部分相干光学系统最佳象面的性质讨论

在部分相干理论的基础上,分别用表观传递函数和能量分布作评价指标,计算了部分相干光学系统的最佳象面位置,并讨论了其与相干度、空间频率及象差的关系。     

Development of new apertures for coherent X‐ray experiments

When one performs a coherent small‐angle X‐ray scattering experiment, the incident beam must be spatially filtered by slits on a length scale smaller than the transverse coherence length of the source which is typically around 10 µm. The Fraunhofer diffraction pattern of the slit is one of the important sources of background in these experiments. New slits which minimize this parasitic background have been designed and tested. The slit configuration apodizes the beam by the use of partially transmitting inclined slit jaws. A model is presented which predicts that the high wavevector tails of the diffraction pattern fall as the inverse fourth power of the wavevector instead of the inverse second power that is observed for standard slits. Using cleaved GaAs single‐crystal edges, Fraunhofer diffraction patterns from 3 and 5.5 keV X‐rays were measured, in agreement with the theoretical model proposed. A novel phase‐peak diffraction pattern associated with phase variations of the transmitted electric field was also observed. The model proposed adequately accounts for this phenomenon.     

一种基于空间一致性降元的高光谱图像非监督分类

为了提高分类精度和边缘辨识性,该文引入图像空间一致性降元(pixels reduction with spatial coherence property, PRSCP)及线性回归分析,提出了一种基于空间一致性降元的非监督分类。该方法从像元光谱相似性出发,利用像元最小关联窗口合并相邻相似像元为像块完成降元。使用线性关系建模像块内像元的光谱向量,并利用F检验判断像块数据的线性显著性。利用一元线性回归(one dimensional linear regression, ODLR)估计出像块的基准向量,根据基准向量合并相似(同类)像块完成分类。利用AVIRIS数据评估了该方法性能,实验结果表明：与K-MEANS和ISODATA方法相比,该方法精度高、边缘辨识度好及鲁棒性强。     

An investigation of the accelerated thermal degradation of different epoxy resin composites using X-ray microcomputed tomography and optical coherence tomography

Epoxy resin composites reinforced with hollow glass microspheres, microlight microspheres, 3D parabeam glass, and E-Glass individually were subjected to accelerated thermal degradation conditions. X-ray microcomputed tomography (XμCT) was used to evaluate density changes, reinforcement filler damage, homogeneity, cracks and microcracks in the bulk of the different epoxy resin composites. XμCT 3D images, 2D reconstructed images and voids calculations revealed microspheres damage, filler distributions and showed cracks in all composites with different shapes and volume in response to the thermal degradation conditions. In addition, expansion of air bubbles/voids was observed and recorded in the microsphere and microlight epoxy composite samples. In a complementary way, optical coherence tomography (OCT) was used as a novel optical characterisation technique to study structural changes of the surface and near-surface regions of the composites, uncovering signs of surface shrinkage caused by the thermal treatment. Thus, combining XμCT and OCT proved useful in examining epoxy resin composites' structure, filler-resin interface and surface characteristics.     

Elucidation of the structures of 3-alkylthio-, 3-benzylthio-, 2-arylthio- and 2-heteroarylthio-N1-(1,3-dimethylbutyl)-N4-phenyl-1,4-phenylenediamines by one- and two-dimensional NMR spectroscopy

Nucleophilic addition of alkyl- and benzylthiols to benzoquinone diimine (1) gave the corresponding 3-alkylthio- or 3-benzylthio-1,4-phenylenediamines (2-5). However, addition of aryl- or heteroarylthiols to 1 formed 2-arylthio- or 2-heteroarylthio-1,4-phenylenediamines (6-14). The structures of 2-14, obtained in 55-91% yields, were confirmed in CDCl3 or DMSO-d6 solution using 1D (NOE difference, coupled 13C NMR spectra, APT and DEPT) and 2D NMR techniques [DQCOSY, NOESY, HETCOR and heteronuclear multiple bond coherence (HMBC)] that resulted in unambiguous proton and carbon NMR resonance assignments. The substituent-induced 13C NMR chemical shift differences were calculated in 2-14 relative to carbon atoms in the model compound N1-(1,3-dimethylbutyl)-N4-phenyl-1,4-phenylenediamine (DMBPPD) (15) (a reduced form of benzoquinone diimine).     

SQSQh: 1H‐detected SQ–SQ experiment for determination of signed silicon–carbon coupling constants

A new variant of SQ–SQ pulse sequence (SQSQh) for relative sign determination and detection of small silicon–carbon couplings over more than one bond is presented. In the SQSQh sequence, proton detection replaces carbon detection used in the original SQ–SQ pulse sequence (SQSQc). The theoretical gain in sensitivity was experimentally tested on two samples (trimethylsiloxyethane, 1, and 1,2,4‐tris(trimethylsiloxy)benzene, 2), the experimentally found gain provided by the SQSQh over the SQSQc method varied between 6 and 8. The method can be applied to linear spin systems, i.e. to systems where the silicon is coupled to the carbon in question and to any hydrogen not necessarily bonded to the carbon. Copyright © 2010 John Wiley & Sons, Ltd.     

Toward multipurpose NMR experiments

Standard phase cycled NMR pulse sequences were generalized such that for each individual step of the pulse phase cycle the free induction decay is stored separately without phase correction. This is in contrast to the usual practice, where pulse responses are phase shifted immediately (by applying a ‘receiver phase’) and co‐added as they are stored. The approach used here allows one to extract different types of NMR information, which are usually referred to as different ‘experiments’, from the same raw data set a posteriori by using complex linear combinations. Storing the free induction decays of individual phase cycle steps separately and using specific linear combinations of these data to obtain a particular type of information increase the overall efficiency of a given set of NMR experiments substantially, because all information can be derived from a single multiplexed data set. This ‘super‐experiment’ requires only as much time as the most complex of the derived specific experiments alone. The principle of this multipurpose approach was demonstrated by performing different multiple‐quantum filtered COSY experiments. It also becomes possible to generate linear combinations, which differ from the conventionally acquired spectra a posteriori. For example, we implemented diagonal peak reduction by using zero‐ and single‐quantum filtered COSY contributions without requiring additional experiment time. Copyright © 2009 John Wiley & Sons, Ltd.     

Monitoring of metabolic profiling and water status of Hayward kiwifruits by nuclear magnetic resonance

The metabolic profiling of kiwifruit (Actinidia deliciosa, Hayward cultivar) aqueous extracts and the water status of entire kiwifruits were monitored over the season (June-December) using nuclear magnetic resonance (NMR) methodologies. The metabolic profiling of aqueous kiwifruit extracts was investigated by means of high field NMR spectroscopy. A large number of water-soluble metabolites were assigned by means of 1D and 2D NMR experiments. The change in the metabolic profiles monitored over the season allowed the kiwifruit development to be investigated. Specific temporal trends of aminoacids, sugars, organic acids and other metabolites were observed.The water status of kiwifruits was monitored directly on the intact fruit measuring the T₂ spin-spin relaxation time by means of a portable unilateral NMR instrument, fully non-invasive. Again, clear trends of the relaxation time were observed during the monitoring period.The results show that the monitoring of the metabolic profiling and the monitoring of the water status are two complementary means suitable to have a complete view of the investigated fruit.     

Precision of Raman depolarization and optical attenuation measurements of sound tooth enamel

The demineralization of enamel that is associated with early caries formation affects the optical properties of the enamel. Polarized Raman spectroscopy and optical coherence tomography have been used to detect these changes and potentially offer a means to detect and monitor early caries development. The total optical attenuation coefficient as measured by optical coherence tomography and the polarization anisotropy of the Raman peak arising from the symmetric ν₁ vibration of at approximately 959 cm⁻¹ have been demonstrated as being sensitive markers of early caries. This ex vivo study on extracted human teeth demonstrates that these measurements can be made with reasonable precision with concomitantly good repeatability and reproducibility in sound enamel. Such reliability is crucial for these techniques to have a practical clinical value.