Effect of Temperature on Electromagnetic Performance of Active Phased Array Antenna

Active phased array antennas (APAAs) can suffer from the effects of harsh thermal environments, which are caused by the large quantity of power generated by densely packed T/R modules and external thermal impacts. The situation may be worse in the case of limited room and severe thermal loads, due to heat radiation and a low temperature sink. The temperature field of the antenna can be changed. Since large numbers of temperature-sensitive electronic components exist in T/R modules, excitation current output can be significantly affected and the electromagnetic performance of APAAs can be seriously degraded. However, due to a lack of quantitative analysis, it is difficult to directly estimate the effect of temperature on the electromagnetic performance of APAAs. Therefore, this study investigated the electromagnetic performance of APAAs as affected by two key factors—the uniformly distributed temperature field and the temperature gradient field—based on different antenna shapes and sizes, to provide theoretical guidance for their thermal design

Study on Low Temperature Oxidation Characteristics of Oil Shale Based on Temperature Programmed System

Oil shale is a kind of high-combustion heat mineral, and its oxidation in mining and storage are worth studying. To investigate the low-temperature oxidation characteristics of oil shale, the temperature, CO, alkane and alkene gases were analyzed using a temperature-programmed device. The results showed that the temperature of oil shale underwent three oxidation stages, namely a slow low-temperature oxidation stage, a rapid temperature-increasing oxidation stage, and a steady temperature-increasing stage. The higher the air supply rate is, the higher the crossing point temperature is. Similar to coal, CO also underwent three stages, namely a slow low-temperature oxidation stage, a rapid oxidation stage, and a steady increase stage. However, unlike coal, alkane and alkene gases produced by oil shale underwent four stages. They all had a concentration reduction stage with the maximum drop of 24.20%. Statistical classification of inflection temperature of various gases as their concentrations change showed that the temperature of 140 °C is the key temperature for group reactions, and above the temperature of 140 °C, all alkane and alkene gases underwent the rapid concentration increase stage

Thermodynamic investigation on para-alkyl chain-substituted phenylbicyclohexyl-type liquid crystals with difluorooxymethylene bridge

We report the results of the study of thermodynamic properties for two difluorooxymethylene-bridged fluorinated liquid crystals. Isobaric heat capacities of the compounds were measured using a Quantum Design Physical Properties Measurement System with heat capacity measurement in the range of 1.9-300 K. Heat capacities of two compounds increased with the temperature increment, and no any thermal anomalies were observed in the whole temperature region, and also the heat capacity values of 5-CCXB(F,F)-F are larger than that of 3-CCXB(F,F)-F due to molecular weight difference even though they are homologs. Standard thermodynamic properties of the liquid crystals were evaluated from the experimental heat capacity temperature dependencies. From the heat capacity results, the standard molar entropies and enthalpies at 298.15 K were determined to be (657.32 +/- 6.57), (741.81 +/- 7.42) J K-1 mol(-1) and (97.17 +/- 0.97), (108.89 +/- 1.09) kJ K-1 mol(-1) for n-CCXB(F,F)-F (n = 3, 5), respectively. Finally, the phase transition sequences and thermodynamical stability of these two fluorinated liquid crystals were performed by differential scanning calorimetry measurements in the temperature range of 253-373 K

Robust Relay in Narrow-Band Communications for Ubiquitous IoT Access

We propose a robust wireless relay scheme in narrow-band communications for IoT access, which matches the typical features of IoT often carrying relatively low data rate with limited bandwidth. This framework is towards offering robustness in QoS guarantees with emphases on security and/or reliability, and we use the security-assured network as the typical scenario. In particular, we consider a dual-hop relay network including a transmitter, a receiver, an amplify-and-forward (AF) untrusted relay, and a jamming node. The jamming node is treated as a helper. Specifically, the jammer broadcasts artificial noise (AN), which in fact pollutes both the untrusted relay and the destination node’s signals. However, we show that such AN can be effectively mitigated after the destination node obtains the forwarded signal from the relay, while the untrusted relay node cannot do so. The core idea for robustness assurance is to exploit higher signal dimensions at the receiver over the untrusted relay node. Simulations and analyses are also conducted to demonstrate that our proposed scheme can make the performance at the untrusted relay an interference-limited manner while completely removing the interferences at the receiver, therefore corroborating our claim in robustness in terms of security and reliability

Sheet Stamping Formability Test System based Servo Crank Press

AbstractProposed the tentative plan that carries on the formability test by simulation practical crank punch press slide speed characteristic, designed the solution to the implementation difficulty, and has carried on the actual attempt. The servo motor drive crank press speed alters at more sects which can get slider speed characteristic coherent with crank press varies. The system can test varies stamping formability that speed changeable based on sine curve. The system is composed of 600kN servo crank press, double action and all-purpose moldbase, date get and inspect analyze system. The moldbase adopted positive direction structural and self-motion, with variable blank holder force and counterforce controlled by hydraulic system with closed loop. The blank holder force can be set up in 5 sects which following with slide position, shortest control sect in 200ms. Appropriate profile of blank holder force can setup with the process needed. Blank holder has quartz force sensor which can inspect blank holder force and the control precision is in 0.1kN

Specific-Ion Effects Directed Noble Metal Aerogels: Versatile Manipulation for Electrocatalysis and Beyond

Noble metal foams (NMFs) are a new class of functional porous materials featuring properties of both noble metals and monolithic porous materials, providing impressive prospects in catalysis, bio-sensing, plasmonic technologies, etc...Among reported synthetic methods to date, the sol-gel approach manifests overwhelming advantages for versatile synthesis of controlled nanostructured NMFs under mild condition. However, limited gelation methods and insufficient understanding of the underlying mechanism retards structure/composition manipulation of NMFs, hampering ondemand designing for practical applications. Herein highly tunable NMFs are fabricated at room temperature by activating specific-ion effects and regulating ion-nanoparticle interactions, affording various single/alloy NMFs with adjustable compositions (Au, Ag, Pd, Pt), ligament sizes (3.1~142.0 nm), and special morphologies. Their superior performance in programmable self-propulsion devices and electrocatalytic alcohol oxidation are demonstrated. This study provides not only a conceptually new route to fabricate and manipulate functional NMFs, but also an overall picture in understanding the gelation mechanism. It may pave the way for on-target designing versatile NMFs for various applications.</div