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Search Results: 1 - 10 of 80802 matches for " Zexin Liu "
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Topologically Fragmental Space and the Proof of Hadwiger's Conjecture
Cao Zexin
Mathematics , 2003,
Abstract: A topological space is introduced in this paper. Just liking the plane, it's continuous, however its $n+1$ regions couldn't be mutually adjacent. Some important phenomenon about its cross-section are discussed. The geometric generating element of the coloring region-map is also an important concept. Every $n$-coloring region map is in the cross-section set of an $n$-color geometric generating element. The proof of four color theorem and Hadwiger's conjecture is obtained by researching them and their cross-sections. And we can see in the context, that those conjectures are not of graph theory, but such topological space.
Rotational and Translational Phonon Modes in Glasses Composed of Ellipsoidal Particles
Peter J. Yunker,Ke Chen,Zexin Zhang,Wouter G. Ellenbroek,Andrea J. Liu,A. G. Yodh
Physics , 2010, DOI: 10.1103/PhysRevE.83.011403
Abstract: The effects of particle shape on the vibrational properties of colloidal glasses are studied experimentally. 'Ellipsoidal glasses' are created by stretching polystyrene spheres to different aspect ratios and then suspending the resulting ellipsoidal particles in water at high packing fraction. By measuring displacement correlations between particles, we extract vibrational properties of the corresponding "shadow" ellipsoidal glass with the same geometric configuration and interactions as the 'source' suspension but without damping. Low frequency modes in glasses composed of ellipsoidal particles with major/minor axis aspect ratios $\sim$1.1 are observed to have predominantly rotational character. By contrast, low frequency modes in glasses of ellipsoidal particles with larger aspect ratios ($\sim$3.0) exhibit a mix of rotational and translational character. All glass samples were characterized by a distribution of particles with different aspect ratios. Interestingly, even within the same sample it was found that small-aspect-ratio particles participate relatively more in rotational modes, while large-aspect-ratio particles tend to participate relatively more in translational modes.
Existence of multiple solutions to a class of nonlinear Schr?dinger system with external sources terms
Zexin Qi,Zhitao Zhang
Mathematics , 2014,
Abstract: We study a class of nonlinear schr\"{o}dinger system with external sources terms as perturbations in order to obtain existence of multiple solutions, this system arises from Bose-Einstein condensates etc..As these external sources terms are positive functions and small in some sense, we use Nehari manifold to get the existence of a positive ground state solution and a positive bound state solution.
On a power-type coupled system of Monge-Ampère equations
Zhitao Zhang,Zexin Qi
Mathematics , 2014,
Abstract: We study an elliptic system coupled by Monge-Amp\`{e}re equations: \begin{center} $\left\{ \begin{array}{ll} det~D^{2}u_{1}={(-u_{2})}^\alpha, & \hbox{in $\Omega,$} det~D^{2}u_{2}={(-u_{1})}^\beta, & \hbox{in $\Omega,$} u_{1}<0, u_{2}<0,& \hbox{in $\Omega,$} u_{1}=u_{2}=0, & \hbox{on $ \partial \Omega,$} \end{array} \right.$ \end{center} here $\Omega$~is a smooth, bounded and strictly convex domain in~$\mathbb{R}^{N}$,~$N\geq2,~\alpha >0,~\beta >0$. When $\Omega$ is the unit ball in $\mathbb{R}^{N}$, we use index theory of fixed points for completely continuous operators to get existence, uniqueness results and nonexistence of radial convex solutions under some corresponding assumptions on $\alpha,\beta$. When $\alpha>0$, $\beta>0$ and $\alpha\beta=N^2$ we also study a corresponding eigenvalue problem in more general domains.
Soil arthropod diversity following an ice storm in a montane evergreen broadleaved forest in Chebaling National Nature Reserve, China

Yuduan Ou,Zhiyao Su,Zhenkui Li,Fuchun Tong,Zexin Liu,

生物多样性 , 2009,
Abstract: In 2008, an ice storm caused extensive damage to the montane evergreen broadleaved forest in Chebaling National Nature Reserve, Guangdong Province, China. To assess the response of soil arthropod diversity and distribution to a gradient of canopy openness following the ice storm, 17 plots, each 400 m~2, were selected within a 2-ha permanent plot. Canopy openness was estimated with hemispherical photography in each plot. We sampled the litter layer and two soil layers (0-10 cm and 10-20 cm) to measure arthropod diversity and soil properties. We used two-way cluster analysis to group sites based on arthropod abundance in the litter layer. We also utilized canonical correspondence analysis to reveal relationships between soil arthropods in the 0-10 cm layer and four environmental variables, i.e., canopy openness (CO), soil organic matter (SOM), electric conductivity (EC), and natural moisture content (NMC). Results showed that abundance, richness and diversity of arthropod communities decreased with depth. A negative association was found between canopy openness and the number of arthropod groups in the litter layer; some arthropod taxa, such as the Oribatida, Prostigmata and Mesostigmata, were found in a wide range of light conditions, whereas the Hymenoptera, Symphyla, Pseudoscorpiones and Lepidoptera larvae may be photophobic. The distribution of arthropods in the 0-10 cm soil layer was closely related to CO, SOM, EC, and NMC on the first and second canonical axes. Hence, a series of changes in canopy structure and soil factors following the ice storm appeared to have affected the composition and distribution of soil arthropod communities. Findings from the present study also indicated that arthropod communities could serve as indicators to characterize the ecosystems they inhabit, thus being particularly suitable for monitoring forest regeneration and successional dynamics following ice storms.
Malignant Transformation Potentials of Human Umbilical Cord Mesenchymal Stem Cells Both Spontaneously and via 3-Methycholanthrene Induction
Qiuling Tang, Qiurong Chen, Xiulan Lai, Sizheng Liu, Yezeng Chen, Zexin Zheng, Qingdong Xie, Martin Maldonado, Zhiwei Cai, Shan Qin, Guyu Ho, Lian Ma
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0081844
Abstract: Human umbilical cord mesenchymal stem cells (HUMSCs) are highly proliferative and can be induced to differentiate into advanced derivatives of all three germ layers. Thus, HUMSCs are considered to be a promising source for cell-targeted therapies and tissue engineering. However there are reports on spontaneous transformation of mesenchymal stem cells (MSCs) derived from human bone marrows. The capacity for HUMSCs to undergo malignant transform spontaneously or via induction by chemical carcinogens is presently unknown. Therefore, we isolated HUMSCs from 10 donors and assessed their transformation potential either spontaneously or by treating them with 3-methycholanthrene (3-MCA), a DNA-damaging carcinogen. The malignant transformation of HUMSCs in vitro was evaluated by morphological changes, proliferation rates, ability to enter cell senescence, the telomerase activity, chromosomal abnormality, and the ability to form tumors in vivo. Our studies showed that HUMSCs from all 10 donors ultimately entered senescence and did not undergo spontaneous malignant transformation. However, HUMSCs from two of the 10 donors treated with 3-MCA displayed an increased proliferation rate, failed to enter senescence, and exhibited an altered cell morphology. When these cells (tHUMSCs) were injected into immunodeficient mice, they gave rise to sarcoma-like or poorly differentiated tumors. Moreover, in contrast to HUMSCs, tHUMSCs showed a positive expression of human telomerase reverse transcriptase (hTERT) and did not exhibit a shortening of the relative telomere length during the long-term culture in vitro. Our studies demonstrate that HUMSCs are not susceptible to spontaneous malignant transformation. However, the malignant transformation could be induced by chemical carcinogen 3-MCA.
Isolation and Characterization of a Type 2 Vaccine-Derived Poliovirus from Environmental Surveillance in China, 2012
Zexin Tao, Yong Zhang, Yao Liu, Aiqiang Xu, Xiaojuan Lin, Hiromu Yoshida, Ping Xiong, Shuangli Zhu, Suting Wang, Dongmei Yan, Lizhi Song, Haiyan Wang, Ning Cui, Wenbo Xu
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0083975
Abstract: Environmental surveillance of poliovirus on sewage has been conducted in Shandong Province, China since 2008. A type 2 vaccine-derived poliovirus (VDPV) with 7 mutations in VP1 coding region was isolated from the sewage collected in the city of Jinan in December 2012. The complete genome sequencing analysis of this isolate revealed 25 nucleotide substitutions, 7 of which resulted in amino acid alteration. No evidence of recombination with other poliovirus serotypes was observed. The virus did not lose temperature sensitive phenotype at 40°C. An estimation based on the evolution rate of the P1 coding region suggested that evolution time of this strain might be 160–176 days. VP1 sequence analysis revealed that this VDPV strain is of no close relationship with other local type 2 polioviruses (n = 66) from sewage collected between May 2012 and June 2013, suggesting the lack of its circulation in the local population. The person who excreted the virus was not known and no closely related virus was isolated in local population via acute flaccid paralysis surveillance. By far this is the first report of VDPV isolated from sewage in China, and these results underscore the value of environmental surveillance in the polio surveillance system even in countries with high rates of OPV coverage.
Molecular Epidemiology of Human Enterovirus Associated with Aseptic Meningitis in Shandong Province, China, 2006–2012
Zexin Tao, Haiyan Wang, Yan Li, Guifang Liu, Aiqiang Xu, Xiaojuan Lin, Lizhi Song, Feng Ji, Suting Wang, Ning Cui, Yanyan Song
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0089766
Abstract: Background Human enteroviruses (HEVs) are common causes of acute meningitis. However, there is limited information about HEV associated with aseptic meningitis in mainland China because it has not been classified as a notifiable disease. Objectives To characterize the HEVs associated with sporadic aseptic meningitis in China and to analyze their genetic features. Study Design Cerebrospinal fluid, throat swab and feces specimens were collected from patients with aseptic meningitis in 5 sentinel hospitals in Shandong Province, China between 2006 and 2012. Virological investigation (viral isolation and molecular identification) and phylogenetic analysis were performed. Results A total of 437 hospitalized patients were reported, and enteroviruses were detected in the specimens from 84 patients (19.2%) and were identified into 17 serotypes. The nine main serotypes were echovirus (E) 30 (27.4%), EV71 (13.1%), coxsackievirus (CV) B1 (9.5%), CVB3 (7.1%), CVB5 (7.1%), E6 (7.1%), E9 (7.1%), CVA9 (6.0%), and CVA10 (3.6%). Monthly distribution of isolated enteroviruses revealed a major peak in summer-fall season and a small second peak in winter constituted totally by EV71. Sequence analysis on VP1 coding region suggested Shandong strains had great genetic divergence with isolates from other countries. Conclusions Multiple serotypes were responsible for enterovirus meningitis in mainland China. Aseptic meningitis caused by EV71 and coxsackie A viruses–the predominant pathogens for the hand, foot, and mouth disease–is currently an important concern in mainland China.
Low-frequency vibrations of soft colloidal glasses
Ke Chen,Wouter G. Ellenbroek,Zexin Zhang,Daniel T. N. Chen,Peter Yunker,Silke Henkes,Carolina Brito,Olivier Dauchot,Wim van Saarloos,Andrea J. Liu,A. G. Yodh
Physics , 2010, DOI: 10.1103/PhysRevLett.105.025501
Abstract: We conduct experiments on two-dimensional packings of colloidal thermosensitive hydrogel particles whose packing fraction can be tuned above the jamming transition by varying the temperature. By measuring displacement correlations between particles, we extract the vibrational properties of a corresponding "shadow" system with the same configuration and interactions, but for which the dynamics of the particles are undamped. The vibrational spectrum and the nature of the modes are very similar to those predicted for zero-temperature idealized sphere models and found in atomic and molecular glasses; there is a boson peak at low frequency that shifts to higher frequency as the system is compressed above the jamming transition.
Do Native Parasitic Plants Cause More Damage to Exotic Invasive Hosts Than Native Non-Invasive Hosts? An Implication for Biocontrol
Junmin Li, Zexin Jin, Wenjing Song
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0034577
Abstract: Field studies have shown that native, parasitic plants grow vigorously on invasive plants and can cause more damage to invasive plants than native plants. However, no empirical test has been conducted and the mechanism is still unknown. We conducted a completely randomized greenhouse experiment using 3 congeneric pairs of exotic, invasive and native, non-invasive herbaceous plant species to quantify the damage caused by parasitic plants to hosts and its correlation with the hosts' growth rate and resource use efficiency. The biomass of the parasitic plants on exotic, invasive hosts was significantly higher than on congeneric native, non-invasive hosts. Parasites caused more damage to exotic, invasive hosts than to congeneric, native, non-invasive hosts. The damage caused by parasites to hosts was significantly positively correlated with the biomass of parasitic plants. The damage of parasites to hosts was significantly positively correlated with the relative growth rate and the resource use efficiency of its host plants. It may be the mechanism by which parasitic plants grow more vigorously on invasive hosts and cause more damage to exotic, invasive hosts than to native, non-invasive hosts. These results suggest a potential biological control effect of native, parasitic plants on invasive species by reducing the dominance of invasive species in the invaded community.
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