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.

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.

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.

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.

A Relay Selection and Power Allocation Scheme for Cooperative Wireless Sensor Networks

( Mujun Qian ),( Chen Liu ),( Youhua Fu ),( Weiping Zhu ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.4

This paper investigates optimal relay selection and power allocation under an aggregate power constraint for cooperative wireless sensor networks assisted by amplify-and-forward relay nodes. By considering both transmission power and circuit power consumptions, the received signal-to-noise ratio (SNR) at the destination node is calculated, based on which, a relay selection and power allocation scheme is developed. The core idea is to adaptively adjust the selected relays and their transmission power to maximize the received SNR according to the channel state information. The proposed scheme is derived by recasting the optimization problem into a three-layered problem ― determining the number of relays to be activated, selecting the active relays, and performing power allocation among the selected relays. Monte Carlo simulation results demonstrate that the proposed scheme provides a higher received SNR and a lower bit error rate as compared to the average power allocation scheme.

ω-MODULES OVER COMMUTATIVE RINGS

Yin, Huayu,Wang, Fanggui,Zhu, Xiaosheng,Chen, Youhua Korean Mathematical Society 2011 대한수학회지 Vol.48 No.1

Let R be a commutative ring and let M be a GV -torsionfree R-module. Then M is said to be a $\omega$-module if $Ext_R^1$(R/J, M) = 0 for any J $\in$ GV (R), and the w-envelope of M is defined by $M_{\omega}$ = {x $\in$ E(M) | Jx $\subseteq$ M for some J $\in$ GV (R)}. In this paper, $\omega$-modules over commutative rings are considered, and the theory of $\omega$-operations is developed for arbitrary commutative rings. As applications, we give some characterizations of $\omega$-Noetherian rings and Krull rings.

ω-MODULES OVER COMMUTATIVE RINGS

Huayu Yin,Fanggui Wang,Xiaosheng Zhu,Youhua Chen 대한수학회 2011 대한수학회지 Vol.48 No.1

Let R be a commutative ring and let M be a GV -torsionfree R-module. Then M is said to be a w-module if Ext<수식> for any J ∈ GV (R), and the ω-envelope of M is defined by Mω = {x ∈E(M)ㅣJx ⊆ M for some J ∈ GV (R)}. In this paper, ω-modules over commutative rings are considered, and the theory of ω-operations is de-veloped for arbitrary commutative rings. As applications, we give some characterizations of ω-Noetherian rings and Krull rings.

Development and supercapacitor application of ionic liquid-incorporated gel polymer electrolyte films

Ravi Muchakayala,Shenhua Song,Jingwei Wang,Youhua Fan,Manjunatha Bengeppagari,Jianjun Chen,Manlin Tan 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.59 No.-

A new gel polymer electrolyte based on 1-methyl-1-propylpyrrolidinium bis(trifluoromethyl sulfonyl)imide ([PMpyr][NTf2]) entrapped in poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) is prepared and optimized for flexible solid state supercapacitor applications. The structural, thermal, electrical and electrochemical properties of the ionic liquid gel polymer electrolyte membranes are studied by different characterization techniques. The transparent gel polymer electrolyte membranes exhibit high amorphicity and excellent thermal stability. The 20PVdF-HFP:80[PMpyr][NTf2] gel polymer electrolyte membrane possesses a high ionic conductivity (1.596 × 10−3 S cm−1) and wide electrochemical stability window (4.7 V) at room temperature. It is used as the electrolyte material for the fabrication of flexible electric double layer supercapacitors (EDLCs) with multiwalled carbon nanotube (MWCNT)-added and unadded activated carbon (AC) electrodes. The performances of flexible EDLCs are evaluated using cyclic voltammetry and galvanostatic charge–discharge measurements. The EDLC with MWCNT-added AC electrodes exhibits apparently higher specific capacitance of electrode (156.64 F g−1), specific energy (30.69 Wh kg−1) and specific power (4.13 kW kg−1) than that with AC electrodes. The cyclic stability of the former is still in a good condition at the 2000th charge–discharge cycle and much better than the latter. The present comparative study indicates that the 20PVdF-HFP:80[PMpyr][NTf2] gel polymer electrolyte is a good candidate for the development of flexible solid-state supercapacitors.