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摘要： Optoacoustic imaging (OAI) is a hybrid imaging modality that integrates the benefits of optical contrast and ultrasound detection. Raster-scan optoacoustic mesoscopy (RSOM) is an emerging OAI method that provides information about several dermatological conditions' structural, functional, and molecular features. We searched PubMed and Google Scholar databases through September 2021 for contributions relevant to OAI in the English language. This review contains 32 studies and other relevant literature. Several studies indicate that RSOM is helpful in inflammatory skin conditions such as psoriasis and eczema, especially as it allows more accurate quantification of inflammation-related alterations such as changes to the dermal vasculature. In psoriasis, RSOM can provide objective early diagnosis and monitoring of disease activity and treatment efficacy. Multispectral RSOM, a method in which skin is lightened at more than a single wavelength, is beneficial in diagnosing and monitoring hypoxia-associated conditions, such as systemic sclerosis and chronic wounds. OAI techniques can visualize the pathologicvascularization of skin cancers and quantify their oxygenation status which helps differentiate them from normal skin. Also, they can measure the depth of malignant melanoma and detect the metastatic spread of melanoma cells to sentinel lymph nodes. As demonstrated in this contribution, there is a large spectrum of potential applications of OAI imaging, especially RSOM, in diagnosing, treating, and managing skin diseases. (c) 2021 Elsevier Inc. All rights reserved.

摘要： We present a method to explore the effect of fluorescence on X-ray attenuation measurements obtained from X-ray absorption spectroscopy (XAS). We use the X-ray extended range technique-like method (XERT-like). The experimental setup includes different sized apertures to control the number of secondary X-rays entering the detector. Comparison of attenuation measurements produced with different aperture combination permit investigation of the effect of fluorescence radiation. In this work, fluorescence has a large impact on the attenuation measurements of thick zinc foils. The correction is energy-dependent and sample thickness-dependent and changes the structure and relative amplitudes of oscillations in the near-edge region. Correction for this systematic is important for absolute measurement, for edge-jump and edge characterization, and for near-edge structure and amplitudes. A significant background scattering due to zinc fluorescence from the beamline optics was identified and treated for the first time. The model theory fits the experimental measurements well. The resulting correction is most significant for thicker foils with the 50 mu m sample experiencing a shift in attenuation of up to 15.5% for the largest aperture while the 25 and 10 mu m samples saw corrections of up to 0.153 and 0.00639% respectively. The standard error from the dispersion and variance was reduced by up to 50.5% after the correction for the 50 mu m sample. This enables high-accuracy data and theoretical and experimental analysis to below 0.03% accuracy. The technology is advanced. There is a cost in preparation and measurement time of less than a factor of two, and the principles are clear and can be routinely implemented on any beamline. This paper focuses on the model and parameters for fluorescence.

关键词： EXAFS   operando   synchrotron   XANES   XAS  

摘要： Although X-ray absorption spectroscopy (XAS) was conceived in the early 20th century, it took 60 years after the advent of synchrotrons for researchers to exploit its tremendous potential. Counterintuitively, researchers are now developing bench type polychromatic X-ray sources that are less brilliant to measure catalyst stability and work with toxic substances. XAS measures the absorption spectra of electrons that X-rays eject from the tightly bound core electrons to the continuum. The spectrum from 10 to 150 eV (kinetic energy of the photoelectrons) above the chemical potential-binding energy of core electrons-identifies oxidation state and band occupancy (X-ray absorption near edge structure, XANES), while higher energies in the spectrum relate to local atomic structure like coordination number and distance, Debye-Waller factor, and inner potential correction (extended X-ray absorption fine structure, EXAFS). Combining XAS with complementary spectroscopic techniques like Raman, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) elucidates the nature of the chemical bonds at the catalyst surface to better understand reaction mechanisms and intermediates. Because synchrotrons continue to be the light source of choice for most researchers, the number of articles Web of Science indexes per year has grown from 1000 in 1991 to 1700 in 2020. Material scientists and physical chemists publish an order of magnitude articles more than chemical engineers. Based on a bibliometric analysis, the research comprises five clusters centred around: electronic and optical properties, oxidation and hydrogenation catalysis, complementary analytical techniques like FTIR, nanoparticles and electrocatalysis, and iron, metals, and complexes.

关键词： Materials Science   general   Characterization and Evaluation of Materials   Polymer Sciences   Solid Mechanics   Crystallography and Scattering Methods   Classical Mechanics  

摘要： PVP (Polyvinylpyrrolidone) and PVP/GR composite nanofibers containing 1.0, 1.5 and 2.0 wt% of graphite (GR) filler were produced by electrospinning. The nanofibrous structure of electrospun mats allows high light-matter interactions, which greatly affects the nonlinear optical character of the materials. SEM measurements showed that the PVP/GR nanofibers are smooth, transparent and of cylindrical morphology in the 161-218 nm diameter range with a high homogeneity. The energy band gap increased from 1.87 to 2.02 eV and then decreased to 1.83 eV with increasing GR filler concentration in PVP while the Urbach energy decreased indicating the existence of localized defect states. To derive the transmission in open aperture Z-scan data at 1064 and 1200 nm, a theoretical model incorporating one-photon, two-photon and free carrier absorptions and their saturations were considered. The nonlinear absorption coefficient (beta(eff)) increased from 3.31 x (-5) to 1.01 x (-4) m\W with increasing GR filler concentration in PVP although increasing GR filler content leads to decrease the number of defect states. The enhanced nonlinear absorption and optical limiting behavior with increasing GR filler content in PVP nanofibers are attributed to the increasing metallic nature, which enhances the FCA contribution. Femtosecond transient absorption spectroscopy measurements indicated that the charge transfer increases in GR-filled nanofibers. Our findings showed that GR-filled nanofibers feature highly desired properties in optical limiting applications such as high linear transmittance (> 80%), high nonlinear absorption and low optical limiting threshold. Therefore, these materials are good optical limiter candidates in the near IR wavelength region.

关键词： Ultrashort pulses  

摘要： We report here on the results of comparative experimental measurements of laser energy absorption in a bulk and different morphology nanowire arrays interacting with relativistically intense, ultra-high temporal contrast femtosecond laser pulses. We compare polished, flat bulk samples with vertically and randomly oriented nanowires made of ZnO semiconductor material. The optical absorption of the 45 & DEG;incident laser pulses of & SIM;40 fs duration with a central wavelength of 400 nm at intensities above 10(19) W/cm(2) was determined using an integrating Ulbricht sphere. We demonstrate an almost twofold enhancement of absorption in both nanowire morphologies with an average of (79.6 & PLUSMN;1.9)% in comparison to the flat bulk sample of (45.8 & PLUSMN;1.9)%. The observed substantially enhanced absorption in nanowire arrays is also confirmed by high-resolution x-ray emission spectroscopy. The spectral analysis of the K-shell x-ray emission lines revealed that the He-like resonance line emission from highly ionized Zn (Zn28+) is only present in the case of nanowire arrays, whereas, for the flat bulk samples, only neutral and low charge states were observed. Our numerical simulations, based on radiative-collisional kinetic code FLYCHK, well reproduce the measured He-like emission spectrum and suggest that high charge state observed in nanowire arrays is due to substantially higher plasma temperature. Our results, which were measured for the first time with femtosecond laser pulses, can be used to benchmark theoretical models and numerical codes for the relativistic interaction of ultrashort laser pulses with nanowires.

关键词： Data structures   Spatial databases   Raster Data   Map algebra operations   Geographic information systems (GIS)   Algorithms  

摘要： We present efficient algorithms to compute simple and complex map algebra operations over raster data stored in main memory, using the k(2)-acc compact data structure. Raster data correspond to numerical data that represent attributes of spatial objects, such as temperature or elevation measures. Compact data structures allow efficient data storage in main memory and query them in their compressed form. A k(2)-acc is a set of k(2)-trees, one for every distinct numeric value in the raster matrix. We demonstrate that map algebra operations can be computed efficiently using this compact data structure. In fact, some map algebra operations perform over five orders of magnitude faster compared with algorithms working over uncompressed datasets.

关键词： High resolution transmission electron microscopy  

摘要： The focused ion beam (FIB) instrument is designed to provide the removal of material with nanometer-scale precision. However, one often needs to remove a substantial amount of material to expose the region of interest or prepare a specimen for transmission electron microscopy analysis. The maximum current available on Ga+ FIB sources is less than 100 nA, and this is a limiting factor when removal on the millimeter scale is desired. Any improvement in the removal rate reduces the analysis time and increases the range of samples that can be analyzed. Optimization of ion beam parameters, such as dwell time and overlap, can improve material removal and reduce redeposition. Since sputtering occurs faster at an edge, the use of a nested arrangement of raster patterns to more frequently present an edge to the ion beam was able to improve the removal of material at the region of interest by over 30% in the silicon and polycrystalline copper substrates used for this study. A confocal laser scanning microscope made possible an accurate determination of the material removed.

摘要： We have measured the X-ray production cross sections (XRPCS) for the L-p (p = l, alpha, eta, beta(1,3,4,6), beta(2,15), gamma(1,5), gamma(2,3,4)) emission lines of Sn and Sb using synchrotron induced mono-chromatic radiation tuned across their respective L-i (i = 1-3) sub-shell absorption edges covering the range 4.0 keV-5.0 keV. These measured XRPCS have been compared with the corresponding values calculated using the non-relativistic Hartree-Fock-Slater model based L-i (i = 1-3) photoionization cross-sections, the Dirac-Fock model based X-ray emission rates and three sets of fluorescence and Coster-Kronig (CK) yields based on the Dirac-Hartree-Slater model, the semi-empirical values tabulated by Krause and recently reported experimental values. The present measured L-p XRPCS for both Sn and Sb at different investigated photon energies are found to be in good agreement with those calculated using the experimental photoionization cross sections, fluorescence and CK yields. Further, a good agreement observed between the present measured and calculated branching ratios for both Sn and Sb indicates the reliability of the Dirac-Fock model based X-ray emission rates. The Lp XRPCS and intensity ratios for Sn and Sb calculated using the experimental photoionization cross sections, the DF model based X-ray emission rates and the experimental fluorescence and CK yields are recommended for use in different applications.

关键词： 机器学习  

ISBN: (纸本)9787513080002

摘要： 本书基于大数据、人工智能中模式分类的研究，以向量数据的机器学习方法为基础，从最优化角度研究张量数据的学习问题，特别关注张量数据分类问题的新模型的建立及其最优化算法的设计。

关键词： 三维角度测量   激光自准直   跟踪式测量   光束平行度测量  

摘要： 角度作为关键的基础几何量之一,实现其高精度测量对科研领域和工业应用具有重要意义。角度测量主要包含对绕坐标轴X轴、Y轴和Z轴旋转的俯仰角、偏摆角和旋转角的三维角度测量。在实际工程应用和科学研究中,许多领域需要对三维角度变化量进行同时测量。例如,坐标测量机的阿贝误差测量、卫星有效载荷姿态角测量、导弹发射位姿监测等都要求同时对三维角度进行高精度测量,测量精度通常要求在角秒甚至亚角秒量级。因此,亟需一种可实现高精度三维角度同时测量的技术和方法。围绕三维角度同时测量的需求,针对传统自准直方法无法实现三维角度测量问题,以及三维角度测量方法因耦合误差导致测量精度低和三维角度测量范围互相限制等问题,本论文提出了“基于光栅分光和组合靶标的自准直三维角度测量方法研究”,旨在实现高精度、测量范围独立的三维角度同时测量。论文主要研究内容如下:针对自准直方法无法实现三维角度同时测量的问题,提出了一种基于透射光栅和组合靶标的自准直三维角度测量方法。该方法利用光栅衍射特性将单束准直光转换为三束准直光,以该三束准直光为次级准直光,通过组合靶标将待测角度变化量转换为准直光束的传播方向变化,通过光电检测单元获取准直光束的方向变化实现三维角度同时测量。针对三维角度测量模型过于简化而忽略角度耦合对测量精度影响的问题,利用光学矩阵变换法建立了基于自准直原理的三维角度几何光学测量模型,该模型能够完整地描述角度耦合量与角度测量值的作用机理。在此基础上,提出了连续迭代算法来减小角度耦合对测量精度的影响。进一步,研究采用光学放大法提高旋转角的测量分辨力使三维角度测量分辨力保持一致。针对基于自准直原理的三维角度测量方法中角度测量范围相互限制的问题,提出了基于透射光栅和柔性偏转机构的跟踪式测量方法。该方法以组合靶标的旋转角度值作为反馈信号,控制柔性偏转机构使透射光栅跟踪组合靶标旋转,此时光电探测器的有效面元仅用来实现偏摆角和俯仰角的测量,旋转角度值可通过柔性偏转机构的输出角度值获取,利用该方法可以实现三维角度测量范围独立,解决角度测量范围相互限制的问题。另外,该方法在增大角度测量范围的同时不影响系统的角度测量分辨力,为提升基于自准直原理的角度测量范围提供了新的途径。针对组合靶标加工误差限制旋转角测量精度进一步提升的问题,提出了基于透射光栅的双反射面垂直度测量方法。基于该方法,首先分析了组合靶标加工误差(双反射面垂直度)对旋转角测量精度的影响机理,并建立了包含组合靶标加工误差的旋转角测量模型。然后,利用CMOS图像传感器结合准直法对双光束之间的平行度进行测量,根据双光束的平行度计算出组合靶标的加工误差,进一步提高旋转角的测量精度。最后,对设计的基于光栅衍射的三维角度测量实验装置及主要组成单元的性能进行测试,包括角度发生装置性能测试、光电检测系统有效分辨力测试、跟踪式测量模块性能测试、组合靶标加工误差测量和三维角度测量系统整体性能测试。实验结果表明,三维角度测量系统的三维角度测量分辨力均达到0.010″,三维角度测量范围相互独立,均为0～250″,偏摆角、俯仰角和旋转角在10″内的扩展不确定度分别为0.060″,0.060″和0.110″(k=2)。