Numerical study on the cavitating flow through poppet valves concerning the influence of flow instability on cavitation dynamics

Cong Yuan,Lisha Zhu,Shiqi Liu,Du Zunling,He Li 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.2

The flow dynamics of the cavitating jet through poppet valves inevitably suffers from the influence of varying openness, but the relevant mechanism remains unclear. Hence, the present study conducts a numerical study on the cavitating flow phenomenon inside poppet valves with two valve seat structures, in order to examine the flow mechanisms underlying varying cavitation phenomenon at different openness. According to the results, the overall cavitation distribution as well as the morphology feature follows a similar pattern due to the same inception mechanism irrelevant of the openness amount. However, examination of the dynamic behaviors confirms discernable variation in 2 coupling effects between flow instability and cavitation. The flow separation at the poppet trailing edge produces non-cavitation flow instability at 0.4 mm openness and attached cavitation at 0.8 mm, which amalgamate with upstream-shed vortex cavitation. The stably attached cavitation within the chamfered groove at 0.4 mm, as the source of non-cavitation flow instability, and the detached cavitation at 0.6 and 0.8 mm openness produce vortex cavitation at the free shearing side. The substantial variation in these two coupling effects contributes sensibly to the increase in the overall cavitation intensity. Meanwhile, the weakened coupling effect between the free shearing vortex and wall shearing vortex, as a consequence of increased potential core thickness at larger openness, leads to the attenuated vortex cavitation at the wall poppet side. Additionally, the vortex cavitation at free shearing side has a larger size in the chamfered valve seat case, due to the coupling of shed flow instability with the Kelvin-Helmholtz instability. As a conclusion, the inception mechanism for the cavitation remains unchanged with openness, while the difference in flow instabilities as well as the associated coupling effects with cavitation contributes to the variation in cavitation intensity.

Evaluation of Galactomannan Enzyme Immunoassay and Quantitative Real-Time PCR for the Diagnosis of Invasive Pulmonary Aspergillosis in a Rat Model

( Jian Cong Lin ),( Yan Li Xing ),( Wen Ming Xu ),( Ming Li ),( Pang Bo ),( Yuan Yuan Niu ),( Chang Ran Zhang ) 한국미생물 · 생명공학회 2014 Journal of microbiology and biotechnology Vol.24 No.8

Since there is no consensus about the most reliable assays to detect invasive aspergillosis from samples obtained by minimally invasive or noninvasive methods, we compared the efficacy of an enzyme-linked immunosorbent assay (ELISA) for galactomannan (GM) detection and quantitative real-time PCR assay (qRT-PCR) for the diagnosis of invasive pulmonary aspergillosis. Neutropenic, male Sprague-Dawley rats (specific pathogen free; 8 weeks old; weight, 200 ± 20 g) were immunosuppressed with cyclophosphamide and infected with Aspergillus fumigatus intratracheally. Tissue and whole blood samples were harvested on days 1, 3, 5, and 7 post-infection and examined with GM ELISA and qRT-PCR. The A. fumigatus DNA detection sequence was detected in the following number of samples from 12 immunosuppressed, infected rats examined on the scheduled days: day 1 (0/12), day 3 (0/12), day 5 (6/12), and day 7 (8/12) post-infection. The sensitivity and specificity of the qRT-PCR assay was 29.2% and 100%, respectively. Receiver operating characteristic curve (ROC) analysis indicated a Ct (cycle threshold) cut-off value of 15.35, and the area under the curve (AUC) was 0.627. The GM assay detected antigen in sera obtained on day 1 (5/12), day 3 (9/12), day 5 (12/12), and day 7 (12/12) post-infection, and thus had a sensitivity of 79.2% and a specificity of 100%. The ROC of the GM assay indicated that the optimal Ct cut-off value was 1.40 (AUC, 0.919). The GM assay was more sensitive than the qRT-PCR assay in diagnosing invasive pulmonary aspergillosis in rats.

Operable Breast Cancer of the Inner Hemisphere Is Associated with Poor Survival

Cong Xue,Rou Jun Peng,Shu Sen Wang,Yan Xia Shi,Xin An,Fei Xu,Zhong Yu Yuan 한국유방암학회 2015 Journal of breast cancer Vol.18 No.1

Purpose: This study investigated the clinicopathological featuresof operable breast cancer lesions located in different hemispheresof the breast and determined related survival outcomes. Methods: Data from 5,330 patients with invasive ductal carcinomawere retrospectively analyzed based on tumor location. Results:The median follow-up time was 68 months (range, 18–176months). Patients with breast cancer located in the outer hemisphereof the breast had lesions with more advanced nodalstages and more frequently received adjuvant chemotherapythan patients with breast cancer in the inner hemisphere. The5-year disease-free survival (DFS) rates of patients with tumorslocated in outer versus inner hemispheres were 81.5% and77.0%, respectively (p=0.004); the overall survival (OS) rateswere 90.7% and 88.8%, respectively (p<0.001). The associationbetween tumor location and the 5-year DFS rate was most apparentin node-positive patients (73.1% vs. 65.8% for outer vs. inner hemisphere lesions, p<0.001) and in patients with primarytumors greater than 2 cm in diameter (78.2% vs. 72.3%,p=0.002). Multivariate analysis showed that tumor location wasan independent predictor of DFS (hazard ratio [HR], 1.23;p=0.002) and OS (HR, 1.28; p=0.006). There were no significantdifferences in 5-year DFS or OS rates between patients with outerversus inner hemisphere tumors when internal mammary nodeirradiation was performed. Conclusion: This study demonstratedthat tumor location was an independent prognostic factor foroperable breast cancer. Internal mammary node irradiation isrecommended for patients with breast cancer of the inner hemisphereand positive axillary lymph nodes or large primary tumors

Determination Method for Topology Configuration of Hybrid Cascaded H-Bridge Rectifiers

Yuan Zhuang,Cong Wang,Chang Wang,Hong Cheng,Yingcai Gong,Hao Wang 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.5

To reduce system complexity and implementation costs, fully-controlled H-bridge (FHB) modules and diode H-bridge PFC (DHB) modules are cascaded to form a hybrid cascaded H-bridge rectifier (HCHR). In this paper, the advantages of such a HCHR over other cascaded rectifiers are analyzed depending on the numbers of FHB modules and DHB modules. Therefore, to assign proper numbers to these two kinds of modules for the HCHR, a configuration determination method is investigated under balanced and imbalanced loads. Three principles are also presented to guide the configuration determination for the HCHR. In addition, the constraints for selecting the step-up ratio and filter inductance are derived based on a phasor diagram analysis. The proposed configuration determination method is validated by simulations under three different conditions in the PSIM environment. Finally, experiments are carried out on a scaled-down prototype where the configuration can be easily adjusted. The feasibility of the proposed theory is then verified by experimental results.

Optimization Design of an Ultra-Low Specific-Speed Centrifugal Pump Using Entropy Production Minimization and Taguchi Method

Cong Wang,Yongxue Zhang,Hucan Hou,Zhiyi Yuan,Ming Liu 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.1

To improve the energy conversion efficiency and cavitation performance of the ultra-low specific-speed centrifugal pump (ULSSCP), the impeller-volute interaction has been studied. Blade outlet setting angle (β₂), wrap angle (φ), volute inlet width (b₃) and throat area (St) were addressed as the design parameters. The entropy production at 0.5 Q0 and NPSHc (critical net positive suction head) at 1.5 Q0 were selected as the target to characterize the energy loss and cavitation performance. The L9 (3⁴) orthogonal matrix was established via Taguchi method. Results show that the contribution ratio of φ on S/NS is the most vital, followed by b₃ and St, while the influence of β₂ is relatively small, and the design parameter combination with β₂=19°, φ=220°, b₃=12mm and St=190㎟ is the best choice for the lowest entropy production at 0.5Q0 and NPSHc. At last, the optimization design reduces the loss greatly before and after cavitation by alleviation of vortex generation and backflow intensity.

Research on Liquefaction Characteristics of SF6 Substitute Gases

Yuan, Zhikang,Tu, Youping,Wang, Cong,Qin, Sichen,Chen, Geng The Korean Institute of Electrical Engineers 2018 Journal of Electrical Engineering & Technology Vol.13 No.6

$SF_6$ has been widely used in high voltage power equipment, such as gas insulated switchgear (GIS) and gas insulated transmission line (GIL), because of its excellent insulation and arc extinguishing performance. However, $SF_6$ faces two environmental problems: greenhouse effect and high liquefaction temperature. Therefore, to find the $SF_6$ substitute gases has become a research hotspot in recent years. In this paper, the liquefaction characteristics of $SF_6$ substitute gases were studied. Peng-Robinson equation of state with the van der Waals mixing rule (PR-vdW model) was used to calculate the dew point temperature of the binary gas mixtures, with $SF_6$, $C_3F_8$, $c-C_4F_8$, $CF_3I$ or $C_4F_7N$ as the insulating gas and $N_2$ or $CO_2$ as the buffer gas. The sequence of the dew point temperatures of the binary gas mixtures under the same pressure and composition ratio was obtained. $SF_6/N_2$ < $SF_6/CO_2$ < $C_3F_8/N_2$ < $C_3F_8/CO_2$ < $CF_3I/N_2$ < $CF_3I/CO_2$ < $c-C_4F_8/N_2$ < $C_4F_7N/N_2$ < $c-C_4F_8/CO_2$ < $C_4F_7N/CO_2$. $SF_6/N_2$ gas mixture showed the best temperature adaptability and $C_4F_7N/CO_2$ gas mixture showed the worst temperature adaptability. Furthermore, the dew point temperatures of the $SF_6$ substitute gases at different pressures and the upper limits of the insulating gas mole fraction at $-30^{\circ}C$, $-20^{\circ}C$ and $-10^{\circ}C$ were obtained. The results would supply sufficient data support for GIS/GIL operators and researchers.

Attenuated Secretion of the Thermostable Xylanase xynB from Pichia pastoris Using Synthesized Sequences Optimized from the Preferred Codon Usage in Yeast

( Huang Yuan Kai ),( Yao Sheng Chen ),( De Lin Mo ),( Pei Qing Cong ),( Zu Yong He ) 한국미생물 · 생명공학회 2012 Journal of microbiology and biotechnology Vol.22 No.3

Xylanase has been used extensively in the industrial and agricultural fields. However, the low-yield production of xylanase from native species cannot meet the increasing demand of the market. Therefore, improving the heterologous expression of xylanase through basic gene optimization may help to overcome the shortage. In this study, we synthesized a high-GC-content native sequence of the thermostable xylanase gene xynB from Streptomyces olivaceoviridis A1 and, also designed a slightly AT-biased sequence with codons completely optimized to be favorable to Pichia pastoris. The comparison of the sequences` expression efficiencies in P. pastoris X33 was determined through the detection of single-copy-number integrants, which were quantified using qPCR. Surprisingly, the high GC content did not appear to be detrimental to the heterologous expression of xynB in yeast, whereas the optimized sequence, with its extremely skewed codon usage, exhibited more abundant accumulation of synthesized recombinant proteins in the yeast cell, but an approximately 30% reduction of the secretion level, deduced from the enzymatic activity assay. In this study, we developed a more accurate method for comparing the expression levels of individual yeast transformants. Moreover, our results provide a practical example for further investigation of what constitutes a rational design strategy for a heterologously expressed and secreted protein.

Case Study on Rock Support Technology for Roadways Based on Characteristics of Plastic Area

Chao Yuan,Liming Cao,Wenjun Wang,Lei Fan,Cong Huang 대한토목학회 2021 KSCE Journal of Civil Engineering Vol.25 No.2

Rocks surrounding deep, high-stress roadways typically undergo a vicious cycle of destruction → repair → re-destruction → re-repair over a long time. This article uses the roadway restoration project of Pingmei Mine No. 6 (400 m underground) as research object. Starting from the plastic area, the characteristics of the distribution of rock surrounding the circular roadway are analyzed, and the influence of the side pressure coefficient, cohesive force, inside friction angle, support strength, and roadway radius on the plastic area is studied. Four types of distribution patterns were observed in rocks surrounding the plastic area of the roadway: round, oval, rounded rectangle, and butterfly. The side pressure coefficient, cohesive force, and inside friction angle affected the distribution and range of rocks surrounding the plastic area of the roadway. The support radius of the roadway and the support strength of its face did not change the distribution of the plastic area, but only affected its size. Therefore, to maintain the long-term stability of weak and broken roadways, the strength of the surrounding rocks must be increased, and roadway renovation should be avoided as it affects the distribution of the plastic area and reduces its scope. Engineering practice has shown that the “anchor net spray + hollow grouting anchor cable” technology for the combined, step-by-step repair and support of roadways, with a hollow grouting anchor cable as core, can suppress the distribution and scope of the plastic area to guarantee safe and long-term use of the roadway.

Mitochondrial Location of Severe Acute Respiratory Syndrome Coronavirus 3b Protein

Yuwen Cong,Xiaoling Yuan,Yajun Shan,Zhenyu Yao,Jianyong Li,Zhenhu Zhao,Jiapei Chen 한국분자세포생물학회 2006 Molecules and cells Vol.21 No.2

Determination Method for Topology Configuration of Hybrid Cascaded H-Bridge Rectifiers

Zhuang, Yuan,Wang, Cong,Wang, Chang,Cheng, Hong,Gong, Yingcai,Wang, Hao The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.5

To reduce system complexity and implementation costs, fully-controlled H-bridge (FHB) modules and diode H-bridge PFC (DHB) modules are cascaded to form a hybrid cascaded H-bridge rectifier (HCHR). In this paper, the advantages of such a HCHR over other cascaded rectifiers are analyzed depending on the numbers of FHB modules and DHB modules. Therefore, to assign proper numbers to these two kinds of modules for the HCHR, a configuration determination method is investigated under balanced and imbalanced loads. Three principles are also presented to guide the configuration determination for the HCHR. In addition, the constraints for selecting the step-up ratio and filter inductance are derived based on a phasor diagram analysis. The proposed configuration determination method is validated by simulations under three different conditions in the PSIM environment. Finally, experiments are carried out on a scaled-down prototype where the configuration can be easily adjusted. The feasibility of the proposed theory is then verified by experimental results.