Molecule Dynamics Simulation of the Effect of Oxidative Aging on Properties of Nitrile Rubber

The effects of oxidative aging on the static and dynamic properties of nitrile rubber at the molecular scale were investigated by molecular dynamics simulation. The aged nitrile rubber models were constructed by introducing hydroxyl groups and carbonyl groups into rubber molecular chains to mimic oxidative aging. The static and dynamic properties of the unaged and aged nitrile rubber under different conditions were evaluated by mean square displacement, self-diffusion coefficients, hydrogen bond, fractional free volume, radial distribution function, cohesive energy density and solubility parameter. The results show that the elevated temperature intensified significantly the mobility of rubber molecular chains and fractional free volume, while the compressive strain displayed the opposite effect resulting in packing and rearrangement of rubber chains. The introduction of hydroxyl groups and carbonyl groups enhanced the polarity, intermolecular interactions, the volume and rigidity of molecular chains, implying weaker mobility of molecular chains as compared to unaged models. The compressive strain and oxidative aging both decreased the fractional free volume, which inhibited gaseous and liquid diffusion into the rubber materials, and slowed down the oxidative aging rate. This study provides insights to better understand the effect of molecular changes due to oxidative aging on the structural and dynamic properties of rubber materials at the molecular level

The effect of reactively-sputtered alumina films on the oxidation resistance of CoCrAlY coatings

Thin alumina films have found applications in electronic circuits and cutting tools and have been recently explored as protective coatings against high temperature oxidation, but these studies have been relatively rare. In this study, amorphous alumina films 3.5 µm thick were produced by reactive sputtering on Co-30Cr-6Al-0.5Y coatings, using a pure aluminum target in Ar + O2 atmosphere. Isothermal oxidation tests were carried out at 1000-1100 °C in static air. The results showed that the alumina films improved the oxidation resistance at all testing temperatures. At 1000°C, the Co-30Cr-6Al-0.5Y coating could form pure alumina scale on its surface, but the reactively-sputtered alumina films reduced the oxidation rate. At 1100 °C, the Co-30Cr-6Al-0.5Y coating could not form pure alumina scale, as a result of a severe internal oxidation of aluminum along the columnar defects. The scales were composed of Al2O3, Cr2O3 and TiO2, which were not so protective as pure alumina scales. On the contrary, the Co-30Cr- 6Al-0.5Y coatings with 3.5 µm preformed alumina films exhibited excellent oxidation resistance at 1100 °C. Only minor amounts of TiO2 were detected on the surface. Moreover, the reactively-sputtered alumina films were very adherent to the CoCrAlY coatings. At 1000 °C no spallation was found, while at 1100 °C only a little spallation produced during cooling was observed

Influences of Cr and Co on the Growth of Thermally Grown Oxide in Thermal Barrier Coating during High-Temperature Exposure

Thermal barrier coating (TBC) is a critical material in the aerospace domain to increase the lifetime of gas turbine components subjected to thermal load. The properties of TBC are strongly related to the growth of thermally grown oxide (TGO) whose main constituent is Al2O3. However, the oxidation of Cr and Co can affect the growth of TGO, which is not studied sufficiently. In this paper, high-temperature exposure at 1000 °C was performed to investigate the effect of Cr and Co oxides on TGO growth. The morphology and composition analysis of the interface between the ceramic top coat and the bond coat (TC/BC) were investigated by using scanning electron microscopy (SEM) and the energy dispersion spectrum (EDS). The thermodynamics and kinetics of oxidation were analyzed. The results indicated that the oxidation kinetics basically followed the sub-parabolic law with exposure time. Additionally, the major factor affecting the formation of oxides was the diffusion rate at the initial stage of exposure, then oxides depended on thermodynamics, and the oxidation was influenced by both of them in the last stage. The major elements to be oxidized were different at different stages. Moreover, the replacement reaction of Cr2O3 and the phase conversion of Al2O3 resulted in thickness variations of the TGO and Al-depleted zone during high-temperature exposure

Synergistic Effects of Multiple Environmental Factors on Degradation of Hydrogenated Nitrile Rubber Seals

Degradation tests of hydrogenated nitrile rubber seals, often used as sealing components in hydraulic systems, were conducted under the free and compression state in air and hydraulic oil at three elevated temperatures for several days to investigate the synergistic effects among three factors. The crosslinking and chain scission reactions both occurred simultaneously at higher temperature during the degradation process, and crosslinking predominated for most cases. Additionally, the synergistic effect between compression stress and hydraulic oil further slowed the degradation rate by limiting oxygen access. However, the higher temperature and hydraulic oil both promoted the formation of oxidation products, whereas the compression stress restrained the formation of amide groups. The fracture morphology results show that the defects gradually formed on the fracture surface, especially for the uncompressed specimens. The increase of the compression set aged in air was more than that in hydraulic oil, implying the more serious degradation. Moreover, rubber seals under the synthetic effect of three environmental factors presented the minimum degradation level. The degradation of the compressed and uncompressed specimens exposed to hydraulic oil is more serious than that of specimens exposed to air

Deblurring of Sound Source Orientation Recognition Based on Deep Neural Network

Underwater target detection and identification technology are currently two of the most important research directions in the information disciplines. Traditionally, underwater target detection technology has struggled to meet the needs of current engineering. However, due to the large manifold error of the underwater sonar array and the complexity of ensuring long-term signal stability, traditional high-resolution array signal processing methods are not ideal for practical underwater applications. In conventional beamforming methods, when the signal-to-noise ratio is lower than −43.05 dB, the general direction can only be vaguely identified in the general direction. To address the above challenges, this paper proposes a beamforming method based on a deep neural network. Through preprocessing, the space-time domain of the target sound signal is converted into two-dimensional data in the angle-time domain. Subsequently, we trained the network with enough sample datasets. Finally, high-resolution recognition and prediction of two-dimensional images are realized. The results of the test dataset in this paper demonstrate the effectiveness of the proposed method, with a minimum signal-to-noise ratio of −48 dB

A Rigorously-Incremental Spatiotemporal Data Fusion Method for Fusing Remote Sensing Images

The spatiotemporal remote sensing images have significant importance in forest ecological monitoring, forest carbon management, and other related fields. Spatiotemporal data fusion technology of remote sensing images combines high spatiotemporal and high temporal resolution images to address the current limitation of single sensors in obtaining high spatiotemporal resolution. This technology has gained widespread attention in recent years. However, the current models still exhibit some shortcomings in dealing with land cover changes, such as poor clustering results, inaccurate incremental spatiotemporal calculations, and sensor differences. In this article, we propose a rigorously-incremental spatiotemporal data fusion method for fusing remote sensing images with different resolutions to address the aforementioned problems. The proposed method utilizes the particle swarm optimization Gaussian mixture model to extract endmembers and establishes a linear relationship between sensors to obtain accurate time increments. Furthermore, bicubic interpolation is used instead of thin plate spline interpolation for spatial interpolation, and also support vector regression is used to calculate weights for obtaining a weighted sum of temporal and spatial increments. In addition, sensor errors are allocated to the calculation of residuals. The experimental results show the efficacy of the proposed algorithm for fusing fine image Landsat with coarse image MODIS data and conclude that the proposed algorithm presents a better solution for heterogeneous data with strong phenological changes and regions with changes in surface types, which provides a better solution for remote sensing image fusion and, hence, improves the accuracy, stability, and robustness of data fusion

Comparative analysis of sRNAs, degradome and transcriptomics in sweet sorghum reveals the regulatory roles of miRNAs in Cd accumulation and tolerance

Main conclusion Key miRNAs including sbi-miR169p/q, sbi-miR171g/j, sbi-miR172a/c/d, sbi-miR172e, sbi-miR319a/b, sbi-miR396a/b, miR408, sbi-miR5384, sbi-miR5565e and nov_23 were identified to function in the regulation of Cd accumulation and tolerance. As an energy plant, sweet sorghum shows great potential in the phytoremediation of Cd-contaminated soils. However, few studies have focused on the regulatory roles of miRNAs and their targets under Cd stress. In this study, comparative analysis of sRNAs, degradome and transcriptomics was conducted in high-Cd accumulation (H18) and low-Cd accumulation (L69) genotypes of sweet sorghum. A total of 38 conserved and 23 novel miRNAs with differential expressions were identified under Cd stress or between H18 and L69, and 114 target genes of 41 miRNAs were validated. Furthermore, 25 miRNA-mRNA pairs exhibited negatively correlated expression profiles and sbi-miR172e together with its target might participate in the distinct Cd tolerance between H18 and L69 as well as sbi-miR172a/c/d. Additionally, two groups of them: miR169p/q-nov_23 and miR408 were focused through the co-expression analysis, which might be involved in Cd uptake and tolerance by regulating their targets associated with transmembrane transportation, cytoskeleton activity, cell wall construction and ROS (reactive oxygen species) homeostasis. Further experiments exhibited that cell wall components of H18 and L69 were different when exposed to cadmium, which might be regulated by miR169p/q, miR171g/j, miR319a/b, miR396a/b, miR5384 and miR5565e through their targets. Through this study, we aim to reveal the potential miRNAs involved in sweet sorghum in response to Cd stress and provide references for developing high-Cd accumulation or high Cd-resistant germplasm of sweet sorghum that can be used in phytoremediation