248 research outputs found
The number of limit cycles for a family of polynomial systems
AbstractIn this paper, the number of limit cycles in a family of polynomial systems was studied by the bifurcation methods. With the help of a computer algebra system (e.g., Maple 7.0), we obtain that the least upper bound for the number of limit cycles appearing in a global bifurcation of systems (2.1) and (2.2) is 5n + 5 + (1 ā (ā1)n)/2 for c ā 0 and n for c ā” 0
Bifurcations of limit cycles from quintic Hamiltonian systems with a double figure eight loopāāThe work was supported in part by Australia Research Counsil under the Discovery Projects scheme (grant ID: DP0559111).
AbstractThis paper deals with LiĆ©nard equations of the form xĖ=y, yĖ=P(x)+yQ(x,y), with P and Q polynomials of degree 5 and 4 respectively. Attention goes to perturbations of the Hamiltonian vector fields with an elliptic Hamiltonian of degree six, exhibiting a double figure eight loop. The number of limit cycles and their distributions are given by using the methods of bifurcation theory and qualitative analysis
SVEIRS: A New Epidemic Disease Model with Time Delays and Impulsive Effects
We first propose a new epidemic disease model governed by system of impulsive delay differential equations. Then, based on theories for impulsive delay differential equations, we skillfully solve the difficulty in analyzing the global dynamical behavior of the model with pulse vaccination and impulsive population input effects at two different periodic moments. We prove the existence and global attractivity of the āinfection-freeā periodic solution and also the permanence of the model. We then carry out numerical simulations to illustrate our theoretical results, showing us that time delay, pulse vaccination, and pulse population input can exert a significant influence on the dynamics of the system which confirms the availability of pulse vaccination strategy for the practical epidemic prevention. Moreover, it is worth pointing out that we obtained an epidemic control strategy for controlling the number of population input
Synchronous Image-Label Diffusion Probability Model with Application to Stroke Lesion Segmentation on Non-contrast CT
Stroke lesion volume is a key radiologic measurement for assessing the
prognosis of Acute Ischemic Stroke (AIS) patients, which is challenging to be
automatically measured on Non-Contrast CT (NCCT) scans. Recent diffusion
probabilistic models have shown potentials of being used for image
segmentation. In this paper, a novel Synchronous image-label Diffusion
Probability Model (SDPM) is proposed for stroke lesion segmentation on NCCT
using Markov diffusion process. The proposed SDPM is fully based on a Latent
Variable Model (LVM), offering a complete probabilistic elaboration. An
additional net-stream, parallel with a noise prediction stream, is introduced
to obtain initial noisy label estimates for efficiently inferring the final
labels. By optimizing the specified variational boundaries, the trained model
can infer multiple label estimates for reference given the input images with
noises. The proposed model was assessed on three stroke lesion datasets
including one public and two private datasets. Compared to several U-net and
transformer-based segmentation methods, our proposed SDPM model is able to
achieve state-of-the-art performance. The code is publicly available
Relationship between EGFR expression, copy number and mutation in lung adenocarcinomas
<p>Abstract</p> <p>Background</p> <p>This study was designed to investigate EGFR protein expression, EGFR copy number and EGFR mutations in lung adenocarcinomas, to explore the relationship of the three markers.</p> <p>Methods</p> <p>EGFR status was analyzed in surgically resected lung adenocarcinoma samples from 133 Chinese patients by three methods: protein expression (n = 133) by standardized immunohistochemistry (IHC), gene copy number (n = 133) by fluorescence in situ hybridization (FISH), and mutation analysis using the Scorpion amplification refractory mutation system (ARMS) (n = 133).</p> <p>Results</p> <p>The results showed that 68.4% of the samples were positive by IHC, 42.1% were positive by FISH, and 63.9% contained activating kinase domain mutations. EGFR mutations were more frequent in non-smoking patients (p = 0.008), and EGFR mutations were associated with EGFR FISH positivity (p < 0.0001). When using 10% positivity and 2+ as cutoffs, EGFR protein expression was significantly correlated with EGFR FISH positivity (p = 0.012) and EGFR mutations (p = 0.008) after Bonferroni correction.</p> <p>Conclusion</p> <p>EGFR protein expression, EGFR copy number and EGFR mutations were closely related to each other. Standard methods and interpretation criteria need to be established.</p
A stage-structured predator-prey si model with disease in the prey and impulsive effects
This paper aims to develop a high-dimensional SI model with stage structure for both the prey (pest) and the predator, and then to investigate the dynamics of it. The model can be used for the study of Integrated Pest Management (IPM) which is a combination of constant pulse releasing of animal enemies and diseased pests at two different fixed moments. Firstly, we use analytical techniques for impulsive delay differential equations to obtain the conditions for global attractivity of the āpest-freeā periodic solution and permanence of the population model. It shows that the conditions strongly depend on time delay, impulsive release of animal enemies and infective pests. Secondly, we present a pest management strategy in which the pest population is kept under the economic threshold level (ETL) when the pest population is permanent. Finally, numerical analysis is presented to illustrate our main conclusion
Study on the quality change of crown pear during storage
Using the high-quality Crown Pear as the subject of experimental research, an analysis of the changes in the quality of Crown Pears during a storage period is conducted to provide a theoretical basis for the development of the pear cold storage industry. The study utilizes a handheld digital refractometer, texture analyzer, colorimeter, T-type thermocouple, and electronic balance to explore six aspects of Crown Pears: soluble solids content, hardness, color difference, freezing point, drying loss, and taste. The results reveal the following changes in pear quality during different storage periods within one cycle: the content of soluble solids in Crown Pears initially increases and then decreases during the storage period; hardness decreases with increasing storage time; the external appearance of pears gradually darkens; and drying loss increases with storage time. During the cold storage process of Crown Pears, the optimal temperature setting for the cold storage should be maintained at -1Ā°C to 0.5Ā°C. The flavor of Crown Pears is not optimal during the early stage of storage. The storage time for Crown Pears should be within four months
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