ABSTRACT
Mn4+-activated fluoride red phosphors exhibit excellent luminescence properties. However, a persistent technical challenge lies in their poor moisture resistance. Current strategies primarily focus on surface modifications to effectively shield the [MnF6]2- species from water molecules while neglecting the underlying structure of the fluoride matrix. In this study, we introduce Si4+ and Ge4+ ions into the K2TiF6:Mn4+ crystal to create covalent fluoride solid solutions, namely, K2Ti1-xSixF6:Mn4+ and K2Ti1-yGeyF6:Mn4+, through crystal reconstruction. The findings reveal that the incorporation of Si4+ leads to increased particle size, enhanced luminescence intensity (by 40%), and improved moisture resistance. Furthermore, after undergoing 1000 h of aging at high temperature and high humidity conditions, the white LED featuring the K2Ti0.97Si0.03F6:Mn4+ phosphor demonstrates remarkable durability by retaining 90% of its initial luminous efficacy. This performance surpasses that of the device utilizing the K2TiF6:Mn4+ phosphor, which only retains 74% of its original efficacy. The crystal reconstruction method and covalent enhancement strategy proposed in this work contribute to enhancing the luminescence efficiency and moisture resistance of fluoride phosphors, thereby offering new insights for advancing the development of high-efficiency and highly stable white light LED devices.
ABSTRACT
The optical compensation method is a promising method to compensate the image motion by driving the optical element of the system. However, the tilt motion of the optical element could induce the degradation of the image quality. Based on the Nodal Aberration Theory (NAT), this paper proposes a novel optical image motion compensation design with a secondary tilt-aplanatic two-mirror optical system (STATOS), which achieves the insensitivity on the image quality of the optical system. First, the properties of coma-free pivot point depending on the location of stop at primary mirror or secondary mirror have been analyzed respectively. Then the calculating method about construction parameters in terms of STATOS is developed. Further, the maximum tilt angle of secondary mirror could be solved using NAT under ordered specific restriction. Finally, a prototype is designed with SM-tilting result of MTF value maintain above 0.32 at the cut-off frequency of detector, where the principal distance could remain stable and the changed distortion is better than 0.03%. A test flight has been carried out to prove the desired results and feasibility of STATOS used in an aerial mapping camera.
ABSTRACT
In order to meet the accuracy requirements of target geo-location of a wide-area reconnaissance camera, it is necessary to calibrate the extrinsic parameters of the camera. A novel calibration method is proposed for the orientation relationship between the camera coordinate system (CCS) and the frame coordinate system (FCS). First, the calibration between the roll axis of the FCS and the CCS is carried out based on the method of the extended Kalman filter. Second, the calibration between the pitch axis of the FCS and the CCS is deduced based on the least mean square combined with the particle swarm optimization method. Then, the calibration accuracy of the proposed method is quantitatively analyzed by numerical simulation. Finally, a calibration experiment is conducted on verifying the effectiveness of the method.
ABSTRACT
In order to improve the performance in the practical engineering applications including so called low-speed video tracking and large-angle swing scanning imaging at the same time for a three-axis universal inertially stabilized platform (UISP), we propose an adaptive nonsingular fast terminal sliding mode control (ANFTSMC) strategy subjected to the uncertain disturbances and input saturation constraints. First of all, a second-order dynamic model is established with uncertain disturbances and input saturation constraints. Secondly, a nonsingular fast terminal sliding mode controller (NTSMC) is constructed to ensure the system error converges to zero fast in a finite time; meanwhile, a novel reaching law based on a modified normal distribution function is designed to adjust the control gain. Thirdly, an adaptive control law is designed to online estimate the parameters of the lumped uncertain disturbances. Additionally, the stability of the control system is proved by Lyapunov theory. Finally, extensive comparative simulations and experiments are carried out, the results comprehensively show the effectiveness and superiority of the proposed control method, which can accelerate convergence, weaken the chattering, and has the better control accuracy and robust performance both in the low-speed tracking and large-angle swing scanning applications. Moreover, the exact dynamic model and the prior knowledge of the upper bounds of the disturbances are not required during the procedure of the controller design, which make it have more extensive application value in practical engineering.
ABSTRACT
OBJECTIVE: To explore the effects of recombinant human Elafin gene transfection on lipopolysaccharide (LPS)-induced airway mucous hypersecretion. METHODS: An eukaryotic expression vector pEGFP-C1-Elafin was first constructed and then transfected into NCI-H292 cell. After co-incubation with polymorphonuclear granulocyte (PMN) plus LPS stimulation for 24 hour, the vital force unit of neutrophil elastase (NE) and the content of mucin (MUC) protein in culture media and the level of MUC 5AC mRNA in culture cells were detected with substrate detection technique, enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR) respectively. RESULTS: All parameters in control group showed a low level (0.13 ± 0.03, 0.28 ± 0.06, 0.29 ± 0.04 respectively). And transfecting NCI-H292 cell with pEGFP-C1 at different levels of LPS, all parameters were obviously different (all P < 0.01) and they all showed a dose-dependent relationship. After LPS stimulation (0.5, 5 mg/L), as compared with the transfection of NCI-H292 cell with pEGFP-C1-Elafin, the vital force unit of NE and the content of MUC5AC protein in culture media and the level of MUC 5AC mRNA in transfecting pEGFP-C1 NCI-H292 cell decreased obviously (all P < 0.05). But after LPS stimulation (25 mg/L), as compared with the transfection of NCI-H292 cell with pEGFP-C1-Elafin, no parameter of transfecting pEGFP-C1 NCI-H292 cell had any obvious alteration (0.67 ± 0.06, 0.64 ± 0.08, 0.67 ± 0.07 respectively, all P > 0.05). CONCLUSION: The transfection of recombinant human elafin gene into NCI-H292 cell may inhibit the force of inflammatory telo-effective factor NE induced by a certain level of LPS and airway mucous hypersecretion. But it can not inhibit the effects induced by a high level of LPS.
