Oxygen transfer in human carotid artery bifurcation
Institute of Scientific and Technical Information of China (English)
Z.G.Zhang; Y.B.Fan; X.Y.Deng
2007-01-01
Arterial bifurcations are places where blood flow may be disturbed and slow recirculation flow may occur.To reveal the correlation between local oxygen transfer and atherogenesis, a finite element method was employed to simulate the blood flow and the oxygen transfer in the human carotid artery bifurcation. Under steady-state flow conditions, the numerical simulation demonstrated a variation in local oxygen transfer at the bifurcation, showing that the convective condition in the disturbed flow region may produce uneven local oxygen transfer at the blood/wall interface.The disturbed blood flow with formation of slow eddies in the carotid sinus resulted in a depression in oxygen supply to the arterial wall at the entry of the sinus, which in turn may lead to an atherogenic response of the arterial wall, and contribute to the development of atherosclerotic stenosis there.
Sex differences in intracranial arterial bifurcations
DEFF Research Database (Denmark)
Lindekleiv, Haakon M; Valen-Sendstad, Kristian; Morgan, Michael K; Mardal, Kent-Andre; Faulder, Kenneth; Magnus, Jeanette H; Waterloo, Knut; Romner, Bertil; Ingebrigtsen, Tor
2010-01-01
Subarachnoid hemorrhage (SAH) is a serious condition, occurring more frequently in females than in males. SAH is mainly caused by rupture of an intracranial aneurysm, which is formed by localized dilation of the intracranial arterial vessel wall, usually at the apex of the arterial bifurcation. T...... female preponderance is usually explained by systemic factors (hormonal influences and intrinsic wall weakness); however, the uneven sex distribution of intracranial aneurysms suggests a possible physiologic factor-a local sex difference in the intracranial arteries....
Shape optimization of the carotid artery bifurcation
Bressloff, N. W.; Forrester, A.I.J.; Banks, J.; Bhaskar, K.V.
2004-01-01
A parametric CAD model of the human carotid artery bifurcation is employed in an initial exploration of the response of shear stress to the variation of the angle of the internal carotid artery and the width of the sinus bulb. Design of experiment and response surface technologies are harnessed for the first time in such an application with the aim of developing a better understanding of the relationship between geometry (anatomy) and sites of arterial disease.
Internal carotid artery bifurcation aneurysms. Surgical experience
International Nuclear Information System (INIS)
Internal carotid artery (ICA) bifurcation aneurysms are relatively uncommon and frequently rupture at a younger age compared to other intracranial aneurysms. We have treated a total of 999 patients for intracranial aneurysms, of whom 89 (8.9%) had ICA bifurcation aneurysms, and 42 of the 89 patients were 30 years of age or younger. The present study analyzed the clinical records of 70 patients with ICA bifurcation aneurysms treated from mid 1997 to mid 2003. Multiple aneurysms were present in 15 patients. Digital subtraction angiography films were studied in 55 patients to identify vasospasm and aneurysm projection. The aneurysm projected superiorly in most of these patients (37/55, 67.3%). We preferred to minimize frontal lobe retraction, so widely opened the sylvian fissure to approach the ICA bifurcation and aneurysm neck. Elective temporary clipping was employed before the final dissection and permanent clip application. Vasospasm was present in 24 (43.6%) of 55 patients. Forty-eight (68.6%) of the 70 patients had good outcome, 14 (20%) had poor outcome, and eight (11.4%) died. Patients with ICA bifurcation aneurysms tend to bleed at a much younger age compared to those with other intracranial aneurysms. Wide opening of the sylvian fissure and elective temporary clipping of the ICA reduces the risk of intraoperative rupture and perforator injury. Mortality was mainly due to poor clinical grade and intraoperative premature aneurysm rupture. (author)
International Nuclear Information System (INIS)
The aim of this study was to investigate the plaques at the left coronary artery (LCA) and their effect on the haemodynamic and wall shear stress (WSS) in realistic patient models. Three sample patients with left coronary disease were selected based on CT data. The plaques were present at the left anterior descending and left circumflex branches with more than 50 % lumen narrowing. Computational fluid dynamics analysis was used to perform simulation of patient-specific models with realistic physiological conditions that demonstrate in vivo cardiac flow. WSS and blood flow in the LCA were measured during cardiac cycles. Our results showed that WSS was found to increase at the stenotic locations and decrease at pre- and post-plaque locations, whilst the recirculation location was found at post-plaque regions. There is a strong correlation between coronary bifurcation plaques and hemodynamic and WSS changes, based on the realistic coronary disease models.
HIGH BIFURCATION OF THE BRACHIAL ARTERY - A COMMON VARIANT
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Sesi
2015-10-01
Full Text Available 28 cadavers were dissected for variations in the bifurcation of brachial artery bilaterally {n=56} at the department of anatomy, Rangaraya Medical College, Kakinada, A.P. from 2010 to 2015 . Found variations during routine dissections for first year MBBS students. The findings have thrown light on the common as well as rare variants in the anatomy of brachial artery bifurcation and the course of radial and ulnar arteries in current study
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Lee, Cheng-Hung [Division of Cardiology, Department of Internal Medicine, Chang Gung Memorial Hospital, Linkou, Chang Gung University College of Medicine, Tao-Yuan, Taiwan (China); Department of Mechanical Engineering, Chang Gung University, Tao-Yuan, Taiwan (China); Jhong, Guan-Heng [Graduate Institute of Medical Mechatronics, Chang Gung University, Tao-Yuan, Taiwan (China); Hsu, Ming-Yi; Wang, Chao-Jan [Department of Medical Imaging and Intervention, Chang Gung Memorial Hospital, Linkou, Tao-Yuan, Taiwan (China); Liu, Shih-Jung, E-mail: shihjung@mail.cgu.edu.tw [Department of Mechanical Engineering, Chang Gung University, Tao-Yuan, Taiwan (China); Hung, Kuo-Chun [Division of Cardiology, Department of Internal Medicine, Chang Gung Memorial Hospital, Linkou, Chang Gung University College of Medicine, Tao-Yuan, Taiwan (China)
2014-05-28
The deployment of metallic stents during percutaneous coronary intervention has become common in the treatment of coronary bifurcation lesions. However, restenosis occurs mostly at the bifurcation area even in present era of drug-eluting stents. To achieve adequate deployment, physicians may unintentionally apply force to the strut of the stents through balloon, guiding catheters, or other devices. This force may deform the struts and impose excessive mechanical stresses on the arterial vessels, resulting in detrimental outcomes. This study investigated the relationship between the distribution of stress in a stent and bifurcation angle using finite element analysis. The unintentionally applied force following stent implantation was measured using a force sensor that was made in the laboratory. Geometrical information on the coronary arteries of 11 subjects was extracted from contrast-enhanced computed tomography scan data. The numerical results reveal that the application of force by physicians generated significantly higher mechanical stresses in the arterial bifurcation than in the proximal and distal parts of the stent (post hoc P < 0.01). The maximal stress on the vessels was significantly higher at bifurcation angle <70° than at angle ≧70° (P < 0.05). The maximal stress on the vessels was negatively correlated with bifurcation angle (P < 0.01). Stresses at the bifurcation ostium may cause arterial wall injury and restenosis, especially at small bifurcation angles. These finding highlight the effect of force-induced mechanical stress at coronary artery bifurcation stenting, and potential mechanisms of in-stent restenosis, along with their relationship with bifurcation angle.
Wall Shear Stress Distribution in Patient Specific Coronary Artery Bifurcation
Directory of Open Access Journals (Sweden)
Vahab Dehlaghi
2010-01-01
Full Text Available Problem statement: Atherogenesis is affected by hemodynamic parameters, such as wall shear stress and wall shear stress spatial gradient. These parameters are largely dependent on the geometry of arterial tree. Arterial bifurcations contain significant flow disturbances. Approach: The effects of branch angle and vessel diameter ratio at the bifurcations on the wall shear stress distribution in the coronary arterial tree based on CT images were studied. CT images were digitally processed to extract geometrical contours representing the coronary vessel walls. The lumen of the coronary arteries of the patients was segmented using the open source software package (VMTK. The resulting lumens of coronary arteries were fed into a commercial mesh generator (GAMBIT, Fluent Inc. to generate a volume that was filled with tetrahedral elements. The FIDAP software (Fluent Corp. was used to carry out the simulation by solving Navier-Stokes equations. The FIELDVIEW software (Version 10.0, Intelligent Light, Lyndhurst, NJ was used for the visualization of flow patterns and the quantification of wall shear stress. Post processing was done with VMTK and MATLAB. A parabolic velocity profile was prescribed at the inlets and outlets, except for 1. Stress free outlet was assigned to the remaining outlet. Results: The results show that for angle lower than 90°, low shear stress regions are observed at the non-flow divider and the apex. For angle larger than 90°, low shear stress regions only at the non-flow divider. By increasing of diameter of side branch ratio, low shear stress regions in the side branch appear at the non-flow divider. Conclusion: It is concluded that not only angle and diameter are important, but also the overall 3D shape of the artery. More research is required to further quantify the effects angle and diameter on shear stress patterns in coronaries.
Sultanov, Renat A
2008-01-01
We report computational results of blood flow through a model of the human aortic arch and a vessel of actual diameter and length. On the top of the aortic arch the branching of the %%three arteries are included: the subclavian and jugular. A realistic pulsatile flow is used in all simulations. Calculations for bifurcation type vessels are also carried out and presented. Different mathematical methods for numerical solution of the fluid dynamics equations have been considered. The non-Newtonian behaviour of the human blood is investigated together with turbulence effects. A detailed time-dependent mathematical convergence test has been carried out. The results of computer simulations of the blood flow in vessels of three different geometries are presented: for pressure, strain rate and velocity component distributions we found significant disagreements between our results obtained with realistic non-Newtonian treatment of human blood and the widely used method in the literature: a simple Newtonian approximati...
Huang, Xu; Yin, Xiaoping; Xu, Yingjin; Jia, Xinwei; Li, Jianhui; Niu, Pei; Shen, Wenzeng; Kassab, Ghassan S; Tan, Wenchang; Huo, Yunlong
2016-03-01
Although atherosclerosis has been widely investigated at carotid artery bifurcation, there is a lack of morphometric and hemodynamic data at different stages of the disease. The purpose of this study was to determine the lesion difference in patients with carotid artery disease compared with healthy control subjects. The three-dimensional (3D) geometry of carotid artery bifurcation was reconstructed from computed tomography angiography (CTA) images of Chinese control subjects (n = 30) and patients with carotid artery disease (n = 30). We defined two novel vector angles (i.e., angles 1 and 2) that were tangential to the reconstructed contour of the 3D vessel. The best-fit diameter was computed along the internal carotid artery (ICA) center line. Hemodynamic analysis was performed at various bifurcations. Patients with stenotic vessels have larger angles 1 and 2 (151 ± 11° and 42 ± 20°) and smaller diameters of the external carotid artery (ECA) (4.6 ± 0.85 mm) compared with control subjects (144 ± 13° and 36 ± 16°, 5.2 ± 0.57 mm) although there is no significant difference in the common carotid artery (CCA) (7.1 ± 1.2 vs. 7.5 ± 1.0 mm, P = 0.18). In particular, all patients with carotid artery disease have a stenosis at the proximal ICA (including both sinus and carina regions), while 20% of patients have stenosis at the middle ICA and 20% have stenosis expansion to the entire cervical ICA. Morphometric and hemodynamic analyses suggest that atherosclerotic plaques initiate at both sinus and carina regions of ICA and progress downstream. PMID:26747497
Narayan, Hari K; Glatz, Andrew C; Rome, Jonathan J
2015-10-01
Balloon angioplasty and stent placement in close proximity to the bifurcation of the branch pulmonary arteries can be challenging. Multiple approaches have been previously described, though none of these approaches both treats bilateral proximal branch pulmonary artery stenosis and provides an anchor for a transcatheter pulmonary valve replacement. We report a novel approach that involves serial stent placement and balloon dilation through the struts of the stent in each pulmonary artery, along with balloon expansion of the proximal portion of the stents to the diameter of the main pulmonary artery. In the two cases we describe, this strategy resulted in significant relief of branch pulmonary artery obstruction without compromising the anatomy of the main pulmonary artery segment. This technique can be an effective way to alleviate stenoses of the bilateral proximal branch pulmonary arteries and provides a landing zone for a future transcatheter pulmonary valve. PMID:26256829
Rotational digital subtraction angiography of carotid artery bifurcation stenoses
International Nuclear Information System (INIS)
Purpose: A prospektive study was designed to evaluate, whether multiplanar imaging with rotational digital subtraction angiography (R-DSA) could improve assessment of carotid artery bifurcation stenosis. Patients and methods: 45 patients with suspected stenosis of the ICA were examined with DSA in standard projections (0 -(45 )-90 ) and additional R-DSA of each ICA from 0-90 in 10 steps. We compared imaging quality and degree of stenosis as well as exposure of the patients to radiation and contrast media. Results: 79/82 R-DSA (96%) were suitable for evaluation of stenosis, 58/82 (70%) matched the quality standard of single projection DSA. Specificity and sensitivity of the R-DSA to diagnose high grade ACI stenosis were 100% and 94%, respectively. 7/79 R-DSA revealed a higher and 3/79 a lower degree of stenosis than the corresponding DSA. Regarding the degree of stenosis there was no significant difference between the two modalities (p>0,05), but R-DSA detected 4 stenoses greater than 60% that were estimated to be lower than 60% by DSA. Radiation dose for R-DSA was equivalent to one DSA run (170 cGycm2). The average amount of contrast media (25 ml) was slightly higher than for 2-3 single-projection DSA (19,8 ml). Conclusions: R-DSA provides high quality imaging of the carotid bifurcation with multiplanar projections facilitating exact grading of vessel stenosis. The number of cases (n=2) is to small to judge the value of R-DSA as to (tandem-) stenosis of the distal ICA. Still, diagnostic value and low radiation exposure justify the use of R-DSA as additional series to standard protocols. (orig.)
Endovascular coil embolization in internal carotid artery bifurcation aneurysms
International Nuclear Information System (INIS)
Aim: To present the clinical and radiological results of coil embolization in internal carotid artery (ICA) bifurcation aneurysms (BA). Materials and methods: The records of 65 patients with 66 ICA BA were retrieved from data prospectively accrued between September 1999 and July 2013. Clinical and morphological outcomes of the aneurysms were assessed, including technical aspects of treatment. Results: The aneurysms under study were directed either superiorly (41/66, 62.1%), anteriorly (24/66, 36.4%), or posteriorly (1/66, 1.5%), and all were devoid of perforators. Aneurysmal necks were situated symmetrically at the terminal ICA (37/66, 56.1%) or slightly deviated to the proximal A1 segment (29/66, 43.9%). The steam-shaped S microcatheter (73.8%) was most commonly used to select the aneurysms, and the single microcatheter technique was most commonly applied (56.1%) to perform coil embolization, followed by balloon remodelling (21.2%), multiple microcatheter (15.1%), and stent-protection (7.6%). Successful aneurysmal occlusion was achieved in 100% of cases, with no procedure-related morbidity or mortality. Imaging performed in the course of follow-up (mean duration 27.3 months) confirmed stable occlusion of most lesions (47/53, 88.7%). Conclusion: Through tailored technical strategies, ICA BA are amenable to safe and effective endovascular coil embolization, with a tendency for stable occlusion long-term
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Objective: to evaluate the efficacy and safety of percutaneous endovascular management with single stent in treating symptomatic series stenosis located at subclavian-vertebral artery bifurcation. Methods: Between February 2009 and April 2010, percutaneous single-stent endovascular treatment was carried out in 7 consecutive patients with symptomatic series stenosis located at subclavian-vertebral artery bifurcation. After implantation of cerebral protection device, percutaneous single-stent endovascular procedure was performed to treat two stenoses at subclavian-vertebral artery bifurcation. All patients were followed up for 3∼15 months. The therapeutic efficacy was evaluated with the observation of clinical symptoms and Doppler ultrasonic examination, the possible occurrence of re-stenosis was checked. Results: Technical success was achieved in all seven patients. After the implantation the residual stenosis of both subclavian and vertebral arteries was less than 10%. No procedure-related complications occurred. During the follow-up period no re-stenosis was observed on Doppler ultrasonography, the clinical symptoms were markedly improved, and no cerebrovascular accident or new cerebral infarction occurred. Conclusion: For the treatment of series stenosis located at subclavian-vertebral artery bifurcation percutaneous single-stent endovascular implantation is a feasible technique. Compared with other methods, this technique carries the advantages of easier manipulation and higher safety for patient although long-term efficacy needs to be further observed. (authors)
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Aim: To investigate the angle changes of the parent arteries after stent-assisted coil embolization of wide-necked intracranial bifurcation aneurysms. Materials and methods: The adjacent parent arterial angles before and after stent-assisted coil embolization were measured in 38 patients with aneurysms of the anterior communicating artery (ACoAA) and 41 patients with bifurcation aneurysms of the middle cerebral artery (MCABA). Variables were analysed in relation to the angle changes. Results: Vascular angles of the parent arteries significantly increased by 27.8° (±18.5°) immediately after stent-assisted coil embolization in 79 cases (p < 0.001), with 25.7° (±14.8°) in ACoAA and 29.7° (±21.4°) in MCABA, respectively. In 51 (64.6%) cases with follow-up angiography (mean interval 13.5 ± 4.1 months), vascular angles increased by 27.2° (±17.1°) immediately after treatment and further increased by 20.7° (±14.3°) at the last follow-up (all p < 0.001). More acute pre-stent angles of the parent arteries correlated with greater post-stent angle changes (p = 0.006). Younger age tended to be inversely related to post-stent angle changes (p = 0.091). Conclusion: Stent placement during coil embolization induced significant changes in the aneurysm–parent artery relationship. Further study is needed to elicit the association between angle change of the parent arteries and aneurysmal stability after coil embolization
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Background: Carpal tunnel syndrome is a sporadically occurring abnormality due to compression of median nerve. It is exceedingly rare for it to be caused by thrombosis of persistent median artery. Case Report: A forty two year old female was referred for ultrasound examination due to ongoing wrist pain, not relived by pain killers and mild paraesthesia on the radial side of the hand. High resolution ultrasound and Doppler revealed a thrombosed persistent median artery and associated bifurcated median nerve. The thrombus resolved on treatment with anticoagulants. Conclusions: Ultrasound examination of the wrist when done for patients with carpal tunnel syndrome should preferably include looking for persistent median artery and its patency. (authors)
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Chen, Yong, E-mail: cheny102@163.com; Ye, Peng, E-mail: thomas19871223@163.com [Southern Medical University, Department of Interventional Radiology, Nanfang Hospital (China); Jiang, Wen-jin, E-mail: 18653501187@163.com [Yantai Yuhuangding Hospital (China); Ma, Shuo-yi, E-mail: mazelong123456789@126.com; Zhao, Jian-bo, E-mail: zhaojianbohgl@163.com; Zeng, Qing-le, E-mail: doctorzengqingle@126.com [Southern Medical University, Department of Interventional Radiology, Nanfang Hospital (China)
2015-10-15
Bifurcation stenoses after end-to-side anastomosis of transplant renal artery (TRA) and external iliac artery (EIA), including stenoses at the anastomosis and the iliac artery proximal to the TRA, are rare. In the present article, we report two successfully managed cases of bifurcation stenoses after end-to-side anastomosis of the TRA and EIA using the technique of T-stenting and small protrusion (TAP stenting)
International Nuclear Information System (INIS)
Bifurcation stenoses after end-to-side anastomosis of transplant renal artery (TRA) and external iliac artery (EIA), including stenoses at the anastomosis and the iliac artery proximal to the TRA, are rare. In the present article, we report two successfully managed cases of bifurcation stenoses after end-to-side anastomosis of the TRA and EIA using the technique of T-stenting and small protrusion (TAP stenting)
Perwaiz Khan, Samia; Gul, Pashmina; Khemani, Saleem; Yaqub, Zia
2013-01-01
Objective: To determine site specific carotid intima-media thickness: common–carotid artery and carotid bifurcation in hypercholesterolemia patients as a marker for atherosclerosis. Methods: Fifty patients with hypercholesterolemia and twenty controls were selected after getting informed consent regarding the investigation of carotid- intima media thickness by B-mode ultrasound. All the patients of hypercholesterolemia with LDL-C > 160mg/dL had family history of coronary artery diseases. This...
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Objective: To preliminarily evaluate the feasibility, safety and efficacy of stent placement for the treatment of wide-necked aneurysms located at internal carotid artery bifurcation. Methods: Eleven patients with wide-necked aneurysms located at internal carotid artery bifurcation, who were encountered during the period from Jan. 2004 to Dec. 2010 in hospital, were collected. A total of 16 intracranial aneurysms were detected, of which 11 were wide-necked and were located at internal carotid artery bifurcation. The diameters of the aneurysms ranged from 2.5 mm to 18 mm. Individual stent type and stenting technique was employed for each patient. Follow-up at 1, 3, 6 and 12 months after the procedure was conducted. Results: A total of 11 different stents were successfully deployed in the eleven patients. The stents included balloon expandable stent (n=1) and self-expanding stent (n=10). According to Raymond grading for the immediate occlusion of the aneurysm, grade Ⅰ (complete obliteration) was obtained in 4, grade Ⅱ (residual neck) in 2 and grade Ⅲ (residual aneurysm) in 5 cases. No procedure-related complications occurred. At the time of discharge, the modified Rankin score was 0-1 in the eleven patients. During the follow-up period lasting for 1-108 months, all the patients were in stable condition and no newly-developed neurological dysfunction or bleeding observed. Follow-up examination with angiography (1-48 months) showed that the aneurysms were cured (no visualization) in 4 cases, improved in 2 cases and in stable condition in one case. Conclusion: For the treatment of wide-necked aneurysms located at internal carotid artery bifurcation, stent implantation is clinically feasible, safe and effective. Further studies are required to evaluate its long-term efficacy. (authors)
Atherosclerosis at arterial bifurcations: evidence for the role of haemodynamics and geometry.
Morbiducci, Umberto; Kok, Annette M; Kwak, Brenda R; Stone, Peter H; Steinman, David A; Wentzel, Jolanda J
2016-03-01
Atherosclerotic plaques are found at distinct locations in the arterial system, despite the exposure to systemic risk factors of the entire vascular tree. From the study of arterial bifurcation regions, emerges ample evidence that haemodynamics are involved in the local onset and progression of the atherosclerotic disease. This observed co-localisation of disturbed flow regions and lesion prevalence at geometrically predisposed districts such as arterial bifurcations has led to the formulation of a 'haemodynamic hypothesis', that in this review is grounded to the most current research concerning localising factors of vascular disease. In particular, this review focuses on carotid and coronary bifurcations because of their primary relevance to stroke and heart attack. We highlight reported relationships between atherosclerotic plaque location, progression and composition, and fluid forces at vessel's wall, in particular shear stress and its 'easier-to-measure' surrogates, i.e. vascular geometric attributes (because geometry shapes the flow) and intravascular flow features (because they mediate disturbed shear stress), in order to give more insight in plaque initiation and destabilisation. Analogous to Virchow's triad for thrombosis, atherosclerosis must be thought of as subject to a triad of, and especially interactions among, haemodynamic forces, systemic risk factors, and the biological response of the wall. PMID:26740210
Directory of Open Access Journals (Sweden)
Cüneyt Eriş
2013-09-01
Full Text Available Arteriosclerosis, is mostly affect coronary and carotid arteriesespecially the ostium and bifurcation due to the natureof the flow. Arterial bifurcation lesions cause dilemmafor the treating physician during both surgical and invasiveprocedures because they require a higher clinical experienceand longer processing time. In carotid artery surgery,it is accepted that patchplasty prevents perioperativeand postoperative restenosis, and as a result of this, itreduces the incidence of ipsilateral stroke. In the presenttime synthetic patch materials (PTFE, Dacron and autologouspatch materials (saphenous and jugular veins areused. We report a case of carotid endarterectomy and ‘Y’shaped saphenous patchplasty to the carotid bifurcation.According to our research in the literature, we didn’t findany case with ‘Y’ shaped saphenous vein patch. Therewas only one Y shaped carotid patchplasty case by usingPTFE material. Our original technic is advantageous interms of easy preparation and application as well as itssuccessful outcome.Key words: Carotid artery diseases, saphenous vein,patchplasty
International Nuclear Information System (INIS)
Purpose: Simple rating scale for calcification in the cervical arteries and the aortic arch on multi-detector computed tomography angiography (MDCTA) was evaluated its reliability and validity. Additionally, we investigated where is the most representative location for evaluating the calcification risk of carotid bifurcation stenosis and atherosclerotic infarction in the overall cervical arteries covering from the aortic arch to the carotid bifurcation. Method: The aortic arch and cervical arteries among 518 patients (292 men, 226 women) were evaluated the extent of calcification using a 4-point grading scale for MDCTA. Reliability, validity and the concomitant risk with vascular stenosis and atherosclerotic infarction were assessed. Results: Calcification was most frequently observed in the aortic arch itself, the orifices from the aortic arch, and the carotid bifurcation. Compared with the bilateral carotid bifurcations, the aortic arch itself had a stronger inter-observer agreement for the calcification score (Fleiss’ kappa coefficients; 0.77), but weaker associations with stenosis and atherosclerotic infarction. Calcification at the orifices of the aortic arch branches had a stronger inter-observer agreement (0.74) and enough associations with carotid bifurcation stenosis and intracranial stenosis. In addition, the extensive calcification at the orifices from the aortic arch was significantly associated with atherosclerotic infarction, similar to the calcification at the bilateral carotid bifurcations. Conclusions: The orifices of the aortic arch branches were the novel representative location of the aortic arch and overall cervical arteries for evaluating the calcification extent. Thus, calcification at the aortic arch should be evaluated with focus on the orifices of 3 main branches
Model generation of coronary artery bifurcations from CTA and single plane angiography
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Cardenes, Ruben; Diez, Jose L.; Duchateau, Nicolas; Pashaei, Ali; Frangi, Alejandro F. [Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB)-Universitat Pompeu Fabra and Networking Biomedical Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Barcelona 08018 (Spain); Cardiology Department, University Hospital Dr. Peset, Valencia 46017 (Spain); Hospital Clinic Provincial de Barcelona, Institut d' investigacions Biomediques August Pi i Sunyer-Universitat de Barcelona, Barcelona 08036 (Spain); Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB)-Universitat Pompeu Fabra and Networking Biomedical Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Barcelona 08018 (Spain); Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB)-Universitat Pompeu Fabra and Networking Biomedical Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Barcelona 08018, Spain and Department of Mechanical Engineering, University of Sheffield, Sheffield S1 3JD (United Kingdom)
2013-01-15
Purpose: To generate accurate and realistic models of coronary artery bifurcations before and after percutaneous coronary intervention (PCI), using information from two image modalities. Because bifurcations are regions where atherosclerotic plaque appears frequently and intervention is more challenging, generation of such realistic models could be of high value to predict the risk of restenosis or thrombosis after stent implantation, and to study geometrical and hemodynamical changes. Methods: Two image modalities have been employed to generate the bifurcation models: computer tomography angiography (CTA) to obtain the 3D trajectory of vessels, and 2D conventional coronary angiography (CCA) to obtain radius information of the vessel lumen, due to its better contrast and image resolution. In addition, CCA can be acquired right before and after the intervention in the operation room; therefore, the combination of CTA and CCA allows the generation of realistic preprocedure and postprocedure models of coronary bifurcations. The method proposed is semiautomatic, based on landmarks manually placed on both image modalities. Results: A comparative study of the models obtained with the proposed method with models manually obtained using only CTA, shows more reliable results when both modalities are used together. The authors show that using preprocedure CTA and postprocedure CCA, realistic postprocedure models can be obtained. Analysis carried out of the Murray's law in all patient bifurcations shows the geometric improvement of PCI in our models, better than using manual models from CTA alone. An experiment using a cardiac phantom also shows the feasibility of the proposed method. Conclusions: The authors have shown that fusion of CTA and CCA is feasible for realistic generation of coronary bifurcation models before and after PCI. The method proposed is efficient, and relies on minimal user interaction, and therefore is of high value to study geometric and
Javadzadegan, Ashkan; Lotfi, Azadeh; Simmons, Anne; Barber, Tracie
2016-08-01
Thrombus in a femoral artery may form under stagnant flow conditions which vary depending on the local arterial waveform. Four different physiological flow waveforms - poor (blunt) monophasic, sharp monophasic, biphasic and triphasic - can exist in the femoral artery as a result of different levels of peripheral arterial disease progression. This study aims to examine the effect of different physiological waveforms on femoral artery haemodynamics. In this regard, a fluid-structure interaction analysis was carried out in idealised models of bifurcated common femoral artery. The results showed that recirculation zones occur in almost all flow waveforms; however, the sites at where these vortices are initiated, the size and structure of vortices are highly dependent on the type of flow waveform being used. It was shown that the reverse diastolic flow in biphasic and triphasic waveforms leads to the occurrence of a retrograde flow which aids in 'washout' of the disturbed flow regions. This may limit the likelihood of thrombus formation, indicating the antithrombotic role of retrograde flow in femoral arteries. Furthermore, our data revealed that the flow particles experience considerably higher residence time under blunt and sharp monophasic waveforms than under biphasic and triphasic waveforms. This confirms that the risk of atherothrombotic plaque initiation and development in femoral arteries is higher under blunt and sharp monophasic waveforms than under biphasic and triphasic flow waveforms. PMID:26582544
Effect of blood flow parameters on flow patterns at arterial bifurcations--studies in models.
Liepsch, D W
1990-01-01
Atherosclerotic lesions are found primarily at arterial bends and bifurcations. Flow disturbances at these anatomic sites play a major role in atherogenesis. How hemodynamic factors such as vessel geometry, the pulsatile nature of blood flow, vessel wall elasticity and the non-Newtonian flow behavior of blood influence the flow field at these sites must be clarified. We have performed fundamental studies using a birefringent solution in a simplified rigid 90 degree T-bifurcation and pulsatile flow. The velocity distribution was measured with a laser Doppler anemometer. Flow in an elastic abdominal aorta model has been visualized using magnetic resonance imaging. In both flow studies, zones with negative velocity were found. These model measurements demonstrate that no flow parameter can be neglected. Further detailed studies are necessary to examine the interaction between fluid dynamic and cellular surface properties. PMID:2404201
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McKinney, Alexander M.; Casey, Sean O.; Teksam, Mehmet; Truwit, Charles L.; Kieffer, Stephen [University of Minnesota Medical School, Departments of Radiology, Minneapolis, MN (United States); Lucato, Leandro T. [Clinics Hospital, University of Sao Paulo, Sao Paulo (Brazil); Smith, Maurice [Johns Hopkins University, Department of Biomedical Engineering, Baltimore, MD (United States)
2005-01-01
The aim of this paper was to determine the correlation between calcium burden (expressed as a volume) and extent of stenosis of the origin of the internal carotid artery (ICA) by CT angiography (CTA). Previous studies have shown that calcification in the coronary arteries correlates with significant vessel stenosis, and severe calcification (measured by CT) in the carotid siphon correlates with significant (greater than 50% stenosis) as determined angiographically. Sixty-one patients (age range 50-85 years) underwent CT of the neck with intravenous administration of iodinated contrast for a variety of conditions. Images were obtained with a helical multidetector array CT scanner and reviewed on a three-dimensional workstation. A single observer manipulated window and level to segment calcified plaque from vascular enhancement in order to quantify vascular calcium volume (cc) in the region of the bifurcation of the common carotid artery/ICA origin, and to measure the extent of ICA stenosis near the origin. A total of 117 common carotid artery bifurcations were reviewed. A ''significant'' stenosis was defined arbitrarily as >40% (to detect lesions before they become hemodynamically significant) of luminal diameter on CTA using NASCET-like criteria. All ''significant'' stenoses (21 out of 117 carotid bifurcations) had measurable calcium. We found a relatively strong correlation between percent stenosis and the calcium volume (Pearson's r= 0.65, P<0.0001). We also found that there was an even stronger correlation between the square root of the calcium volume and the percent stenosis as measured by CTA (r= 0.77, P<0.0001). Calcium volumes of 0.01, 0.03, 0.06, 0.09 and 0.12 cc were used as thresholds to evaluate for a ''significant'' stenosis. A receiver operating characteristic (ROC) curve demonstrated that thresholds of 0.06 cc (sensitivity 88%, specificity 87%) and 0.03 cc (sensitivity 94%, specificity
International Nuclear Information System (INIS)
The aim of this paper was to determine the correlation between calcium burden (expressed as a volume) and extent of stenosis of the origin of the internal carotid artery (ICA) by CT angiography (CTA). Previous studies have shown that calcification in the coronary arteries correlates with significant vessel stenosis, and severe calcification (measured by CT) in the carotid siphon correlates with significant (greater than 50% stenosis) as determined angiographically. Sixty-one patients (age range 50-85 years) underwent CT of the neck with intravenous administration of iodinated contrast for a variety of conditions. Images were obtained with a helical multidetector array CT scanner and reviewed on a three-dimensional workstation. A single observer manipulated window and level to segment calcified plaque from vascular enhancement in order to quantify vascular calcium volume (cc) in the region of the bifurcation of the common carotid artery/ICA origin, and to measure the extent of ICA stenosis near the origin. A total of 117 common carotid artery bifurcations were reviewed. A ''significant'' stenosis was defined arbitrarily as >40% (to detect lesions before they become hemodynamically significant) of luminal diameter on CTA using NASCET-like criteria. All ''significant'' stenoses (21 out of 117 carotid bifurcations) had measurable calcium. We found a relatively strong correlation between percent stenosis and the calcium volume (Pearson's r= 0.65, P<0.0001). We also found that there was an even stronger correlation between the square root of the calcium volume and the percent stenosis as measured by CTA (r= 0.77, P<0.0001). Calcium volumes of 0.01, 0.03, 0.06, 0.09 and 0.12 cc were used as thresholds to evaluate for a ''significant'' stenosis. A receiver operating characteristic (ROC) curve demonstrated that thresholds of 0.06 cc (sensitivity 88%, specificity 87%) and 0.03 cc (sensitivity 94%, specificity 76%) generated the best combinations of sensitivity and
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Kweon-Ho Nam
Full Text Available Despite considerable research efforts on the relationship between arterial geometry and cardiovascular pathology, information is lacking on the pulsatile geometrical variation caused by arterial distensibility and cardiomotility because of the lack of suitable in vivo experimental models and the methodological difficulties in examining the arterial dynamics. We aimed to investigate the feasibility of using a chick embryo system as an experimental model for basic research on the pulsatile variation of arterial geometry. Optical microscope video images of various arterial shapes in chick chorioallantoic circulation were recorded from different locations and different embryo samples. The high optical transparency of the chorioallantoic membrane (CAM allowed clear observation of tiny vessels and their movements. Systolic and diastolic changes in arterial geometry were visualized by detecting the wall boundaries from binary images. Several to hundreds of microns of wall displacement variations were recognized during a pulsatile cycle. The spatial maps of the wall motion harmonics and magnitude ratio of harmonic components were obtained by analyzing the temporal brightness variation at each pixel in sequential grayscale images using spectral analysis techniques. The local variations in the spectral characteristics of the arterial wall motion were reflected well in the analysis results. In addition, mapping the phase angle of the fundamental frequency identified the regional variations in the wall motion directivity and phase shift. Regional variations in wall motion phase angle and fundamental-to-second harmonic ratio were remarkable near the bifurcation area. In summary, wall motion in various arterial geometry including straight, curved and bifurcated shapes was well observed in the CAM artery model, and their local and cyclic variations could be characterized by Fourier and wavelet transforms of the acquired video images. The CAM artery model with
BOUKTIR, Yasser; Chalal, Hocine; HADDAD, Moussa; ABED-MERAIM, Farid
2015-01-01
The ductility limits of an St14 steel are investigated using an elastic‒plastic‒damage model and bifurcation theory. An associative J2-flow theory of plasticity is coupled with damage within the framework of continuum damage mechanics. For strain localization prediction, the bifurcation analysis is adopted. Both the constitutive equations and the localization bifurcation criterion are implemented into the finite element code ABAQUS, within the framework of large strains and a fully three-dime...
NUMERICAL ANALYSIS OF THE NON-NEWTONIAN BLOOD FLOW IN THE NON-PLANAR ARTERY WITH BIFURCATION
Institute of Scientific and Technical Information of China (English)
CHEN Jie; LU Xi-yun; ZHUANG Li-xian; WANG Wen
2004-01-01
A numerical analysis of non-Newtonian fluid flow in non-planar artery with bifurcation was performed by using a finite element method to solve the three-dimensional Navier-Stokes equations coupled with the non-Newtonian constitutive models, including Carreau,Cross and Bingham models. The objective of this study is to investigate the effects of the non-Newtonian properties of blood as well as curvature and out-of-plane geometry in the non-planar daughter vessels on the velocity distribution and wall shear stress. The results of this study support the view that the non-planarity of blood vessels and the non-Newtonian properties of blood are of important in hemodynamics and play a significant role in vascular biology and pathophysiology.
Denisenko, N. S.; Chupakhin, A. P.; Khe, A. K.; Cherevko, A. A.; Yanchenko, A. A.; Tulupov, A. A.; Boiko, A. V.; Krivoshapkin, A. L.; Orlov, K. Yu; Moshkin, M. P.; Akulov, A. E.
2016-06-01
In our experiments, we investigate a flow of a viscous fluid in the model of the common carotid artery bifurcation. The studies are carried out using three hardware equipments: two magnetic resonance scanners by Philips and Bruker, and intravascular guidewire ComboWire. The flux is generated by a special pump CompuFlow that is designed to reproduce a flow similar to the one in the blood vessels. A verification of the obtained data is carried out. Conducted research shows the capabilities of the measurement instruments and reflects the character of fluid flow inside the model.
Classification of coronary artery bifurcation lesions and treatments: Time for a consensus!
DEFF Research Database (Denmark)
Louvard, Yves; Thomas, Martyn; Dzavik, Vladimir;
2007-01-01
, heterogeneity, and inadequate description of techniques implemented. Methods: The aim is to propose a consensus established by the European Bifurcation Club (EBC), on the definition and classification of bifurcation lesions and treatments implemented with the purpose of allowing comparisons between techniques...... proposes a new classification of bifurcation lesions and their treatments to permit accurate comparisons of well described techniques in homogeneous lesion groups. (c) 2008 Wiley-Liss, Inc. Udgivelsesdato: 2007-Nov-5...
Clinical outcome after crush versus culotte stenting of coronary artery bifurcation lesions
DEFF Research Database (Denmark)
Kervinen, Kari; Niemelä, Matti; Romppanen, Hannu;
2013-01-01
The aim of the study was to compare long-term follow-up results of crush versus culotte stent techniques in coronary bifurcation lesions.......The aim of the study was to compare long-term follow-up results of crush versus culotte stent techniques in coronary bifurcation lesions....
Long-term results after simple versus complex stenting of coronary artery bifurcation lesions
DEFF Research Database (Denmark)
Maeng, Michael; Holm, Niels Ramsing; Erglis, Andrejs;
2013-01-01
Objectives This study sought to report the 5-year follow-up results of the Nordic Bifurcation Study. Background Randomized clinical trials with short-term follow-up have indicated that coronary bifurcation lesions may be optimally treated using the optional side branch stenting strategy. Methods ...
Saho, Tatsunori; Onishi, Hideo
2016-07-01
In this study, we evaluated the hemodynamics of carotid artery bifurcation with various geometries using simulated and volunteer models based on magnetic resonance imaging (MRI). Computational fluid dynamics (CFD) was analyzed by use of OpenFOAM. The velocity distribution, streamline, and wall shear stress (WSS) were evaluated in a simulated model with known bifurcation angles (30°, 40°, 50°, 60°, derived from patients' data) and in three-dimensional (3D) healthy volunteer models. Separated flow was observed at the outer side of the bifurcation, and large bifurcation models represented upstream transfer of the point. Local WSS values at the outer bifurcation [both simulated (100 Pa). The bifurcation angle had a significant negative correlation with the WSS value (p<0.05). The results of this study show that the carotid artery bifurcation angle is related to the WSS value. This suggests that hemodynamic stress can be estimated based on the carotid artery geometry. The construction of a clinical database for estimation of developing atherosclerosis is warranted. PMID:27255300
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Yamada, Shigeki, E-mail: shigekiyamada3@gmail.com [Department of Neurosurgery and Stroke Center, Rakuwakai Otowa Hospital, Otowachinji-cho 2, Yamashina-ku, Kyoto 607-8602 (Japan); Department of Neurosurgery, Hamamatsu Rosai Hospital, 25 Shogen-cho, Higashi-ku, Hamamatsu city, Shizuoka 430-8525 (Japan); Interfaculty Initiative in Information Studies/Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Oshima, Marie, E-mail: marie@iis.u-tokyo.ac.jp [Interfaculty Initiative in Information Studies/Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Watanabe, Yoshihiko, E-mail: ynabe@magic.odn.ne.jp [Department of Neurosurgery, Hamamatsu Rosai Hospital, 25 Shogen-cho, Higashi-ku, Hamamatsu city, Shizuoka 430-8525 (Japan); Ogata, Hideki, E-mail: hidogata@gmail.com [Department of Neurosurgery, Hamamatsu Rosai Hospital, 25 Shogen-cho, Higashi-ku, Hamamatsu city, Shizuoka 430-8525 (Japan); Hashimoto, Kenji, E-mail: hashiken8022@yahoo.co.jp [Department of Neurosurgery, Kishiwada Municipal Hospital, 1001 Gakuhara-cho, Kishiwada city, Osaka 596-8501 (Japan); Miyake, Hidenori, E-mail: hi-miyake@hamamatsuh.rofuku.go.jp [Department of Neurosurgery, Hamamatsu Rosai Hospital, 25 Shogen-cho, Higashi-ku, Hamamatsu city, Shizuoka 430-8525 (Japan)
2014-06-15
Purpose: The purpose of this study was to investigate the association between internal carotid artery (ICA) stenosis and intramural location and size of calcification at the ICA origins and the origins of the cervical arteries proximal to the ICA. Method: A total of 1139 ICAs were evaluated stenosis and calcification on the multi-detector row CT angiography. The intramural location was categorized into none, outside and inside location. The calcification size was evaluated on the 4-point grading scale. The multivariate analyses were adjusted for age, serum creatinine level, hypertension, hyperlipidemia, diabetes mellitus, smoking and alcohol habits. Results: Outside calcification at the ICA origins showed the highest multivariate odds ratio (OR) for the presence of ICA stenosis (30.0) and severe calcification (a semicircle or more of calcification at the arterial cross-sectional surfaces) did the second (14.3). In the subgroups of >70% ICA stenosis, the multivariate OR of outside location increased to 44.8 and that of severe calcification also increased to 32.7. Four of 5 calcified carotid plaque specimens extracted by carotid endarterectomy were histologically confirmed to be calcified burdens located outside the internal elastic lamia which were defined as arterial medial calcification. Conclusions: ICA stenosis was strongly associated with severe calcification located mainly outside the carotid plaque. Outside calcification at the ICA origins should be evaluated separately from inside calcification, as a marker for the ICA stenosis. Additionally, we found that calcification at the origins of the cervical arteries proximal to the ICA was significantly associated with the ICA stenosis.
International Nuclear Information System (INIS)
Purpose: The purpose of this study was to investigate the association between internal carotid artery (ICA) stenosis and intramural location and size of calcification at the ICA origins and the origins of the cervical arteries proximal to the ICA. Method: A total of 1139 ICAs were evaluated stenosis and calcification on the multi-detector row CT angiography. The intramural location was categorized into none, outside and inside location. The calcification size was evaluated on the 4-point grading scale. The multivariate analyses were adjusted for age, serum creatinine level, hypertension, hyperlipidemia, diabetes mellitus, smoking and alcohol habits. Results: Outside calcification at the ICA origins showed the highest multivariate odds ratio (OR) for the presence of ICA stenosis (30.0) and severe calcification (a semicircle or more of calcification at the arterial cross-sectional surfaces) did the second (14.3). In the subgroups of >70% ICA stenosis, the multivariate OR of outside location increased to 44.8 and that of severe calcification also increased to 32.7. Four of 5 calcified carotid plaque specimens extracted by carotid endarterectomy were histologically confirmed to be calcified burdens located outside the internal elastic lamia which were defined as arterial medial calcification. Conclusions: ICA stenosis was strongly associated with severe calcification located mainly outside the carotid plaque. Outside calcification at the ICA origins should be evaluated separately from inside calcification, as a marker for the ICA stenosis. Additionally, we found that calcification at the origins of the cervical arteries proximal to the ICA was significantly associated with the ICA stenosis
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Goltz, Jan Peter, E-mail: janpeter.goltz@uksh.de; Loesaus, Julia; Frydrychowicz, Alex; Barkhausen, Jörg [University Hospital of Schleswig-Holstein, Department for Radiology and Nuclear Medicine (Germany); Wiedner, Marcus [University Hospital of Schleswig-Holstein, Clinic for Surgery (Germany)
2016-02-15
We report an endovascular technique for the treatment of type Ia endoleak after a plain tubular stentgraft had been implanted for a large common iliac artery aneurysm with an insufficient proximal landing zone and without occlusion of the hypogastric in another hospital. CT follow-up showed an endoleak with continuous sac expansion over 12 months. This was classified as type Ia by means of dynamic contrast-enhanced MRI. Before a bifurcated stentgraft was implanted to relocate the landing zone more proximally, the still perfused ipsilateral hypogastric artery was embolized to prevent a type II endoleak. A guidewire was manipulated alongside the indwelling stentgraft. The internal iliac artery could then be selectively intubated followed by successful plug embolization of the vessel’s orifice despite the stentgraft being in place.
Investigation of homoclinic bifurcation of plasma fireball in a double plasma device
International Nuclear Information System (INIS)
Plasma fire balls are generated due to localized discharge and it is a sharp boundary of the glow region, which suggests a localized electric field such as an electrical sheath or double layer structure. In this paper, homoclinic bifurcation phenomena in the plasma fireball dynamics which is produced in the target chamber of double plasma device have been explored. Homoclinic bifurcation is noticed in the plasma fireball as the system evolving from large time period oscillation to small time period oscillation. The control parameters of this observations are density ratio of target to source chamber (nT/nS), applied electrode voltage to produce fireball, grid bias voltage etc. The dynamical transition of plasma fire balls have been investigated by recurrence quantification analysis (RQA) and by different statistical measures. The gradual increment of kurtosis and decrement of skewness with the change of nT has been observed which are strongly indicative of homoclinic bifurcation in the system. The visual changes of recurrence plot and the gradual changes in recurrence quantifiers reflect the bifurcation with the variation in the control parameter of the double plasma device. The combination of RQA and statistical measures like 1/f power spectrum, clearly conjectured the homoclinic bifurcation due to plasma fire ball in the experimental conditions. (author)
Institute of Scientific and Technical Information of China (English)
Jiang Junhao; Chen Bin; Dong Zhihui; Shi Yun; Li Weimiao; Yue Jianing
2014-01-01
Background Crossover stenting across the origin of the profunda femoral artery (PFA) and occasionally into the common femoral artery (CFA) is commonly used after suboptimal balloon angioplasty of ostial occlusive lesions of the superficial femoral artery (SFA) involving the bifurcation.Late stent occlusion at the bifurcation is not rare and results in severe lower extremity ischemia.Therefore,we tried to assess its possible causes,prevention and reintervention.Methods Using a prospectively maintained single-center database,12-month femoral bifurcation patency was retrospectively compared and lesion and procedural predictors of stent occlusion were determined among 63 patients (64 lesions) who between July 2011 and February 2013 underwent crossover (36 non-jailed and 15 jailed SFA,and 12 distal and 1 complete CFA) stenting of de novo ostial SFA lesions.Results Twelve-month overall patency rate at the femoral bifurcation was 88％,with no significant difference between jailed-ostial SFA (80％) and distal CFA (67％) stenting (P=0.731),and significant differences between either and non-jailed ostial stenting (100％,P=0.035 and 0.002).When PFA ostium was jailed by the stent,patients with preexisting CFA or PFA lesions had a 12-month bifurcation patency rate of 20％,significantly lower than those with simple ostial SFA lesions (83％,P=0.015).Stent induced intimal hyperplasia caused bifurcation occlusion in 6 surgical reintervention cases.Conclusions In crossover stenting of ostial lesions in SFA,bifurcation patency loss was significantly higher in distal CFA and jailed ostial SFA stenting than non-jailed ostial SFA stenting.Preexisting CFA or PFA lesion is a significant risk factor for bifurcation patency loss when PFA ostium is jailed by crossover stenting.
DK crush technique: modified treatment of bifurcation lesions in coronary artery
Institute of Scientific and Technical Information of China (English)
CHEN Shao-liang; GE Jun-bo; YE Fei; ZHANG Jun-jie; ZHU Zhong-sheng; LIN Song; SHAN Shou-jie; LIU Zhi-zhong; LIU Yan; DUAN Bao-xiang
2005-01-01
@@ Bifurcation lesions are still technically challenging even in the era of modern stents.1 High incidence of restenosis both in main vessel and side branch limits the long-term prognosis although several kinds of techniques have been identified to be successful for coronary bifurcations.2-5 Reports have demonstrated the main reason for higher incidence of ostial side branch even though drug-eluting stent used in side vessel lies in that there were gaps in metal coverage and drug application.6-9 Therefore, new technique ensuring complete vessel scaffolding without gaps in drug delivery at the bifurcation is crush technique which is similar to other techniques including T- and Y- stenting still needing postdilatation of kissing balloon angioplasty to expand the stent fully in the ostial side branch and to prevent stent distortion in main vessel.10 As a result, kissing balloon angioplasty is a key step to improve the final result and to reduce the restenosis after stenting bifurcation lesions. However, kissing angioplasty is difficult to be underwent or impossible because operators usually fail to rewire two layers of metal strut, which would result in suboptimal stent deployment, a main reason of high incidence of restenosis, and acute- or-late-thrombosus. The present study reports modified DK crush technique improving success rate of kissing balloon angioplasty under the guidance of intravascular ultrasound (IVUS).
Kabinejadian, Foad; Nezhadian, Mercedeh Kaabi; Cui, Fangsen; Ho, Pei; Leo, Hwa Liang
2016-02-01
In this study, a polymeric membrane has been designed and developed for carotid stents to prevent detachment of emboli from the arterial wall and subsequent stroke, while maintaining side-branch flow. Prototypes of different geometrical design parameters have been fabricated and their performance has been evaluated in vitro under physiological pulsatile flow condition in a life-size silicone anastomotic model of carotid artery bifurcation. These evaluations include both quantitative and qualitative experimental (in vitro) assessments of emboli prevention capability, side-branch flow preservation, and flow visualization. The covered stents with the novel membrane demonstrated significantly higher emboli prevention capability than the corresponding bare nitinol stent as well as some earlier related designs, while preserving more than 93% of the original flow of the external carotid artery (ECA). Flow in the ECA through these covered stents was uniform without evidence of undesirable flow recirculation or retrograde flow that might predispose the vessel wall to intimal thickening and atherosclerotic plaque formation. This study demonstrated the potential of these novel covered stent designs for the treatment of carotid atherosclerotic stenosis and prevention of late embolic stroke. However, further in vivo investigations of biological effects and mechanical performance of this covered stent design (e.g., its thrombogenicity potential and biocompatibility) are warranted. PMID:26147531
International Nuclear Information System (INIS)
We present a case of a 73-year-old man in whom a celiac trunk aneurysm close to the hepato-splenic bifurcation was discovered and treated by using celiac-hepatic stent-grafts implantation and splenic artery embolization
Directory of Open Access Journals (Sweden)
Patrick Bastos Metzger
2014-03-01
Full Text Available Embolization due to a firearm projectile entering the bloodstream is a rare event that is unlikely to be suspected during initial treatment of trauma patients. We describe and discuss a case of bullet embolism of the abdominal aortic bifurcation, complicated by a pseudoaneurysm of the thoracoabdominal aorta and occlusion of the right common iliac artery, but successfully treated using a combination of endovascular methods and conventional surgery.
International Nuclear Information System (INIS)
Objective: To investigate flow patterns at carotid bifurcation in vivo by combining computational fluid dynamics (CFD)and MR angiography imaging. Methods: Seven subjects underwent contrast-enhanced MR angiography of carotid artery in Siemens 3.0 T MR. Flow patterns of the carotid artery bifurcation were calculated and visualized by combining MR vascular imaging post-processing and CFD. Results: The flow patterns of the carotid bifurcations in 7 subjects were varied with different phases of a cardiac cycle. The turbulent flow and back flow occurred at bifurcation and proximal of internal carotid artery (ICA) and external carotid artery (ECA), their occurrence and conformation were varied with different phase of a cardiac cycle. The turbulent flow and back flow faded out quickly when the blood flow to the distal of ICA and ECA. Conclusion: CFD combined with MR angiography can be utilized to visualize the cyclical change of flow patterns of carotid bifurcation with different phases of a cardiac cycle. (authors)
The clinical application of 64-slice spiral CT angiography in carotid artery bifurcation disease
International Nuclear Information System (INIS)
Objective: To explore the clinical value of 64-slice spiral CT angiography (CTA) in carotid stenosis and atherosclerotic plaque. Methods: 40 patients (80 carotid arteries) underwent CTA and DSA. These two examinations within one week. The results of CTA were compared with that of DSA, the sensitivity and specificity of CTA and DSA were figured out. Results: CTA performed well in the detection of mild (0% to 29%) carotid stenosis, as well as carotid occlusion, with values for sensitivity and specificity both near 100%. In determining that a stenosis was >50% by DSA measurement, CTA with a sensitivity, specificity of 89% and 91% respectively. While CTA was quite specific in identifying degrees of stenoses in either the 50% to 69% or the 70% to 99% ranges, in this task it was much less sensitive: 65% and 73% respectively. CTA can detect all kinds of ulcers while DSA can not. Conclusions: 64-slice CTA and DSA were correctly identified in detecting carotid stenosis. CTA could demonstrate ulcers associated with the carotid stenosis, hut DSA only show stenosis. (authors)
Evaluation of the cervical carotid bifurcation using MR angiography and cine MRI
Energy Technology Data Exchange (ETDEWEB)
Yamane, Kanji; Shima, Takeshi; Okada, Yoshikazu; Nishida, Masahiro; Okita, Shinji; Hatayama, Takashi; Kagawa, Reiko [Chugoku Rousai Hospital, Kure, Hiroshima (Japan); Yokoyama, Noboru
1995-08-01
MR angiography (MRA) can less invasively evaluate the carotid bifurcation without contrast material. Previous reports on MRA of carotid bifurcation revealed problems of overestimation and false-positive interpretation of stenosis. To clarify reasons causing overestimation and false-positive interpretation we investigated flow dynamics in the carotid bifurcation by cine MRI. Twenty-eight patients who were suspected to have stenosis of the internal carotid artery by MRA were studied. Images of the carotid bifurcation were obtained with 3-D phase contrast method by 0.5-T MR scanner. All patients were examined by IV-DSA or direct carotid angiography. Cine MRI of the carotid bifurcation was obtained with gradinet-echo sequence by 1.5-T MR scanner. Comparison of MRA and conventional angiography in evaluating degree of stenosis in the carotid bifurcation demonstrated that there were 57.1% agreement, 32.1% false-positive estimation and 10.7% overestimation. Cine MRI demonstration turbulent flow in the normal carotid bifurcation and also in the sclerotic bifurcation. Turbulence in the carotid bifurcation with severe sclerosis was greater than that in the normal carotid bifurcation. Turbulent flow could be seen extending distally to the stenotic site of the internal carotid artery. Turbulent flow in the carotid bifurcation, causing a decrease or loss in signal intensity of MRA according to the severity of the turbulence, must be a major contributing factor in false-positive estimation and overestimation of stenosis. (author).
Energy Technology Data Exchange (ETDEWEB)
Saha, Debajyoti, E-mail: debajyoti.saha@saha.ac.in; Kumar Shaw, Pankaj; Janaki, M. S.; Sekar Iyengar, A. N.; Ghosh, Sabuj; Mitra, Vramori, E-mail: vramorimitra@yahoo.com; Michael Wharton, Alpha [Plasma Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India)
2014-03-15
Order-chaos-order was observed in the relaxation oscillations of a glow discharge plasma with variation in the discharge voltage. The first transition exhibits an inverse homoclinic bifurcation followed by a homoclinic bifurcation in the second transition. For the two regimes of observations, a detailed analysis of correlation dimension, Lyapunov exponent, and Renyi entropy was carried out to explore the complex dynamics of the system.
Directory of Open Access Journals (Sweden)
Kirill Lykov
2015-08-01
Full Text Available When blood flows through a bifurcation, red blood cells (RBCs travel into side branches at different hematocrit levels, and it is even possible that all RBCs enter into one branch only, leading to a complete separation of plasma and RBCs. To quantify this phenomenon via particle-based mesoscopic simulations, we developed a general framework for open boundary conditions in multiphase flows that is effective even for high hematocrit levels. The inflow at the inlet is duplicated from a fully developed flow generated in a pilot simulation with periodic boundary conditions. The outflow is controlled by adaptive forces to maintain the flow rate and velocity gradient at fixed values, while the particles leaving the arteriole at the outlet are removed from the system. Upon validation of this approach, we performed systematic 3D simulations to study plasma skimming in arterioles of diameters 20 to 32 microns. For a flow rate ratio 6:1 at the branches, we observed the "all-or-nothing" phenomenon with plasma only entering the low flow rate branch. We then simulated blood-plasma separation in arteriolar bifurcations with different bifurcation angles and same diameter of the daughter branches. Our simulations predict a significant increase in RBC flux through the main daughter branch as the bifurcation angle is increased. Finally, we demonstrated the effectiveness of the new methodology in simulations of blood flow in vessels with multiple inlets and outlets, constructed using an angiogenesis model.
Energy Technology Data Exchange (ETDEWEB)
Peters, John W.; Miller, Anne-Frances; Jones, Anne K.; King, Paul W.; Adams, Michael W. W.
2016-04-01
Electron bifurcation is the recently recognized third mechanism of biological energy conservation. It simultaneously couples exergonic and endergonic oxidation-reduction reactions to circumvent thermodynamic barriers and minimize free energy loss. Little is known about the details of how electron bifurcating enzymes function, but specifics are beginning to emerge for several bifurcating enzymes. To date, those characterized contain a collection of redox cofactors including flavins and iron-sulfur clusters. Here we discuss the current understanding of bifurcating enzymes and the mechanistic features required to reversibly partition multiple electrons from a single redox site into exergonic and endergonic electron transfer paths.
An Experimental and Numerical Investigation of Bifurcations in a Kolmogorov-Like Flow
Tithof, Jeffrey; Pallantla, Ravi; Grigoriev, Roman O; Schatz, Michael F
2016-01-01
We present a combined experimental and numerical study of the primary and secondary bifurcations for a Kolmogorov-like flow. The experimental system is a quasi-two-dimensional incompressible fluid flow consisting of two immiscible layers of fluid for which electromagnetic forces drive a shear flow that approximates Kolmogorov flow. The two-dimensional (2D) direct numerical simulations (DNS) integrate a depth-averaged version of the full three-dimensional Navier-Stokes equations Suri ${\\it et}$ ${\\it al.}$ (2014), which contains a (non-unity) prefactor on the advection term, previously unaccounted for in all studies. Specifically, we present three separate 2D DNS: one that is doubly-periodic, one that is singly-periodic, and one that is non-periodic (i.e. no-slip is imposed at the lateral boundaries). All parameters are directly calculated or measured from experimental quantities. We show that inclusion of the advection term prefactor substantially improves agreement between experiment and numerics. However, g...
1991-01-01
Dynamical Bifurcation Theory is concerned with the phenomena that occur in one parameter families of dynamical systems (usually ordinary differential equations), when the parameter is a slowly varying function of time. During the last decade these phenomena were observed and studied by many mathematicians, both pure and applied, from eastern and western countries, using classical and nonstandard analysis. It is the purpose of this book to give an account of these developments. The first paper, by C. Lobry, is an introduction: the reader will find here an explanation of the problems and some easy examples; this paper also explains the role of each of the other paper within the volume and their relationship to one another. CONTENTS: C. Lobry: Dynamic Bifurcations.- T. Erneux, E.L. Reiss, L.J. Holden, M. Georgiou: Slow Passage through Bifurcation and Limit Points. Asymptotic Theory and Applications.- M. Canalis-Durand: Formal Expansion of van der Pol Equation Canard Solutions are Gevrey.- V. Gautheron, E. Isambe...
Feng, J; Rajeswaran, T; He, S; Wilkinson, F L; Serracino-Inglott, F; Azzawi, M; Parikh, V; Miraftab, M; Alexander, M Y
2015-08-01
Stroke is mainly caused by a narrowing of the carotid artery from a build-up of plaque. The risk of plaque rupture and subsequent stroke is dependent on plaque composition. Advances in imaging modalities offer a non-invasive means to assess the health of blood vessels and detect damage. However, the current diagnosis fails to identify patients with soft lipid plaque that are more susceptible to fissure, resulting in stroke. The aim of this study was to use waveform analysis to identify plaque composition and the risk of rupture. We have investigated pressure and flow by combining an artificial blood flow circuit with tubing containing different materials, to simulate plaques in a blood vessel. We used fat and bone to model lipid and calcification respectively to determine if the composition of plaques can be identified by arterial waveforms. We demonstrate that the arterial plaque models with different percentages of calcification and fat, results in significantly different arterial waveforms. These findings imply that arterial waveform analysis has the potential for further development to identify the vulnerable plaques prone to rupture. These findings could have implications for improved patient prognosis by speed of detection and a more appropriate treatment strategy. PMID:26736431
Liu, Yu; Jiang, Lanlan; Zhu, Ningjun; Zhao, Yuechao; Zhang, Yi; Wang, Dayong; Yang, Mingjun; Zhao, Jiafei; Song, Yongchen
2015-09-01
The study of immiscible fluid displacement between aqueous-phase liquids and non-aqueous-phase liquids in porous media is of great importance to oil recovery, groundwater contamination, and underground pollutant migration. Moreover, the attendant viscous, capillary, and gravitational forces are essential to describing the two-phase flows. In this study, magnetic resonance imaging was used to experimentally examine the detailed effects of the viscous, capillary, and gravitational forces on water-oil flows through a vertical straight capillary, bifurcate channel, and monolayered glass-bead pack. Water flooding experiments were performed at atmospheric pressure and 37.8°C, and the evolution of the distribution and saturation of the oil as well as the characteristics of the two-phase flow were investigated and analyzed. The results showed that the flow paths, i.e., the fingers of the displacing phase, during the immiscible displacement in the porous medium were determined by the viscous, capillary, and gravitational forces as well as the sizes of the pores and throats. The experimental results afford a fundamental understanding of immiscible fluid displacement in a porous medium. PMID:25940392
Ben Bettaieb, Mohamed; ABED-MERAIM, Farid
2015-01-01
Localized necking is often considered as precursor to failure in metal components. In modern technologies, functional components (e.g., in flexible electronic devices) may be affected by this necking phenomenon, and to avoid the occurrence of strain localization, elastomer substrates are bonded to the metal layers. This paper proposes an investigation of the development of localized necking in both freestanding metal layers and elastomer/metal bilayers. Finite strain versions of both rigid–pl...
Multiple Bifurcations in the Periodic Orbit around Eros
Ni, Yanshuo; Baoyin, Hexi
2016-01-01
We investigate the multiple bifurcations in periodic orbit families in the potential field of a highly irregular-shaped celestial body. Topological cases of periodic orbits and four kinds of basic bifurcations in periodic orbit families are studied. Multiple bifurcations in periodic orbit families consist of four kinds of basic bifurcations. We found both binary period-doubling bifurcations and binary tangent bifurcations in periodic orbit families around asteroid 433 Eros. The periodic orbit family with binary period-doubling bifurcations is nearly circular, with almost zero inclination, and is reversed relative to the body of the asteroid 433 Eros. This implies that there are two stable regions separated by one unstable region for the motion around this asteroid. In addition, we found triple bifurcations which consist of two real saddle bifurcations and one period-doubling bifurcation. A periodic orbit family generated from an equilibrium point of asteroid 433 Eros has five bifurcations, which are one real ...
Lee, Sang Hoon; Choi, Hyoung Gwon; Yoo, Jung Yul
2012-11-01
The effect of artery wall hypertrophy and stiffness on the flow field is investigated using three-dimensional finite element method for simulating the blood flow. To avoid the complexity due to the necessity of additional mechanical constraints, we use the combined formulation which includes both the fluid and structural equations of motion into single coupled variational equation. A P2P1 Galerkin finite element method is used to solve the Navier-Stokes equations for fluid flow and arbitrary Lagrangian-Eulerian formulation is used to achieve mesh movement. The Newmark method is employed for solving the dynamic equilibrium equations for linear elastic solid mechanics. The pulsatile, incompressible flows of Newtonian fluids constrained in the flexible wall are analyzed with Womersley velocity profile at the inlet and constant pressure at the outlet. The study shows that the stiffness of carotid artery wall affects significantly the flow phenomena during the pulse cycle. Similarly, it is found that the flow field is also strongly influenced by wall hypertrophy. This work was supported by Mid-career Researcher Program and Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2009-0079936 & 2011-0029613).
Cakur, Binali; Yıldırım, Eren; Demirtaş, Ömer
2015-01-01
Aim: Carotid artery calcification can results in important vascular obstruction. It is reported that the combination of risk factors such as periodontitis, pulp stones contribute to carotid artery calcification. However in the literature, no study has yet investigated carotid artery calcification with respect to tonsillolith. The objective of this study was to investigate whether carotid artery calcification correlate with tonsillolith using dental panoramic radiography.Material and method: P...
Global Bifurcations With Symmetry
Porter, J B
2001-01-01
Symmetry is a ubiquitous feature of physical systems with profound implications for their dynamics. This thesis investigates the role of symmetry in global bifurcations. In particular, the structure imposed by symmetry can encourage the formation of complex solutions such as heteroclinic cycles and chaotic invariant sets. The first study focuses on the dynamics of 1:n steady-state mode interactions in the presence of O(2) symmetry. The normal form equations considered are relevant to a variety of physical problems including Rayleigh-Bénard convection with periodic boundary conditions. In open regions of parameter space these equations contain structurally stable heteroclinic cycles composed of connections between standing wave, pure mode, and trivial solutions. These structurally stable cycles exist between two global bifurcations, the second of which involves an additional mixed mode state and creates as many as four distinct kinds of structurally unstable heteroclinic cycles. The various cycles c...
Directory of Open Access Journals (Sweden)
Emin Gurleyik
2014-01-01
Full Text Available Background: Anatomical variations of the recurrent laryngeal nerve (RLN such as extralaryngeal terminal bifurcation is an important risk for its motor function. Aims: The objective is to study surgical anatomy of bilateral bifurcation of the RLNs in order to decrease risk of vocal cord palsy in patients with bifurcated nerves. Materials and Methods: Surgical anatomy including terminal bifurcation was established in 292 RLNs of 146 patients. We included patients with bilateral bifurcation of RLN in this study. Based on two anatomical landmarks (nerve-artery crossing and laryngeal entry, the cervical course of RLN was classified in four segments: Pre-arterial, arterial, post-arterial and pre-laryngeal. According to these segments, bifurcation point locations along the cervical course of RLNs were compared between both sides in bilateral cases. Results: RLNs were exposed throughout their entire courses. Seventy (48% patients had bifurcated RLNs. We identified terminal bifurcation in 90 (31% of 292 RLNs along the cervical course. Bilateral bifurcation was observed in 20 (28.6% patients with bifurcated RLNs. Bifurcation points were located on arterial and post-arterial segments in 37.5% and 32.5% of cases, respectively. Pre-arterial and pre-laryngeal segments contained bifurcations in 15% of cases. Comparison of both sides indicated that bifurcation points were similar in 5 (25% and different in 15 (75% patients with bilateral bifurcation. Permanent nerve injury did not occur in this series. Conclusion: Bilateral bifurcation of both RLNs was observed in approximately 30% of patients with extralaryngeal bifurcation which is a common anatomical variation. Bifurcation occurred in different segments along cervical course of RLN. Bifurcation point locations differed between both sides in the majority of bilateral cases. Increasing surgeons′ awareness of this variation may lead to safely exposing bifurcated nerves and prevent the injury to extralaryngeal
International Nuclear Information System (INIS)
This work aims to study effects of toroidal flow on the L-H transition phenomenon in tokamak plasmas using bifurcation concept. Two-field (thermal and particle) transport equations with both neoclassical and turbulent effects included are solved simultaneously. The transport suppression mechanism used in this work is flow shear, which is assumed to affect only the turbulent transport. The flow shear can be calculated from the force balance equation with toroidal flow as a main contributor. The toroidal velocity profile is calculated using three different models. The first model is an empirical model in which the velocity is dependent on local ion temperature. The second model is based on neoclassical toroidal viscosity theory in which the velocity is driven by ion temperature gradient. In the third model, the velocity is dependent on current density flow in plasma. The two transport equations are solved both analytically and numerically using MATLAB to study the criteria for H-mode formation, pedestal width and its dynamics. The results from three toroidal velocity models are compared and analyzed with respect to bifurcation behavior and plasma performance.
BIFURCATIONS OF AIRFOIL IN INCOMPRESSIBLE FLOW
Institute of Scientific and Technical Information of China (English)
LiuFei; YangYiren
2005-01-01
Bifurcations of an airfoil with nonlinear pitching stiffness in incompressible flow are investigated. The pitching spring is regarded as a spring with cubic stiffness. The motion equations of the airfoil are written as the four dimensional one order differential equations. Taking air speed and the linear part of pitching stiffness as the parameters, the analytic solutions of the critical boundaries of pitchfork bifurcations and Hopf bifurcations are obtained in 2 dimensional parameter plane. The stabilities of the equilibrium points and the limit cycles in different regions of 2 dimensional parameter plane are analyzed. By means of harmonic balance method, the approximate critical boundaries of 2-multiple semi-stable limit cycle bifurcations are obtained, and the bifurcation points of supercritical or subcritical Hopf bifurcation are found. Some numerical simulation results are given.
International Nuclear Information System (INIS)
A 42-year-old female with a giant intracranial aneurysm of the right IC bifurcation is reported. She had experienced severe headache with nausea and vomiting on July 6, 1984, and was admitted to a certain hospital. She was then transferred to our hospital on July 23; she was asymptomatic then. There was no neurological deficit, and a craniogram showed no abnormal findings. A plain CT scan, however, showed a round, homogenous, slightly high-density area on the right basal ganglia, and it was intensely enhanced by the infusion of a contrast medium. The right anterior horn was compressed to the anteromedial side. By the angiographical study, we found a large aneurysmal shadow with a bleb on its top, arising from the right IC bifurcation. While she waited for an operation, meanwhile undergoing reported Matas tests, the aneurysm began to bleed again. Suddenly generalized convulsions and the rapidly progressing left hemiparesis occurred, and she lost consciousness. The CT scan at that time showed a ring-shaped high-density area surrounding the aneurysms, accompanied by perifocal edema and a midline shift. An urgent operation was performed, but she died three days after the second attack. The autopsy showed a ruptured saccular aneurysm (3.5 x 4.0 x 4.0 cm in size) on the right IC bifurcation, with its neck extending to the M1 portion. There was neither calcification on the wall nor any organized thrombosis. Giant aneurysms usually affect the surrounding brain tissue as mass lesions. In this case, though, there was no sign or symptoms of any compression of the brain tissue or cranial nerves, though a CT scan soon after the rupture showed progressive perifocal edema. This suggests that there had been a previous disturbance of the autoregulation of the surrounding brain tissue, caused by the mass effect of the giant aneurysm. (author)
Investigation of Brain Arterial Circle Malformations Using Electrical Modelling and Simulation
Directory of Open Access Journals (Sweden)
Klara Capova
2006-01-01
Full Text Available The paper deals with the cerebral arterial system investigation by means of electrical modelling and simulations. The main attention is paid to the brain arterial circle malformations (stenoses and aneurysms and their determination and evaluation by computer-aided methods as tools of a non-invasive diagnostics. The compensation possibilities of brain arterial circle in case of presence of concrete arterial malformations are modelled and simulated. The simulation results of brain arteries blood pressures and volume flow velocities time dependences are presented and discussed under various health conditions.
Multiple bifurcations in the periodic orbit around Eros
Ni, Yanshuo; Jiang, Yu; Baoyin, Hexi
2016-05-01
We investigate the multiple bifurcations in periodic orbit families in the potential field of a highly irregular-shaped celestial body. Topological cases of periodic orbits and four kinds of basic bifurcations in periodic orbit families are studied. Multiple bifurcations in periodic orbit families consist of four kinds of basic bifurcations. We found both binary period-doubling bifurcations and binary tangent bifurcations in periodic orbit families around asteroid 433 Eros. The periodic orbit family with binary period-doubling bifurcations is nearly circular, with almost zero inclination, and is reversed relative to the body of the asteroid 433 Eros. This implies that there are two stable regions separated by one unstable region for the motion around this asteroid. In addition, we found triple bifurcations which consist of two real saddle bifurcations and one period-doubling bifurcation. A periodic orbit family generated from an equilibrium point of asteroid 433 Eros has five bifurcations, which are one real saddle bifurcation, two tangent bifurcations, and two period-doubling bifurcations.
International Nuclear Information System (INIS)
Background: A longstanding hypothesis that correlates fluid dynamic forces and atherosclerotic disease has led to numerous analytical, numerical, and experimental studies over the years because it is very difficult to measure the hemodynamic variables of blood in vivo. Purpose: To investigate the technique of visualization and quantitation of hemodynamic variables at carotid artery bifurcation in vivo by combining computational fluid dynamics (CFD) and vascular imaging. Material and Methods: Twenty-six healthy volunteers underwent magnetic resonance (MR) angiography of the bilateral carotid artery by a 3.0T whole-body scanner. Hemodynamic variables at these carotid bifurcations were calculated and visualized by combining vascular imaging post-processing and CFD. Results: The average velocity of the carotid bifurcation in the systolic phase and the diastolic phase was 0.46±0.24 m/s and 0.23±0.05 m/s, respectively. Eddy current and back flows were observed at bifurcation and the lateral part of the proximal internal carotid arteries (ICA) and external carotid arteries (ECA), and the shapes of them changed with phases of the cardiac cycle, which were significant at the middle of the systolic phase and faded out quickly downstream of the ICA and ECA. The average range of wall shear stress (WSS) at the bifurcation was 4.36±1.32 Pa, and the maximum WSS was 18.02±4.11 Pa. The WSS map revealed a large region of low WSS at the carotid bulb and extended to the outer wall in the proximal end of the ICA (the lowest value was below 0.5 Pa), and there was also a small region of low WSS at the outer wall in the proximal end of the ECA. Conclusion: CFD combined with vascular imaging can calculate and visualize hemodynamic variables at carotid bifurcation in vivo individually
About Bifurcational Parametric Simplification
Gol'dshtein, V; Yablonsky, G
2015-01-01
A concept of "critical" simplification was proposed by Yablonsky and Lazman in 1996 for the oxidation of carbon monoxide over a platinum catalyst using a Langmuir-Hinshelwood mechanism. The main observation was a simplification of the mechanism at ignition and extinction points. The critical simplification is an example of a much more general phenomenon that we call \\emph{a bifurcational parametric simplification}. Ignition and extinction points are points of equilibrium multiplicity bifurcations, i.e., they are points of a corresponding bifurcation set for parameters. Any bifurcation produces a dependence between system parameters. This is a mathematical explanation and/or justification of the "parametric simplification". It leads us to a conjecture that "maximal bifurcational parametric simplification" corresponds to the "maximal bifurcation complexity." This conjecture can have practical applications for experimental study, because at points of "maximal bifurcation complexity" the number of independent sys...
Tang, Abraham Yik-Sau; Chung, Wai-Choi; Liu, Eric Tian-Yang; Qu, Jie-Qiong; Tsang, Anderson Chun-On; Leung, Gilberto Ka-Kit; Leung, Kar-Ming; Yu, Alfred Cheuk-Hang; Chow, Kwok-Wing
2015-01-01
An intracranial aneurysm, abnormal swelling of the cerebral artery, may lead to undesirable rates of mortality and morbidity upon rupture. Endovascular treatment involves the deployment of a flow-diverting stent that covers the aneurysm orifice, thereby reducing the blood flow into the aneurysm and mitigating the risk of rupture. In this study, computational fluid dynamics analysis is performed on a bifurcation model to investigate the change in hemodynamics with various side branch diameters...
Singular limit cycle bifurcations to closed orbits and invariant tori
International Nuclear Information System (INIS)
This paper investigates singular limit cycle bifurcations for a singularly perturbed system. Based on a series of transformations (the modified curvilinear coordinate, blow-up, and near-identity transformation) and bifurcation theory of periodic orbits and invariant tori, the bifurcations of closed orbits and invariant tori near singular limit cycles are discussed
Singular limit cycle bifurcations to closed orbits and invariant tori
Energy Technology Data Exchange (ETDEWEB)
Ye Zhiyong [Department of Mathematics, Shanghai Jiaotong University, Shanghai 200240 (China); Department of Mathematics, Chongqing Institute of Technology, Chongqing 400050 (China); E-mail: yezhiyong@sjtu.edu.cn; Han Maoan [Department of Mathematics, Shanghai Jiaotong University, Shanghai 200240 (China); E-mail: mahan@sjtu.edu.cn
2006-02-01
This paper investigates singular limit cycle bifurcations for a singularly perturbed system. Based on a series of transformations (the modified curvilinear coordinate, blow-up, and near-identity transformation) and bifurcation theory of periodic orbits and invariant tori, the bifurcations of closed orbits and invariant tori near singular limit cycles are discussed.
Bifurcation of steady tearing states
International Nuclear Information System (INIS)
We apply the bifurcation theory for compact operators to the problem of the nonlinear solutions of the 3-dimensional incompressible visco-resistive MHD equations. For the plane plasma slab model we compute branches of nonlinear tearing modes, which are stationary for the range of parameters investigated up to now
Directory of Open Access Journals (Sweden)
JA Mitchell
2009-06-01
Full Text Available Blood flow to the hindbrain, via the paired vertebral arteries, must be uncompromised for adequate neurological functioning of its vital centres. Therefore, it would seem unlikely that the intracranial vertebral artery would need to vasoconstrict, thus reducing its blood flow. In order to investigate the existence and location of a noradrenaline-mediated constrictor mechanism in the wall of the intracranial vertebral artery, transverse sections of ten baboon and ten monkey vessels were stained with sucrose-potassium phosphate-glyoxylic acid (counterstained with malachite-green. This method allows the visualisation of catecholaminergic nerves when the sections are exposed to ultraviolet light. In this study of primate vascular tissue, however, none of the monkey or baboon vertebral artery sections showed the presence of noradrenergic nerves in the tunica media – tunica adventitia junction or penetrating the tunica media of the arteries. These findings indicate that the intracranial vertebral artery does not have a neurogenic vasomotor function in primates.
Preliminary study on hemodynamics in human carotid bifurcation by computational fluid dynamics
International Nuclear Information System (INIS)
Objective: To investigate the visualization and quantitation of hemodynamic variables at carotid artery bifurcation in vivo by combining computational fluid dynamics (CFD) and vascular imaging. Methods: A healthy volunteer underwent CT angiography of left carotid artery by SIEMENS multi-slice CT. Parameters of hemodynamics at this carotid bifurcation were calculated and visualized by combining vascular imaging post-processing and CFD. Results: (1) The average range of flow velocity was 0.04-0.36 m/s. A region of high velocity was seen at medial wall of internal carotid artery (ICA) and medial wall of external carotid artery (ECA), respectively. The largest contiguous region of low velocity occurred at the carotid bulb. (2)The average range of absolute pressure, static pressure and dynamic pressure was 100 266.70-101 615.90 Pa, -1058.34-290.88 Pa, and 6.12-553.25 Pa, respectively. (3) The average range of wall shear stress (WSS) at the bifurcation was 0.59-5.35 Pa. There was a large region of low WSS at carotid bulb and posterior wall of ICA, with the lowest value of 0.25 Pa. Also there was a small region of low WSS at anterior and lateral wall of ECA. Conclusion: CFD combined with vascular imaging can calculate and visualize the parameters of hemodynamics at carotid bifurcation in vivo individually. It is an interdisciplinary science of computer, radiology and hemodynamics and provides a new method to investigate the relationship of vascular geometry and flow condition with atherosclerotic pathological changes. (authors)
Unfolding the Riddling Bifurcation
DEFF Research Database (Denmark)
Maistrenko, Yu.; Popovych, O.; Mosekilde, Erik
1999-01-01
We present analytical conditions for the riddling bifurcation in a system of two symmetrically coupled, identical, smooth one-dimensional maps to be soft or hard and describe a generic scenario for the transformations of the basin of attraction following a soft riddling bifurcation.......We present analytical conditions for the riddling bifurcation in a system of two symmetrically coupled, identical, smooth one-dimensional maps to be soft or hard and describe a generic scenario for the transformations of the basin of attraction following a soft riddling bifurcation....
Comparative anatomical studies on the thyroid and thymic arteries. II. Polyprotodont marsupials.
Yamasaki, M
1993-01-01
The thyroid and thymic arteries were investigated in 27 specimens from 9 species belonging to the Australian Polyprotodont marsupials, which are subdivided into 2 superfamilies, Dasyuroidea and Perameloidea. The results were compared with those in rats and humans. The site of origin of the superior thyroid artery ranged from the external carotid artery to the common carotid in Dasyuroids, and converged on the external carotid and the bifurcation of the common carotid in Perameloids. The cours...
Anomalous origin of the occipital artery diagnosed by magnetic resonance angiography
Energy Technology Data Exchange (ETDEWEB)
Uchino, Akira; Saito, Naoko; Mizukoshi, Waka; Okada, Yoshitaka [Saitama Medical University International Medical Center, Department of Diagnostic Radiology, Hidaka, Saitama (Japan)
2011-11-15
It is well known that the occipital artery (OA) can arise from the internal carotid artery (ICA) or vertebral artery (VA). However, the incidence of an anomalously originating OA has not been reported. We investigate its incidence and characteristic features on magnetic resonance angiography (MRA). We retrospectively reviewed MRA images of 2,866 patients that included the carotid bifurcation; images were obtained using a standard noncontrast MRA protocol and two 1.5-T MR units. We diagnosed six cases (seven arteries) of anomalously originating OA, which represented an incidence of 0.21%. The OA arose from the ICA in four patients (five arteries), from the carotid bifurcation in one, and from the VA in one. Five of the seven arteries occurred on the right. Anomalously originating OA is rare and occurs with right-side predominance. Correct diagnosis is necessary before or during cerebral angiography, especially when selective catheterization to the OA is required. (orig.)
Codimension-Two Bifurcation Analysis in Hindmarsh-Rose Model with Two Parameters
Institute of Scientific and Technical Information of China (English)
DUAN Li-Xia; LU Qi-Shao
2005-01-01
@@ Bifurcation phenomena in a Hindmarsh-Rose neuron model are investigated. Special attention is paid to the bifurcation structures off two parameters, where codimension-two generalized-Hopf bifurcation and fold-Hopf bifurcation occur. The classification offiring patterns as well as the transition mechanism in different regions on the parameter plane are obtained.
Supercritical as well as subcritical Hopf bifurcation in nonlinear flutter systems
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
The Hopf bifurcations of an airfoil flutter system with a cubic nonlinearity are investigated,with the flow speed as the bifurcation parameter.The center manifold theory and complex normal form method are used to obtain the bifurcation equation.Interestingly,for a certain linear pitching stiffness the Hopf bifurcation is both supercritical and subcritical.It is found,mathematically,this is caused by the fact that one coefficient in the bifurcation equation does not contain the first power of the bifurcation parameter.The solutions of the bifurcation equation are validated by the equivalent linearization method and incremental harmonic balance method.
Semiclassical interference of bifurcations
Schomerus, H
1997-01-01
In semiclassical studies of systems with mixed phase space, the neighbourhood of bifurcations of co-dimension two is felt strongly even though such bifurcations are ungeneric in classical mechanics. We discuss a scenario which reveals this fact and derive the correct semiclassical contribution of the bifurcating orbits to the trace of the unitary time evolution operator. That contribution has a certain collective character rather than being additive in the individual periodic orbits involved. The relevance of our observation is demonstrated by a numerical study of the kicked top; the collective contribution derived is found to considerably improve the semiclassical approximation of the trace.
Relative Lyapunov Center Bifurcations
DEFF Research Database (Denmark)
Wulff, Claudia; Schilder, Frank
2014-01-01
Relative equilibria (REs) and relative periodic orbits (RPOs) are ubiquitous in symmetric Hamiltonian systems and occur, for example, in celestial mechanics, molecular dynamics, and rigid body motion. REs are equilibria, and RPOs are periodic orbits of the symmetry reduced system. Relative Lyapunov...... center bifurcations are bifurcations of RPOs from REs corresponding to Lyapunov center bifurcations of the symmetry reduced dynamics. In this paper we first prove a relative Lyapunov center theorem by combining recent results on the persistence of RPOs in Hamiltonian systems with a symmetric Lyapunov...... center theorem of Montaldi, Roberts, and Stewart. We then develop numerical methods for the detection of relative Lyapunov center bifurcations along branches of RPOs and for their computation. We apply our methods to Lagrangian REs of the N-body problem....
Hemodynamics of Stent Implantation Procedures in Coronary Bifurcations: an in vitro study
Brindise, Melissa C; Burzotta, Francesco; Migliavacca, Francesco; Vlachos, Pavlos P
2016-01-01
Stent implantation in coronary bifurcations presents unique challenges and currently there is no universally accepted stent deployment approach. Despite clinical and computational studies, to date, the effect of each stent implantation method on the coronary artery hemodynamics is not well understood. In this study the hemodynamics of stented coronary bifurcations under pulsatile flow conditions were investigated experimentally. Three implantation methods, provisional side branch (PSB), culotte (CUL), and crush (CRU), were investigated using time-resolved particle image velocimetry (PIV) to measure the velocity fields. Subsequently, hemodynamic parameters including wall shear stress (WSS), oscillatory shear index (OSI), and relative residence time (RRT) were calculated and the pressure field through the vessel was non-invasively quantified. The effects of each stented case were evaluated and compared against an un-stented case. CRU provided the lowest compliance mismatch, but demonstrated detrimental stent in...
Wall shear stress in intracranial aneurysms and adjacent arteries
Institute of Scientific and Technical Information of China (English)
Fuyu Wang; Bainan Xu; Zhenghui Sun; Chen Wu; Xiaojun Zhang
2013-01-01
Hemodynamic parameters play an important role in aneurysm formation and growth. However, it is difficult to directly observe a rapidly growing de novo aneurysm in a patient. To investigate possible associations between hemodynamic parameters and the formation and growth of intracranial aneurysms, the present study constructed a computational model of a case with an internal carotid artery aneurysm and an anterior communicating artery aneurysm, based on the CT angiography findings of a patient. To simulate the formation of the anterior communicating artery aneurysm and the growth of the internal carotid artery aneurysm, we then constructed a model that virtually removed the anterior communicating artery aneurysm, and a further two models that also progressively decreased the size of the internal carotid artery aneurysm. Computational simulations of the fluid dynamics of the four models were performed under pulsatile flow conditions, and wall shear stress was compared among the different models. In the three aneurysm growth models, increasing size of the aneurysm was associated with an increased area of low wall shear stress, a significant decrease in wall shear stress at the dome of the aneurysm, and a significant change in the wall shear stress of the parent artery. The wall shear stress of the anterior communicating artery remained low, and was significantly lower than the wall shear stress at the bifurcation of the internal carotid artery or the bifurcation of the middle cerebral artery. After formation of the anterior communicating artery aneurysm, the wall shear stress at the dome of the internal carotid artery aneurysm increased significantly, and the wall shear stress in the upstream arteries also changed significantly. These findings indicate that low wall shear stress may be associated with the initiation and growth of aneurysms, and that aneurysm formation and growth may influence hemodynamic parameters in the local and adjacent arteries.
Bifurcation Analysis in a Delayed Diffusive Leslie-Gower Model
Directory of Open Access Journals (Sweden)
Shuling Yan
2013-01-01
Full Text Available We investigate a modified delayed Leslie-Gower model under homogeneous Neumann boundary conditions. We give the stability analysis of the equilibria of the model and show the existence of Hopf bifurcation at the positive equilibrium under some conditions. Furthermore, we investigate the stability and direction of bifurcating periodic orbits by using normal form theorem and the center manifold theorem.
Codimension 2 reversible heteroclinic bifurcations with inclination flips
Institute of Scientific and Technical Information of China (English)
2009-01-01
In this paper, the heteroclinic bifurcation problem with real eigenvalues and two incli- nation-flips is investigated in a four-dimensional reversible system. We perform a detailed study of this case by using the method originally established in the papers "Problems in Homoclinic Bifurcation with Higher Dimensions" and "Bifurcation of Heteroclinic Loops," and obtain fruitful results, such as the existence and coexistence of R-symmetric homoclinic orbit and R-symmetric heteroclinic loops, R-symmetric homoclinic orbit and R-symmetric periodic orbit. The double R-symmetric homoclinic bifurcation (i.e., two-fold R-symmetric homoclinic bifurcation) for reversible heteroclinic loops is found, and the existence of infinitely many R-symmetric periodic orbits accumulating onto a homoclinic orbit is demonstrated. The relevant bifurcation surfaces and the existence regions are also located.
Bifurcation Analysis for Neural Networks in Neutral Form
Chen, Hong-Bing; Sun, Xiao-Ke
2016-06-01
In this paper, a system of neural networks in neutral form with time delay is investigated. Further, by introducing delay τ as a bifurcation parameter, it is found that Hopf bifurcation occurs when τ is across some critical values. The direction of the Hopf bifurcations and the stability are determined by using normal form method and center manifold theory. Next, the global existence of periodic solution is established by using a global Hopf bifurcation result. Finally, an example is given to support the theoretical predictions.
Bifurcation phenomena in control flows
Colonius, Fritz; Fabbri, Roberta; Johnson, Russell; Spadini, Marco
2007-01-01
We study bifurcation phenomena in control flows and the bifurcation of control sets. A Mel'nikov method and the Conley index together with exponential dichotomy theory and integral manifold theory are used.
Digital subtraction angiography of carotid bifurcation
International Nuclear Information System (INIS)
This study demonstrates the reliability of digital subtraction angiography (DSA) by means of intra- and interobserver investigations as well as indicating the possibility of substituting catheterangiography by DSA in the diagnosis of carotid bifurcation. Whenever insufficient information is obtained from the combination of non-invasive investigation and DSA, a catheterangiogram will be necessary. (Auth.)
Energetics and monsoon bifurcations
Seshadri, Ashwin K.
2016-04-01
Monsoons involve increases in dry static energy (DSE), with primary contributions from increased shortwave radiation and condensation of water vapor, compensated by DSE export via horizontal fluxes in monsoonal circulations. We introduce a simple box-model characterizing evolution of the DSE budget to study nonlinear dynamics of steady-state monsoons. Horizontal fluxes of DSE are stabilizing during monsoons, exporting DSE and hence weakening the monsoonal circulation. By contrast latent heat addition (LHA) due to condensation of water vapor destabilizes, by increasing the DSE budget. These two factors, horizontal DSE fluxes and LHA, are most strongly dependent on the contrast in tropospheric mean temperature between land and ocean. For the steady-state DSE in the box-model to be stable, the DSE flux should depend more strongly on the temperature contrast than LHA; stronger circulation then reduces DSE and thereby restores equilibrium. We present conditions for this to occur. The main focus of the paper is describing conditions for bifurcation behavior of simple models. Previous authors presented a minimal model of abrupt monsoon transitions and argued that such behavior can be related to a positive feedback called the `moisture advection feedback'. However, by accounting for the effect of vertical lapse rate of temperature on the DSE flux, we show that bifurcations are not a generic property of such models despite these fluxes being nonlinear in the temperature contrast. We explain the origin of this behavior and describe conditions for a bifurcation to occur. This is illustrated for the case of the July-mean monsoon over India. The default model with mean parameter estimates does not contain a bifurcation, but the model admits bifurcation as parameters are varied.
Hopf Bifurcation in a Nonlinear Wave System
Institute of Scientific and Technical Information of China (English)
HE Kai-Fen
2004-01-01
@@ Bifurcation behaviour of a nonlinear wave system is studied by utilizing the data in solving the nonlinear wave equation. By shifting to the steady wave frame and taking into account the Doppler effect, the nonlinear wave can be transformed into a set of coupled oscillators with its (stable or unstable) steady wave as the fixed point.It is found that in the chosen parameter regime, both mode amplitudes and phases of the wave can bifurcate to limit cycles attributed to the Hopf instability. It is emphasized that the investigation is carried out in a pure nonlinear wave framework, and the method can be used for the further exploring routes to turbulence.
Stability and bifurcations in a nonlocal delayed reaction-diffusion population model
Chen, Shanshan; Yu, Jianshe
2016-01-01
A nonlocal delayed reaction-diffusion equation with Dirichlet boundary condition is considered in this paper. It is shown that a positive spatially nonhomogeneous equilibrium bifurcates from the trivial equilibrium. The stability/instability of the bifurcated positive equilibrium and associated Hopf bifurcation are investigated, providing us with a complete picture of the dynamics.
Stability and Hopf Bifurcation Analysis of a Vector-Borne Disease with Time Delay
Yuanyuan Chen; Ya-Qing Bi
2014-01-01
A delay-differential modelling of vector-borne is investigated. Its dynamics are studied in terms of local analysis and Hopf bifurcation theory, and its linear stability and Hopf bifurcation are demonstrated by studying the characteristic equation. The stability and direction of Hopf bifurcation are determined by applying the normal form theory and the center manifold argument.
Local and global bifurcation and its applications in a predator-prey system with several parameters
International Nuclear Information System (INIS)
A predator-prey system, depending on several parameters, is investigated for bifurcation of equilibria, Hopf bifurcation, global bifurcation occurring saddle connection, and global existence and non-existence of limit cycles, and changes of the topological structure of trajectory as parameters are varied. (author). 8 refs, 4 figs
Equilibrium Point Bifurcation and Singularity Analysis of HH Model with Constraint
2014-01-01
We present the equilibrium point bifurcation and singularity analysis of HH model with constraints. We investigate the effect of constraints and parameters on the type of equilibrium point bifurcation. HH model with constraints has more transition sets. The Matcont toolbox software environment was used for analysis of the bifurcation points in conjunction with Matlab. We also illustrate the stability of the equilibrium points.
Stability and Hopf bifurcation in a symmetric Lotka-Volterra predator-prey system with delays
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Jing Xia
2013-01-01
Full Text Available This article concerns a symmetrical Lotka-Volterra predator-prey system with delays. By analyzing the associated characteristic equation of the original system at the positive equilibrium and choosing the delay as the bifurcation parameter, the local stability and Hopf bifurcation of the system are investigated. Using the normal form theory, we also establish the direction and stability of the Hopf bifurcation. Numerical simulations suggest an existence of Hopf bifurcation near a critical value of time delay.
Stability and Bifurcation Analysis in a Diffusive Brusselator-Type System
Liao, Maoxin; Wang, Qi-Ru
2016-06-01
In this paper, the dynamic properties for a Brusselator-type system with diffusion are investigated. By employing the theory of Hopf bifurcation for ordinary and partial differential equations, we mainly obtain some conditions of the stability and Hopf bifurcation for the ODE system, diffusion-driven instability of the equilibrium solution, and the direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions for the PDE system. Finally, some numerical simulations are presented to verify our results.
Noise induced Hopf bifurcation
Shuda, I. A.; Borysov, S S; A.I. Olemskoi
2008-01-01
We consider effect of stochastic sources upon self-organization process being initiated with creation of the limit cycle induced by the Hopf bifurcation. General relations obtained are applied to the stochastic Lorenz system to show that departure from equilibrium steady state can destroy the limit cycle in dependence of relation between characteristic scales of temporal variation of principle variables. Noise induced resonance related to the limit cycle is found to appear if the fastest vari...
Post-Treatment Hemodynamics of a Basilar Aneurysm and Bifurcation
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Ortega, J; Hartman, J; Rodriguez, J; Maitland, D
2008-01-16
Aneurysm re-growth and rupture can sometimes unexpectedly occur following treatment procedures that were initially considered to be successful at the time of treatment and post-operative angiography. In some cases, this can be attributed to surgical clip slippage or endovascular coil compaction. However, there are other cases in which the treatment devices function properly. In these instances, the subsequent complications are due to other factors, perhaps one of which is the post-treatment hemodynamic stress. To investigate whether or not a treatment procedure can subject the parent artery to harmful hemodynamic stresses, computational fluid dynamics simulations are performed on a patient-specific basilar aneurysm and bifurcation before and after a virtual endovascular treatment. The simulations demonstrate that the treatment procedure produces a substantial increase in the wall shear stress. Analysis of the post-treatment flow field indicates that the increase in wall shear stress is due to the impingement of the basilar artery flow upon the aneurysm filling material and to the close proximity of a vortex tube to the artery wall. Calculation of the time-averaged wall shear stress shows that there is a region of the artery exposed to a level of wall shear stress that can cause severe damage to endothelial cells. The results of this study demonstrate that it is possible for a treatment procedure, which successfully excludes the aneurysm from the vascular system and leaves no aneurysm neck remnant, to elevate the hemodynamic stresses to levels that are injurious to the immediately adjacent vessel wall.
Spiral blood flow in aorta-renal bifurcation models.
Javadzadegan, Ashkan; Simmons, Anne; Barber, Tracie
2016-07-01
The presence of a spiral arterial blood flow pattern in humans has been widely accepted. It is believed that this spiral component of the blood flow alters arterial haemodynamics in both positive and negative ways. The purpose of this study was to determine the effect of spiral flow on haemodynamic changes in aorta-renal bifurcations. In this regard, a computational fluid dynamics analysis of pulsatile blood flow was performed in two idealised models of aorta-renal bifurcations with and without flow diverter. The results show that the spirality effect causes a substantial variation in blood velocity distribution, while causing only slight changes in fluid shear stress patterns. The dominant observed effect of spiral flow is on turbulent kinetic energy and flow recirculation zones. As spiral flow intensity increases, the rate of turbulent kinetic energy production decreases, reducing the region of potential damage to red blood cells and endothelial cells. Furthermore, the recirculation zones which form on the cranial sides of the aorta and renal artery shrink in size in the presence of spirality effect; this may lower the rate of atherosclerosis development and progression in the aorta-renal bifurcation. These results indicate that the spiral nature of blood flow has atheroprotective effects in renal arteries and should be taken into consideration in analyses of the aorta and renal arteries. PMID:26414530
Dynamical Systems with a Codimension-One Invariant Manifold: The Unfoldings and Its Bifurcations
Saputra, Kie Van Ivanky
2015-06-01
We investigate a dynamical system having a special structure namely a codimension-one invariant manifold that is preserved under the variation of parameters. We derive conditions such that bifurcations of codimension-one and of codimension-two occur in the system. The normal forms of these bifurcations are derived explicitly. Both local and global bifurcations are analyzed and yield the transcritical bifurcation as the codimension-one bifurcation while the saddle-node-transcritical interaction and the Hopf-transcritical interactions as the codimension-two bifurcations. The unfolding of this degeneracy is also analyzed and reveal global bifurcations such as homoclinic and heteroclinic bifurcations. We apply our results to a modified Lotka-Volterra model and to an infection model in HIV diseases.
Symmetric/asymmetric bifurcation behaviours of a bogie system
Xue-jun, Gao; Ying-hui, Li; Yuan, Yue; True, Hans
2013-02-01
Based on the bifurcation and stability theory of dynamical systems, the symmetric/asymmetric bifurcation behaviours and chaotic motions of a railway bogie system under a complex nonlinear wheel-rail contact relation are investigated in detail by the 'resultant bifurcation diagram' method with slowly increasing and decreasing speed. It is found that the stationary equilibrium solution and the periodic motions coexist due to the sub-critical Hopf bifurcation in the railway bogie system. It is also found that multiple solutions coexist in many speed ranges. The coexistence of multiple solutions may result in a jump and hysteresis of the oscillating amplitude for different kinds of disturbances. It should be avoided in the normal operation. Furthermore, it is found that symmetry-breaking of the system through a pitchfork bifurcation leads to asymmetric chaotic motions in the railway bogie system. The speed ranges of asymmetric chaotic motions are, however, small.
The Analysis of PPG Morphology: Investigating the Effects of Aging on Arterial Compliance
Yousef, Q.; Reaz, M. B. I.; Ali, M. A. M.
2012-12-01
This study presents the variations of photoplethysmogram (PPG) morphology with age. PPG measurement is done noninvasively at the index finger on both right and left hands for a sample of erectile dysfunction (ED) subjects. Some parameters are derived from the analysis of PPG contour showed in association with age. The age is found to be an important factor that affects the contour of PPG signals which accelerates the disappearance of PPG’s dicrotic notch and PPG’s inflection point as well. Arterial compliance is found to be degraded with age due to the fall of arterial elasticity. This study approaches the establishment of usefulness of PPG’s contour analysis as an investigator to the changes in the elastic properties of the vascular system, and as a detector of early sub-clinical atherosclerosis.
International Nuclear Information System (INIS)
Two angiographic instances of anomalous external carotid artery (ECA) and internal carotid artery (ICA) anastomosis are described, each occurring at the C2-3 level and bearing remnants of proximal ICA. The ICA remnant of one patient (identifiable immediately upon bifurcation of the common carotid artery) was hypoplastic, and that of the other patient was an occluded arterial stump. These features are not typical of non-bifurcating ICA. The occipital artery originated from an anomalous connection in one instance and from the main trunk of the ECA (just past the ECA-ICA connection) in the other
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Kim, Chang Hun [Dept. of Neurology, Stroke Center, Myongji Hospital, Goyang (Korea, Republic of); Cho, Young Dae; Kang, Hyun Seung; Kim, Jeong Eun; Han, Moon Hee [Seoul National University Hospital, Seoul National University College of Medicine, Seoul (Korea, Republic of); Jung, Seung Chai [Dept. of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul (Korea, Republic of); Ahn, Jun Hyong [Dept. of Neurosurgery, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang (Korea, Republic of)
2015-08-15
Two angiographic instances of anomalous external carotid artery (ECA) and internal carotid artery (ICA) anastomosis are described, each occurring at the C2-3 level and bearing remnants of proximal ICA. The ICA remnant of one patient (identifiable immediately upon bifurcation of the common carotid artery) was hypoplastic, and that of the other patient was an occluded arterial stump. These features are not typical of non-bifurcating ICA. The occipital artery originated from an anomalous connection in one instance and from the main trunk of the ECA (just past the ECA-ICA connection) in the other.
International Nuclear Information System (INIS)
Objective: To investigate the function of transferrin-DNA complex, transported by transferrin(Tf) and trans-arterial injection via interventional approach be the duel-target-orientated delivery and the transferring into malignant cells to get more effective therapy. Methods: p53-LipofectAMINE ligand with different concentrations of Tf (0, 10, 25, 50, 100 μg)transfected the 4 strains including LM6,Hep3B,YY and L02 in vitro to evaluate the gene transfection efficiency through western blot. Then, after setting up the VX2 hepatocarcinoma models, we delivered the Tf-p53-LipofectAMlNE complex into the hepatic arteries via interventional techniques to analyse the transfection efficiency in vivo. Results: Tf, within the range of l0 100 μg, could increase gene transfection efficiency mediated by liposome, and the efficiency increases with the raise of Tf concentration. Combination with interventional technique to inject Tf-DNA complex into tumor arteries, gene transfection efficiency was enhanced in rabbit models. Conclusion: Tf can enhance gene-liposome transfection efficiency, furthermore with combination of interventional catheter technique, there would be a potential duel-target-orientated gene therapy method. (authors)
International Nuclear Information System (INIS)
Highlights: • A ratio-dependent predator–prey system involving two discrete maturation time delays is studied. • Hopf bifurcations are analyzed by choosing delay parameters as bifurcation parameters. • When a delay parameter passes through a critical value, Hopf bifurcations occur. • The direction of bifurcation, the period and the stability of periodic solution are also obtained. - Abstract: In this paper we give a detailed Hopf bifurcation analysis of a ratio-dependent predator–prey system involving two different discrete delays. By analyzing the characteristic equation associated with the model, its linear stability is investigated. Choosing delay terms as bifurcation parameters the existence of Hopf bifurcations is demonstrated. Stability of the bifurcating periodic solutions is determined by using the center manifold theorem and the normal form theory introduced by Hassard et al. Furthermore, some of the bifurcation properties including direction, stability and period are given. Finally, theoretical results are supported by some numerical simulations
Directory of Open Access Journals (Sweden)
Zizhen Zhang
2013-01-01
Full Text Available Hopf bifurcation of a delayed predator-prey system with prey infection and the modified Leslie-Gower scheme is investigated. The conditions for the stability and existence of Hopf bifurcation of the system are obtained. The state feedback and parameter perturbation are used for controlling Hopf bifurcation in the system. In addition, direction of Hopf bifurcation and stability of the bifurcated periodic solutions of the controlled system are obtained by using normal form and center manifold theory. Finally, numerical simulation results are presented to show that the hybrid controller is efficient in controlling Hopf bifurcation.
Directory of Open Access Journals (Sweden)
Yanhui Zhai
2014-01-01
Full Text Available The paper investigated an avian influenza virus propagation model with nonlinear incidence rate and delay based on SIR epidemic model. We regard delay as bifurcating parameter to study the dynamical behaviors. At first, local asymptotical stability and existence of Hopf bifurcation are studied; Hopf bifurcation occurs when time delay passes through a sequence of critical values. An explicit algorithm for determining the direction of the Hopf bifurcations and stability of the bifurcation periodic solutions is derived by applying the normal form theory and center manifold theorem. What is more, the global existence of periodic solutions is established by using a global Hopf bifurcation result.
Introduction to bifurcation theory
International Nuclear Information System (INIS)
Bifurcation theory is a subject with classical mathematical origins. The modern development of the subject starts with Poincare and the qualitative theory of differential equations. In recent years, the theory has undergone a tremendous development with the infusion of new ideas and methods from dynamical systems theory, singularity theory, group theory, and computer-assisted studies of dynamics. As a result, it is difficult to draw the boundaries of the theory with any confidence. In this review, the objects in question will be parameterized families of dynamical systems (vector fields or maps). In the sciences these families commonly arise when one formulates equations of motion to model a physical system. We specifically analyze how the time evolution near an equilibrium can change as parameters are varied; for simplicity we consider the case of a single parameter only
Hopf bifurcations in a predator-prey system with multiple delays
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Hu Guangping [School of Mathematics and Statistics, Lanzhou University, Lanzhou 730000 (China); School of Mathematics and Physics, Nanjing University of Information and Technology, Nanjing 210044 (China); Li Wantong [School of Mathematics and Statistics, Lanzhou University, Lanzhou 730000 (China)], E-mail: wtli@lzu.edu.cn; Yan Xiangping [Department of Applied Mathematics, Lanzhou Jiaotong University, Lanzhou 730070 (China)
2009-10-30
This paper is concerned with a two species Lotka-Volterra predator-prey system with three discrete delays. By regarding the gestation period of two species as the bifurcation parameter, the stability of positive equilibrium and Hopf bifurcations of nonconstant periodic solutions are investigated. Furthermore, the direction of Hopf bifurcations and the stability of bifurcated periodic solutions are determined by applying the normal form theory and the center manifold reduction for functional differential equations (FDEs). In addition, the global existence of bifurcated periodic solutions are also established by employing the topological global Hopf bifurcation theorem, which shows that the local Hopf bifurcations imply the global ones after the second critical value of parameter. Finally, to verify our theoretical predictions, some numerical simulations are also included.
Hopf bifurcations in a predator-prey system with multiple delays
International Nuclear Information System (INIS)
This paper is concerned with a two species Lotka-Volterra predator-prey system with three discrete delays. By regarding the gestation period of two species as the bifurcation parameter, the stability of positive equilibrium and Hopf bifurcations of nonconstant periodic solutions are investigated. Furthermore, the direction of Hopf bifurcations and the stability of bifurcated periodic solutions are determined by applying the normal form theory and the center manifold reduction for functional differential equations (FDEs). In addition, the global existence of bifurcated periodic solutions are also established by employing the topological global Hopf bifurcation theorem, which shows that the local Hopf bifurcations imply the global ones after the second critical value of parameter. Finally, to verify our theoretical predictions, some numerical simulations are also included.
Bifurcations sights, sounds, and mathematics
Matsumoto, Takashi; Kokubu, Hiroshi; Tokunaga, Ryuji
1993-01-01
Bifurcation originally meant "splitting into two parts. " Namely, a system under goes a bifurcation when there is a qualitative change in the behavior of the sys tem. Bifurcation in the context of dynamical systems, where the time evolution of systems are involved, has been the subject of research for many scientists and engineers for the past hundred years simply because bifurcations are interesting. A very good way of understanding bifurcations would be to see them first and study theories second. Another way would be to first comprehend the basic concepts and theories and then see what they look like. In any event, it is best to both observe experiments and understand the theories of bifurcations. This book attempts to provide a general audience with both avenues toward understanding bifurcations. Specifically, (1) A variety of concrete experimental results obtained from electronic circuits are given in Chapter 1. All the circuits are very simple, which is crucial in any experiment. The circuits, howev...
Santer, R M; Owen, R. G.
1986-01-01
A combination of morphological and semiquantitative techniques has been employed to characterise the arterial supply to the rat superior cervical ganglion. Microfil and ink-injected preparations indicate that the major supply is from the carotid body artery which sends several branches to the rostral part of the ganglion and a recurrent branch to its caudal part. Occlusion of the proximal part of the external carotid artery, and hence the carotid body artery (whether it be derived from the ex...
International Nuclear Information System (INIS)
Objective: To investigate and analyze the cause of the tumble which occurs after transcatheter arterial chemoembolization (TACE), and to discuss its related factors. Methods: During the period from January 2003 to February 2010 in the Department of Interventional Radiology of Union Hospital (Wuhan city), post-TACE tumble occurred in 28 patients. The causes of the tumble were investigated and analyzed. Results: (1) The total number of the tumble occurrence after TACE was declining with the year. (2) Certain relationship existed between the occurrence of post-TACE tumble and the patient's age, drugs used in surgery, unit environment, nurse's shift, etc. Conclusion: Based on the patient's individual condition, intentionally enhancing the perioperative nursing care and adjusting the nurse's shift are very important measures to prevent the occurrence of post-TACE tumble. (authors)
Application of Bifurcation Theory to Subsynchronous Resonance in Power Systems
Harb, Ahmad M.
1996-01-01
A bifurcation analysis is used to investigate the complex dynamics of two heavily loaded single-machine-infinite-busbar power systems modeling the characteristics of the BOARDMAN generator with respect to the rest of the North-Western American Power System and the CHOLLA$#$ generator with respect to the SOWARO station. In the BOARDMAN system, we show that there are three Hopf bifurcations at practical co...
Bursting oscillations, bifurcation and synchronization in neuronal systems
International Nuclear Information System (INIS)
Highlights: → We investigate bursting oscillations and related bifurcation in the modified Morris-Lecar neuron. → Two types of fast-slow bursters are analyzed in detail. → We show the properties of some crucial bifurcation points. → Synchronization transition and the neural excitability are explored in the coupled bursters. - Abstract: This paper investigates bursting oscillations and related bifurcation in the modified Morris-Lecar neuron. It is shown that for some appropriate parameters, the modified Morris-Lecar neuron can exhibit two types of fast-slow bursters, that is 'circle/fold cycle' bursting and 'subHopf/homoclinic' bursting with class 1 and class 2 neural excitability, which have different neuro-computational properties. By means of the analysis of fast-slow dynamics and phase plane, we explore bifurcation mechanisms associated with the two types of bursters. Furthermore, the properties of some crucial bifurcation points, which can determine the type of the burster, are studied by the stability and bifurcation theory. In addition, we investigate the influence of the coupling strength on synchronization transition and the neural excitability in two electrically coupled bursters with the same bursting type. More interestingly, the multi-time-scale synchronization transition phenomenon is found as the coupling strength varies.
DYNAMIC BIFURCATION OF NONLINEAR EVOLUTION EQUATIONS
Institute of Scientific and Technical Information of China (English)
MA TIAN; WANG SHOUHONG
2005-01-01
The authors introduce a notion of dynamic bifurcation for nonlinear evolution equations, which can be called attractor bifurcation. It is proved that as the control parameter crosses certain critical value, the system bifurcates from a trivial steady state solution to an attractor with dimension between m and m + 1, where m + 1 is the number of eigenvalues crossing the imaginary axis. The attractor bifurcation theory presented in this article generalizes the existing steady state bifurcations and the Hopf bifurcations. It provides a unified point of view on dynamic bifurcation and can be applied to many problems in physics and mechanics.
Bifurcation dynamics of the tempered fractional Langevin equation
Zeng, Caibin; Yang, Qigui; Chen, YangQuan
2016-08-01
Tempered fractional processes offer a useful extension for turbulence to include low frequencies. In this paper, we investigate the stochastic phenomenological bifurcation, or stochastic P-bifurcation, of the Langevin equation perturbed by tempered fractional Brownian motion. However, most standard tools from the well-studied framework of random dynamical systems cannot be applied to systems driven by non-Markovian noise, so it is desirable to construct possible approaches in a non-Markovian framework. We first derive the spectral density function of the considered system based on the generalized Parseval's formula and the Wiener-Khinchin theorem. Then we show that it enjoys interesting and diverse bifurcation phenomena exchanging between or among explosive-like, unimodal, and bimodal kurtosis. Therefore, our procedures in this paper are not merely comparable in scope to the existing theory of Markovian systems but also provide a possible approach to discern P-bifurcation dynamics in the non-Markovian settings.
Bifurcation theory for hexagonal agglomeration in economic geography
Ikeda, Kiyohiro
2014-01-01
This book contributes to an understanding of how bifurcation theory adapts to the analysis of economic geography. It is easily accessible not only to mathematicians and economists, but also to upper-level undergraduate and graduate students who are interested in nonlinear mathematics. The self-organization of hexagonal agglomeration patterns of industrial regions was first predicted by the central place theory in economic geography based on investigations of southern Germany. The emergence of hexagonal agglomeration in economic geography models was envisaged by Krugman. In this book, after a brief introduction of central place theory and new economic geography, the missing link between them is discovered by elucidating the mechanism of the evolution of bifurcating hexagonal patterns. Pattern formation by such bifurcation is a well-studied topic in nonlinear mathematics, and group-theoretic bifurcation analysis is a well-developed theoretical tool. A finite hexagonal lattice is used to express uniformly distri...
Grazing bifurcation and chaos in response of rubbing rotor
International Nuclear Information System (INIS)
This paper investigates the grazing bifurcation in the nonlinear response of a complex rotor system. For a rotor with overhung disc, step diameter shaft and elastic supports, the motion equations are derived based on the Transition Matrix Method. When the rotor speed increases, the disc will touch the case and lead to rubbing of rotor. When the disc rubs with the case, the elastic force and friction force of the case will make the rotor exhibit nonlinear characteristics. For the piecewise ODEs, the numerical method is applied to obtain its nonlinear response. From the results, the grazing bifurcation, which happens at the moment of touching between disc and case, can be observed frequently. The grazing bifurcation can lead to the jump between periodic orbits. The response can go to chaos from periodic motion under grazing bifurcation. When grazing occurs, response can become quasi-period from period
Bifurcation dynamics of the tempered fractional Langevin equation.
Zeng, Caibin; Yang, Qigui; Chen, YangQuan
2016-08-01
Tempered fractional processes offer a useful extension for turbulence to include low frequencies. In this paper, we investigate the stochastic phenomenological bifurcation, or stochastic P-bifurcation, of the Langevin equation perturbed by tempered fractional Brownian motion. However, most standard tools from the well-studied framework of random dynamical systems cannot be applied to systems driven by non-Markovian noise, so it is desirable to construct possible approaches in a non-Markovian framework. We first derive the spectral density function of the considered system based on the generalized Parseval's formula and the Wiener-Khinchin theorem. Then we show that it enjoys interesting and diverse bifurcation phenomena exchanging between or among explosive-like, unimodal, and bimodal kurtosis. Therefore, our procedures in this paper are not merely comparable in scope to the existing theory of Markovian systems but also provide a possible approach to discern P-bifurcation dynamics in the non-Markovian settings. PMID:27586627
Bifurcations, instabilities, degradation in geomechanics
Exadaktylos, George
2007-01-01
Leading international researchers and practitioners of bifurcations and instabilities in geomechanics debate the developments and applications which have occurred over the last few decades. The topics covered include modeling of bifurcation, structural failure of geomaterials and geostructures, advanced analytical, numerical and experimental techniques, and application and development of generalised continuum models etc. In addition analytical solutions, numerical methods, experimental techniques, and case histories are presented. Beside fundamental research findings, applications in geotechni
Does the principle of minimum work apply at the carotid bifurcation: a retrospective cohort study
International Nuclear Information System (INIS)
There is recent interest in the role of carotid bifurcation anatomy, geometry and hemodynamic factors in the pathogenesis of carotid artery atherosclerosis. Certain anatomical and geometric configurations at the carotid bifurcation have been linked to disturbed flow. It has been proposed that vascular dimensions are selected to minimize energy required to maintain blood flow, and that this occurs when an exponent of 3 relates the radii of parent and daughter arteries. We evaluate whether the dimensions of bifurcation of the extracranial carotid artery follow this principle of minimum work. This study involved subjects who had computed tomographic angiography (CTA) at our institution between 2006 and 2007. Radii of the common, internal and external carotid arteries were determined. The exponent was determined for individual bifurcations using numerical methods and for the sample using nonlinear regression. Mean age for 45 participants was 56.9 ± 16.5 years with 26 males. Prevalence of vascular risk factors was: hypertension-48%, smoking-23%, diabetes-16.7%, hyperlipidemia-51%, ischemic heart disease-18.7%. The value of the exponent ranged from 1.3 to 1.6, depending on estimation methodology. The principle of minimum work (defined by an exponent of 3) may not apply at the carotid bifurcation. Additional factors may play a role in the relationship between the radii of the parent and daughter vessels
Fast automatic algorithm for bifurcation detection in vascular CTA scans
Brozio, Matthias; Gorbunova, Vladlena; Godenschwager, Christian; Beck, Thomas; Bernhardt, Dominik
2012-02-01
Endovascular imaging aims at identifying vessels and their branches. Automatic vessel segmentation and bifurcation detection eases both clinical research and routine work. In this article a state of the art bifurcation detection algorithm is developed and applied on vascular computed tomography angiography (CTA) scans to mark the common iliac artery and its branches, the internal and external iliacs. In contrast to other methods our algorithm does not rely on a complete segmentation of a vessel in the 3D volume, but evaluates the cross-sections of the vessel slice by slice. Candidates for vessels are obtained by thresholding, following by 2D connected component labeling and prefiltering by size and position. The remaining candidates are connected in a squared distanced weighted graph. With Dijkstra algorithm the graph is traversed to get candidates for the arteries. We use another set of features considering length and shape of the paths to determine the best candidate and detect the bifurcation. The method was tested on 119 datasets acquired with different CT scanners and varying protocols. Both easy to evaluate datasets with high resolution and no apparent clinical diseases and difficult ones with low resolution, major calcifications, stents or poor contrast between the vessel and surrounding tissue were included. The presented results are promising, in 75.7% of the cases the bifurcation was labeled correctly, and in 82.7% the common artery and one of its branches were assigned correctly. The computation time was on average 0.49 s +/- 0.28 s, close to human interaction time, which makes the algorithm applicable for time-critical applications.
DEFF Research Database (Denmark)
Willerslev, Anne; Li, Xiao Q; Munch, Inger C;
2014-01-01
from the population-based, observational Copenhagen Child Cohort 2000 study. RESULTS: The blood stream in retinal arteries maintains a figure-of-8 SD-OCT profile consistent with a laminar flow in concentric sheets and a parabolic velocity distribution up to the point of divergence at arterial...... bifurcations. In contrast, the blood stream at the site of confluence of two retinal veins remains divided into two parallel sets of sheets with separate velocity distribution for a downstream distance of at least four trunk vessel diameters. Consequently, retinal trunk vessels near bifurcations...
Bifurcated Helical Core Equilibrium States in Tokamaks
International Nuclear Information System (INIS)
Full text: Tokamaks with weak to moderate reversed central magnetic shear in which the minimum of the inverse rotational transform qmin is in the neighbourhood of unity can trigger bifurcated MagnetoHydroDynamic (MHD) equilibrium states. In addition to the standard axisymmetric branch that can be obtained with standard Grad-Shafranov solvers, a novel branch with a three-dimensional (3D) helical core has been computed with the ANIMEC code, an anisotropic pressure extension of the VMEC code. The solutions have imposed nested magnetic flux surfaces and are similar to saturated ideal internal kink modes. The difference in energy between both possible branches is very small. Plasma elongation, current and β enhance the susceptibility for bifurcations to occur. An initial value nonlinear ideal MHD evolution of the axisymmetric branch compares favourably with the helical core equilibrium structures calculated. Peaked prescribed pressure profiles reproduce the 'snake' structures observed in many tokamaks which has led to a new explanation of the snake as a bifurcated helical equilibrium state that results from a saturated ideal internal kink in which pellets or impurities induce a hollow current profile. Snake equilibrium structures are computed in free boundary TCV tokamak simulations. Magnetic field ripple and resonant magnetic perturbations in MAST free boundary calculations do not alter the helical core deformation in a significant manner when qmin is near unity. These bifurcated solutions constitute a paradigm shift that motivates the application of tools developed for stellarator research in tokamak physics investigations. The examination of fast ion confinement in this class of equilibria is performed with the VENUS code in which a coordinate independent noncanonical phase-space Lagrangian formulation of guiding centre drift orbit theory has been implemented. (author)
International Nuclear Information System (INIS)
Atherosclerosis is a progressive disease that causes lesions in large and medium-sized arteries. There is increasing evidence that the function of vascular endothelial cells is impaired by oxidation reactions, and that metal ions may participate in these processes. The nuclear microscopy facility in NUS, which has the ability to focus a 2 MeV proton beam down to sub micron spot sizes, was used to investigate the trace elemental changes (e.g. Zn and Fe) in atherosclerotic lesions in the common carotid artery of apolipoprotein E deficient mice fed a high fat diet. In this preliminary study, which is part of a larger study to investigate the effects of probucol on carotid artery atherosclerosis, two sets of mice were used; a test set fed a high fat diet +1% probucol, and a control set which was fed a high fat diet only. The results show that the Zn/Fe ratio was significantly higher in the media of arteries of probucol treated animals without overlying lesion (4.3) compared to the media with overlying lesion (1.3) (p = 0.004) for test mice. For the control mice, the arterial Zn/Fe ratio was 1.8 for media without overlying lesion, compared with 1.0 for media with overlying lesion (p = 0.1). Thus, for media without overlying lesion, the Zn/Fe ratio was significantly higher (p = 0.009) in probucol-treated (4.3) than control mice (1.8), whereas there was little difference in the ratios between the two groups in media with overlying lesion (1.3 compared with 1.0). These preliminary results are consistent with the idea that the levels of iron and zinc concentrations within the artery wall may influence the formation of atherosclerotic plaque in the carotid artery
Effects of Bifurcations on Aft-Fan Engine Nacelle Noise
Nark, Douglas M.; Farassat, Fereidoun; Pope, D. Stuart; Vatsa, Veer N.
2004-01-01
Aft-fan engine nacelle noise is a significant factor in the increasingly important issue of aircraft community noise. The ability to predict such noise within complex duct geometries is a valuable tool in studying possible noise attenuation methods. A recent example of code development for such predictions is the ducted fan noise propagation and radiation code CDUCT-LaRC. This work focuses on predicting the effects of geometry changes (i.e. bifurcations, pylons) on aft fan noise propagation. Beginning with simplified geometries, calculations show that bifurcations lead to scattering of acoustic energy into higher order modes. In addition, when circumferential mode number and the number of bifurcations are properly commensurate, bifurcations increase the relative importance of the plane wave mode near the exhaust plane of the bypass duct. This is particularly evident when the bypass duct surfaces include acoustic treatment. Calculations involving more complex geometries further illustrate that bifurcations and pylons clearly affect modal content, in both propagation and radiation calculations. Additionally, results show that consideration of acoustic radiation results may provide further insight into acoustic treatment effectiveness for situations in which modal decomposition may not be straightforward. The ability of CDUCT-LaRC to handle complex (non-axisymmetric) multi-block geometries, as well as axially and circumferentially segmented liners, allows investigation into the effects of geometric elements (bifurcations, pylons).
Stability and Bifurcation of Two Kinds of Three-Dimensional Fractional Lotka-Volterra Systems
Directory of Open Access Journals (Sweden)
Jinglei Tian
2014-01-01
Full Text Available Two kinds of three-dimensional fractional Lotka-Volterra systems are discussed. For one system, the asymptotic stability of the equilibria is analyzed by providing some sufficient conditions. And bifurcation property is investigated by choosing the fractional order as the bifurcation parameter for the other system. In particular, the critical value of the fractional order is identified at which the Hopf bifurcation may occur. Furthermore, the numerical results are presented to verify the theoretical analysis.
Complex dynamics in biological systems arising from multiple limit cycle bifurcation.
Yu, P; Lin, W
2016-12-01
In this paper, we study complex dynamical behaviour in biological systems due to multiple limit cycles bifurcation. We use simple epidemic and predator-prey models to show exact routes to new types of bistability, that is, bistability between equilibrium and periodic oscillation, and bistability between two oscillations, which may more realistically describe the real situations. Bifurcation theory and normal form theory are applied to investigate the multiple limit cycles bifurcating from Hopf critical point. PMID:27042877
Stability and Hopf Bifurcation for a Delayed SLBRS Computer Virus Model
Zizhen Zhang; Huizhong Yang
2014-01-01
By incorporating the time delay due to the period that computers use antivirus software to clean the virus into the SLBRS model a delayed SLBRS computer virus model is proposed in this paper. The dynamical behaviors which include local stability and Hopf bifurcation are investigated by regarding the delay as bifurcating parameter. Specially, direction and stability of the Hopf bifurcation are derived by applying the normal form method and center manifold theory. Finally, an illustrative examp...
Schomerus, H
1997-01-01
We investigate classical and semiclassical aspects of codimension--two bifurcations of periodic orbits in Hamiltonian systems. A classification of these bifurcations in autonomous systems with two degrees of freedom or time-periodic systems with one degree of freedom is presented. We derive uniform approximations to be used in semiclassical trace formulas and determine also certain global bifurcations in conjunction with Stokes transitions that become important in the ensuing diffraction catastrophe integrals.
Pathological observation of brain arteries and spontaneous aneurysms in hypertensive rats
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
Objective To investigate the role of hypertension in the pathogenesis of cerebral aneurysms in rats.Methods Twenty spontaneous hypertensive rats (SHR) and 10 Wistar-Kyoto rats (WKY) were included in this observational study. Animals were fed with normal diet and drinking water. No experimental modifications were undertaken in either group. They were sacrificed at one year of age, the bifurcations of the circle of Willis were dissected and longitudinal serial sections were prepared for light microscopic and transmission electron microscopic study.Results In the SHR group, 2 of the 20 rats formed an aneurysm respectively at the bifurcations of the basilar artery. As revealed by electron microscopy, injury at the bifurcation of the artery first occurred on the steeper side of the intimal pad. Furthermore, loss of endothelial cells, small depressions on the intima, disruptive internal elastic lamina and lymphocytes or red blood cells infiltration were noted at the steeper side of the intimal pad. No significant changes were observed in WKY group.Conclusions Cerebral aneurysms can form spontaneously in SHR without ligation of the common carotid artery and without a diet containing β-aminoproprionitrile. Long-standing systemic arterial hypertension is one of the etiological factors that contributes to aneurysm formation in SHR rats.
Prediction of fibre architecture and adaptation in diseased carotid bifurcations.
LENUS (Irish Health Repository)
Creane, Arthur
2011-12-01
Many studies have used patient-specific finite element models to estimate the stress environment in atherosclerotic plaques, attempting to correlate the magnitude of stress to plaque vulnerability. In complex geometries, few studies have incorporated the anisotropic material response of arterial tissue. This paper presents a fibre remodelling algorithm to predict the fibre architecture, and thus anisotropic material response in four patient-specific models of the carotid bifurcation. The change in fibre architecture during disease progression and its affect on the stress environment in the plaque were predicted. The mean fibre directions were assumed to lie at an angle between the two positive principal strain directions. The angle and the degree of dispersion were assumed to depend on the ratio of principal strain values. Results were compared with experimental observations and other numerical studies. In non-branching regions of each model, the typical double helix arterial fibre pattern was predicted while at the bifurcation and in regions of plaque burden, more complex fibre architectures were found. The predicted change in fibre architecture in the arterial tissue during plaque progression was found to alter the stress environment in the plaque. This suggests that the specimen-specific anisotropic response of the tissue should be taken into account to accurately predict stresses in the plaque. Since determination of the fibre architecture in vivo is a difficult task, the system presented here provides a useful method of estimating the fibre architecture in complex arterial geometries.
Rarefaction and blood pressure in systemic and pulmonary arteries.
Olufsen, Mette S; Hill, N A; Vaughan, Gareth D A; Sainsbury, Christopher; Johnson, Martin
2012-08-01
The effects of vascular rarefaction (the loss of small arteries) on the circulation of blood are studied using a multiscale mathematical model that can predict blood flow and pressure in the systemic and pulmonary arteries. We augmented a model originally developed for the systemic arteries (Olufsen et al. 1998, 1999, 2000, 2004) to (a) predict flow and pressure in the pulmonary arteries, and (b) predict pressure propagation along the small arteries in the vascular beds. The systemic and pulmonary arteries are modelled as separate, bifurcating trees of compliant and tapering vessels. Each tree is divided into two parts representing the `large' and `small' arteries. Blood flow and pressure in the large arteries are predicted using a nonlinear cross-sectional area-averaged model for a Newtonian fluid in an elastic tube with inflow obtained from magnetic resonance measurements. Each terminal vessel within the network of the large arteries is coupled to a vascular bed of small `resistance' arteries, which are modelled as asymmetric structured trees with specified area and asymmetry ratios between the parent and daughter arteries. For the systemic circulation, each structured tree represents a specific vascular bed corresponding to major organs and limbs. For the pulmonary circulation, there are four vascular beds supplied by the interlobar arteries. This manuscript presents the first theoretical calculations of the propagation of the pressure and flow waves along systemic and pulmonary large and small arteries. Results for all networks were in agreement with published observations. Two studies were done with this model. First, we showed how rarefaction can be modelled by pruning the tree of arteries in the microvascular system. This was done by modulating parameters used for designing the structured trees. Results showed that rarefaction leads to increased mean and decreased pulse pressure in the large arteries. Second, we investigated the impact of decreasing vessel
Bifurcation analysis of a predator–prey model with anti-predator behaviour
International Nuclear Information System (INIS)
We investigated a predator–prey model with a nonmonotonic functional response and anti-predator behaviour such that the adult prey can attack vulnerable predators. By analyzing the existence and stability of all possible equilibria and conducting a bifurcation analysis, we obtained the global dynamics of the proposed system. The system could undergo a saddle-node bifurcation, (supercritical and subcritical) Hopf bifurcation, homoclinic bifurcation and a Bogdanov–Takens bifurcation of codimension 2. Further, we obtained a generic family unfolding for the system by choosing the environmental carrying capacity of the prey and the death rate of the predator as bifurcation parameters. Numerical studies showed that anti-predator behaviour not only makes the coexistence of the prey and predator populations less likely, but also damps the predator–prey oscillations. Therefore, anti-predator behaviour helps the prey population to resist predator aggression
Bifurcation Analysis of a Lotka-Volterra Mutualistic System with Multiple Delays
Directory of Open Access Journals (Sweden)
Xin-You Meng
2014-01-01
Full Text Available A class of Lotka-Volterra mutualistic system with time delays of benefit and feedback delays is introduced. By analyzing the associated characteristic equation, the local stability of the positive equilibrium and existence of Hopf bifurcation are obtained under all possible combinations of two or three delays selecting from multiple delays. Not only explicit formulas to determine the properties of the Hopf bifurcation are shown by using the normal form method and center manifold theorem, but also the global continuation of Hopf bifurcation is investigated by applying a global Hopf bifurcation result due to Wu (1998. Numerical simulations are given to support the theoretical results.
Control of Fold Bifurcation Application on Chemostat around Critical Dilution Rate
DEFF Research Database (Denmark)
Pedersen, Kurt; Jørgensen, Sten Bay
1999-01-01
Based on a bifurcation analysis of a process it is possible to point out where there might be operational problems due to change of stability of the process. One such change is investigated, Fold bifurcations. This type of bifurcation is associated with hysteresis/multiple steady states, which co...... complicates operation close to these bifurcations. Typically only one of the steady states is interesting from a production point of view. A novel control law is proposed herein which is able to cope with the operational problems of the process....
Stability and bifurcation analysis in a magnetic bearing system with time delays
International Nuclear Information System (INIS)
A kind of magnetic bearing system with time delay is considered. Firstly, linear stability of the model is investigated by analyzing the distribution of the roots of the associated characteristic equation. According to the analysis results, the bifurcation diagram is drawn in the appropriate parameter plane. It is found that the Ho pf bifurcation occurs when the delay passes through a sequence of critical values. Then the explicit algorithm for determining the direction of the Ho pf bifurcations and the stability of the bifurcating periodic solutions are derived, using the theory of normal form and center manifold. Finally, some numerical simulations are carried out to illustrate the results found
Stochastic bifurcation for a tumor-immune system with symmetric Lévy noise
Xu, Yong; Feng, Jing; Li, JuanJuan; Zhang, Huiqing
2013-10-01
In this paper, we investigate stochastic bifurcation for a tumor-immune system in the presence of a symmetric non-Gaussian Lévy noise. Stationary probability density functions will be numerically obtained to define stochastic bifurcation via the criteria of its qualitative change, and bifurcation diagram at parameter plane is presented to illustrate the bifurcation analysis versus noise intensity and stability index. The effects of both noise intensity and stability index on the average tumor population are also analyzed by simulation calculation. We find that stochastic dynamics induced by Gaussian and non-Gaussian Lévy noises are quite different.
Invariant manifolds and global bifurcations.
Guckenheimer, John; Krauskopf, Bernd; Osinga, Hinke M; Sandstede, Björn
2015-09-01
Invariant manifolds are key objects in describing how trajectories partition the phase spaces of a dynamical system. Examples include stable, unstable, and center manifolds of equilibria and periodic orbits, quasiperiodic invariant tori, and slow manifolds of systems with multiple timescales. Changes in these objects and their intersections with variation of system parameters give rise to global bifurcations. Bifurcation manifolds in the parameter spaces of multi-parameter families of dynamical systems also play a prominent role in dynamical systems theory. Much progress has been made in developing theory and computational methods for invariant manifolds during the past 25 years. This article highlights some of these achievements and remaining open problems. PMID:26428557
Bifurcations and intermittent magnetic activity
International Nuclear Information System (INIS)
The sequence of equilibria of two-dimensional reduced magnetohydrodynamics has been studied as a function of the tearing mode stability parameter Δ'. After a symmetry-breaking bifurcation occurring at Δ' ∼ 0, which originates a state with a small magnetic island, the system undergoes a second bifurcation, of tangent type, at Δ' ∼ 1. Above this value, no stationary solutions with small islands exist. The system rapidly develops an island of macroscopic size. This general property is proposed as a basic ingredient of the intermittent events observed in magnetically confined plasmas. (author)
Bifurcations and intermittent magnetic activity
Energy Technology Data Exchange (ETDEWEB)
Tebaldi, C.; Ottaviani, M.; Porcelli, F. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking
1996-04-01
The sequence of equilibria of two-dimensional reduced magnetohydrodynamics has been studied as a function of the tearing mode stability parameter {Delta}`. After a symmetry-breaking bifurcation occurring at {Delta}` {approx} 0, which originates a state with a small magnetic island, the system undergoes a second bifurcation, of tangent type, at {Delta}` {approx} 1. Above this value, no stationary solutions with small islands exist. The system rapidly develops an island of macroscopic size. This general property is proposed as a basic ingredient of the intermittent events observed in magnetically confined plasmas. (author).
Global Hopf Bifurcation on Two-Delays Leslie-Gower Predator-Prey System with a Prey Refuge
Directory of Open Access Journals (Sweden)
Qingsong Liu
2014-01-01
Full Text Available A modified Leslie-Gower predator-prey system with two delays is investigated. By choosing τ1 and τ2 as bifurcation parameters, we show that the Hopf bifurcations occur when time delay crosses some critical values. Moreover, we derive the equation describing the flow on the center manifold; then we give the formula for determining the direction of the Hopf bifurcation and the stability of bifurcating periodic solutions. Numerical simulations are carried out to illustrate the theoretical results and chaotic behaviors are observed. Finally, using a global Hopf bifurcation theorem for functional differential equations, we show the global existence of the periodic solutions.
Institute of Scientific and Technical Information of China (English)
DUAN XianZhong; WEN JinYu; CHENG ShiJie
2009-01-01
In this paper, an introduction to the bifurcation theory and its applicability to the study of sub-syn-chronous resonance (SSR) phenomenon in power system are presented. The continuation and bifur-cation analysis software AUTO97 is adopted to investigate SSR for a single-machine-infinite-bus power system with series capacitor compensation. The investigation results show that SSR is the result of unstable limit cycle after bifurcation. When the system exhibits SSR, some complex periodical orbit bifurcations, such as torus bifurcation and periodical fold bifurcation, may happen with the variation of limit cycle. Furthermore, the initial operation condition may greatly influence the ultimate state of the system. The time-domain simulation is carried out to verify the effectiveness of the results obtained from the bifurcation analysis.
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
In this paper,an introduction to the bifurcation theory and its applicability to the study of sub-synchronous resonance (SSR) phenomenon in power system are presented. The continuation and bifurcation analysis software AUTO97 is adopted to investigate SSR for a single-machine-infinite-bus power system with series capacitor compensation. The investigation results show that SSR is the result of unstable limit cycle after bifurcation. When the system exhibits SSR, some complex periodical orbit bifurcations, such as torus bifurcation and periodical fold bifurcation, may happen with the variation of limit cycle. Furthermore, the initial operation condition may greatly influence the ultimate state of the system. The time-domain simulation is carried out to verify the effectiveness of the results obtained from the bifurcation analysis.
Multiple Bifurcations of a Cylindrical Dynamical System
Han Ning; Cao Qingjie
2016-01-01
This paper focuses on multiple bifurcations of a cylindrical dynamical system, which is evolved from a rotating pendulum with SD oscillator. The rotating pendulum system exhibits the coupling dynamics property of the bistable state and conventional pendulum with the ho- moclinic orbits of the first and second type. A double Andronov-Hopf bifurcation, two saddle-node bifurcations of periodic orbits and a pair of homoclinic bifurcations are detected by using analytical analysis and nu- merical ...
Bifurcations associated with sub-synchronous resonance
Mitani, Yasunori; K. Tsuji; M.Varghese; Wu, F. F.; VARAIYA, P
1998-01-01
This paper describes a set of results of detecting nonlinear phenomena appearing in a turbine generator power system with series-capacitor compensation. The analysis was based on the Floquet theory as well as the Hopf bifurcation theorem. After the first Hopf bifurcation, the stable limit cycle bifurcates to a stable torus and an unstable limit cycle which connects to a stable limit cycle by a supercritical torus bifurcation. The stable limit cycle joins with an unstable limit cycle at a cycl...
Institute of Scientific and Technical Information of China (English)
ZHANG Zi-Zhen; YANG Hui-Zhong
2013-01-01
In this paper,we consider a predator-prey system with modified Leslie-Gower and Holling type III schemes.By regarding the time delay as the bifurcation parameter,the local asymptotic stability of the positive equilibrium is investigated.And we find that Hopf bifurcations can occur as the time delay crosses some critical values.In particular,special attention is paid to the direction of the Hopf bifurcation and the stability of bifurcating periodic solutions.In addition,the global existence of periodic solutions bifurcating from the Hopf bifurcation are considered by applying a global Hopf bifurcation result.Finally,numerical simulations are carried out to illustrate the main theoretical results.
Stability and Hopf bifurcations in a competitive Lotka-Volterra system with two delays
Energy Technology Data Exchange (ETDEWEB)
Song Yongli E-mail: songyl@sjtu.edu.cn; Han Maoan; Peng Yahong
2004-12-01
We consider a Lotka-Volterra competition system with two delays. We first investigate the stability of the positive equilibrium and the existence of Hopf bifurcations, and then using the normal form theory and center manifold argument, derive the explicit formulas which determine the stability, direction and other properties of bifurcating periodic solutions.
Bifurcation Analysis of Gene Propagation Model Governed by Reaction-Diffusion Equations
Directory of Open Access Journals (Sweden)
Guichen Lu
2016-01-01
Full Text Available We present a theoretical analysis of the attractor bifurcation for gene propagation model governed by reaction-diffusion equations. We investigate the dynamical transition problems of the model under the homogeneous boundary conditions. By using the dynamical transition theory, we give a complete characterization of the bifurcated objects in terms of the biological parameters of the problem.
Anti-control of Hopf Bifurcation in a Delayed Predator-prey Gomp ertz Mo del
Institute of Scientific and Technical Information of China (English)
XU Chang-jin; CHEN Da-xue
2013-01-01
A delayed predator-prey Gompertz model is investigated. The stability is ana-lyzed. Anti-control of Hopf bifurcation for the model is presented. Numerical simulations are performed to confirm that the new feedback controller using time delay is efficient in creating Hopf bifurcation. Finally, main conclusions are included.
Full system bifurcation analysis of endocrine bursting models.
Tsaneva-Atanasova, Krasimira; Osinga, Hinke M; Riess, Thorsten; Sherman, Arthur
2010-06-21
Plateau bursting is typical of many electrically excitable cells, such as endocrine cells that secrete hormones and some types of neurons that secrete neurotransmitters. Although in many of these cell types the bursting patterns are regulated by the interplay between voltage-gated calcium channels and calcium-sensitive potassium channels, they can be very different. We investigate so-called square-wave and pseudo-plateau bursting patterns found in endocrine cell models that are characterized by a super- or subcritical Hopf bifurcation in the fast subsystem, respectively. By using the polynomial model of Hindmarsh and Rose (Proceedings of the Royal Society of London B 221 (1222) 87-102), which preserves the main properties of the biophysical class of models that we consider, we perform a detailed bifurcation analysis of the full fast-slow system for both bursting patterns. We find that both cases lead to the same possibility of two routes to bursting, that is, the criticality of the Hopf bifurcation is not relevant for characterizing the route to bursting. The actual route depends on the relative location of the full-system's fixed point with respect to a homoclinic bifurcation of the fast subsystem. Our full-system bifurcation analysis reveals properties of endocrine bursting that are not captured by the standard fast-slow analysis. PMID:20307553
Research on bifurcation characters of rotor-SMA bearing system
International Nuclear Information System (INIS)
Based on Landau-Devonshire model, the bifurcation characteristic of rotor-shape memory alloy bearings(SMAB) system was investigated in this paper. Heteronomous system was transformed into autonomous system in averaging method and Van der Pol transformation, and the existence of Hopf bifurcation was proved in theory. The concept of broadened set of equilibrium point was introduced to improve centre manifold method to be adapted to heteronomous system. The equation of the flow on the centre manifold of rotor-SMAB system was obtained, and the existence of transcritical bifurcation and supercritical pitchfork bifurcation was proved in theory. Finally the results in centre manifold method and averaging method were compared with each other. The comparison shows that the results of the two methods were both the parts of global dynamic characteristic of rotor-SMAB system, while centre manifold method can be applied to research bifurcation behavior in the case of more dimensions. It means that the two methods both have limitation, and global dynamic characteristic must be obtained in kinds of method
Bifurcations analysis of turbulent energy cascade
Energy Technology Data Exchange (ETDEWEB)
Divitiis, Nicola de, E-mail: n.dedivitiis@gmail.com
2015-03-15
This note studies the mechanism of turbulent energy cascade through an opportune bifurcations analysis of the Navier–Stokes equations, and furnishes explanations on the more significant characteristics of the turbulence. A statistical bifurcations property of the Navier–Stokes equations in fully developed turbulence is proposed, and a spatial representation of the bifurcations is presented, which is based on a proper definition of the fixed points of the velocity field. The analysis first shows that the local deformation can be much more rapid than the fluid state variables, then explains the mechanism of energy cascade through the aforementioned property of the bifurcations, and gives reasonable argumentation of the fact that the bifurcations cascade can be expressed in terms of length scales. Furthermore, the study analyzes the characteristic length scales at the transition through global properties of the bifurcations, and estimates the order of magnitude of the critical Taylor-scale Reynolds number and the number of bifurcations at the onset of turbulence.
International Nuclear Information System (INIS)
Congenital absence of the unilateral internal carotid artery (ICA) was found in a patient during MR imaging examination for right trigeminal neuralgia. Magnetic resonance angiography showed complete absence of the right ICA and a large tortuous basilar artery (BA). The source images revealed a deformed right trigeminal nerve resulting from compression by the BA. Computed tomography of the skull base showed absence of the right carotid canal, suggesting agenesis of the right ICA. Longstanding hemodynamic stress may have caused the BA to become extremely tortuous, resulting in the trigeminal neuralgia. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Uchino, A.; Sawada, A.; Kudo, S. [Department of Radiology, Saga Medical School, 5-1-1, Nabeshima, Saga (Japan); Hirakawa, N.; Totoki, T. [Department of Anesthesiology, Saga Medical School, 5-1-1, Nabeshima, Saga (Japan)
2002-09-01
Congenital absence of the unilateral internal carotid artery (ICA) was found in a patient during MR imaging examination for right trigeminal neuralgia. Magnetic resonance angiography showed complete absence of the right ICA and a large tortuous basilar artery (BA). The source images revealed a deformed right trigeminal nerve resulting from compression by the BA. Computed tomography of the skull base showed absence of the right carotid canal, suggesting agenesis of the right ICA. Longstanding hemodynamic stress may have caused the BA to become extremely tortuous, resulting in the trigeminal neuralgia. (orig.)
Bifurcation and Secondary Bifurcation of Heavy Periodic Hydroelastic Travelling Waves
Baldi, Pietro; Toland, John F.
2008-01-01
The paper deals with a problem of interaction between hydrodynamics and mechanics of nonlinear elastic bodies. The existence question for two-dimensional symmetric steady waves travelling on the surface of a deep ocean beneath a heavy elastic membrane is analyzed as a problem in bifurcation theory. The behaviour of the two-dimensional cross-section of the membrane is modelled as a thin (unshearable), heavy, hyperelastic Cosserat rod, following Antman's elasticity theory, and the fluid beneath...
E. V. Nikolaeva; I. A. Kurmukov; N N Yudkina; A. V. Volkov
2015-01-01
Pulmonary arterial hypertension (PAH) associated with systemic connective tissue diseases (SCTD) is a poor prognostic manifestation of the latter that result in death if untreated. The invasive determination of hemodynamic parameters is prominent in diagnosing the disease and determining its treatment policy and prognosis.Objective: to analyze the results of catheterization in PAH-SCTD patients admitted to the V.A. Nasonova Research Institute of Rheumatology.Subjects and methods. The investig...
Bifurcations in the optimal elastic foundation for a buckling column
International Nuclear Information System (INIS)
We investigate the buckling under compression of a slender beam with a distributed lateral elastic support, for which there is an associated cost. For a given cost, we study the optimal choice of support to protect against Euler buckling. We show that with only weak lateral support, the optimum distribution is a delta-function at the centre of the beam. When more support is allowed, we find numerically that the optimal distribution undergoes a series of bifurcations. We obtain analytical expressions for the buckling load around the first bifurcation point and corresponding expansions for the optimal position of support. Our theoretical predictions, including the critical exponent of the bifurcation, are confirmed by computer simulations.
Bifurcations in the optimal elastic foundation for a buckling column
Rayneau-Kirkhope, Daniel; Farr, Robert; Ding, K.; Mao, Yong
2010-12-01
We investigate the buckling under compression of a slender beam with a distributed lateral elastic support, for which there is an associated cost. For a given cost, we study the optimal choice of support to protect against Euler buckling. We show that with only weak lateral support, the optimum distribution is a delta-function at the centre of the beam. When more support is allowed, we find numerically that the optimal distribution undergoes a series of bifurcations. We obtain analytical expressions for the buckling load around the first bifurcation point and corresponding expansions for the optimal position of support. Our theoretical predictions, including the critical exponent of the bifurcation, are confirmed by computer simulations.
Bifurcations in the optimal elastic foundation for a buckling column
Rayneau-Kirkhope, Daniel; Ding, K; Mao, Yong
2010-01-01
We investigate the buckling under compression of a slender beam with a distributed lateral elastic support, for which there is an associated cost. For a given cost, we study the optimal choice of support to protect against Euler buckling. We show that with only weak lateral support, the optimum distribution is a delta-function at the centre of the beam. When more support is allowed, we find numerically that the optimal distribution undergoes a series of bifurcations. We obtain analytical expressions for the buckling load around the first bifurcation point and corresponding expansions for the optimal position of support. Our theoretical predictions, including the critical exponent of the bifurcation, are confirmed by computer simulations.
Hopf bifurcation and chaos in macroeconomic models with policy lag
International Nuclear Information System (INIS)
In this paper, we consider the macroeconomic models with policy lag, and study how lags in policy response affect the macroeconomic stability. The local stability of the nonzero equilibrium of this equation is investigated by analyzing the corresponding transcendental characteristic equation of its linearized equation. Some general stability criteria involving the policy lag and the system parameter are derived. By choosing the policy lag as a bifurcation parameter, the model is found to undergo a sequence of Hopf bifurcation. The direction and stability of the bifurcating periodic solutions are determined by using the normal form theory and the center manifold theorem. Moreover, we show that the government can stabilize the intrinsically unstable economy if the policy lag is sufficiently short, but the system become locally unstable when the policy lag is too long. We also find the chaotic behavior in some range of the policy lag
Bifurcation Analysis for Surface Waves Generated by Wind
Schweizer, Ben
2001-01-01
We study the generation of surface waves on water as a bifurcation phenomenon. For a critical wind-speed there appear traveling wave solutions. While linear waves do not transport mass (in the mean), nonlinear effects create a shear-flow and result in a net mass transport in the direction of the wind. We derive an asymptotic formula for the average tangential velocity along the free surface. Numerical investigations confirm the appearance of the shear-flow and yield results on the bifurcation...
Song, Yongli; Zhang, Tonghua; Tadé, Moses O
2008-12-01
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. PMID:19123623
Aberrant right hepatic artery; A case report
International Nuclear Information System (INIS)
We present a rare case of aberrant hepatic artery in a 40-year-old male with a history of chronic cholecystitis. During laparoscopic surgery, the artery found to pass anterior to the body the gallbladder and bifurcating anterior to the gallbladder body. The surgery was un eventful. We present this anomaly of the rare condition of aberrant right hepatic artery which should be in mind during laparoscopic cholecystectomy, because inadverant injury could lead to massive bleeding and increase co morbidities. (author)
International Nuclear Information System (INIS)
For the last two decades, pulse oximetry has been used as a standard procedure for monitoring arterial oxygen saturation (SpO2). However, SpO2 measurements made from extremities such as the finger, ear lobe and toes become susceptible to inaccuracies when peripheral perfusion is compromised. To overcome these limitations, the external auditory canal has been proposed as an alternative monitoring site for estimating SpO2, on the hypothesis that this central site will be better perfused. Therefore, a dual wavelength optoelectronic probe along with a processing system was developed to investigate the suitability of measuring photoplethysmographic (PPG) signals and SpO2 in the human auditory canal. A pilot study was carried out in 15 healthy volunteers to validate the feasibility of measuring PPGs and SpO2 from the ear canal (EC), and comparative studies were performed by acquiring the same signals from the left index finger (LIF) and the right index finger (RIF) in conditions of induced peripheral vasoconstriction (right hand immersion in ice water). Good quality baseline PPG signals with high signal-to-noise ratio were obtained from the EC, the LIF and the RIF sensors. During the ice water immersion, significant differences in the amplitude of the red and infrared PPG signals were observed from the RIF and the LIF sensors. The average drop in amplitude of red and infrared PPG signals from the RIF was 52.7% and 58.3%. Similarly, the LIF PPG signal amplitudes have reduced by 47.52% and 46.8% respectively. In contrast, no significant changes were seen in the red and infrared EC PPG amplitude measurements, which changed by +2.5% and −1.2% respectively. The RIF and LIF pulse oximeters have failed to estimate accurate SpO2 in seven and four volunteers respectively, while the EC pulse oximeter has only failed in one volunteer. These results suggest that the EC may be a suitable site for reliable monitoring of PPGs and SpO2s even in the presence of peripheral
Tibial hemimelia and femoral bifurcation.
Ugras, Ali Akin; Sungur, Ibrahim; Akyildiz, Mustafa Fehmi; Ercin, Ersin
2010-02-01
Femoral bifurcation and tibial agenesis are rare anomalies and have been described in both the Gollop-Wolfgang complex and tibial agenesis-ectrodactyly syndrome. This article presents a case of Gollop-Wolfgang complex without hand ectrodactyly. Tibial agenesis-ectrodactyly syndrome and Gollop-Wolfgang complex are variants of tibial field defect, which includes distal femoral duplication, tibial aplasia, oligo-ectrodactylous toe defects, and preaxial polydactyly, occasionally associated with hand ectrodactyly.This article describes the case of a patient with bilateral tibial hemimelia and left femoral bifurcation. The proximal tibial anlage had not been identified in the patient's left leg. After failed fibular transfer procedure, the knee was disarticulated. The other leg was treated with tibiofibular synostosis and centralization of fibula to os calcis. At 7-year follow-up, the patient ambulates with an above-knee prosthesis and uses an orthopedic boot for ankle stability.In patients with a congenital absence of the tibia, accurate diagnosis is of the utmost importance in planning future treatment. In the absence of proximal tibial anlage, especially in patients with femoral bifurcation, the knee should be disarticulated. Tibiofibular synostosis is a good choice in the presence of a proximal tibial anlage and good quadriceps function. PMID:20192156
Oscillatory flow in bifurcating tubes
International Nuclear Information System (INIS)
Respiratory fluid mechanics is characterized by flow through bifurcating, Y-shaped, tubes. Steady flow through such geometries has been studied in detail by several authors. However, the recent widespread use of high frequency mechanical assistance of ventilation has generated interest in unsteady flows. A symmetric, singly branching pipe has been constructed, with its bifurcation shaped to model pulmonary conditions. The form of the bifurcation is based on CAT scans of human tracheal carinas. Its features include an area change of the parent tube from circular to roughly elliptical near the junction, a pinch-off effect on the parent tube, smoothly curved outer walls at the junction, and a sharp flow divider. Parent and daughter tubes have an l/d ratio of > 50, so that entrance effects are avoided. In order to better understand the effects of unsteadiness, piston driven, laminar, purely oscillatory flow has been established in the pipe for a variety of Womersley numbers. By appropriate choices of flow frequency and amplitude, fluid viscosity, and pipe diameter, tracheal Reynolds and Womersley numbers have been matched for resting breathing (tidal volume of 600 ml to 0.25 Hz), high frequency breathing (50 ml at 5 Hz), and intermediate breathing levels
Experimental bifurcation analysis of an impact oscillator – Determining stability
DEFF Research Database (Denmark)
Bureau, Emil; Schilder, Frank; Elmegård, Michael; Santos, Ilmar; Thomsen, Jon Juel; Starke, Jens
2014-01-01
We propose and investigate three different methods for assessing stability of dynamical equilibrium states during experimental bifurcation analysis, using a control-based continuation method. The idea is to modify or turn off the control at an equilibrium state and study the resulting behavior. As...
Limit theorems for bifurcating integer-valued autoregressive processes
Blandin, Vassili
2012-01-01
We study the asymptotic behavior of the weighted least squares estimators of the unknown parameters of bifurcating integer-valued autoregressive processes. Under suitable assumptions on the immigration, we establish the almost sure convergence of our estimators, together with the quadratic strong law and central limit theorems. All our investigation relies on asymptotic results for vector-valued martingales.
Hahn, C; Mahajan, A; Chu, T; Schoen, M
2007-08-01
This paper presents a lumped-parameter model for the big-toe region that investigates the effect of plantar pressure on the diameter of the blood vessels, specifically the arteries, in the presence of arterial and/or tissue changes. The model developed in this paper uses a multi-domain energy system approach to develop the lumped-parameter differential equations. Blood flow is modelled as fluidic flow through compliant pipes that have inertia, stiffness, and damping. The tissue material is treated as a soft compliant material that transmits the external force to the blood vessels. Conclusions have been drawn to show the effect of plantar pressure, tissue damage, and their combination on the diameter of the blood vessels. The principles used here can be used to model the entire foot and the model used to investigate the effect of plantar pressure, tissue damage, and arterial changes on different parts of the foot. The work presented here may also have applications in other vascular diseases. PMID:17937206
Description of the celiac artery in domestic pigeons (Columba livia
Directory of Open Access Journals (Sweden)
Cibele Geeverghese
2012-06-01
Full Text Available This paper aimed to define the origin and distribution of the celiac artery and its collateral branches in 15 fowls from the Columba livia species, which were obtained from the Zoonosis Control Center of Brasilia, Brazil. In order to mark the arterial system of the specimens, the left brachiocephalic trunk was canullated and a colored water-latex solution was injected there. Afterwards, fowls were fixed in a 10% v/v formaldehyde solution and dissected with appropriate equipment, presenting the results described in this paper. The celiac artery originated from the ventral face of the descendent aorta. The first collateral branch arose from the celiac artery itself, forming the esophageal artery. Then, the celiac artery has bifurcated into two branches, named left and right branches of the celiac artery. The left branch emitted the proventricular ventral artery, followed by the splenic arteries, proventricular dorsal artery, and the left hepatic artery. The left branch has bifurcated into two branches, known as ventral and left gastric arteries. The right branch emitted the right hepatic artery, followed by the ileal artery and the right gastric artery. Finally, the right branch turned into the pancreaticoduodenal artery. Our findings showed a great similarity with the avian lineages of the Gallus gallus species, except for the lack of ileocecal artery, cystic branches, and dorsal gastric artery.
International Nuclear Information System (INIS)
This paper is concerned with a delayed cooperation diffusion system with Dirichlet boundary conditions. By applying the implicit function theorem, the normal form theory and the center manifold reduction, the asymptotic stability of positive equilibrium and Hopf bifurcation are investigated. It is shown that an increase in delay will destabilize the positive equilibrium and lead to the occurrence of a supercritical Hopf bifurcation when the delay crosses through a sequence of critical values. Based on the normal form theory and the center manifold reduction for partial functional differential equations (PFDEs), we find that the bifurcating periodic solution occurring from the first Hopf bifurcation point is stable on the center manifold and those occurring from the other bifurcation points are unstable. Finally, some numerical simulations are given to illustrate our results
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Li Wantong [School of Mathematics and Statistics, Lanzhou University, Lanzhou 730000 (China)], E-mail: wtli@lzu.edu.cn; Yan Xiangping; Zhang Cunhua [School of Mathematics and Statistics, Lanzhou University, Lanzhou 730000 (China); Department of Mathematics, Lanzhou Jiaotong University, Lanzhou 730070 (China)
2008-10-15
This paper is concerned with a delayed cooperation diffusion system with Dirichlet boundary conditions. By applying the implicit function theorem, the normal form theory and the center manifold reduction, the asymptotic stability of positive equilibrium and Hopf bifurcation are investigated. It is shown that an increase in delay will destabilize the positive equilibrium and lead to the occurrence of a supercritical Hopf bifurcation when the delay crosses through a sequence of critical values. Based on the normal form theory and the center manifold reduction for partial functional differential equations (PFDEs), we find that the bifurcating periodic solution occurring from the first Hopf bifurcation point is stable on the center manifold and those occurring from the other bifurcation points are unstable. Finally, some numerical simulations are given to illustrate our results.
Bifurcation mechanisms of regular and chaotic network signaling in brain astrocytes
Matrosov, V. V.; Kazantsev, V. B.
2011-06-01
Bifurcation mechanisms underlying calcium oscillations in the network of astrocytes are investigated. Network model includes the dynamics of intracellular calcium concentration and intercellular diffusion of inositol 1,4,5-trisphosphate through gap junctions. Bifurcation analysis of underlying nonlinear dynamical system is presented. Parameter regions and principle bifurcation boundaries have been delineated and described. We show how variations of the diffusion rate can lead to generation of network calcium oscillations in originally nonoscillating cells. Different scenarios of regular activity and its transitions to chaotic dynamics have been obtained. Then, the bifurcations have been associated with statistical characteristics of calcium signals showing that different bifurcation scenarios yield qualitative changes in experimentally measurable quantities of the astrocyte activity, e.g., statistics of calcium spikes.
High resolution wavenumber analysis for investigation of arterial pulse wave propagation
Hasegawa, Hideyuki; Sato, Masakazu; Irie, Takasuke
2016-07-01
The propagation of the pulse wave along the artery is relatively fast (several m/s), and a high-temporal resolution is required to measure pulse wave velocity (PWV) in a regional segment of the artery. High-frame-rate ultrasound enables the measurement of the regional PWV. In analyses of wave propagation phenomena, the direction and propagation speed are generally identified in the frequency-wavenumber space using the two-dimensional Fourier transform. However, the wavelength of the pulse wave is very long (1 m at a propagation velocity of 10 m/s and a temporal frequency of 10 Hz) compared with a typical lateral field of view of 40 mm in ultrasound imaging. Therefore, PWV cannot be identified in the frequency-wavenumber space owing to the low resolution of the two-dimensional Fourier transform. In the present study, PWV was visualized in the wavenumber domain using phases of arterial wall acceleration waveforms measured by high-frame-rate ultrasound.
Scale dependence of branching in arterial and bronchial trees
Restrepo, J G; Hunt, B R; Restrepo, Juan G.; Ott, Edward; Hunt, Brian R.
2005-01-01
Although models of branching in arterial and bronchial trees often predict a dependence of bifurcation parameters on the scale of the bifurcating vessels, direct verifications of this dependence with data are uncommon. We compare measurements of bifurcation parameters in airways and arterial trees of different mammals as a function of scale to general features predicted by theoretical models. We find that the size dependence is more complex than existing theories based solely on energy minimization explain, and suggest additional factors that may govern the branching at different scales.
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Rebrov A.P.
2012-03-01
Full Text Available Aim: to evaluate arterial wall rigidity, clinical condition and prognosis in active and standard therapy of patients with chronic heart failure (CHF. Materials and methods. A total of 211 patients with CHF experienced Q-wave myocardial infarction was enrolled in the study. At admission to the hospital all patients were randomized into two groups. Patients of the first group (n=106 were managed actively after discharge from the hospital, patients of the second group (n=105 were managed conventionally after discharge from the hospital. Patients were observed for three years. Re-sults. Over three year-investigation actively managed patients demonstrated significant (p<0,05 decrease in systolic and diastolic blood pressure, heart rate, blood serum levels of total cholesterol, N-terminal cerebral natriuretic peptide, increase of 6-minute walk-test, left ventricle ejection fraction reduction and decrease in number hospitalization of patients with CHF as compared to those who were conventionally managed. At patients of II group pulse wave speed in aorta (PWVA since the first year, an index of augmentation of brachial artery and systolic pressure in aorta in three years of supervision above (p<0,05 in comparison with patients of group I. Conclusion. One of deterioration factors of systolic functions of the left ventricle and the prognosis in patients with CHF of group of standard therapy was progressing of arterial wall rigidity pathology
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In this investigation, surgical operations of blocked intestinal artery have been conducted on pigs to simulate the condition of acute mesenteric arterial occlusion. The empirical mode decomposition method and the algorithm of linguistic analysis were applied to verify the blood pressure signals in simulated situation. We assumed that there was some information hidden in the high-frequency part of the blood pressure signal when an intestinal artery is blocked. The empirical mode decomposition method (EMD) has been applied to decompose the intrinsic mode functions (IMF) from a complex time series. But, the end effects and phenomenon of intermittence damage the consistence of each IMF. Thus, we proposed the complementary ensemble empirical mode decomposition method (CEEMD) to solve the problems of end effects and the phenomenon of intermittence. The main wave of blood pressure signals can be reconstructed by the main components, identified by Monte Carlo verification, and removed from the original signal to derive a riding wave. Furthermore, the concept of linguistic analysis was applied to design the blocking index to verify the pattern of riding wave of blood pressure using the measurements of dissimilarity. Blocking index works well to identify the situation in which the sampled time series of blood pressure signal was recorded. Here, these two totally different algorithms are successfully integrated and the existence of the existence of information hidden in high-frequency part of blood pressure signal has been proven
Einstein's Field Equations as a Fold Bifurcation
Kohli, Ikjyot Singh
2016-01-01
It is shown that Einstein's field equations for \\emph{all} perfect-fluid $k=0$ FLRW cosmologies have the same form as the topological normal form of a fold bifurcation. In particular, we assume that the cosmological constant is a bifurcation parameter, and as such, fold bifurcation behaviour is shown to occur in a neighbourhood of Minkowski spacetime in the phase space. We show that as this cosmological constant parameter is varied, an expanding and contracting de Sitter universe \\emph{emerge} via this bifurcation.
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A delay-differential modelling with stage-structure for prey is investigated. Its dynamics are studied in terms of local analysis and Hopf bifurcation theory, and its linear stability and Hopf bifurcation are demonstrated by studying the characteristic equation. The stability and direction of Hopf bifurcation are determined by applying the normal form theory and the center manifold argument, and numerical simulations are given to illustrate the analytical result
Stability and Bifurcation in a Delayed Reaction-Diffusion Equation with Dirichlet Boundary Condition
Guo, Shangjiang; Ma, Li
2016-04-01
In this paper, we study the dynamics of a diffusive equation with time delay subject to Dirichlet boundary condition in a bounded domain. The existence of spatially nonhomogeneous steady-state solution is investigated by applying Lyapunov-Schmidt reduction. The existence of Hopf bifurcation at the spatially nonhomogeneous steady-state solution is derived by analyzing the distribution of the eigenvalues. The direction of Hopf bifurcation and stability of the bifurcating periodic solution are also investigated by means of normal form theory and center manifold reduction. Moreover, we illustrate our general results by applications to the Nicholson's blowflies models with one- dimensional spatial domain.
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Paun Marla
2007-03-01
Full Text Available Abstract Background In order to establish a consistent method for brachial artery reactivity assessment, we analyzed commonly used approaches to the test and their effects on the magnitude and time-course of flow mediated dilation (FMD, and on test variability and repeatability. As a popular and noninvasive assessment of endothelial function, several different approaches have been employed to measure brachial artery reactivity with B-mode ultrasound. Despite some efforts, there remains a lack of defined normal values and large variability in measurement technique. Methods Twenty-six healthy volunteers underwent repeated brachial artery diameter measurements by B-mode ultrasound. Following baseline diameter recordings we assessed endothelium-dependent flow mediated dilation by inflating a blood pressure cuff either on the upper arm (proximal or on the forearm (distal. Results Thirty-seven measures were performed using proximal occlusion and 25 with distal occlusion. Following proximal occlusion relative to distal occlusion, FMD was larger (16.2 ± 1.2% vs. 7.3 ± 0.9%, p p = 0.0001. Measurement of the test repeatability showed that differences between the repeated measures were greater on average when the measurements were done using the proximal method as compared to the distal method (2.4%; 95% CI 0.5–4.3; p = 0.013. Conclusion These findings suggest that forearm compression holds statistical advantages over upper arm compression. Added to documented physiological and practical reasons, we propose that future studies should use forearm compression in the assessment of endothelial function.
Bifurcation analysis of a semiconductor laser subject to phase conjugate feedback
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In this thesis we present a detailed bifurcation analysis of a semiconductor laser subject to phase-conjugate feedback (PCF). Mathematically, lasers with feedback are modelled by delay differential equations (DDEs) with an infinite-dimensional phase space. This is why, in the past, systems described by DDEs were only studied by numerical simulation. We employ new numerical bifurcation tools for DDEs that go much beyond mere simulation. More precisely, we continue steady states and periodic orbits, irrespective of their stability with the package DDE-BIFTOOL, and present here the first algorithm for computing unstable manifolds of saddle-periodic orbits with one unstable Floquet multiplier in systems of DDEs. Together, these tools make it possible, for the first time, to numerically study global bifurcations in DDEs. Specifically, we first show how periodic solutions of the PCF laser are all connected to one another via a locked steady state solution. A one-parameter study of these steady states reveals heteroclinic bifurcations, which turn out to be responsible for bistability and excitability at the locking boundaries. We then perform a full two-parameter investigation of the locking range, where we continue bifurcations of steady states and heteroclinic bifurcations. This leads to the identification of a number of codimension- two bifurcation points. Here, we also make a first attempt at providing a two-parameter study of bifurcations of periodic orbits in a system of DDEs. Finally, our new method for the computation of unstable manifolds of saddle periodic orbits is used to show how a torus breaks up with a sudden transition to chaos in a crisis bifurcation. In more general terms, we believe that the results presented in this thesis showcase the usefulness of continuation and manifold computations and will contribute to the theory of global bifurcations in DDEs. (author)
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The complex interplay of neural, metabolic, myogenic and mechanical mechanisms that regulate blood flow in skeletal muscle (MBF) is still incompletely understood. For the first time, a method is presented for high time-resolution recording of MBF from a purely muscular artery in physiological conditions. Ultrasound perivascular flow probes were implanted (n = 15) mono- or bilaterally around the masseteric branch of the facial artery in nine rabbits and tested up to 16 days after implant. Reliable and stable recordings were achieved in 50% of implants. Blood flow was observed to increase from a resting level of 0.2–0.3 ml min−1 up to 4.0–6.0 ml min−1 during spontaneous masticatory activity. In addition, within single masticatory cycles marked back flow transients could be observed (peak flow = −10 ml min−1) during powerful masticatory strokes but not during mild mastication. The possibility of (1) surgically removing the sympathetic supply to the relevant vascular bed and of (2) bilaterally monitoring the perfusion of masseter muscles thus allowing to use one side as control side for different types of interventions makes this model a useful tool for disentangling the different mechanisms involved in the control of MBF. (note)
Coronary bifurcation lesions treated with simple or complex stenting
DEFF Research Database (Denmark)
Behan, Miles W; Holm, Niels R; de Belder, Adam J;
2016-01-01
from two large bifurcation coronary stenting trials with similar methodology: the Nordic Bifurcation Study (NORDIC I) and the British Bifurcation Coronary Study: old, new, and evolving strategies (BBC ONE). METHODS AND RESULTS: Both multicentre randomized trials compared simple (provisional T...
Bifurcation Tools for Flight Dynamics Analysis and Control System Design Project
National Aeronautics and Space Administration — Modern bifurcation analysis methods have been proposed for investigating flight dynamics and control system design in highly nonlinear regimes and also for the...
Stability switches and Hopf bifurcations in a pair of identical tri-neuron network loops
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The dynamical behavior of a delayed neural network coupled by a pair of identical tri-neuron loops is considered. Conditional/absolute stability, stability switches and Hopf bifurcations induced by time delay are investigated.
Energy Technology Data Exchange (ETDEWEB)
Nagata, Shun-ichi; Kazekawa, Kiyoshi; Matsubara, Shuko [Fukuoka University Chikushi Hospital, Department of Neurosurgery, Chikushino, Fukuoka (Japan); Sugata, Sei [Bironoki Neurosurgical Hospital, Shibushi, Kagoshima (Japan)
2006-08-15
Obstructions of the supraaortic vessels are an important cause of morbidity associated with a variety of symptoms. Percutaneous transluminal angioplasty has evolved as an effective and safe treatment modality for occlusive lesions of the supraaortic vessels. However, the endovascular management of an innominate bifurcation has not previously been reported. A 53-year-old female with a history of systematic hypertension, diabetes mellitus and hypercholesterolemia presented with left hemiparesis and dysarthria. Angiography of the innominate artery showed a stenosis of the innominate bifurcation. The lesion was successfully treated using the retrograde kissing stent technique via a brachial approach and an exposed direct carotid approach. The retrograde kissing stent technique for the treatment of a stenosis of the innominate bifurcation was found to be a safe and effective alternative to conventional surgery. (orig.)
International Nuclear Information System (INIS)
Obstructions of the supraaortic vessels are an important cause of morbidity associated with a variety of symptoms. Percutaneous transluminal angioplasty has evolved as an effective and safe treatment modality for occlusive lesions of the supraaortic vessels. However, the endovascular management of an innominate bifurcation has not previously been reported. A 53-year-old female with a history of systematic hypertension, diabetes mellitus and hypercholesterolemia presented with left hemiparesis and dysarthria. Angiography of the innominate artery showed a stenosis of the innominate bifurcation. The lesion was successfully treated using the retrograde kissing stent technique via a brachial approach and an exposed direct carotid approach. The retrograde kissing stent technique for the treatment of a stenosis of the innominate bifurcation was found to be a safe and effective alternative to conventional surgery. (orig.)
Bifurcation Analysis and Chaos Control in a Discrete Epidemic System
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Wei Tan
2015-01-01
Full Text Available The dynamics of discrete SI epidemic model, which has been obtained by the forward Euler scheme, is investigated in detail. By using the center manifold theorem and bifurcation theorem in the interior R+2, the specific conditions for the existence of flip bifurcation and Neimark-Sacker bifurcation have been derived. Numerical simulation not only presents our theoretical analysis but also exhibits rich and complex dynamical behavior existing in the case of the windows of period-1, period-3, period-5, period-6, period-7, period-9, period-11, period-15, period-19, period-23, period-34, period-42, and period-53 orbits. Meanwhile, there appears the cascade of period-doubling 2, 4, 8 bifurcation and chaos sets from the fixed point. These results show the discrete model has more richer dynamics compared with the continuous model. The computations of the largest Lyapunov exponents more than 0 confirm the chaotic behaviors of the system x→x+δ[rN(1-N/K-βxy/N-(μ+mx], y→y+δ[βxy/N-(μ+dy]. Specifically, the chaotic orbits at an unstable fixed point are stabilized by using the feedback control method.
Bifurcation of the spin-wave equations
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We study the bifurcations of the spin-wave equations that describe the parametric pumping of collective modes in magnetic media. Mechanisms describing the following dynamical phenomena are proposed: (i) sequential excitation of modes via zero eigenvalue bifurcations; (ii) Hopf bifurcations followed (or not) by Feingenbaum cascades of period doubling; (iii) local and global homoclinic phenomena. Two new organizing center for routes to chaos are identified; in the classification given by Guckenheimer and Holmes [GH], one is a codimension-two local bifurcation, with one pair of imaginary eigenvalues and a zero eigenvalue, to which many dynamical consequences are known; secondly, global homoclinic bifurcations associated to splitting of separatrices, in the limit where the system can be considered a Hamiltonian subjected to weak dissipation and forcing. We outline what further numerical and algebraic work is necessary for the detailed study following this program. (author)
Voltage stability, bifurcation parameters and continuation methods
Energy Technology Data Exchange (ETDEWEB)
Alvarado, F.L. [Wisconsin Univ., Madison, WI (United States)
1994-12-31
This paper considers the importance of the choice of bifurcation parameter in the determination of the voltage stability limit and the maximum power load ability of a system. When the bifurcation parameter is power demand, the two limits are equivalent. However, when other types of load models and bifurcation parameters are considered, the two concepts differ. The continuation method is considered as a method for determination of voltage stability margins. Three variants of the continuation method are described: the continuation parameter is the bifurcation parameter the continuation parameter is initially the bifurcation parameter, but is free to change, and the continuation parameter is a new `arc length` parameter. Implementations of voltage stability software using continuation methods are described. (author) 23 refs., 9 figs.
CENTER CONDITIONS AND BIFURCATION OF LIMIT CYCLES FOR A CLASS OF FIFTH DEGREE SYSTEMS
Institute of Scientific and Technical Information of China (English)
HuangWentao; LiuYirong
2004-01-01
The center conditions and bifurcation of limit cycles for a class of fifth degree systems are investigated. Two recursive formulas to compute singular quantities at infinity and at the origin are given. The first nine singular point quantities at infinity and first seven singular point quantities at the origin for the system are given in order to get center conditions and study bifurcation of limit cycles. Two fifth degree systems are constructed. One allows the appearance of eight limit cycles in the neighborhood of infinity,which is the first example that a polynomial differential system bifurcates eight limit cycles at infinity. The other perturbs six limit cycles at the origin.
Dynamics near manifolds of equilibria of codimension one and bifurcation without parameters
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Stefan Liebscher
2011-05-01
Full Text Available We investigate the breakdown of normal hyperbolicity of a manifold of equilibria of a flow. In contrast to classical bifurcation theory we assume the absence of any flow-invariant foliation at the singularity transverse to the manifold of equilibria. We call this setting bifurcation without parameters. We provide a description of general systems with a manifold of equilibria of codimension one as a first step towards a classification of bifurcations without parameters. This is done by relating the problem to singularity theory of maps.
Bifurcations, chaos, and sensitivity to parameter variations in the Sato cardiac cell model
Otte, Stefan; Berg, Sebastian; Luther, Stefan; Parlitz, Ulrich
2016-08-01
The dynamics of a detailed ionic cardiac cell model proposed by Sato et al. (2009) is investigated in terms of periodic and chaotic action potentials, bifurcation scenarios, and coexistence of attractors. Starting from the model's standard parameter values bifurcation diagrams are computed to evaluate the model's robustness with respect to (small) parameter changes. While for some parameters the dynamics turns out to be practically independent from their values, even minor changes of other parameters have a very strong impact and cause qualitative changes due to bifurcations or transitions to coexisting attractors. Implications of this lack of robustness are discussed.
Bifurcation in a thin liquid film flowing over a locally heated surface
Katkar, Harshwardhan H
2014-01-01
We investigate the non-linear dynamics of a two-dimensional film flowing down a finite heater, for a non-volatile and a volatile liquid. An oscillatory instability is predicted beyond a critical value of Marangoni number using linear stability theory. Continuation along the Marangoni number using non-linear evolution equation is used to trace bifurcation diagram associated with the oscillatory instability. Hysteresis, a characteristic attribute of a sub-critical Hopf bifurcation, is observed in a critical parametric region. The bifurcation is universally observed for both, a non-volatile film and a volatile film.
Bifurcation and solitary waves of the nonlinear wave equation with quartic polynomial potential
Institute of Scientific and Technical Information of China (English)
化存才; 刘延柱
2002-01-01
For the nonlinear wave equation with quartic polynomial potential, bifurcation and solitary waves are investigated. Based on the bifurcation and the energy integral of the two-dimensional dynamical system satisfied by the travelling waves, it is very interesting to find different sufficient and necessary conditions in terms of the bifurcation parameter for the existence and coexistence of bright, dark solitary waves and shock waves. The method of direct integration is developed to give all types of solitary wave solutions. Our method is simpler than other newly developed ones. Some results are similar to those obtained recently for the combined KdV-mKdV equation.
Stability and bifurcation analysis for a delayed Lotka-Volterra predator-prey system
Yan, Xiang-Ping; Chu, Yan-Dong
2006-11-01
The present paper deals with a delayed Lotka-Volterra predator-prey system. By linearizing the equations and by analyzing the locations on the complex plane of the roots of the characteristic equation, we find the necessary conditions that the parameters should verify in order to have the oscillations in the system. In addition, the normal form of the Hopf bifurcation arising in the system is determined to investigate the direction and the stability of periodic solutions bifurcating from these Hopf bifurcations. To verify the obtained conditions, a special numerical example is also included.
Stability and bifurcation analysis on a three-species food chain system with two delays
Cui, Guo-Hu; Yan, Xiang-Ping
2011-09-01
The present paper deals with a three-species Lotka-Volterra food chain system with two discrete delays. By linearizing the system at the positive equilibrium and analyzing the associated characteristic equation, the asymptotic stability of the positive equilibrium and existence of local Hopf bifurcations are investigated. Furthermore, by using the normal form theory and the center manifold reduction, explicit formulae are derived to determine the direction of bifurcations and the stability of bifurcating periodic solutions. Finally, to verify our theoretical predictions, some numerical simulations are also included at the end of this paper.
Bifurcation analysis of the logistic map via two periodic impulsive forces
International Nuclear Information System (INIS)
The complex dynamics of the logistic map via two periodic impulsive forces is investigated in this paper. The influences of the system parameter and the impulsive forces on the dynamics of the system are studied respectively. With the parameter varying, the system produces the phenomenon such as periodic solutions, chaotic solutions, and chaotic crisis. Furthermore, the system can evolve to chaos by a cascading of period-doubling bifurcations. The Poincaré map of the logistic map via two periodic impulsive forces is constructed and its bifurcation is analyzed. Finally, the Floquet theory is extended to explore the bifurcation mechanism for the periodic solutions of this non-smooth map. (general)
Bifurcation analysis of periodic orbits of a non-smooth Jeffcott rotor model
Páez Chávez, Joseph; Wiercigroch, Marian
2013-09-01
We investigate complex dynamics occurring in a non-smooth model of a Jeffcott rotor with a bearing clearance. A bifurcation analysis of the rotor system is carried out by means of the software TC-HAT [25], a toolbox of AUTO 97 [6] allowing path-following and detection of bifurcations of periodic trajectories of non-smooth dynamical systems. The study reveals a rich variety of dynamics, which includes grazing-induced fold and period-doubling bifurcations, as well as hysteresis loops produced by a cusp singularity. Furthermore, an analytical expression predicting grazing incidences is derived.
Bifurcation Analysis and Chaos Control in a Modified Finance System with Delayed Feedback
Yang, Jihua; Zhang, Erli; Liu, Mei
2016-06-01
We investigate the effect of delayed feedback on the finance system, which describes the time variation of the interest rate, for establishing the fiscal policy. By local stability analysis, we theoretically prove the existences of Hopf bifurcation and Hopf-zero bifurcation. By using the normal form method and center manifold theory, we determine the stability and direction of a bifurcating periodic solution. Finally, we give some numerical solutions, which indicate that when the delay passes through certain critical values, chaotic oscillation is converted into a stable equilibrium or periodic orbit.
STABILITY AND LOCAL BIFURCATION IN A SIMPLY-SUPPORTED BEAM CARRYING A MOVING MASS
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The stability and local bifurcation of a simply-supported flexible beam (Bernoulli-Euler type) carrying a moving mass and subjected to harmonic axial excitation are investigated.In the theoretical analysis, the partial differential equation of motion with the fifth-order nonlinear term is solved using the method of multiple scales (a perturbation technique). The stability and local bifurcation of the beam are analyzed for 1/2 sub harmonic resonance. The results show that some of the parameters, especially the velocity of moving mass and external excitation, affect the local bifurcation significantly. Therefore, these parameters play important roles in the system stability.
Analysis of the flow at a T-bifurcation for a ternary unit
Campero, P.; Beck, J.; Jung, A.
2014-03-01
The motivation of this research is to understand the flow behavior through a 90° T- type bifurcation, which connects a Francis turbine and the storage pump of a ternary unit, under different operating conditions (namely turbine, pump and hydraulic short-circuit operation). As a first step a CFD optimization process to define the hydraulic geometry of the bifurcation was performed. The CFD results show the complexity of the flow through the bifurcation, especially under hydraulic short-circuit operation. Therefore, it was decided to perform experimental investigations in addition to the CFD analysis, in order to get a better understanding of the flow. The aim of these studies was to investigate the flow development upstream and downstream the bifurcation, the estimation of the bifurcation loss coefficients and also to provide comprehensive data of the flow behavior for the whole operating range of the machine. In order to evaluate the development of the velocity field Stereo Particle Image Velocimetry (S-PIV) measurements at different sections upstream and downstream of the bifurcation on the main penstock and Laser Doppler Anemometrie (LDA) measurements at bifurcation inlet were performed. This paper presents the CFD results obtained for the final design for different operating conditions, the model test procedures and the model test results with special attention to: 1) The bifurcation head loss coefficients, and their extrapolation to prototype conditions, 2) S-PIV and LDA measurements. Additionally, criteria to define the minimal uniformity conditions for the velocity profiles entering the turbine are evaluated. Finally, based on the gathered flow information a better understanding to define the preferred location of a bifurcation is gained and can be applied to future projects.
Numerical bifurcation analysis of conformal formulations of the Einstein constraints
International Nuclear Information System (INIS)
The Einstein constraint equations have been the subject of study for more than 50 years. The introduction of the conformal method in the 1970s as a parametrization of initial data for the Einstein equations led to increased interest in the development of a complete solution theory for the constraints, with the theory for constant mean curvature (CMC) spatial slices and closed manifolds completely developed by 1995. The first general non-CMC existence result was establish by Holst et al. in 2008, with extensions to rough data by Holst et al. in 2009, and to vacuum spacetimes by Maxwell in 2009. The non-CMC theory remains mostly open; moreover, recent work of Maxwell on specific symmetry models sheds light on fundamental nonuniqueness problems with the conformal method as a parametrization in non-CMC settings. In parallel with these mathematical developments, computational physicists have uncovered surprising behavior in numerical solutions to the extended conformal thin sandwich formulation of the Einstein constraints. In particular, numerical evidence suggests the existence of multiple solutions with a quadratic fold, and a recent analysis of a simplified model supports this conclusion. In this article, we examine this apparent bifurcation phenomena in a methodical way, using modern techniques in bifurcation theory and in numerical homotopy methods. We first review the evidence for the presence of bifurcation in the Hamiltonian constraint in the time-symmetric case. We give a brief introduction to the mathematical framework for analyzing bifurcation phenomena, and then develop the main ideas behind the construction of numerical homotopy, or path-following, methods in the analysis of bifurcation phenomena. We then apply the continuation software package AUTO to this problem, and verify the presence of the fold with homotopy-based numerical methods. We discuss these results and their physical significance, which lead to some interesting remaining questions to
Assessment of carotid arteri calcification using 3D-CT angiography
International Nuclear Information System (INIS)
The aim of this study was to evaluate carotid arteri calcifications using 3D-CT angiography. We performed a retrospective review of 181 patients referred for 64-slice multi-detector row computed tomography. Using curved multiplanar reformation (curved MPR) images of ZIOSOFT M900 QUADRA, we evaluated the distribution of calcifications around the carotid bifurcation. Among the 181 patients, 66 patients (36%) had arterial calcifications. The present study found that almost arterial calcifications localized at the carotid bifurcation. Furthermore, in the group with carotid arterial stenosis, we found arterial calcifications localized not only at the carotid bifurcation, but also at the distal side of internal carotid artery. Curved MPR imaging using 3D-CT angiography is a helpful tool for evaluating calcification of carotid arteries. (author)
On the effect of AVR gain on bifurcations of subsynchronous resonance in power systems
Energy Technology Data Exchange (ETDEWEB)
Widyan, Mohammad S. [Electrical Engineering Department, The Hashemite University, 13115 Zarqa (Jordan)
2010-07-15
This paper presents the effect of the automatic voltage regulator (AVR) gain on the bifurcations of subsynchronous resonance (SSR) in power systems. The first system of the IEEE second benchmark model of SSR is chosen for numerical investigations. The dynamics of both axes damper windings of the generator and that of the power system stabilizer (PSS) are included. The bifurcation parameter is the compensation factor. Hopf bifurcation, where a pair of complex conjugate eigenvalues of the linearized model around the operating point transversally crosses from left- to right-half of the complex plane, is detected in all AVR gains. It is shown that the Hopf bifurcation is of subcritical type. The results also show that the location of the Hopf bifurcation point i.e. the stable operating point regions are affected by the value of the AVR gain. The variation of the location of the Hopf bifurcation point as function of the AVR gain for two operating conditions is obtained. Time domain simulation results based on the nonlinear dynamical mathematical model carried out at different compensation factors and AVR gains agree with that of the bifurcation analysis. (author)
Bifurcation Structures in a Family of 1D Discontinuous Linear-Hyperbolic Invertible Maps
Makrooni, Roya; Gardini, Laura; Sushko, Iryna
2015-12-01
We consider a family of one-dimensional discontinuous invertible maps from an application in engineering. It is defined by a linear function and by a hyperbolic function with real exponent. The presence of vertical and horizontal asymptotes of the hyperbolic branch leads to particular codimension-two border collision bifurcation (BCB) such that if the parameter point approaches the bifurcation value from one side then the related cycle undergoes a regular BCB, while if the same bifurcation value is approached from the other side then a nonregular BCB occurs, involving periodic points at infinity, related to the asymptotes of the map. We investigate the bifurcation structure in the parameter space. Depending on the exponent of the hyperbolic branch, different period incrementing structures can be observed, where the boundaries of a periodicity region are related either to subcritical, or supercritical, or degenerate flip bifurcations of the related cycle, as well as to a regular or nonregular BCB. In particular, if the exponent is positive and smaller than one, then the period incrementing structure with bistability regions is observed and the corresponding flip bifurcations are subcritical, while if the exponent is larger than one, then the related flip bifurcations are supercritical and, thus, also the regions associated with cycles of double period are involved into the incrementing structure.
Stability and Hopf bifurcation on a model for HIV infection of CD4+ T cells with delay
International Nuclear Information System (INIS)
In this paper, a delayed differential equation model that describes HIV infection of CD4+ T cells is considered. The stability of the positive equilibrium and the existence of Hopf bifurcation are investigated. In succession, using the normal form theory and center manifold argument, we derive the explicit formulas which determine the stability, direction and other properties of bifurcating periodic solutions.
Judd, S L; Judd, Stephen L.; Silber, Mary
1998-01-01
This paper investigates the competition between both simple (e.g. stripes, hexagons) and ``superlattice'' (super squares, super hexagons) Turing patterns in two-component reaction-diffusion systems. ``Superlattice'' patterns are formed from eight or twelve Fourier modes, and feature structure at two different length scales. Using perturbation theory, we derive simple analytical expressions for the bifurcation equation coefficients on both rhombic and hexagonal lattices. These expressions show that, no matter how complicated the reaction kinectics, the nonlinear reaction terms reduce to just four effective terms within the bifurcation equation coefficients. Moreover, at the hexagonal degeneracy -- when the quadratic term in the hexagonal bifurcation equation disappears -- the number of effective system parameters drops to two, allowing a complete characterization of the possible bifurcation results at this degeneracy. The general results are then applied to specific model equations, to investigate the stabilit...
Nonlinear stability control and λ-bifurcation
International Nuclear Information System (INIS)
Passive techniques for nonlinear stability control are presented for a model of fluidelastic instability. They employ the phenomena of λ-bifurcation and a generalization of it. λ-bifurcation occurs when a branch of flutter solutions bifurcates supercritically from a basic solution and terminates with an infinite period orbit at a branch of divergence solutions which bifurcates subcritically from the basic solution. The shape of the bifurcation diagram then resembles the greek letter λ. When the system parameters are in the range where flutter occurs by λ-bifurcation, then as the flow velocity increase the flutter amplitude also increases, but the frequencies of the oscillations decrease to zero. This diminishes the damaging effects of structural fatigue by flutter, and permits the flow speed to exceed the critical flutter speed. If generalized λ-bifurcation occurs, then there is a jump transition from the flutter states to a divergence state with a substantially smaller amplitude, when the flow speed is sufficiently larger than the critical flutter speed
Santos, AMF; dos santos, rm; castro, pmac; Azevedo, E.; Sousa, L. de; tavares, jmrs
2013-01-01
A novel algorithm is proposed for the segmentation of the lumen and bifurcation boundaries of the carotid artery in B-mode ultrasound images. It uses the image contrast characteristics of the lumen and bifurcation of the carotid artery in relation to other tissues and structures for their identification. The relevant ultrasound data regarding the artery presented in the input image is identified using morphologic operators and processed by an anisotropic diffusion filter for speckle noise rem...
Stability and Hopf bifurcation in a delayed competitive web sites model
Energy Technology Data Exchange (ETDEWEB)
Xiao Min [Department of Mathematics, Southeast University, Nanjing 210096 (China): Department of Mathematics, Nanjing Xiaozhuang College, Nanjing 210017 (China); Cao Jinde [Department of Mathematics, Southeast University, Nanjing 210096 (China)]. E-mail: jdcao@seu.edu.cn
2006-04-24
The delayed differential equations modeling competitive web sites, based on the Lotka-Volterra competition equations, are considered. Firstly, the linear stability is investigated. It is found that there is a stability switch for time delay, and Hopf bifurcation occurs when time delay crosses through a critical value. Then the direction and stability of the bifurcated periodic solutions are determined, using the normal form theory and the center manifold reduction. Finally, some numerical simulations are carried out to illustrate the results found.
Stability and Hopf bifurcation in a delayed competitive web sites model
Xiao, Min; Cao, Jinde
2006-04-01
The delayed differential equations modeling competitive web sites, based on the Lotka Volterra competition equations, are considered. Firstly, the linear stability is investigated. It is found that there is a stability switch for time delay, and Hopf bifurcation occurs when time delay crosses through a critical value. Then the direction and stability of the bifurcated periodic solutions are determined, using the normal form theory and the center manifold reduction. Finally, some numerical simulations are carried out to illustrate the results found.
Bifurcation analysis and the travelling wave solutions of the Klein–Gordon–Zakharov equations
Indian Academy of Sciences (India)
Zaiyun Zhang; Fnag-Li Xia; Xin-Ping Li
2013-01-01
In this paper, we investigate the bifurcations and dynamic behaviour of travelling wave solutions of the Klein–Gordon–Zakharov equations given in Shang et al, Comput. Math. Appl. 56, 1441 (2008). Under different parameter conditions, we obtain some exact explicit parametric representations of travelling wave solutions by using the bifurcation method (Feng et al, Appl. Math. Comput. 189, 271 (2007); Li et al, Appl. Math. Comput. 175, 61 (2006)).
Hopf Bifurcation of an SIQR Computer Virus Model with Time Delay
2015-01-01
A delayed SIQR computer virus model is considered. It has been observed that there exists a critical value of delay for the stability of virus prevalence by choosing the delay as a bifurcation parameter. Furthermore, the properties of the Hopf bifurcation such as direction and stability are investigated by using the normal form method and center manifold theory. Finally, some numerical simulations for supporting our theoretical results are also performed.
Jianguo Ren; Yonghong Xu
2014-01-01
A new computer virus propagation model with delay and incomplete antivirus ability is formulated and its global dynamics is analyzed. The existence and stability of the equilibria are investigated by resorting to the threshold value R0. By analysis, it is found that the model may undergo a Hopf bifurcation induced by the delay. Correspondingly, the critical value of the Hopf bifurcation is obtained. Using Lyapunov functional approach, it is proved that, under suitable conditions, the unique v...
Bifurcations and sudden current change in ensembles of classically chaotic ratchets
Kenfack, A.; Sweetnam, S.; Pattanayak, A.K.
2007-01-01
In \\prl 84, 258 (2000), Mateos conjectured that current reversal in a classical deterministic ratchet is associated with bifurcations from chaotic to periodic regimes. This is based on the comparison of the current and the bifurcation diagram as a function of a given parameter for a periodic asymmetric potential. Barbi and Salerno, in \\pre 62, 1988 (2000), have further investigated this claim and argue that, contrary to Mateos' claim, current reversals can occur also in the absence of bifurca...
Abed-Meraim, F Farid; Peerlings, RHJ Ron; Geers, MGD Marc
2014-01-01
The present contribution deals with the prediction of diffuse necking in the context of forming and stretching of metal sheets. For this purpose, two approaches are investigated, namely bifurcation and the maximum force principle, with a systematic comparison of their respective ability to predict necking. While the bifurcation approach is of quite general applicability, some restrictions are shown for the application of maximum force conditions. Although the predictions of the two approaches...
Bifurcations of non-smooth systems
Angulo, Fabiola; Olivar, Gerard; Osorio, Gustavo A.; Escobar, Carlos M.; Ferreira, Jocirei D.; Redondo, Johan M.
2012-12-01
Non-smooth systems (namely piecewise-smooth systems) have received much attention in the last decade. Many contributions in this area show that theory and applications (to electronic circuits, mechanical systems, …) are relevant to problems in science and engineering. Specially, new bifurcations have been reported in the literature, and this was the topic of this minisymposium. Thus both bifurcation theory and its applications were included. Several contributions from different fields show that non-smooth bifurcations are a hot topic in research. Thus in this paper the reader can find contributions from electronics, energy markets and population dynamics. Also, a carefully-written specific algebraic software tool is presented.
Backward Bifurcation in Simple SIS Model
Institute of Scientific and Technical Information of China (English)
Zhan-wei Wang
2009-01-01
We describe and analyze a simple SIS model with treatment.In particular,we give a completely qualitative analysis by means of the theory of asymptotically autonomous system.It is found that a backward bifurcation occurs if the adequate contact rate or the capacity is small.It is also found that there exists bistable endemic equilibria.In the case of disease-induced death,it is shown that the backward bifurcation also occurs.Moreover,there is no limit cycle under some conditions,and the subcritical Hopf bifurcation occurs under another conditions.
Bifurcations of Periodic Orbits and Uniform Approximations
Schomerus, H; Schomerus, Henning; Sieber, Martin
1997-01-01
We derive uniform approximations for contributions to Gutzwiller's periodic-orbit sum for the spectral density which are valid close to bifurcations of periodic orbits in systems with mixed phase space. There, orbits lie close together and give collective contributions, while the individual contributions of Gutzwiller's type would diverge at the bifurcation. New results for the tangent, the period doubling and the period tripling bifurcation are given. They are obtained by going beyond the local approximation and including higher order terms in the normal form of the action. The uniform approximations obtained are tested on the kicked top and are found to be in excellent agreement with exact quantum results.
Cellular Cell Bifurcation of Cylindrical Detonations
Institute of Scientific and Technical Information of China (English)
HAN Gui-Lai; JIANG Zong-Lin; WANG Chun; ZHANG Fan
2008-01-01
Cellular cell pattern evolution of cylindrically-diverging detonations is numerically simulated successfully by solving two-dimensional Euler equations implemented with an improved two-step chemical kinetic model. From the simulation, three cell bifurcation modes are observed during the evolution and referred to as concave front focusing, kinked and wrinkled wave front instability, and self-merging of cellular cells. Numerical research demonstrates that the wave front expansion resulted from detonation front diverging plays a major role in the cellular cell bifurcation, which can disturb the nonlinearly self-sustained mechanism of detonations and finally lead to cell bifurcations.
Bifurcations and Transitions to Chaos in An Inverted Pendulum
Kim, Sang-Yoon; Hu, Bambi
1998-01-01
We consider a parametrically forced pendulum with a vertically oscillating suspension point. It is well known that, as the amplitude of the vertical oscillation is increased, its inverted state (corresponding to the vertically-up configuration) undergoes a cascade of ``resurrections,'' i.e., it becomes stabilized after its instability, destabilize again, and so forth ad infinitum. We make a detailed numerical investigation of the bifurcations associated with such resurrections of the inverted...
Computer simulation of the carotid artery
Santos, A.; Sousa, L. de; Tavares, J.; Santos, R.; Castro, P.; Azevedo, E.
2012-01-01
Background: Disturbed flow conditions at the bifurcation of common carotid artery and proximal internal carotid artery plays an important role in the development of local atherosclerotic plaques, which are important causes of stroke. Being able to build 3D models based on ultrasound imaging can improve diagnostic assessment and support interventions like endarterectomy or carotid stenting. Our aim was to describe a carotid segmentation algorithm to build these 3D models.Methods: We developed ...
Angiographic features of unilateral nonbifurcating cervical carotid artery: A case report
International Nuclear Information System (INIS)
Nonbifurcating cervical carotid artery is a rare anomaly of the common carotid artery (CCA), in which the branches of the external carotid artery (ECA) arise directly from the CCA or proximal internal carotid artery without bifurcation, and therefore there is no proximal main trunk of the ECA. We report a unilateral nonbifurcating cervical carotid artery of a 67-year-old woman, incidentally found during cerebral aneurismal treatment
Angiographic features of unilateral nonbifurcating cervical carotid artery: A case report
Energy Technology Data Exchange (ETDEWEB)
En, Na Lae [Dept. of Radiology, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul (Korea, Republic of); Lee, Seung Koo [Dept. of Radiology, Severance Hospital, Yonsei University College of Medicine, Seoul (Korea, Republic of)
2015-08-15
Nonbifurcating cervical carotid artery is a rare anomaly of the common carotid artery (CCA), in which the branches of the external carotid artery (ECA) arise directly from the CCA or proximal internal carotid artery without bifurcation, and therefore there is no proximal main trunk of the ECA. We report a unilateral nonbifurcating cervical carotid artery of a 67-year-old woman, incidentally found during cerebral aneurismal treatment.
Aortoiliac aneurysm with arteriocaval fistula treated by a bifurcated endovascular stent-graft
International Nuclear Information System (INIS)
A 71-year-old patient with high-output cardiac failure was found to have an aneurysmal distal aorta with evidence of an arteriocaval fistula on ultrasound scanning. CT demonstrated an aneurysm of the distal aorta and right common iliac artery and an intraarterial digital subtraction angiogram confirmed an arteriocaval fistula. In view of the patient's cardiac failure and general condition an endovascular stent was considered. The right internal iliac artery was occluded with Tungsten coils prior to the insertion of a bifurcated stent-graft. This resulted in total occlusion of the aneurysm and obliteration of the arteriocaval fistula. To our knolwedge such a case has not been previously reported.
Aortoiliac Aneurysm with Arteriocaval Fistula Treated by a Bifurcated Endovascular Stent-Graft
International Nuclear Information System (INIS)
A 71-year-old patient with high-output cardiac failure was found to have an aneurysmal distal aorta with evidence of an arteriocaval fistula on ultrasound scanning. CT demonstrated an aneurysm of the distal aorta and right common iliac artery and an intraarterial digital subtraction angiogram confirmed an arteriocaval fistula. In view of the patient's cardiac failure and general condition an endovascular stent was considered. The right internal iliac artery was occluded with Tungsten coils prior to the insertion of a bifurcated stent-graft. This resulted in total occlusion of the aneurysm and obliteration of the arteriocaval fistula. To our knowledge such a case has not been previously reported
Mining data from CFD simulation for aneurysm and carotid bifurcation models.
Miloš, Radović; Dejan, Petrović; Nenad, Filipović
2011-01-01
Arterial geometry variability is present both within and across individuals. To analyze the influence of geometric parameters, blood density, dynamic viscosity and blood velocity on wall shear stress (WSS) distribution in the human carotid artery bifurcation and aneurysm, the computer simulations were run to generate the data pertaining to this phenomenon. In our work we evaluate two prediction models for modeling these relationships: neural network model and k-nearest neighbor model. The results revealed that both models have high prediction ability for this prediction task. The achieved results represent progress in assessment of stroke risk for a given patient data in real time. PMID:22256273
Calcium deposits in the common carotid artery
International Nuclear Information System (INIS)
Complete text of publication follows. Arterial calcification consists mainly of calcium apatite and takes place at two sites in the vessel wall: the intima and the media. Intimal calcification occurs exclusively within atherosclerotic plaques, while medial calcification may develop independently [1]. Ultrasound examination of the carotid arteries is performed routinely to assess pathological alterations. Large calcified plaques in the carotid arteries can be detected by B-mode ultrasonography easily as high frequency ultrasound does not penetrate calcium and have been investigated extensively. In this study our aim was to determine the calcium distribution in the vessel wall itself, excluding large plaques, and to make the first step towards investigating the relationship between the calcium distributional maps and the respective ultrasonic images. The carotid arteries of five elderly (age 71±9 years) and one young (age 27 years) deceased patients were excised at autopsy and were investigated with a medical ultrasound equipment in a tank containing saline solution. Scan sequences were videotaped and images of previously marked cross-sections were transferred to a computer. Small pieces of the arteries were cut and quench frozen. Sections of 60μm from the middle of the scanned segments (30mm proximal to the bifurcation) were cut in a cryostat. The cryosections were transferred to microprobe target holders. The elemental distribution of the samples were determined by particle induced X-ray emission (PIXE) at the Debrecen microprobe [2]. True elemental maps and absolute concentration values were evaluated with a new software (True Pixe Imaging) [3]. The average calcium content of the scanned areas varied between 1000 and 9000μg/g in the slices of the common carotid arteries of the elderly patients. In contrast, scanned areas in the slices from the young subject contained only 600-800μg/g calcium. The concentration of calcium could reach even 3.75% along the wide
The influences of curvature and torsions on flows in a helical bifurcated stent-graft
Shim, Jeong Hyun; Eun Lee, Kyung; Yoo, Jung Yul
2008-11-01
A bifurcated stent-graft signifies an improvement in surgical technique for treatment of a lesion in the branched blood vessel. However, there still remains a high failure rate regarding bifurcated stent-graft due to the occurrence of thrombosis or re-stenosis. The objectives of this study are to understand the effect of torsion in helical bifurcated geometries, to explain how the mixing of flows there may be advantageous to the prevention of the occurrence of thrombosis, and to keep the patency of stent-graft in the aspect of hemodynamics. For clinical applications, flows in a helical bifurcated stent-graft are simulated three-dimensionally using an incompressible Navier-Stokes solver. In this study, the hemodynamics is investigated in terms of mechanical factors, i.e., velocity profiles, vortex patterns and wall shear stress distributions.
Hopf bifurcation in a environmental defensive expenditures model with time delay
International Nuclear Information System (INIS)
In this paper a three-dimensional environmental defensive expenditures model with delay is considered. The model is based on the interactions among visitors V, quality of ecosystem goods E, and capital K, intended as accommodation and entertainment facilities, in Protected Areas (PAs). The tourism user fees (TUFs) are used partly as a defensive expenditure and partly to increase the capital stock. The stability and existence of Hopf bifurcation are investigated. It is that stability switches and Hopf bifurcation occurs when the delay t passes through a sequence of critical values, τ0. It has been that the introduction of a delay is a destabilizing process, in the sense that increasing the delay could cause the bio-economics to fluctuate. Formulas about the stability of bifurcating periodic solution and the direction of Hopf bifurcation are exhibited by applying the normal form theory and the center manifold theorem. Numerical simulations are given to illustrate the results.
Bifurcation Analysis in an n-Dimensional Diffusive Competitive Lotka-Volterra System with Time Delay
Chang, Xiaoyuan; Wei, Junjie
2015-06-01
In this paper, we investigate the stability and Hopf bifurcation of an n-dimensional competitive Lotka-Volterra diffusion system with time delay and homogeneous Dirichlet boundary condition. We first show that there exists a positive nonconstant steady state solution satisfying the given asymptotic expressions and establish the stability of the positive nonconstant steady state solution. Regarding the time delay as a bifurcation parameter, we explore the system that undergoes a Hopf bifurcation near the positive nonconstant steady state solution and derive a calculation method for determining the direction of the Hopf bifurcation. Finally, we cite the stability of a three-dimensional competitive Lotka-Volterra diffusion system with time delay to illustrate our conclusions.
Bifurcation and chaos analysis of a nonlinear electromechanical coupling relative rotation system
International Nuclear Information System (INIS)
Hopf bifurcation and chaos of a nonlinear electromechanical coupling relative rotation system are studied in this paper. Considering the energy in air-gap field of AC motor, the dynamical equation of nonlinear electromechanical coupling relative rotation system is deduced by using the dissipation Lagrange equation. Choosing the electromagnetic stiffness as a bifurcation parameter, the necessary and sufficient conditions of Hopf bifurcation are given, and the bifurcation characteristics are studied. The mechanism and conditions of system parameters for chaotic motions are investigated rigorously based on the Silnikov method, and the homoclinic orbit is found by using the undetermined coefficient method. Therefore, Smale horseshoe chaos occurs when electromagnetic stiffness changes. Numerical simulations are also given, which confirm the analytical results. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
DNS of bifurcations in an air-filled rotating baroclinic annulus
Randriamampianina, A; Read, P L; Maubert, P; Randriamampianina, Anthony; Fruh, Wolf-Gerrit; Read, Peter L.; Maubert, Pierre
2006-01-01
Three-dimensional Direct Numerical Simulation (DNS) on the nonlinear dynamics and a route to chaos in a rotating fluid subjected to lateral heating is presented here and discussed in the context of laboratory experiments in the baroclinic annulus. Following two previous preliminary studies by Maubert and Randriamampianina, the fluid used is air rather than a liquid as used in all other previous work. This study investigated a bifurcation sequence from the axisymmetric flow to a number of complex flows. The transition sequence, on increase of the rotation rate, from the axisymmetric solution via a steady, fully-developed baroclinic wave to chaotic flow followed a variant of the classical quasi-periodic bifurcation route, starting with a subcritical Hopf and associated saddle-node bifurcation. This was followed by a sequence of two supercritical Hopf-type bifurcations, first to an amplitude vacillation, then to a three-frequency quasi-periodic modulated amplitude vacillation (MAV), and finally to a chaotic MAV\\...
Bifurcation and complex dynamics of a discrete-time predator-prey system involving group defense
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S. M. Sohel Rana
2015-09-01
Full Text Available In this paper, we investigate the dynamics of a discrete-time predator-prey system involving group defense. The existence and local stability of positive fixed point of the discrete dynamical system is analyzed algebraically. It is shown that the system undergoes a flip bifurcation and a Neimark-Sacker bifurcation in the interior of R+2 by using bifurcation theory. Numerical simulation results not only show the consistence with the theoretical analysis but also display the new and interesting dynamical behaviors, including phase portraits, period-7, 20-orbits, attracting invariant circle, cascade of period-doubling bifurcation from period-20 leading to chaos, quasi-periodic orbits, and sudden disappearance of the chaotic dynamics and attracting chaotic set. The Lyapunov exponents are numerically computed to characterize the complexity of the dynamical behaviors.
Hopf bifurcation and chaos from torus breakdown in voltage-mode controlled DC drive systems
International Nuclear Information System (INIS)
Period-doubling bifurcation and its route to chaos have been thoroughly investigated in voltage-mode and current-mode controlled DC motor drives under simple proportional control. In this paper, the phenomena of Hopf bifurcation and chaos from torus breakdown in a voltage-mode controlled DC drive system is reported. It has been shown that Hopf bifurcation may occur when the DC drive system adopts a more practical proportional-integral control. The phenomena of period-adding and phase-locking are also observed after the Hopf bifurcation. Furthermore, it is shown that the stable torus can breakdown and chaos emerges afterwards. The work presented in this paper provides more complete information about the dynamical behaviors of DC drive systems.
Stability and Bifurcation Analysis of a Modified Epidemic Model for Computer Viruses
Directory of Open Access Journals (Sweden)
Chuandong Li
2014-01-01
Full Text Available We extend the three-dimensional SIR model to four-dimensional case and then analyze its dynamical behavior including stability and bifurcation. It is shown that the new model makes a significant improvement to the epidemic model for computer viruses, which is more reasonable than the most existing SIR models. Furthermore, we investigate the stability of the possible equilibrium point and the existence of the Hopf bifurcation with respect to the delay. By analyzing the associated characteristic equation, it is found that Hopf bifurcation occurs when the delay passes through a sequence of critical values. An analytical condition for determining the direction, stability, and other properties of bifurcating periodic solutions is obtained by using the normal form theory and center manifold argument. The obtained results may provide a theoretical foundation to understand the spread of computer viruses and then to minimize virus risks.
Delay-induced stochastic bifurcations in a bistable system under white noise
Energy Technology Data Exchange (ETDEWEB)
Sun, Zhongkui, E-mail: sunzk@nwpu.edu.cn; Fu, Jin; Xu, Wei [Department of Applied Mathematics, Northwestern Polytechnical University, Xi' an 710072 (China); Xiao, Yuzhu [Department of Mathematics and Information Science, Chang' an University, Xi' an 710086 (China)
2015-08-15
In this paper, the effects of noise and time delay on stochastic bifurcations are investigated theoretically and numerically in a time-delayed Duffing-Van der Pol oscillator subjected to white noise. Due to the time delay, the random response is not Markovian. Thereby, approximate methods have been adopted to obtain the Fokker-Planck-Kolmogorov equation and the stationary probability density function for amplitude of the response. Based on the knowledge that stochastic bifurcation is characterized by the qualitative properties of the steady-state probability distribution, it is found that time delay and feedback intensity as well as noise intensity will induce the appearance of stochastic P-bifurcation. Besides, results demonstrated that the effects of the strength of the delayed displacement feedback on stochastic bifurcation are accompanied by the sensitive dependence on time delay. Furthermore, the results from numerical simulations best confirm the effectiveness of the theoretical analyses.
Delay-induced stochastic bifurcations in a bistable system under white noise.
Sun, Zhongkui; Fu, Jin; Xiao, Yuzhu; Xu, Wei
2015-08-01
In this paper, the effects of noise and time delay on stochastic bifurcations are investigated theoretically and numerically in a time-delayed Duffing-Van der Pol oscillator subjected to white noise. Due to the time delay, the random response is not Markovian. Thereby, approximate methods have been adopted to obtain the Fokker-Planck-Kolmogorov equation and the stationary probability density function for amplitude of the response. Based on the knowledge that stochastic bifurcation is characterized by the qualitative properties of the steady-state probability distribution, it is found that time delay and feedback intensity as well as noise intensity will induce the appearance of stochastic P-bifurcation. Besides, results demonstrated that the effects of the strength of the delayed displacement feedback on stochastic bifurcation are accompanied by the sensitive dependence on time delay. Furthermore, the results from numerical simulations best confirm the effectiveness of the theoretical analyses. PMID:26328553
BIFURCATIONS OF A CANTILEVERED PIPE CONVEYING STEADY FLUID WITH A TERMINAL NOZZLE
Institute of Scientific and Technical Information of China (English)
Xu Jian; Huang Yuying
2000-01-01
This paper studies interactions of pipe and fluid and deals with bifurcations of a cantilevered pipe conveying a steady fluid, clamped at one end and having a nozzle subjected to nonlinear constraints at the free end. Either the nozzle parameter or the flow velocity is taken as a variable parameter. The discrete equations of the system are obtained by the Ritz-Galerkin method. The static stability is studied by the Routh criteria. The method of averaging is employed to investigate the stability of the periodic motions. A Runge-Kutta scheme is used to examine the analytical results and the chaotic motions. Three critical values are given. The first one makes the system lose the static stability by pitchfork bifurcation. The second one makes the system lose the dynamical stability by Hopf bifurcation. The third one makes the periodic motions of the system lose the stability by doubling-period bifurcation.
Delay-induced stochastic bifurcations in a bistable system under white noise
International Nuclear Information System (INIS)
In this paper, the effects of noise and time delay on stochastic bifurcations are investigated theoretically and numerically in a time-delayed Duffing-Van der Pol oscillator subjected to white noise. Due to the time delay, the random response is not Markovian. Thereby, approximate methods have been adopted to obtain the Fokker-Planck-Kolmogorov equation and the stationary probability density function for amplitude of the response. Based on the knowledge that stochastic bifurcation is characterized by the qualitative properties of the steady-state probability distribution, it is found that time delay and feedback intensity as well as noise intensity will induce the appearance of stochastic P-bifurcation. Besides, results demonstrated that the effects of the strength of the delayed displacement feedback on stochastic bifurcation are accompanied by the sensitive dependence on time delay. Furthermore, the results from numerical simulations best confirm the effectiveness of the theoretical analyses
Coexistence of periods in a bifurcation
International Nuclear Information System (INIS)
Highlights: ► The bifurcation of the Varley–Gradwell–Hassell population model is revisited. ► The structure of the attractor mediating the bifurcation to chaos is studied. ► Geometric arguments are given for the coexistence of periods in the attractor. ► An algebraic method for the localization of these bifurcations is provided. - Abstract: A particular type of order-to-chaos transition mediated by an infinite set of coexisting neutrally stable limit cycles of different periods is studied in the Varley–Gradwell–Hassell population model. We prove by an algebraic method that this kind of transition can only happen for a particular bifurcation parameter value. Previous results on the structure of the attractor at the transition point are here simplified and extended.
Directory of Open Access Journals (Sweden)
M.D. Cabral
2009-05-01
Full Text Available Subclinical hypothyroidism (SHT is a disease for which exact therapeutic approaches have not yet been established. Previous studies have suggested an association between SHT and coronary heart disease. Whether this association is related to SHT-induced changes in serum lipid levels or to endothelial dysfunction is unclear. The aim of this study was to determine endothelial function measured by the flow-mediated vasodilatation of the brachial artery and the carotid artery intima-media thickness (IMT in a group of women with SHT compared with euthyroid subjects. Triglycerides, total cholesterol, HDL-C, LDL-C, apoprotein A (apo A, apo B, and lipoprotein(a were also determined. Twenty-one patients with SHT (mean age: 42.4 ± 10.8 years and mean thyroid-stimulating hormone (TSH levels: 8.2 ± 2.7 µIU/mL and 21 euthyroid controls matched for body mass index, age and atherosclerotic risk factors (mean age: 44.2 ± 8.5 years and mean TSH levels: 1.4 ± 0.6 µIU/mL participated in the study. Lipid parameters (except HDL-C and apo A, which were lower and IMT values were higher in the common carotid and carotid bifurcation of SHT patients with positive serum thyroid peroxidase antibodies (TPO-Ab (0.62 ± 0.2 and 0.62 ± 0.16 mm for the common carotid and carotid bifurcation, respectively when compared with the negative TPO-Ab group (0.55 ± 0.24 and 0.58 ± 0.13 mm, for common carotid and carotid bifurcation, respectively. The difference was not statistically significant. We conclude that minimal thyroid dysfunction had no adverse effects on endothelial function in the population studied. Further investigation is warranted to assess whether subclinical hypothyroidism, with and without TPO-Ab-positive serology, has any effect on endothelial function.
BIFURCATIONS AND CHAOS CONTROL IN TCP-RED SYSTEM
Institute of Scientific and Technical Information of China (English)
Liu Fang
2006-01-01
Objective Analyzing the nonlinear dynamics of the TCP-RED congestion control system is of great importance. This study will help investigate the loss of stability in Internet and design a proper method for controlling bifurcation and chaos in such system. Methods Based on bifurcation diagram, the effect of parameter on system performance is discussed. By using the state feedback and parameter variation strategy, a simple real time control method is proposed to modify the existing RED scheme. Results With our control method, the parametric sensitivity of RED mechanism is attenuated. Moreover, a sufficient condition on the robust stability of the system is also derived to adjust the parameters in TCP-RED system. Conclusion The proposed method has the advantages of simple implementation and unnecessary knowledge of the exact system.
Stability and bifurcation analysis of rotor-bearing-seal system
Ying, G. Y.; Liu, S. L.; Ma, R.; Zheng, S. Y.
2016-05-01
Labyrinth seals were extensively used in turbine units, and the seal fluid forces may induce self-excited vibrations of rotor under certain conditions. It has become the main factor to instability of rotor system. In this paper Muszynska seal fluid force model is used to investigate the stability of the rotor system. Nonlinear equations are numerically solved by Newmark integration method. The effect of different seal clearances and differential pressures on system stability is studied. The calculation results show that the dominant vibration component leading to instability changes with different seal clearance. With the differential pressure increased, the unstable speed is reduced. Then the bifurcation behavior of the system with and without seal force is calculated. Results show that the rotor vibration becomes severe and complicated, and the bifurcation behavior of the system has been changed when seal force is considered.
Morphological Transitions of Sliding Drops -- Dynamics and Bifurcations
Engelnkemper, Sebastian; Gurevich, Svetlana V; Thiele, Uwe
2016-01-01
We study fully three-dimensional droplets that slide down an incline employing a thin-film equation that accounts for capillarity, wettability and a lateral driving force in small-gradient (or long-wave) approximation. In particular, we focus on qualitative changes in the morphology and behavior of stationary sliding drops. We employ the inclination angle of the substrate as control parameter and use continuation techniques to analyze for several fixed droplet sizes the bifurcation diagram of stationary droplets, their linear stability and relevant eigenmodes. The obtained predictions on existence ranges and instabilities are tested via direct numerical simulations that are also used to investigate a branch of time-periodic behavior (corresponding to pearling-coalescence cycles) which emerges at a global instability, the related hysteresis in behavior and a period-doubling cascade. The non-trivial oscillatory behavior close to a Hopf bifurcation of drops with a finite-length tail is also studied. Finally, it ...
Continuation and Bifurcation software in MATLAB
Ravnås, Eirik
2008-01-01
This article contains discussions of the algorithms used for the construction of the continuation software implemented in this thesis. The aim of the continuation was to be able to perform continuation of equilibria and periodic solutions originating from a Hopf bifurcation point. Algorithms for detection of simple branch points, folds, and Hopf bifurcation points have also been implemented. Some considerations are made with regard to optimization, and two schemes for mesh adaptation of perio...
Stability and bifurcation of mutual system with time delay
International Nuclear Information System (INIS)
In this paper, we study the stability and bifurcation in a mutual model with a delay τ, where τ is regarded as a parameter. It is found that there are stability switches, and Hopf bifurcation occur when the delay τ passes through a sequence of critical values. A formula for determining the direction of the Hopf bifurcation and the stability of bifurcating periodic solutions in the first bifurcation value is given using the normal form method and center manifold theorem
Bifurcation Analysis of the Wound Rotor Induction Motor
Salas-Cabrera, R.; Hernandez-Colin, A.; Roman-Flores, J.; Salas-Cabrera, N.
This work deals with the bifurcation phenomena that occur during the open-loop operation of a single-fed three-phase wound rotor induction motor. This paper demonstrates the occurrence of saddle-node bifurcation, hysteresis, supercritical saddle-node bifurcation, cusp and Hopf bifurcation during the individual operation of this electromechanical system. Some experimental results associated with the bifurcation phenomena are presented.
... version AMERICAN THORACIC SOCIETY Patient Information Series Arterial Catheterization An arterial catheter is a thin, hollow tube ... PHYSICIANS: AND COPY Why Do I Need Arterial Catheterization? Common reasons an arterial catheterization is done include: ■ ...
Endovascular management of giant middle cerebral artery aneurysms
Huang, Lei; Cao, Wenjie; Ge, Liang; Lu, Gang; Wan, Jun; Zhang, Lei; Gu, Weijin; Zhang, Xiaolong; Geng, Daoying
2015-01-01
Background: This article reported the experience of endovascular treatment in giant middle cerebral artery (MCA) aneurysms with parent artery occlusion or stent-assisted coiling. Material and methods: Eleven consecutive patients with giant MCA aneurysms were included. The aneurysms predominantly involved the M1 segment in two cases, bifurcation in four cases, and M2 in five cases. Four M2 fusiform aneurysms were treated with parent artery sacrifice after balloon occlusion test. The seven unru...
Successful Reconstruction of Asymptomatic Bilateral External Carotid Artery Aneurysms.
Loja, Melissa N; Pevec, William C
2016-04-01
True aneurysms of the external carotid artery (ECA) are extremely rare with an unknown incidence and natural history. We present the successful operative management of an asymptomatic 65-year-old man found to have bilateral internal carotid artery stenosis and bilateral ECA aneurysms. His bilateral carotid arteries were reconstructed with bifurcated interposition grafts in a staged fashion. The patient recovered without sequelae and continues to be asymptomatic 1 year after reconstruction. We present the operative management of this rare case. PMID:26802292
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The bidirectional associative memory (BAM) neural network with four neurons and two delays is considered in the present paper.A linear stability analysis for the trivial equilibrium is firstly employed to provide a possible critical point at which a zero and a pair of pure imaginary eigenvalues occur in the corresponding characteristic equation.A fold-Hopf bifurcation is proved to happen at this critical point by the nonlinear analysis.The coupling strength and the delay are considered as bifurcation parameters to investigate the dynamical behaviors derived from the fold-Hopf bifurcation.Various dynamical behaviours are qualitatively classified in the neighbourhood of the fold-Hopf bifurcation point by using the center manifold reduction (CMR) together with the normal form.The bifurcating periodic solutions are expressed analytically in an approximate form.The validity of the results is shown by their consistency with the numerical simulation.
Ternary choices in repeated games and border collision bifurcations
International Nuclear Information System (INIS)
Highlights: ► We extend a model of binary choices with externalities to include more alternatives. ► Introducing one more option affects the complexity of the dynamics. ► We find bifurcation structures which where impossible to observe in binary choices. ► A ternary choice cannot simply be considered as a binary choice plus one. - Abstract: Several recent contributions formalize and analyze binary choices games with externalities as those described by Schelling. Nevertheless, in the real world choices are not always binary, and players have often to decide among more than two alternatives. These kinds of interactions are examined in game theory where, starting from the well known rock-paper-scissor game, several other kinds of strategic interactions involving more than two choices are examined. In this paper we investigate how the dynamics evolve introducing one more option in binary choice games with externalities. The dynamics we obtain are always in a stable regime, that is, the structurally stable dynamics are only attracting cycles, but of any possible positive integer as period. We show that, depending on the structure of the game, the dynamics can be quite different from those existing when considering binary choices. The bifurcation structure, due to border collisions, is explained, showing the existence of so-called big-bang bifurcation points.
Homoclinic bifurcations in low-Prandtl-number Rayleigh-B\\'{e}nard convection with uniform rotation
Maity, P; Pal, P
2014-01-01
We present results of direct numerical simulations on homoclinic gluing and ungluing bifurcations in low-Prandtl-number ($ 0 \\leq Pr \\leq 0.025 $) Rayleigh-B\\'{e}nard system rotating slowly and uniformly about a vertical axis. We have performed simulations with \\textit{stress-free} top and bottom boundaries for several values of Taylor number ($5 \\leq Ta \\leq 50$) near the instability onset. We observe a single homoclinic ungluing bifurcation, marked by the spontaneous breaking of a larger limit cycle into two limit cycles with the variation of the reduced Rayleigh number $r$ for smaller values of $Ta (< 25)$. A pair of homoclinic bifurcations, instead of one bifurcation, is observed with variation of $r$ for slightly higher values of $Ta$ ($25 \\leq Ta \\leq 50$) in the same fluid dynamical system. The variation of the bifurcation threshold with $Ta$ is also investigated. We have also constructed a low-dimensional model which qualitatively captures the dynamics of the system near the homoclinic bifurcations...
Emergence of the bifurcation structure of a Langmuir–Blodgett transfer model
Köpf, Michael H
2014-10-07
© 2014 IOP Publishing Ltd & London Mathematical Society. We explore the bifurcation structure of a modified Cahn-Hilliard equation that describes a system that may undergo a first-order phase transition and is kept permanently out of equilibrium by a lateral driving. This forms a simple model, e.g., for the deposition of stripe patterns of different phases of surfactant molecules through Langmuir-Blodgett transfer. Employing continuation techniques the bifurcation structure is numerically investigated using the non-dimensional transfer velocity as the main control parameter. It is found that the snaking structure of steady front states is intertwined with a large number of branches of time-periodic solutions that emerge from Hopf or period-doubling bifurcations and end in global bifurcations (sniper and homoclinic). Overall the bifurcation diagram has a harp-like appearance. This is complemented by a two-parameter study in non-dimensional transfer velocity and domain size (as a measure of the distance to the phase transition threshold) that elucidates through which local and global codimension 2 bifurcations the entire harp-like structure emerges.
Bifurcations and sudden current change in ensembles of classically chaotic ratchets
Kenfack, Anatole; Sweetnam, Sean M.; Pattanayak, Arjendu K.
2007-05-01
Mateos [Phys. Rev. Lett. 84, 258 (2000)] conjectured that current reversal in a classical deterministic ratchet is associated with bifurcations from chaotic to periodic regimes. This is based on the comparison of the current and the bifurcation diagram as a function of a given parameter for a periodic asymmetric potential. Barbi and Salerno [Phys. Rev. E 62, 1988 (2000)] have further investigated this claim and argue that, contrary to Mateos’ claim, current reversals can occur also in the absence of bifurcations. Barbi and Salerno’s studies are based on the dynamics of one particle rather than the statistical mechanics of an ensemble of particles moving in the chaotic system. The behavior of ensembles can be quite different, depending upon their characteristics, which leaves their results open to question. In this paper we present results from studies showing how the current depends on the details of the ensemble used to generate it, as well as conditions for convergent behavior (that is, independent of the details of the ensemble). We are then able to present the converged current as a function of parameters, in the same system as Mateos as well as Barbi and Salerno. We show evidence for current reversal without bifurcation, as well as bifurcation without current reversal. We conjecture that it is appropriate to correlate abrupt changes in the current with bifurcation, rather than current reversals, and show numerical evidence for our claims.
Directory of Open Access Journals (Sweden)
Yan Zhang
2014-01-01
Full Text Available We revisit a homogeneous reaction-diffusion Turing model subject to the Neumann boundary conditions in the one-dimensional spatial domain. With the help of the Hopf bifurcation theory applicable to the reaction-diffusion equations, we are capable of proving the existence of Hopf bifurcations, which suggests the existence of spatially homogeneous and nonhomogeneous periodic solutions of this particular system. In particular, we also prove that the spatial homogeneous periodic solutions bifurcating from the smallest Hopf bifurcation point of the system are always unstable. This together with the instability results of the spatially nonhomogeneous periodic solutions by Yi et al., 2009, indicates that, in this model, all the oscillatory patterns from Hopf bifurcations are unstable.
Retinal Artery Occlusion Treatment with Hyperbaric Oxygen
Directory of Open Access Journals (Sweden)
Harun Cakmak
2016-01-01
Full Text Available Retinal artery occlusion is one of the vision-threating emergency situations in ophthalmology. In this paper, a case of retinal artery occlusion is presented. Fifty seven year- old female patient presented with a sudden onset visual loss in her left eye. Best corrected visual acuity (BCVA levels were 1.0 and 0.7 in the right and left eye, respectiveley. Dilated fundus examination revealed no pathological finding in the right eye. Whereas calcified plaque was seen in upper arquat artery bifurcation in the left eye. Pallorness with retinal edema was seen in this arterial trace. Retinal artery occlusion was diagnosed and patient was referred for hyperbaric oxygen therapy. After a total of 20 sessions of hyperbaric oxygen therapy, the calcified plaques disappeared and her BCVA increased to 20/20. Hyperbaric oxygen treatment is vision-saving method which should be considered in retinal artery occlusion.
Modeling of blood flow in arterial trees.
Anor, Tomer; Grinberg, Leopold; Baek, Hyoungsu; Madsen, Joseph R; Jayaraman, Mahesh V; Karniadakis, George E
2010-01-01
Advances in computational methods and medical imaging techniques have enabled accurate simulations of subject-specific blood flows at the level of individual blood cell and in complex arterial networks. While in the past, we were limited to simulations with one arterial bifurcation, the current state-of-the-art is simulations of arterial networks consisting of hundreds of arteries. In this paper, we review the advances in methods for vascular flow simulations in large arterial trees. We discuss alternative approaches and validity of various assumptions often made to simplify the modeling. To highlight the similarities and discrepancies of data computed with different models, computationally intensive three-dimensional (3D) and inexpensive one-dimensional (1D) flow simulations in very large arterial networks are employed. Finally, we discuss the possibilities, challenges, and limitations of the computational methods for predicting outcomes of therapeutic interventions for individual patients. PMID:20836052
Xu, Jinhu; Zhou, Yicang
2016-04-01
A within-host viral infection model with both virus-to-cell and cell-to-cell transmissions and time delay in immune response is investigated. Mathematical analysis shows that delay may destabilize the infected steady state and lead to Hopf bifurcation. Moreover, the direction of the Hopf bifurcation and the stability of the periodic solutions are investigated by normal form and center manifold theory. Numerical simulations are done to explore the rich dynamics, including stability switches, Hopf bifurcations, and chaotic oscillations. PMID:27105992
Huang, Er-Wen; Peng, Long-Yun; Zheng, Jin-Xiang; Wang, Dan; Tan, Xiao-Hong; Yang, Zhong-Yi; Li, Xue-Mei; Wu, Qiu-Ping; Tang, Shuang-Bo; Luo, Bin; Quan, Li; Liu, Shui-Ping; Liu, Xiao-Shan; Li, Zhao-Hui; Shi, He; Lv, Guo-Li; Zhao, Jian; Liu, Chao; Cheng, Jian-Ding
2016-05-01
A large-scale meta-analysis of 14 genome-wide association studies has identified and replicated a series of susceptibility polymorphisms for coronary artery disease (CAD) in European ancestry populations, but evidences for the associations of these loci with CAD in other ethnicities remain lacking. Herein we investigated the associations between ten (rs579459, rs12413409, rs964184, rs4773144, rs2895811, rs3825807, rs216172, rs12936587, rs46522 and rs3798220) of these loci and CAD in Southern Han Chinese (CHS). Genotyping was performed in 1716 CAD patients and 1572 controls using mass spectrography. Both allelic and genotypic associations of rs964184, rs2895811 and rs3798220 with CAD were significant, regardless of adjustment for covariates of gender, age, hypertension, type 2 diabetes, blood lipid profiles and smoking. Significant association of rs12413409 was initially not observed, but after the adjustment for the covariates, both allelic and genotypic associations were identified as significant. Neither allelic nor genotypic association of the other six polymorphisms with CAD was significant regardless of the adjustment. Our results indicated that four loci of the total 10 were associated with CAD in CHS. Therefore, some of the CAD-related loci in European ancestry populations are indeed susceptibility loci for the risk of CAD in Han Chinese. PMID:26740236
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E. V. Nikolaeva
2015-01-01
Full Text Available Pulmonary arterial hypertension (PAH associated with systemic connective tissue diseases (SCTD is a poor prognostic manifestation of the latter that result in death if untreated. The invasive determination of hemodynamic parameters is prominent in diagnosing the disease and determining its treatment policy and prognosis.Objective: to analyze the results of catheterization in PAH-SCTD patients admitted to the V.A. Nasonova Research Institute of Rheumatology.Subjects and methods. The investigation included 59 patients admitted to the V.A. Nasonova Research Institute of Rheumatology from September 2009 to September 2014. PAH was diagnosed in accordance with the conventional guidelines. All the patients underwent right heart and pulmonary artery (PA catheterization at the diagnosis and over time during treatment.Results and discussion. All the patients included in the trial met the pre-capillary pulmonary hypertension (PH criteria: mean pulmonary artery pressure (MPAP ≥25 mm Hg; and PA wedge pressure (PAWP <15 mm Hg. The exclusion of other causes of PH (pulmonary fibrosis, left heart disease, and thromboembolism, as well as a high transpulmonary pressure gradient >15 mm Hg and pulmonary vascular resistance (PVR >3 Wood units could diagnose PAH in all our patients. There was a statistically highly significant association between pathological hemodynamic changes and functional class (FC. FC was found to be most closely correlated with right atrial pressure (RAP, cardiac output (CO, PVR, and cardiac index (CI. Among the most common manifestations of heart failure, only the presence of peripheral edemas was associated with worse hemodynamic parameters in PAH. It should be noted that out of two biomarkers (N-terminal pro-brain natriuretic peptide and uric acid, the former is largely related to the magnitude of changes in hemodynamic factors. The critical values of hemodynamic parameters were due to extreme edema – anasarca (RAP >17 mm Hg
Crisis bifurcations in plane Poiseuille flow
Zammert, Stefan
2015-01-01
Direct numerical simulations of transitional plane Poiseuille flow in a mirror-symmetric subspace reveal several interior and exterior crisis bifurcations. They appear in the upper branch that emerges in a saddle-node bifurcation near $Re_{SN}=641$ and then undergoes several bifurcations into a chaotic attractor. Near $Re_{XC}=785.95$ the attractor collides with the lower-branch state and turns into a chaotic saddle in a exterior crisis, with a characteristic $(Re-Re_{XC})^{-\\delta}$ variation in lifetimes. For intermediate Reynolds numbers, the attractor undergoes several interior crises, in which new states appear and intermittent behavior can be observed. They contribute to increasing the complexity of the dynamics and to a more dense coverage of state space. The exterior crisis marks the onset of transient turbulence in this subspace of plane Poiseuille flow.
Emergence of Network Bifurcation Triggered by Entanglement
Yong, Xi; Gao, Xun; Li, Angsheng
2016-01-01
In many non-linear systems, such as plasma oscillation, boson condensation, chemical reaction, and even predatory-prey oscillation, the coarse-grained dynamics are governed by an equation containing anti-symmetric transitions, known as the anti-symmetric Lotka-Volterra (ALV) equations. In this work, we prove the existence of a novel bifurcation mechanism for the ALV equations, where the equilibrium state can be drastically changed by flipping the stability of a pair of fixed points. As an application, we focus on the implications of the bifurcation mechanism for evolutionary networks; we found that the bifurcation point can be determined quantitatively by the quantum entanglement in the microscopic interactions. The equilibrium state can be critically changed from one type of global demographic condensation to another state that supports global cooperation for homogeneous networks. In other words, our results indicate that there exist a class of many-body systems where the macroscopic properties are, to some ...
Stolzenburg, Nicola; Breinl, Janni; Bienek, Stephanie; Jaguszewski, Milosz; Löchel, Melanie; Taupitz, Matthias; Speck, Ulrich; Wagner, Susanne; Schnorr, Jörg
2016-01-01
Purpose Beyond antiproliferative properties, paclitaxel exhibits anti-inflammatory activity, which might be beneficial in the local treatment of nonocclusive coronary artery disease. Paclitaxel release and tissue concentrations after paclitaxel-coated balloon treatment using different pressures have not been investigated so far. The aim of the study was to investigate in an atherosclerotic rabbit model whether drug transfer from paclitaxel-coated balloons into the vessel wall is affected by t...
Lassen, Jens Flensted; Holm, Niels Ramsing; Banning, Adrian; Burzotta, Francesco; Lefèvre, Thierry; Chieffo, Alaide; Hildick-Smith, David; Louvard, Yves; Stankovic, Goran
2016-05-17
Coronary bifurcations are involved in 15-20% of all percutaneous coronary interventions (PCI) and remain one of the most challenging lesions in interventional cardiology in terms of procedural success rate as well as long-term cardiac events. The optimal management of bifurcation lesions is, despite a fast growing body of scientific literature, the subject of considerable debate. The European Bifurcation Club (EBC) was initiated in 2004 to support a continuous overview of the field, and aims to facilitate a scientific discussion and an exchange of ideas on the management of bifurcation disease. The EBC hosts an annual, compact meeting, dedicated to bifurcations, which brings together physicians, engineers, biologists, physicists, epidemiologists and statisticians for detailed discussions. Every meeting is finalised with a consensus statement which reflects the unique opportunity of combining the opinions of interventional cardiologists with the opinions of a large variety of other scientists on bifurcation management. The present 11th EBC consensus document represents the summary of the up-to-date EBC consensus and recommendations. It points to the fact that there is a multitude of strategies and approaches to bifurcation stenting within the provisional strategy and in the different two-stent strategies. The main EBC recommendation for PCI of bifurcation lesions remains to use main vessel (MV) stenting with a proximal optimisation technique (POT) and provisional side branch (SB) stenting as a preferred approach. The consensus document covers a moving target. Much more scientific work is needed in non-left main (LM) and LM bifurcation lesions for continuous improvement of the outcome of our patients. PMID:27173860
CAVITATION BIFURCATION FOR COMPRESSIBLE ANISOTROPIC HYPERELASTIC MATERIALS
Institute of Scientific and Technical Information of China (English)
ChengChangjun; RenJiusheng
2004-01-01
The effect of material anisotropy on the bifurcation for void tormation in anisotropic compressible hyperelastic materials is examined. Numerical solutions are obtained in an anisotropic sphere, whose material is transversely isotropic in the radial direction. It is shown that the bifurcation may occur either to the right or to the left, depending on the degree of material anisotropy. The deformation and stress contribution in the sphere before cavitation are different from those after cavitation. The stability of solutions is discussed through a comparison of energy.
Bifurcation of Jovian magnetotail current sheet
Directory of Open Access Journals (Sweden)
P. L. Israelevich
2006-07-01
Full Text Available Multiple crossings of the magnetotail current sheet by a single spacecraft give the possibility to distinguish between two types of electric current density distribution: single-peaked (Harris type current layer and double-peaked (bifurcated current sheet. Magnetic field measurements in the Jovian magnetic tail by Voyager-2 reveal bifurcation of the tail current sheet. The electric current density possesses a minimum at the point of the B_{x}-component reversal and two maxima at the distance where the magnetic field strength reaches 50% of its value in the tail lobe.
Split Right Coronary Artery Its Definition and Its Territory
Sawaya, Fadi J.; Sawaya, Jaber I.; Angelini, Paolo
2008-01-01
We report here, for perhaps the 1st time in the English-language literature, the extent of the territory fed by the anterior bifurcation of the (anomalous) split right coronary artery (RCA). A 64-year-old man presented with an occlusion of the anterior bifurcation of a split RCA—which resulted in an infarct that involved both the inferoseptal left ventricular wall and the anterior right ventricular free wall. Split RCA is the same anomaly as the improperly named “double right coronary artery....
Bifurcations of a class of singular biological economic models
International Nuclear Information System (INIS)
This paper studies systematically a prey-predator singular biological economic model with time delay. It shows that this model exhibits two bifurcation phenomena when the economic profit is zero. One is transcritical bifurcation which changes the stability of the system, and the other is singular induced bifurcation which indicates that zero economic profit brings impulse, i.e., rapid expansion of the population in biological explanation. On the other hand, if the economic profit is positive, at a critical value of bifurcation parameter, the system undergoes a Hopf bifurcation, i.e., the increase of delay destabilizes the system and bifurcates into small amplitude periodic solution. Finally, by using Matlab software, numerical simulations illustrate the effectiveness of the results obtained here. In addition, we study numerically that the system undergoes a saddle-node bifurcation when the bifurcation parameter goes through critical value of positive economic profit.
Codimension-2 bifurcations of the Kaldor model of business cycle
International Nuclear Information System (INIS)
Research highlights: → The conditions are given such that the characteristic equation may have purely imaginary roots and double zero roots. → Purely imaginary roots lead us to study Hopf and Bautin bifurcations and to calculate the first and second Lyapunov coefficients. → Double zero roots lead us to study Bogdanov-Takens (BT) bifurcation. → Bifurcation diagrams for Bautin and BT bifurcations are obtained by using the normal form theory. - Abstract: In this paper, complete analysis is presented to study codimension-2 bifurcations for the nonlinear Kaldor model of business cycle. Sufficient conditions are given for the model to demonstrate Bautin and Bogdanov-Takens (BT) bifurcations. By computing the first and second Lyapunov coefficients and performing nonlinear transformation, the normal forms are derived to obtain the bifurcation diagrams such as Hopf, homoclinic and double limit cycle bifurcations. Some examples are given to confirm the theoretical results.
International Nuclear Information System (INIS)
To avoid gastric complications when we perform transcatheter treatment via left hepatic artery, we analyzed the topography of ALGA (accessory left gastric artery) by left hepatic arteriography and CT angiography from left hepatic artery. Six hundred seventy eight cases of CT angiography were performed between 1995 and 2000. Among them, selective left hepatic arteriography was done in 85 cases. We analyzed the frequency and the course of ALGA on the hepatic angiogram and CT angiogram. ALGA were identified in eighteen (21.2 %) of the 85 cases. We classified them into eleven cases of the proximal type and six cases of the distal type. When ALGA bifurcated from the left hepatic artery very close to the bifurcation of A2 (dorsolateral branch) and A3 (ventrolateral branch), we classified them as the distal type on hepatic angiogram. On the other hand, when ALGA bifurcated from the left hepatic artery apart from the bifurcation of A2 and A3 they were classified as the proximal type. In one rare case ALGA originated from the dorsolateral branch of the left hepatic artery. ALGA were classified as the distal and proximal types. Distal type of ALGA often overlapped dorsolateral branch of the left hepatic artery, and it was sometimes difficult to notice the existence of them. We should check the existence of ALGA on the arterial phase of dynamic CT before we plan to make a transcatheter treatment from the left hepatic artery. Then we can avoid gastric complications caused by a transcatheter treatment from the left hepatic artery. (author)
Bifurcation Analysis of a Discrete Logistic System with Feedback Control
Institute of Scientific and Technical Information of China (English)
WU Dai-yong
2015-01-01
The paper studies the dynamical behaviors of a discrete Logistic system with feedback control. The system undergoes Flip bifurcation and Hopf bifurcation by using the center manifold theorem and the bifurcation theory. Numerical simulations not only illustrate our results, but also exhibit the complex dynamical behaviors of the system, such as the period-doubling bifurcation in periods 2, 4, 8 and 16, and quasi-periodic orbits and chaotic sets.
Delay-induced multistability near a global bifurcation
Hizanidis, J.; Aust, R.; Schoell, E.
2007-01-01
We study the effect of a time-delayed feedback within a generic model for a saddle-node bifurcation on a limit cycle. Without delay the only attractor below this global bifurcation is a stable node. Delay renders the phase space infinite-dimensional and creates multistability of periodic orbits and the fixed point. Homoclinic bifurcations, period-doubling and saddle-node bifurcations of limit cycles are found in accordance with Shilnikov's theorems.
Nomura, Yasuyuki; Saito, Satoshi; Ishiwata, Ryosuke; Sugiyama, Yuki
2016-01-01
A dissipative system with asymmetric interaction, the optimal velocity model, shows a Hopf bifurcation concerned with the transition from a homogeneous motion to the formation of a moving cluster, such as the emergence of a traffic jam. We investigate the properties of Hopf bifurcation depending on the particle density, using the dynamical system for the traveling cluster solution of the continuum system derived from the original discrete system of particles. The Hopf bifurcation is revealed as a subcritical one, and the property explains well the specific phenomena in highway traffic: the metastability of jamming transition and the hysteresis effect in the relation of car density and flow rate. PMID:26871081
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Zhihui Wang
2013-01-01
Full Text Available This study investigates the frequency bifurcation phenomena of a typical voltage-fed resonant converter based on mutual induction model. It is found that the Zero Current Switching (ZCS operating frequency has the bifurcation region as the coupling coefficient varies due to the distance. The expression for the bifurcation boundary is derived and analyzed. Such results are very useful for guiding the design of practical Inductively Coupled Power Transfer (ICPT systems especially in applications which have the requirement of the position flexibility. Analytical results are verified both via MATLAB simulations and experimental prototype.
... the main arteries in the forearm (radial and ulnar arteries). The procedure is done as follows: The ... Arteries also have thicker walls and have more nerves. When the needle is inserted, there may be ...
Stability and Hopf Bifurcation in the Watt Governor System
Sotomayor, Jorge; Mello, Luis Fernando; Braga, Denis de Carvalho
2006-01-01
In this paper we study the Lyapunov stability and Hopf bifurcation in a system coupling a Watt-centrifugal-governor with a steam-engine. Sufficient conditions for the stability of the equilibrium state in terms of the physical parameters and of the bifurcating periodic orbit at most critical parameters on the bifurcation surface are given.
The Bifurcations of Traveling Wave Solutions of the Kundu Equation
Yating Yi; Zhengrong Liu
2013-01-01
We use the bifurcation method of dynamical systems to study the bifurcations of traveling wave solutions for the Kundu equation. Various explicit traveling wave solutions and their bifurcations are obtained. Via some special phase orbits, we obtain some new explicit traveling wave solutions. Our work extends some previous results.
Bifurcation structure of a model of bursting pancreatic cells
DEFF Research Database (Denmark)
Mosekilde, Erik; Lading, B.; Yanchuk, S.; Maistrenko, Y.
One- and two-dimensional bifurcation studies of a prototypic model of bursting oscillations in pancreatic P-cells reveal a squid-formed area of chaotic dynamics in the parameter plane, with period-doubling bifurcations on one side of the arms and saddle-node bifurcations on the other. The...
NUMERICAL HOPF BIFURCATION OF DELAY-DIFFERENTIAL EQUATIONS
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
In this paper we consider the numerical solution of some delay differential equations undergoing a Hopf bifurcation. We prove that if the delay differential equations have a Hopf bifurcation point atλ=λ*, then the numerical solution of the equation also has a Hopf bifurcation point atλh =λ* + O(h).
Equilibrium points and bifurcation control of a chaotic system
Institute of Scientific and Technical Information of China (English)
Liang Cui-Xiang; Tang Jia-Shi
2008-01-01
Based on the Routh-Hurwitz criterion,this paper investigates the stability of a new chaotic system.State feedback controllers are designed to control the chaotic system to the unsteady equilibrium points and limit cycle.Theoretical analyses give the range of value of control parameters to stabilize the unsteady equilibrium points of the chaotic system and its critical parameter for generating Hopf bifurcation.Certain nP periodic orbits can be stabilized by parameter adjustment.Numerical simulations indicate that the method can effectively guide the system trajectories to unsteady equilibrium points and periodic orbits.
One-dimensional map lattices: Synchronization, bifurcations, and chaotic structures
DEFF Research Database (Denmark)
Belykh, Vladimir N.; Mosekilde, Erik
1996-01-01
The paper presents a qualitative analysis of coupled map lattices (CMLs) for the case of arbitrary nonlinearity of the local map and with space-shift as well as diffusion coupling. The effect of synchronization where, independently of the initial conditions, all elements of a CML acquire uniform...... dynamics is investigated and stable chaotic time behaviors, steady structures, and traveling waves are described. Finally, the bifurcations occurring under the transition from spatiotemporal chaos to chaotic synchronization and the peculiarities of CMLs with specific symmetries are discussed....
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Alex Lederman
2009-09-01
Full Text Available Treating narrow arteries and their bifurcations is a major challenge to the endovascular surgeon. We describe a new endovascular technique that was used to treat a narrow aorta and that may also be used to preserve other bifurcations. Using three straight stents may enable the endovascular surgeon to treat bifurcation while maintaining flow to both distal arteries.O tratamento de artérias de pequeno calibre e suas bifurcações é um grande desafio para o cirurgião endovascular. Descrevemos uma nova técnica endovascular que foi usada no tratamento de uma aorta de pequeno calibre e que também pode ser usada para preservar outras bifurcações. O uso de três stents retos pode permitir ao cirurgião endovascular o tratamento de bifurcação mantendo o fluxo em ambas as artérias distais.
Wen, Jun; Liu, Kai; Khoshmanesh, Khashayar; Jiang, Wentao; Zheng, Tinghui
2015-01-01
The classic single-phase Newtonian blood flow model ignores the motion of red blood cells (RBCs) and their interaction with plasma. To address these issues, we adopted a multiphase non-Newtonian model to carry out a comparative study between a helical artery bypass graft (ABG) and a conventional ABG in which the blood flow is composed of plasma and RBCs. The investigation focused on the mechanism of RBC buildup in an ABG but the haemodynamic parameters obtained by single-phase and multiphase models were also compared. The aggregation of RBCs along the inside wall of a conventional ABG and at the heel of its distal anastomosis was predicted while a poor aggregation was observed along the helical ABG. In addition, RBCs were observed to gradually sediment along the gravity direction. However, the computed haemodynamic parameters by multiphase model qualitatively agreed well with those by single-phase model. It was concluded that (1) the single-phase computational fluid dynamics (CFD) is reasonable to do the computation of haemodynamic parameters in ABGs; (2) secondary flow does not definitely produce buildup of RBCs in the inside curvature, its configuration played an important role in the movement of RBCs and the dominating one-way rotating flow in a helical ABG guaranteed no buildup of RBCs on its inside wall and (3) gravity direction is important for the movement of RBCs which may help to explain why doing exercise is good for human health. This study helps to shed light on the migration of RBCs in ABGs, which cannot be explored by single-phase CFD models, and provides more understanding of the underlying flow mechanism for ABG failure. PMID:24156553
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Shaoyong Li
2013-01-01
Full Text Available Using bifurcation method of dynamical systems, we investigate the nonlinear waves for the generalized Zakharov equations utt-cs2uxx=β(|E|2xx, iEt+αExx-δ1uE+δ2|E|2E+δ3|E|4E=0, where α,β,δ1,δ2,δ3, and cs are real parameters, E=E(x,t is a complex function, and u=u(x,t is a real function. We obtain the following results. (i Three types of explicit expressions of nonlinear waves are obtained, that is, the fractional expressions, the trigonometric expressions, and the exp-function expressions. (ii Under different parameter conditions, these expressions represent symmetric and antisymmetric solitary waves, kink and antikink waves, symmetric periodic and periodic-blow-up waves, and 1-blow-up and 2-blow-up waves. We point out that there are two sets of kink waves which are called tall-kink waves and low-kink waves, respectively. (iii Five kinds of interesting bifurcation phenomena are revealed. The first kind is that the 1-blow-up waves can be bifurcated from the periodic-blow-up and 2-blow-up waves. The second kind is that the 2-blow-up waves can be bifurcated from the periodic-blow-up waves. The third kind is that the symmetric solitary waves can be bifurcated from the symmetric periodic waves. The fourth kind is that the low-kink waves can be bifurcated from four types of nonlinear waves, the symmetric solitary waves, the 1-blow-up waves, the tall-kink waves, and the antisymmetric solitary waves. The fifth kind is that the tall-kink waves can be bifurcated from the symmetric periodic waves. We also show that the exp-function expressions include some results given by pioneers.
HOMOCLINIC TWIST BIFURCATIONS WITH Z(2) SYMMETRY
ARONSON, DG; VANGILS, SA; KRUPA, M
1994-01-01
We analyze bifurcations occurring in the vicinity of a homoclinic twist point for a generic two-parameter family of Z2 equivariant ODEs in four dimensions. The results are compared with numerical results for a system of two coupled Josephson junctions with pure capacitive load.
Bifurcation structure of successive torus doubling
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Sekikawa, Munehisa [Department of Information Science, Faculty of Engineering, Utsunomiya University (Japan)]. E-mail: muse@aihara.jst.go.jp; Inaba, Naohiko [Department of Information Science, Faculty of Engineering, Utsunomiya University (Japan)]. E-mail: inaba@is.utsunomiya-u.ac.jp; Yoshinaga, Tetsuya [Department of Radiologic Science and Engineering, School of Health Sciences, The University of Tokushima (Japan)]. E-mail: yosinaga@medsci.tokushima-u.ac.jp; Tsubouchi, Takashi [Institute of Engineering Mechanics and Systems, University of Tsukuba (Japan)]. E-mail: tsubo@esys.tsukuba.ac.jp
2006-01-02
The authors discuss the 'embryology' of successive torus doubling via the bifurcation theory, and assert that the coupled map of a logistic map and a circle map has a structure capable of generating infinite number of torus doublings.
Higher division of popliteal artery: a case report
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Prakash Babu Billakanti
2014-08-01
Full Text Available During the routine dissection of anatomy in an adult male cadaver at the department of anatomy, Manipal University, Manipal, higher division of popliteal artery was observed on the right side. This artery divided proximal to upper border of popliteus muscle into anterior and posterior tibial arteries. Inferomedial genicular artery which is usually a branch of popliteal artery was found to be arising from anterior tibial artery. However arterial branching pattern and point of bifurcation of popliteal artery on the left side were usual. The knowledge of these variations will be useful for angiography or various surgical approaches during knee joint surgery. [Int J Res Med Sci 2014; 2(4.000: 1723-1725
Directory of Open Access Journals (Sweden)
Hunor Santha
2012-01-01
Full Text Available This paper describes a three-layer head phantom with artificial pulsating arteries at five different depths (1.2 mm, 3.7 mm, 6.8 mm, 9.6 mm and 11.8 mm. The structure enables formation of spatially and temporally varying tissue properties similar to those of living tissues. In our experiment, pressure pulses were generated in the arteries by an electronically controlled pump. The physical and optical parameters of the layers and the liquid in the artificial arteries were similar to those of real tissues and blood. The amplitude of the pulsating component of the light returning from the phantom tissues was measured at each artery depth mentioned above. The build-up of the in-house-developed pulse oximeter used for performing the measurements and the physical layout of the measuring head are described. The radiant flux generated by the LED on the measuring head was measured to be 1.8 mW at 910 nm. The backscattered radiant flux was measured, and found to be 0.46 nW (0.26 ppm, 0.55 nW (0.31 ppm, and 0.18 nW (0.10 ppm for the 1.2 mm, 3.7 mm and 6.8 mm arteries, respectively. In the case of the 9.6 mm and 11.8 mm arteries, useful measurement data were not obtained owing to weak signals. We simulated the phantom with the arteries at the above-mentioned five depths and at two additional ones (2.5 mm and 5.3 mm in depth using the Monte Carlo method. The measurement results were verified by the simulation results. We concluded that in case of 11 mm source-detector separation the arteries at a depth of about 2.5 mm generate the strongest pulse oximeter signal level in a tissue system comprising three layers of thicknesses: 1.5 mm (skin, 5.0 mm (skull, and > 50 mm (brain.
International Nuclear Information System (INIS)
Objective: To investigate variation in the carotid bifurcation geometry of adults of different age by MR angiography images combining image post-processing technique. Methods: Images of the carotid bifurcations of 27 young adults (≤40 years old) and 30 older subjects ( > 40 years old) were acquired via contrast-enhanced MR angiography. Three dimensional (3D) geometries of the bifurcations were reconstructed and geometric parameters were measured by post-processing technique. Results: The geometric parameters of the young versus older groups were as follows: bifurcation angle (70.268 degree± 16.050 degree versus 58.857 degree±13.294 degree), ICA angle (36.893 degree±11.837 degree versus 30.275 degree±9.533 degree), ICA planarity (6.453 degree ± 5.009 degree versus 6.263 degree ±4.250 degree), CCA tortuosity (0.023±0.011 versus 0.014± 0.005), ICA tortuosity (0.070±0.042 versus 0.046±0.022), ICA/CCA diameter ratio (0.693± 0.132 versus 0.728±0.106), ECA/CCA diameter ratio (0.750±0.123 versus 0.809±0.122), ECA/ ICA diameter ratio (1.103±0.201 versus 1.127±0.195), bifurcation area ratio (1.057±0.281 versus 1.291±0.252). There was significant statistical difference between young group and older group in-bifurcation angle, ICA angle, CCA tortuosity, ICA tortuosity, ECA/CCA and bifurcation area ratio (F= 17.16, 11.74, 23.02, 13.38, 6.54, 22.80, respectively, P<0.05). Conclusions: MR angiography images combined with image post-processing technique can reconstruct 3D carotid bifurcation geometry and measure the geometric parameters of carotid bifurcation in vivo individually. It provides a new and convenient method to investigate the relationship of vascular geometry and flow condition with atherosclerotic pathological changes. (authors)
Althouse, Andrew D.; Abbott, J . Dawn; Forker, Alan D.; Bertolet, Marnie; Barinas-Mitchell, Emma; Thurston, Rebecca C.; Mulukutla, Suresh; Aboyans, Victor; Brooks, Maria Mori; ,
2014-01-01
OBJECTIVE The aim of this article was to define risk factors for incidence of peripheral arterial disease (PAD) in a large cohort of patients with type 2 diabetes mellitus (T2DM), overall and within the context of differing glycemic control strategies. RESEARCH DESIGN AND METHODS The Bypass Angioplasty Revascularization Investigation in Type 2 Diabetes (BARI 2D) randomized controlled trial assigned participants to insulin-sensitizing (IS) therapy versus insulin-providing (IP) therapy. A total...
Tankó, László B; Mikkelsen, Erich O; Simonsen, Ulf
1999-01-01
The aim of this study was to investigate whether the balloon-based impedance planimetry technique could be a useful tool in endothelium-dependent investigations. Porcine large coronary arteries contracted with prostaglandin F2α (PGF2α, 10 μM) did not relax to bradykinin (0.1 nM–0.1 μM), but did relax to sodium nitroprusside (SNP, 10 μM). However, after eversion of the segments, bradykinin induced relaxations with pD2 values and maximal responses of 8.78±0.09 and 75±2% (n=6), respectively. Incubation with captopril (1 μM) did not reveal a relaxation to bradykinin in the normal vessel configuration and had no influence on the concentration-relaxation relationship in everted segments. Lowering the luminal pressure in contracted segments from 131±5 mmHg (isometric, n=5) to 60 mmHg (isobaric, n=5) did not facilitate the action of bradykinin. Eversion of segments did not influence the concentration-response relationship for K+ (4.7–125 mM), PGF2α (0.3–30 μM), and SNP (30 nM–30 μM), although the time-courses of responses were faster when the agents were added from the intimal compared to the adventitial side of the preparation. In the same everted segment contracted with PGF2α, the concentration-response relationship for bradykinin was not different under isometric and isobaric conditions. These results indicate that, (1) reduced endothelium-dependent relaxations to adventitially administered substances can be ascribed to a diffusion barrier in the vessel wall, while enzymatic degradation, luminal pressure and precontractile responses seem not to play a role, (2) impedance planimetry applied to everted cylindrical segments could be a useful experimental approach in pharmacological studies of endothelium-dependent responses under isobaric and isometric conditions. PMID:10498848
Invariants, Attractors and Bifurcation in Two Dimensional Maps with Polynomial Interaction
Hacinliyan, Avadis Simon; Aybar, Orhan Ozgur; Aybar, Ilknur Kusbeyzi
This work will present an extended discrete-time analysis on maps and their generalizations including iteration in order to better understand the resulting enrichment of the bifurcation properties. The standard concepts of stability analysis and bifurcation theory for maps will be used. Both iterated maps and flows are used as models for chaotic behavior. It is well known that when flows are converted to maps by discretization, the equilibrium points remain the same but a richer bifurcation scheme is observed. For example, the logistic map has a very simple behavior as a differential equation but as a map fold and period doubling bifurcations are observed. A way to gain information about the global structure of the state space of a dynamical system is investigating invariant manifolds of saddle equilibrium points. Studying the intersections of the stable and unstable manifolds are essential for understanding the structure of a dynamical system. It has been known that the Lotka-Volterra map and systems that can be reduced to it or its generalizations in special cases involving local and polynomial interactions admit invariant manifolds. Bifurcation analysis of this map and its higher iterates can be done to understand the global structure of the system and the artifacts of the discretization by comparing with the corresponding results from the differential equation on which they are based.
Forced phase-locked response of a nonlinear system with time delay after Hopf bifurcation
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The trivial equilibrium of a nonlinear autonomous system with time delay may become unstable via a Hopf bifurcation of multiplicity two, as the time delay reaches a critical value. This loss of stability of the equilibrium is associated with two coincident pairs of complex conjugate eigenvalues crossing the imaginary axis. The resultant dynamic behaviour of the corresponding nonlinear non-autonomous system in the neighbourhood of the Hopf bifurcation is investigated based on the reduction of the infinite-dimensional problem to a four-dimensional centre manifold. As a result of the interaction between the Hopf bifurcating periodic solutions and the external periodic excitation, a primary resonance can occur in the forced response of the system when the forcing frequency is close to the Hopf bifurcating periodic frequency. The method of multiple scales is used to obtain four first-order ordinary differential equations that determine the amplitudes and phases of the phase-locked periodic solutions. The first-order approximations of the periodic solutions are found to be in excellent agreement with those obtained by direct numerical integration of the delay-differential equation. It is also found that the steady state solutions of the nonlinear non-autonomous system may lose their stability via either a pitchfork or Hopf bifurcation. It is shown that the primary resonance response may exhibit symmetric and asymmetric phase-locked periodic motions, quasi-periodic motions, chaotic motions, and coexistence of two stable motions
Von Bertalanffy's dynamics under a polynomial correction: Allee effect and big bang bifurcation
Leonel Rocha, J.; Taha, A. K.; Fournier-Prunaret, D.
2016-02-01
In this work we consider new one-dimensional populational discrete dynamical systems in which the growth of the population is described by a family of von Bertalanffy's functions, as a dynamical approach to von Bertalanffy's growth equation. The purpose of introducing Allee effect in those models is satisfied under a correction factor of polynomial type. We study classes of von Bertalanffy's functions with different types of Allee effect: strong and weak Allee's functions. Dependent on the variation of four parameters, von Bertalanffy's functions also includes another class of important functions: functions with no Allee effect. The complex bifurcation structures of these von Bertalanffy's functions is investigated in detail. We verified that this family of functions has particular bifurcation structures: the big bang bifurcation of the so-called “box-within-a-box” type. The big bang bifurcation is associated to the asymptotic weight or carrying capacity. This work is a contribution to the study of the big bang bifurcation analysis for continuous maps and their relationship with explosion birth and extinction phenomena.
International Nuclear Information System (INIS)
An aggressive mediastinal fibrosis was found in a 42-year-old female, suffering from dysphagia, stabbing pain in the chest, and an unclear weight loss. In this case, the rare combination of esophageal involvement, bronchial narrowing, and pulmonary artery obstruction could easily be demonstrated with a barium study and a helical CT examination including three-dimensional reconstructions. (orig.)
ABED-MERAIM, Farid; Peerlings, Ron; Geers, Marc
2015-01-01
In the present work, diffuse necking is investigated for stretched metal sheets using two different approaches, namely bifurcation theory and maximum force principle. The contribution includes a critical analysis and a systematic comparison of their respective ability to predict necking. In particular it is shown that, in contrast to bifurcation theory, which is of quite general applicability, some restrictions are associated with the application of maximum force conditions. It is noteworthy ...
BIFURCATION ANALYSIS OF EQUILIBRIUM POINT IN TWO NODE POWER SYSTEM
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Halima Aloui
2014-01-01
Full Text Available This study presents a study of bifurcation in a dynamic power system model. It becomes one of the major precautions for electricity suppliers and these systems must maintain a steady state in the neighborhood of the operating points. We study in this study the dynamic stability of two node power systems theory and the stability of limit cycles emerging from a subcritical or supercritical Hopf bifurcation by computing the first Lyapunov coefficient. The MATCONT package of MATLAB was used for this study and detailed numerical simulations presented to illustrate the types of dynamic behavior. Results have proved the analyses for the model exhibit dynamical bifurcations, including Hopf bifurcations, Limit point bifurcations, Zero Hopf bifurcations and Bagdanov-taknes bifurcations.
SUMMARY SECTION CHANGES OF SUBEPICARDIAL ARTERIAL CHANNEL IN PEOPLE OF OLD AGE
O.A. Buzarova; A.A. Korobkeev
2009-01-01
The dynamics of summary section changes of different levels of coronary arteries branching in people of old age within different variations of the coronary arteries bifurcation has been under the study. The research results in the determination of the summary section changes of coronary vessels and their connection with both topography, and the variations of their branching.
Hopf bifurcation in a diffusive Lotka-Volterra type system with nonlocal delay effect
Guo, Shangjiang; Yan, Shuling
2016-01-01
The dynamics of a diffusive Lotka-Volterra type model for two species with nonlocal delay effect and Dirichlet boundary conditions is investigated in this paper. The existence and multiplicity of spatially nonhomogeneous steady-state solutions are obtained by means of Lyapunov-Schmidt reduction. The stability of spatially nonhomogeneous steady-state solutions and the existence of Hopf bifurcation with the changes of the time delay are obtained by analyzing the distribution of eigenvalues of the infinitesimal generator associated with the linearized system. By the normal form theory and the center manifold reduction, the stability and bifurcation direction of Hopf bifurcating periodic orbits are derived. Finally, our theoretical results are illustrated by a model with homogeneous kernels and one-dimensional spatial domain.
Metamorphosis of plasma turbulence-shear-flow dynamics through a transcritical bifurcation
International Nuclear Information System (INIS)
The structural properties of an economical model for a confined plasma turbulence governor are investigated through bifurcation and stability analyses. A close relationship is demonstrated between the underlying bifurcation framework of the model and typical behavior associated with low- to high-confinement transitions such as shear-flow stabilization of turbulence and oscillatory collective action. In particular, the analysis evinces two types of discontinuous transition that are qualitatively distinct. One involves classical hysteresis, governed by viscous dissipation. The other is intrinsically oscillatory and nonhysteretic, and thus provides a model for the so-called dithering transitions that are frequently observed. This metamorphosis, or transformation, of the system dynamics is an important late side-effect of symmetry breaking, which manifests as an unusual nonsymmetric transcritical bifurcation induced by a significant shear-flow drive
Metamorphosis of plasma turbulence-shear flow dynamics through a transcritical bifurcation
Ball, R; Sugama, H
2002-01-01
The structural properties of an economical model for a confined plasma turbulence governor are investigated through bifurcation and stability analyses. A close relationship is demonstrated between the underlying bifurcation framework of the model and typical behavior associated with low- to high-confinement transitions such as shear flow stabilization of turbulence and oscillatory collective action. In particular, the analysis evinces two types of discontinuous transition that are qualitatively distinct. One involves classical hysteresis, governed by viscous dissipation. The other is intrinsically oscillatory and non-hysteretic, and thus provides a model for the so-called dithering transitions that are frequently observed. This metamorphosis, or transformation, of the system dynamics is an important late side-effect of symmetry-breaking, which manifests as an unusual non-symmetric transcritical bifurcation induced by a significant shear flow drive.
Example of a non-smooth Hopf bifurcation in an aero-elastic system
Magri, Luca
2012-01-01
We investigate a typical aerofoil section under dynamic stall conditions, the structural model is linear and the aerodynamic loading is represented by the Leishman-Beddoes semi-empirical dynamic stall model. The loads given by this model are non-linear and non-smooth, therefore we have integrated the equation of motion using a Runge-Kutta-Fehlberg algorithm equipped with event detection. The main focus of the paper is on the interaction between the Hopf bifurcation typical of aero-elastic systems, which causes flutter oscillations, and the discontinuous definition of the stall model. The paper shows how the non-smooth definition of the dynamic stall model can generate a non-smooth Hopf bifurcation. The mechanisms for the appearance of limit cycle attractors are described by using standard tools of the theory of dynamical systems such as phase plots and bifurcation diagrams.
Bifurcation of a nonlinear Schrödinger equation with a symmetrical double well
International Nuclear Information System (INIS)
The bifurcation of a one-dimensional Gross–Pitaevskii-type equation with a symmetrical double well is investigated. A general relation for the critical power, above which a kind of bifurcation transition from a supercritical pitchfork to a subcritical pitchfork occurs, is presented in terms of the ratio of the nonlinear tunneling to the nonlinear interaction. When the nonlinearity is very weak, our relation reduces to a universal power law; when the nonlinearity is strong, this universal critical power depends on the nonlinearity, the shape of the trap and even the dimension. By means of a numerical calculation, a possible bifurcation transition induced by nonlinearity is predicted for both the ground state and the first excited state. (paper)
Codimension-Two Bifurcation, Chaos and Control in a Discrete-Time Information Diffusion Model
Ren, Jingli; Yu, Liping
2016-07-01
In this paper, we present a discrete model to illustrate how two pieces of information interact with online social networks and investigate the dynamics of discrete-time information diffusion model in three types: reverse type, intervention type and mutualistic type. It is found that the model has orbits with period 2, 4, 6, 8, 12, 16, 20, 30, quasiperiodic orbit, and undergoes heteroclinic bifurcation near 1:2 point, a homoclinic structure near 1:3 resonance point and an invariant cycle bifurcated by period 4 orbit near 1:4 resonance point. Moreover, in order to regulate information diffusion process and information security, we give two control strategies, the hybrid control method and the feedback controller of polynomial functions, to control chaos, flip bifurcation, 1:2, 1:3 and 1:4 resonances, respectively, in the two-dimensional discrete system.
Cortese, Bernardo; Piraino, Davide; Buccheri, Dario; Alfonso, Fernando
2016-10-01
Bifurcation lesion management still represents a challenge for interventional cardiologists and currently there is a number of different approaches/techniques involving coronary stents. The use of a drug-coated balloon for native coronary vessel management is emerging as an alternative treatment, although in selected patient populations only. In particular, this technology has been tested for the treatment of bifurcations, both for the main vessel and the side branches. Several studies have evaluated this treatment as an alternative or as a therapeutic option complementary to stents, with conflicting and debatable results. However, the perspective of leaving lower metallic burden in this type of lesions is highly appealing and should be deeply investigated. We review here the currently available scientific data and future perspectives on drug-coated balloon use for bifurcation lesions. PMID:27390995
Institute of Scientific and Technical Information of China (English)
Nan Zhang; Tong Qiu; Bingzhen Chen
2015-01-01
The major difficulty in achieving good performance of industrial polymerization reactors lies in the lack of under-standing of their nonlinear dynamics and the lack of wel-developed techniques for the control of nonlinear pro-cesses, which are usually accompanied with bifurcation phenomenon. This work aims at investigating the nonlinear behavior of the parameterized nonlinear system of vinyl acetate polymerization and further modifying the bifurcation characteristics of this process via a washout filter-aid control er, with all the original steady state equilibria preserved. Advantages and possible extensions of the proposed methodology are discussed to provide scientific guide for further controller design and operation improvement.
Observation of bifurcation property of radial electric field using a heavy ion beam probe in CHS
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Bifurcation nature of potential profile of a toroidal helical plasma is investigated in the Compact Helical System (CHS), using a heavy ion beam probe. The measurements reveal that there exist three main branches of potential profiles in electron cyclotron resonance (ECR) heated plasmas with low density of ne∼0.5x1013cm-3. The branches with higher central potential exhibit a rather strong radial electric field shear that should result in fluctuation reduction and formation of transport barrier. Lissajous expression is useful to extract the bifurcation characteristics of potential structure. (author)
Jiang, Heping; Jiang, Jiao; Song, Yongli
In this paper, we firstly employ the normal form theory of delayed differential equations according to Faria and Magalhães to derive the normal form of saddle-node-Hopf bifurcation for the general retarded functional differential equations. Then, the dynamical behaviors of a Leslie-Gower predator-prey model with time delay and nonmonotonic functional response are considered. Specially, the dynamical classification near the saddle-node-Hopf bifurcation point is investigated by using the normal form and the center manifold approaches. Finally, the numerical simulations are employed to support the theoretical results.
Codimension 3 nonresonant bifurcations of homoclinic orbits with two inclination flips
Institute of Scientific and Technical Information of China (English)
SHUI; Shuliang; ZHU; Deming
2005-01-01
Homoclinic bifurcations in four-dimensional vector fields are investigated by setting up a local coordinate near a homoclinic orbit. This homoclinic orbit is principal but its stable and unstable foliations take inclination flip. The existence, nonexistence, and uniqueness of the 1-homoclinic orbit and 1-periodic orbit are studied. The existence of the two-fold 1-periodic orbit and three-fold 1 -periodic orbit are also obtained. It is indicated that the number of periodic orbits bifurcated from this kind of homoclinic orbits depends heavily on the strength of the inclination flip.
Hopf bifurcation analysis and circuit implementation for a novel four-wing hyper-chaotic system
International Nuclear Information System (INIS)
In the paper, a novel four-wing hyper-chaotic system is proposed and analyzed. A rare dynamic phenomenon is found that this new system with one equilibrium generates a four-wing-hyper-chaotic attractor as parameter varies. The system has rich and complex dynamical behaviors, and it is investigated in terms of Lyapunov exponents, bifurcation diagrams, Poincaré maps, frequency spectrum, and numerical simulations. In addition, the theoretical analysis shows that the system undergoes a Hopf bifurcation as one parameter varies, which is illustrated by the numerical simulation. Finally, an analog circuit is designed to implement this hyper-chaotic system. (general)
Border-Collision Bifurcations and Chaotic Oscillations in a Piecewise-Smooth Dynamical System
DEFF Research Database (Denmark)
Zhusubaliyev, Z.T.; Soukhoterin, E.A.; Mosekilde, Erik
2002-01-01
investigation in the present paper is the dynamical model of a constant voltage converter which represents a three-dimensional piecewise-smooth system of nonautonomous differential equations. A specific type of phenomena that arise in the dynamics of piecewise-smooth systems are the so-called border....... We show that a denumerable set of unstable cycles can arise together with stable cycles at border-collision bifurcations. The characteristic peculiarities of border-collision bifurcational transitions in piecewise-smooth systems are described and we provide a comparison with some recent results....
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Jianguo Ren
2014-01-01
Full Text Available A new computer virus propagation model with delay and incomplete antivirus ability is formulated and its global dynamics is analyzed. The existence and stability of the equilibria are investigated by resorting to the threshold value R0. By analysis, it is found that the model may undergo a Hopf bifurcation induced by the delay. Correspondingly, the critical value of the Hopf bifurcation is obtained. Using Lyapunov functional approach, it is proved that, under suitable conditions, the unique virus-free equilibrium is globally asymptotically stable if R01. Numerical examples are presented to illustrate possible behavioral scenarios of the mode.
Quelques problèmes de stabilité et de bifurcation des solides visqueux
ABED-MERAIM, Farid
1999-01-01
This PhD thesis is composed essentially of two main parts, of unequal sizes, which are summarized as follows: Part I: It is concerned with stability and bifurcation issues relating to strain-rate-independent solids and structures (i.e., elastic or elasto-plastic). A thorough and comprehensive review of the various investigations in this field allowed us to propose an original and compact presentation of the theory of stability and bifurcation. An illustration of this theory is then shown thro...
Hopf bifurcation control for a coupled nonlinear relative rotation system with time-delay feedbacks
Liu, Shuang; Li, Xue; Tan, Shu-Xian; Li, Hai-Bin
2014-10-01
This paper investigates the Hopf bifurcations resulting from time delay in a coupled relative-rotation system with time-delay feedbacks. Firstly, considering external excitation, the dynamical equation of relative rotation nonlinear dynamical system with primary resonance and 1:1 internal resonance under time-delay feedbacks is deduced. Secondly, the averaging equation is obtained by the multiple scales method. The periodic solution in a closed form is presented by a perturbation approach. At last, numerical simulations confirm that time-delay theoretical analyses have influence on the Hopf bifurcation point and the stability of periodic solution.
Bifurcation and chaos in a ratio-dependent predator-prey system with time delay
International Nuclear Information System (INIS)
In this paper, a ratio-dependent predator-prey model with time delay is investigated. We first consider the local stability of a positive equilibrium and the existence of Hopf bifurcations. By using the normal form theory and center manifold reduction, we derive explicit formulae which determine the stability, direction and other properties of bifurcating periodic solutions. Finally, we consider the effect of impulses on the dynamics of the above time-delayed population model. Numerical simulations show that the system with constant periodic impulsive perturbations admits rich complex dynamic, such as periodic doubling cascade and chaos.
Hopf Bifurcation Analysis and Chaos Control of a Chaotic System without ilnikov Orbits
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Na Li
2015-01-01
Full Text Available This paper mainly investigates the dynamical behaviors of a chaotic system without ilnikov orbits by the normal form theory. Both the stability of the equilibria and the existence of local Hopf bifurcation are proved in view of analyzing the associated characteristic equation. Meanwhile, the direction and the period of bifurcating periodic solutions are determined. Regarding the delay as a parameter, we discuss the effect of time delay on the dynamics of chaotic system with delayed feedback control. Finally, numerical simulations indicate that chaotic oscillation is converted into a steady state when the delay passes through a certain critical value.
Stochastic D-bifurcation for a damped sine-Gordon equation with noise
Energy Technology Data Exchange (ETDEWEB)
Huang, Qiongwei; Xue, Changfeng, E-mail: cfxue@163.com [Department of Fundamental Sciences, Yancheng Institute of Technology, Yancheng 224051 (China); Tang, Jiashi [College of Mechanical and Vehicle Engineering, Hunan University, Changsha 410082 (China)
2015-04-15
We investigate the stochastic bifurcation of a damped sine-Gordon equation with Dirichlet boundary conditions under the influence of multiplicative Gaussian white noise. Introducing a slow time scale, we derive the amplitude equations near the trivial solution by multiscale analysis. And the stationary probability density functions are formulated analytically using the stochastic averaging of energy envelope. The numerical calculations show that the system undergoes a stochastic D-bifurcation of energy envelope from a delta measure to new stationary measures when the control parameter crosses a critical point.
Tate, Quinn; Kim, Seong-Eun; Treiman, Gerald; Parker, Dennis L.; Hadley, J. Rock
2012-01-01
The purpose of this work was to design and construct a multi-channel receive-only RF coil for 3 Tesla magnetic resonance imaging of the human carotid artery and bifurcation with optimized signal to noise ratio in the carotid vessels along the full extent of the neck. A neck phantom designed to match the anatomy of a subject with a neck representing the body habitus often seen in subjects with carotid arterial disease, was constructed. Sixteen circular coil elements were arranged on a semi-rig...
Proposition of an outflow boundary approach for carotid artery stenosis CFD simulation.
Zhang, Yu; Furusawa, Toyoki; Sia, Sheau Fung; Umezu, Mitsuo; Qian, Yi
2013-01-01
The purpose of this study was to propose an innovative approach of setting outlet boundary conditions for the computational fluid dynamics (CFD) simulation of human common carotid arteries (CCAs) bifurcation based on the concept of energy loss minimisation at flow bifurcation. Comparisons between this new approach and previously reported boundary conditions were also made. The results showed that CFD simulation based on the proposed boundary conditions gave an accurate prediction of the critical stenosis ratio of carotid arteries (at around 65%). Other boundary conditions, such as the constant external pressure (P = 0) and constant outflow ratio, either overestimated or underestimated the critical stenosis ratio of carotid arteries. The patient-specific simulation results furthermore indicated that the calculated internal carotid artery flow ratio at CCA bifurcation (61%) coincided with the result obtained by clinical measurements through the use of Colour Doppler ultrasound. PMID:22288780
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Yamada, Naoaki; Ogino, Hitoshi; Hanabusa, Yuji; Sasaki, Hiroaki; Minatoya Kenji [National Cardiovascular Center, Suita, Osaka (Japan)
2003-01-01
We reviewed 106 cases who underwent MR angiography to visualize the Adamkiewicz artery (AKA) as a preoperative evaluation of the thoracic descending and thoracoabdominal aortic aneurysms. MR angiography depicted the AKA successfully in 68% of the patients. However, segmental artery that gives rise the AKA was occluded in 41% at its origin from the aorta. In one patient with postoperative paraplegia, broad infarction in the upper thoracic cord seems not to be related to the territory of the AKA that was visualized by MR angiography. Preoperative MR angiography serves planning of surgery, and can reduce time of aortic cross-clamping. However, our understanding of the value of MR angiography to prevent spinal cord ischemic injury requires further clinical investigation. (author)
International Nuclear Information System (INIS)
Full text: Introduction: Yttrium-90 (Y-90) microsphere radioembolization is increasingly used for the treatment of unresectable hepatocellular carcinoma and liver metastasis. Objectives and tasks: We aim to present the upper abdominal wall skin involvement detected during routine pre-therapy Technetium-99m-macroaggregated albumin (Tc-99m-MAA) on SPECT/CT due to patent hepatic falciform artery and the precautions to avoid this potential complication. Material and methods: 38-year-old male with colon cancer and multiple liver metastasis was evaluated prior to radioembolization and Tc-99 MAA was slowly hand injected at the bifurcation of the proper hepatic artery. Then, the SPECT/CT scan was performed in order to investigate the systemic shunt or gastric involvement. Results: On SPECT/CT scan, involvement of the upper abdominal wall through falciform ligament was seen. Re-evaluation of the hepatic angiogram identified a patent hepatic falciform artery arising from the left hepatic artery. Y-90 microspheres were slowly hand injected to the left hepatic artery superselectively and no extra-hepatic activity was seen on SPECT/CT scan. Conclusion: Upper abdominal pain and dermatitis are uncommon findings after radioembolization and may occur due to inadvertent delivery of Y-90 microspheres into patent hepatic falciform artery. To prevent these complications, either patent hepatic falciform artery must be embolized by coil or Y-90 injection must be performed superselectively
International Nuclear Information System (INIS)
We show that maps describing border collision bifurcations (continuous but non-differentiable discrete time maps) are subject to a curse of dimensionality: it is impossible to reduce the study of the general case to low dimensions, since in every dimension the bifurcation can produce fundamentally different attractors (contrary to the case of local bifurcations in smooth systems). In particular we show that n-dimensional border collision bifurcations can have invariant sets of dimension k for integer k from 0 to n. We also show that the border collision normal form is related to grazing-sliding bifurcations of switching dynamical systems. This implies that the dynamics of these two apparently distinct bifurcations (one for discrete time dynamics, the other for continuous time dynamics) are closely related and hence that a similar curse of dimensionality holds in grazing-sliding bifurcations. (paper)
Carotid artery disease : plaque features and vulnerability
Jashari, Fisnik
2015-01-01
Background: Atherosclerosis is an important cause of stroke. Ultrasound offers the convenience of real-time and detailed assessment of carotid plaque features as well as arterial wall thickening and composition. Evaluation of these features is important for determining patients’ risk of suffering vascular events and also contributes to selecting the best treatment strategy. Methods: Using ultrasound data analysis we have determined plaque features in the bifurcation and internal carotid arter...
Parametric Controller Design of Hopf Bifurcation System
Directory of Open Access Journals (Sweden)
Jinbo Lu
2015-01-01
Full Text Available A general parametric controller design method is proposed for Hopf bifurcation of nonlinear dynamic system. This method does not increase the dimension of the system. Compared with the existing methods, the controller designed by this method has a lower controller order and a simpler structure, and it does not contain equilibrium points. The method keeps equilibrium of the origin system unchanged. Symbolic computation is used to deduce the constraints of controller, and cylindrical algebraic decomposition is used to find the stability parameter regions in parameter space of controller. The method is then employed for Hopf bifurcation control. Taking Lorenz system as an example, the controller design steps of the method and numerical simulations are discussed. Computer simulation results are presented to confirm the analytical predictions.
Periodic orbits near a bifurcating slow manifold
DEFF Research Database (Denmark)
Kristiansen, Kristian Uldall
2015-01-01
This paper studies a class of $1\\frac12$-degree-of-freedom Hamiltonian systems with a slowly varying phase that unfolds a Hamiltonian pitchfork bifurcation. The main result of the paper is that there exists an order of $\\ln^2\\epsilon^{-1}$-many periodic orbits that all stay within an $\\mathcal O......(\\epsilon^{1/3})$-distance from the union of the normally elliptic slow manifolds that occur as a result of the bifurcation. Here $\\epsilon\\ll 1$ measures the time scale separation. These periodic orbits are predominantly unstable. The proof is based on averaging of two blowup systems, allowing one to estimate...... the effect of the singularity, combined with results on asymptotics of the second Painleve equation. The stable orbits of smallest amplitude that are {persistently} obtained by these methods remain slightly further away from the slow manifold being distant by an order $\\mathcal O(\\epsilon^{1/3}\\ln^{1...
Torus bifurcations in multilevel converter systems
DEFF Research Database (Denmark)
Zhusubaliyev, Zhanybai T.; Mosekilde, Erik; Yanochkina, Olga O.
2011-01-01
embedded one into the other and with their basins of attraction delineated by intervening repelling tori. The paper illustrates the coexistence of three stable tori with different resonance behaviors and shows how reconstruction of these tori takes place across the borders of different dynamical regimes....... The paper also demonstrates how pairs of attracting and repelling tori emerge through border-collision torus-birth and border-collision torus-fold bifurcations. © 2011 World Scientific Publishing Company....
Perturbed period-doubling bifurcation. I. Theory
DEFF Research Database (Denmark)
Svensmark, Henrik; Samuelsen, Mogens Rugholm
1990-01-01
-defined way that is a function of the amplitude and the frequency of the signal. New scaling laws between the amplitude of the signal and the detuning δ are found; these scaling laws apply to a variety of quantities, e.g., to the shift of the bifurcation point. It is also found that the stability and the...... of a microwave-driven Josephson junction confirm the theory. Results should be of interest in parametric-amplification studies....
Vural, Mutlu; Satiroglu, Omer; Akbas, Berfu; Goksel, Isin; Karabay, Ocal
2009-01-01
In search of associations between coronary artery disease and symptoms of depression and anxiety, we conducted a prospective cross-sectional study of 314 patients (age range, 19–79 yr) who had presented with chest pain. Coronary angiographic findings were classified into 5 categories (0–4), in which higher numbers indicated more severe disease. Symptoms of depression and anxiety were evaluated by the Beck depression and anxiety inventories, in which higher scores indicated more severe symptom...
Influence of noise and near-resonant perturbations on bifurcations in Josephson junctions
DEFF Research Database (Denmark)
Svensmark, Henrik; Hansen, Jørn Bindslev; Pedersen, Niels Falsig
1987-01-01
The stabilization of a nonlinear system against period-doubling bifurcations by means of a periodic perturbation has been investigated. With the Josephson junction as a model system, both numerical simulations (including noise) and measurements on Josephson tunnel junctions have been performed. The...
REMARKS ON BIFURCATIONS OF u″ + μu- uk = 0 (4 ≤ k ∈ Z+)
Institute of Scientific and Technical Information of China (English)
李常品
2001-01-01
In this paper, we investigate the bifurcations of one class of steady-state reaction-diffusion equations of the form u" +μu-uκ =0, subject to u(0)=u(π)=0, where μ is a parameter, 4≤k∈Z+.Using the singularity theory based on the Liapunov-Schmidt reduction, some satisfactory results are obtained.
Stability and bifurcations of relative equilibria of a pendulum suspended on the equator
Burov, A. A.; Kosenko, I. I.
2013-05-01
The problem of equilibria of a pendulum suspended at an equatorial point relative to the rotating Earth is considered. An altitude is determined at which the degree of instability of the inverted pendulum changes from two to unity. Relative equilibria are investigated that bifurcate from the radial one when its degree of instability changes. Their stability properties are studied.
International Nuclear Information System (INIS)
Using the model of a generalized Van der Pol oscillator in the regime of subcritical Hopf bifurcation, we investigate the influence of time delay on noise-induced oscillations. It is shown that for appropriate choices of time delay, either suppression or enhancement of coherence resonance can be achieved. Analytical calculations are combined with numerical simulations and experiments on an electronic circuit
Helical CT evaluation of internal carotid artery stenoses
International Nuclear Information System (INIS)
To determine the utility of helical CT angiography in the evaluation of carotid artery stenoses, helical CT images (reconstructed three-dimensional images, reconstructed multiplanar images, and two-dimensional axial images) obtained from 60 patients were compared with images obtained using conventional angiography. Based on conventional angiographic criteria, 22 arteries had no stenosis, 26 had mild stenosis. 69 had severe stenosis, and 3 were occluded. All carotid bifurcations were clearly identified on helical CT scanning and there were no complications. There were no motion artifacts due to the short examination time. In normal arteries, reconstructed three-dimensional images provided accurate anatomic depiction of the carotid bifurcation. Calcification was present at the stenotic lesion in 52 arteries. In 43 arteries in which the stenotic lesion was free of calcification, the degree of carotid stenosis determined using reconstructed three-dimensional images correlated with that determined using conventional angiography. In 19 of 52 arteries with calcification at the stenotic lesion, the calcification was focal and did not obscure the vessel lumen significantly when viewed from multiple angles. In the other 33 arteries, the calcification was dense and/or circumferential, making it difficult to evaluate the axial images allowed evaluation of the vessel lumen in the area of calcification, and the degree of stenosis was similar to that determined by conventional angiography. In 3 arteries, occlusion of the internal carotid artery was seen in reconstructed three-dimensional images and was confirmed by conventional angiography. (K.H.)
Helical CT evaluation of internal carotid artery stenoses
Energy Technology Data Exchange (ETDEWEB)
Akiyama, Yoshinori; Imakita, Satoshi; Suzuki, Susumu; Yamamoto, Satoshi; Tsukahara, Tetsuya; Hashimoto, Nobuo [National Cardiovascular Center, Suita, Osaka (Japan)
1997-06-01
To determine the utility of helical CT angiography in the evaluation of carotid artery stenoses, helical CT images (reconstructed three-dimensional images, reconstructed multiplanar images, and two-dimensional axial images) obtained from 60 patients were compared with images obtained using conventional angiography. Based on conventional angiographic criteria, 22 arteries had no stenosis, 26 had mild stenosis. 69 had severe stenosis, and 3 were occluded. All carotid bifurcations were clearly identified on helical CT scanning and there were no complications. There were no motion artifacts due to the short examination time. In normal arteries, reconstructed three-dimensional images provided accurate anatomic depiction of the carotid bifurcation. Calcification was present at the stenotic lesion in 52 arteries. In 43 arteries in which the stenotic lesion was free of calcification, the degree of carotid stenosis determined using reconstructed three-dimensional images correlated with that determined using conventional angiography. In 19 of 52 arteries with calcification at the stenotic lesion, the calcification was focal and did not obscure the vessel lumen significantly when viewed from multiple angles. In the other 33 arteries, the calcification was dense and/or circumferential, making it difficult to evaluate the axial images allowed evaluation of the vessel lumen in the area of calcification, and the degree of stenosis was similar to that determined by conventional angiography. In 3 arteries, occlusion of the internal carotid artery was seen in reconstructed three-dimensional images and was confirmed by conventional angiography. (K.H.)
On the Crack Bifurcation and Fanning of Crack Growth Data
Forman, Royce G.; Zanganeh, Mohammad
2015-01-01
Crack growth data obtained from ASTM load shedding method for different R values show some fanning especially for aluminum alloys. It is believed by the authors and it has been shown before that the observed fanning is due to the crack bifurcation occurs in the near threshold region which is a function of intrinsic properties of the alloy. Therefore, validity of the ASTM load shedding test procedure and results is confirmed. However, this position has been argued by some experimentalists who believe the fanning is an artifact of the test procedure and thus the obtained results are invalid. It has been shown that using a special test procedure such as using compressively pre-cracked specimens will eliminate the fanning effect. Since not using the fanned data fit can result in a significantly lower calculated cyclic life, design of a component, particularly for rotorcraft and propeller systems will considerably be impacted and therefore this study is of paramount importance. In this effort both test procedures i.e. ASTM load shedding and the proposed compressive pre-cracking have been used to study the fatigue crack growth behavior of compact tension specimens made of aluminum alloy 2524-T3. Fatigue crack growth paths have been closely observed using SEM machines to investigate the effects of compression pre-cracking on the crack bifurcation behavior. The results of this study will shed a light on resolving the existing argument by better understanding of near threshold fatigue crack growth behavior.
Bifurcation analysis of a Lyapunov-based controlled boost converter
Spinetti-Rivera, Mario; Olm, Josep M.; Biel, Domingo; Fossas, Enric
2013-11-01
Lyapunov-based controlled boost converters have a unique equilibrium point, which is globally asymptotically stable, for known resistive loads. This article investigates the dynamic behaviors that appear in the system when the nominal load differs from the actual one and no action is taken by the controller to compensate for the mismatch. Exploiting the fact that the closed-loop system is, in fact, planar and quadratic, one may provide not only local but also global stability results: specifically, it is proved that the number of equilibria of the converter may grow up to three and that, in any case, the system trajectories are always bounded, i.e. it is a bounded quadratic system. The possible phase portraits of the closed-loop system are also characterized in terms of the selected bifurcation parameters, namely, the actual load value and the gain of the control law. Accordingly, the analysis allows the numerical illustration of many bifurcation phenomena that appear in bounded quadratic systems through a physical example borrowed from power electronics.
Dynamics of Surfactant Liquid Plugs at Bifurcating Lung Airway Models
Tavana, Hossein
2013-11-01
A surfactant liquid plug forms in the trachea during surfactant replacement therapy (SRT) of premature babies. Under air pressure, the plug propagates downstream and continuously divides into smaller daughter plugs at continuously branching lung airways. Propagating plugs deposit a thin film on airway walls to reduce surface tension and facilitate breathing. The effectiveness of SRT greatly depends on the final distribution of instilled surfactant within airways. To understand this process, we investigate dynamics of splitting of surfactant plugs in engineered bifurcating airway models. A liquid plug is instilled in the parent tube to propagate and split at the bifurcation. A split ratio, R, is defined as the ratio of daughter plug lengths in the top and bottom daughter airway tubes and studied as a function of the 3D orientation of airways and different flow conditions. For a given Capillary number (Ca), orienting airways farther away from a horizontal position reduced R due to the flow of a larger volume into the gravitationally favored daughter airway. At each orientation, R increased with 0.0005 surfactant distribution in airways and develop effective SRT strategies.
Stability and Bifurcation in Magnetic Flux Feedback Maglev Control System
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Wen-Qing Zhang
2013-01-01
Full Text Available Nonlinear properties of magnetic flux feedback control system have been investigated mainly in this paper. We analyzed the influence of magnetic flux feedback control system on control property by time delay and interfering signal of acceleration. First of all, we have established maglev nonlinear model based on magnetic flux feedback and then discussed hopf bifurcation’s condition caused by the acceleration’s time delay. The critical value of delayed time is obtained. It is proved that the period solution exists in maglev control system and the stable condition has been got. We obtained the characteristic values by employing center manifold reduction theory and normal form method, which represent separately the direction of hopf bifurcation, the stability of the period solution, and the period of the period motion. Subsequently, we discussed the influence maglev system on stability of by acceleration’s interfering signal and obtained the stable domain of interfering signal. Some experiments have been done on CMS04 maglev vehicle of National University of Defense Technology (NUDT in Tangshan city. The results of experiments demonstrate that viewpoints of this paper are correct and scientific. When time lag reaches the critical value, maglev system will produce a supercritical hopf bifurcation which may cause unstable period motion.
International Nuclear Information System (INIS)
The coexistence of a resting condition and period-1 firing near a subcritical Hopf bifurcation point, lying between the monostable resting condition and period-1 firing, is often observed in neurons of the central nervous systems. Near such a bifurcation point in the Morris—Lecar (ML) model, the attraction domain of the resting condition decreases while that of the coexisting period-1 firing increases as the bifurcation parameter value increases. With the increase of the coupling strength, and parameter and initial value dependent synchronization transition processes from non-synchronization to compete synchronization are simulated in two coupled ML neurons with coexisting behaviors: one neuron chosen as the resting condition and the other the coexisting period-1 firing. The complete synchronization is either a resting condition or period-1 firing dependent on the initial values of period-1 firing when the bifurcation parameter value is small or middle and is period-1 firing when the parameter value is large. As the bifurcation parameter value increases, the probability of the initial values of a period-1 firing neuron that lead to complete synchronization of period-1 firing increases, while that leading to complete synchronization of the resting condition decreases. It shows that the attraction domain of a coexisting behavior is larger, the probability of initial values leading to complete synchronization of this behavior is higher. The bifurcations of the coupled system are investigated and discussed. The results reveal the complex dynamics of synchronization behaviors of the coupled system composed of neurons with the coexisting resting condition and period-1 firing, and are helpful to further identify the dynamics of the spatiotemporal behaviors of the central nervous system. (general)
Atherosclerosis and the internal mammary arteries
International Nuclear Information System (INIS)
One hundred and fifty patients with coronary artery disease (CAD), 14 (9.3%) of whom had coexisting peripheral vascular disease, underwent bilateral internal mammary arteriography to study the incidence and extent of atherosclerosis in these vessels. Significant atherosclerosis of the internal mammary arteries (IMAs) was present in three patients (2%), of whom one had coexisting peripheral vascular disease. Lesions in the IMAs were found either proximally, close to the origin or distally, around the terminal bifurcation. Six of the 14 patients with peripheral vascular disease (4% of total subjects) had significant atherosclerosis of the brachiocephalic arteries. Atherosclerotic involvement of the IMA is very unusual and rarely interferes with the use of these vessels for coronary bypass. More common, however, is atherosclerosis of the subclavian arteries, a contraindication for IMA grafting if the lesion is proximal to the IMA origin. (orig.)
Classification of solitary wave bifurcations in generalized nonlinear Schr\\"odinger equations
Yang, Jianke
2012-01-01
Bifurcations of solitary waves are classified for the generalized nonlinear Schr\\"odinger equations with arbitrary nonlinearities and external potentials in arbitrary spatial dimensions. Analytical conditions are derived for three major types of solitary wave bifurcations, namely saddle-node bifurcations, pitchfork bifurcations and transcritical bifurcations. Shapes of power diagrams near these bifurcations are also obtained. It is shown that for pitchfork and transcritical bifurcations, their power diagrams look differently from their familiar solution-bifurcation diagrams. Numerical examples for these three types of bifurcations are given as well. Of these numerical examples, one shows a transcritical bifurcation, which is the first report of transcritical bifurcations in the generalized nonlinear Schr\\"odinger equations. Another shows a power loop phenomenon which contains several saddle-node bifurcations, and a third example shows double pitchfork bifurcations. These numerical examples are in good agreeme...
The significance of enhanced radionuclide deposition at bronchial bifurcations
International Nuclear Information System (INIS)
Experiments were conducted to quantitate deposition patterns of monodisperse aerosols in surrogates of the human upper respiratory tract. Laryngeal casts and most upper airway bifurcations were sites of preferential particle deposition. Highly concentrated deposits were detected at carinal ridges within bifurcation zones. Together with impaired mucociliary clearance at branching sites, this initial deposition pattern results in localized accumulations of radionuclides within bifurcation zones. For inhaled radon progeny radiation doses are calculated for 3 regions of bronchial airways: tubular airway segments, bifurcation zones (including the carina), and carinal ridges. These calculations indicated that enhanced deposition at branching sites leads to significantly higher doses to epithelial cells located at bifurcations than along tubular airway segments. If cell killing is included in the analysis of lung cancer risk, it reduces carcinogenic potential at bifurcation sites, particularly at high doses. (author)
Nonlinear instability and dynamic bifurcation of a planeinterface during solidification
Institute of Scientific and Technical Information of China (English)
吴金平; 侯安新; 黄定华; 鲍征宇; 高志农; 屈松生
2001-01-01
By taking average over the curvature, the temperature and its gradient, the solute con-centration and its gradient at the flange of planar interface perturbed by sinusoidal ripple during solidifi-cation, the nonlinear dynamic equations of the sinusoidal perturbation wave have been set up. Analysisof the nonlinear instability and the behaviors of dynamic bifurcation of the solutions of these equationsshows that (i) the way of dynamic bifurcation of the flat-to-cellular interface transition vades with differ-ent thermal gradients. The quasi-subcritical-lag bifurcation occurs in the small interface thermal gradientscope, the supercritical-lag bifurcation in the medium thermal gradient scope and the supercritical bifur-cation in the large thermal gradient scope. (ii) The transition of cellular-to-flat interface is realizedthrough supercritical inverse bifurcation in the rapid solidification area.
Directory of Open Access Journals (Sweden)
Sareh Sepahvand Hossein Beigi
2015-09-01
Full Text Available Background: Coronary Artery Disease (CAD is an important disease where the arteries and vessels supplying oxygen and nutrients to the heart are narrowed or blocked. Early diagnosis and recognition of CAD leads to its complete treatment. Drug therapy, angiography, coronary angioplasty, and in advanced cases, coronary artery bypass surgery restore the normal flow of blood to the heart muscle. Objectives: The present study aimed to identify the association between rs4977574 polymorphism in ANRIL gene and CAD in Iranian patients. Materials and Methods: Blood samples were collected from 100 subjects with positive angiography (case group and 93 ones with negative angiography (control group. Using Taq Man Real Time PCR, the extracted DNAs from the patients and controls were genotyped for rs4977574 polymorphism in ANRIL gene (applied biosystem, USA. Then, the genotypes and clinical parameters were compared by the SPSS statistical software, version 18 (Chicago, USA. The results were compared by one-way ANOVA, simple T-test, and Chi-square test and were presented as mean ± Standard Deviation (SD. P values < 0.05 were considered as statistically significant. Results: The results showed a significant relationship between CAD and Diastolic Blood Pressure (DBP, Body Mass Index (BMI, uric acid, Low Density Lipoprotein (LDL, cholesterol, and triglyceride. However, no significant association was observed between rs4977574 polymorphism and biochemical characteristics in the two groups. Allele frequency was AA = 22%, AG = 44%, and GG = 34% in the case group and AA = 17%, AG = 44%, and GG = 32% in the control group. Conclusions: The present study examined the association between rs4977574 polymorphism in ANRIL gene and CAD in a population of Iranian patients. The study findings revealed no direct relationship between rs4977574 polymorphism and the disease in Iranian population.
Identification of Bifurcations from Observations of Noisy Biological Oscillators
Salvi, Joshua D; Hudspeth, A J
2016-01-01
Hair bundles are biological oscillators that actively transduce mechanical stimuli into electrical signals in the auditory, vestibular, and lateral-line systems of vertebrates. A bundle's function can be explained in part by its operation near a particular type of bifurcation, a qualitative change in behavior. By operating near different varieties of bifurcation, the bundle responds best to disparate classes of stimuli. We show how to determine the identity of and proximity to distinct bifurcations despite the presence of substantial environmental noise.
Singularly perturbed bifurcation subsystem and its application in power systems
Institute of Scientific and Technical Information of China (English)
An Yichun; Zhang Qingling; Zhu Yukun; Zhang Yan
2008-01-01
The singularly perturbed bifurcation subsystem is described,and the test conditions of subsystem persistence are deduced.By use of fast and slow reduced subsystem model,the result does not require performing nonlinear transformation.Moreover,it is shown and proved that the persistence of the periodic orbits for Hopf bifurcation in the reduced model through center manifold.Van der Pol oscillator circuit is given to illustrate the persistence of bifurcation subsystems with the full dynamic system.
Topography of human ankle joint: focused on posterior tibial artery and tibial nerve
Kim, Deog-Im; Kim, Yi-Suk; Han, Seung-Ho
2015-01-01
Most of foot pain occurs by the entrapment of the tibial nerve and its branches. Some studies have reported the location of the tibial nerve; however, textbooks and researches have not described the posterior tibial artery and the relationship between the tibal nerve and the posterior tibial artery in detail. The purpose of this study was to analyze the location of neurovascular structures and bifurcations of the nerve and artery in the ankle region based on the anatomical landmarks. Ninety f...
An Incidental Finding of the Thyroidea Ima Artery:-A Case Report Study
Directory of Open Access Journals (Sweden)
Lalit C. Ratanpara
2015-12-01
Full Text Available We are here reporting a case of an incidental finding of the thyroidea ima artery emerging from the brachiocephalic trunk with a typical inferior thyroid vessels on both sides emerging from the thyrocervical trunk. The thyroidea ima artery entered the thyroid gland near to anterior surface of right lobe of thyroid gland. It arose from the brachiocephalic artery proximal to its bifurcation.
AUTOMATIC SEGMENTATION ALGORITHM FOR THE LUMEN OF THE CAROTID ARTERY IN ULTRASOUND B-MODE IMAGES
Santos, AMF; João Manuel R. S. Tavares; Sousa, L. de; Santos, R.; Castro, P.; Azevedo, E.
2012-01-01
A new algorithm is proposed for the identification and segmentation of the lumen and bifurcation boundaries of the carotid artery in 2D longitudinal ultrasound B-mode images. It uses the hipoechogenic characteristics defining the lumen of the carotid for its identification and echogenic characteristics for the identification of the bifurcation. The input image is preprocessed with the application of an anisotropic diffusion filter for speckle removal, and morphologic operators for the detecti...
Automatic segmentation of the lumen of the carotid artery in ultrasound B-mode images
Santos, AMF; tavares, jmrs; Sousa, L. de; Santos, R.; Castro, P.; Azevedo, E.
2013-01-01
A new algorithm is proposed for the segmentation of the lumen and bifurcation boundaries of the carotid artery in B-mode ultrasound images. It uses the hipoechogenic characteristics of the lumen for the identification of the carotid boundaries and the echogenic characteristics for the identification of the bifurcation boundaries. The image to be segmented is processed with the application of an anisotropic diffusion filter for speckle removal and morphologic operators are employed in the dete...
Periodic solutions and flip bifurcation in a linear impulsive system
Institute of Scientific and Technical Information of China (English)
Jiang Gui-Rong; Yang Qi-Gui
2008-01-01
In this paper,the dynamical behaviour of a linear impulsive system is discussed both theoretically and numerically.The existence and the stability of period-one solution are discussed by using a discrete map.The conditions of existence for flip bifurcation are derived by using the centre manifold theorem and bifurcation theorem.The bifurcation analysis shows that chaotic solutions appear via a cascade of period-doubling in some interval of parameters.Moreover,the periodic solutions,the bifurcation diagram,and the chaotic attractor,which show their consistence with the theoretical analyses,are given in an example.中图分类:O547
Safe, explosive, and dangerous bifurcations in dissipative dynamical systems
Energy Technology Data Exchange (ETDEWEB)
Thompson, J.M.T. (Centre for Nonlinear Dynamics and Its Applications, Civil Engineering Building, University College London, Gower Street, London WC1E6BT (United Kingdom)); Stewart, H.B. (Mathematical Sciences Group, Building 490-A, Department of Applied Science, Brookhaven National Laboratory, Upton, New York 11973 (United States)); Ueda, Y. (Department of Electrical Engineering, Kyoto University, Kyoto 606 (Japan))
1994-02-01
A comprehensive listing of the generic codimension-1 attractor bifurcations of dissipative dynamical systems is presented. It includes local and global bifurcations of regular and chaotic attractors. The bifurcations are classified according to the continuity or discontinuity of the attractor path, which governs the physical outcome that would be observed under a slow control sweep. Related issues of determinacy, hysteresis, basin structure, and intermittency are addressed. Recently discovered chaotic bifurcations are discussed in some detail, with particular reference to the regular or chaotic saddle-type destroyer with which an attractor may collide.
Safe, explosive, and dangerous bifurcations in dissipative dynamical systems
International Nuclear Information System (INIS)
A comprehensive listing of the generic codimension-1 attractor bifurcations of dissipative dynamical systems is presented. It includes local and global bifurcations of regular and chaotic attractors. The bifurcations are classified according to the continuity or discontinuity of the attractor path, which governs the physical outcome that would be observed under a slow control sweep. Related issues of determinacy, hysteresis, basin structure, and intermittency are addressed. Recently discovered chaotic bifurcations are discussed in some detail, with particular reference to the regular or chaotic saddle-type destroyer with which an attractor may collide
Lee, Seung-Jun; Park, Sung-Ha
2013-01-01
Arterial ageing is characterized by age associated degeneration and sclerosis of the media layer of the large arteries. However, besides ageing, clinical conditions, which enhance oxidative stress and inflammation act to accelerate the degree of arterial ageing. In this review, we summarized the pathophysiology and contributing factors that accelerate arterial ageing. Among them, we focused on hypertension, the renin-angiotensin-aldosterone system and vascular inflammation which are modifiabl...
Chen, Kuen-Bao; Chen, Kuan-Chung; Chang, Ya-Lin; Chang, Kun-Lung; Chang, Pei-Chun; Chang, Tung-Ti; Chen, Yu-Chian
2016-01-01
Coronary artery disease (CAD) is the most common cause of heart attack and the leading cause of mortality in the world. It is associated with mitochondrial dysfunction and increased level of reactive oxygen species production. According to the Ottawa Heart Genomics Study genome-wide association study, a recent research identified that Q688 spastic paraplegia 7 (SPG7) variant is associated with CAD as it bypasses the regulation of tyrosine phosphorylation of AFG3L2 and enhances the processing and maturation of SPG7 protein. This study aims to identify potential compounds isolated from Traditional Chinese Medicines (TCMs) as potential lead compounds for paraplegin (SPG7) inhibitors. For the crystallographic structure of paraplegin, the disordered disposition of key amino acids in the binding site was predicted using the PONDR-Fit protocol before virtual screening. The TCM compounds saussureamine C and 3-(2-carboxyphenyl)-4(3H)-quinazolinone, have potential binding affinities with stable H-bonds and hydrophobic contacts with key residues of paraplegin. A molecular dynamics simulation was performed to validate the stability of the interactions between each candidate and paraplegin under dynamic conditions. Hence, we propose these compounds as potential candidates as lead drug from the compounds isolated from TCM for further study in drug development process with paraplegin protein for coronary artery disease. PMID:27164068
Zhang, Ying; Menon, Nishanth V; Li, Chuan; Chan, Vincent; Kang, Yuejun
2016-02-23
Vascular smooth muscle cells (SMCs) are located in the middle of the tunica media and regulate the vasodilation and vasoconstriction of the blood vessels. SMCs also play a critical role during the development of atherosclerotic lesions, which are mainly found at sites of disturbed blood flow such as arterial branch points and bifurcations. Although the migratory and proliferative activities of SMCs and their phenotypic switch have been widely studied, the mechanotransduction of the SMC layer underlying atherosclerotic plaques remains unclear. In this study, bifurcate micropatterns with different angles were fabricated with polydimethylsiloxane and polyacrylamide gel for SMC culture and characterization of cell traction force. The cellular morphology, density and orientation-specific adaptation during branched cell layer formation on this platform were monitored until they became confluence. The results indicated that the characteristic cell traction forces and the von Mises stresses were dependent on bifurcation angles, which might provide important geometrical cues associated with the development of atherosclerosis. Immunofluorescence staining and gene analysis further revealed the proliferative and migratory states of SMCs in response to different bifurcation angles, which might elucidate the localization and progression of atherosclerotic lesions. PMID:26648015
ANGIOGRAPHIC PROFILE OF LEFT MAIN CORONARY ARTERY (LMCA STENOSIS
Directory of Open Access Journals (Sweden)
Malladi Srinivasa
2015-02-01
Full Text Available Among patients with coronary artery disease, left coronary artery (LMCA stenosis is the dangerous form of coronary arterial involvement, associated with increased mortality and morbidity unless immediate intervention is done. The gold standard treatment for left main coronary artery (LMCA stenosis is the emergency coronary artery bypass grafting to its branches, left anterior descending artery (LAD, and left circumflex artery (LCX. Of percutaneous intervention in the form of angioplasty and stenting of left main coronary artery are increasingly done. The anatomy and the site of stenosi s in the left main coronary artery determine the management option. In this context, the involvement of left main coronary artery and its anatomical pattern are important in deciding management options. AIM: To study the angiographic profile of significant Left main coronary artery (LMCA stenosis among the patients who underwent coronary angiography. METHODS: A total of 1911 cases of significant coronary arterial disease, who underwent coronary angiography a t King George Hospital, Visakhapatnam were studied in the present study and their coronary angiograms were analysed with respect to the pattern of involvement. RESULTS: of the 1911 cases of coronary artery disease, 118 patients have left main coronary arte ry disease. M/F ratio is 93/25. Of them 68.4% are hypertensive, 41.5 % are diabetics, 34.7% are smokers. Mean age of presentation was 59 yrs. Isolated LMCA involvement is seen in 5, associated with single vessel disease in 9, double vessel disease in 12 an d triple vessel diseases in 93. Ostio - proximal involvement is seen in 21, mid segment involvement in 13, distal – bifurcation involvement in 93 and total occlusion of LMCA in 1 case. CONCLUSION: Significant LMCA involvement is seen in 6.1%. In majority of c ases, it is associated with triple vessel disease and distal bifurcation is the commonest site involved.
Homoclinic bifurcation in Chua’s circuit
Indian Academy of Sciences (India)
S K Dana; S Chakraborty; G Ananthakrishna
2005-03-01
We report our experimental observations of the Shil’nikov-type homoclinic chaos in asymmetry-induced Chua’s oscillator. The asymmetry plays a crucial role in the related homoclinic bifurcations. The asymmetry is introduced in the circuit by forcing a DC voltage. For a selected asymmetry, when a system parameter is controlled, we observed transition from large amplitude limit cycle to homoclinic chaos via a sequence of periodic mixed-mode oscillations interspersed by chaotic states. Moreover, we observed two intermediate bursting regimes. Experimental evidences of homoclinic chaos are verified with PSPICE simulations.
Bifurcation Control, Manufacturing Planning and Formation Control
Institute of Scientific and Technical Information of China (English)
Wei Kang; Mumin Song; Ning Xi
2005-01-01
The paper consists of three topics on control theory and engineering applications, namely bifurcation control, manufacturing planning, and formation control. For each topic, we summarize the control problem to be addressed and some key ideas used in our recent research. Interested readers are referred to related publications for more details. Each of the three topics in this paper is technically independent from the other ones. However, all three parts together reflect the recent research activities of the first author, jointly with other researchers in different fields.
Bifurcation structure of an optical ring cavity
DEFF Research Database (Denmark)
Kubstrup, C.; Mosekilde, Erik
1996-01-01
One- and two-dimensional continuation techniques are applied to determine the basic bifurcation structure for an optical ring cavity with a nonlinear absorbing element (the Ikeda Map). By virtue of the periodic structure of the map, families of similar solutions develop in parameter space. Within...... the individual family, the organization of the solutions exhibit an infinite number of regulatory arranged domains, the so-called swallow tails. We discuss the origin of this structure which has recently been observed in a variety of other systems as well....
Longitudinal stent deformation during coronary bifurcation stenting.
Vijayvergiya, Rajesh; Sharma, Prafull; Gupta, Ankush; Goyal, Praveg; Panda, Prashant
2016-03-01
A distortion of implanted coronary stent along its longitudinal axis during coronary intervention is known as longitudinal stent deformation (LSD). LSD is frequently seen with newer drug eluting stents (DES), specifically with PROMUS Element stent. It is usually caused by impact of guide catheter tip, or following passage of catheters like balloon catheter, IVUS catheter, guideliner, etc. We hereby report a case of LSD during coronary bifurcation lesion intervention, using two-stents technique. Patient had acute stent thrombosis as a complication of LSD, which was successfully managed. PMID:26811144
Bifurcation analysis of a preloaded Jeffcott rotor
International Nuclear Information System (INIS)
A model of two-degrees-of-freedom Jeffcott rotor system with bearing clearance subjected of an out-of-balance excitation is considered. The influence of preloading and viscous damping of the snubber ring is introduced in the mathematical description. A programme of numerical simulations is conducted to show how the preloading and viscous damping change the dynamics of the rotor system. Bifurcation diagrams and Lyapunov exponents are constructed to explore stability. It is shown that dynamics of the rotor system can be effectively controlled by varying the preloading and the damping both of the rotor and the snubber ring. In the most considered cases preloading stabilises the dynamic responses
Bifurcation analysis of a preloaded Jeffcott rotor
Energy Technology Data Exchange (ETDEWEB)
Karpenko, Evgueni V.; Pavlovskaia, Ekaterina E.; Wiercigroch, Marian E-mail: m.wiercigroch@eng.abdn.ac.uk
2003-01-01
A model of two-degrees-of-freedom Jeffcott rotor system with bearing clearance subjected of an out-of-balance excitation is considered. The influence of preloading and viscous damping of the snubber ring is introduced in the mathematical description. A programme of numerical simulations is conducted to show how the preloading and viscous damping change the dynamics of the rotor system. Bifurcation diagrams and Lyapunov exponents are constructed to explore stability. It is shown that dynamics of the rotor system can be effectively controlled by varying the preloading and the damping both of the rotor and the snubber ring. In the most considered cases preloading stabilises the dynamic responses.
Nadeem, S.; Ijaz, S.
2016-07-01
In this paper hemodynamics of stenosis are discussed to predict effect of atherosclerosis by means of mathematical models in the presence of uniform transverse magnetic field. The analysis is carried out using silver and copper nanoparticles as a drug carrier. Exact solution for the fluid temperature, velocity, axial induced magnetic field and current density distribution are obtained under mild stenosis approximation. The results indicate that with an increase in the concentration of nanoparticle hemodynamics effects of stenosis reduces throughout the inclined composite stenosed arteries. The considered analysis also summarizes that the drug silver nanoparticles is more efficient to reduce hemodynamics of stenosis when compare to the drug copper nanoparticle. In future this model could be helpful to predict important properties in some biomedical applications.
Directory of Open Access Journals (Sweden)
F Joibar
2013-12-01
Results: The outcome of nitric oxide plasmatic density measurement showed that nitric oxide level in animal ’s blood in 175 mg/kg/day dose recipient group and 350 mg/kg/day dose recipient group increased significantly compared with the control group at the level of P ≤ 0.05. Also thickness of media layer decreased in maximum dose group (350 mg/kg/day dose compared to the control group. Conclusion: Based on the results of different doses of sodium nitrite, the nitric oxide levels in the blood were increased, and the thickness of middle layer of the lung arteries at dose 350 mg of sodium nitrite was reduced.
International Nuclear Information System (INIS)
A port catheter system for hepatic artery infusion chemotherapy was implanted percutaneously via the left subclavian artery in 41 patients for treatment of unresectable liver metastases. The catheter tip was inserted into the gastroduodenal artery (GDA), the end hole was occluded with a guidewire fragment, and a side-hole for infusion was positioned at the bifurcation of the proper hepatic artery and the GDA. The GDA was embolized with steel coils around the infusion catheter tip via a transfemoral catheter. This procedure is designed to reduce the incidence of hepatic artery occlusion and infusion catheter dislocation
International Nuclear Information System (INIS)
A port catheter system for hepatic artery infusion chemotherapy was implanted percutaneously via the left subclavian artery in 41 patients for treatment of unresectable liver metastases. The catheter tip was inserted into the gastroduodenal artery (GDA), the end hole was occluded with a guidewire fragment, and a side-hole for infusion was positioned at the bifurcation of the proper hepatic artery and the GDA. The GDA was embolized with steel coils around the infusion catheter tip via a transfemoral catheter. This procedure is designed to reduce the incidence of hepatic artery occlusion and infusion catheter dislocation.
Swept-parameter-induced postponements and noise on the Hopf bifurcation.
Fronzoni, L.; Moss, F; McClintock, Peter V. E.
1987-01-01
The postponement of Hopf bifurcations driven by a swept bifurcation parameter is demonstrated with an electronic Brusselator. Noise on the swept parameter destroys the postponement and the bifurcation as it is usually defined.
On the application of Newton's and Chord methods to bifurcation problems
Directory of Open Access Journals (Sweden)
M. B. M. Elgindi
1994-01-01
Full Text Available This paper is concerned with the applications of Newton's and chord methods in the computations of the bifurcation solutions in a neighborhood of a simple bifurcation point for prescribed values of the bifurcation parameter.
Bifurcation sequences in the symmetric 1:1 Hamiltonian resonance
Marchesiello, Antonella
2015-01-01
We present a general review of the bifurcation sequences of periodic orbits in general position of a family of resonant Hamiltonian normal forms with nearly equal unperturbed frequencies, invariant under $Z_2 \\times Z_2$ symmetry. The rich structure of these classical systems is investigated with geometric methods and the relation with the singularity theory approach is also highlighted. The geometric approach is the most straightforward way to obtain a general picture of the phase-space dynamics of the family as is defined by a complete subset in the space of control parameters complying with the symmetry constraint. It is shown how to find an energy-momentum map describing the phase space structure of each member of the family, a catastrophe map that captures its global features and formal expressions for action-angle variables. Several examples, mainly taken from astrodynamics, are used as applications.
Directory of Open Access Journals (Sweden)
Kanchan Kulkarni
2015-01-01
Full Text Available Sudden cardiac death instigated by ventricular fibrillation (VF is the largest cause of natural death in the USA. Alternans, a beat-to-beat alternation in the action potential duration, has been implicated as being proarrhythmic. The onset of alternans is mediated via a bifurcation, which may occur through either a smooth or a border-collision mechanism. The objective of this study was to characterize the mechanism of bifurcation to alternans based on experiments in isolated whole rabbit hearts. High resolution optical mapping was performed and the electrical activity was recorded from the left ventricle (LV epicardial surface of the heart. Each heart was paced using an “alternate pacing protocol,” where the basic cycle length (BCL was alternatively perturbed by ±δ. Local onset of alternans in the heart, BCLstart, was measured in the absence of perturbations (δ=0 and was defined as the BCL at which 10% of LV exhibited alternans. The influences of perturbation size were investigated at two BCLs: one prior to BCLstart (BCLprior=BCLstart+20 ms and one preceding BCLprior (BCLfar=BCLstart+40 ms. Our results demonstrate significant spatial correlation of the region exhibiting alternans with smooth bifurcation characteristics, indicating that transition to alternans in isolated rabbit hearts occurs predominantly through smooth bifurcation.
International Nuclear Information System (INIS)
In this paper we investigate non-radial stationary solutions of a free boundary problem modelling tumour growth under the action of inhibitors. The model consists of two elliptic equations describing the concentration of nutrients and inhibitors, respectively, and a Stokes equation for the velocity of tumour cells and internal pressure. The ratio μ/γ of the proliferation rate μ and the cell-to-cell adhesiveness γ plays the role of the bifurcation parameter. We prove that in certain situations there exists a positive sequence {(μ/γ)n}n≥n* such that for each (μ/γ)n(n even ⩾n*) there exist non-radial stationary solutions bifurcating from the radial stationary solution, while in the other situations there exists at most a finite number of bifurcation points. This is a remarkable difference from the corresponding inhibitor-free model where there always exist infinitely many branches of non-radial stationary bifurcation solutions. Our analysis also indicates that inhibitor supply may lower the ability of tumour invasion, and even make the tumour unaggressive and stable. (paper)
Fast-scale border collision bifurcation in SEPIC power factor pre-regulators
International Nuclear Information System (INIS)
In this paper we report a kind of fast-scale instability occurring in the single-ended primary inductance converter (SEPIC) power factor pre-regulator, which is designed to operate in discontinuous conduction mode. Main results are given by exact cycle-by-cycle computer simulations as well as theoretical analysis. It is found that the instability phenomenon manifests itself as a fast-scale bifurcation at the switching period, which implies the occurrence of border collision bifurcation, or is related to the transition of the regular operating mode of the SEPIC. According to the theoretical analysis and simulation results, the effects of parameters on system stability, and the locations of the bifurcation points are confirmed. Moreover, the effects of such an instability on power factor and switching stress are also discussed. Finally, the occurrence of the asymmetric bifurcation locations is investigated. The results show that this work provides a convenient means of predicting stability boundaries which can facilitate the selection of the practical parameters. (general)
Fast-scale border collision bifurcation in SEPIC power factor pre-regulators
Institute of Scientific and Technical Information of China (English)
Liu Fang
2008-01-01
In this paper we report a kind of fast-scale instability occurring in the single-ended primary inductance converter (SEPIC) power factor pre-regulator, which is designed to operate in discontinuous conduction mode. Main results are given by exact cycle-by-cycle computer simulations as well as theoretical analysis. It is found that the instability phenomenon manifests itself as a fast-scale bifurcation at the switching period, which implies the occurrence of border collision bifurcation, or is related to the transition of the regular operating mode of the SEPIC. According to the theoretical analysis and simulation results, the effects of parameters on system stability, and the locations of the bifurcation points are confirmed. Moreover, the effects of such an instability on power factor and switching stress are also discussed. Finally, the occurrence of the asymmetric bifurcation locations is investigated. The results show that this work provides a convenient means of predicting stability boundaries which can facilitate the selection of the practical parameters.
[An integrated segmentation method for 3D ultrasound carotid artery].
Yang, Xin; Wu, Huihui; Liu, Yang; Xu, Hongwei; Liang, Huageng; Cai, Wenjuan; Fang, Mengjie; Wang, Yujie
2013-07-01
An integrated segmentation method for 3D ultrasound carotid artery was proposed. 3D ultrasound image was sliced into transverse, coronal and sagittal 2D images on the carotid bifurcation point. Then, the three images were processed respectively, and the carotid artery contours and thickness were obtained finally. This paper tries to overcome the disadvantages of current computer aided diagnosis method, such as high computational complexity, easily introduced subjective errors et al. The proposed method could get the carotid artery overall information rapidly, accurately and completely. It could be transplanted into clinical usage for atherosclerosis diagnosis and prevention. PMID:24195385
Inversion of hematocrit partition at microfluidic bifurcations
Shen, Zaiyi; Kaoui, Badr; Polack, Benoît; Harting, Jens; Misbah, Chaouqi; Podgorski, Thomas
2016-01-01
Partitioning of red blood cells (RBCs) at the level of bifurcations in the microcirculatory system affects many physiological functions yet it remains poorly understood. We address this problem by using T-shaped microfluidic bifurcations as a model. Our computer simulations and in vitro experiments reveal that the hematocrit ($\\phi_0$) partition depends strongly on RBC deformability, as long as $\\phi_0 <20$% (within the normal range in microcirculation), and can even lead to complete deprivation of RBCs in a child branch. Furthermore, we discover a deviation from the Zweifach-Fung effect which states that the child branch with lower flow rate recruits less RBCs than the higher flow rate child branch. At small enough $\\phi_0$, we get the inverse scenario, and the hematocrit in the lower flow rate child branch is even higher than in the parent vessel. We explain this result by an intricate up-stream RBC organization and we highlight the extreme dependence of RBC transport on geometrical and cell mechanical p...
Acute arterial occlusion - kidney
... arterial thrombosis; Renal artery embolism; Acute renal artery occlusion; Embolism - renal artery ... often result in permanent kidney failure. Acute arterial occlusion of the renal artery can occur after injury ...
A Case of Behcet’s Disease with Arterial Occlusion and Multiple Aneurysms
Directory of Open Access Journals (Sweden)
S. A. Mostofy
2005-06-01
Full Text Available Vascular involvement in Behçet’s disease is divided into venous and arterial thrombosis and arterial aneurismal formation. Multiple arterial aneurysms rarely occur in Behçet’s disease; however, when they do occur, they cause so me complex signs and symptoms related to the location of arterial involvement. We descri be a 22-year-old male with Behçet’s disease and multiple arterial aneurysms in the main arterial branches of the neck, such as left and right subclavian aneurysms, innominate and left caro tid bifurcation arterial aneurysms, together with right vertebral and left subclavian artery occlusions. This case shows that multiple arterial involvem ents should be considered as one of the possible manifestations of Behçet’s disease.
International Nuclear Information System (INIS)
Variation of the branches of the external carotid artery (ECA) is well known, but it is extremely rare for the occipital artery (OA) to arise from the internal carotid artery (ICA). A 87-year-old man was found to have this anatomical variation on the right side by threedimensional computed tomography angiography for vascular mapping of the carotid arteries before superselective intra-arterial catheterization for advanced tongue cancer. Imaging showed the OA arose from the anterior aspect of the right ICA with the origin located 8.8 mm distal from the carotid bifurcation. The inner diameter of the origin of the OA was 2.1 mm and the angle between the OA and the ICA was 62 degrees. It is important to recognize this anatomic variation of the branches of the ECA before head and neck microsurgical reconstruction or superselective intra-arterial chemotherapy for oral cancer
Bifurcation of the femur with tibial agenesis and additional anomalies
van der Smagt, JJ; Bos, CFA; van Haeringen, A; Hogendoorn, PCW; Breuning, MH
2005-01-01
Bifurcation of the femur and tibial agenesis are rare anomalies and have been described in both the Gollop-Wolfgang Complex and the tibial agenesis-ectrodactyly syndrome. We report on two patients with bifurcation of the femur and tibial agenesis. Hand ectrodactyly was seen in one of these patients.
Degenerate Orbit Flip Homoclinic Bifurcations with Higher Dimensions
Institute of Scientific and Technical Information of China (English)
Ran Chao WU; Jian Hua SUN
2006-01-01
Bifurcations of a degenerate homoclinic orbit with orbit flip in high dimensional system are existence and uniqueness of 1-homoclinic orbit and 1-periodic orbit are given. Also considered is the existence of 2-homoclinic orbit and 2-periodic orbit. In additon, the corresponding bifurcation surfaces are given.
Hopf Bifurcation in a New Four-Dimensional Hyperchaotic System
Li, Xin; Yan, Zhen-Ya
2015-08-01
In this paper, the Hopf bifurcation in a new hyperchaotic system is studied. Based on the first Lyapunov coefficient theory and symbolic computation, the conditions of supercritical and subcritical bifurcation in the new hyperchaotic system are obtained. Numerical simulations are used to illustrate some main results. Supported by National Key Bsic Research Program of China under Grant No. 2011CB302400
Views on the Hopf bifurcation with respect to voltage instabilities
Energy Technology Data Exchange (ETDEWEB)
Roa-Sepulveda, C.A. [Universidad de Concepcion, Concepcion (Chile). Dept. de Ingenieria Electrica; Knight, U.G. [Imperial Coll. of Science and Technology, London (United Kingdom). Dept. of Electrical and Electronic Engineering
1994-12-31
This paper presents a sensitivity study of the Hopf bifurcation phenomenon which can in theory appear in power systems, with reference to the dynamics of the process and the impact of demand characteristics. Conclusions are drawn regarding power levels at which these bifurcations could appear and concern the concept of the imaginary axis as a `hard` limit eigenvalue analyses. (author) 20 refs., 31 figs.
Sediment discharge division at two tidally influenced river bifurcations
Sassi, M.G.; Hoitink, A.J.F.; Vermeulen, B.; Hidayat, H.
2013-01-01
[1] We characterize and quantify the sediment discharge division at two tidally influenced river bifurcations in response to mean flow and secondary circulation by employing a boat-mounted acoustic Doppler current profiler (ADCP), to survey transects at bifurcating branches during a semidiurnal tida
Non-Gaussian bifurcating models and quasi-likelihood estimation
Basawa, I. V.; J. Zhou
2004-01-01
A general class of Markovian non-Gaussian bifurcating models for cell lineage data is presented. Examples include bifurcating autoregression, random coefficient autoregression, bivariate exponential, bivariate gamma, and bivariate Poisson models. Quasi-likelihood estimation for the model parameters and large-sample properties of the estimates are discussed.
Identification of Bifurcations from Observations of Noisy Biological Oscillators.
Salvi, Joshua D; Ó Maoiléidigh, Dáibhid; Hudspeth, A J
2016-08-23
Hair bundles are biological oscillators that actively transduce mechanical stimuli into electrical signals in the auditory, vestibular, and lateral-line systems of vertebrates. A bundle's function can be explained in part by its operation near a particular type of bifurcation, a qualitative change in behavior. By operating near different varieties of bifurcation, the bundle responds best to disparate classes of stimuli. We show how to determine the identity of and proximity to distinct bifurcations despite the presence of substantial environmental noise. Using an improved mechanical-load clamp to coerce a hair bundle to traverse different bifurcations, we find that a bundle operates within at least two functional regimes. When coupled to a high-stiffness load, a bundle functions near a supercritical Hopf bifurcation, in which case it responds best to sinusoidal stimuli such as those detected by an auditory organ. When the load stiffness is low, a bundle instead resides close to a subcritical Hopf bifurcation and achieves a graded frequency response-a continuous change in the rate, but not the amplitude, of spiking in response to changes in the offset force-a behavior that is useful in a vestibular organ. The mechanical load in vivo might therefore control a hair bundle's responsiveness for effective operation in a particular receptor organ. Our results provide direct experimental evidence for the existence of distinct bifurcations associated with a noisy biological oscillator, and demonstrate a general strategy for bifurcation analysis based on observations of any noisy system. PMID:27558723
Critical bifurcation surfaces of 3D discrete dynamics
Directory of Open Access Journals (Sweden)
Michael Sonis
2000-01-01
Full Text Available This paper deals with the analytical representation of bifurcations of each 3D discrete dynamics depending on the set of bifurcation parameters. The procedure of bifurcation analysis proposed in this paper represents the 3D elaboration and specification of the general algorithm of the n-dimensional linear bifurcation analysis proposed by the author earlier. It is proven that 3D domain of asymptotic stability (attraction of the fixed point for a given 3D discrete dynamics is bounded by three critical bifurcation surfaces: the divergence, flip and flutter surfaces. The analytical construction of these surfaces is achieved with the help of classical Routh–Hurvitz conditions of asymptotic stability. As an application the adjustment process proposed by T. Puu for the Cournot oligopoly model is considered in detail.
Comments on the Bifurcation Structure of 1D Maps
DEFF Research Database (Denmark)
Belykh, V.N.; Mosekilde, Erik
1997-01-01
The paper presents a complementary view on some of the phenomena related to the bifurcation structure of unimodal maps. An approximate renormalization theory for the period-doubling cascade is developed, and a mapping procedure is established that accounts directly for the box-within-a-box struct......The paper presents a complementary view on some of the phenomena related to the bifurcation structure of unimodal maps. An approximate renormalization theory for the period-doubling cascade is developed, and a mapping procedure is established that accounts directly for the box......-within-a-box structure of the total bifurcation set. This presents a picture in which the homoclinic orbit bifurcations act as a skeleton for the bifurcational set. At the same time, experimental results on continued subharmonic generation for piezoelectrically amplified sound waves, predating the Feigenbaum theory, are...
Cone-beam CT of the internal carotid artery
Hyde, Derek E.; Naik, Sandeep; Habets, Damiaan F.; Holdsworth, David W.
2002-05-01
The gold standard for NASCET-type stenosis measurements is currently 2D digital subtraction angiography (DSA). In this paper, we evaluate the efficacy of 3D cone-beam, Volumetric Subtraction Angiography (VSA) for assessing internal carotid artery stenosis, by comparison with conventional DSA. VSA perspective maximum intensity projections (MIPs) and DSAs were assessed separately for NASCET-type, minimum stenosis measurements. Although virtually any viewing angle of the VSA was possible, the minimum stenosis grades were not significantly higher than that of the DSAs. Our study of 38 arteries yielded a sensitivity and specificity of 100% (using a clinically relevant 60% stenosis threshold). Measurements from three neuroradiologists provided an average stenosis grade of 75 +/- 6% and 76 +/- 7% for the DSA and VSA respectively. A paired student t-test indicated a 98% confidence of no statistical difference in the means. Thus, VSA provides gold standard 3D information about carotid lumen geometry. While not intended to supplant noninvasive techniques during routine clinical diagnosis, it does provide a 3D reference standard for research investigations. Additionally, cone-beam CT can provide quantification of calcification around the carotid bifurcation.
Construction of a coronary artery atlas from CT angiography.
Medrano-Gracia, Pau; Ormiston, John; Webster, Mark; Beier, Susann; Ellis, Chris; Wang, Chunliang; Young, Alistair A; Cowan, Brett R
2014-01-01
Describing the detailed statistical anatomy of the coronary artery tree is important for determining the aetiology of heart disease. A number of studies have investigated geometrical features and have found that these correlate with clinical outcomes, e.g. bifurcation angle with major adverse cardiac events. These methodologies were mainly two-dimensional, manual and prone to inter-observer variability, and the data commonly relates to cases already with pathology. We propose a hybrid atlasing methodology to build a population of computational models of the coronary arteries to comprehensively and accurately assess anatomy including 3D size, geometry and shape descriptors. A random sample of 122 cardiac CT scans with a calcium score of zero was segmented and analysed using a standardised protocol. The resulting atlas includes, but is not limited to, the distributions of the coronary tree in terms of angles, diameters, centrelines, principal component shape analysis and cross-sectional contours. This novel resource will facilitate the improvement of stent design and provide a reference for hemodynamic simulations, and provides a basis for large normal and pathological databases. PMID:25485418
Neary, Joseph M; Gould, Daniel H; Garry, Franklyn B; Knight, Anthony P; Dargatz, David A; Holt, Timothy N
2013-03-01
Producer reports from ranches over 2,438 meters in southwest Colorado suggest that the mortality of preweaned beef calves may be substantially higher than the national average despite the selection of low pulmonary pressure herd sires for over 20 years. Diagnostic investigations of this death loss problem have been limited due to the extensive mountainous terrain over which these calves are grazed with their dams. The objective of the current study was to determine the causes of calf mortality on 5 high-altitude ranches in Colorado that have been selectively breeding sires with low pulmonary pressure (branding (6 weeks of age) in the spring to weaning in the fall (7 months of age). Clinical signs were recorded, and blood samples were taken from sick calves. Postmortem examinations were performed, and select tissue samples were submitted for aerobic culture and/or histopathology. On the principal study ranch, 9.6% (59/612) of the calves that were branded in the spring either died or were presumed dead by weaning in the fall. In total, 28 necropsies were performed: 14 calves (50%) had lesions consistent with pulmonary hypertension and right-sided heart failure, and 14 calves (50%) died from bronchopneumonia. Remodeling of the pulmonary arterial system, indicative of pulmonary hypertension, was evident in the former and to varying degrees in the latter. There is a need to better characterize the additional risk factors that complicate pulmonary arterial pressure testing of herd sires as a strategy to control pulmonary hypertension. PMID:23512918
Characterization of volumetric flow rate waveforms at the carotid bifurcations of older adults
International Nuclear Information System (INIS)
While it is widely appreciated that volumetric blood flow rate (VFR) dynamics change with age, there has been no detailed characterization of the typical shape of carotid bifurcation VFR waveforms of older adults. Toward this end, retrospectively gated phase contrast magnetic resonance imaging was used to measure time-resolved VFR waveforms proximal and distal to the carotid bifurcations of 94 older adults (age 68 ± 8 years) with little or no carotid artery disease, recruited from the BLSA cohort of the VALIDATE study of factors in vascular aging. Timings and amplitudes of well-defined feature points from these waveforms were extracted automatically and averaged to produce representative common, internal and external carotid artery (CCA, ICA and ECA) waveform shapes. Relative to young adults, waveforms from older adults were found to exhibit a significantly augmented secondary peak during late systole, resulting in significantly higher resistance index (RI) and flow augmentation index (FAI). Cycle-averaged VFR at the CCA, ICA and ECA were 389 ± 74, 245 ± 61 and 125 ± 49 mL min−1, respectively, reflecting a significant cycle-averaged outflow deficit of 5%, which peaked at around 10% during systole. A small but significant mean delay of 13 ms between arrivals of ICA versus CCA/ECA peak VFR suggested differential compliance of these vessels. Sex and age differences in waveform shape were also noted. The characteristic waveforms presented here may serve as a convenient baseline for studies of VFR waveform dynamics or as suitable boundary conditions for models of blood flow in the carotid arteries of older adults
Climate bifurcation during the last deglaciation?
Directory of Open Access Journals (Sweden)
T. M. Lenton
2012-07-01
Full Text Available There were two abrupt warming events during the last deglaciation, at the start of the Bølling-Allerød and at the end of the Younger Dryas, but their underlying dynamics are unclear. Some abrupt climate changes may involve gradual forcing past a bifurcation point, in which a prevailing climate state loses its stability and the climate tips into an alternative state, providing an early warning signal in the form of slowing responses to perturbations, which may be accompanied by increasing variability. Alternatively, short-term stochastic variability in the climate system can trigger abrupt climate changes, without early warning. Previous work has found signals consistent with slowing down during the last deglaciation as a whole, and during the Younger Dryas, but with conflicting results in the run-up to the Bølling-Allerød. Based on this, we hypothesise that a bifurcation point was approached at the end of the Younger Dryas, in which the cold climate state, with weak Atlantic overturning circulation, lost its stability, and the climate tipped irreversibly into a warm interglacial state. To test the bifurcation hypothesis, we analysed two different climate proxies in three Greenland ice cores, from the Last Glacial Maximum to the end of the Younger Dryas. Prior to the Bølling warming, there was a robust increase in climate variability but no consistent slowing down signal, suggesting this abrupt change was probably triggered by a stochastic fluctuation. The transition to the warm Bølling-Allerød state was accompanied by a slowing down in climate dynamics and an increase in climate variability. We suggest that the Bølling warming excited an internal mode of variability in Atlantic meridional overturning circulation strength, causing multi-centennial climate fluctuations. However, the return to the Younger Dryas cold state increased climate stability. We find no consistent evidence for slowing down during the Younger Dryas, or in a longer
International Nuclear Information System (INIS)
This paper deals with periodic solutions of the Hamilton equation x-dot (t)=J∇x H(x(t),λ), where H element of C2,0(R2n×Rk,R) and λ element of Rk is a parameter. Theorems on global bifurcation of solutions with periods (2π)/j, j element of N, from a stationary point (x0,λ0) element of R2n×Rk are proved. ∇x2 H(x0,λ0) can be singular. However, it is assumed that the local topological degree of ∇xH(·, λ0) at x0 is nonzero. For systems satisfying ∇xH(x0, λ) = 0 for all λ element of Rk it is shown that (global) bifurcation points of solutions with periods (2π)/j can be identified with zeros of appropriate continuous functions Fj:Rk→R. If, for all λ element of Rk, ∇x2H(x0,λ)=diag(A(λ),B(λ)), where A(λ) and B(λ) are (n × n)-matrices, then Fj can be defined by Fj(λ) = det[A(λ)B(λ) − j2I]. Symmetry breaking results concerning bifurcation of solutions with different minimal periods are obtained. A geometric description of the set of bifurcation points is given. Examples of constructive application of the theorems proved to analytical and numerical investigation and visualization of the set of all bifurcation points in given domain are provided. This paper is based on a part of the author's thesis (Radzki 2005 Branching points of periodic solutions of autonomous Hamiltonian systems (Polish) PhD Thesis Nicolaus Copernicus University, Faculty of Mathematics and Computer Science, Toruń)
Malvè, M; Gharib, A M; Yazdani, S K; Finet, G; Martínez, M A; Pettigrew, R; Ohayon, J
2015-01-01
The purpose of the present study was to determine whether in vivo bifurcation geometric factors would permit prediction of the risk of atherosclerosis. It is worldwide accepted that low or oscillatory wall shear stress (WSS) is a robust hemodynamic factor in the development of atherosclerotic plaque and has a strong correlation with the local site of plaque deposition. However, it still remains unclear how coronary bifurcation geometries are correlated with such hemodynamic forces. Computational fluid dynamics simulations were performed on left main (LM) coronary bifurcation geometries derived from CT of eight patients without significant atherosclerosis. WSS amplitudes were accurately quantified at two high risk zones of atherosclerosis, namely at proximal left anterior descending artery (LAD) and at proximal left circumflex artery (LCx), and also at three high WSS concentration sites near the bifurcation. Statistical analysis was used to highlight relationships between WSS amplitudes calculated at these five zones of interest and various geometric factors. The tortuosity index of the LM-LAD segment appears to be an emergent geometric factor in determining the low WSS amplitude at proximal LAD. Strong correlations were found between the high WSS amplitudes calculated at the endothelial regions close to the flow divider. This study not only demonstrated that CT imaging studies of local risk factor for atherosclerosis could be clinically performed, but also showed that tortuosity of LM-LAD coronary branch could be used as a surrogate marker for the onset of atherosclerosis. PMID:24986333
The simplest normal form of Hopf bifurcation
Yu, P.; Leung, A. Y. T.
2003-01-01
Recently, further reduction on normal forms of differential equations leading to the simplest normal forms (SNFs) has received considerable attention. However, the computation of the SNF has been mainly restricted to systems which do not contain perturbation parameters (unfolding), since the computation of the SNF with unfolding is much more complicated than that of the SNF without unfolding. From the practical point of view, only the SNF with perturbation (bifurcation) parameters is useful in analysing physical or engineering problems. It is shown that the SNF with unfolding cannot be obtained using only near-identity transformation. Additional transformations such as time and parameter rescaling need to be introduced. An efficient computational method is presented for computing the algebraic equations that can be used to find the SNF. A physical example is given to show the applicability of the new method.
Chua Corsage Memristor Oscillator via Hopf Bifurcation
Mannan, Zubaer Ibna; Choi, Hyuncheol; Kim, Hyongsuk
This paper demonstrates that the Chua Corsage Memristor, when connected in series with an inductor and a battery, oscillates about a locally-active operating point located on the memristor’s DC V-I curve. On the operating point, a small-signal equivalent circuit is derived via a Taylor series expansion. The small-signal admittance Y (s,V ) is derived from the small-signal equivalent circuit and the value of inductance is determined at a frequency where the real part of the admittance ReY (iω) of the small-signal equivalent circuit of Chua Corsage Memristor is zero. Oscillation of the circuit is analyzed via an in-depth application of the theory of Local Activity, Edge of Chaos and the Hopf-bifurcation.
Bifurcated SEN with Fluid Flow Conditioners
Directory of Open Access Journals (Sweden)
F. Rivera-Perez
2014-01-01
Full Text Available This work evaluates the performance of a novel design for a bifurcated submerged entry nozzle (SEN used for the continuous casting of steel slabs. The proposed design incorporates fluid flow conditioners attached on SEN external wall. The fluid flow conditioners impose a pseudosymmetric pattern in the upper zone of the mold by inhibiting the fluid exchange between the zones created by conditioners. The performance of the SEN with fluid flow conditioners is analyzed through numerical simulations using the CFD technique. Numerical results were validated by means of physical simulations conducted on a scaled cold water model. Numerical and physical simulations confirmed that the performance of the proposed SEN is superior to a traditional one. Fluid flow conditioners reduce the liquid free surface fluctuations and minimize the occurrence of vortexes at the free surface.
Brownrigg, J R W; Hinchliffe, R J; Apelqvist, J; Boyko, E J; Fitridge, R; Mills, J L; Reekers, J; Shearman, C P; Zierler, R E; Schaper, N C
2016-01-01
Non-invasive tests for the detection of peripheral artery disease (PAD) among individuals with diabetes mellitus are important to estimate the risk of amputation, ulceration, wound healing and the presence of cardiovascular disease, yet there are no consensus recommendations to support a particular diagnostic modality over another and to evaluate the performance of index non-invasive diagnostic tests against reference standard imaging techniques (magnetic resonance angiography, computed tomography angiography, digital subtraction angiography and colour duplex ultrasound) for the detection of PAD among patients with diabetes. Two reviewers independently screened potential studies for inclusion and extracted study data. Eligible studies evaluated an index test for PAD against a reference test. An assessment of methodological quality was performed using the quality assessment for diagnostic accuracy studies instrument. Of the 6629 studies identified, ten met the criteria for inclusion. In these studies, the patients had a median age of 60-74 years and a median duration of diabetes of 9-24 years. Two studies reported exclusively on patients with symptomatic (ulcerated/infected) feet, two on patients with asymptomatic (intact) feet only, and the remaining six on patients both with and without foot ulceration. Ankle brachial index (ABI) was the most widely assessed index test. Overall, the positive likelihood ratio and negative likelihood ratio (NLR) of an ABI threshold diabetes mellitus is variable and is adversely affected by the presence of neuropathy. Limited evidence suggests that toe brachial index, pulse oximetry and wave form analysis may be superior to ABI for diagnosing PAD in patients with neuropathy with and without foot ulcers. There were insufficient data to support the adoption of one particular diagnostic modality over another and no comparisons existed with clinical examination. The quality of studies evaluating diagnostic techniques for the detection of
Tate, Quinn; Kim, Seong-Eun; Treiman, Gerald; Parker, Dennis L.; Hadley, J. Rock
2012-01-01
The purpose of this work was to design and construct a multi-channel receive-only RF coil for 3 Tesla magnetic resonance imaging of the human carotid artery and bifurcation with optimized signal to noise ratio in the carotid vessels along the full extent of the neck. A neck phantom designed to match the anatomy of a subject with a neck representing the body habitus often seen in subjects with carotid arterial disease, was constructed. Sixteen circular coil elements were arranged on a semi-rigid fiberglass former that closely fit the shape of the phantom, resulting in a 16-channel bilateral phased array coil. Comparisons were made between this coil and a typical 4-channel carotid coil in a study of 10 carotid vessels in 5 healthy volunteers. The 16-channel carotid coil showed a 73% average improvement in signal to noise ratio (SNR) at the carotid bifurcation. This coil also maintained an SNR greater than the peak SNR of the 4-channel coil over a vessel length of 10 cm. The resulting increase in SNR improved vessel depiction of the carotid arteries over an extended field of view, and demonstrated better image quality for higher parallel imaging reduction factors compared to the 4-channel coil. PMID:22777692
Ven, A.C. van de; Bredie, S.J.H.; Vleuten, C.J.M. van der; Holewijn, S.; Thien, Th.
2004-01-01
BACKGROUND: The aim of the current study was to investigate whether the StethoDop can serve as a valid and reproducible instrument for measuring the ankle-brachial index (ABI) and assessing venous reflux, even when used by inexperienced investigators, in comparison with the classic Doppler. METHODS:
Ye, Swe Soe; Ju, Meongkeun; Kim, Sangho
2016-07-01
Unequal RBC partitioning at arteriolar bifurcations contributes to dissimilar flow developments between daughter vessels in a bifurcation. Due to the importance of the cell-free layer (CFL) and the wall shear stress (WSS) to physiological processes such as vasoregulation and gas diffusion, we investigated the effects of a bifurcation disturbance on the development of the CFL width and WSS in bifurcation daughter branches. The analysis was performed on a two-dimensional (2-D) computational model of a transverse arteriole at three different flow rates corresponding to parent branch (PB) pseudoshear rates of 60, 170 and 470s(-1), while maintaining a 2-D hematocrit of about 55% in the PB. Flow symmetry was defined using the statistical similarity of the CFL and WSS distributions between the two walls of the vessel branch. In terms of the flow symmetry recovery, higher flow rates caused larger reductions in the flow symmetry indices in the MB and subsequently required longer vessel lengths for complete recovery. Lower tube hematocrits in the SB led to complete symmetry recovery for all flow rates despite the higher initial asymmetry in the SB than in the MB. Arteriolar bifurcations produce unavoidable local CFL asymmetry and the persistence of the asymmetry downstream may increase effective blood viscosity which is especially significant at higher physiological flow rates. PMID:26969106
International Nuclear Information System (INIS)
Purpose: To investigate an automatic bronchial and vessel bifurcations detection algorithm for deformable image registration (DIR) assessment to improve lung cancer radiation treatment. Methods: 4DCT datasets were acquired and exported to Varian treatment planning system (TPS) EclipseTM for contouring. The lungs TPS contour was used as the prior shape for a segmentation algorithm based on hierarchical surface deformation that identifies the deformed lungs volumes of the 10 breathing phases. Hounsfield unit (HU) threshold filter was applied within the segmented lung volumes to identify blood vessels and airways. Segmented blood vessels and airways were skeletonised using a hierarchical curve-skeleton algorithm based on a generalized potential field approach. A graph representation of the computed skeleton was generated to assign one of three labels to each node: the termination node, the continuation node or the branching node. Results: 320 ± 51 bifurcations were detected in the right lung of a patient for the 10 breathing phases. The bifurcations were visually analyzed. 92 ± 10 bifurcations were found in the upper half of the lung and 228 ± 45 bifurcations were found in the lower half of the lung. Discrepancies between ten vessel trees were mainly ascribed to large deformation and in regions where the HU varies. Conclusions: We established an automatic method for DIR assessment using the morphological information of the patient anatomy. This approach allows a description of the lung's internal structure movement, which is needed to validate the DIR deformation fields for accurate 4D cancer treatment planning
Energy Technology Data Exchange (ETDEWEB)
Uchino, A.; Sawada, A.; Takase, Y.; Kudo, S. [Department of Radiology, Saga Medical School, 5-1-1, Nabeshima, Saga, 849-8501 (Japan); Koizumi, T. [Department of Neurosurgery, Saga Medical School, 5-1-1, Nabeshima, Saga, 849-8501 (Japan)
2002-07-01
The authors present a case of moyamoya disease associated with a persistent trigeminal artery from which the anterior inferior cerebellar artery arose. We reviewed previously reported cases of moyamoya disease associated with persistent carotid-basilar arterial anastomosis and investigated the embryology of this rare arterial variation. (orig.)
Kralev, Stefan; Haag, Benjamin; Spannenberger, Jens; Lang, Siegfried; Brockmann, Marc A.; Bartling, Soenke; Marx, Alexander; Haase, Karl-Konstantin; Borggrefe, Martin; Süselbeck, Tim
2011-01-01
Background Treatment of coronary bifurcation lesions remains challenging, beyond the introduction of drug eluting stents. Dedicated stent systems are available to improve the technical approach to the treatment of these lesions. However dedicated stent systems have so far not reduced the incidence of stent restenosis. The aim of this study was to assess the expansion of the Multi-Link (ML) Frontier™ stent in human and porcine coronary arteries to provide the cardiologist with useful in-vitro ...
Seo, Jae-Bin; Park, Kyung Woo; Lee, Hae-Young; Kang, Hyun-Jae; Koo, Bon-Kwon; Kim, Sang-Hyun; Kim, Hyo-Soo
2015-01-01
Although the favored strategy for coronary bifurcation intervention is stenting main vessel with provisional side branch (SB) stenting, we occasionally use two-stent strategy. The objective of this study was to investigate the angiographic outcome of SB ostium in two-stent group, compared with one-stent group. We analyzed 199 patients with bifurcation lesion who underwent percutaneous coronary intervention (PCI) with drug-eluting stent and follow up angiography. The patients were divided into...
Directory of Open Access Journals (Sweden)
Kim Taehong
2007-03-01
Full Text Available Abstract Background This paper presents calculations of the temperature distribution in an atherosclerotic plaque experiencing an inflammatory process; it analyzes the presence of hot spots in the plaque region and their relationship to blood flow, arterial geometry, and inflammatory cell distribution. Determination of the plaque temperature has become an important topic because plaques showing a temperature inhomogeneity have a higher likelihood of rupture. As a result, monitoring plaque temperature and knowing the factors affecting it can help in the prevention of sudden rupture. Methods The transient temperature profile in inflamed atherosclerotic plaques is calculated by solving an energy equation and the Navier-Stokes equations in 2D idealized arterial models of a bending artery and an arterial bifurcation. For obtaining the numerical solution, the commercial package COMSOL 3.2 was used. The calculations correspond to a parametric study where arterial type and size, as well as plaque geometry and composition, are varied. These calculations are used to analyze the contribution of different factors affecting arterial wall temperature measurements. The main factors considered are the metabolic heat production of inflammatory cells, atherosclerotic plaque length lp, inflammatory cell layer length lmp, and inflammatory cell layer thickness dmp. Results The calculations indicate that the best location to perform the temperature measurement is at the back region of the plaque (0.5 ≤ l/lp ≤ 0.7. The location of the maximum temperature, or hot spot, at the plaque surface can move during the cardiac cycle depending on the arterial geometry and is a direct result of the blood flow pattern. For the bending artery, the hot spot moves 0.6 millimeters along the longitudinal direction; for the arterial bifurcation, the hot spot is concentrated at a single location due to the flow recirculation observed at both ends of the plaque. Focusing on the
Optimization Design and Application of Underground Reinforced Concrete Bifurcation Pipe
Directory of Open Access Journals (Sweden)
Chao Su
2015-01-01
Full Text Available Underground reinforced concrete bifurcation pipe is an important part of conveyance structure. During construction, the workload of excavation and concrete pouring can be significantly decreased according to optimized pipe structure, and the engineering quality can be improved. This paper presents an optimization mathematical model of underground reinforced concrete bifurcation pipe structure according to real working status of several common pipe structures from real cases. Then, an optimization design system was developed based on Particle Swarm Optimization algorithm. Furthermore, take the bifurcation pipe of one hydropower station as an example: optimization analysis was conducted, and accuracy and stability of the optimization design system were verified successfully.
FFT Bifurcation Analysis of Routes to Chaos via Quasiperiodic Solutions
Directory of Open Access Journals (Sweden)
L. Borkowski
2015-01-01
Full Text Available The dynamics of a ring of seven unidirectionally coupled nonlinear Duffing oscillators is studied. We show that the FFT analysis presented in form of a bifurcation graph, that is, frequency distribution versus a control parameter, can provide a valuable and helpful complement to the corresponding typical bifurcation diagram and the course of Lyapunov exponents, especially in context of detailed identification of the observed attractors. As an example, bifurcation analysis of routes to chaos via 2-frequency and 3-frequency quasiperiodicity is demonstrated.
Statistical multimoment bifurcations in random-delay coupled swarms
Mier-y-Teran-Romero, Luis; Lindley, Brandon; Schwartz, Ira B.
2012-11-01
We study the effects of discrete, randomly distributed time delays on the dynamics of a coupled system of self-propelling particles. Bifurcation analysis on a mean field approximation of the system reveals that the system possesses patterns with certain universal characteristics that depend on distinguished moments of the time delay distribution. Specifically, we show both theoretically and numerically that although bifurcations of simple patterns, such as translations, change stability only as a function of the first moment of the time delay distribution, more complex patterns arising from Hopf bifurcations depend on all of the moments.
Arctic melt ponds and bifurcations in the climate system
Sudakov, Ivan; Golden, Kenneth M
2014-01-01
Understanding how sea ice melts is critical to climate projections. In the Arctic, melt ponds that develop on the surface of sea ice floes during the late spring and summer largely determine their albedo $-$ a key parameter in climate modeling. Here we explore the possibility of a simple sea ice climate model passing through a bifurcation point $-$ an irreversible critical threshold as the system warms, by incorporating geometric information about melt pond evolution. This study is based on a nonlinear phase transition model for melt ponds, and bifurcation analysis of a simple climate model with ice - albedo feedback as the key mechanism driving the system to a potential bifurcation point.
Bifurcation diagrams in relation to synchronization in chaotic systems
Indian Academy of Sciences (India)
Debabrata Dutta; Sagar Chakraborty
2010-06-01
We numerically study some of the three-dimensional dynamical systems which exhibit complete synchronization as well as generalized synchronization to show that these systems can be conveniently partitioned into equivalent classes facilitating the study of bifurcation diagrams within each class. We demonstrate how bifurcation diagrams may be helpful in predicting the nature of the driven system by knowing the bifurcation diagram of driving system and vice versa. The study is extended to include the possible generalized synchronization between elements of two different equivalent classes by taking the Rössler-driven-Lorenz-system as an example.
Bifurcations of a parametrically excited oscillator with strong nonlinearity
Institute of Scientific and Technical Information of China (English)
唐驾时; 符文彬; 李克安
2002-01-01
A parametrically excited oscillator with strong nonlinearity, including van der Poi and Duffing types, is studied for static bifurcations. The applicable range of the modified Lindstedt-Poincaré method is extended to 1/2 subharmonic resonance systems. The bifurcation equation of a strongly nonlinear oscillator, which is transformed into a small parameter system, is determined by the multiple scales method. On the basis of the singularity theory, the transition set and the bifurcation diagram in various regions of the parameter plane are analysed.
Bifurcation control of nonlinear oscillator in primary and secondary resonance
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
A weakly nonlinear oscillator was modeled by a sort of differential equation, a saddle-node bifurcation was found in case of primary and secondary resonance. To control the jumping phenomena and the unstable region of the nonlinear oscillator, feedback controllers were designed. Bifurcation control equations were obtained by using the multiple scales method. And through the numerical analysis, good controller could be obtained by changing the feedback control gain. Then a feasible way of further research of saddle-node bifurcation was provided. Finally, an example shows that the feedback control method applied to the hanging bridge system of gas turbine is doable.
Codimension 3 Non-resonant Bifurcations of Rough Heteroclinic Loops with One Orbit Flip
Institute of Scientific and Technical Information of China (English)
Shuliang SHUI; Deming ZHU
2006-01-01
Heteroclinic bifurcations in four dimensional vector fields are investigated by setting up a local coordinates near a rough heteroclinic loop. This heteroclinic loop has a principal heteroclinic orbit and a non-principal heteroclinic orbit that takes orbit flip. The existence, nonexistence, coexistence and uniqueness of the 1-heteroclinic loop, 1-homoclinic orbit and 1-periodic orbit are studied. The existence of the two-fold or three-fold 1-periodic orbit is also obtained.
CODIMENSION 3 BIFURCATIONS OF HOMOCLINIC ORBITS WITH ORBIT FLIPS AND INCLINATION FLIPS
Institute of Scientific and Technical Information of China (English)
SHUI SHULIANG; ZHU DEMING
2004-01-01
The homoclinic bifurcations in four dimensional vector fields are investigated by setting up a local coordinates near the homoclinic orbit. This homoclinic orbit is nonprincipal in the meanings that its positive semi-orbit takes orbit flip and its unstable foliation takes inclination flip. The existence, nonexistence, uniqueness and coexistence of the 1-homoclinic orbit and the 1-periodic orbit are studied. The existence of the twofold periodic orbit and three-fold periodic orbit are also obtained.
Directory of Open Access Journals (Sweden)
Tanuja Agrawal
2014-03-01
Full Text Available In this paper, a two species host-parasitoid model system is considered. The global dynamic behavior of the model is investigated through (local stability results for its equilibriums and large time computer simulations. Many forms of complex dynamics such as chaos, periodic windows etc. are observed. The Hopf point and attractor crises exist for different set of parameter values. Keywords: Predator-Prey; Bifurcation; Chaos; Stability.
Experimental bifurcation analysis—Continuation for noise-contaminated zero problems
DEFF Research Database (Denmark)
Schilder, Frank; Bureau, Emil; Santos, Ilmar Ferreira;
2015-01-01
Noise contaminated zero problems involve functions that cannot be evaluated directly, but only indirectly via observations. In addition, such observations are affected by a non-deterministic observation error (noise). We investigate the application of numerical bifurcation analysis for studying t......, we demonstrate and test our algorithms on a mechanical nonlinear oscillator experiment using control based continuation, which we used as a main application and test case for development of the Coco compatible Matlab toolbox Continex that implements our algorithms....
Ductility limit prediction using a GTN damage model coupled with localization bifurcation analysis
MANSOURI, Lotfi; Chalal, Hocine; ABED-MERAIM, Farid
2014-01-01
Because the localization of deformation into narrow planar bands is often precursor to material failure, several approaches have been proposed to predict this phenomenon. In this paper, the Gurson–Tvergaard– Needleman (GTN) elastic–plastic–damage model for ductile materials is considered. A large-strain version of this constitutive model is coupled with the Rice localization criterion, which is based on bifurcation theory, to investigate strain localization. The resulting loss of ellipticity ...
Complex Dynamics and Chaos Control in Coronary Artery System%冠状动脉系统的复杂动态与混沌控制
Institute of Scientific and Technical Information of China (English)
石艳香; 刘桂荣; 白定勇
2011-01-01
研究两类冠状动脉系统:N型与S型.利用Melnikov方法,得到两类系统在参数条件下产生Smale马蹄意义上的混沌的阀值.通过数值模拟,不仅可以证明理论分析的正确性,同时显示出理想的分支图形和更多新的复杂动力学行为.数值模拟包括相图、势能图、同宿分支曲线和分支图,通过这些较直观地反映出系统随周期激励外力强弱变化的动态特性、复杂性和非线性特征,揭示了系统的分支形式以及通向混沌运动的道路.最后对系统的混沌运动状态进行了有效的控制.%N-type and S-type, two types of coronary artery system are investigated. Applying Melnikov method,the threshold conditions for the occurrence of Smale horse chaos of the two types are obtained respectively. By numerical simulation,not only the correctness of theoretical analysis is proven but also the ideal graphics and more new bifurcation of the complex dynamic behavior are shown. Numerical simulations.including phase diagram, potential diagrams, homoclinic bifurcation curve diagrams and bifurcation diagrams,are used to investigate the dynamic characteristics,the complexity and the nonlinear dynamics characteristic of the two systems,and to reveal bifurcation forms and the road leading to chaotic motion. Finally the chaotic states of motion are effectively controlled.
Directory of Open Access Journals (Sweden)
Shugang Song
2014-01-01
Full Text Available We investigate multiple limit cycles bifurcation and center-focus problem of the degenerate equilibrium for a three-dimensional system. By applying the method of symbolic computation, we obtain the first four quasi-Lyapunov constants. It is proved that the system can generate 3 small limit cycles from nilpotent critical point on center manifold. Furthermore, the center conditions are found and as weak foci the highest order is proved to be the fourth; thus we obtain at most 3 small limit cycles from the origin via local bifurcation. To our knowledge, it is the first example of multiple limit cycles bifurcating from a nilpotent singularity for the flow of a high-dimensional system restricted to the center manifold.
Winant, Celeste D.; Aparici, Carina Mari; Zelnik, Yuval R.; Reutter, Bryan W.; Sitek, Arkadiusz; Bacharach, Stephen L.; Gullberg, Grant T.
2012-01-01
Computer simulations, a phantom study and a human study were performed to determine whether a slowly rotating single-photon computed emission tomography (SPECT) system could provide accurate arterial input functions for quantification of myocardial perfusion imaging using kinetic models. The errors induced by data inconsistency associated with imaging with slow camera rotation during tracer injection were evaluated with an approach called SPECT/P (dynamic SPECT from positron emission tomography (PET)) and SPECT/D (dynamic SPECT from database of SPECT phantom projections). SPECT/P simulated SPECT-like dynamic projections using reprojections of reconstructed dynamic 94Tc-methoxyisobutylisonitrile (94Tc-MIBI) PET images acquired in three human subjects (1 min infusion). This approach was used to evaluate the accuracy of estimating myocardial wash-in rate parameters K1 for rotation speeds providing 180° of projection data every 27 or 54 s. Blood input and myocardium tissue time-activity curves (TACs) were estimated using spatiotemporal splines. These were fit to a one-compartment perfusion model to obtain wash-in rate parameters K1. For the second method (SPECT/D), an anthropomorphic cardiac torso phantom was used to create real SPECT dynamic projection data of a tracer distribution derived from 94Tc-MIBI PET scans in the blood pool, myocardium, liver and background. This method introduced attenuation, collimation and scatter into the modeling of dynamic SPECT projections. Both approaches were used to evaluate the accuracy of estimating myocardial wash-in parameters for rotation speeds providing 180° of projection data every 27 and 54 s. Dynamic cardiac SPECT was also performed in a human subject at rest using a hybrid SPECT/CT scanner. Dynamic measurements of 99mTc-tetrofosmin in the myocardium were obtained using an infusion time of 2 min. Blood input, myocardium tissue and liver TACs were estimated using the same spatiotemporal splines. The spatiotemporal maximum
International Nuclear Information System (INIS)
Computer simulations, a phantom study and a human study were performed to determine whether a slowly rotating single-photon computed emission tomography (SPECT) system could provide accurate arterial input functions for quantification of myocardial perfusion imaging using kinetic models. The errors induced by data inconsistency associated with imaging with slow camera rotation during tracer injection were evaluated with an approach called SPECT/P (dynamic SPECT from positron emission tomography (PET)) and SPECT/D (dynamic SPECT from database of SPECT phantom projections). SPECT/P simulated SPECT-like dynamic projections using reprojections of reconstructed dynamic 94Tc-methoxyisobutylisonitrile (94Tc-MIBI) PET images acquired in three human subjects (1 min infusion). This approach was used to evaluate the accuracy of estimating myocardial wash-in rate parameters K1 for rotation speeds providing 180° of projection data every 27 or 54 s. Blood input and myocardium tissue time-activity curves (TACs) were estimated using spatiotemporal splines. These were fit to a one-compartment perfusion model to obtain wash-in rate parameters K1. For the second method (SPECT/D), an anthropomorphic cardiac torso phantom was used to create real SPECT dynamic projection data of a tracer distribution derived from 94Tc-MIBI PET scans in the blood pool, myocardium, liver and background. This method introduced attenuation, collimation and scatter into the modeling of dynamic SPECT projections. Both approaches were used to evaluate the accuracy of estimating myocardial wash-in parameters for rotation speeds providing 180° of projection data every 27 and 54 s. Dynamic cardiac SPECT was also performed in a human subject at rest using a hybrid SPECT/CT scanner. Dynamic measurements of 99mTc-tetrofosmin in the myocardium were obtained using an infusion time of 2 min. Blood input, myocardium tissue and liver TACs were estimated using the same spatiotemporal splines. The spatiotemporal maximum
International Nuclear Information System (INIS)
The structural properties of an economical model for a confined plasma turbulence governor are investigated through bifurcation and stability analyses. Two types of discontinuous low to high confinement transition are found. One involves classical hysteresis, governed by viscous dissipation. The other is intrinsically oscillatory and non-hysteretic, and thus provides a model for observed 'dithering' transitions. This metamorphosis of the system dynamics is an important late side-effect of symmetry-breaking, which manifests as an unusual non-symmetric transcritical bifurcation induced by a significant shear flow drive
International Nuclear Information System (INIS)
In this paper, a kind of discrete delay food-limited model obtained by the Euler method is investigated, where the discrete delay τ is regarded as a parameter. By analyzing the associated characteristic equation, the linear stability of this model is studied. It is shown that Neimark—Sacker bifurcation occurs when τ crosses certain critical values. The explicit formulae which determine the stability, direction, and other properties of bifurcating periodic solution are derived by means of the theory of center manifold and normal form. Finally, numerical simulations are performed to verify the analytical results
Dynamical Analysis of Nonlinear Bifurcation in Current-Controlled Boost Converter
Institute of Scientific and Technical Information of China (English)
Quan-Min Niu; Bo Zhang; Yan-Ling Li
2007-01-01
Based on the bifurcation theory in nonlinear dynamics, this paper analyzes quantitatively period solution dynamic characteristic. In particular, the ones of period1 and period2 solutions are deeply studied. From locus of Jacobian matrix eigenvalue, we conclude that the bifurcations between period1 and period2 solutions are pitchfork bifurcations while the bifurcations between period2 and period3 solutions are border collision bifurcations. The double period bifurcation condition is verified from complex plane locus of eigenvalues,furthermore, the necessary condition occurred pitchfork bifurcation is obtained from the cause of border collisionbifurcation.
Microsurgical anatomy of the middle cerebral artery
Directory of Open Access Journals (Sweden)
Pai S
2005-01-01
Full Text Available Background: The microsurgical anatomy of the middle cerebral artery (MCA is of particular interest to the cerebrovascular surgeon. The purpose of this study was to define the microsurgical anatomy of the MCA and its various branches in the Indian population. Methods: Ten MCAs were studied from five cadaveric brain specimens. The authors studied the outer diameter, length, branches, perforators and site of these on the main trunk (M1, the division of the main trunk, the secondary trunks and their various cortical branches using the operating microscope under 5-20x magnification. Results: The outer diameter of the MCA main trunk ranges from 2.5 to 4 mm with a mean of 3.35 mm. The superolateral branches consisted of polar temporal artery and anterior temporal artery that had a common origin and sometimes the uncal artery or the accessory uncal artery. Perforators or lenticulostriate arteries were seen in the inferomedial surface all along the length of M1. Eight bifurcations and two trifurcations were noted. Cortical branches and their origin are discussed. Conclusion: Although the microsurgical anatomy of the MCA in Indian population correlated with the findings in the western literature, some structural and statistical variations were noted.
Bifurcation methods of dynamical systems for handling nonlinear wave equations
Indian Academy of Sciences (India)
Dahe Feng; Jibin Li
2007-05-01
By using the bifurcation theory and methods of dynamical systems to construct the exact travelling wave solutions for nonlinear wave equations, some new soliton solutions, kink (anti-kink) solutions and periodic solutions with double period are obtained.
Cardiac Alternans Arising from an Unfolded Border-Collision Bifurcation
Zhao, Xiaopeng; Berger, Carolyn M; Krassowska, Wanda; Gauthier, Daniel J
2007-01-01
Following an electrical stimulus, the transmembrane voltage of cardiac tissue rises rapidly and remains at a constant value before returning to the resting value, a phenomenon known as an action potential. When the pacing rate of a periodic train of stimuli is increased above a critical value, the action potential undergoes a period-doubling bifurcation, where the resulting alternation of the action potential duration is known as alternans in the medical literature. Existing cardiac models treat alternans either as a smooth or as a border-collision bifurcation. However, recent experiments in paced cardiac tissue reveal that the bifurcation to alternans exhibits hybrid smooth/nonsmooth behaviors, which can be qualitatively described by a model of so-called unfolded border-collision bifurcation. In this paper, we obtain analytical solutions of the unfolded border-collision model and use it to explore the crossover between smooth and nonsmooth behaviors. Our analysis shows that the hybrid smooth/nonsmooth behavi...
Hopf bifurcation in doubly fed induction generator under vector control
International Nuclear Information System (INIS)
This paper first presents the Hopf bifurcation phenomena of a vector-controlled doubly fed induction generator (DFIG) which is a competitive choice in wind power industry. Using three-phase back-to-back pulse-width-modulated (PWM) converters, DFIG can keep stator frequency constant under variable rotor speed and provide independent control of active and reactive power output. Main results are illustrated by 'exact' cycle-by-cycle simulations. The detailed mathematical model of the closed-loop system is derived and used to analyze the observed bifurcation phenomena. The loci of the Jacobian's eigenvalues are computed and the analysis shows that the system loses stability via a Hopf bifurcation. Moreover, the boundaries of Hopf bifurcation are also given to facilitate the selection of practical parameters for guaranteeing stable operation.
CISM Session on Bifurcation and Stability of Dissipative Systems
1993-01-01
The first theme concerns the plastic buckling of structures in the spirit of Hill’s classical approach. Non-bifurcation and stability criteria are introduced and post-bifurcation analysis performed by asymptotic development method in relation with Hutchinson’s work. Some recent results on the generalized standard model are given and their connection to Hill’s general formulation is presented. Instability phenomena of inelastic flow processes such as strain localization and necking are discussed. The second theme concerns stability and bifurcation problems in internally damaged or cracked colids. In brittle fracture or brittle damage, the evolution law of crack lengths or damage parameters is time-independent like in plasticity and leads to a similar mathematical description of the quasi-static evolution. Stability and non-bifurcation criteria in the sense of Hill can be again obtained from the discussion of the rate response.
Bifurcation control of the Hodgkin-Huxley equations
Energy Technology Data Exchange (ETDEWEB)
Wang Jiang [School of Electrical and Automation Engineering, Tianjin University, 300072 Tianjin (China)]. E-mail: jiangwang@tju.edu.cn; Chen Liangquan [School of Electrical and Automation Engineering, Tianjin University, 300072 Tianjin (China); Fei Xianyang [School of Electrical and Automation Engineering, Tianjin University, 300072 Tianjin (China)
2007-07-15
The Hodgkin-Huxley equations (HH) are parameterized by a number of parameters and show a variety of qualitatively different behaviors. This paper finds that when the externally applied current I {sub ext} varies the bifurcation would occur in the HH equations. The HH model's Hopf bifurcation is controlled by permanent or interval Washout filters (WF), which can transform the subcritical bifurcations into supercritical bifurcations, and can make the HH equations stable directly. Simulation results show the validity of those controllers. We choose the membrane voltage V as an input to the washout filter because V can be readily measured, and the controller can be realized easily. The controller designs described here may boost the development of electrical stimulation systems for patients suffering from different neuron-system dysfunctions.
Hopf bifurcation and multistability in a system of phase oscillators
Astakhov, Sergey; Fujiwara, Naoya; Gulay, Artem; Tsukamoto, Naofumi; Kurths, Jürgen
2013-09-01
We study the phase reduction of two coupled van der Pol oscillators with asymmetric repulsive coupling under an external harmonic force. We show that the system of two phase oscillators undergoes a Hopf bifurcation and possesses multistability on a 2π-periodic phase plane. We describe the bifurcation mechanisms of formation of multistability in the phase-reduced system and show that the Andronov-Hopf bifurcation in the phase-reduced system is not an artifact of the reduction approach but, indeed, has its prototype in the nonreduced system. The bifurcational mechanisms presented in the paper enable one to describe synchronization effects in a wide class of interacting systems with repulsive coupling e.g., genetic oscillators.
2D bifurcations and Newtonian properties of memristive Chua's circuits
Marszalek, W.; Podhaisky, H.
2016-01-01
Two interesting properties of Chua's circuits are presented. First, two-parameter bifurcation diagrams of Chua's oscillatory circuits with memristors are presented. To obtain various 2D bifurcation images a substantial numerical effort, possibly with parallel computations, is needed. The numerical algorithm is described first and its numerical code for 2D bifurcation image creation is available for free downloading. Several color 2D images and the corresponding 1D greyscale bifurcation diagrams are included. Secondly, Chua's circuits are linked to Newton's law φ ''= F(t,φ,φ')/m with φ=\\text{flux} , constant m > 0, and the force term F(t,φ,φ') containing memory terms. Finally, the jounce scalar equations for Chua's circuits are also discussed.
Multiple bifurcations and periodic 'bubbling' in a delay population model
International Nuclear Information System (INIS)
In this paper, the flip bifurcation and periodic doubling bifurcations of a discrete population model without delay influence is firstly studied and the phenomenon of Feigenbaum's cascade of periodic doublings is also observed. Secondly, we explored the Neimark-Sacker bifurcation in the delay population model (two-dimension discrete dynamical systems) and the unique stable closed invariant curve which bifurcates from the nontrivial fixed point. Finally, a computer-assisted study for the delay population model is also delved into. Our computer simulation shows that the introduction of delay effect in a nonlinear difference equation derived from the logistic map leads to much richer dynamic behavior, such as stable node → stable focus → an lower-dimensional closed invariant curve (quasi-periodic solution, limit cycle) or/and stable periodic solutions → chaotic attractor by cascading bubbles (the combination of potential period doubling and reverse period-doubling) and the sudden change between two different attractors, etc
DEFF Research Database (Denmark)
Johansson, Helle Wulf; Hay-Schmidt, Anders; Poulsen, Asser Nyander;
2009-01-01
Large conductance calcium-activated potassium (BK(Ca)) channels are fundamental in the regulation of cerebral vascular basal tone. We investigated the expression of the mRNA transcripts for the BK(Ca) channel and its modulatory beta-subunits (beta1-beta4) in porcine basilar and middle cerebral...
Unusual looping of the internal carotid artery in relation to an enlarged lymph node
Directory of Open Access Journals (Sweden)
Nayak SB
2010-06-01
Full Text Available Knowledge of variations of internal carotid artery is important to surgeons doing head and neck surgery as well as to radiologists doing imaging and invasive techniques. In the current case, the right internal carotid artery showed a characteristic loop at its beginning. An abnormal, enlarged lymph node was found at the carotid bifurcation, which was projecting into the loop. The left internal carotid artery was normal. The unusual looping of internal carotid artery at its beginning might result in altered blood flow to the brain and may lead to confusions in surgical, imaging and invasive techniques.
Duplex scanning of carotid artery following thrombo-endarteriectomy and plastic dilation
International Nuclear Information System (INIS)
40 carotid arteries were studied in 32 patients following thrombo-endarteriectomy with plastic patching, with 27 cases having additional digital angiography findings available for control. Both the communal carotid arteries and the carotid bifurcations were sufficiently assessable in the B-image in 95%. Safe image diagnosis of the internal carotid arteries was possible in 82% only. Proximal formation of steps (40%) and stenoses of the external carotid artery (43%) were found most frequently. Only 4 cases revealed discrepancies to DSA findings. Duplex scanning should not be performed until a fortnight after operation due to soft tissue swellings. (orig.)
Super Persistent Chaotic Transients And Catastrophic Bifurcation From Riddled To Fractal Basins
Andrade, V A
2002-01-01
This dissertation treats two related problems in chaotic dynamics: (1) super persistent chaotic transients in physical systems, and (2) catastrophic bifurcation from riddled to fractal basins. For the first problem, we investigate super persistent chaotic transient by studying the effect of noise on phase synchronization of coupled chaotic oscillators. A super persistent chaotic transient is typically induced by an unstable-unstable pair bifurcation in which two unstable periodic orbits of the same period coalesce and disappear as a system parameter is changed through a critical value. So far examples illustrating this type of transient chaos utilize discrete-time maps. We present a class of continuous-time dynamical systems that exhibit super persistent chaotic transients in parameter regimes of positive measure. In particular, we examine the effect of noise on phase synchronization of coupled chaotic oscillators. It is found that additive white noise can induce phase slips in integer multi...
Bifurcation and chaos of a pest-control food chain model with impulsive effects
International Nuclear Information System (INIS)
According to biological and chemical control strategy for pest control, we investigate the dynamics of a predator-prey food chain with impulsive effect, periodic releasing natural enemies and spraying pesticide at different fixed times, by using impulsive differential equation. Choose pest birth rate r2 as control parameter, we show that there exists a stable pest-eradication periodic solution when r2 is less than some critical value r2* and the system is permanence when r2 is larger than the critical value r2*. By use of standard techniques of bifurcation theory, we prove that above this threshold there are periodic oscillations in prey, middle-predator and top predator. Furthermore, bifurcation diagrams have shown that there exists complexity for the pulsed system including periodic doubling cascade.
Experimental bifurcation analysis-Continuation for noise-contaminated zero problems
Schilder, Frank; Bureau, Emil; Santos, Ilmar Ferreira; Thomsen, Jon Juel; Starke, Jens
2015-12-01
Noise contaminated zero problems involve functions that cannot be evaluated directly, but only indirectly via observations. In addition, such observations are affected by a non-deterministic observation error (noise). We investigate the application of numerical bifurcation analysis for studying the solution set of such noise contaminated zero problems, which is highly relevant in the context of equation-free analysis (coarse grained analysis) and bifurcation analysis in experiments, and develop specialized algorithms to address challenges that arise due to the presence of noise. As a working example, we demonstrate and test our algorithms on a mechanical nonlinear oscillator experiment using control based continuation, which we used as a main application and test case for development of the COCO compatible MATLAB toolbox CONTINEX that implements our algorithms.
A perturbation-incremental scheme for studying Hopf bifurcation in delayed differential systems
Institute of Scientific and Technical Information of China (English)
CHUNG; Kwok; Wai
2009-01-01
A new method, called perturbation-incremental scheme (PIS), is presented to investigate the periodic solution derived from Hopf bifurcation due to time delay in a system of first-order delayed differential equations. The method is summarized as three steps, namely linear analysis at critical value, perturba- tion and increment for continuation. The PIS can bypass and avoid the tedious calculation of the center manifold reduction (CMR) and normal form. Meanwhile, the PIS not only inherits the advantages of the method of multiple scales (MMS) but also overcomes the disadvantages of the incremental harmonic balance (IHB) method. Three delayed systems are used as illustrative examples to demonstrate the validity of the present method. The periodic solution derived from the delay-induced Hopf bifurcation is obtained in a closed form by the PIS procedure. The validity of the results is shown by their consis- tency with the numerical simulation. Furthermore, an approximate solution can be calculated in any required accuracy.
A perturbation-incremental scheme for studying Hopf bifurcation in delayed differential systems
Institute of Scientific and Technical Information of China (English)
XU Jian; CHUNG Kwok Wai
2009-01-01
A new method, called perturbation-incremental scheme (PIS), is presented to investigate the periodic solution derived from Hopf bifurcation due to time delay in a system of first-order delayed differential equations. The method is summarized as three steps, namely linear analysis at critical value, perturba-tion and increment for continuation. The PIS can bypass and avoid the tedious calculation of the center manifold reduction (CMR) and normal form. Meanwhile, the PIS not only inherits the advantages of the method of multiple scales (MMS) but also overcomes the disadvantages of the incremental harmonic balance (IHB) method. Three delayed systems are used as illustrative examples to demonstrate the validity of the present method. The periodic solution derived from the delay-induced Hopf bifurcation is obtained in a closed form by the PIS procedure. The validity of the results is shown by their consis-tency with the numerical simulation. Furthermore, an approximate solution can be calculated in any required accuracy.
Stochastic Bifurcations induced by correlated Noise in a Birhythmic van der Pol System
Yonkeu, R Mbakob; Filatrella, G; Tchawoua, C
2015-01-01
We investigate the effects of exponentially correlated noise on birhythmic van der Pol type oscillators. The analytical results are obtained applying the quasi-harmonic assumption to the Langevin equation to derive an approximated Fokker-Planck equation. This approach allows to analytically derive the probability distributions as well as the activation energies associated to switching between coexisting attractors. The stationary probability density function of the van der Pol oscillator reveals the influence of the correlation time on the dynamics. Stochastic bifurcations are discussed through a qualitative change of the stationary probability distribution, which indicates that noise intensity and correlation time can be treated as bifurcation parameters. Comparing the analytical and numerical results, we find good agreement both when the frequencies of the attractors are about equal or when they are markedly different.
Pirker, Stefan; Kahrimanovic, Damir; Schneiderbauer, Simon
2015-04-01
The submerged entry nozzle (SEN) flow behavior is crucial for continuous casting of slab steel since it controls the mold flow pattern. In this study, we focus on the bottom zone of a bifurcated SEN where the flow deflection determines the port outflow. By applying a hybrid finite volume and lattice Boltzmann-based turbulence model, the dynamic behavior of horizontally orientated secondary vortices is investigated. In addition to the pure liquid metal flow, gas bubbles are traced in both discrete and continuous way. Simulation results indicate the existence of highly turbulent secondary vortices in the deflection zone of a bifurcated SEN, which attract gas bubbles in form of bubble threads or continuous gas volumes at their rotational axes. In addition, cyclically detaching gas volumes are formed at the upper port region at higher gas flow rates. Numerical predictions agree well with observations from physical water-air models.
Hopf-Bifurcations and Van der Pol Oscillator Models of the Mammalian Cochlea
Duifhuis, Hendrikus
2011-11-01
The successful modeling of the non-linear behavior in stiffness properties of hair bundles of auditory hair cells in sub-mammals and in vitro preparations of mammalian hair cells has stimulated several investigators to propose far-reaching similarity of the functioning of the mammalian organ of Corti. Models have been proposed that share the common background of a Hopf-bifurcation and its relation to a newly defined class of critical oscillators. Some of the proposals are rather similar to the classical line of nonlinear cochlea models whereas others start with assumptions that put them in a different class. It can be shown that the Hopf-bifurcation and the Van der Pol oscillator belong to the same class of nonlinear models. Differences between the models arise at the physical definition of the parameters, and at the question: how to account for individual SOAE patterns.
Wang, Tong; Xing, Zhongwen
2016-01-01
Blood exhibits a heterogeneous nature of hematocrit, velocity, and effective viscosity in microcapillaries. Microvascular bifurcations have a significant influence on the distribution of the blood cells and blood flow behavior. This paper presents a simulation study performed on the two-dimensionalmotions and deformation of multiple red blood cells in microvessels with diverging and converging bifurcations. Fluid dynamics and membrane mechanics were incorporated. Effects of cell shape, hematocrit, and deformability of the cell membrane on rheological behavior of the red blood cells and the hemodynamics have been investigated. It was shown that the blood entering the daughter branch with a higher flow rate tended to receive disproportionally more cells. The results also demonstrate that red blood cells in microvessels experienced lateral migration in the parent channel and blunted velocity profiles in both straight section and daughter branches, and this effect was influenced by the shape and the initial posit...
Theoretical analysis of three-dimensional bifurcated flow inside a diagonally lid-driven cavity
Feldman, Yuri
2015-08-01
The instability mechanism of fully three-dimensional, highly separated, shear-driven confined flow inside a diagonally lid-driven cavity was investigated. The analysis was conducted on 1003 and 2003 stretched grids by a series of direct numerical simulations utilizing a standard second-order accuracy finite volume code, openFoam. The observed oscillatory instability was found to set in via a subcritical symmetry breaking Hopf bifurcation. Critical values of the Reynolds number Re cr = 2320 and the non-dimensional angular oscillating frequency for the transition from steady to oscillatory flow were accurately determined. An oscillatory regime of the bifurcated flow was analyzed in depth, revealing and characterizing the spontaneous symmetry breaking mechanism. Characteristic spatial patterns of the base flow and the main flow harmonic were determined for the velocity, vorticity and helicity fields. Lagrangian particle tracers were utilized to visualize the mixing phenomenon of the flow from both sides of the diagonal symmetry plane.
Subcritical dynamo bifurcation in the Taylor Green flow
Ponty, Yannick; Dubrulle, Berengere; Daviaud, François; Pinton, Jean-François
2007-01-01
We report direct numerical simulations of dynamo generation for flow generated using a Taylor-Green forcing. We find that the bifurcation is subcritical, and show its bifurcation diagram. We connect the associated hysteretic behavior with hydrodynamics changes induced by the action of the Lorentz force. We show the geometry of the dynamo magnetic field and discuss how the dynamo transition can be induced when an external field is applied to the flow.
Optimization Design and Application of Underground Reinforced Concrete Bifurcation Pipe
Chao Su; Zhenxue Zhu; Yangyang Zhang; Niantang Jiang
2015-01-01
Underground reinforced concrete bifurcation pipe is an important part of conveyance structure. During construction, the workload of excavation and concrete pouring can be significantly decreased according to optimized pipe structure, and the engineering quality can be improved. This paper presents an optimization mathematical model of underground reinforced concrete bifurcation pipe structure according to real working status of several common pipe structures from real cases. Then, an optimiza...
Bunch lengthening with bifurcation in electron storage rings
Energy Technology Data Exchange (ETDEWEB)
Kim, Eun-San; Hirata, Kohji [National Lab. for High Energy Physics, Tsukuba, Ibaraki (Japan)
1996-08-01
The mapping which shows equilibrium particle distribution in synchrotron phase space for electron storage rings is discussed with respect to some localized constant wake function based on the Gaussian approximation. This mapping shows multi-periodic states as well as double bifurcation in dynamical states of the equilibrium bunch length. When moving around parameter space, the system shows a transition/bifurcation which is not always reversible. These results derived by mapping are confirmed by multiparticle tracking. (author)
A Bifurcation Monte Carlo Scheme for Rare Event Simulation
Liu, Hongliang
2016-01-01
The bifurcation method is a way to do rare event sampling -- to estimate the probability of events that are too rare to be found by direct simulation. We describe the bifurcation method and use it to estimate the transition rate of a double well potential problem. We show that the associated constrained path sampling problem can be addressed by a combination of Crooks-Chandler sampling and parallel tempering and marginalization.
A Weak Bifurcation Theory for Discrete Time Stochastic Dynamical Systems
Diks, Cees; Wagener, Florian
2006-01-01
This article presents a bifurcation theory of smooth stochastic dynamical systems that are governed by everywhere positive transition densities. The local dependence structure of the unique strictly stationary evolution of such a system can be expressed by the ratio of joint and marginal probability densities; this 'dependence ratio' is a geometric invariant of the system. By introducing a weak equivalence notion of these dependence ratios, we arrive at a bifurcation theory for which in the c...
Iterative Controller Tuning for Process with Fold Bifurcations
DEFF Research Database (Denmark)
Huusom, Jakob Kjøbsted; Poulsen, Niels Kjølstad; Jørgensen, Sten Bay
2007-01-01
Processes involving fold bifurcation are notoriously difficult to control in the vicinity of the fold where most often optimal productivity is achieved . In cases with limited process insight a model based control synthesis is not possible. This paper uses a data driven approach with an improved...... version of iterative feedback tuning to optimizing a closed loop performance criterion, as a systematic tool for tuning process with fold bifurcations....
Dynamics of Bloch oscillating transistor near the bifurcation threshold
Sarkar, Jayanta; Puska, Antti; Hassel, Juha; Hakonen, Pertti J.
2013-01-01
The tendency to bifurcate can often be utilized to improve performance characteristics of amplifiers or even to build detectors. The Bloch oscillating transistor is such a device. Here, we show that bistable behavior can be approached by tuning the base current and that the critical value depends on the Josephson coupling energy EJ of the device. We demonstrate current-gain enhancement for the device operating near the bifurcation point at small EJ. From our results for the current gains at v...
Subcritical dynamo bifurcation in the Taylor Green flow
Ponty, Yannick; Laval, Jean-Phillipe; Dubrulle, Berengere; Daviaud, François; Pinton, Jean-François
2007-01-01
4 pages We report direct numerical simulations of dynamo generation for flow generated using a Taylor-Green forcing. We find that the bifurcation is subcritical, and show its bifurcation diagram. We connect the associated hysteretic behavior with hydrodynamics changes induced by the action of the Lorentz force. We show the geometry of the dynamo magnetic field and discuss how the dynamo transition can be induced when an external field is applied to the flow.
Noise Delays Bifurcation in a Positively Coupled Neural Circuit
Gutkin, Boris; Hely, Tim; Jost, Juergen
2000-01-01
We report a noise induced delay of bifurcation in a simple pulse-coupled neural circuit. We study the behavior of two neural oscillators, each individually governed by saddle-node dynamics, with reciprocal excitatory synaptic connections. In the deterministic circuit, the synaptic current amplitude acts as a control parameter to move the circuit from a mono-stable regime through a bifurcation into a bistable regime. In this regime stable sustained anti-phase oscillations in both neurons coexi...
Institute of Scientific and Technical Information of China (English)
Pengnian CHEN; Huashu QIN; Shengwei MEI
2005-01-01
This paper deals with the problems of bifurcation suppression and bifurcation suppression with stability of nonlinear systems. Necessary conditions and sufficient conditions for bifurcation suppression via dynamic output feedback are presented;Sufficient conditions for bifurcation suppression with stability via dynamic output feedback are obtained. As an application, a dynamic compensator, which guarantees that the bifurcation point of rotating stall in axial flow compressors is stably suppressed, is constructed.
Hopf Bifurcation Analysis for a Computer Virus Model with Two Delays
Zizhen Zhang; Huizhong Yang
2013-01-01
This paper is concerned with a computer virus model with two delays. Its dynamics are studied in terms of local stability and Hopf bifurcation. Sufficient conditions for local stability of the positive equilibrium and existence of the local Hopf bifurcation are obtained by regarding the possible combinations of the two delays as a bifurcation parameter. Furthermore, explicit formulae for determining direction of the Hopf bifurcation and stability of the bifurcating periodic solutions are o...
Emergency stenting to control massive bleeding of injured iliac artery following lumbar disk surgery
Energy Technology Data Exchange (ETDEWEB)
Bierdrager, Edwin; Rooij, Willem Jan van; Sluzewski, Menno [Department of Radiology, St. Elisabeth Ziekenhuis, Tilburg (Netherlands)
2004-05-01
The purpose of this study was to demonstrate the use of endovascular stenting to repair an iliac artery injury following lumbar discectomy, thus obviating the need for major surgery. A 57-year-old woman developed a distended abdomen and signs of hypovolemic shock immediately following discectomy at the L4-L5 level. Ultrasound showed a large amount of abdominal fluid. Angiography revealed a laceration of the right iliac artery bifurcation with extravasation of contrast material. After occlusion of the internal iliac artery with fibered coils to prevent retrograde flow to the iliac bifurcation, a self-expanding covered stent was inserted to seal the iliac laceration. The leakage of blood stopped immediately. The clinical condition of the patient gradually improved and she was discharged home 5 weeks later. Sealing of arterial laceration as a complication of lumbar disc surgery with a covered stent is a simple and effective alternative to major pelvic surgery. (orig.)
Misra, G. P.
1992-04-01
Oscillatory characteristics of the Belousov—Zhabotinskii reaction as a function of temperature have been investigated in a continuous flow stirred tank reactor. Oscillations are not observed above a critical temperature limit. The limit is found to be associated with a Hopf bifurcation. Numerical computations show that the results can be qualitatively interpreted on the basis of the Oregonator model.
Bifurcation Analysis Using Rigorous Branch and Bound Methods
Smith, Andrew P.; Crespo, Luis G.; Munoz, Cesar A.; Lowenberg, Mark H.
2014-01-01
For the study of nonlinear dynamic systems, it is important to locate the equilibria and bifurcations occurring within a specified computational domain. This paper proposes a new approach for solving these problems and compares it to the numerical continuation method. The new approach is based upon branch and bound and utilizes rigorous enclosure techniques to yield outer bounding sets of both the equilibrium and local bifurcation manifolds. These sets, which comprise the union of hyper-rectangles, can be made to be as tight as desired. Sufficient conditions for the existence of equilibrium and bifurcation points taking the form of algebraic inequality constraints in the state-parameter space are used to calculate their enclosures directly. The enclosures for the bifurcation sets can be computed independently of the equilibrium manifold, and are guaranteed to contain all solutions within the computational domain. A further advantage of this method is the ability to compute a near-maximally sized hyper-rectangle of high dimension centered at a fixed parameter-state point whose elements are guaranteed to exclude all bifurcation points. This hyper-rectangle, which requires a global description of the bifurcation manifold within the computational domain, cannot be obtained otherwise. A test case, based on the dynamics of a UAV subject to uncertain center of gravity location, is used to illustrate the efficacy of the method by comparing it with numerical continuation and to evaluate its computational complexity.
Stability and bifurcation of quasiparallel Alfven solitons
Hamilton, R. L.; Kennel, C. F.; Mjolhus, E.
1992-01-01
The inverse scattering transformation (IST) is used to study the one-parameter and two-parameter soliton families of the derivative nonlinear Schroedinger (DNLS) equation. The two-parameter soliton family is determined by the discrete complex eigenvalue spectrum of the Kaup-Newell scattering problem and the one-parameter soliton family corresponds to the discrete real eigenvalue spectrum. The structure of the IST is exploited to discuss the existence of discrete real eigenvalues and to prove their structural stability to perturbations of the initial conditions. Also, though the two-parameter soliton is structurally stable in general, it is shown that a perturbation of the initial conditions may change the two-parameter soliton into a degenerate soliton which, in turn, is structurally unstable. This degenerate, or double pole, soliton may bifurcate due to a perturbation of the initial conditions into a pair of one-parameter solitons. If the initial profile is on compact support, then this pair of one-parameter solitons must be compressive and rarefactive respectively. Finally, the Gelfand-Levitan equations appropriate for the double pole soliton are solved.
Prolegomena to a theory of bifurcating universes
International Nuclear Information System (INIS)
We outline a framework for describing the bifurcation of the universe into disconnected pieces, and formulate criteria for a system in which such phenomena occur, to describe local quantum physics in a single connected universe. The formalism is a four-dimensional analog of string field theory which we call Universal Field Theory (UFT). We argue that local dynamics in a single universe is a good approximation to UFT if the universal field is classical and if the vertex for emission of a new connected component of the universe is concentrated on universes of small volume. We show that classical UFT is equivalent to a Wheeler-DeWitt equation for a single connected universe plus a set of nonlocal gap equations for the couplings in the spacetime lagrangian. The effective action must be stationary with respect to the couplings. Nonlocality shows up only at short distances. We solve the equation for the low-energy cosmological constant and show that if the universe undergoes substantial inflation then the cosmological constant is determined to be negative and very small. Its precise value may depend on the fate of nonrelativistic matter in the very late stages of universal expansion. Finally, we argue that corrections to the classical UFT are nonlocal and must be suppressed if the theory is to make sense. This may be the reason that supersymmetric vacua of string theory are not realized in nature. (orig.)
Bifurcation readout of a Josephson phase qubit
International Nuclear Information System (INIS)
The standard method to read out a Josephson phase qubit is using a dc-SQUID to measure the state-dependent magnetic flux of the qubit by switching to the non-superconducting state. This process generates heat directly on the qubit chip and quasi-particles in the circuitry. Both effects require a relatively long cool-down time after each switching event. This, together with the time needed to ramp up the bias current of the SQUID limits the repetition rate of the experiment. In our ongoing experiments we replace the standard readout scheme by a SQUID shunted by a capacitor. This nonlinear resonator is operated close to its bifurcation point between two oscillating states which depend on the qubit flux. The measurement is done by detecting either the resonance amplitude or phase shift of the reflected probe signal. We verified that our SQUID resonator works as linear resonator for low excitation powers and observed the periodic dependence of the resonance frequency on the externally applied magnetic flux. For higher excitation powers the device shows a hysteretic behavior between the two oscillating states. Current experiments are focused on a pulsed rf-readout to measure coherent evolution of the qubit states. We hope to achieve longer coherence times, perform faster measurements, and test non-destructive measurement schemes with Josephson phase qubits.
Attractors, bifurcations, & chaos nonlinear phenomena in economics
Puu, Tönu
2003-01-01
The present book relies on various editions of my earlier book "Nonlinear Economic Dynamics", first published in 1989 in the Springer series "Lecture Notes in Economics and Mathematical Systems", and republished in three more, successively revised and expanded editions, as a Springer monograph, in 1991, 1993, and 1997, and in a Russian translation as "Nelineynaia Economicheskaia Dinamica". The first three editions were focused on applications. The last was differ ent, as it also included some chapters with mathematical background mate rial -ordinary differential equations and iterated maps -so as to make the book self-contained and suitable as a textbook for economics students of dynamical systems. To the same pedagogical purpose, the number of illus trations were expanded. The book published in 2000, with the title "A ttractors, Bifurcations, and Chaos -Nonlinear Phenomena in Economics", was so much changed, that the author felt it reasonable to give it a new title. There were two new math ematics ch...
Axisymmetric bifurcations of thick spherical shells under inflation and compression
deBotton, G.
2013-01-01
Incremental equilibrium equations and corresponding boundary conditions for an isotropic, hyperelastic and incompressible material are summarized and then specialized to a form suitable for the analysis of a spherical shell subject to an internal or an external pressure. A thick-walled spherical shell during inflation is analyzed using four different material models. Specifically, one and two terms in the Ogden energy formulation, the Gent model and an I1 formulation recently proposed by Lopez-Pamies. We investigate the existence of local pressure maxima and minima and the dependence of the corresponding stretches on the material model and on shell thickness. These results are then used to investigate axisymmetric bifurcations of the inflated shell. The analysis is extended to determine the behavior of a thick-walled spherical shell subject to an external pressure. We find that the results of the two terms Ogden formulation, the Gent and the Lopez-Pamies models are very similar, for the one term Ogden material we identify additional critical stretches, which have not been reported in the literature before.© 2012 Published by Elsevier Ltd.
Zuluaga, M. A.; Orkisz, M.; Delgado, E. J. F.; Doré, V.; Pinzón, A. M.; Hoyos, M. H.
2010-01-01
This paper describes the adaptations of MARACAS algorithm to the segmentation and quantification of vascular structures in CTA images of the carotid artery. The MARACAS algorithm, which is based on an elastic model and on a multi-scale eigen-analysis of the inertia matrix, was originally designed to segment a single artery in MRA images. The modifications are primarily aimed at addressing the specificities of CT images and the bifurcations. The algorithms implemented in this new version are c...
Automatic segmentation of the lumen of the carotid artery in ultrasound B-mode images
Santos, André M. F.; Tavares, Jão. Manuel R. S.; Sousa, Luísa; Santos, Rosa; Castro, Pedro; Azevedo, Elsa
2013-02-01
A new algorithm is proposed for the segmentation of the lumen and bifurcation boundaries of the carotid artery in B-mode ultrasound images. It uses the hipoechogenic characteristics of the lumen for the identification of the carotid boundaries and the echogenic characteristics for the identification of the bifurcation boundaries. The image to be segmented is processed with the application of an anisotropic diffusion filter for speckle removal and morphologic operators are employed in the detection of the artery. The obtained information is then used in the definition of two initial contours, one corresponding to the lumen and the other to the bifurcation boundaries, for the posterior application of the Chan-vese level set segmentation model. A set of longitudinal B-mode images of the common carotid artery (CCA) was acquired with a GE Healthcare Vivid-e ultrasound system (GE Healthcare, United Kingdom). All the acquired images include a part of the CCA and of the bifurcation that separates the CCA into the internal and external carotid arteries. In order to achieve the uppermost robustness in the imaging acquisition process, i.e., images with high contrast and low speckle noise, the scanner was adjusted differently for each acquisition and according to the medical exam. The obtained results prove that we were able to successfully apply a carotid segmentation technique based on cervical ultrasonography. The main advantage of the new segmentation method relies on the automatic identification of the carotid lumen, overcoming the limitations of the traditional methods.
Directory of Open Access Journals (Sweden)
Archana
2016-01-01
Full Text Available CONTEXT Cerebrovascular accident or stroke is one of the most common causes of death. Ultrasonography of the carotid arteries is an easily available, cost effective, non-invasive method of evaluation. Treatment of stroke depends on reaching the most accurate diagnosis. Accurate and prompt diagnosis is crucial because timely and appropriate therapy can significantly reduce the risk of stroke and long-term sequelae. Several modalities of investigation are available to determine carotid artery status. The value of safe, non-invasive screening test is therefore great. AIMS The purpose of this study is to compare the diagnostic value of extracranial carotid and vertebral artery Doppler and Magnetic Resonance Angiography for the diagnosis of carotid artery pathology in patients with stroke. SETTINGS AND DESIGN The principal appealing points in favour of sonography are patient comfort, accuracy and lack of risk. MR Angiography produces reproducible three dimensional image of carotid bifurcation with good sensitivity for high-grade stenosis. METHODS AND MATERIAL After taking consent, 50 patients presenting with focal neurological deficit underwent Colour Doppler and Gadolinium enhanced MRA examination of the carotid and vertebral arteries at KIMS Hospital, Bangalore, with the help of VOLUSON 730 [WIPRO GE ULTRASOUND MACHINE] and GE SIGNA HDXT 1.5 TESLA 16 CHANNEL MRI. RESULTS The highest incidence of stroke was found in the age group of 50-70 years with male population commonly affected. The various risk factors include family history of stroke, hypertension and diabetes mellitus. Total pathologies were most commonly found on the right side. Most common site for atheromatous plaque was carotid bifurcation. Grading of stenosis was done based on the NASCET criteria and the findings of Doppler and MRA were compared. MRA had a better role than Doppler for detecting 80-99% stenosis. CONCLUSIONS MRA has progressively gained clinical relevance in the
Bifurcation and chaos of thin circular functionally graded plate in thermal environment
Energy Technology Data Exchange (ETDEWEB)
Hu Yuda, E-mail: huyuda03@163.com [School of Civil Engineering and Mechanics, Yanshan University, Qinhuangdao 066004 (China); Zhang Zhiqiang, E-mail: zhangzqvib@126.com [School of Civil Engineering and Mechanics, Yanshan University, Qinhuangdao 066004 (China)
2011-09-15
Highlights: > We study bifurcations and chaotic dynamics of a FGM circular plate. > We consider the effect of temperature-dependent material properties. > Increasing volume fraction index will increase chaotic regions. > Increasing temperature will reduce chaotic regions. > The FGM plate exists chaotic motions, multiple periodic and periodic motions. - Abstract: A ceramic/metal functionally graded circular plate under one-term and two-term transversal excitations in the thermal environment is investigated, respectively. The effects of geometric nonlinearity and temperature-dependent material properties are both taken into account. The material properties of the functionally graded plate are assumed to vary continuously through the thickness, according to a power law distribution of the volume fraction of the constituents. Using the principle of virtual work, the nonlinear partial differential equations of FGM plate subjected to transverse harmonic forcing excitation and thermal load are derived. For the circular plate with clamped immovable edge, the Duffing nonlinear forced vibration equation is deduced using Galerkin method. The criteria for existence of chaos under one-term and two-term periodic perturbations are given with Melnikov method. Numerical simulations are carried out to plot the bifurcation curves for the homolinic orbits. Effects of the material volume fraction index and temperature on the criterions are discussed and the existences of chaos are validated by plotting phase portraits, Poincare maps. Also, the bifurcation diagrams and corresponding maximum Lyapunov exponents are plotted. It was found that periodic, multiple periodic solutions and chaotic motions exist for the FGM plate under certain conditions.
Energy Technology Data Exchange (ETDEWEB)
Luo, Kang; Yi, Hong-Liang, E-mail: yihongliang@hit.edu.cn; Tan, He-Ping, E-mail: tanheping@hit.edu.cn [School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China)
2014-05-15
Transitions and bifurcations of transient natural convection in a horizontal annulus with radiatively participating medium are numerically investigated using the coupled lattice Boltzmann and direct collocation meshless (LB-DCM) method. As a hybrid approach based on a common multi-scale Boltzmann-type model, the LB-DCM scheme is easy to implement and has an excellent flexibility in dealing with the irregular geometries. Separate particle distribution functions in the LBM are used to calculate the density field, the velocity field and the thermal field. In the radiatively participating medium, the contribution of thermal radiation to natural convection must be taken into account, and it is considered as a radiative term in the energy equation that is solved by the meshless method with moving least-squares (MLS) approximation. The occurrence of various instabilities and bifurcative phenomena is analyzed for different Rayleigh number Ra and Prandtl number Pr with and without radiation. Then, bifurcation diagrams and dual solutions are presented for relevant radiative parameters, such as convection-radiation parameter Rc and optical thickness τ. Numerical results show that the presence of volumetric radiation changes the static temperature gradient of the fluid, and generally results in an increase in the flow critical value. Besides, the existence and development of dual solutions of transient convection in the presence of radiation are greatly affected by radiative parameters. Finally, the advantage of LB-DCM combination is discussed, and the potential benefits of applying the LB-DCM method to multi-field coupling problems are demonstrated.
Analysis of bifurcation and stability for a tractor semi-trailer in planar motion
Ding, Nenggen; Shi, Xiaobo; Zhang, Yipeng; Chen, Wen
2014-12-01
This paper is intended for bifurcation analysis of a nonlinear tractor semi-trailer vehicle model in planar motion and for investigating its stability under constant running conditions. Bifurcation analysis shows that bifurcation diagrams of a tractor semi-trailer are quite different from those of a single-unit vehicle. Some instability phenomena of the vehicle system such as jackknifing, sideslip, and spinning are explained by correlating them with the behaviour in the neighbourhood of unstable fixed points based on analysis of eigenvectors, phase trajectories, and status of lateral tyre force saturation. It is also found that yaw planar instability of a tractor semi-trailer is caused by lateral tyre force saturation of the tractor's rear axles and/or the trailer's axles. Moreover, the stability region in the state space is demarcated, and a stability index for evaluating size of the stability region in a feasible domain is proposed. Yaw stability under constant driving conditions is analysed by using the proposed stability index.
Bifurcation and buckling analysis of a unilaterally confined self-rotating cantilever beam
Institute of Scientific and Technical Information of China (English)
Shifu Xiao; Bin Chen; Min Yang
2006-01-01
A nonlinear dynamic model of a simple non-holonomic system comprising a self-rotating cantilever beam subjected to a unilateral locked or unlocked constraint is established by employing the general Hamilton's Variational Principle.The critical values,at which the trivial equilibrium loses its stability or the unilateral constraint is activated or a saddle-node bifurcation occurs,and the equilibria are investigated by approximately analytical and numerical methods.The results indicate that both the buckled equilibria and the bifurcation mode of the beam are different depending on whether the distance of the clearance of unilateral constraint equals zero or not and whether the unilateral constraint is locked or not.The unidirectional snap-through phenomenon (i.e.catastrophe phenomenon) is destined to occur in the system no matter whether the constraint is lockable or not.The saddle-node bifurcation can occur only on the condition that the unilateral constraint is lockable and its clearance is non-zero.The results obtained by two methods are consistent.
Mitsui, Takahito; Aihara, Kazuyuki
2015-01-01
Glacial-interglacial cycles are large variations in continental ice mass and greenhouse gases, which have dominated climate variability over the Quaternary. The dominant periodicity of the cycles is $\\sim $40 kyr before the so-called middle Pleistocene transition between $\\sim$1.2 and $\\sim$0.7 Myr ago, and it is $\\sim $100 kyr after the transition. In this paper, the dynamics of glacial-interglacial cycles are investigated using a phase oscillator model forced by the time-varying incoming solar radiation (insolation). We analyze the bifurcations of the system and show that strange nonchaotic attractors appear through nonsmooth saddle-node bifurcations of tori. The bifurcation analysis indicates that mode-locking is likely to occur for the 41 kyr glacial cycles but not likely for the 100 kyr glacial cycles. The sequence of mode-locked 41 kyr cycles is robust to small parameter changes. However, the sequence of 100 kyr glacial cycles can be sensitive to parameter changes when the system has a strange nonchaoti...
Bifurcations and chaos of a vibration isolation system with magneto-rheological damper
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Hailong Zhang
2016-03-01
Full Text Available Magneto-rheological (MR damper possesses inherent hysteretic characteristics. We investigate the resulting nonlinear behaviors of a two degree-of-freedom (2-DoF MR vibration isolation system under harmonic external excitation. A MR damper is identified by employing the modified Bouc-wen hysteresis model. By numerical simulation, we characterize the nonlinear dynamic evolution of period-doubling, saddle node bifurcating and inverse period-doubling using bifurcation diagrams of variations in frequency with a fixed amplitude of the harmonic excitation. The strength of chaos is determined by the Lyapunov exponent (LE spectrum. Semi-physical experiment on the 2-DoF MR vibration isolation system is proposed. We trace the time history and phase trajectory under certain values of frequency of the harmonic excitation to verify the nonlinear dynamical evolution of period-doubling bifurcations to chaos. The largest LEs computed with the experimental data are also presented, confirming the chaotic motion in the experiment. We validate the chaotic motion caused by the hysteresis of the MR damper, and show the transitions between distinct regimes of stable motion and chaotic motion of the 2-DoF MR vibration isolation system for variations in frequency of external excitation.
Local Bifurcations Analysis of a State-Dependent Delay Diﬀerential Equation
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V. O. Golubenets
2015-12-01
Full Text Available In this paper, a ﬁrst-order equation with state-dependent delay and with a nonlinear right-hand side is considered. Conditions of existence and uniqueness of the solution of initial value problem aresupposed to be executed. The task is to study the behavior of solutions of the considered equation in a small neighborhood of its zero equilibrium. Local dynamics depends on real parameters which are coeﬃcients of equation right-hand side decomposition in a Taylor series. The parameter which is a coeﬃcient at the linear part of this decomposition has two critical values which determine a stability domain of zero equilibrium. We introduce a small positive parameter and use the asymtotic method of normal forms in order to investigate local dynamics modiﬁcations of the equation near each two critical values. We show that the stability exchange bifurcation occurs in the considered equation near the ﬁrst of these critical values, and the supercritical Andronov – Hopf bifurcation occurs near the second of them (if the suﬃcient condition is executed. Asymptotic decompositions according to correspondent small parameters are obtained for each stable solution. Next, a logistic equation with state-dependent delay is considered as an example. The bifurcation parameter of this equation has one critical value. A simple suﬃcient condition of Andronov – Hopf bifurcation occurence in the considered equation near a critical value is obtained as a result of applying the method of normal forms.
NEW METHOD FOR IMPROVED CALCULATIONS OF UNSTEADY COMPLEX FLOWS IN LARGE ARTERIES
Institute of Scientific and Technical Information of China (English)
A. Cheer; Harry A. Dwyer; T. Kim
2011-01-01
Using an improved computational fluid dynamics (CFD) method developed for highly unsteady three-dimensional flows,numerical simulations for oscillating flow cycles and detailed unsteady simulations of the flow and forces on the aortic vessels at the iliac bifurcation,for both healthy and diseased patients,are analyzed.Improvements in computational efficiency and acceleration in convergence are achieved by calculating both an unsteady pressure gradient which is due to fluid acceleration and a good global pressure field correction based on mass flow for the pressure Poisson equation.Applications of the enhanced method to oscillatory flow in curved pipes yield an order of magnitude increase in speed and efficiency,thus allowing the study of more complex flow problems such as flow through the mammalian abdominal aorta at the iliac arteries bifurcation.To analyze the large forces which can exist on stent graft of patients with abdominal aortic aneurysm (AAA) disease,a complete derivation of the force equations is presented.The accelerated numerical algorithm and the force equations derived are used to calculate flow and forces for two individuals whose geometry is obtained from CT data and whose respective blood pressure measurements are obtained experimentally.Although the use of endovascular stent grafts in diseased patients can alter vessel geometries,the physical characteristics of stents are still very different when compared to native blood vessels of healthy subjects.The geometry for the AAA stent graph patient studied in this investigation induced flows that resulted in large forces that are primarily caused by the blood pressure.These forces are also directly related to the flow cross-sectional area and the angle of the iliac arteries relative to the main descending aorta.Furthermore,the fluid flow is significantly disturbed in the diseased patient with large flow recirculation and stagnant regions which are not present for healthy subjects.
Pulse propagation in the pulmonary arteries
Hill, Nicholas; Vaughan, Gareth; Olufsen, Mette; Johnson, Martin; Sainsbury, Christopher
2007-11-01
The model of Olufsen [1,2] has been extended to study pulse propagation in the pulmonary circulation. The pulmonary arteries are treated as a bifurcating tree of compliant and tapering vessels. The model is divided into two coupled parts: the larger and smaller arteries. Blood flow and pressure in the larger arteries are predicted from a nonlinear 1D cross-sectional area-averaged model for a Newtonian fluid in an elastic tube. The initial cardiac output is obtained from magnetic resonance measurements. The smaller blood vessels are modelled as an asymmetric structured tree with specified area and asymmetry ratios between the parent and daughter arteries. Womersley's theory gives the wave equation in the frequency domain for the 1D flow in these smaller vessels, resulting in a linear system. The impedances of the smallest vessels are set to a constant and then back-calculation gives the required outflow boundary condition for the Navier-Stokes equations in the larger vessels. The number of generations of blood vessels, and the compliance of the arterial wall are shown to affect both the systolic and diastolic pressures. [1] Olufsen MS et al. Ann Biomed Eng. 2000;28:1281-99. [2] Olufsen MS. Am J Physiol. 1999;276:H257-68.
Coanda effect on ductal flow in the pulmonary artery.
Guntheroth, W; Miyaki-Hull, C
1999-03-01
The Coanda effect (the tendency of a jet stream to adhere to a boundary wall), and the relevant anatomy, may explain the location of ductal jets within the main pulmonary artery. With the usual insertion of the duct close to the left pulmonary artery, during right ventricular ejection, the ductal jet adheres to the left wall of the main pulmonary artery. When right ventricular ejection is absent in pulmonary atresia, the ductal jet streams down the right wall of the pulmonary artery to the pulmonary valve, reverses, and maintains a parallel column back toward the bifurcation. If the reversed flow is mistaken for ejection from the right ventricle, the diagnosis of pulmonary atresia may be missed. PMID:10082354
Bifurcation phenomena near homoclinic systems: A two-parameters analysis
International Nuclear Information System (INIS)
The bifurcations of periodic orbits in a class of autonomous three-variable, nonlinear-differential-equation systems possessing a homoclinic orbit associated with a saddle focus with eigenvalues (rho +- iω, lambda), where Vertical Barrho/lambdaVertical Bar<1 (Sil'nikov's condition), are studied in a two-parameters space. The perturbed homoclinic systems undergo a countable set of tangent bifurcation followed by period-doubling bifurcations leading to a periodic orbits which may be attractors if Vertical Barlambda/lVertical Bar<1/2. The accumulation rate of the critical parameter values at the homoclinic system is exp(-2πVertical Barrho/ωVertical Bar). A global mechanism for the onset of homoclinicity in strongly contractive flows is analyzed. Cusp bifurcations with bistability and hysteresis phenomena exist locally near the onset of homoclinicity. A countable set of these cusp bifurcations with scaling properties related to the eigenvalues rho +- iω of the stationary state are shown to occur in infinitely contractive flows. In the two-parameter space, the periodic orbit attractor domain exhibits a spiral structure globally, around the set of homoclinic systems, in which all the different periodic orbits are continuously connected
Experimental Study of Bifurcations in A Parametrically Forced Pendulum
Kim, S Y; Yi, J; Jang, J W; Kim, Sang-Yoon
1997-01-01
An experimental study of bifurcations associated with stability of stationary points (SP's) in a parametrically forced magnetic pendulum and a comparison of its results with numerical results are presented. The critical values for which the SP's lose or gain their stability are experimentally measured by varying the two parameters $\\Omega$ (the normalized natural frequency) and $A$ (the normalized driving amplitude). It is observed that, when the amplitude $A$ exceeds a critical value, the normal SP with $\\theta=0$ ($\\theta$ is the angle between the permanent magnet and the magnetic field) becomes unstable either by a period-doubling bifurcation or by a symmetry-breaking pitchfork bifurcation, depending on the values of $\\Omega$. However, in contrast with the normal SP the inverted SP with $\\theta=\\pi$ is observed to become stable as $A$ is increased above a critical value by a pitchfork bifurcation, but it also destabilizes for a higher critical value of $A$ by a period-doubling bifurcation. All of these exp...
Grazing bifurcations and chatter in a pressure relief valve model
Hős, Csaba; Champneys, Alan R.
2012-11-01
This paper considers a simple mechanical model of a pressure relief valve. For a wide region of parameter values, the valve undergoes self-oscillations that involve impact with the valve seat. These oscillations are born in a Hopf bifurcation that can be either super- or sub-critical. In either case, the onset of more complex oscillations is caused by the occurrence of grazing bifurcations, where the limit cycle first becomes tangent to the discontinuity surface that represents valve contact. The complex dynamics that ensues from such points as the flow speed is decreased has previously been reported via brute-force bifurcation diagrams. Here, the nature of the transitions is further elucidated via the numerical continuation of impacting orbits. In addition, two-parameter continuation results for Hopf and grazing bifurcations as well as the continuation of period-doubling bifurcations of impacting orbits are presented. For yet lower flow speeds, new results reveal chattering motion, that is where there are many impacts in a finite time interval. The geometry of the chattering region is analysed via the computation of several pre-images of the grazing set. It is shown how these pre-images organise the dynamics, in particular by separating initial conditions that lead to complete chatter (an accumulation of impacts) from those which do not.
Inverse bifurcation analysis: application to simple gene systems
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Schuster Peter
2006-07-01
Full Text Available Abstract Background Bifurcation analysis has proven to be a powerful method for understanding the qualitative behavior of gene regulatory networks. In addition to the more traditional forward problem of determining the mapping from parameter space to the space of model behavior, the inverse problem of determining model parameters to result in certain desired properties of the bifurcation diagram provides an attractive methodology for addressing important biological problems. These include understanding how the robustness of qualitative behavior arises from system design as well as providing a way to engineer biological networks with qualitative properties. Results We demonstrate that certain inverse bifurcation problems of biological interest may be cast as optimization problems involving minimal distances of reference parameter sets to bifurcation manifolds. This formulation allows for an iterative solution procedure based on performing a sequence of eigen-system computations and one-parameter continuations of solutions, the latter being a standard capability in existing numerical bifurcation software. As applications of the proposed method, we show that the problem of maximizing regions of a given qualitative behavior as well as the reverse engineering of bistable gene switches can be modelled and efficiently solved.
Doubly twisted Neimark-Sacker bifurcation and two coexisting two-dimensional tori
Sekikawa, Munehisa; Inaba, Naohiko
2016-01-01
We discuss a complicated bifurcation structure involving several quasiperiodic bifurcations generated in a three-coupled delayed logistic map where a doubly twisted Neimark-Sacker bifurcation causes a transition from two coexisting periodic attractors to two coexisting invariant closed circles (ICCs) corresponding to two two-dimensional tori in a vector field. Such bifurcation structures are observed in Arnol'd tongues. Lyapunov and bifurcation analyses suggest that the two coexisting ICCs and the two coexisting periodic solutions almost overlap in the two-parameter bifurcation diagram.
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The bifurcation locus for numbers of bounded type
Carminati, Carlo
2011-01-01
We define a family B(t) of compact subsets of the unit interval which generalizes the sets of numbers whose continued fraction expansion has bounded digits. We study how the set B(t) changes as one moves the parameter t, and see that the family undergoes period-doubling bifurcations and displays the same transition pattern from periodic to chaotic behavior as the usual family of quadratic polynomials. The set E of bifurcation parameters is a fractal set of measure zero. We also show that the Hausdorff dimension of B(t) varies continuously with the parameter, and the dimension of each individual set equals the dimension of a corresponding section of the bifurcation set E.
Implicit ordinary differential equations: bifurcations and sharpening of equivalence
International Nuclear Information System (INIS)
We obtain a formal classification of generic local bifurcations of an implicit ordinary differential equation at its singular points as a single external parameter varies. This classification consists of four normal forms, each containing a functional invariant. We prove that every deformation in the contact equivalence class of an equation germ which remains quadratic in the derivative can be obtained by a deformation of the independent and dependent variables. Our classification is based on a generalization of this result for families of equations. As an application, we obtain a formal classification of generic local bifurcations on the plane for a linear second-order partial differential equation of mixed type at the points where the domains of ellipticity and hyperbolicity undergo Morse bifurcations
Dynamical systems V bifurcation theory and catastrophe theory
1994-01-01
Bifurcation theory and catastrophe theory are two of the best known areas within the field of dynamical systems. Both are studies of smooth systems, focusing on properties that seem to be manifestly non-smooth. Bifurcation theory is concerned with the sudden changes that occur in a system when one or more parameters are varied. Examples of such are familiar to students of differential equations, from phase portraits. Moreover, understanding the bifurcations of the differential equations that describe real physical systems provides important information about the behavior of the systems. Catastrophe theory became quite famous during the 1970's, mostly because of the sensation caused by the usually less than rigorous applications of its principal ideas to "hot topics", such as the characterization of personalities and the difference between a "genius" and a "maniac". Catastrophe theory is accurately described as singularity theory and its (genuine) applications. The authors of this book, the first printing of w...
An explicit example of Hopf bifurcation in fluid mechanics
Kloeden, P.; Wells, R.
1983-01-01
It is observed that a complete and explicit example of Hopf bifurcation appears not to be known in fluid mechanics. Such an example is presented for the rotating Benard problem with free boundary conditions on the upper and lower faces, and horizontally periodic solutions. Normal modes are found for the linearization, and the Veronis computation of the wave numbers is modified to take into account the imposed horizontal periodicity. An invariant subspace of the phase space is found in which the hypotheses of the Joseph-Sattinger theorem are verified, thus demonstrating the Hopf bifurcation. The criticality calculations are carried through to demonstrate rigorously, that the bifurcation is subcritical for certain cases, and to demonstrate numerically that it is subcritical for all the cases in the paper.
EXPERIMENTAL STUDY ON SEDIMENT DISTRIBUTION AT CHANNEL BIFURCATION
Institute of Scientific and Technical Information of China (English)
G.M. Tarekul ISLAM; M.R. KABIR; Ainun NISHAT
2002-01-01
This paper presents the experimental results on the distribution of sediments at channel bifurcation.The experiments have been conducted in a physical model of channel bifurcation. It consists of a straight main channel which bifurcates into two branch channels of different widths. The test rig is a mobile bed with fixed bank. Four different noses have been used to study the phenomenon. For each nose, three upstream discharges viz. 20 l/s, 30 l/s and 40 l/s have been employed. From the measured data, discharges and sediment transport ratios per unit width are calculated in the downstream branches.These data have been set to the general nodal point relation and a set of equations has been developed to describe the distribution of sediments to the downstream branches for different nose angles.
High-resolution mapping of bifurcations in nonlinear biochemical circuits
Genot, A. J.; Baccouche, A.; Sieskind, R.; Aubert-Kato, N.; Bredeche, N.; Bartolo, J. F.; Taly, V.; Fujii, T.; Rondelez, Y.
2016-08-01
Analog molecular circuits can exploit the nonlinear nature of biochemical reaction networks to compute low-precision outputs with fewer resources than digital circuits. This analog computation is similar to that employed by gene-regulation networks. Although digital systems have a tractable link between structure and function, the nonlinear and continuous nature of analog circuits yields an intricate functional landscape, which makes their design counter-intuitive, their characterization laborious and their analysis delicate. Here, using droplet-based microfluidics, we map with high resolution and dimensionality the bifurcation diagrams of two synthetic, out-of-equilibrium and nonlinear programs: a bistable DNA switch and a predator–prey DNA oscillator. The diagrams delineate where function is optimal, dynamics bifurcates and models fail. Inverse problem solving on these large-scale data sets indicates interference from enzymatic coupling. Additionally, data mining exposes the presence of rare, stochastically bursting oscillators near deterministic bifurcations.
Bifurcated equilibria in two-dimensional MHD with diamagnetic effects
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Ottaviani, M. [CEA Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee; Tebaldi, C. [Lecce University (Italy). Dept. of Mathematics
1998-12-01
In this work we analyzed the sequence of bifurcated equilibria in two-dimensional reduced magnetohydrodynamics. Diamagnetic effects are studied under the assumption of a constant equilibrium pressure gradient, not altered by the formation of the magnetic island. The formation of an island when the symmetric equilibrium becomes unstable is studied as a function of the tearing mode stability parameter {Delta}` and of the diamagnetic frequency, by employing fixed-points numerical techniques and an initial value code. At larger values of {Delta}` a tangent bifurcation takes place, above which no small island solutions exist. This bifurcation persists up to fairly large values of the diamagnetic frequency (of the order of one tenth of the Alfven frequency). The implications of this phenomenology for the intermittent MHD dynamics observed in tokamaks is discussed. (authors) 20 refs.