Publications by authors named "Tonghua Zhang"

18 Publications

  • Page 1 of 1

A Diffusive Sveir Epidemic Model with Time Delay and General Incidence.

Acta Math Sci 2021 1;41(4):1385-1404. Epub 2021 Jun 1.

Department of Mathematics, Swinburne University of Technology, Hawthorn, Victoria 3122 Australia.

In this paper, we consider a delayed diffusive SVEIR model with general incidence. We first establish the threshold dynamics of this model. Using a Nonstandard Finite Difference (NSFD) scheme, we then give the discretization of the continuous model. Applying Lyapunov functions, global stability of the equilibria are established. Numerical simulations are presented to validate the obtained results. The prolonged time delay can lead to the elimination of the infectiousness.

Electronic Supplementary Material: Supplementary material is available in the online version of this article at 10.1007/s10473-021-0421-9.
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http://dx.doi.org/10.1007/s10473-021-0421-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8167310PMC
June 2021

Efficient development of silk fibroin membranes on liquid surface for potential use in biomedical materials.

Int J Biol Macromol 2021 Jul 6;182:237-243. Epub 2021 Apr 6.

State Key Laboratory of Silkworm Genome Biology, Chongqing Engineering Research Center of Biomaterial Fiber and Modern Textile, College of Sericulture, Textile and Biomass Science, Southwest University, Chongqing 400715, China. Electronic address:

Silk fibroin (SF) protein is versatile for the application of biomaterials due to its excellent mechanical properties, biocompatibility and biodegradability. However, the efficient way to fabricate SF membranes with special structure is still challenging. Here, we develop an efficient and simple way to create SF membranes on the liquid (i.e. subphase) surface. It is essential to prepare highly concentrated SF solution with low surface tension by dissolving the degummed SF powders in 6% (w/v) LiBr/methanol solution by one step. 95 wt% polyethylene glycol (PEG) 200 and 30 wt% (NH)SO are the subphases, on which the SF solution spreads quickly, generating nonporous and microporous SF membranes (SFM-1 and SFM-2), respectively. PEG 200 causes more ordered molecular packing (β-sheets) in SFM-1. While Fast diffusion and denaturation of SF on (NH)SO solution lead to the formation of microporous, water-unstable membrane SFM-2. Both membranes have good transparency, hydrophilicty, and mechanical properties. To fabricate antibacterial biomaterials, we design a composite membrane by SFM-1 and SFM-2 sandwiching a layer of hydroxypropyl trimethylammonium chloride chitosan (HACC) to provide antibacterial functions. The sandwich membrane has good cell viability and antibacterial properties, showing potential use for biomedical materials.
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http://dx.doi.org/10.1016/j.ijbiomac.2021.04.019DOI Listing
July 2021

Stability and bifurcation analysis of a diffusive miR-9/Hes1 network with time delay.

IEEE/ACM Trans Comput Biol Bioinform 2021 Jan 8;PP. Epub 2021 Jan 8.

In this paper, a model of miR-9/Hes1 interaction network involving one time delay and diffusion effect under the Neumann boundary conditions is studied. First of all, the stability of the positive equilibrium and the existence of local Hopf bifurcation and Turing-Hopf bifurcation are investigated by analyzing the associated characteristic equation. Second, a algorithm for determining the direction, stability and period of the corresponding bifurcating periodic solutions is presented. The obtained results suggest that the quiescent progenitors (high steady-state Hes1) can be easily excited into oscillation by time delay whereas the differentiated state (low steady-state Hes1) is basically unaffected, and the integrated effect of delay and diffusion can induce the occurrence of spatially inhomogeneous patterns. More importantly, spatially homogeneous/inhomogeneous periodic solutions can exist simultaneously when the diffusion coefficients of Hes1 mRNA and Hes1 protein are appropriately small, conversely, there is only spatially homogeneous periodic solutions. Intriguingly, both temporal patterns and spatial-temporal patterns show that time delay can prompt Hes1 protein to shift from the high concentration state to the low concentration one ("ON" ← "OFF"), where Hes1 protein shows low level whereas miR-9 shows high level. Finally, some numerical examples are presented to verify and visualize theoretical results.
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http://dx.doi.org/10.1109/TCBB.2021.3050006DOI Listing
January 2021

Competitive Exclusion in a General Multi-species Chemostat Model with Stochastic Perturbations.

Bull Math Biol 2021 Jan 2;83(1). Epub 2021 Jan 2.

Department of Mathematics, Swinburne University of Technology, Hawthorn, VIC, 3122, Australia.

Based on the fact that the continuous culture of microorganisms in a chemostat is subject to environmental noises, we present and analyze a stochastic competition chemostat model with general monotonic response functions and differential removal rates. The existence and boundedness of the unique positive solution are first obtained. By defining a stochastic break-even concentration for every species, we prove that at most one competitor survives in the chemostat and the winner has the smallest stochastic break-even concentration, provided its response function satisfies a technical assumption. That is to say, the competitive exclusion principle holds for the stochastic competition chemostat model. Furthermore, we find that the noise experienced by one species is adverse to its growth while may be favorable for the growth of other one species. Namely, the destinies can be exchanged between two microorganism species in the chemostat due to the environmental noise.
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http://dx.doi.org/10.1007/s11538-020-00843-7DOI Listing
January 2021

Stability and Hopf bifurcation for a delayed diffusive competition model with saturation effect.

Math Biosci Eng 2020 11;17(6):8037-8051

College of Science, University of Shanghai for Science and Technology, Shanghai 200093, China.

This paper presents an investigation on the dynamics of a delayed diffusive competition model with saturation effect. We first perform the stability analysis of the positive equilibrium and the existence of Hopf bifurcations. It is shown that the positive equilibrium is asymptotically stable under some conditions, and that there exists a critical value of delay, when the delay increases across it, the positive equilibrium loses its stability and a spatially homogeneous or inhomogeneous periodic solution emerges from the positive equilibrium. Then, we derive the formulas for the determination of the direction of Hopf bifurcation and the properties of the bifurcating periodic solutions. Finally, some numerical simulations are performed to illustrate the obtained results.
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http://dx.doi.org/10.3934/mbe.2020407DOI Listing
November 2020

Baicalin rescues hyperglycemia-induced neural tube defects via targeting on retinoic acid signaling.

Am J Transl Res 2020 15;12(7):3311-3328. Epub 2020 Jul 15.

Division of Histology and Embryology, International Joint Laboratory for Embryonic Development & Prenatal Medicine, Medical College, Jinan University Guangzhou 510632, China.

We, in this study, studied whether or not antioxidant activities of Baicalin could reduce the incidence of neural tube defects (NTDs) in the presence of hyperglycemia. Using early chick embryos, we demonstrated that Baicalin at 6 μM dramatically reduced NTDs rate and impaired neurogenesis in E4.5-day and HH10 chick embryo neural tubes induced by high glucose (HG). Likewise, immunofluorescent staining showed that Baicalin mitigated the HG-induced regression of Pax7 expression in neural tubes of both HH10 and E4.5-day chick embryos. Additionally, PHIS3 immunofluorescent staining in neural tubes of both HH10 and E4.5-day chick embryos manifested that cell proliferation inhibited by HG was significantly reversed by the administration of Baicalin, and similar result could also be observed in neurosphere assay . c-Caspase3 or γH2AX immunofluorescent staining and quantitative PCR showed that Baicalin administration alleviated HG-induced cell apoptosis and DNA damage. Bioinformatics results indicated that retinoic acid (RA) was likely to be the signaling pathway that Baicalin targeted on, and this was confirmed by whole-mount RALDH2 hybridization and quantitative PCR of HH10 chick embryos in the absence/presence of Baicalin. In addition, blocking RA with an inhibitor abolished Baicalin's protective role in HG-induced NTDs, suppression of neurogenesis and cell proliferation, and induction of apoptosis, which further verified the centrality of RA in the process of Baicalin confronting HG-induced abnormal neurodevelopment.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7407732PMC
July 2020

Combine contrast-enhanced 3D T2-weighted short inversion time inversion recovery MR neurography with MR angiography at 1.5 T in the assessment of brachial plexopathy.

MAGMA 2021 Apr 13;34(2):229-239. Epub 2020 Jul 13.

Department of Radiology, The Affiliated Zhangjiagang Hospital of Soochow University, 68 Jiyang West Road, Zhangjiagang, 215600, Jiangsu, China.

Purpose: To explore the benefits of using a single injection of contrast agent at a 1.5 T system to perform both contrast-enhanced MR angiography (MRA) and 3D-T2-STIR MR neurography (MRN) to assess of brachial plexopathy.

Methods: In this prospective study, 27 patients with suspected brachial plexopathy, received an imaging procedure composed sequentially of non-enhanced 3D-T2-STIR, CE-MRA, and contrast-enhanced 3D-T2-STIR, using a 1.5 T MR scanner. Signal intensities and contrast ratios were compared with and without contrast agent. The non-enhanced and contrast-enhanced 3D-T2-STIR images were mixed for two experienced radiologists to rate image diagnostic quality in a blind manner. 3D images of MRN and MRA were merged to reveal the spatial relation between brachial plexopathy and concomitant vascular disorders.

Results: By comparing the non-enhanced with contrast-enhanced 3D-T2-STIR images, it revealed that the use of the contrast agent in 3D-T2-STIR MRN could significantly suppress the background signals contributed by small vein (P < 0.001), lymph node (P < 0.001), muscle (P < 0.001) and bone (P < 0.001). This improved the contrast ratios between the brachial plexus and its surrounding tissues (P < 0.001) and boosted the image's quality score (P < 0.01). Examining both CE-MRA and 3D-T2-STIR images revealed a relatively high incidence of concurrent vascular dysfunction in brachial plexopathy, with 39% of confirmed cases accompanied with subclavian and axillary vessel abnormalities.

Conclusion: Combining contrast-enhanced 3D-T2-STIR MRN with MRA at a 1.5 T system significantly suppresses background signals, improves brachial-plexus display, and provides a direct assessment for both brachial plexus lesion and surrounding vascular injury.
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http://dx.doi.org/10.1007/s10334-020-00867-zDOI Listing
April 2021

Fast self-assembly of microporous silk fibroin membranes on liquid surface.

Int J Biol Macromol 2020 Aug 11;156:633-639. Epub 2020 Apr 11.

State Key Laboratory of Silkworm Genome Biology, Chongqing Engineering Research Center of Biomaterial Fiber and Modern Textile, College of Textile and Garment, Southwest University, Chongqing 400715, China. Electronic address:

The air-liquid interface has been used to create micro- and nanostructured polymeric membranes. Here, we employed a novel silk fibroin (SF) solution to create ultrathin membranes effectively on the surface of subphase (30 wt% ammonium sulphate). The SF droplets spread instantaneously at the air-liquid interface driven by the surface tension difference between subphase and SF solutions. Conformational changes for SF molecules from disordered structure to ordered structure occur simultaneously. During the process, SF molecules self-assemble by rearranging hydrophobic and hydrophilic domains to minimize the free energy of the system. Dehydration and denaturation of proteins by high concentration of salt in the subphase promote the polymer solidification. Phase separation results in the porous structure of the SF membrane. Mixing aqueous gelatin with SF solution causes the reduction of pore size, porosity and mechanical properties of the membranes. More aqueous gelatin hinders the polymer solidification within short time. The as-prepared membranes have excellent transparency and cytocompatibility, which have potential for the applications of biotechnology, biomedicine and organ-on-chip.
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http://dx.doi.org/10.1016/j.ijbiomac.2020.04.053DOI Listing
August 2020

A Novel Approach for Imaging of Thoracic Outlet Syndrome Using Contrast-Enhanced Magnetic Resonance Angiography (CE-MRA), Short Inversion Time Inversion Recovery Sampling Perfection with Application-Optimized Contrasts Using Different Flip Angle Evolutions (T2-STIR-SPACE), and Volumetric Interpolated Breath-Hold Examination (VIBE).

Med Sci Monit 2019 Oct 10;25:7617-7623. Epub 2019 Oct 10.

Department of Radiology, Zhangjiagang Hospital Affiliated to Soochow University, Suzhou, Jiangsu, China (mainland).

BACKGROUND The aim of this study was to introduce a novel method combining contrast-enhanced magnetic resonance angiography (CE-MRA), short inversion time inversion recovery sampling perfection with application-optimized contrasts using different flip angle evolutions (T2-STIR-SPACE) and volumetric interpolated breath-hold examination (VIBE) sequences in the assessment of thoracic outlet syndrome (TOS). MATERIAL AND METHODS CE-MRA, T2-STIR-SPACE, and VIBE techniques were employed to evaluate neurovascular bundles in 27 patients clinically suspected of TOS. Images were evaluated to determine the cause of neurovascular bundle compression. Surgical exploration was performed in patients with abnormal magnetic resonance imaging (MRI) results. RESULTS Twenty patients were found to be abnormal: 6 cases showed only neurogenic TOS and the correlates included infraclavicular hemangiomas (n=1) and transverse cervical artery (n=5). Arterial-neurogenic TOS was found in 4 cases, including subclavian lymph node metastasis from breast cancer (n=3) and schwannoma (n=1). Arterial-venous-neurogenic TOS was found in 1 subject, and the correlates included a fibrous band from the cervical rib and elongated C7 transverse process. In this case, the subclavian artery/vein was compressed dynamically. Venous-neurogenic TOS was noted in one subject. Nine patients were considered as post-traumatic TOS, including brachial plexus edema (n=3), the brachial plexus rupture (n=2), peri-brachial plexus effusion (n=3), and stenosis of the SCA (n=1). In the remaining 7 patients, MRI did not detect abnormalities. CONCLUSIONS TOS can be evaluated by CE-MRA, T2-STIR-SPACE, and VIBE during a single examination, with a reduced contrast material dose. This imaging modality performs well in showing the anatomical structure of the neurovascular bundle and the cause of the compression.
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http://dx.doi.org/10.12659/MSM.919358DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6798723PMC
October 2019

Stochastic modeling of algal bloom dynamics with delayed nutrient recycling.

Math Biosci Eng 2018 12;16(1):1-24

College of Science, University of Shanghai for Science and Technology,Shanghai, 200093, China.

Using the discrete Markov chain, in this paper we develop a stochastic model for algal bloom, in which white noise terms are introduced to describe the effects of environmental random fluctuations and time delay to account for the time needed in the conversion of detritus into nutrient. For the proposed model, we firstly discuss the well-posedness, namely the existence and uniqueness of the global positive solution. Then, it is followed by seeking the sufficient conditions for the stochastic stability of its washout equilibrium. Then by using Fourier transform method, the spectral densities of the nutrient and the algae population are estimated. Finally, we show that larger noise can make the algae population extinct exponentially with probability one. Our theoretical and numerical results suggest that the environmental random fluctuations may have more significant influences on the dynamics of the model than the delay. These findings are helpful for a better understanding of the formation mechanism of algal blooms.
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http://dx.doi.org/10.3934/mbe.2019001DOI Listing
December 2018

Theoretical study and control optimization of an integrated pest management predator-prey model with power growth rate.

Math Biosci 2016 09 1;279:13-26. Epub 2016 Jul 1.

School of Information Engineering, Dalian University, Dalian 116622, China. Electronic address:

This work presents a pest control predator-prey model, where rate of change in prey density follows a scaling law with exponent less than one and the control is by an integrated management strategy. The aim is to investigate the change in system dynamics and determine a pest control level with minimum control price. First, the dynamics of the proposed model without control is investigated by taking the exponent as an index parameter. And then, to determine the frequency of spraying chemical pesticide and yield releases of the predator, the existence of the order-1 periodic orbit of the control system is discussed in cases. Furthermore, to ensure a certain robustness of the adopted control, i.e., for an inaccurately detected species density or a deviation, the control system could be stabilized at the order-1 periodic orbit, the stability of the order-1 periodic orbit is verified by an stability criterion for a general semi-continuous dynamical system. In addition, to minimize the total cost input in pest control, an optimization problem is formulated and the optimum pest control level is obtained. At last, the numerical simulations with a specific model are carried out to complement the theoretical results.
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http://dx.doi.org/10.1016/j.mbs.2016.06.006DOI Listing
September 2016

[Value of diffusion-weighted MRI in differentiation between benign and malignant polypoid gallbladder lesions].

Zhonghua Yi Xue Za Zhi 2015 Oct;95(39):3201-4

Imaging Department, Zhangjiagang First People's Hospital, Suzhou 215600, China.

Objective: To evaluate the efficiency of diffusion-weighted MRI in differentiating between benign and malignant polypoid gallbladder lesions.

Methods: The study population consisted of 10 benign (5 polyps, 3 adenomyomatosis and 2 adenomas) and 13 malignant (all adenocarcinomas) polypoid gallbladder lesions treated in hospital from November 2007 to May 2014. DWI was evaluated by two observers. Qualitatively, the signal intensity of the lesions on DWI was visually evaluated and categorized as iso, high, or very high signal.Quantitatively, the ADC values of the lesions were measured from ADC maps. Statistical analysis was performed using a two-tailed Fisher's exact test and the Mann-Whitney test, respectively. The cut-off values were determined by receiver operating characteristic analysis.

Results: Qualitative analysis revealed a statistical difference (P=0.036). In the 10 benign lesions, three were categorized as iso, 5 as high, and 2 as very high signal.Four of the 13 malignant lesions were categorized as high, and the remaining 9 were categorized as very high signal. The mean ADC value of the malignant lesions [(1.13±0.28)×10(-3) mm2/s] was significantly lower than that of benign lesions [(2.22±0.42)×10(-3) mm2/s, P<0.01]. The cut-off value between cancer and the benign lesions was 1.5×10(-3) mm2/s, the sensitivity, specificity, and accuracy were 92%, 100% and 96%, respectively.

Conclusion: Diffusion-weighted MRI may be useful in differentiating between benign and malignant polypoid gallbladder lesions.
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October 2015

Global Dynamics of a Virus Dynamical Model with Cell-to-Cell Transmission and Cure Rate.

Comput Math Methods Med 2015 1;2015:758362. Epub 2015 Oct 1.

Department of Mathematics, Swinburne University of Technology, P.O. Box 218, Hawthorn, VIC 3122, Australia.

The cure effect of a virus model with both cell-to-cell transmission and cell-to-virus transmission is studied. By the method of next generation matrix, the basic reproduction number is obtained. The locally asymptotic stability of the virus-free equilibrium and the endemic equilibrium is considered by investigating the characteristic equation of the model. The globally asymptotic stability of the virus-free equilibrium is proved by constructing suitable Lyapunov function, and the sufficient condition for the globally asymptotic stability of the endemic equilibrium is obtained by constructing suitable Lyapunov function and using LaSalle invariance principal.
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http://dx.doi.org/10.1155/2015/758362DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4609528PMC
June 2016

Delay-induced Turing instability in reaction-diffusion equations.

Phys Rev E Stat Nonlin Soft Matter Phys 2014 Nov 10;90(5-1):052908. Epub 2014 Nov 10.

Hubei Key Lab of Intelligent Robot, Wuhan Institute of Technology, Wuhan 430073, China.

Time delays have been commonly used in modeling biological systems and can significantly change the dynamics of these systems. Quite a few works have been focused on analyzing the effect of small delays on the pattern formation of biological systems. In this paper, we investigate the effect of any delay on the formation of Turing patterns of reaction-diffusion equations. First, for a delay system in a general form, we propose a technique calculating the critical value of the time delay, above which a Turing instability occurs. Then we apply the technique to a predator-prey model and study the pattern formation of the model due to the delay. For the model in question, we find that when the time delay is small it has a uniform steady state or irregular patterns, which are not of Turing type; however, in the presence of a large delay we find spiral patterns of Turing type. For such a model, we also find that the critical delay is a decreasing function of the ratio of carrying capacity to half saturation of the prey density.
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http://dx.doi.org/10.1103/PhysRevE.90.052908DOI Listing
November 2014

Spatial dynamics in a predator-prey model with herd behavior.

Chaos 2013 Sep;23(3):033102

College of Science, University of Shanghai for Science and Technology, Shanghai 200093, People's Republic China.

In this paper, a spatial predator-prey model with herd behavior in prey population and quadratic mortality in predator population is investigated. By the linear stability analysis, we obtain the condition for stationary pattern. Moreover, using standard multiple-scale analysis, we establish the amplitude equations for the excited modes, which determine the stability of amplitudes towards uniform and inhomogeneous perturbations. By numerical simulations, we find that the model exhibits complex pattern replication: spotted pattern, stripe pattern, and coexistence of the two. The results may enrich the pattern dynamics in predator-prey models and help us to better understand the dynamics of predator-prey interactions in a real environment.
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http://dx.doi.org/10.1063/1.4812724DOI Listing
September 2013

Bifurcation, amplitude death and oscillation patterns in a system of three coupled van der Pol oscillators with diffusively delayed velocity coupling.

Chaos 2011 Jun;21(2):023111

Department of Mathematics, Tongji University, Shanghai 200092, China.

In this paper, we study a system of three coupled van der Pol oscillators that are coupled through the damping terms. Hopf bifurcations and amplitude death induced by the coupling time delay are first investigated by analyzing the related characteristic equation. Then the oscillation patterns of these bifurcating periodic oscillations are determined and we find that there are two kinds of critical values of the coupling time delay: one is related to the synchronous periodic oscillations, the other is related to eight branches of asynchronous periodic solutions bifurcating simultaneously from the zero solution. The stability of these bifurcating periodic solutions are also explicitly determined by calculating the normal forms on center manifolds, and the stable synchronous and stable phase-locked periodic solutions are found. Finally, some numerical simulations are employed to illustrate and extend our obtained theoretical results and numerical studies also describe the switches of stable synchronous and phase-locked periodic oscillations.
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http://dx.doi.org/10.1063/1.3578046DOI Listing
June 2011

Stability and multiple bifurcations of a damped harmonic oscillator with delayed feedback near zero eigenvalue singularity.

Chaos 2008 Dec;18(4):043113

Department of Mathematics, Tongji University, Shanghai 200092, China.

We investigate the dynamics of a damped harmonic oscillator with delayed feedback near zero eigenvalue singularity. We perform a linearized stability analysis and multiple bifurcations of the zero solution of the system near zero eigenvalue singularity. Taking the time delay as the bifurcation parameter, the presence of steady-state bifurcation, Bogdanov-Takens bifurcation, triple zero, and Hopf-zero singularities is demonstrated. In the case when the system has a simple zero eigenvalue, center manifold reduction and normal form theory are used to investigate the stability and the types of steady-state bifurcation. The stability of the zero solution of the system near the simple zero eigenvalue singularity is completely solved.
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http://dx.doi.org/10.1063/1.3013195DOI Listing
December 2008

Some bifurcation methods of finding limit cycles.

Math Biosci Eng 2006 Jan;3(1):67-77

Department of Mathematics, Shanghai Normal University, Guilin Rd. 100, Shanghai, 200234 PR China.

In this paper we outline some methods of finding limit cycles for planar autonomous systems with small parameter perturbations. Three ways of studying Hopf bifurcations and the method of Melnikov functions in studying Poincare bifurcations are introduced briefly. A new method of stability- changing in studying homoclinic bifurcation is described along with some interesting applications to polynomial systems.
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http://dx.doi.org/10.3934/mbe.2006.3.67DOI Listing
January 2006