Reduction of speckle in digital holography by discrete Fourier filtering

We present a digital signal processing technique that reduces the speckle content in reconstructed digital holograms. The method is based on sequential sampling of the discrete Fourier transform of the reconstructed image field. Speckle reduction is achieved at the expense of a reduced intensity and resolution, but this trade-off is shown to be greatly superior to that imposed by the traditional mean and median filtering techniques. In particular, we show that the speckle can be reduced by half with no loss of resolution (according to standard definitions of both metrics).     

FID modulus: a simple and efficient technique to phase and align MR spectra

Object

The post-processing of MR spectroscopic data requires several steps more or less easy to automate, including the phase correction and the chemical shift assignment. First, since the absolute phase is unknown, one of the difficulties the MR spectroscopist has to face is the determination of the correct phase correction. When only a few spectra have to be processed, this is usually performed manually. However, this correction needs to be automated as soon as a large number of spectra is involved, like in the case of phase coherent averaging or when the signals collected with phased array coils have to be combined. A second post-processing requirement is the frequency axis assignment. In standard mono-voxel MR spectroscopy, this can also be easily performed manually, by simply assigning a frequency value to a well-known resonance (e.g. the water or NAA resonance in the case of brain spectroscopy). However, when the correction of a frequency shift is required before averaging a large amount of spectra (due to B ₀ spatial inhomogeneities in chemical shift imaging, or resulting from motion for example), this post-processing definitely needs to be performed automatically.

Materials and methods

Zero-order phase and frequency shift of a MR spectrum are linked respectively to zero-order and first-order phase variations in the corresponding free induction decay (FID) signal. One of the simplest ways to remove the phase component of a signal is to calculate the modulus of this signal: this approach is the basis of the correction technique presented here.

Results

We show that selecting the modulus of the FID allows, under certain conditions that are detailed, to automatically phase correct and frequency align the spectra. This correction technique can be for example applied to the summation of signals acquired from combined phased array coils, to phase coherent averaging and to B ₀ shift correction.

Conclusion

We demonstrate that working on the modulus of the FID signal is a simple and efficient way to both phase correct and frequency align MR spectra automatically. This approach is particularly well suited to brain proton MR spectroscopy.     

How can flexibility be integrated into coexistence regulations? A review

Member states in the European Union (EU) implemented both ex ante coexistence regulations and ex post liability schemes to ensure that genetically modified (GM) and non‐GM crops can be cultivated side by side without excluding any agricultural option. Although proportionate coexistence is best achieved if regulated in a flexible manner, most implemented coexistence regulations merely rely on rigid measures. Flexible coexistence regulations, however, would reduce the regulatory burden on certain agricultural options and avoid jeopardizing economic incentives for coexistence. Flexibility can be integrated at: (i) the regulatory level by relaxing the rigidity of coexistence measures in ex ante regulations, yet without offsetting incentives to implement coexistence measures; (ii) the farm level by recommending the use of pollen barriers instead of large and fixed isolation distances; and (iii) the national/regional level by allowing diversified coexistence measures, which are adapted to the heterogeneity of farming in the EU. Owing to difficulties of implementation, the adoption of flexible and proportionate coexistence regulations will inevitably entail challenges. © 2013 Society of Chemical Industry     

A Highly Efficient Olefin Metathesis Process for the Synthesis of Terminal Alkenes from Fatty Acid Esters

Recently, considerable attention has been focused on the use of olefin metathesis to convert oleochemicals into value-added products such as the bifunctional molecule methyl 9-decenoate, but the implementation of this process has been hampered by low ethenolysis efficiencies. We report herein the use of alpha olefins as ethylene surrogates in cross metathesis reactions with methyl oleate and soybean oil fatty acid methyl esters (soy FAME) resulting in considerable increases in catalyst efficiencies in the production of this promising chemical product. Additional gains in efficiency were realized by using a peroxide-scavenging feedstock pretreatment.     

Photonics based on carbon nanotubes

Among direct-bandgap semiconducting nanomaterials, single-walled carbon nanotubes (SWCNT) exhibit strong quasi-one-dimensional excitonic optical properties, which confer them a great potential for their integration in future photonics devices as an alternative solution to conventional inorganic semiconductors. In this paper, we will highlight SWCNT optical properties for passive as well as active applications in future optical networking. For passive applications, we directly compare the efficiency and power consumption of saturable absorbers (SAs) based on SWCNT with SA based on conventional multiple quantum wells. For active applications, exceptional photoluminescence properties of SWCNT, such as excellent light-emission stabilities with temperature and excitation power, hold these nanometer-scale materials as prime candidates for future active photonics devices with superior performances.     

Use of enzyme tests to monitor the biomass activity of a trickling biofilter treating domestic wastewaters

Easy enzyme tests were used to monitor the biomass activity of a trickling biological aerated filter processing a domestic influent. Biofilter wash‐waters were used as biomass source. Enzyme tests (hydrolases and dehydrogenases) carried out on wash‐waters showed relationships with the process active biomass (estimated by volatile suspended solids). Differences in dehydrogenase (DHA) specific activities were observed in two sampling campaigns and were linked to process performance. The DHA activity evaluated using glucose or acetate was also related to the substrate mass applied on the biological aerated filter (kg CODt m⁻³ biolite). These results indicated that, under normal operation, DHA activity is related to quantity of substrate applied to the biofilter. Similar relationships were obtained for hydrolases. However, β‐glucuronidase, Leu‐aminopeptidase and protease, expressed specifically, were more significantly inversely related to process removal performance. This reaction was probably caused by the biomass reacting with an influent that is difficult to biodegrade. Generally speaking, these tests can be easily applied to the regular monitoring of the active biomass from a process using biological filters or simply as an indicator of the active biomass content in the process. © 2000 Society of Chemical Industry     

Triaxial behaviour of concrete under high stresses: Influence of the loading path on compaction and limit states

The aim of this study is to characterize the behaviour of concrete under high triaxial loading at levels of confinement and axial stress of the order of the GigaPascal. This study is carried out within a more general scope of understanding concrete behaviour under impact. The studied concrete has properties as close as possible to those used in current construction projects. A triaxial press of high capacity is used to characterize the triaxial behaviour of concrete according to various loading paths. Hydrostatic, triaxial, proportional and oedometric tests are performed and show the influence of the loading path on the compaction process. The triaxial and proportional tests show the existence of strain limit states, defining a limit states threshold independent from the loading path.     

面向重大社会事件的电力应急资源两阶段规划方法

重大社会事件融合了信息、物理、社会多元信息,增大了传统电力应急资源规划的难度和复杂度,为此,提出面向重大社会事件的电力应急资源两阶段规划方法。分析电力应急资源规划的信息、物理、社会耦合因素,引入负荷重要度来量化重大社会事件对应急资源规划的影响,给出整合应急服务点规划与应急资源配置的两阶段规划框架;建立考虑负荷重要度的停电风险量化指标,综合考虑负荷停电风险、服务点投资成本和应急服务时限约束,构建应急服务点多点多目标规划模型,并提出基于ε约束的多目标模型求解方法;考虑应急资源需求的不确定性,提出基于区间优化的应急资源优化配置模型,并将原区间优化模型转化为乐观优化问题和悲观优化问题进行求解。算例仿真结果验证了所提两阶段规划方法的有效性。     

PLA/MRPs乳液膜的制备及性能研究

以碱溶性半纤维素木聚糖和玉米醇溶蛋白合成的美拉德反应产物（MRPs）纳米颗粒水溶液为水相、聚乳酸/二氯甲烷溶液（PLA/DCM）为油相,通过乳液聚合法和模压成型工艺制备了PLA/MRPs乳液膜。分别利用傅里叶变换红外光谱仪、热重分析仪、扫描电子显微镜和紫外可见吸收光谱仪分析了PLA/MRPs复合材料的形貌结构和抗氧化性能,并对PLA/MRPs乳液膜的力学性能进行了探究。探讨了MRPs纳米颗粒水溶液的质量分数对PLA/MRPs乳液膜的抗氧化性能和力学性能的影响。结果表明,制得的PLA/MRPs复合材料具有水包油型结构,以质量分数0.50%MRPs制备的PLA/MRPs乳液膜在反应时间为30 h后,DPPH自由基清除率最大,为26.55%;而随着MRPs质量分数的增加,PLA/MRPs乳液膜的拉伸强度和断裂伸长率逐渐降低。