3D-Aware Object Goal Navigation via Simultaneous Exploration and Identification

Object goal navigation (ObjectNav) in unseen environments is a fundamental task for Embodied AI. Agents in existing works learn ObjectNav policies based on 2D maps, scene graphs, or image sequences. Considering this task happens in 3D space, a 3D-aware agent can advance its ObjectNav capability via learning from fine-grained spatial information. However, leveraging 3D scene representation can be prohibitively unpractical for policy learning in this floor-level task, due to low sample efficiency and expensive computational cost. In this work, we propose a framework for the challenging 3D-aware ObjectNav based on two straightforward sub-policies. The two sub-polices, namely corner-guided exploration policy and category-aware identification policy, simultaneously perform by utilizing online fused 3D points as observation. Through extensive experiments, we show that this framework can dramatically improve the performance in ObjectNav through learning from 3D scene representation. Our framework achieves the best performance among all modular-based methods on the Matterport3D and Gibson datasets, while requiring (up to 30x) less computational cost for training.Comment: To appear in CVPR 202

Treatment of microalgae in ballast water using hydroxyl radical in accordance with the D-2 ballast water discharge standard

The effect of hydroxyl radical (·OH) on microalgae in ballast water is experimentally investigated. An (OH plasma generator, which has a thin plate discharge Ag electrode covered by two α-Al2O3 dielectric layers, is built. The plasma generator is filled with O2 and gaseous H2O and is powered by a homemade power supply. ·OH radicals are generated by a series of plasma reactions and then dissolved into ballast water to kill microalgae. The maximum density of the killed microalgae is about 11000 cells per milliliter. At this density, the microalgae are not reactivated at the 48th hour and the 120th hour in the treated ballast waters, and the content of chlorophyll in these microalgae decreases by 100%. The water quality returns to a normal level after 120 hours without secondary pollution of aquatic organisms and environment. These results show that the requirements of the D-2 ballast water discharge standard defined by the International Maritime Organization (IMO) are satisfied with the proposed treatment, and that ·OH is an ideal substance for killing microalgae during ballast water replacement of ships

Treatment system of ballast water in oceanic ships using hydroxyl radical (?OH) based on strong electric-field discharge

Exchanging ballast water from ships might cause the interactive bio-invasion of different seawater, and break ecological balance. Therefore, we described a ship ballast water system which generates hydroxyl radical from strong electric field ionization discharge. The discharge at atmospheric pressure could ionize O2 in air and gaseous H2O to form a large amount of oxygen active particles, which were injected into a tube of the ballast water treatment system to generate a high concentration of ?OH solution through the cavitation effect. The ?OH solution could kill harmful micro-organisms in ballast water quickly and efficiently. Test results showed that, after being treated by the system at a flow speed of 10 t/h, the single-cell algae and bacteria in ballast water were almost completely eliminated, and the micro-organisms did not reactivate at 48 h and 120 h. In the treated ballast water, the concentration of malondialdehyde (MDA) obviously increased while BOD and COD decreased significantly. According to the MDA test, ?OH probably kills algae and bacteria though preoxidating their cytolipin. The treatment can effectively lower the pollution from the ballast water. The results indicate that solution of high ?OH concentration significantly improves the quality of ballast water, hence it relieves the environmental threats of the ballast water discharge on local marine system

MOF-based core-shell structures nanofiltration membranes for water purification

Metal-organic framework (MOFs) are emerging as promising materials for water purification membranes, owing to their uniform microporous structures and chemical functionalities. Here, we report a simple procedure for depositing MOF-based nanofiltration membranes on commercial ceramic tubular supports, completely avoiding the use of dispersants or binders. Zeolite imidazolate frameworks-8 (ZIF-8) nanocrystals were synthesized using a hydrothermal method and subsequently coated with an amorphous SiO2-ZrO2 gel to generate a dispersion of ZIF-8@SiO2-ZrO2 core-shell nanoparticles. The amorphous SiO2-ZrO2 gel served as a binding agent for the ZIF-8 nanocrystals, thus forming a defect-free continuous membrane layer. After repeating the coating twice, the active layer had a thickness of 0.96 µm, present a rejection rate > 90 % for the total organic carbon in an aquaculture effluent and in a wastewater treatment plant, while reducing the concentration of trimethoprim, here used as a target pollutant. Moreover, the oxide gel provided the MOF-based active layer with good adhesion to the support and enhanced its hydrophilicity, resulting in a membrane with excellent mechanical stability and resistance to fouling during the crossflow filtration of the real wastewater samples. These results implied the high potential of the MOF-based nanocomposite membrane for effective treatment of actual wastewater streams

Metal-organic framework-intercalated graphene oxide nanofiltration membranes for enhanced treatment of wastewater effluents

Graphene oxide membranes (GO) hold immense potential in the field of water purification. However, when applied directly to real wastewater effluents, pure GO membranes suffer from drawbacks such as fouling sensitivity and limited stability. To address these challenges and unlock the full potential of GO membranes, novel nanocomposite membranes have been developed by the intercalation of GO with nanoparticles of ZIF-8 (a type of zeolitic imidazolate framework). The prepared GO/ZIF-8 (GZ) nanocomposite membranes have exhibited enhanced hydrophilicity and exceptional water purification capabilities. Specifically, the GZ membranes have demonstrated a permeance enhancement of over two-fold when compared to the pristine GO reference membrane. This enhancement is coupled with anti-fouling performance and competitive rejection rates for both salts and organic pollutants. GZ membranes have been effectively employed for the purification by cross-flow filtration of 3 industrial wastewater effluents. They have shown improved separation performance compared to the pristine GO reference membrane, and high stability under cross-flow conditions. The origin of the high performances of the GZ membrane has been clarified using structural and morphological analyses. This work highlights the significant progress made in the field of water treatment using graphene-based membranes.</p