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121.
We show that high photon-number squeezing in bright light can be
generated in both lasers and optical bistabilities by the
injections of a squeezed vacuum and a classical field, and the
high squeezing is maintained for very strong field. 相似文献
122.
123.
黄龙病是柑桔果树的毁灭性病害,对柑桔产业危害巨大。基于模型平均理论,探讨联用可见与近红外光谱技术,提高柑桔黄龙病快速无损检测精度的可行性。采集记录柑桔叶片的可见与近红外光谱,经实时荧光定量PCR鉴别黄龙病叶片为轻度、中度和重度三类,缺素和正常样品也经PCR鉴定,共五类叶片。基于光谱直接拼接、光谱归一化拼接和模型平均三种不同策略,结合偏最小二乘判别分析(PLS-DA)和多元线性回归(MLR)方法,分别建立了柑桔黄龙病可见与近红外光谱联用无损检测模型。经比较发现,光谱联用模型的检测精度均高于可见或近红外单一检测模型,且经导数处理后的光谱直接拼接PLS-DA模型检测精度最高,模型预测相关系数为0.97,预测均方根误差为0.67,模型总误判率为3%,其原因是导数消除了光谱的基线漂移。光谱归一化拼接的PLS-DA模型检测精度次之,模型总误判率为7%。可见与近红外模型平均的检测精度最低,模型总误判率为7.2%。实验结果表明,联用可见与近红外光谱,结合光谱拼接方法,提高了柑桔黄龙病无损检测模型的检测精度,研究可为其他领域的光谱联用提供参考依据。 相似文献
124.
125.
l1-SPIRiT is a fast magnetic resonance imaging (MRI) method which combines parallel imaging (PI) with compressed sensing (CS) by performing a joint l1-norm and l2-norm optimization procedure. The original l1-SPIRiT method uses two-dimensional (2D) Wavelet transform to exploit the intra-coil data redundancies and a joint sparsity model to exploit the inter-coil data redundancies. In this work, we propose to stack all the coil images into a three-dimensional (3D) matrix, and then a novel 3D Walsh transform-based sparsity basis is applied to simultaneously reduce the intra-coil and inter-coil data redundancies. Both the 2D Wavelet transform-based and the proposed 3D Walsh transform-based sparsity bases were investigated in the l1-SPIRiT method. The experimental results show that the proposed 3D Walsh transform-based l1-SPIRiT method outperformed the original l1-SPIRiT in terms of image quality and computational efficiency. 相似文献
126.
The ultrasound echo attenuation depends on frequency, propagating depth and tissue characteristics. Thus, the attenuation dependent on frequency results in a larger attenuation of high frequencies than lower when the wave propagates through the tissue. As a result, the central frequency of the echo generates the increasing downshift with the increasing of depth. In the traditional I/Q demodulation method, it is assumed that the central frequency of the echo is the same as the transmitting frequency and unchanged all time. The assumption directly causes that the acquired I/Q signals are not perfect baseband ones but biased due to the echo attenuation. In addition, the unreasonable assumption will keep the echo from getting better signal-to-noise ratio. A quadrature demodulation method based on tracking the ultrasound echo frequency is proposed in this paper. The method consists of the traditional I/Q demodulator, the frequency tracking module, the phase compensation module and the dynamic filtering module. The outputs of I/Q demodulator are biased. Autocorrelation technique is utilized in the frequency tracking unit to estimate the frequency bias according to the outputs of I/Q demodulator. The estimated bias feeds to the phase compensation unit which can eliminate the frequency bias by simple trigonometric function transform. The compensated signals feed to the dynamic filter and are further processed. The bandwidth of the dynamic filter decreases with the increasing of the depth, which makes the echo acquire better SNR in different depth. The efficiency of the proposed method is testified by both simulations and experiments. 相似文献
127.
石墨烯及其衍生物作为新型碳纳米结构,由于其优异的光限幅性能而受到广泛关注,但现有的工作多侧重于其在液相体系中光限幅效应及其起因研究.本文以壳聚糖为成膜基质,将氧化石墨烯(GO)与壳聚糖(CS)在液相中均匀共混后成膜,对比研究GO溶液和GO-CS复合膜的光限幅效应及其起因.结果表明在线性透过率相同的情况下,GO在固相基质中表现出比液相基质更强的光限幅效应和更弱的非线性散射.这说明不同于碳纳米管简单的非线性散射,在GO中可能存在多种非线性光学效应. 相似文献
128.
Applications for piezoelectric efect have grown rapidly,and piezoelectric materials play important roles in countless areas of modern life.By means of twoscale method and coupled boundary layer,some new kinds of twoscale asymptotic expansions for solutions to the electrical potential and the displacement in quasi-periodic structure under coupled piezoelectric efect are derived,and the homogenization constants of piezoelectric materials are presented.The coupled twoscale relation between the electrical potential and the displacement is set up,and some improved asymptotic error estimates are analyzed. 相似文献
129.
We successfully fabricated a high-performance half-wave plate for the 405 nm wavelength based on monolithic integration of two nanograting layers. Each of the nanograting layers functions as a quarter-wave plate. Both of the nanograting layers were fully filled and planarized to achieve the monolithic integration. UV-nanoimprint lithography, along with thin-film deposition, high-aspect-ratio reactive ion etching, and trench-filling technologies, was used in fabrication and integration of the individual nanograting layers. High-aspect-ratio nanogratings with sub-50 nm linewidths and 100 nm spacing were fabricated to achieve good optical performance at the near-UV wavelength. The ability to integrate multiple nanostructure-based optical layers opens a path for integrated multifunction devices, as well as a new strategy for driving both miniaturization and cost. 相似文献
130.
吖啶红与铬(Ⅵ)的高灵敏度荧光反应及应用 总被引:4,自引:0,他引:4
研究了在硫酸介质中,铬(Ⅵ)氧化吖啶红荧光增强反应的最佳实验条件,建立了测定痕量铬(Ⅵ)的新的高灵敏度荧光分析法。该方法的检出限为0.6 μg·L-1,线性范围为2.0~32 μg·L-1,对含量为4.0和28 μg·L-1的Cr(Ⅵ)标准溶液进行11次平行测定, 其相对标准偏差分别为2.0%和1.0%。该法用于电镀液、废铬酸洗液及合金钢中痕量铬(Ⅵ)的测定,与标准样品和二苯碳酰二肼分光光度法进行了对照,获得了满意结果。 相似文献