We have studied the chemistry of the molecular gas in evolved planetary nebulae. Three pseudo‐time‐dependent gas‐phase models have been constructed for dense (104–105 cm−3) and cool (T∼15 K) clumpy envelopes of the evolved nebulae NGC 6781, M4‐9 and NGC 7293. The three nebulae are modelled as carbon‐rich stars evolved from the asymptotic giant branch to the late planetary nebula phase. The clumpy neutral envelopes are subjected to ultraviolet radiation from the central star and X‐rays that enhance the rate of ionization in the clumps. With the ionization rate enhanced by four orders of magnitude over that of the ISM, we find that resultant abundances of the species HCN, HNC, HC3N and SiC2 are in good agreement with observations, while those of CN, HCO+, CS and SiO are in rough agreement. The results indicate that molecular species such as CH, CH2, CH2+, HCl, OH and H2O are anticipated to be highly abundant in these objects.
A microstrip patch antenna on Low Temperature Co-fired Ceramic (LTCC) substrate operating at 350GHzfor THz communication has been designed. CST MWS package has been used for simulation and S 11 reached a minimum of -25.6dB at 349GHz with 8.6% bandwidth. The maximum gain achieved is 5dBi. Furthermore, a prototype for a downscaled antenna designed at 10GHz with available FR4 substrate has been fabricated and measured.
One of the fundamental objectives for research and development of space solar cells is to improve their radiation resistance. InGaP solar cells with low base carrier concentrations under low-energy proton irradiations have shown high radiation resistances. In this study, an analytical model for low-energy proton radiation damage to InGaP subcells based on a fundamental approach for radiative and nonradiative recombinations has been proposed. The radiation resistance of InGaP subcells as a function of base carrier concentration has been analyzed by using the radiative recombination lifetime and damage coefficient K for the minority-carrier lifetime of InGaP. Numerical analysis shows that an InGaP solar cell with a lower base carrier concentration is more radiation-resistant. Satisfactory agreements between analytical and experimental results have been obtained, and these results show the validity of the analytical procedure. The damage coefficients for minority-carrier diffusion length and carrier removal rate with low-energy proton irradiations have been observed to be dependent on carrier concentration through this study. As physical mechanisms behind the difference observed between the radiation-resistant properties of various base doping concentrations, two mechanisms, namely, the effect of a depletion layer as a carrier collection layer and generation of the impurity-related complex defects due to low-energy protons stopping within the active region, have been proposed.
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