Sensitivity of Tropical Cyclone Intensity and Structure to Vertical Resolution in WRF

Zhanhong Ma,Jianfang Fei,Xiaogang Huang,Xiaoping Cheng 한국기상학회 2012 Asia-Pacific Journal of Atmospheric Sciences Vol.48 No.1

In this paper the impacts of vertical resolution on the simulations of Typhoon Talim (2005) are examined using the Weather Research and Forecasting (WRF) model, with cumulus parameterization scheme representing the cumulus convection implicitly. It is shown that the tropical cyclone (TC) track has little sensitivity to vertical resolution, whereas the TC intensity and structure are highly sensitive to vertical resolution. It is partly determined by the sensitivity of the planetary boundary layer (and the surface layer) and the cumulus convection processes to vertical resolution. Increasing vertical resolution in the lower layer could strengthen the TC effectively. Increasing vertical resolution in the upper layer is also beneficial for the storm intensification, but to a lesser degree. In contrast, improving the midlevel resolution may cause the convergence of environmental air,which inhibits the TC intensification. The results also show that the impacts of vertical resolution on features of the TC structure, such as the tangential winds, secondary circulations and the evolution of the warm-core structure, are consistent with the impacts on the TC intensity. It is suggested that in the simulations of TCs, the vertical levels should be distributed properly rather than the more the better,with higher vertical resolution being expected both in the lower and upper layer, while the middle layer should not hold too many levels.

Construction of Recombinant Corynebacterium glutamicum for L-threonine Production

Yangyong Lv,Zhanhong Wu,Shuangyan Han,Ying Lin,Suiping Zheng 한국생물공학회 2012 Biotechnology and Bioprocess Engineering Vol.17 No.1

L-threonine is an essential amino acid which is widely used in feed and pharmaceutical industries. We recently engineered Corynebacterium glutamicum R102(AHVr) for improved production of L-threonine. Inactivation of genes metX and dapA encoding dihydrodipicolinate synthase and homoserine O-acetyltransferase, respectively,was firstly conducted by homologous recombination, which differed from the common random mutagenesis method. Then operon gene hom-thrB (O) and export gene thrE (E)from R102 were over-expressed alone or together to obtain a series of recombinant strains. qPCR was employed to evaluate the transcript quantification of the target genes. In flask fermentation, the newly constructed strain R102ΔmetXΔdapA (pEC-Box) was able to accumulate 3.35 g threonine/L compared with 1.80 g threonine/L of strain R102 (AHVr). L-threonine is an essential amino acid which is widely used in feed and pharmaceutical industries. We recently engineered Corynebacterium glutamicum R102(AHVr) for improved production of L-threonine. Inactivation of genes metX and dapA encoding dihydrodipicolinate synthase and homoserine O-acetyltransferase, respectively,was firstly conducted by homologous recombination, which differed from the common random mutagenesis method. Then operon gene hom-thrB (O) and export gene thrE (E)from R102 were over-expressed alone or together to obtain a series of recombinant strains. qPCR was employed to evaluate the transcript quantification of the target genes. In flask fermentation, the newly constructed strain R102ΔmetXΔdapA (pEC-Box) was able to accumulate 3.35 g threonine/L compared with 1.80 g threonine/L of strain R102 (AHVr).

Recoating slurry process effects on the SiC-based casting foam filter properties

Fengzhang Ren,Gangjun Zhai,Zhanhong Ma,Alex A. Volinsky,Baohong Tian 한양대학교 세라믹연구소 2014 Journal of Ceramic Processing Research Vol.15 No.2

Polyurethane foam was used as a precursor for fabricating SiC-based ceramic foam filters. Two recoating slurry processes were adopted to enhance the strength of ceramic foam. One was the recoating slurry of stoved green body and another was the recoating slurry of pre-sintered green body. The differences in weight increase and thermal shock resistance of ceramic foams fabricated by the two recoating slurry processes were investigated. The effects of pre-sintering temperature on weight increase and thermal shock resistance are discussed. Thermal shock resistance of ceramic foams fabricated by two recoating slurry processes is lower than that by the single coating slurry process. Compared with recoating slurry of pre-sintered green bodies, with the same slurry, the weight increase of ceramic foams fabricated by recoating slurry of the stoved green bodies is less, but the number of thermal cycles to failure is much higher. For ceramic foams fabricated by recoating slurry of presintered green bodies with the same slurry, the weight increase and the number of thermal cycles to failure decreased with the pre-sintering temperature.

Microstructure and quality of SiC foam filters for casting

Fengzhang Ren,Gangjun Zhai,Zhanhong Ma,Xiaobo Chen,Alex A. Volinsky 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.6

Maximum compressive strain at high temperature was introduced as a new quality indicator of ceramic foam filters used in metal casting. Maximum compressive strain at high temperature, number of thermal cycles before failure, room temperature compressive strength and bulk density of SiC-based ceramic foam filters with the same pore size produced by four manufacturers were measured. The best quality product exhibited the highest number of thermal cycles before failure and minimum strain at high temperature. Differences in properties were elucidated based on X-ray diffraction and scanning electron microscope microstructural characterization. The best quality filter has less glass phase and more quartz phase, while lower quality filters have more glass and cristobalite phases. The glass phase increases the maximum strain at high temperature, while both glass and cristobalite phases reduce the number of thermal cycles before failure. The maximum compressive strain at high temperature can be utilized as the main indicator for evaluating the quality of ceramic foam filters.

Degradation behavior of deep UV-LEDs studied by electro-optical methods and transmission electron microscopy

Huixin Xiu,Yang Zhang,Jiajia Fu,Zhanhong Ma,Lixia Zhao,Jijun Feng 한국물리학회 2019 Current Applied Physics Vol.19 No.1

Degradation mechanism of 265-nm deep ultraviolet light emitting diodes (UV-LEDs) has been investigated by means of electroluminescence, current-voltage measurement, capacitance-voltage measurement, and transmission electron microscopy (TEM) equipped with energy dispersive X-ray spectrometer (EDAX). It is revealed that a major degradation mode of UV-LEDs may be the leakage current induced optical degradation. The current pathway is demonstrated by TEM with EDAX, indicating that the contact metals can partially interact with ptype materials, which accelerate the degradation of LEDs. The presented results can help to understand the degradation mechanisms and improve the reliability of deep UV-LEDs.

Quantitative Analysis Method for Subsynchronous Oscillation Power Propagation Characteristics of Wind Power Connected to Grid

Sun Xuebo,Chen Wei,Wei Zhanhong,Shi Jinhui,Pei Xiping 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.5

The subsynchronous oscillation power caused by large-scale wind power connection to the grid and the large-scale propagation of oscillation energy in the grid leads to system power fluctuations and may result in grid cascading accidents. This paper proposes a quantitative analysis method for the propagation and distribution characteristics of the oscillation power. First, the manifestation and formation mechanism of subsynchronous oscillation power is studied based on instantaneous power theory. Second, two quantitative indicators, namely the oscillating power node propagation intensity and branch transfer coefficient, are proposed to characterize the oscillating power propagation characteristics. Analysis of the oscillating power propagation characteristics and their influencing factors shows that the frequency of the oscillating power is the frequency of the system power frequency minus that of the oscillating current. The two quantitative indicators provide an effective method for locating the critical nodes and identifying the propagation path of the oscillating power propagation. Finally, simulations are conducted to verify the accuracy of the theoretical analysis and demonstrate the validity of the proposed quantitative analysis method.