AU-PD: An Arbitrary-size and Uniform Downsampling Framework for Point Clouds

Point cloud downsampling is a crucial pre-processing operation to downsample the points in the point cloud in order to reduce computational cost, and communication load, to name a few. Recent research on point cloud downsampling has achieved great success which concentrates on learning to sample in a task-aware way. However, existing learnable samplers can not perform arbitrary-size sampling directly. Moreover, their sampled results always comprise many overlapping points. In this paper, we introduce the AU-PD, a novel task-aware sampling framework that directly downsamples point cloud to any smaller size based on a sample-to-refine strategy. Given a specified arbitrary size, we first perform task-agnostic pre-sampling to sample the input point cloud. Then, we refine the pre-sampled set to make it task-aware, driven by downstream task losses. The refinement is realized by adding each pre-sampled point with a small offset predicted by point-wise multi-layer perceptrons (MLPs). In this way, the sampled set remains almost unchanged from the original in distribution, and therefore contains fewer overlapping cases. With the attention mechanism and proper training scheme, the framework learns to adaptively refine the pre-sampled set of different sizes. We evaluate sampled results for classification and registration tasks, respectively. The proposed AU-PD gets competitive downstream performance with the state-of-the-art method while being more flexible and containing fewer overlapping points in the sampled set. The source code will be publicly available at https://zhiyongsu.github.io/Project/AUPD.html

Experiment, modelling, mechanism and significance of multiscale and dynamic diffusion-permeability of gas through micro-nano series pores in coal

As one of the hot issues at the frontiers of science in the world, the multi-scale scientific question has occurred in the fields of natural science and engineering. The seepage in coal-rock, a branch of the multi-scale science, shows its multi-scale scientific question. Coal is a porous medium that contains multi-scale pores with the aperture from millimeter to nanometer. The pore size differential can reach one million orders of magnitude, which causes the multi-scale characteristics in space and time for coal permeability. Therefore, the research on the multi-scale permeability of coal is a critical scientific issue of the coal gas flow as well as an engineering extension of methane drainage. The unsteady diffusion-seepage experiment is conducted for CH4/He with and without stress using a cylindrical coal sample, accompanied by steady state seepage experiment. The experimental results show that the apparent diffusion coefficient of a cylindrical coal sample attenuates with time. This apparent diffusion coefficient shows two different multi-scale characteristics in time, the smooth and dynamic attenuation and the dynamic attenuation in a two-stage step. A dynamic model for the apparent diffusion coefficient is proposed, and it can accurately describe the complete unsteady flow process of gas in a cylindrical coal sample. The physical and mathematical models of the multi-scale pores in series are put forward. Then, the multi-scale structure of pore in series is validated by the mercury injection experiment. After that, the multi-scale permeability model is mathematically proved. Based on the Knudsen number (Kn), the continuous flow, slip flow, transition flow and free molecular flow are identified and introduced with the multi-scale pore size to build a multi-scale permeability model that reflects the effect of the effective stress and gas flow regime. The mechanism of the multi-scale seepage is revealed in this study. The size and the number of pores in series connection are the critical factors to influence the multi-scale permeability. The multi-scale effect can reach tens of thousands orders of magnitude within measurable range. The gas outflow firstly starts from the outside fractures, and then the inside small pores and finally the nano pores. With time goes on, the gradual increase in the number of pores in series connection leads to the gradual decrease in the equivalent pore size, which causes the equivalent pore aperture to get close to the minimum pore aperture. Therefore, the equivalent permeability quickly decreases with time, which is a reflection of the multi-scale space in coal. During the later stage of gas flow, the effect of slip and transition flow regime is larger than that of effective stress with Kn increasing and dominates the permeability. The new experimental observation and modelling of the multi-scale permeability provides an experimental solution for the research of the multi-scale seepage and overcomes the shortcoming of single tube theory. The diffusion and seepage are apparently unified, and the micro-level distinguishment and macro-level union of the multi-scale permeability are realized

Alkali extraction and physicochemical characterization of hemicelluloses from young bamboo (Phyllostachys pubescens Mazel)

Two hemicellulose fractions were obtained by extraction of one-month- old young bamboo (Phyllostachys pubescens Mazel). The fractionation procedure employed 2% NaOH as extractant, followed by filtration, acidification, precipitation, and washing with 70% ethanol solution. The total yield was 26.2%, based on the pentosan content in bamboo. The physicochemical properties were determined and sugar composition analysis showed that the hemicelluloses consisted mainly of xylose, arabinose, galactose, and a small amount of uronic acid. Furthermore, based on FT-IR and NMR spectra analyses, the structure of hemicelluloses was determined to be mainly arabinoxylans linked via (1→4)-β-glycosidic bonds with branches of arabinose and 4-O-methyl-D-glucuronic acid. The molecular weights were 6387 Da and 4076 Da, corresponding to the hemicelluloses HA and HB. Finally, the thermal stability was elucidated using the TG-DTG method. The obtained results can provide important information for understanding young bamboo and the hemicelluloses in it

Plasmon-driven nanowire actuators for on-chip manipulation.

Funder: National Natural Science Foundation of China (11674230); Shanghai Rising-Star Program (18QA1403200)Chemically synthesized metal nanowires are promising building blocks for next-generation photonic integrated circuits, but technological implementation in monolithic integration will be severely hampered by the lack of controllable and precise manipulation approaches, due to the strong adhesion of nanowires to substrates in non-liquid environments. Here, we demonstrate this obstacle can be removed by our proposed earthworm-like peristaltic crawling motion mechanism, based on the synergistic expansion, friction, and contraction in plasmon-driven metal nanowires in non-liquid environments. The evanescently excited surface plasmon greatly enhances the heating effect in metal nanowires, thereby generating surface acoustic waves to drive the nanowires crawling along silica microfibres. Advantages include sub-nanometer positioning accuracy, low actuation power, and self-parallel parking. We further demonstrate on-chip manipulations including transporting, positioning, orientation, and sorting, with on-situ operation, high selectivity, and great versatility. Our work paves the way to realize full co-integration of various functionalized photonic components on single chips

Transcriptome analysis of Hpa1Xoo transformed cotton revealed constitutive expression of genes in multiple signalling pathways related to disease resistance

The transcriptome profile in leaves and roots of the transgenic cotton line T-34 expressing hpa1Xoo from Xanthomonas oryzae pv. oryzae was analysed using a customized 12k cotton cDNA microarray. A total of 530 cDNA transcripts involved in 34 pathways were differentially expressed in the transgenic line T-34, in which 123 differentially expressed genes were related to the cotton defence responses including the hypersensitive reaction, defence responses associated with the recognition of pathogen-derived elicitors, and defence signalling pathways mediated by salicylic acid, jasmonic acid, ethylene, auxin, abscicic acid, and Ca2+. Furthermore, transcripts encoding various leucine-rich protein kinases and mitogen-activated protein kinases were up-regulated in the transgenic line T-34 and expression of transcripts related to the energy producing and consuming pathway was also increased, which suggested that the enhanced metabolism related to the host defence response in the transgenic line T-34 imposed an increased energy demand on the transgenic plant