Ponder: Point Cloud Pre-training via Neural Rendering

We propose a novel approach to self-supervised learning of point cloud representations by differentiable neural rendering. Motivated by the fact that informative point cloud features should be able to encode rich geometry and appearance cues and render realistic images, we train a point-cloud encoder within a devised point-based neural renderer by comparing the rendered images with real images on massive RGB-D data. The learned point-cloud encoder can be easily integrated into various downstream tasks, including not only high-level tasks like 3D detection and segmentation, but low-level tasks like 3D reconstruction and image synthesis. Extensive experiments on various tasks demonstrate the superiority of our approach compared to existing pre-training methods.Comment: Project page: https://dihuang.me/ponder

Effect of anion co-existence on ionic organic pollutants removal over Ca based layered double hydroxide

The effects of co-existing anions (NO or SO ) on the removal of sodium dodecylsulfate (SDS), representing anionic organic pollutants, by Ca-based layered double hydroxide (CaAl-LDH-Cl) are investigated to provide fundamental insights on the ionic surfactant removal in the presence of co-existing anions, and facilitate the establishment of a practical and advanced water treatment for environmental remediation. The SO system shows higher adsorption capacity (4.43 mmol·g) and larger d-spacing of adsorption resultant (3.4 nm) than the control system with no co-existing anion (3.64 mmol·g, 3.25 nm) and the NO system (3.82 mmol·g, 3.27 nm). The macroscopic and microscopic analyses reveal that, NO had a little influence on the SDS removal due to strong electrolysis, while SO could significantly promote the SDS removal. Moreover, the reaction mechanism varies under different molar ratios of DS/SO

Enhanced removal of ionic dyes by hierarchical organic three-dimensional layered double hydroxide prepared via soft-template synthesis with mechanism study

In this work, we report, for the first time, that cationic (Rhodamine B, RhB) and anionic dyes (Methyl orange, MO) were removed efficiently by hierarchical organic three-dimensional MgAl-LDH, which was successfully synthesized via a one-step hydrothermal strategy using sodium dodecyl sulfate (SDS) as a soft template agent. The removal mechanisms of RhB and MO were extensively investigated and determined to be surface adsorption and anion exchange, respectively. In addition, the influence of reaction parameters affecting dyes removal including dosage, contact time, initial dye concentrations and temperature were investigated. The maximum adsorption capacity of MO (377.89 mg.g(-1)) was far beyond that of RhB (48.29 mg.g(-1)) as well as other adsorbents. Multilayer adsorption occurred in RhB or MO at a low concentration, while monolayer adsorption was the dominant process in MO at high concentration (> 200 mg.L-1). The thermodynamic calculations demonstrated that the adsorption process for both RhB and MO was spontaneous and endothermic. This work significantly broadens the application prospects of 3D-LDHs by modifying their surface properties and exploring O3D-LDHs as excellent adsorbents for organic pollutants in environmental remediation

Persistent organic pollutants removal via hierarchical flower-like layered double hydroxide: adsorption behaviors and mechanism investigation

Nanostructured hierarchical flower-like MgAl layered double hydroxide (HMA-LDH) was synthesized via the one-pot soft-template method and employed for the adsorption of persistent organic pollutants: anionic methyl orange (MO) and non-ionic naphthalene (NAP). The adsorption performance and mechanism comparison of MO and NAP were investigated via adsorption kinetics, isotherms, thermodynamics, and microstructural characterization. The maximum adsorption capacity of MO and NAP could reach 380.2 and 43.7 mg·g at 298 K, respectively. The kinetic studies illustrated that the adsorption equilibria reached in 2 and 1 h for MO and NAP, respectively. The adsorption isotherms indicated that HMA-LDH fitted the Langmuir model toward MO removal, while partition model for NAP. The comparative mechanism between MO and NAP were determined by X-ray diffraction (XRD), Fourier transform spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Anion exchange dominated the MO adsorption, whereas partition was deemed as the predominated mechanism for NAP. Furthermore, the recycle performance stated that HMA-LDH could be reused in five cycles in MO adsorption, while failed after two cycles for NAP. This study provided a theoretical foundation for the practical application of hierarchical flower-like LDH in the adsorption of persistent organic pollutants in the aquatic environment

The enhancement roles of sulfate on the adsorption of sodium dodecylsulfate by calcium-based layered double hydroxide: microstructure and thermal behaviors

As a commonly used surfactant, sodium dodecyl sulfate (SDS) usually coexists with inorganic anions in the industrial wastewater. These anions have a significant influence on SDS removal, indirectly threatening the environment. It is important to understand the relationship between the adsorption of SDS and inorganic anions. In this study, calcium-based layered double hydroxide (CaAl-LDH-Cl) as an efficient adsorbent was synthesized for investigating the effect of SO on SDS removal. The SDS adsorption capacities were enhanced to 3.21 and 4.21 mmol g in the presence of SO with low/high SDS concentration, respectively. The phenomenon and mechanism were confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Scanning electron microscopy (SEM). Anionic exchange played a dominant role in the adsorption of SDS onto CaAl-LDH-Cl at DS/SO < 2, while both anion exchange and precipitation occurred when DS/SO exceeded 2. Moreover, the thermal analysis (TG-DTA) was employed to further reveal the interaction mechanism. The results showed the highest total mass loss and the lowest loss temperature of interlayer water in the sulfate coexist system, confirming the enhancement of SDS adsorption amount in the presence of SO

Ultrahigh removal performance of lead from wastewater by tricalcium aluminate via precipitation combining flocculation with amorphous aluminum

Lead (Pb) removal is an urgent issue of industrial wastewater treatment due to its fatal harm on human health. In this study, for the first time, the efficient removal of Pb by cement-based material tricalcium aluminate (C(3)A) have been reported. The ultrahigh removal capacity of 1747.1 mg.g(-1) for Pb by C(3)A was achieved at the dosage of 0.5 g.L-1 within 1 h. The removal behaviors investigated by batch experiments illustrated that the C(3)A dosage and initial Pb concentration significantly influenced the removal behavior. And the removal process was identified to be a pH-independence process accompanying with a chemical reaction. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the chemical precipitation thermodynamic model PHREEQC were employed to elucidate the removal mechanism. Amorphous aluminum released by C(3)A hydration played a major role in Pb removal via flocculation at low Pb concentration (600 mg.L-1). C(3)A could remove Pb to an acceptable level (WHO standard) from authentic wastewaters at low Pb concentration (similar to 20 mg.L-1), or remove similar to 70% Pb from authentic wastewaters at high concentration (ca. 700 mg.L-1). This work presents C(3)A as an excellent material for lead removal and broadens the potential application of cement-based materials in environmental remediation. (C) 2019 Elsevier Ltd. All rights reserved

THE OBJECTIVE AND IMPLEMENTATION OF DYNAMIC VISUALIZATION OF SPATIO-TEMPORAL GEOGRAPHICAL PROCESSES

ABSTRACT: The Spatio-temporal data is the description of the time, space, and attribute information of the geographic spatiotemporal process, which reflects the spatio-temporal process information of geographical phenomenon changing with the time on the earth-surface space. The spatio-temporal process information is complex and changing. Thus according to the objective of dynamic visualization of geographic process, a break-through dynamic visualization method was developed in this paper to express the geographical spatio-temporal evolution process intuitively

Footprint Location Prediction Method of ZY3-02 Altimeter

On-orbit geometric calibration is an essential way to improve plane and elevation accuracy of laser altimeter data, and the laser footprint location prediction is a prerequisite for calibration based on land infrared detector. This paper builds a laser footprint location prediction model for China's first space-borne laser altimeter carried by ZY3-02, which refers to the satellite optical camera rigorous geometry imaging model. The model takes full account of the law of platform movement, and correlates laser emission center with ground footprint point. We get the precise predicted laser pointing by Pyramid terrain matching, ephemerisby acceleration prediction, and attitude by frequency analysis. The laser footprint location can be predicted. This laser footprint location prediction model were successfully applied in the calibration test of the laser altimeter on ZY3-02 satellite, and the maximum error between the predicted location and real footprint location obtained by triggered detectors is less than 150 m, which proves the validity of the proposed model. The proposed method provides the precise point-to-point prediction from satellite to ground for Chinese remote sensing satellite, and offers a technological support for the space-borne laser altimeter calibration in future

A Scenario-based risk framework for determining consequences of different failure modes of earth dams

Failure modes for earth dams are extensively reviewed and analysed using a three-pronged approach including a literature review, physical observations of a representative earth dam site and finite element structural analysis of the dam wall. Several failure scenarios are used for predicting consequences in terms of downstream inundation and damage. The fluid flow component is performed using the mesh-free smoothed particle hydrodynamics method. For a representative earthen dam, piping and landslip are identified as key failure modes based on a combination of finite element analysis, theory and physical observations. Inundation behaviour is very different for the two failure modes. The landslip failure is the most critical one for the dam studied with flood water breaking the river bank and affecting surrounding property and farmland. For the piping failures, water flow from the initial pipes formed for significant periods before they collapse, but the flow rates are small compared with that of the much larger landslip mode. After failure, fragments of the collapsing wall block the breach and can considerably restrict the flood discharge. In some cases, the water pressure is able to push the obstructing material downstream and some minor flooding occurs, but in others cases the breach can remain blocked with little flooding occurring. A prototype risk framework is developed using the small database of the pre-computed flooding scenarios and key variables that affect inundation such as water level in the reservoir. This can be used to estimate inundation maps for as yet non-computed scenarios through interpolation and superposition techniques. The implementation of the risk framework is demonstrated by the estimation of inundation maps for two in-between non-computed reservoir levels. Inundation due to multiple breaches is also estimated by superposition of three single-breach scenarios. Results are compared against the simulated multiple breach. A preliminary implementation of this risk framework into a geographic information system is also described.42 page(s

Insights into efficient removal and mechanism for ammonium from aqueous solution on tricalcium aluminate

Ammonium (NH4+) has been causing severe environmental pollution while the development of material with high capacity for ammonium removal remains a challenge. Herein, the cement-based material tricalcium aluminate (C3A) was employed to remove NH4+ from digested piggery wastewater. The conditions influencing the removal capacity were investigated, including contact time, initial ammonium concentration, temperature, dosage and initial co-existing phosphate concentration. The physicochemical structure of C3A and the resultant were characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and N2 adsorption–desorption isotherms. The maximum removal capacity of NH4+ by C3A was 155.4 mg·g−1 at 298 K. The characterization revealed that the resultant was CaAl-Cl-LDH. The hydroxyl groups and Al(OH)4− from the C3A hydration played an important role in ammonium removal. High alkalinity could enhance the removal capacity. This work presents an efficient solution for ammonium removal, thus providing new insight into the mechanism of cement-based materials for water pollutant removal