Current Issue : January - March Volume : 2019 Issue Number : 1 Articles : 5 Articles
The objective of this study is to design a broadband and wide-angle emitter based\non metamaterials with a cut-off wavelength of 2.1 â?¦m to improve the spectral efficiency of\nthermophotovoltaic emitters. To obtain broadband emission, we conducted the geometric parameter\noptimization of the number of stacked layers, the inner and outer radii of the nano-rings,\nand the thickness of the nano-rings. The numerical simulation results showed that the proposed\nemitter had an average emissivity of 0.97 within the targeted wavelength, which ranged from 0.2 â?¦m to\n2.1..m. In addition, the presented multilayer nano-ring emitter obtained 79.6% spectral efficiency with\nan InGaAs band gap of 0.6 eV at 1400 K....
The improvement of ferromagnetic properties is critical for the practical application of\nmultiferroic materials, to be exact, BiFeO3 (BFO). Herein, we have investigated the evolution in\nthe structure and morphology of Ho or/and Mn-doped thin films and the related diversification\nin ferromagnetic behavior. BFO, Bi0.95Ho0.05FeO3 (BHFO), BiFe0.95Mn0.05O3 (BFMO) and\nBi0.95Ho0.05Fe0.95Mn0.05O3 (BHFMO) thin films are synthesized via the conventional sol-gel method.\nDensity, size and phase structure are crucial to optimize the ferromagnetic properties. Specifically,\nunder the applied magnetic field of 10 kOe, BHFO and BFMO thin films can produce obvious\nmagnetic properties during magnetization and, additionally, doping with Ho and Mn (BHFMO) can\nachieve better magnetic properties. This enhancement is attributed to the lattice distortions caused by\nthe ionic sizes difference between the doping agent and the host, the generation of the new exchange\ninteractions and the inhibition of the antiferromagnetic spiral modulated spin structure. This study\nprovides key insights of understanding the tunable ferromagnetic properties of co-doped BFO....
In the exploration of new energy sources and the search for a path to sustainable\ndevelopment the reliable operation of wind turbines is of great importance to the stability of\npower systems. To ensure the stable and reliable operation of the Insulated Gate Bipolar Transistor\n(IGBT) power module, in this work the influence of changes with aging of different electro-thermal\nparameters on the junction temperature and the case temperature was studied. Firstly, power thermal\ncycling tests were performed on the IGBT power module, and the I-V characteristic curve, switching\nloss and transient thermal impedance are recorded every 1000 power cycles, and then the electrical\nparameters (saturation voltage drop and switching loss) and the thermal parameters (junction-to-case\nthermal resistance) of the IGBT are obtained under different aging states. The obtained electro-thermal\nparameters are substituted into the established electro-thermal coupling model to obtain the junction\ntemperature and the case temperature under different aging states. The degrees of influence of\nthese electro-thermal parameters on the junction temperature and case temperature under different\naging states are analyzed by the single variable method. The results show that the changes of the\nelectro-thermal parameters under different aging states affects the junction temperature and the case\ntemperature as follows: (1) Compared with other parameters, the transient thermal impedance has the\ngreatest influence on the junction temperature, which is 60.1%. (2) Compared with other parameters,\nthe switching loss has the greatest influence on the case temperature, which is 79.8%. The result\nprovides a novel method for the junction temperature calculation model and lays a foundation\nfor evaluating the aging state by using the case temperature, which has important theoretical and\npractical significance for the stable operation of power electronic systems....
In this work, we show the performance improvement of p-type thin-film transistors\n(tfts) with ge2 sb2Te5 (gst) semiconductor layers on flexible polyimide substrates, achieved by\ndownscaling of the gst thickness. Prior works on gst tft s have typically shown poor current\nmodulation capabilities with on/off ratiosâ?¦ and non-saturating output characteristics.\nby reducing the gst thickness to 5 nm, we achieve on/off ratios up to and a channel\npinch-off leading to drain current saturation. We compare the gst tfts in their amorphous (as\ndeposited) state and in their crystalline (annealed atâ?¦) state. The highest effective field-effect\nmobility of 6.7 cm2/Vs is achieved for 10-nm-thick crystalline gst tfts, which have an on/off\nratio ofâ?¦ The highest effective field-effect mobility in amorphous gst tfts is 0.04 cm2/Vs, which is obtained in devices with a gst thickness of 5 nm. The devices remain fully operational upon bending to a radius of 6 mm. Furthermore, we find that the tfts with amorphous channels are more sensitive to bias stress than the ones with crystallized channels. These results show that gst semiconductors are compatible with flexible electronics technology, where high-performance p-type tfts are strongly needed for the realization of hybrid complementary metal-oxide-semiconductor (cmos) technology in conjunction with popular n-type oxide semiconductor materials....
We study the dependence of the superconducting gaps on both the disorder and the\ntemperature within the two-band model for iron-based materials. In the clean limit, the system is in\nthe sâ?¦ state with sign-changing gaps. Scattering by nonmagnetic impurities leads to the change of the\nsign of the smaller gap, resulting in a transition from the sâ?¦ to the sâ?¦ state with the sign-preserving\ngaps. We show here that the transition is temperature-dependent. Thus, there is a line of sâ?¦\ntransition in the temperatureâ??disorder phase diagram. There is a narrow range of impurity scattering\nrates, where the disorder-induced sâ?¦ transition occurs at low temperatures, but then the\nlow-temperature sâ?¦ state transforms back to the sâ?¦state at higher temperatures. With increasing\nimpurity scattering rate, the temperature of such â?¦ sâ?¦ transition shifts to the critical temperature\ntc, and only the sâ?¦ state is left for higher amounts of disorder....
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