The structures under different pressures, elastic properties, electronic structures and lattice vibrations of the X_2N_2O（X = C, Si, Ge） compounds are investigated by using the first-principle method. Based on the p...The structures under different pressures, elastic properties, electronic structures and lattice vibrations of the X_2N_2O（X = C, Si, Ge） compounds are investigated by using the first-principle method. Based on the phonon density of state,the thermodynamic properties of the present compounds are studied under different pressures and at different temperatures. The structural parameters including the bond lengths and bond angles are in agreement with available experimental measurements and theoretical calculations. We employ the elastic theory to calculate the nine independent elastic constants（C_（ij）） and the derived elastic moduli（B, G, E, v）. Results indicate that these X_2N_2O（X = C, Si, Ge） compounds are mechanically stable and show the brittle behaviors. The electronic properties of the present compounds are analyzed by using the band structure and density of states. The phonon dispersion calculations imply that the present compounds are dynamically stable. Based on the quasi-harmonic approximation, the calculations of the specific heat indicate that the temperature in a range of 0 K–1500 K and pressure in a range of 0 GPa–40 GPa have a large effect on the thermal quantities of Ge_2N_2O,compared with on those of the C_2N_2O and Si_2N_2O compounds.展开更多
该文分析了 B 超检查32例外伤性脾破裂的结果,总结了真性破裂、包膜下破裂、中央破裂3种类型的声像图特点,探讨了 B 超诊断外伤性脾破裂的应用价值,以及在诊断脾破裂中应吸取的一些经验教训,提出 B 超可作为外伤性脾破裂诊断及观察的首...该文分析了 B 超检查32例外伤性脾破裂的结果,总结了真性破裂、包膜下破裂、中央破裂3种类型的声像图特点,探讨了 B 超诊断外伤性脾破裂的应用价值,以及在诊断脾破裂中应吸取的一些经验教训,提出 B 超可作为外伤性脾破裂诊断及观察的首选检查。展开更多
根据课堂教学场景设计了三维卷积神经网络(3D-convolutional neural network,3D-CNN),以动态性为主要特征,对教师进行课堂行为识别;提出了经过改进损失函数的YOLO-v5(you only look once version 5th)模型,并以多目标为主要特征,对学生...根据课堂教学场景设计了三维卷积神经网络(3D-convolutional neural network,3D-CNN),以动态性为主要特征,对教师进行课堂行为识别;提出了经过改进损失函数的YOLO-v5(you only look once version 5th)模型,并以多目标为主要特征,对学生进行课堂行为识别.2种模型均取得了较好的识别结果.为验证所选用模型的有效性,在所标注课堂行为数据集上进行了模型性能对比试验.试验结果表明:所选用模型在教育场景下课堂行为识别工作中展现了较好的性能;课堂行为的精准识别能够帮助教师和学生了解课堂学情,有助于推动智慧课堂的发展.展开更多
基金Project supported by the Fundamental Research Funds for the Central Universities,China(Grant No.FRF-TP-14-029Al)
文摘The structures under different pressures, elastic properties, electronic structures and lattice vibrations of the X_2N_2O（X = C, Si, Ge） compounds are investigated by using the first-principle method. Based on the phonon density of state,the thermodynamic properties of the present compounds are studied under different pressures and at different temperatures. The structural parameters including the bond lengths and bond angles are in agreement with available experimental measurements and theoretical calculations. We employ the elastic theory to calculate the nine independent elastic constants（C_（ij）） and the derived elastic moduli（B, G, E, v）. Results indicate that these X_2N_2O（X = C, Si, Ge） compounds are mechanically stable and show the brittle behaviors. The electronic properties of the present compounds are analyzed by using the band structure and density of states. The phonon dispersion calculations imply that the present compounds are dynamically stable. Based on the quasi-harmonic approximation, the calculations of the specific heat indicate that the temperature in a range of 0 K–1500 K and pressure in a range of 0 GPa–40 GPa have a large effect on the thermal quantities of Ge_2N_2O,compared with on those of the C_2N_2O and Si_2N_2O compounds.
文摘根据课堂教学场景设计了三维卷积神经网络(3D-convolutional neural network,3D-CNN),以动态性为主要特征,对教师进行课堂行为识别;提出了经过改进损失函数的YOLO-v5(you only look once version 5th)模型,并以多目标为主要特征,对学生进行课堂行为识别.2种模型均取得了较好的识别结果.为验证所选用模型的有效性,在所标注课堂行为数据集上进行了模型性能对比试验.试验结果表明:所选用模型在教育场景下课堂行为识别工作中展现了较好的性能;课堂行为的精准识别能够帮助教师和学生了解课堂学情,有助于推动智慧课堂的发展.
