Testing adaptive regime shifts for range size evolution of endemic birds of China

Youhua Chen 국립중앙과학관 2016 Journal of Asia-Pacific Biodiversity Vol.9 No.1

In this brief report, adaptive regime shifts for the range size evolution of the endemic birds of China were identified. Four models with different biological meanings were tested and compared through maximum likelihood models, including the Brownian motion model, one global optimal range size model for all lineages in the phylogeny, two optimal regime model of range sizes for lineages with large and small range sizes (OU2), and three optimal regime model in which an additional regime is added to the ancestral lineages. The results of model evaluation and comparison using the maximum likelihood technique show that over 48 endemic taxa, two optimal regimes (the OU2 model) were observed for bird lineages with large and small range sizes in the country. The possible reasons for such an observation were outlined accordingly, including the different evolutionary times, which were subjected to different historical and geological conditions, heterogeneous environmental conditions, and complex climatic fluctuations. Overall, the range size evolution of the endemic taxa was subjected to multiple selective stresses. For future implications, more studies are desired to provide a holistic view of the evolution and divergence of endemic taxa.

Effect of 3C-SiC Intermediate Layer in GaN-Based Light Emitting Diodes Grown on Si(111) Substrate

Youhua Zhu,Meiyu Wang,Yi Li,Shuxin Tan,Honghai Deng,Xinglong Guo,Haihong Yin,Takashi Egawa 대한금속·재료학회 2017 ELECTRONIC MATERIALS LETTERS Vol.13 No.2

GaN-based light emitting diodes (LEDs) have been grown by metalorganicchemical vapor deposition on Si(111) substrate with and without3C-SiC intermediate layer (IL). Structural property has been characterizedby means of atomic force microscope, X-ray diffraction, andtransmission electron microscope measurements. It has been revealedthat a significant improvement in crystalline quality of GaN and superlatticeepitaxial layers can be achieved by using 3C-SiC as IL. Regardingof electrical and optical characteristics, it is clearly observed that theLEDs with its IL have a smaller leakage current and higher light outputpower comparing with the LEDs without IL. The better performance ofLEDs using 3C-SiC IL can be contributed to both of the improvementsin epitaxial layers quality and light extraction efficiency. As aconsequence, in terms of optical property, a double enhancement of thelight output power and external quantum efficiency has been realized.

A maximum likelihood model for fitting power functions with data uncertainty: A case study on the relationship between body lengths and masses for Sciuridae species worldwide

Youhua Chen 국립중앙과학관 2016 Journal of Asia-Pacific Biodiversity Vol.9 No.3

In this report, a maximum likelihood model is developed to incorporate data uncertainty in response and explanatory variables when fitting power-law bivariate relationships in ecology and evolution. This simple likelihood model is applied to an empirical data set related to the allometric relationship between body mass and length of Sciuridae species worldwide. The results show that the values of parameters estimated by the proposed likelihood model are substantially different from those fitted by the nonlinear least-of-square (NLOS) method. Accordingly, the power-law models fitted by both methods have different curvilinear shapes. These discrepancies are caused by the integration of measurement errors in the proposed likelihood model, in which NLOS method fails to do. Because the current likelihood model and the NLOS method can show different results, the inclusion of measurement errors may offer new insights into the interpretation of scaling or power laws in ecology and evolution.

Power Quality Optimal Control of Railway Static Power Conditioners Based on Electric Railway Power Supply Systems

Youhua Jiang,Wenji Wang,Xiangwei Jiang,Le Zhao,Yilong Cao 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.5

Aiming at the negative sequence and harmonic problems in the operation of railway static power conditioners, an optimization compensation strategy for negative sequence and harmonics is studied in this paper. First, the hybrid RPC topology and compensation principle are analyzed to obtain different compensation zone states and current capacities. Second, in order to optimize the RPC capacity configuration, the minimum RPC compensation capacity is calculated according to constraint conditions, and the optimal compensation coefficient and compensation angle are obtained. In addition, the voltage unbalance EU and power factor requirements are satisfied. A PSO (Particle Swarm Optimization) algorithm is used to calculate the three indexes for minimum compensating energy. The proposed method can precisely calculate the optimal compensation capacity in real time. Finally, MATLAB simulations and an experimental platform verify the effectiveness and economics of the proposed algorithm.

Study on the lubrication state and pitting damage of spur gear using a 3D mixed EHL model with fractal surface roughness

Youhua Li,Lubing Shi,Zhongming Liu,Xiaopeng Wang,Xuetao Qiao,Zhihong Zhang,Shidang Yan 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.12

For high-speed, heavy-load gear units, the meshing tooth surfaces are generally under the mixed lubrication state, which is crucial for gear pitting or micro pitting damage. To clarify the effects of lubrication state on tooth pitting damage, carrying out both numerical and experimental studies on the contact severity of gears under different lubrication states is necessary. In this paper, a 3D line-contact elasto hydrodynamic lubrication model considering fractal surface roughness was developed and used to investigate the lubrication characteristics of involute gears. Both the distributions of pressure and film thickness fluctuated under the rolling contact of rough surfaces. The fluctuations became more substantial with the increase of load and roughness. Furthermore, from the calculated film thickness ratio λ, the contact of gear tooth surfaces with a fractal roughness of Ra = 0.8 μm was always under full lubrication state (λ > 1). When the roughness was increased to Ra = 3.2 μm, the contact was first transmitted into the mixed lubrication state (0.2 < λ < 1) under the load of 1000 N*m and finally deteriorated to boundary lubrication state (λ < 0.2) under the load of 2000 N*m. The boundary lubrication state that occurred under the contact of highly rough surfaces could induce the formation of gear pitting damage. The contact fatigue test showed the gear tooth surface roughness increased from 0.7 μm to around 2.7 μm after 8 million running cycles and then suffered pitting failure after another 2 million cycles, which was consistent with the simulation analysis prediction.

A comparison on the impacts of short-term micro-environmental and long-term macro-climatic variability on structuring beta diversity of microarthropod communities

Youhua Chen 한국응용곤충학회 2014 Journal of Asia-Pacific Entomology Vol.17 No.3

It is unknown whether long-term climatic variability or short-term microhabitat environmental fluctuationwould be the key mechanism in determining the microarthropod compositional variation. In the present briefreport, by utilizing microarthropod communities as the study model, I aimed to test the relative importanceof macro-climatic versus micro-environmental variability on structuring the beta diversity patterns ofmicroarthropod communities. The random sampling effect in quantifying beta diversity has been controlledusing a null model. Variation partitioning technique is employed to test the relative importance of both mechanisms. The results showed that microarthropod beta diversity pattern is exclusively influenced by microenvironmentalcondition, especially for oribatids and collembolans. The influence of macro-climatic variabilityon structuring microarthropod community structure is exactly zero as indicated by variation partitioning analyses. Correspondingly, the interaction between micro-environment and macro-climate plays no roles on structuringmicroarthropod beta diversity too. Conclusively, microhabitat condition, but not regional climate, is the driverof microarthropod diversity patterns in SW Canada.

Tempo of Diversification of Global Amphibians

Youhua Chen 한국동물분류학회 2014 Animal Systematics, Evolution and Diversity Vol.30 No.1

In this brief report, alternative time-varying diversification rate models were fitted onto the phylogeny of global amphibians by considering one-constant-rate (OCR), one-continuous-shift (OCS) and multiplediscrete- shifts (MDS) situations. The OCS diversification model was rejected by γ statistic (γ=-5.556, p? 0.001), implying the existence of shifting diversification rates for global amphibian phylogeny. Through model selection, MDS diversification model outperformed OCS and OCR models using “laser” package under Renvironment. Moreover, MDS models, implemented using another R package “MEDUSA”, indicated that there were sixteen shifts over the internal nodes for amphibian phylogeny. Conclusively, both OCS and MDS models are recommended to compare so as to better quantify rate-shifting trends of species diversification. MDS diversification models should be preferential for large phylogenies using “MEDUSA” package in which any arbitrary numbers of shifts are allowed to model.

Power Quality Optimal Control of Railway Static Power Conditioners Based on Electric Railway Power Supply Systems

Jiang, Youhua,Wang, Wenji,Jiang, Xiangwei,Zhao, Le,Cao, Yilong The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.5

Aiming at the negative sequence and harmonic problems in the operation of railway static power conditioners, an optimization compensation strategy for negative sequence and harmonics is studied in this paper. First, the hybrid RPC topology and compensation principle are analyzed to obtain different compensation zone states and current capacities. Second, in order to optimize the RPC capacity configuration, the minimum RPC compensation capacity is calculated according to constraint conditions, and the optimal compensation coefficient and compensation angle are obtained. In addition, the voltage unbalance ${\varepsilon}_U$ and power factor requirements are satisfied. A PSO (Particle Swarm Optimization) algorithm is used to calculate the three indexes for minimum compensating energy. The proposed method can precisely calculate the optimal compensation capacity in real time. Finally, MATLAB simulations and an experimental platform verify the effectiveness and economics of the proposed algorithm.

Tempo of Diversification of Global Amphibians: One-Constant Rate, One-Continuous Shift or Multiple-Discrete Shifts?

Chen, Youhua The Korean Society of Systematic Zoology 2014 Animal Systematics, Evolution and Diversity Vol.30 No.1

In this brief report, alternative time-varying diversification rate models were fitted onto the phylogeny of global amphibians by considering one-constant-rate (OCR), one-continuous-shift (OCS) and multiple-discrete- shifts (MDS) situations. The OCS diversification model was rejected by ${\gamma}$ statistic (${\gamma}=-5.556$, p<0.001), implying the existence of shifting diversification rates for global amphibian phylogeny. Through model selection, MDS diversification model outperformed OCS and OCR models using "laser" package under R environment. Moreover, MDS models, implemented using another R package "MEDUSA", indicated that there were sixteen shifts over the internal nodes for amphibian phylogeny. Conclusively, both OCS and MDS models are recommended to compare so as to better quantify rate-shifting trends of species diversification. MDS diversification models should be preferential for large phylogenies using "MEDUSA" package in which any arbitrary numbers of shifts are allowed to model.

Nanotexturing of Conjugated Polymers via One-Step Maskless Oxygen Plasma Etching for Enhanced Tunable Wettability

Jiang, Youhua,Xu, Jian,Lee, Junghoon,Du, Ke,Yang, Eui-Hyeok,Moon, Myoung-Woon,Choi, Chang-Hwan American Chemical Society 2017 Langmuir Vol.33 No.27

<P>A one-step maskless oxygen plasma etching process is investigated to nanopattern conjugated polymer dodecylbenzenesulfonate doped polypyrrole (PPy(DBS)) and to examine the effects of nanostructures on the inherent tunable wettability of the surface and the droplet mobility. Etching characteristics such as the geometry and dimensions of the nanostructures are systematically examined for the etching power and duration. The mechanism of self-formation of vertically aligned dense-array pillared nanostructures in the one-step maskless oxygen plasma etching process is also investigated. Results show that lateral dimensions such as the periodicity and diameter of the pillared nanostructures are insensitive to the etching power and duration, whereas the length and aspect ratio of the nanostructures increase with them. X-ray photoelectron spectroscopy analysis and thermal treatment of the polymer reveal that the codeposition of impurities on the surface resulting from the holding substrate is the primary reason for the self-formation of nanostructures during the oxygen plasma etching, whereas the local crystallinity subject to thermal treatment has a minor effect on the lateral dimensions. Retaining the tunable wettability (oleophobicity) for organic droplets during the electrochemical redox (i.e., reduction and oxidization) process, the nanotextured PPy(DBS) surface shows significant enhancement of droplet mobility compared to that of the flat PPy(DBS) surface with no nanotexture by making the surface superoleophobic (i.e., in a Cassie-Baxter wetting state). Such enhancement of the tunable oleophobicity and droplet mobility of the conjugated polymer will be of great significance in many applications such as microfluidics, lab-on-a-chip devices, and water/oil treatment.</P>