No abstract

In this study, the junction temperature (Tj) and thermal resistance (Rth) of five high-power multi-chip COB (chip-on-board) LED packages with different chip spacings were compared. The actual Tjwas measured by an IR camera and compared with the simulation results from a computational fluid dynamics (CFD) software. In addition, the effects of heat slugs with different thermal conductivity, heat sinks of various thicknesses, chip size, and forced convection cooling on the Tjand Rthof high-powered LED components were investigated. The experimental results show that smaller chip spacing resulted in higher Tjand Rth. The heat dissipation performance can be improved by using a heat slug with a high thermal conductivity; and increasing the thickness of the heat sink, or employing forced convection cooling.

With the rapid development of wireless network technology, wireless networks have been widely used in many fields due to the flexibility of wireless access. However, in the field of video transmission, because the link state is instability and the transmission is easily interfered in wireless networks, the quality of video transmission is affected badly. In fading and shadowing channels, some users can’t watch the video normally. This paper provides an adaptive QoS solution of real-time video stream in wireless network, by adding a relay server it can provide multicast or unicast video stream satisfying multiple QoS for users with different network state. This solution has been successfully applied in Qingdao Public safety emergency video surveillance system.

Defects of components as a result of entrapped gases during an injection process could be minimized with the utilization of a gas-permeable metal die material in the mold, due to its excellent permeability of air. Conventional gas-permeable die materials employ low temperature sintering of loosely packed steel powders with or without the addition of pore-forming polymers, whose microstructures are usually weak and their gas permeability values are also low. In this study, gas-permeable metal die materials are developed using tool steel powder, packed in a mold having the insertion of orthogonally arrayed polymer wires. Linear gas-permeable channels in orthogonal array are thus developed by the burning out of the polymer wires, which yield a large value of air permeability. The value of air permeability can be adjusted by changing the diameter and number density of the polymer wires. The tool steel powder can be made fully dense by supersolidus liquid phase sintering, yielding a microstructure with a wear resistance value much larger than that of the conventional gas-permeable die material.

Tungsten heavy alloys with different ratios of Mo and Ni-Fe matrix were liquid-phasesintered to investigate their microstructural evolution. Specimens were sintered at 1500 for 240 minutes and then were either furnace-cooled or water-quenched. The microstructures of the sintered specimens were examined employing SEM, EMPA, DTA, XRD and TEM. Results indicated that increased Mo in the alloy promoted the formation of a (W,Mo)(Ni,Fe) type intermetallic compound in the furnace-cooled condition. It was a monoeutectic reaction when the added Mo content was higher than 49at.%, or a eutectic reaction when this value was between 37at.% to 49at.%. When Mo was added between 25at.% to 37at.%, the precipitation of the intermetallic compound took place by either a eutectoid or peritectoid reaction. No intermetallic compound was found for the Mo adding level being lower than 15at.%. In the water-quenched condition, a lamellar structure with a thickness around 100nm to 200nm was observed in the specimen whose Mo addition was over 27at.%. The lamellar structure was very tiny and uniformly dispersed in the matrix, which could be a reinforcing phase for the matrix phase.