Search

This study investigates the effects of high-energy electron beam irradiation on fumed silica fillers and the subsequent impact on the properties of synthesized silicone rubber. A systematic examination of the physical and electrical properties of the modified fumed silica and silicone rubber materials is conducted, and the underlying mechanisms behind the irradiated fumed silica’s influence on the silicone rubber are analyzed using first principles calculations. The findings reveal that as the irradiation dose increases, more defect structures emerge, and the defect center transitions from a dimer configuration to a puckered configuration. First principles calculations confirm that this defect center alteration leads to reduced surface energy. Fumed silica containing a higher number of defect structures results in improved mechanical properties and decreased dielectric properties for the silicone rubber material. These outcomes primarily stem from the increased presence of oxygen vacancies in the irradiated fumed silica, which correlates with reduced surface energy and energy band gap in the first principles calculations. This research is essential for understanding the microscopic changes in fumed silica as a filler under irradiation and the mechanism of its effect on silicone rubber, ultimately providing guidance for enhancing the functionality of silicone rubber materials.

In this article, the spacecraft attitude takeover control (ATC) problem with limited communication and the unavailable angular velocity using cellular satellites is addressed. First, a dynamic uniform quantizer (DUQ) is proposed to quantize unit quaternion between sensor cellular satellites and controller cellular satellite. Second, an adaptive fuzzy observer is proposed to estimate the unavailable angular velocity. Further, between controller cellular satellite and actuator cellular satellites, an event-triggered mechanism (ETM) is provided to lighten the communication burden. By combing DUQ, adaptive fuzzy observer, the adaptive fuzzy control law and the ETM is established. The stability of the ATC systems with the proposed control method is ensured. Finally, the simulation results illustrate the effectiveness of the developed control laws.

The impact of high-energy electron beam irradiation on silicone rubber composite insulator is investigated in this article. It was discovered that as the irradiation dose increased, the related properties of silicone rubber increased first and then decreased, with the static contact angle increasing to 111.8°, the tensile strength increasing to 4.59 MPa, the tear strength increasing to 26.8 kN/m, and the crosslinking density increasing to $7.09\times 10^{-{4}}$ mol/cm3, but the elongation decreasing. SEM observation revealed that silicone rubber was more compact after irradiation. attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) studies revealed that when the irradiation dose increased, the irradiation of silicone rubber shifted from crosslinking to degradation, and a new Si(−O)4 structure formed. Considering comprehensive performances, 40–50 kGy is the optimal irradiation dose. This article can provide support for understanding the irradiation modification of silicone rubber materials for composite insulator and also guide the preparation method of new silicone rubber.

Significantly enhanced varistor properties via tailoring interface states were obtained in Ca 1–2 x /3 Y x Cu 3 Ti 4 O 12 -SrCu 3 Ti 4 O 12 composite ceramics. The breakdown field was improved to 35.8 kV cm−1 and the nonlinear coefficient in 0.1–1 mA cm−2 was enhanced to 14.6 for Ca 0.67 Y 0.5 Cu 3 Ti 4 O 12 -SrCu 3 Ti 4 O 12. Noticeably, the withstand voltage of single grain boundary reached up to 24 V while the reported ones were constant to about 3 V. Greatly improved properties were attributed to the formation of superior grain boundary rather than the reduced grain size. Surprisingly, with distinct discrepancy of nonlinear performance in the composites, the resistance and activation energy of grain boundary exhibited little differences. Based on the double Schottky barrier at grain boundary and the field-assisted thermal emission model, it was found that the excellent electrical nonlinearity arose from the formation of deeper and broader interface states at grain boundary. In this case, interface states were not easily entirely filled and the barrier could maintain its height under applied voltage. This work provides a novel routine for enhancing the varistor properties of CaCu 3 Ti 4 O 12 based ceramics by manipulating interface states at grain boundary. [ABSTRACT FROM AUTHOR]

In order to improve the service life of the V-ribbed belt and the ride comfort of the vehicle, the friction noise of V-ribbed belt was studied by simulation and experiment. A theoretical model of V-ribbed belts vibration is established, and the conditions for unstable vibration are derived. Based on the theory of mode coupling, the causes of high frequency friction noise of V-ribbed belts are analyzed, and it is considered that the coupling between the vibration of the V-ribbed belts and the natural frequency of the belts’ cross section causes the self-excited vibration of the belt, resulting in high frequency friction noise. Firstly, ANSYS Workbench is used to identify the belts’ cross sections with 3, 4, and 6 wedges, and the natural frequencies of the belts’ cross sections are obtained. Then on the belt drive friction tester, the influences of tension and relative sliding speed on the frequency of high frequency friction noise is studied using a single factor test method, and the frequency response curve of high frequency friction noise is also analyzed. The results of the experiment and simulation show that the transverse vibration of the V-ribbed belts is closely related to the phase and amplitude of the high frequency friction noise, and the changes in tension and relative sliding speed do not affect the frequency of the high frequency friction noise. The frequency of high frequency friction noise has a good consistency with the natural frequency of belts’ cross section, which shows that mode coupling causes the strong self-excited vibration of the V-ribbed belts and the high frequency friction noise. It provides a method and theoretical basis for the control of friction noise.

The electrocatalytic reduction of carbon dioxide into valued chemicals such as formic acid has the most promising potential in applying renewable energy for useful materials and mitigating the greenhouse effect. However, the studies still focus on developing catalysts with low price and high catalytic properties. In this study, nitrogen atoms were decorated into carbon structure by a unique ultrasonic method, then the nitrogen-doped carbon material was applied as catalyst in CO2reduction, it exhibited excellent electrochemical activity, 4 times higher than the normal method. The improved activity should be attributed to the interaction between nitrogen and carbon atoms through analysis.

Exploring the surface energy exchange between atmosphere and water bodies is essential to gain a quantitative understanding of regional climate change, especially for the lakes in the desert. In this study, measurements of energy flux and water vapor were performed over a lake in the Badain Jaran Desert, China from March 2012 to March 2013. The studied lake had about a 2-month frozen period (December and January) and a 10-month open-water period (February–November). Latent heat flux (LE) and sensible heat flux (Hs) acquired using the eddy covariance technique were argued by measurements of longwave and shortwave radiation. Both fluxes of longwave and shortwave radiation showed seasonal dynamics and daily fluctuations during the study period. The reflected solar radiation was much higher in winter than in other seasons. LE exhibited diurnal and seasonal variations. On a daily scale, LE was low in the morning and peaked in the afternoon. From spring (April) to winter (January), the diurnal amplitude of LE decreased slowly. LE was the dominant heat flux throughout the year and consumed most of the energy from the lake. Generally speaking, LE was mostly affected by changes in the ambient wind speed, while Hs was primarily affected by the product of water-air temperature difference and wind speed. The diurnal LE and Hs were negatively correlated in the open-water period. The variations in Hs and LE over the lake were differed from those on the nearby land surface. The mean evaporation rate on the lake was about 4.0 mm/d over the entire year, and the cumulative annual evaporation rate was 1445 mm/a. The cumulative annual evaporation was 10 times larger than the cumulative annual precipitation. Furthermore, the average evaporation rates over the frozen period and open-water period were approximately 0.6 and 5.0 mm/d, respectively. These results can be used to analyze the water balance and quantify the source of lake water in the Badain Jaran Desert.

Many lakes exist in southeastern Badain Jaran Desert and its hinterland, including 110 perennial lakes and some seasonal or extinct lakes. Geomorphological, sedimentological, and bioglyph evidence obtained from field investigations on Badain Jaran Desert lake group, alongside measurements and dating performed on lake relic, prove that these lakes expanded while the climate was relatively wet during early and middle Holocene. The dating results suggest that the pan-lake period of the Badain Jaran Desert began at 10 cal kyr BP, before which the limnic peat period occurred (11–10 cal kyr BP). Many lakes reached their maximal water-level during 8.6–6.3 cal kyr BP and retreated or dried up in the late Holocene (about 3.5–0 cal kyr BP). During that period, the precipitation at Badain Jaran Desert may have reached 200 mm yr?1 for 7.7–5.3 cal kyr BP, inferred from both the age and precipitation rate of calcareous root tubes. The water balance calculation shows that wetter and warmer climate and the increase of underground water recharge were key factors in maintaining and developing the lake group at both centennial and millennial time scales. Furthermore, lake surface expansion and the increasing fresh water availability set the background for the prosperous prehistoric culture.

The Badain Jaran Desert is the second-largest area of shifting sands in China. Our first measurements of the energy components and water vapor fluxes on a megadune using eddy covariance technology were taken from April 2012 to April 2013. The results indicate that the longwave and shortwave radiative fluxes exhibited large fluctuations and seasonal dynamics. The total radiative energy loss by longwave and shortwave radiation was greater on the megadune than from other underlying surfaces. The radiation partitioning was different in different seasons. The land-atmosphere interaction was primarily represented by the sensible heat flux. The average sensible heat flux (40.1 W/m2) was much larger than the average latent heat flux (14.5 W/m2). Soil heat flux played an important role in the energy balance. The mean actual evaporation was 0.41 mm/d, and the cumulative actual evaporation was approximately 150 mm/a. The water vapor would transport downwardly and appear as dew condensation water. The amount of precipitation determined the actual evaporation. The actual evaporation was supposed to be equal to the precipitation on the megadune and the precipitation was difficult to recharge the groundwater. Our study can provide a foundation for further research on land-atmosphere interactions in this area.

According to complex geological environment of underground space，drilling parameters were obtained based on the research of drilling process. As a sensor for collecting the date of drilling parameter, photoelectric encoder was chosen to combine field test. The change curve of drilling depth with torque in different strata was collected successfully by using photoelectric encoder and can reflect the change of torque during drilling. It is found that there are different response characteristics in different strata, but these response characteristics show the certain orderliness.

The phenomenon of solvent-induced crystallization observed in some polymer–solvent pair was well documented. It is generally believed that solvent-induced crystallization occurs during sorption of the solvent. However, this is actually a hypothesis and needs to be proven. To clarify the true situation, the present article investigates crystalline structural variation of polyetheretherketone before and after treatment of methylene chloride. The results indicate that crystallization of the polymer was induced by the solvent mainly when the solvent was desorbed. The possible mechanism is discussed in the light of molecular motion. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3376–3379, 1999