A quasi-Monte Carlo method for computing areas of point-sampled surfaces

A novel and efficient quasi-Monte Carlo method for computing the area of a point-sampled surface with associated surface normal for each point is presented. Our method operates directly on the point cloud without any surface reconstruction procedure. Using the Cauchy–Crofton formula, the area of the point-sampled surface is calculated by counting the number of intersection points between the point cloud and a set of uniformly distributed lines generated with low-discrepancy sequences. Based on a clustering technique, we also propose an effective algorithm for computing the intersection points of a line with the point-sampled surface. By testing on a number of point-based models, experiments suggest that our method is more robust and more efficient than those conventional approaches based on surface reconstruction.postprin

Performance evaluation of Bragg coherent diffraction imaging

In this study,we present a numerical framework for modeling three-dimensional (3D) diffraction data in Bragg coherent diffraction imaging (BraggCDI) experiments and evaluating the quality of obtained 3D complex-valued real-space images recovered by reconstruction algorithms under controlled conditions. The approach is used to systematically explore the performance and the detection limit of this phase-retrieval-based microscopy tool. The numerical investigation suggests that the superb performance of Bragg CDI is achieved with an oversampling ratio above 30 and a detection dynamic range above 6 orders. The observed performance degradation subject to the data binning processes is also studied. This numerical tool can be used to optimize experimental parameters and has the potential to significantly improve the throughput of Bragg CDI method

A high-efficiency portable system for insulation condition assessment of wind farm inter-array cables with double-sided partial discharge detection and localisation

Partial discharge (PD) diagnosis is a crucial tool to assess the insulation condition of wind farm cables. Among PD diagnosis techniques, PD localisation is promising as it can provide target maintenance indicators on the insulation weak points of the cables. Accordingly, this paper developed a portable PD detection and location system for wind farm inter-array cables. The system consists of two non-invasive and lightweight testing units, which can be conveniently deployed on an energised cable, enabling highly efficient online PD diagnosis of the widely distributed inter-array cables. The system achieves accurate PD localisation of the energised cable via an improved double-sided travelling wave method. The method exhibits two superior features: the double-sided testing units are accurately synchronised via the joint application of Global Position Systems and a pulse-based interaction process, and a windowed phase difference method is proposed and integrated into the system to robustly estimate the time-of-arrival difference in low signal-to-noise ratio environment. Validation experiments were conducted on both a 10-kV cable in the laboratory and a real 35-kV cable in an on-shore wind farm

Artifact mitigation of ptychography integrated with on-the-fly scanning probe microscopy

We report our experiences with conducting ptychography simultaneously with the X-ray fluorescence measurement using the on-the-fly mode for efficient multi-modality imaging. We demonstrate that the periodic artifact inherent to the raster scan pattern can be mitigated using a sufficiently fine scan step size to provide an overlap ratio of >70%. This allows us to obtain transmitted phase contrast images with enhanced spatial resolution from ptychography while maintaining the fluorescence imaging with continuous-motion scans on pixelated grids. This capability will greatly improve the competence and throughput of scanning probe X-ray microscopy

Extending the depth of field for ptychography using complex-valued wavelets

Ptychography is a scanning variation of the coherent diffractive imaging method for providing high-resolution quantitative images from specimen with extended dimensions. Its capability of achieving diffraction-limited spatial resolution can be compromised by the sample thickness, which is generally required to be thinner than the depth of field of the imaging system. In this Letter, we present a method to extend the depth of field for ptychography by numerically generating the focus stack from reconstructions with propagated illumination wavefronts and combining the in-focus features to a single sharp image using an algorithm based on the complex-valued discrete wavelet transform. This approach does not require repeated measurements by translating the sample along the optical axis as in the conventional focus stacking method, and offers a computation-efficient alternative to obtain high-resolution images with extended depth of fields, complementary to the multi-slice ptychography

Extending the depth of field for ptychography using complex-valued wavelets (vol 44, pg 503, 2019)

This publisher’s note corrects an error in Eq. (3) of Opt. Lett. 44, 503 (2019)

Reducing the contents of free phenol and formaldehyde in phenolic foam

The problem of overly high contents of remnant monomers (free phenol and free formaldehyde) in phenolic foam was studied. Free phenol was characterized by iodimetry, and free formaldehyde was characterized by a hydroxylamine hydrochloride method. The effect of the phenol /formaldehyde molar ratios and the reaction temperature on the contents of the remnant monomers was examined. The effect of adding urea on the content of free formaldehyde was investigated. The effect of the foaming process on the contents of the remnant monomers was examined in detail. Phenolic foams in which the content of free phenol was 0.09% and the content of free formaldehyde was less than 0.1% were successfully prepared. A prepolymer of polyurethane, which toughened the phenolic foam, lowered the contents of free phenol and free formaldehyde. (C) 2003 Wiley Periodicals, Inc

11 nm hard X-ray focus from a large-aperture multilayer Laue lens

The focusing performance of a multilayer Laue lens (MLL) with 43.4 μm aperture, 4 nm finest zone width and 4.2 mm focal length at 12 keV was characterized with X-rays using ptychography method. The reconstructed probe shows a full-width-at-half-maximum (FWHM) peak size of 11.2 nm. The obtained X-ray wavefront shows excellent agreement with the dynamical calculations, exhibiting aberrations less than 0.3 wave period, which ensures the MLL capable of producing a diffraction-limited focus while offering a sufficient working distance. This achievement opens up opportunities of incorporating a variety of in-situ experiments into ultra high-resolution X-ray microscopy studies

Optimization of overlap uniformness for ptychography

We demonstrate the advantages of imaging with ptychography scans that follow a Fermat spiral trajectory. This scan pattern provides a more uniform coverage and a higher overlap ratio with the same number of scan points over the same area than the presently used mesh and concentric [13] patterns. Under realistically imperfect measurement conditions, numerical simulations show that the quality of the reconstructed image is improved significantly with a Fermat spiral compared with a concentric scan pattern. The result is confirmed by the performance enhancement with experimental data, especially under low-overlap conditions. These results suggest that the Fermat spiral pattern increases the quality of the reconstructed image and tolerance to data with imperfections

Identification of two phosphatidylinositol/phosphatidylcholine transfer protein genes that are predominately transcribed in the flowers of Arabidopsis thaliana

The Sec14 protein (Sec14p) and its homologs are involved in the transfer of phosphatidylinositol/phosphatidylcholine phospholipids in eukaryotic cells. In the completely sequenced genome of Arabidopsis thaliana, multiple genes encoding putative Sec14p homologs have been Here we report the identification of two yeast Sec14-like genes (designated as AtSFH3 and AtSFH12, respectively) that are predominately transcribed in Arabidopsis flowers. The deduced amino acid sequences of, AtSfh3p and AtSfh12p exhibited high similarity to that of Sec14p. Ectopic expression of AtSfh3p or AtSfh12p corrected the high temperature sensitive phenotype caused by Sec14p functional deficiency in Saccharomyces cerevisiae, indicating that the two plant homologs are functional in the intracellular environment. AtSFH3 transcripts were detected in flowers, stems and immature siliques but not roots and leaves, with a relatively higher transcript level in the flowers. In contrast, AtSFH12 transcripts were only detectable in the flowers. Based on histochemical staining of beta-glucuronidase (GUS) activities in the transgenic Arabidopsis plants harboring promoter::GUS constructs, AtSFH3 transcription was first detected in the stigma papillae of the flowers at stage 11, and then in the pollen grains before and after fertilization. On the other hand, AtSFH12 transcription was only found in the mature and germinating pollen grains. The information from this study may provide useful clue for further analysis of the function of plant Sec14p homologs in the development of the mate gametic cells and/or the fertilization process in higher plants. (c) 2006 Elsevier GmbH. All rights reserved