大幅提高视觉密度国家基准测量水平的方法研究

随着生物医学影像和航天军事测量的发展,对用于光学成像底片和视觉校正的视觉密度的测量范围和不确定度的要求越来越高.以自行设计的光纤半球发射器形成的复合漫射器为特征的新方案将视觉漫透射密度国家基准的光源漫射系数提高到0.945,比欧美国家基准高0.02—0.03.实验得到新基准的测量范围为0—6.0,合成不确定度为0.0015(0相似文献   

常规速调管空间功率合成微波源

基于常规速调管,研制了用于开展空间功率合成实验的微波源系统。介绍了50 MW超大功率速调管发射机的系统组成、大功率速调管、相位控制及高功率测试系统等。重点阐述了超大功率速调管发射机的关键技术,并针对超大功率发射机的设计难点提出了具体的解决方案。为提高超大功率发射机的可靠性,设计了基于绝缘栅双极晶体管（IGBT）的感应叠加型全固态调制器。给出了超大功率发射机的测试结果,并探讨了超大功率速调管发射机的改进方法。最后对基于常规速调管,研制用于空间功率合成微波源系统的发展进行了展望。     

Dark pulse generation in a dispersion-managed fiber laser

We report an experimental observation of dark pulse generation in a dispersion-managed erbium-doped fiber laser with net anomalous cavity group-velocity dispersion. It is found that apart from the bright soliton pulses, dark pulses with spectral sidebands could be obtained in the laser under appropriate operating conditions. The generation of dark pulses may be attributed to soliton shaping in the cavity.     

Dereplication of known pregnane glycosides and structural characterization of novel pregnanes in Marsdenia tenacissima by high-performance liquid chromatography and electrospray ionization-tandem mass spectrometry

In the search for novel natural products in plants, particularly those with potential bioactivity, it is important to efficiently distinguish novel compounds from previously isolated, known compounds, a process known as dereplication. In this study, electrospray ionization-multiple stage tandem mass spectrometry (ESI-MS(n)) was used to study the behaviour of 12 pregnane glycosides and genins previously isolated from Marsdenia tenacissima, a traditional Chinese medicinal plant, as a basis for dereplication of compounds in a plant extract. In addition to [M + Na](+) and [M + NH(4)](+) ions, a characteristic [M-glycosyl + H](+) ion was observed in full-scan mode with in-source fragmentation. Sequential in-trap collision-induced dissociation of [M + Na](+) ions from 11,12-diesters revealed consistent preferred losses of substituents first from C-12, then from C-11, followed by losses of monosaccharide fragments from the C-3 tri- and tetrasaccharide substituents. A crude methanol extract of M. tenacissima stems was analysed using high-performance liquid chromatography coupled to ESI-MS. Several previously isolated pregnane glycosides were dereplicated, and the presence of an additional nine novel pregnane glycosides is predicted on the basis of the primary and fragment ions observed, including two with a previously unreported C(4)H(7)O C-11/C-12 substituent of pregnane glycosides. This study is the first report of prediction of the structures of novel pregnane glycosides in a crude plant extract by a combination of in-source fragmentation and in-trap collision-induced dissociation and supports the usefulness of LC-ESI-MS(n) not only for dereplication of active compounds in extracts of medicinal plants but also for detecting the presence of novel related compounds.     

Developing a wireless sensing method for the measurement of gamma radiation dose based on the polymerization of acrylamide

A wireless sensing method for the measurement of gamma radiation dose has been developed based on the fact that gamma rays can initiate the polymerization of acrylamide, which causes an increase in solution viscosity that can be detected with a wireless magnetoelastic sensor. The magnetoelastic sensor is able to wirelessly detect the resonance frequency shifts of a magnetoelastic foil in response to changes in solution viscosity. There is a linear relationship between the resonance frequency shift and gamma radiation dose in the range of 0–50 Gy (under optimal conditions) with a detection limit of 0.25 Gy. This method has the advantage of providing real-time, continuous measurement in situ. The method has been used successfully to determine the gamma radiation dose in real exposure scenarios, with satisfactory results.     

Level crossing in a two-photon Jaynes—Cummings model

In this paper,the energy spectrum of the two-photon Jaynes-Cummings model(TPJCM) is calculated exactly in the non-rotating wave approximation(non-RWA),and we study the level-crossing problem by means of fidelity.A narrow peak of the fidelity is observed at the level-crossing point,which does not appear at the avoided-crossing point.Therefore fidelity is perfectly suited for detecting the level-crossing point in the energy spectrum.     

Switchable different operation states in an erbium-doped fiber laser cavity with normal dispersion

We demonstrate different operation states which can be switched by the polarization control in an erbium-doped fiber laser cavity with normal dispersion, including passive single-pulse and multiple-pulse mode-locking, coherent pulse pattern, and passive Q-switching. The mode-locked single pulse has a smooth and broad rectangular-shaped spectrum. With increasing pump power, multiple pulses appear and finally six pulses are observed, where the pulses have no interaction with each other. Keeping the pump power at 407 mW and adjusting the polarization state, we observe the coherent pulse pattern with the pulse numbers from 2 to 5. It is the first time five coherent pulses in the 1.55 μm normal dispersion cavity have been observed, to our knowledge. The mode-locked spectra are highly modulated and the largest pulse separation of 31.9 ps is observed for the two-pulse case. When the pump power exceeds 180 mW, the mode-locked operation can be switched to the passively Q-switched operation by controlling the polarization state. The repetition rate and pulse width can be changed by pump power variation, and the spectrum is tunable in the range of 8.45 nm.     

Resolution and sensitivity enhancements in strong grating based fiber Fabry–Perot interferometric sensor system utilizing multiple reflection beams

We investigate an asymmetric intensive fiber Bragg grating (FBG) defined Fabry–Perot (F–P) sensor system decoded by a multiple-path-matched Michelson interferometer. The interrogation of higher order reflection beams cannot only solve the problem of the degraded resolution induced by the spectral mismatch of the FBGs, but also amplify the effect of the fiber strain on the phase of the light. We demonstrate multiple reflection beams in the F–P cavity based on the concept of the FBG effective length for constructing respective interrogation interferometers, and present a cost function with optimized system parameters to improve noise properties. The performances of interrogating the second, third and fourth order reflection beams are compared in a strain sensing experiment arrangement. Under the condition of the same optical path length mismatch, the interrogation of the fourth order reflection beam can achieve 9.8 dB sensitivity enhancement and 3 dB resolution promotion compared with the result using the second order reflection beam.     

低光泽度印刷色谱色貌数据组的建立与评价

色貌预测是现代颜色科学领域的基本理论和技术。为了评价低光泽度彩色印刷色谱的色貌,以丽印胶版纸印制的彩色印刷色谱为研究对象,根据颜色科学和心理物理学相关实验,建立其色貌参数样本数据组。采用相对系数R2和差异系数CV等数理统计方法,评价这种印刷色谱中Y-M内页在三种不同的照明光源下色貌的视觉评估结果。实验数据分析表明,在D65、A和TL84三种光源中,人眼在A光源下对颜色的识别能力明显不同于D65和TL84光源;同样在这三种光源中人眼对明度和色调的评估准确度最高,彩度最差。