Target spectra guided spectral unmixing for hyperspectral images

针对现在高光谱图像混合像元分解方法需要对所提取的端元的物理含义进行诠释的问题,提出了一种目标光谱指导下的混合像元分解方法,并给出了其具体算法实现.该方法首先针对若干给定的、具有明确物理含义的目标光谱,将光谱识别步骤引入混合像元分解过程,建立端元光谱与目标光谱间的对应关系,其次在最小距离限制的非负矩阵分解(MDC-NMF)方法基础上,引入光谱特征距离(SFD)作为正则项,以度量和保持存在对应关系的端元光谱与目标光谱间的相似性,并给出求解相应优化问题的优化算法.分别用模拟数据和真实数据对该方法的可行性和实际混合像元分解效果进行了验证,并将其与非监督情况下混合像元分解结果进行了比较分析.实验结果表明,该方法能够在目标光谱指导下较好诠释端元的物理含义,同时解决端元提取中的病态性问题.     

Obtaining spectral stereo images with electronic spectral tuning and polarization separation

The problem of obtaining stereo images of objects in arbitrary narrow spectral intervals is considered. A method of accomplishing this task is proposed, according to which the two light beams forming a stereopair are simultaneously filtered in one acousto-optic cell and the output beams are separated with respect to polarization. An optimum geometry of diffraction is found and requirements to the acousto-optic filter are formulated. The main characteristics of the spectral stereo system are determined.     

Characterization and quantitative analysis with GC/TOFMS comparing enhanced separation with tandem-column stop-flow GC and spectral deconvolution of overlapping peaks

Time-of-flight mass spectrometry is unique in that ion abundance ratios are constant over the chromatographic peak profile provided that the peak contains only one component. This provides the means for the automated finding and spectral deconvolution of overlapping chromatographic peaks from completely unknown mixtures if the mass spectra for the overlapping components are sufficiently unique. This can greatly reduce the chromatographic resolution requirements, which allows for very rapid quantitative analysis as well as for high-speed mixture characterization. High-speed GC with stop-flow operation of a series-coupled column ensemble can be used to completely separate some component pairs that coelute from the column ensemble, thus eliminating the need for spectral deconvolution of those mixture components. This provides two options for high-speed qualitative and quantitative analysis, using either the mass spectra from deconvoluted overlapping peaks or the mass spectra from the completely separated peaks obtained with stop-flow operation of the tandem column ensemble. These options are compared with respect to the similarity for spectral matching with a library and to peak area linearity with concentration, calibration plot correlation coefficients, and shot-to-shot reproducibility.     

Stochastic BEM with spectral approach in elastostatic and elastodynamic problems with geometrical uncertainty

The present paper proposes a method for stochastic problems that have uncertainty in the boundary geometry. The method is developed by applying the spectral stochastic approach to the boundary element method and is called the spectral stochastic boundary element method (SSBEM). In the SSBEM, the uncertainty in the boundary geometry is represented by the Karhunen–Loève expansion. It is shown that, by utilizing material derivative, variation of boundary element matrices associated with the geometrical fluctuation of the boundary can be approximated by the Taylor expansion. The solution is represented by a stochastic process expressed in the form of polynomial chaos expansion. The stochastic equation is then projected on a homogeneous chaos space. This procedure reduces a stochastic equation to an ordinary linear matrix equation that can be solved by conventional schemes. The SSBEM can estimate not only mean values and variances of the solutions but also their probability density functions. In order to examine the performance, the SSBEM is applied to two-dimensional elastostatic and elastodynamic problems with geometrical boundary uncertainty. Computation results of the SSBEM exhibit good agreement with those obtained by Monte Carlo simulation. The efficiency of the SSBEM is verified by comparison of their computation times.     

Stochastic inverse heat conduction using a spectral approach

An adjoint‐based functional optimization technique in conjunction with the spectral stochastic finite element method is proposed for the solution of an inverse heat conduction problem in the presence of uncertainties in material data, process conditions and measurement noise. The ill‐posed stochastic inverse problem is restated as a conditionally well‐posed L₂ optimization problem. The gradient of the objective function is obtained in a distributional sense by defining an appropriate stochastic adjoint field. The L₂ optimization problem is solved using a conjugate‐gradient approach. Accuracy and effectiveness of the proposed approach is appraised with the solution of several stochastic inverse heat conduction problems. Copyright © 2004 John Wiley & Sons, Ltd.     

Stochastic modelling of Rice fading channels with temporal, spatial and spectral correlation

A statistical characterisation of a small-scale fading mobile radio channel is presented and a fading simulator for the simulation of multiple input-multiple output multicarrier systems is introduced. The derivation of the equivalent lowpass channel as a function of time, transmit and receive antenna positions and subcarrier frequency, leads to a tapped delay-line model with time, space and frequency-selective taps. The taps are modelled as a sum of a deterministic line-of-sight or dominant scattered path and a zero-mean Gaussian part composed of a number of unresolvable scattered paths, and are therefore Rice fading. The Gaussian parts can have the desired temporal and spatiospectral correlations generated by time-correlation shaping filtering and a space-frequency correlation transformation, respectively. The structure and details of the simulator are presented, and the simulator is shown to achieve good accuracy while retaining a reasonable computational complexity.     

基于功率谱密度的盲信号分离

提出一种新的基于功率谱密度的盲信号分离方法。该方法在传感器数与源数关系不明确情况下,且源信号相互独立时,直接通过混合信号功率谱密度函数比值求解混合阵,并通过混合阵判定观测信号是完备混合、超定混合还是欠定混合,由此进一步分离信号。理论分析、仿真数据证明了算法的有效性。同时还仿真了噪声对分离性能的影响。     

Nanoporous polymeric materials: A new class of materials with enhanced properties

Nanoporous polymeric materials are porous materials with pore sizes in the nanometer range (i.e., below 200 nm), processed as bulk or film materials, and from a wide set of polymers. Over the last several years, research and development on these novel materials have progressed significantly, because it is believed that the reduction of the pore size to the nanometer range could strongly influence some of the properties of porous polymers, providing unexpected and improved properties compared to conventional porous and microporous polymers and non-porous solids.In this review, the key properties of these nanoporous polymeric materials (mechanical, thermal, dielectric, optical, filtration, sensing, etc.) are analyzed. The experimental and theoretical results obtained up to date related to the structure–property relations are presented. In several sections, in order to present a more compressive approach, the trends obtained for nanoporous polymers are compared to those for metallic and ceramic nanoporous systems. Moreover, some specific characteristics of these materials, such as the consequences of the confinement of both gas and solid phases, are described. Likewise, the main production methods are briefly described. Finally, some of the potential applications of these materials are also discussed in this paper.     

Dynamic cross-flow filtration: enhanced continuous small-scale solid-liquid separation

Abstract

In a previous study, a small-scale dynamic filtration device (SFD) was analyzed and the basic mechanisms governing the filtration process were characterized. The present work aims at improving the device’s performance in terms of actual production. Various operation modes were tested in order to increase permeate flow and concentration factors (CF), while maintaining a fully continuous production mode. Both, a vacuum-enhanced and a pulsating operation mode, proved to be superior to the currently implemented open-operation mode. For example, for lactose, an increase of the CF could be achieved from 1.7 in open mode to 7.6 in pulsating operation mode. The investigated operation strategy enables process control systems to rapidly react to fluctuating feeds that may occur due to changes in upstream manufacturing steps. As a result, not only filtration performance in terms of permeate rate but also process flexibility can be significantly increased. Overall, vacuum-enhanced operation was shown to be most promising for integration into an industrial environment. The option to elevate achievable concentration factors, ease of flow monitoring as well as the ability to react to changes in the feed conditions allow for effective and efficient continuous small-scale filtration.     

原位生长制备ZIF-8/聚酰胺双层复合纳滤膜及其染料分离性能

以2,6-二氨基吡啶、均苯三甲酰氯为水相和油相单体,通过界面聚合法制备吡啶功能化聚酰胺(PA-PY)膜,随后利用酰氯水解羧基和吡啶氮原子与锌离子的配位作用,在膜表面原位生长ZIF-8(类沸石咪唑酯骨架材料-8),制备了ZIF-8/聚酰胺(ZIF-8/PA-PY)双层复合纳滤膜。扫描电镜分析结果表明:原位生长法可在PA-PY分离层生成晶型结构完整、致密的ZIF-8层,且随着原位生长时间的增加,ZIF-8层逐渐增厚。ZIF-8/PA-PY双层复合纳滤膜对负电性染料的截留率较高,原位生长时间为12h时,双层复合纳滤膜对甲基蓝截留率为97.9%,刚果红为99.6%。     

Whole-column radioactivity detection: simultaneous separation and enhanced detectability.

The development of a whole-column radiation detector for measurement and separation of low amounts of beta emitting analytes is described. The design of this detector is unique with all of the chromatography media located within the detector volume. This whole-column design provides the advantage of increased radiation signal without loss of chromatographic efficiency, which translates to increased detectability. This increase was compared theoretically with flow-through radiation detection, and the theory was tested experimentally. Using two analytes, carbon-11-labeled m-hydroxyephedrine and alpha-methylepinephrine, only 3 and 8 Bq (80 and 220 pCi), respectively, were needed to obtain a 10% coefficient of variation using whole-column detection. For [11C]-m-hydroxyephedrine, 100 times more radioactivity was required to achieve the same coefficient of variation using flow-through detection. A limit of detection (LD) for the analytes of 2 Bq (54 pCi) was obtained for whole-column detection, an improvement of 50 in LD compared with flow-through detection. Signal improvement increased linearly with the chromatographic resolution. The whole-column detection method is robust and applicable to many chromatographic separations.     

Microbial enhanced separation of oil from a petroleum refinery sludge

Petroleum refineries around the world have adopted different technological options to manage the solid wastes generated during the refining process and stocking of crude oil. These include physical, chemical and biological treatment methods. In this investigation bacterial mediated oil separation is effected. Two strains of Bacillus were isolated from petroleum-contaminated soils, and inoculated into slurry of sludge, and sludge-sand combinations. The bacteria could effect the separation of oil so as to form a floating scum within 48h with an efficiency of 97% at < or =5% level of sludge in the sludge-sand mixture. The activity was traced to the production of biosurfactants by bacteria.     

Stochastic averaging for a class of single degree of freedom systems with combined Gaussian noises

We develop the stochastic averaging method to investigate the asymptotic stationary solution and the stochastic bifurcations of a class of single degree of freedom system with combined Gaussian white and colored noises, and to derive the Fokker–Planck–Kolmogorov (FPK) equations. The general stationary solutions will be obtained analytically under some suitable conditions. Theoretically, a general algebraic expression of the stationary probability density function of amplitude for the dynamical system is presented to consider the influences of correlation time of the noise and the noise intensity on stochastic bifurcations. Then, an example is given to illustrate the averaging method, and the effectiveness of the averaging method is verified via comparing the analytical results with those from Monte Carlo simulation. Finally, stochastic bifurcations are discussed through a qualitative change of the stationary probability distribution. It indicates that system parameters, noise intensity, and noise correlation time can be treated as bifurcation parameters, respectively.     

Polypyrrole/Bi2WO6 composite with high charge separation efficiency and enhanced photocatalytic activity

The recombination of photogenerated electrons and holes is a crucial factor that limits the efficiency of photocatalysis and dye-sensitized solar cells. Conducting polymers are known to have high charge carrier mobility. Herein, a polypyrrole (PPy)/Bi₂WO₆ composite with promoted charge separation efficiency was designed by a “photocatalytic oxidative polymerization” method. The photo-degradation of a typical model pollutant, phenol, demonstrated that the PPy/Bi₂WO₆ composite possessed significantly enhanced photo-activity than pure Bi₂WO₆ under simulated sunlight irradiation. The higher photo-activity was attributed to the synergetic effect between PPy and Bi₂WO₆. The photogenerated holes on the valence band of Bi₂WO₆ could transfer to the highest occupied molecular orbital of PPy, leading to rapid photoinduced charge separation and enhancing the photocatalytic activity. This work provided a new concept for rational design and development of highly efficient polymer-semiconductor photocatalysts for environmental purification under simulated sunlight.     

Agile dual-channel spectral imaging with spectral zooming

A dual-channel spectral imaging system with agile spectral band access and spectral bandwidth tuning capability is presented. A diffractive grating and an acousto-optic tunable filter (AOTF) are respectively used as spectral dispersion and spectral filtering elements for the two channels. A 4f spectral filtering channel using an adjustable slit is set up at the first diffraction order of the grating to realize coarse spectral band selection. The AOTF selectively filters the spectrum of the nondispersed zero order to realize fine spectral imaging. The spectral zooming function is achieved without increasing spectral frame number facilitating real-time spectral imaging operation. Feasibility of the spectral imaging has been demonstrated through preliminary experiments. Minimum 6 nm spectral resolution and 1.2 degrees field of view have been achieved. The real-time spectral imaging capable of wide spectral band operation without loosing desired fine spectral capability is particularly useful for a variety of defense, medical, and environmental monitoring applications.     

Aluminum nanostructured films as substrates for enhanced fluorescence in the ultraviolet-blue spectral region

Particulate aluminum films of varied thicknesses were deposited on quartz substrates by thermal evaporation. These nanostructured substrates were characterized by scanning electron microscopy (SEM). With the increase of aluminum thickness, the films progress from articulate toward smooth surfaces as observed by SEM images. To date, metal-enhanced fluorescence (MEF) has primarily been observed in the visible - NIR wavelength region using silver or gold island films or roughened surfaces. We now show that fluorescence could also be enhanced in the ultraviolet-blue region of the spectrum using nanostructured aluminum films. Two probes, one in the ultraviolet and another one in the blue spectral region, have been chosen for the present study. We observed increased emission, decrease in fluorescence lifetime, and increase in photostability of a DNA base analogue 2-aminopurine and a coumarin derivative (7-HC) in 10-nm spin-casted poly(vinyl alcohol) film on Al nanostructured surfaces. The fluorescence enhancement factor depends on the thickness of the Al films as the size of the nanostructures formed varies with Al thickness. Both probes showed increased photostability near aluminum nanostructured substrates, which is consistent with the shorter lifetime. Our preliminary studies indicate that Al nanostructured substrates can potentially find widespread use in MEF applications particularly in the UV-blue spectral regime. Furthermore, these Al nanostructured substrates are very stable in buffers that contain chloride salts compared to usual silver colloid-based substrates for MEF, thus furthering the usefulness of these Al-based substrates in many biological assays where high concentration of salts are required. Finite-Difference Time-Domain calculations were also employed to study the enhanced near-fields induced around aluminum nanoparticles by a radiating fluorophore, and the effect of such enhanced fields on the fluorescence enhancement observed was discussed.     

Greatly enhanced infrared normal spectral emissivity of microstructured silicon using a femtosecond laser

The infrared normal spectral emissivity of microstructured silicon prepared by femtosecond laser irradiation in SF₆ was measured for the wavelength range 2.5 μm to 25 μm. Greatly enhanced emissivity compared to that of flat silicon was observed over the entire wavelength range. For a sample with 13-14 μm high spikes, the emissivity at a temperature of 100 °C is approximately 0.96. The emissivity decreases slightly in the wavelength region above 8 μm, but remains higher than 0.9 over most of the measured wavelength range. Also the average emissivity is less than Nextel- Velvet-811-21 Coating, it can be used stably at more wide temperatures from 100 °C to 400 °C. These results show the potential for microstructured silicon to be used as a flat blackbody source or silicon-based pyroelectric and microbolometer devices.