Self-supervised learning aims to learn a universal feature representation without labels. To date, most existing self-supervised learning methods are designed and optimized for image classification. ...These pre-trained models can be sub-optimal for dense prediction tasks due to the discrepancy between image-level prediction and pixel-level prediction. To fill this gap, we aim to design an effective, dense self-supervised learning framework that directly works at the level of pixels (or local features) by taking into account the correspondence between local features. Specifically, we present dense contrastive learning (DenseCL), which implements self-supervised learning by optimizing a pairwise contrastive (dis)similarity loss at the pixel level between two views of input images. Compared to the supervised ImageNet pre-training and other self-supervised learning methods, our self-supervised DenseCL pre-training demonstrates consistently superior performance when transferring to downstream dense prediction tasks including object detection, semantic segmentation and instance segmentation. Specifically, our approach significantly outperforms the strong MoCo-v2 by 2.0% AP on PASCAL VOC object detection, 1.1% AP on COCO object detection, 0.9% AP on COCO instance segmentation, 3.0% mIoU on PASCAL VOC semantic segmentation and 1.8% mIoU on Cityscapes semantic segmentation. The improvements are up to 3.5% AP and 8.8% mIoU over MoCo-v2, and 6.1% AP and 6.1% mIoU over supervised counterpart with frozen-backbone evaluation protocol.
Code and models are available at: https://git.io/DenseCL
Ammonium phosphate fertilizer is the compounds containing nitrogen and phosphorus that are usually produced through the neutralization reaction of phosphoric acid and ammonia. At present, there are a ...variety of products, such as slurry monoammonium phosphate (MAP), diammonium phosphate (DAP), industrial grade MAP, water soluble MAP, water soluble ammonium polyphosphate (APP) and so on. After more than 60 years of development, China’s ammonium phosphate fertilizer industry has experienced the road of from scratch and from weak to strong. The successful development of the slurry MAP technology ended the history that the high concentration phosphate fertilizer cannot be produced by using the medium and low grade phosphate ore. The continuous, stable and large-scale production of DAP plant provides sufficient guarantee for DAP products in China. The development of new ammonium phosphate fertilizer products, such as industrial grade MAP, water soluble MAP, water soluble APP, provides technical support for the transformation and upgrading of phosphorus chemical enterprises. In this paper, the production methods, the development history and the latest research progress of ammonium phosphate fertilizers were reviewed.
Two new enantiomerically chiral 3D architectures, l-(Zn(H2O)3)3MnMo9O32·4H2O and d-(Zn(H2O)3)3MnMo9O32·4H2O, have been produced from a new way. The compounds were composed of the discrete chiral ...MnMo9O326- polyoxoanions linked by zinc(II) atoms to a 3D framework with a 2-fold interpenetrating net, which is the first examples of POM-based chiral 3D frameworks consisting of only inorganic components.
In the production of high-purity industrial phosphoric acid by wet process, the symbiotic elements are often treated as solid or liquid waste. This causes a waste of natural resources. In this work, ...a new wet-process phosphoric acid (WAP) purification route was proposed. In particular, the regeneration process of extractant was optimized, and the recovery process of aluminum was studied in detail (including stripping and crystallization). The effects of operational parameters and composition on the stripping behavior were investigated by single factor experiment and relevant analysis. Dissolution equilibrium date indicated the mother liquor could be circulated when the crystallization temperature was 298.15 K. Aiming to yield the purified extractant, the theoretical stages of stripping were simulated by plotting McCabe-Thiele diagram. Two-stage countercurrent extraction was carried out through a series of cascade experiments, indicating that over 95% Al3+ was stripped into aqueous phase. Furthermore, Al3+ in WPA was successfully changed into ammonium aluminum sulfate by this process, and it had higher purity than industrial grade. The results provide a basis for the high-quality utilization of associated resources in WPA.
The kinetics of the forward extraction of aluminum ion had been investigated using Lewis cells. The influences of the aluminum concentration, temperature, and interfacial area were studied. The ...extracted species was demonstrated to be AlL3·(HL)3 by stoichiometry studies and the mechanism of the extraction was explained. The results indicated that the extraction process was under mixed-control by the extraction reaction at the interface and the diffusion of the resultant in the organic phase. The activation energy was calculated to be 23.26 kJ/mol and was concordant with the mixed-control regime. Further analysis suggested that the reaction orders with respect to aluminum and extractant were 1 and 2, respectively, and the extraction rate constant was 10−4.526 L2·g−2·s−1. The total rate of the extraction reaction for AlL3·(HL)3 was given based on kinetic steps.
Fe3O4@C nanoparticles were prepared by an in situ, solid-phase reaction, without any precursor, using FeSO4, FeS2, and PVP K30 as raw materials. The nanoparticles were utilized to decolorize high ...concentrations methylene blue (MB). The results indicated that the maximum adsorption capacity of the Fe3O4@C nanoparticles was 18.52 mg/g, and that the adsorption process was exothermic. Additionally, by employing H2O2 as the initiator of a Fenton-like reaction, the removal efficiency of 100 mg/L MB reached ~99% with Fe3O4@C nanoparticles, while that of MB was only ~34% using pure Fe3O4 nanoparticles. The mechanism of H2O2 activated on the Fe3O4@C nanoparticles and the possible degradation pathways of MB are discussed. The Fe3O4@C nanoparticles retained high catalytic activity after five usage cycles. This work describes a facile method for producing Fe3O4@C nanoparticles with excellent catalytic reactivity, and therefore, represents a promising approach for the industrial production of Fe3O4@C nanoparticles for the treatment of high concentrations of dyes in wastewater.
When considering the problem of a vertical magnetic levitation bearing system, the rotor eccentric fall is more likely to cause the failure of the protective bearing. In this paper, a rotor drop ...collision model and a protective bearing dynamics model are constructed. It compares and analyzes the evolution of collision force values of the rotor eccentric drop as well as the non-eccentric drop. Further, this paper discusses the law of influence of three factors, rotor quality, rotational speed, and axial protection clearance, on the collision characteristics of the protected bearing in eccentric and non-eccentric cases. It has also experimentally verified this characteristic of rotor speed. The results show that compared with the non-eccentric condition, the axial impact force and radial impact forces of the rotor in the eccentric condition increase by 14% and 114%, respectively. Compared with the non-eccentric condition, with the increase in rotor quality, the axial and radial impact force increase by 68% on average, and the axial depth amplitude of the rotor increases by 350%. With the increase of rotor speed, the axial impact force without an eccentric drop is basically unchanged; the axial impact force of an eccentric drop increases slightly, and the radial impact force increases by 110%. With the increase of axial protection clearance, the radial displacement vibration of the rotor axis increases; the average increase of the maximum axial force is 120 N, and the average increase of the maximum radial force is 100%.
The Mars rovers are the key to Mars exploration missions. In order to achieve long-time autonomous roving and perform science operations, Mars rovers need to have the capability of high-precision ...autonomous navigation. According to the characteristics of the Martian environment, an innovative scheme of strap-down inertial navigation system/celestial navigation system (SINS/CNS) deep integration for the Mars rover and its implementation are proposed. First, the large field of view (FOV) star sensor is utilized to assist the attitude matrix of SINS by continually observing and correcting the misalignment angles and gyro drifts. Thus, the high-precision mathematic reference is obtained. Then, the star sensor makes use of the reference provided by SINS to obtain the local position vector. The rover's position and attitude can be determined by CNS. On the basis of the mathematics reference, the innovative scheme of SINS/CNS deep integration which takes full advantage of the navigation information of each subsystem is presented. Moreover, the errors of inertial measurement unit (IMU) and the navigation parameters in SINS are estimated and corrected. And the deep integration of SINS/CNS is performed. Compared to the optimal integration mode, this scheme improves navigation accuracy. In the end, the simulation results indicate that this scheme is steady and reliable.
Two novel high-nuclear Ni-substituted polyoxometalates Na9KNi7(OH)4(H2O)(CO3)2(HCO3)(A-α-SiW9O34)(β-SiW10O37)·5H3O·18H2O (1) and K6Na4{Ni6(H2O)4(μ2-H2O)4(μ3-OH)2}(x-SiW9O34)2·17.5H2O (2) have been ...obtained by reaction of K8γ-SiW10O36 with NiCl2·2H2O in basic conditions. Compounds 1 and 2 all represent the first polyoxometalates substituted by seven and six Ni centers, respectively. Also, compound 1 exhibits a novel asymmetric dimeric structure, composed of A-α-SiW9O3410- and β-SiW10O3710- units linked by a Ni7 cluster and three carbonates, which exhibit tri- and bidentate coordination modes in 1.
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