Sensitivity of Extreme Temperature Events to Urbanization in the Pearl River Delta Region

Zhixiang Xiao,Ziqian Wang,Weijuan Pan,Yongli Wang,Song Yang 한국기상학회 2019 Asia-Pacific Journal of Atmospheric Sciences Vol.55 No.3

The urbanization effect on extreme temperature related to heat wave events in the Pearl River Delta (PRD) of China is investigated using a regional model. Several experiments with different urbanization levels are carried out. Results indicate that the air temperature of heat wave events is sensitive to urban land cover and the urbanized warming intensifies along with urban expansion. The regional model performs better on the simulations of maximum and minimum 2-m air temperature when urban land cover is close to the observed value. Because of the urbanization effect, the surface skin temperature shows a maximum warming (~2.5 °C) at daytime, while the maximum warming of 2-m air temperature (~1.5 °C) occurs at nighttime. Consequently, an increased (a decreased) diurnal range in surface skin temperature (2-m air temperature) is induced. According to the diagnostic equations, the 2-m air temperature is not only related to surface skin temperature, but also regulated by surface sensible heat flux. At daytime, although the increased solar absorption and the decreased upward latent heat flux (due to the deficit of surface evaporation) sharply enhance the surface skin temperature in the higher urbanization experiment, the simultaneously increased sensible heat flux suppresses the 2-m air temperature. At nighttime, however, the difference in surface sensible heat flux is relatively small, thus 2-m air temperature largely depends on surface skin temperature influenced by ground heat release. This study emphasizes the different variations and physical mechanisms of surface skin temperature and 2-m air temperature under the urbanization in the PRD region.

A Comparative Study on the Offshore Intensification of Supertyphoon Rammasun (2014) and Typhoon Rumbia (2013): the Role of Summer Monsoon

Zhixiang Xiao,Cai Yao,Xiaoli Luo,Hongmei Sun 한국기상학회 2021 Asia-Pacific Journal of Atmospheric Sciences Vol.57 No.3

The offshore intensificationmechanisms of Supertyphoon Rammasun (2014) and Typhoon Rumbia (2013) are analyzed and compared based on the best track typhoon data provided by the Shanghai Typhoon Institute of China Meteorological Administration (STI/CMA), ECMWF (CMA and JMA) objective (subjective) predicted typhoon track and intensity, and reanalysis data of the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). Results show that the offshore sea surface temperature over 28 °C was conducive to the intensification of the two typhoons in the coastal area prior to their landfall in South China. Rammasun was embedded in an extremely active phase of a 10–20-day oscillation in the summer monsoon over the South China Sea and western North Pacific prior to its landfall. The low-level jet transported warm and moist air to the inner core of Rammasun and the deepening of the southwesterly monsoon flow up to 200 hPa reduced vertical wind shear, both favorable for the offshore rapid intensification of Rammasun. In 2013, the summer monsoon over the South China Sea and western North Pacific experienced quasi-20-day and quasi-10-day oscillations. The out of phase of the two oscillations resulted in relatively weak tropical and subtropical summer monsoon flow prior to the landfall of Rumbia. As a result, the low-level monsoon flow transported relatively less moist air into Rumbia, and the shallow monsoon flow was not conducive to the weakening of vertical wind shear, resulting in a less rapid offshore intensification of Rumbia than Rammasun.

Global Attractivity and Oscillations in a Nonlinear Impulsive Parabolic Equation with Delay

Wang, Xiao,Li, Zhixiang Department of Mathematics 2008 Kyungpook mathematical journal Vol.48 No.4

Global attractivity and oscillatory behavior of the following nonlinear impulsive parabolic differential equation which is a general form of many population models $$\array{\{{{\frac {{\partial}u(t,x)}{{\partial}t}=\Delta}u(t,x)-{\delta}u(t,x)+f(u(t-\tau,x)),\;t{\neq}t_k,\\u(t^+_k,x)-u(t_k,x)=g_k(u(t_k,x)),\;k{\in}I_\infty,}\;\;\;\;\;\;\;\;(*)$$ are considered. Some new sufficient conditions for global attractivity and oscillation of the solutions of (*) with Neumann boundary condition are established. These results no only are true but also improve and complement existing results for (*) without diffusion or impulses. Moreover, when these results are applied to the Nicholson's blowflies model and the model of Hematopoiesis, some new results are obtained.

Research on influence of harmonic wear wheel on wheel/rail contact geometry of high-speed train

Qian Xiao,Zhixiang Luo,Xu Xu,Jifeng Zheng,Shu Cheng 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.2

Harmonic wear is one of the common wear phenomena of high-speed train wheels. The change of wheel/rail rolling contact geometry leads to unstable characteristics of wheel/rail contact, which directly affects the quality and safety of high-speed train operation. Because wheelset lateral displacement directly affected the wheel/rail contact geometry, in this paper, the UM software was used to establish a high-speed train vehicle-track coupled dynamics simulation model of the CRH2 (China Railway High-speed 2) head car. Lateral displacement of harmonic wear wheel was calculated under different wear condition to analyze the influence of harmonic wear wheels on wheelset lateral displacement. Then according to macroscopic dimension change of the wheel profile from lateral and radial directions of high-speed train induced by harmonic wear wheels, wheel profiles under different wear condition were selected. And wheel/rail contact geometry under different harmonic wear stages was calculated to discuss the influence of harmonic wear wheel on wheel/rail contact geometry. The results show that harmonic order and wave depth of harmonic wear wheel have small influence on the lateral displacement of wheelset, but the influence of wave depth is greater than harmonic order. The average difference of lateral displacement between harmonic wear wheel and no harmonic wear wheel increases with the increase of wave depth and order. In a harmonic wave length, the maximum value of both equivalent conicity and contact angle appear in deepest wave depth. The greater the wave depth, the more obvious the fluctuations, and equivalent conicity changes are less obvious.

Application of the sheet electrode to enhance the geometric characteristics of micro-holes fabricated by electrochemical discharge machining

Zhongning Guo,Shunzhi Qiao,Liangliang Wang,Kai Zhang,Yingjie Xiao,Zhixiang Zou 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.11

The electrochemical discharge machining (ECDM) is an advanced machining technology used to fabricate micro-holes in glass. In this study, a sheet tool electrode is employed to increase electrolyte circulation in machining zone. The effect of pulse voltage, frequency, duty cycle, electrolyte concentration, and tool rotation speed on the geometric properties of micro-holes were evaluated. The results showed that when using a sheet tool electrode, the machining depth increased by 42.9 %, and the machining efficiency increased by 51.1 %, while the entrance diameter was reduced by 13.9 % than cylindrical tool electrode. Additionally, the heat-affected zone (HAZ) and entrance hole surface quality is improved. On the other hand, the Taguchi method was employed to analyze the relative importance of the machining parameters on geometric characteristics of micro-holes (i.e. drilled depth and entrance diameter of micro-holes). Finally, the entrance hole overcut of 148 μm was successfully fabricated with a depth of 2520 μm. It was discovered that using a sheet tool electrode is a simple method for machining a deep micro-hole with high machining efficiency and a range entrance hole diameter overcut that is acceptable.