     

微通道内分叉流动换热特性研究

本文建立了具有分叉结构的微通道内层流流动换热理论模型并进行了数值求解,分析讨论了分叉处的流动和换热特性,给出了微通道内分叉处附近的沿程压降和Nusselt数分布。数值模拟结果表明:在具有分叉结构的微通道内,在分叉后通道壁面附近产生了回流现象,导致分叉处压降产生波动。由于分叉流动,使得分叉后流动热边界层的重新生成和流体冲刷作用导致了微通道内的整体流动换热得到了强化。     

金属催化非晶碳转化制备石墨烯方法的研究进展

石墨烯自2004年被首次发现以来, 以其独特、优异的结构和特性引起了广泛关注。目前, 石墨烯的制备已取得了众多进展, 但在大尺寸、高质量、宏量石墨烯可控制备上仍存在挑战, 对制备技术仍需要进行更广泛地探索。非晶碳与石墨烯互为碳的同素异形体, 也可作为制备石墨烯的前驱体, 近些年利用非晶碳制备石墨烯的新颖方法引起了研究学者的兴趣。本文系统论述了利用非晶碳作为固体碳源, 通过金属催化制备大尺寸高质量石墨烯的技术优势, 并着重从金属种类、退火温度、碳源及金属含量比例等方面对石墨烯生成质量的影响进行了阐述。最后, 总结了该方法生长石墨烯的机理, 并对未来的发展方向进行了展望。     

表面活性剂十二烷基硫酸钠协助超声波提取甘薯叶总黄酮

目的 探究表面活性剂十二烷基硫酸钠(sodium dodecyl sulfate, SDS)协助超声波提取甘薯叶总黄酮的最佳工艺条件。方法 以甘薯叶总黄酮提取量为考察指标, 采用Box-Behnken法进行试验设计, 对SDS质量浓度、乙醇体积分数、料液比、超声时间进行响应面优化。结果 各因素对甘薯叶总黄酮提取量的影响程度为C(料液比)>A (SDS质量浓度)>B(乙醇体积分数)>D(超声时间), 甘薯叶总黄酮最佳提取工艺参数为SDS质量浓度1.0%、乙醇体积分数81%、料液比1:50 (g:mL)、超声时间49 min, 在此条件下, 总黄酮提取量为 132.08 mg/g, 与回归模型预测值134.63 mg/g相差1.89%, 表明该模型与实际情况拟合良好。结论 利用表面活性剂十二烷基硫酸钠协同超声提取甘薯叶总黄酮的工艺方法稳定可行, 可为甘薯叶总黄酮的进一步开发利用提供参考依据。     

电感耦合等离子体发射光谱法测定奶粉中微量元素含量的不确定度评定

目的评定电感耦合等离子体发射光谱法测定奶粉中微量元素含量的不确定度。方法对电感耦合等离子体发射光谱法测定奶粉中锌、铁、锰、铜、钙、镁、钠、钾8种微量元素的整个实验过程可能引入的各种不确定度来源进行分析,建立不确定度数学模型,计算各不确定度分量及扩展不确定度。结果在置信区间为95%的范围内,奶粉中钙、镁、钠、钾、锌、铁、锰、铜的扩展不确定度分别为0.07330、0.1136、0.07380、0.07340、0.05598、0.05272、0.08542、0.05190。结论标准溶液配制带来的不确定度对钙、钠、钾、锌、铁、铜元素的贡献率最大,由标准曲线拟合带来的不确定度对镁元素的贡献率最大,测量结果重复性带来的不确定度对锰的贡献率最大。     

Two-dimensional electronic spectra investigated using hierarchical equation of motion and cumulant expansion

Abstract

We investigate the two-dimensional third-order nonlinear electronic spectra using the cumulant expansion (CE) and hierarchical equation of motion (HEM) methods. The HEM method is non-Markovian and nonperturbative. In the CE method, the Markovian approximations are always applied in solving dynamical equations and calculating the line-broadening function. If the Markovian approximation is used in the dynamical solutions and theaffected by the line-broadenin calculations of the line-broadening function in the CE method, the nonlinear electronic spectra obtained are different from those obtained using the HEM method. However, using the non-Markovian line-broadening function, we obtain almost the same spectra from the two methods, even when keeping the Markovian approximation in the dynamical solutions. This may imply that in order to obtain the correct nonlinear electronic spectra, it is crucial to include the non-Markovian effect in the line-broadening function, but it may not matter if the Markovian approximation is used in solving the dynamical equations.     

Excitation-induced tunable luminescent properties of polyhedral CaMoO4 microcrystallites

Journal of Materials Science: Materials in Electronics - Polyhedral CaMoO4 microcrystallites with excitation-induced tunable luminescent characteristics were successfully synthesized by a...     

In-situ growth of mesoporous Nb2O5 microspheres on g-C3N4 nanosheets for enhanced photocatalytic H2 evolution under visible light irradiation

Large-surface-area mesoporous Nb₂O₅ microspheres were successfully grown in-situ on the surface of g-C₃N₄ nanosheets via a facile solvothermal process with the aid of Pluronic P123 as a structure-directing agent. The resultant g-C₃N₄/Nb₂O₅ nanocomposites exhibited enhanced photocatalytic activity for H₂ evolution from water splitting under visible light irradiation as compared to pure g-C₃N₄. The optimal composite with 38.1 wt% Nb₂O₅ showed a hydrogen evolution rate of 1710.04 μmol h^?1 g^?1, which is 4.7 times higher than that of pure g-C₃N₄. The enhanced photocatalytic activity could be attributed to the sufficient contact interface in the heterostructure and large specific surface area, which leads to effective charge separation between g-C₃N₄ and Nb₂O₅.     

基于挥发性风味物质分析的小麦储藏年份鉴别方法研究

目的 基于挥发性风味物质分析鉴别小麦储藏年份。方法 采用固相微萃取-气相色谱-质谱法对小麦籽粒样品进行检测,采用主成分分析、凝聚层次聚类并结合偏最小二乘法判别分析对不同储藏年份的小麦样品的挥发性风味物质种类和含量进行分析,建立基于挥发性风味物质分析的小麦储藏年份鉴别模型。结果 对收获期为2018年至2022年共5个年份的小麦样品进行检测,检出挥发性风味物质73种,包括醇类、醛类、酮类、杂环化合物、酸类、酯类、醚类、烃类和酚类物质。基于变量投影重要性筛选出37种对主成分分类贡献较大的差异化合物,其中γ-辛内酯、γ-庚内酯、γ-己内酯、γ-壬内酯、1-庚醇、1-己醇和1-戊醇含量与小麦储藏年份呈正相关,被确定为特征差异化合物。结论 不同储藏年份小麦中挥发性风味物质含量存在差异,基于特征差异化合物构建的分类模型有望用于小麦储藏年份的快速、准确鉴别,为小麦的品质鉴别提供一定的技术支撑。