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This paper proposes an optimal dynamic supply of parking permits under uncertainties in the mixed traffic environment of regular vehicles (RVs) and autonomous vehicles (AVs). The uncertainties from queuing delay and cruising-for-parking time, respectively, are derived from parking permit holders’ unascertainable early arrival/late departure and the randomness of vehicle speed for cruising-for-parking users. We formulate the dynamic system optimum as a stochastic optimal control problem, aiming to minimize the total time lost for all parking users. On this basis, we express the optimality condition as Hamilton-Jacobi-Bellman equation and propose an optimal control strategy for dynamic supply of parking permits (called optimal parking supply scheme). The proposed scheme is determined by two observable and measurable variables, i.e., queuing time and cruising-for-parking time. We find that the scheme can significantly reduce the total system time lost, especially when the uncertainty from parking permit holders is at a high level or the percentage of AVs is small. Finally, a case study of a selected sample area in Beijing is conducted, which verifies the efficiency of the proposed scheme numerically. [ABSTRACT FROM AUTHOR]

Cr/Al/Ti/Au stacks with two thicknesses of Al layers were employed as reflective n-type electrodes for 274 nm AlGaN-based flip-chip deep ultraviolet light-emitting diodes (DUV LEDs). Large bulges arose in the annealed n-type electrode with 120-nm-thick Al layer, resulting in cracks within the upper rugged SiO2 passivation layer after burn-in test. Sn atoms from solder paste migrated along the cracks and served as leakage current channels, which accelerated device degradation. In contrast, the annealed n-type electrode with 60-nm-thick Al layer retained uniform morphology. And the DUV LEDs with such n-type electrode exhibited good reliability and normalized optical power of 86.8% after burn-in test of 1000 h. This study provides insight into electrode defects related degradation behavior and helps to improve the reliability of AlGaN-based flip-chip DUV LEDs with reflective electrode. [ABSTRACT FROM AUTHOR]

In this article, we developed a color converter of phosphor–AlN–sapphire (PAS) plate to enhance the heat dissipation of phosphor film in high-power white light-emitting diodes (WLEDs). The improved heat dissipation performance is observed by introducing the AlN film with high thermal conductivity (TC), which was demonstrated by finite-element analysis (FEA) simulation. The proposed PAS plate was prepared by printing and sintering a yellow phosphor film on an AlN-coated sapphire plate. It is observed that the TC of the AlN-coated sapphire plate is increased with the reduction of the threading dislocation (TD) density of the AlN film. High TD density decreases TC by causing strong scattering of heat transfer phonons. The thermal and optical characteristics of the converters were further measured after this structure was used for packaging WLEDs as a remote phosphor configuration. Notably, the surface temperature of the PAS converter with the highest TC is reduced by nearly 23 °C and the luminous efficiency (LE) is increased by 17% at the current of 900 mA compared with the converter without AlN film coated. It is believed that the PAS plate is an effective converter to improve the heat dissipation of the phosphor layer and optical properties of high-power WLEDs. [ABSTRACT FROM AUTHOR]

Currently, white light-emitting diodes (WLEDs) have been widely applied in lighting, display, and medical fields. However, there still exists the problem of low color rendering index (CRI, Ra). In this work, phosphor-converted WLEDs (pc-WLEDs) with ultrahigh Ra were fabricated using Y3Al2Ga2O12:Ce3+ green phosphor and CaAlSiN3:Eu2+ red phosphor configuration structure. The broad emission spectrum of the green phosphor compensates for the gap of the cyan-emitting region that realizes full-spectrum white-light emission. The weight ratio of green/red phosphors was controlled to optimize the optical performances of pc-WLEDs. At the ratio of 0.15/0.012, the fabricated pc-WLED exhibits a natural white light with an ultrahigh Ra of 95.2 and an incredibly small International Commission on Illumination (CIE) chromaticity coordinates deviation (Duv = −0.0034) at 350 mA. The corresponding correlated color temperature (CCT) and luminous efficiency (LE) are 4526 K and 62.34 lm/W, respectively. Furthermore, two separated phosphor configuration structures were constructed for pc-WLEDs. The R up/G down structure achieves the highest LE of 64.93 lm/W, and the corresponding CCT and Ra are 5714 K and 95.8, respectively, chiefly due to the compensation for reabsorption effect caused by the large difference in the luminous efficacy of radiation (LER) between dichromatic phosphors. The results demonstrate that by adjusting the phosphor configuration structure, the pc-WLEDs with high color rendering can be obtained, which have great applications in high-quality lighting. [ABSTRACT FROM AUTHOR]