To resolve the problem of grain coarsening occurring in the fusion zone and the heat-affected zone during conventional gas tungsten arc welding(C-GTAW) welded titanium alloy, which severely restricts the improvement of weld mechanical properties, welding experiments on Ti-6Al-4V titanium alloy by adopting ultra-high frequency pulse gas tungsten arc welding (UHFP-GTAW) technique were carried out to study arc characteristics and weld bead microstructure. Combined with image processing technique, arc shapes during welding process were observed by high-speed camera. Meanwhile the average arc pressure under various welding parameters were obtained by adopting pressure measuring equipment with high-precision. In addition, the metallographic samples of the weld cross section were prepared for observing weld bead geometry and microstructure of the fusion zone. The experimental results show that, compared with C-GTAW, UHFP-GTAW process provides larger arc energy density and higher proportion of arc core region to the whole arc area. Moreover, UHFP-GTAW process has the obviously effect on grain refinement, which can decrease the grain size of the fusion zone. The results also revealed that a significant increase of arc pressure while increasing pulse frequency of UHFP-GTAW, which could improve the depth-to-width ratio of weld beads.

Most of the currently existed settling time design methods for the Miller-compensated two-stage operational amplifiers are based on the approximate analytical model and can obtain only inaccurate results. This paper presents an approach for the exact settling time design for this widely used circuit. By the compensation of the errors in the analytical settling behavior model and executing the conventional design procedure repeatedly, an iterative design scheme is developed. The overall errors are removed by the exact performance computation with the SPICE simulation and the accurate MOS model based sizing in the entire design process. Taking advantage of the fast convergence and precision feature of this method, an efficient process variation-aware design algorithm is further presented. Simulated design results for the amplifiers in 0.18 lm and 90 nm technology are provided to illustrate the effectiveness of the proposed method.

Near-wall microenvironment of a building refers to parameters such as wind speed, temperature, relative humidity, solar radiation near the building’s façade, etc. The distribution of these parameters on the building façade shows a certain variation based on changes in height. As a technology of passive heating and ventilation, the effectiveness of this application on heat collection wall is significantly affected by the near-wall microclimate, which is manifested by the differences, and rules of the thermal process of the components present at different elevations. To explore the feasibility and specificity of this application of heat collection wall in high-rise buildings, this study uses three typical high-rise buildings from Zhengzhou, China, as research buildings. Periodic measurements of the near-wall microclimate during winter and summer were carried out, and the changing rules of vertical and horizontal microclimate were discussed in detail. Later, by combining these measured data with numerical method, thermal process and performance of heat collection wall based on increasing altitude were quantitatively analyzed through numerical calculations, and the optimum scheme for heat collection wall components was summarized to provide a theoretical basis for the structural design of heat-collecting wall in high-rise buildings.

Ultra-high-frequency pulse modulation is an innovative and effective means of arc regulation. However, the application of this technique in gas tungsten arc welding (GTAW) faces several problems. To solve these problems, this paper selects a main circuit topology for the welding power sources, and designs a dual processor digital control system, in which the pulse width modulation (PWM) signals are generated collaboratively by a digital signal processor (DSP) and a complex programmable logic device (CPLD). Through simulations and experiments, it is learned that our control system could output ultra-high pulsed GTAW current of over 100A, and realize a fast current conversion rate. Besides, multiple welding modes could be realized easily without changing the system design or electrical connection. The proposed control system effectively automates ultrahigh-frequency pulsed gas tungsten arc welding (UHFP-GTAW), and promotes the engineering application of ultra-high-frequency pulse modulation.

The Ultra Wide band (UWB) antennas play an important role in UWB system. As a crucial component of the UWB system, the UWB antennas affect performance of the system significantly and have advantages of low profile, low power consumption and integration easily, so they are widely used in communication systems. The Federal Communication Commission (FCC) authorized the unlicensed use of the UWB (3.1GHz~10.6 GHz) in February 2002. This dissertation firstly gives a brief introduction on the development history and research status of UWB antenna. Secondly, the main performance parameters, the method and the performance of the UWB antenna are analyzed in detail. Combined with these characteristics of UWB system, this paper provides the design requirements of ultra-wide band antenna. Then, based on the above research and analysis, the author designs an ultra-wide band antenna structure by using CST MWS simulation software, and realizes the WLAN band notched performance by loading structure. Finally the author comes to the conclusion.