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991.
992.
以共轭聚合物MEH-PPV和DD-PPV为研究对象,利用UV-Vis吸收光谱和荧光光谱,研究了它们在不同溶剂中及固体膜状态下的发光性质,探索了聚合物的微观结构与其发光性能之间的关系.结果表明,由于聚合物在固体膜状态下较溶液状态有紧密的排列,因此其UV-Vis吸收光谱和荧光光谱与溶液相比发生了较大的红移;相同主链的聚合物,侧链取代基的电负性减弱,可使UV-Vis吸收光谱和荧光光谱发生蓝移;在混合溶剂中,由于每种溶剂对聚合物的溶解能力不同,而使两种构象共存于溶液中,因此在不同配比的混合溶剂中,聚合物的吸收光谱发生相应的变化. 相似文献
993.
994.
This paper deals with dynamics of a predator-prey model with Allee effect and herd behavior. We first study the stability of non-negative constant solutions for such system. We also establish the existence of Hopf bifurcation solutions for such predator-prey model. The stability and bifurcation direction of Hopf bifurcation solution in the case of spatial homogeneity are further discussed. At the same time, several examples are given by MATLAB. Finally, the numerical simulations of the system are carried out through MATLAB, which intuitively verifies and supplements the theoretical analysis results. 相似文献
995.
将石墨烯薄膜置于不同环境气氛中,探究其在不同波长和功率密度可见光辐照下的导电特性.结果表明,石墨烯薄膜在不同条件光照下电阻缓慢上升,光照停止后电阻缓慢下降.氮气环境下石墨烯导电性能最稳定,真空下变化最大,在相同功率密度红光辐照下,样品在氮气、大气和真空下相对电阻变化分别为0.09%、0.22%、0.4%.相同环境下,波长越短,光子能量越大,对样品影响越大,在大气环境下,相同功率密度的蓝光、绿光和红光对样品相对电阻的影响分别为20%、3%、0.22%. 相似文献
996.
HAN Zhichao;HAN Yiping 《光子学报》2022,51(10):421-430
In recent years, Terahertz-waves have brought a brand-new, label-free, non-invasive detection method to biomedical research due to their non-ionization, broadband, and high signal-to-noise ratio. With the development of Terahertz sources, especially the generation of Terahertz pulses with energy up to mJ, the study of biological tissues in Terahertz band is no longer limited to non-thermal effects. Histopathological test is considered as the gold standard for diagnosing skin cancer and other tumors. However, the borders of some tumors are blurred, which may result in excessive surgery, mistaken resection, or inability to fully resection in the process of histopathological test. It is of great value to combine the physical properties of skin tissue and Basal Cell Carcinoma （BCC） with their optical properties in the Terahertz band for the non-destructive diagnosis of skin cancer. The purpose of this paper is to provide a certain theoretical basis for the non-destructive detection of early skin cancer by studying the photoacoustic effect of Terahertz-Waves in in vivo tissues （normal skin tissue, skin tissue containing basal cell carcinoma）. In this paper, according to the dendritic growth law of basal cell carcinoma in the basal layer of skin tissue, combined with the absorption characteristics of skin tissue in the Terahertz band and the difference in water content between skin tissues, a skin tissue model containing basal cell carcinoma is established. The model includes the stratum corneum, epidermis, and lesions of different basal cell carcinomas. As a control, a structural model of normal skin tissue is also established. Using the Pennes heat transfer equation, the Terahertz radiative heat effects of normal skin tissue models and skin tissue models containing basal cell carcinoma are analyzed. Finally, the differences and components of photoacoustic signals between normal skin tissue models and skin tissue models containing different basal cell carcinoma growth stages are analyzed using the photoacoustic effect of Terahertz-Waves. The simulation results show that the absorption of Terahertz-Waves in the epidermis is most obvious. It is difficult for high-energy pulsed terahertz waves to penetrate deep into the dermis for both normal skin tissue and skin tissue containing basal cell carcinoma. However, there are significant differences in thermal effects between skin tissue containing basal cell carcinoma and normal skin tissue. Skin tissue containing basal cell carcinomas is more sensitive to temperature changes from Terahertz-Waves irradiation. The analysis of different basal cell carcinoma growth stages shows that the temperature response of Terahertz-Waves could be used to detect the growth changes of basal cell carcinomas. As basal cell carcinomas spread and grow in skin tissue, it is easier to distinguish the different basal cell carcinoma growth phases by thermal effects. Furthermore, rapid diagnosis of basal cell carcinoma can be achieved by Terahertz-Waves irradiation with a single pulse energy of the order of μJ. Analysis of the difference in the photoacoustic signals between the two models shows that the skin tissue containing basal cell carcinoma produces stronger photoacoustic signals than normal skin tissue. As basal cell carcinoma spreads and grows, the photoacoustic signal received on the outer surface of the skin has a greater amplitude, and the photoacoustic signal generated by the stratum corneum and epidermis decays faster, which make it easier to detect and analyze. The findings are suitable for non-destructive diagnosis of early-stage skin cancer by Terahertz-Waves. The application value of Terahertz photoacoustic effect in the field of non-destructive test and fast real-time imaging is revealed. At the same time, it has certain significance for the selection of detectors, detection methods, Terahertz sources and suitable types of biological tissues in the experimental research of Terahertz photoacoustic imaging. 相似文献
997.
建立了一种固相萃取/气相色谱-质谱法同时测定土壤中23种有机氯农药的方法,并研究了不同基质效应补偿方式。土壤样品经正己烷∶丙酮(体积比1∶1)提取,弗罗里土小柱净化,采用气相色谱-质谱仪检测。结果发现7种有机氯存在中/强程度的基质效应;在10mL二氯甲烷∶正己烷(体积比1∶9)+10mL丙酮∶正己烷(体积比1∶9)为固相萃取的洗脱剂,且脉冲压力为275.8kPa条件下,可将23种有机氯的基质效应均控制在20%以内。23种有机氯农药在04~10μg·mL-1质量浓度范围内线性良好,相关系数(r2)均不小于0.9992,检出限为1.0~8.6μg·kg-1,定量下限为4.0~34.4μg·kg-1;在20、60、100μg·kg-13个加标水平下空白土壤中的平均回收率为46.3%~127%,相对标准偏差(n=6)为0.68%~15%。采用该方法在某土壤样品中检出α-六六六、γ-六六六、p,p′-DDE、异狄氏剂醛、p,p′-DDT5种有机氯农药。 相似文献
998.
999.
利用声波的多普勒频移可以对窄带运动声源进行单传感器无源测速,其性能很大程度上取决于能否精确地估计出声波的瞬时频率.Wigner-Ville分布虽然时频分辨率高,但存在交叉项干扰,很少被直接用于瞬时频率估计。对此,提出了抵消Wigner-Ville分布交叉项的单传感器窄带声源无源测速方法。利用交叉项与声源速度的关系构造一个抵消项,引入到Wigner-Ville分布中,通过对声源速度估计值进行迭代更新,使抵消项与交叉项相位相反,从而约掉交叉项。经实测噪声数据验证,对一辆以6.07 m/s匀速运动的卡车(信噪比约为29 dB)测速误差为0.1 m/s,运行时间为4.6 s,对一架以28.90 m/s匀速运动的直升机(信噪比约为16 dB)测速误差为0.46 m/s,运行时间为1.2 s,均优于匹配Wigner变换和多普勒线性调频小波变换测速方法. 相似文献
1000.
为研究环氧树脂玻璃钢在静、动态载荷作用下的力学性能,采用材料测试系统（MTS）和分离式霍普金森压杆（Split Hopkinson pressure bar,SHPB）对材料进行面内和面外方向的压缩实验,获得了不同应变率下材料的应力-应变曲线及相关力学参数。通过扫描电子显微镜（SEM）观察材料的微观破坏形貌,分析了材料的失效机理。静、动态压缩实验结果表明：环氧树脂玻璃钢具有明显的应变率敏感性以及各向异性;分层损伤是材料受面内加载发生破坏的原因,两个加载方向下材料均会产生层间贯穿的剪切裂纹。断口微观观测分析显示：动态载荷作用下,被拔出的纤维表面附着大量树脂基体,表明纤维-基体界面的作用力增强可能是导致环氧树脂玻璃钢动、静态力学响应差异的原因之一。针对材料的动态力学响应特性,建立了考虑应变率效应的非线性动态损伤模型。通过对比实验数据与拟合结果发现,该模型可以较好地描述环氧树脂玻璃钢在高应变率下的力学行为和特性。
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