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....
Numerical bifurcation of Hamiltonian relative periodic orbits
DEFF Research Database (Denmark)
Wulff, Claudia; Schilder, Frank
2009-01-01
that the family of choreographies rotating around the $e^2$-axis bifurcates to the family of rotating choreographies that connects to the Lagrange relative equilibrium. Moreover, we compute several relative period-doubling bifurcations and a turning point of the family of planar rotating choreographies, which...... to symmetry-breaking/symmetry-increasing pitchfork bifurcations or to period-doubling/period-halving bifurcations. We apply our methods to the family of rotating choreographies which bifurcate from the famous figure eight solution of the three-body problem as angular momentum is varied. We find...
DEFF Research Database (Denmark)
Behan, Miles W; Holm, Niels Ramsing; Curzen, Nicholas P;
2011-01-01
Background— Controversy persists regarding the correct strategy for bifurcation lesions. Therefore, we combined the patient-level data from 2 large trials with similar methodology: the NORDIC Bifurcation Study (NORDIC I) and the British Bifurcation Coronary Study (BBC ONE). Methods and Results— B...
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.
Anatomy and function relation in the coronary tree: from bifurcations to myocardial flow and mass.
Kassab, Ghassan S; Finet, Gerard
2015-01-01
The study of the structure-function relation of coronary bifurcations is necessary not only to understand the design of the vasculature but also to use this understanding to restore structure and hence function. The objective of this review is to provide quantitative relations between bifurcation anatomy or geometry, flow distribution in the bifurcation and degree of perfused myocardial mass in order to establish practical rules to guide optimal treatment of bifurcations including side branches (SB). We use the scaling law between flow and diameter, conservation of mass and the scaling law between myocardial mass and diameter to provide geometric relations between the segment diameters of a bifurcation, flow fraction distribution in the SB, and the percentage of myocardial mass perfused by the SB. We demonstrate that the assessment of the functional significance of an SB for intervention should not only be based on the diameter of the SB but also on the diameter of the mother vessel as well as the diameter of the proximal main artery, as these dictate the flow fraction distribution and perfused myocardial mass, respectively. The geometric and flow rules for a bifurcation are extended to a trifurcation to ensure optimal therapy scaling rules for any branching pattern.
Stochastic Parameter Resonance of Road-Vehicle Systems and Related Bifurcation Problems
Wedig, Walter V.
The paper investigates stochastic dynamics of road-vehicle systems and related bifurcation problems. The ride on rough roads generates vertical car vibrations whose root-mean-squares are resonant for critical car speeds and vanish when the car velocity is increasing, infinitely. These investigations are extended to wheel suspensions with progressive spring characteristics. For weak but still positive damping, the car vibrations become unstable when the velocity reaches the parameter resonance near twice the critical speed bifurcating into stochastic chaos of larger non-stationary car vibrations.
Travelling-wave solutions bifurcating from relative periodic orbits in plane Poiseuille flow
Rawat, Subhendu; Rincon, François
2016-01-01
Travelling-wave solutions are shown to bifurcate from relative periodic orbits in plane Poiseuille flow at Re = 2000 in a saddle-node infinite period bifurcation. These solutions consist in self-sustaining sinuous quasi-streamwise streaks and quasi- streamwise vortices located in the bulk of the flow. The lower branch travelling-wave solutions evolve into spanwise localized states when the spanwise size Lz of the domain in which they are computed is increased. On the contrary, upper branch of travelling-wave solutions develop multiple streaks when Lz is increased. Upper branch travelling-wave solutions can be continued into coherent solutions of the filtered equations used in large-eddy simulations where they represent turbulent coherent large-scale motions.
The steady expiratory pressure-flow relation in a model pulmonary bifurcation.
Collins, J M; Shapiro, A H; Kimmel, E; Kamm, R D
1993-08-01
Experiments were conducted over a range of Reynolds numbers from 50 to 8000 to study the pressure-flow relationship for a single bifurcation in a multi-generation model during steady expiratory flow. Using the energy equation, the measured static pressure drop was decomposed into separate components due to fluid acceleration and viscous energy dissipation. The frictional pressure drop was found to closely approximate that for an equivalent length of curved tube with the same curvature ratio as in the model bifurcation. The sensitivity of these results to changes in airway cross-sectional shape, non-planar configuration, and flow regime (laminar-turbulent) was investigated. In separate experiments using dye visualization and hot-wire anemometry, a transition to turbulent flow was observed at Reynolds numbers between 1000 and 1500. Transition had very little effect on the pressure-flow relation.
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.
Titantah, John Tatini; Karttunen, Mikko
2013-10-21
Structure and dynamics of water remain a challenge. Resolving the properties of hydrogen bonding lies at the heart of this puzzle. We employ ab initio Molecular Dynamics (AIMD) simulations over a wide temperature range. The total simulation time was ≈ 2 ns. Both bulk water and water in the presence of a small hydrophobic molecule were simulated. We show that large-angle jumps and bond bifurcations are fundamental properties of water dynamics and that they are intimately coupled to both local density and hydrogen bond strength oscillations in scales from about 60 to a few hundred femtoseconds: Local density differences are the driving force for bond bifurcations and the consequent large-angle jumps. The jumps are intimately connected to the recently predicted hydrogen bond energy asymmetry. Our analysis also appears to confirm the existence of the so-called negativity track provided by the lone pairs of electrons on the oxygen atom to enable water rotation.
Amador-Noguez, Daniel; Feng, Xiao-Jiang; Fan, Jing; Roquet, Nathaniel; Rabitz, Herschel; Rabinowitz, Joshua D
2010-09-01
Obligatory anaerobic bacteria are major contributors to the overall metabolism of soil and the human gut. The metabolic pathways of these bacteria remain, however, poorly understood. Using isotope tracers, mass spectrometry, and quantitative flux modeling, here we directly map the metabolic pathways of Clostridium acetobutylicum, a soil bacterium whose major fermentation products include the biofuels butanol and hydrogen. While genome annotation suggests the absence of most tricarboxylic acid (TCA) cycle enzymes, our results demonstrate that this bacterium has a complete, albeit bifurcated, TCA cycle; oxaloacetate flows to succinate both through citrate/alpha-ketoglutarate and via malate/fumarate. Our investigations also yielded insights into the pathways utilized for glucose catabolism and amino acid biosynthesis and revealed that the organism's one-carbon metabolism is distinct from that of model microbes, involving reversible pyruvate decarboxylation and the use of pyruvate as the one-carbon donor for biosynthetic reactions. This study represents the first in vivo characterization of the TCA cycle and central metabolism of C. acetobutylicum. Our results establish a role for the full TCA cycle in an obligatory anaerobic organism and demonstrate the importance of complementing genome annotation with isotope tracer studies for determining the metabolic pathways of diverse microbes.
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...
Energy Technology Data Exchange (ETDEWEB)
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.
Impedance matching at arterial bifurcations.
Brown, N
1993-01-01
Reflections of pulse waves will occur in arterial bifurcations unless the impedance is matched continuously through changing geometric and elastic properties. A theoretical model is presented which minimizes pulse wave reflection through bifurcations. The model accounts for the observed linear changes in area within the bifurcation, generalizes the theory to asymmetrical bifurcations, characterizes changes in elastic properties from parent to daughter arteries, and assesses the effect of branch angle on the mechanical properties of daughter vessels. In contradistinction to previous models, reflections cannot be minimized without changes in elastic properties through bifurcations. The theoretical model predicts that in bifurcations with area ratios (beta) less than 1.0 Young's moduli of daughter vessels may be less than that in the parent vessel if the Womersley parameter alpha in the parent vessel is less than 5. Larger area ratios in bifurcations are accompanied by greater increases in Young's moduli of branches. For an idealized symmetric aortic bifurcation (alpha = 10) with branching angles theta = 30 degrees (opening angle 60 degrees) Young's modulus of common iliac arteries relative to that of the distal abdominal aorta has an increase of 1.05, 1.68 and 2.25 for area ratio of 0.8, 1.0 and 1.15, respectively. These predictions are consistent with the observed increases in Young's moduli of peripheral vessels.(ABSTRACT TRUNCATED AT 250 WORDS)
Lee, Cheng-Hung; Jhong, Guan-Heng; Hsu, Ming-Yi; Liu, Shih-Jung; Wang, Chao-Jan; Hung, Kuo-Chun
2014-05-01
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 stenting, and potential mechanisms of in-stent restenosis, along with their relationship with bifurcation angle.
Lagrangian relative equilibria for a gyrostat in the three-body problem: bifurcations and stability
Energy Technology Data Exchange (ETDEWEB)
Guirao, Juan L G; Vera, Juan A, E-mail: juan.garcia@upct.e, E-mail: juanantonio.vera@upct.e [Departamento de Matematica Aplicada y EstadIstica, Universidad Politecnica de Cartagena, Hospital de Marina, 30203 Cartagena, Region de Murcia (Spain)
2010-05-14
In this paper we consider the non-canonical Hamiltonian dynamics of a gyrostat in the frame of the three-body problem. Using geometric/mechanic methods we study the approximate dynamics of the truncated Legendre series representation of the potential of an arbitrary order. Working in the reduced problem, we study the existence of relative equilibria that we refer to as Lagrange type following the analogy with the standard techniques. We provide necessary and sufficient conditions for the linear stability of Lagrangian relative equilibria if the gyrostat morphology form is close to a sphere. Thus, we generalize the classical results on equilibria of the three-body problem and many results on them obtained by the classic approach for the case of rigid bodies.
Sprinkler Bifurcations and Stability
Sorensen, Jody; Rykken, Elyn
2010-01-01
After discussing common bifurcations of a one-parameter family of single variable functions, we introduce sprinkler bifurcations, in which any number of new fixed points emanate from a single point. Based on observations of these and other bifurcations, we then prove a number of general results about the stabilities of fixed points near a…
Characteristics of Period-Adding Bursting Bifurcation Without Chaos in the Chay Neuron Model
Institute of Scientific and Technical Information of China (English)
YANG Zhuo-Qin; LU Qi-Shao
2004-01-01
@@ A period-adding bursting sequence without bursting-chaos in the Chay neuron model is studied by bifurcation analysis. The genesis of each periodic bursting is separately evoked by the corresponding periodic spiking patterns through two period-doubling bifurcations, except for the period-1 bursting occurring via Hopf bifurcation. Hence,it is concluded that this period-adding bursting bifurcation without chaos has a compound bifurcation structure closely related to period-doubling bifurcations of periodic spiking in essence.
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...
Symmetric/asymmetric bifurcation behaviours of a bogie system
DEFF Research Database (Denmark)
Xue-jun, Gao; Ying-hui, Li; Yuan, Yue;
2013-01-01
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 slo...
Electron-Dominated Spontaneous Bifurcation of Harris Equilibrium
Lee, Kuang-Wu
2012-01-01
In this letter the spontaneous bifurcation of Harris equilibrium current sheet is reported. The collisionless current bifurcation is simulated by a 2D particle-in-cell approach. Explicit particle advancing method is used to resolve the transient electron dynamics. Unlike previous implicit investigations no initial perturbations is applied to trigger current bifurcation. Instead, an electron-dominated spontaneously bifurcation is observed. Electromagnetic fluctuations grow from thermal noise initially. Soon the noise triggers the eigenmodes and eventually causes current sheet bifurcation. The relative entropy of the bifurcated state exceeds the value of initial Harris equilibrium. It is also found that the Helmholtz free energy decreases in the bifurcation process. Hence it is concluded that Harris equilibrium evolves toward a more stable (smaller free energy) bifurcated state.
Optimal escape from potential wells-patterns of regular and chaotic bifurcation
Stewart, H. B.; Thompson, J. M. T.; Ueda, Y.; Lansbury, A. N.
The patterns of bifurcation governing the escape of periodically forced oscillations from a potential well over a smooth potential barrier are studied by numerical simulation. Both the generic asymmetric single-well cubic potential and the symmetric twin-well potential Duffing oscillator are surveyed by varying three parameters: forcing frequency, forcing amplitude, and damping coefficient. The close relationship between optimal escape and nonlinear resonance within the well is confirmed over a wide range of damping. Subtle but significant differences are observed at higher damping ratios. The possibility of indeterminate outcomes of jumps to and from resonance near optimal escape is cmppletely suppressed above a critical level of the damping ratio (about 0.12 for the asymmetric single-well oscillator). Coincidentally, at almost the same level of damping, the optimal escape condition becomes distinct from the apex in the (ω, F) plane of the bistable regime; this corresponds to the appearance of chaotic attractors which subsume both resonant and non-resonant motions within one well. At higher damping levels, further changes occur involving conversions from chaotic-saddle to regular-saddle bifurcations. These changes in optimal escape phenomena correspond to codimension three bifurcations at exceptional points in the space of three parameters. These bifurcations are described in terms of homoclinic and heteroclinic structures of invariant manifolds, and changes in accessible boundary orbits. The same sequence of codimension three bifurcations is observed in both the twin-well Duffing oscillator and the asymmetric single-well escape equation. Within the codimension three bifurcation patterns governing escape, one particular codimension two global bifurcation involves a chaotic attractor explosion, or interior crisis, compounded with a blue sky catastrophe or boundary crisis of the exploded attractor. This codimension two bifurcation has structure containing a form of
Torus Bifurcation Under Discretization
Institute of Scientific and Technical Information of China (English)
邹永魁; 黄明游
2002-01-01
Parameterized dynamical systems with a simple zero eigenvalue and a couple of purely imaginary eigenvalues are considered. It is proved that this type of eigen-structure leads to torns bifurcation under certain nondegenerate conditions. We show that the discrete systems, obtained by discretizing the ODEs using symmetric, eigen-structure preserving schemes, inherit the similar torus bifurcation properties. Fredholm theory in Banach spaces is applied to obtain the global torns bifurcation. Our results complement those on the study of discretization effects of global bifurcation.
Directory of Open Access Journals (Sweden)
Haiyan Hu
1996-01-01
Full Text Available One critical case for the motion of a periodically excited oscillator with continuous and piecewise-linear restoring force is that the motion happens to graze a switching plane between two linear regions of the restoring force. This article presents a numerical scheme for locating the periodic grazing orbit first. Then, through a brief analysis, the article shows that the grazing phenomenon turns the stability trend of the periodic orbit so abruptly that it may be impossible to predict an incident local bifurcation with the variation of a control parameter from the concept of smooth dynamic systems. The numerical simulation in the article well supports the scheme and the analysis, and shows an abundance of grazing phenomena in an engineering range of the excitation frequency.
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....
Complex Dynamics Caused by Torus Bifurcation in Power Systems
Institute of Scientific and Technical Information of China (English)
YU Xiaodan; JIA Hongjie; DONG Cun
2006-01-01
Torus bifurcation is a relatively complicated bifurcation caused by a pair of complex conjuployed to reveal the relationship between torus bifurcation and some complex dynamics.Based on theoretical analysis and simulation studies, it is found that torus bifurcation is a typical route to chaos in power system.Some complex dynamics usually occur after a torus bifurcation, such as self-organization, deep bifurcations, exquisite structure, coexistence of chaos and divergence.It is also found that chaos has close relationship with various instability scenarios of power systems.Studies of this paper are helpful to understand the mechanism of torus bifurcation in power system and relationship of chaos and power system instabilities.
Bifurcation and instability problems in vortex wakes
DEFF Research Database (Denmark)
Aref, Hassan; Brøns, Morten; Stremler, Mark A.
2007-01-01
A number of instability and bifurcation problems related to the dynamics of vortex wake flows are addressed using various analytical tools and approaches. We discuss the bifurcations of the streamline pattern behind a bluff body as a vortex wake is produced, a theory of the universal Strouhal......-Reynolds number relation for vortex wakes, the bifurcation diagram for "exotic" wake patterns behind an oscillating cylinder first determined experimentally by Williamson & Roshko, and the bifurcations in topology of the streamlines pattern in point vortex streets. The Hamiltonian dynamics of point vortices...... in a periodic strip is considered. The classical results of von Kármán concerning the structure of the vortex street follow from the two-vortices-in-a-strip problem, while the stability results follow largely from a four-vortices-in-a-strip analysis. The three-vortices-in-a-strip problem is argued...
Bifurcation and instability problems in vortex wakes
Energy Technology Data Exchange (ETDEWEB)
Aref, H [Center for Fluid Dynamics and Department of Physics, Technical University of Denmark, Kgs. Lyngby, DK-2800 (Denmark); Broens, M [Center for Fluid Dynamics and Department of Mathematics, Technical University of Denmark, Kgs. Lyngby, DK-2800 (Denmark); Stremler, M A [Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 (United States)
2007-04-15
A number of instability and bifurcation problems related to the dynamics of vortex wake flows are addressed using various analytical tools and approaches. We discuss the bifurcations of the streamline pattern behind a bluff body as a vortex wake is produced, a theory of the universal Strouhal-Reynolds number relation for vortex wakes, the bifurcation diagram for 'exotic' wake patterns behind an oscillating cylinder first determined experimentally by Williamson and Roshko, and the bifurcations in topology of the streamlines pattern in point vortex streets. The Hamiltonian dynamics of point vortices in a periodic strip is considered. The classical results of von Karman concerning the structure of the vortex street follow from the two-vortices-in-a-strip problem, while the stability results follow largely from a four-vortices-in-a-strip analysis. The three-vortices-in-a-strip problem is argued to be relevant to the wake behind an oscillating body.
Multiparametric bifurcations of an epidemiological model with strong Allee effect.
Cai, Linlin; Chen, Guoting; Xiao, Dongmei
2013-08-01
In this paper we completely study bifurcations of an epidemic model with five parameters introduced by Hilker et al. (Am Nat 173:72-88, 2009), which describes the joint interplay of a strong Allee effect and infectious diseases in a single population. Existence of multiple positive equilibria and all kinds of bifurcation are examined as well as related dynamical behavior. It is shown that the model undergoes a series of bifurcations such as saddle-node bifurcation, pitchfork bifurcation, Bogdanov-Takens bifurcation, degenerate Hopf bifurcation of codimension two and degenerate elliptic type Bogdanov-Takens bifurcation of codimension three. Respective bifurcation surfaces in five-dimensional parameter spaces and related dynamical behavior are obtained. These theoretical conclusions confirm their numerical simulations and conjectures by Hilker et al., and reveal some new bifurcation phenomena which are not observed in Hilker et al. (Am Nat 173:72-88, 2009). The rich and complicated dynamics exhibit that the model is very sensitive to parameter perturbations, which has important implications for disease control of endangered species.
Defining universality classes for three different local bifurcations
Leonel, Edson D.
2016-10-01
The convergence to the fixed point at a bifurcation and near it is characterized via scaling formalism for three different types of local bifurcations of fixed points in differential equations, namely: (i) saddle-node; (ii) transcritical; and (iii) supercritical pitchfork. At the bifurcation, the convergence is described by a homogeneous function with three critical exponents α, β and z. A scaling law is derived hence relating the three exponents. Near the bifurcation the evolution towards the fixed point is given by an exponential function whose relaxation time is marked by a power law of the distance of the bifurcation point with an exponent δ. The four exponents α, β, z and δ can be used to defined classes of universality for the local bifurcations of fixed points in differential equations.
Codimension Two Bifurcations and Rythms in Neural Mass Models
Touboul, Jonathan
2009-01-01
Temporal lobe epilepsy is one of the most common chronic neurological disorder characterized by the occurrence of spontaneous recurrent seizures which can be observed at the level of populations through electroencephalogram (EEG) recordings. This paper summarizes some preliminary works aimed to understand from a theoretical viewpoint the occurrence of this type of seizures and the origin of the oscillatory activity in some classical cortical column models. We relate these rhythmic activities to the structure of the set of periodic orbits in the models, and therefore to their bifurcations. We will be mainly interested Jansen and Rit model, and study the codimension one, two and a codimension three bifurcations of equilibria and cycles of this model. We can therefore understand the effect of the different biological parameters of the system of the apparition of epileptiform activity and observe the emergence of alpha, delta and theta sleep waves in a certain range of parameter. We then present a very quick stud...
Femoral bifurcation disease: balloon or knife.
Bosiers, Marc; Deloose, Koen
2009-10-01
Arterial occlusive disease at the level of the femoral bifurcation mostly occurs in combination with inflow and/or outflow lesions. Surgical endarterectomy of the femoral bifurcation is a well-proven low-risk and easy surgical intervention with known durable success, while, although proven to be safe, evidence is lacking about the durability of the endovascular approach. Based on the evidence at hand, the surgical approach should be recommended for the vast majority of patients and the endovascular approach should only be indicated as the first strategy in selected cases presenting with factors that might compromise the outcome of surgery in the groin. If feasible, the hybrid approach with endarterectomy at the level of the bifurcation and endovascular repair of the inflow and outflow lesions is preferred in patients with multilevel disease.
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.
Minton, Roland; Pennings, Timothy J.
2007-01-01
When a dog (in this case, Tim Pennings' dog Elvis) is in the water and a ball is thrown downshore, it must choose to swim directly to the ball or first swim to shore. The mathematical analysis of this problem leads to the computation of bifurcation points at which the optimal strategy changes.
Bifurcation of hyperbolic planforms
Chossat, Pascal; Faugeras, Olivier
2010-01-01
Motivated by a model for the perception of textures by the visual cortex in primates, we analyse the bifurcation of periodic patterns for nonlinear equations describing the state of a system defined on the space of structure tensors, when these equations are further invariant with respect to the isometries of this space. We show that the problem reduces to a bifurcation problem in the hyperbolic plane D (Poincar\\'e disc). We make use of the concept of periodic lattice in D to further reduce the problem to one on a compact Riemann surface D/T, where T is a cocompact, torsion-free Fuchsian group. The knowledge of the symmetry group of this surface allows to carry out the machinery of equivariant bifurcation theory. Solutions which generically bifurcate are called "H-planforms", by analogy with the "planforms" introduced for pattern formation in Euclidean space. This concept is applied to the case of an octagonal periodic pattern, where we are able to classify all possible H-planforms satisfying the hypotheses o...
Local Bifurcations in DC-DC Converters
2012-01-01
Three local bifurcations in DC-DC converters are reviewed. They are period-doubling bifurcation, saddle-node bifurcation, and Neimark bifurcation. A general sampled-data model is employed to study the types of loss of stability of the nominal (periodic) solution and their connection with local bifurcations. More accurate prediction of instability and bifurcation than using the averaging approach is obtained. Examples of bifurcations associated with instabilities in DC-DC converters are given.
Bifurcation of Scramjet Unstart
Jang, Ik; Nichols, Joseph; Duraisamy, Karthik; Moin, Parviz
2011-11-01
We investigate the bifurcation structure of catastrophic unstart in scramjets. The bifurcation of quasi-one-dimensional Rayleigh flow is first analyzed, followed by a numerical investigation of a more realistic model scramjet isolator (Wagner et al., AIAA paper, 2010). We show that the quasi-one-dimensional model recovers a similar hysteresis behavior as that observed in steady Reynolds-Averaged Navier-Stokes simulations of the model scramjet isolator close to the onset of unstart. In the hysteresis zone, steady but unstable solutions are obtained by means of pseudo-arclength continuation. Automatic differentiation permits the use of fully discrete Jacobians that result in an accurate representation of functional dependencies and linearized dynamics. Furthermore, we use an Arnoldi method to extract the least stable direct and adjoint eigenfunctions spanning the system dynamics close to unstart and obtain the system response to both harmonic and stochastic forcing. This information, along with the final bifurcation structure, allows us to evaluate the effectiveness of different metrics as indicators of the onset of unstart. Supported by the PSAAP program of DOE
Bifurcations of nontwisted heteroclinic loop
Institute of Scientific and Technical Information of China (English)
田清平; 朱德明
2000-01-01
Bifurcations of nontwisted and fine heteroclinic loops are studied for higher dimensional systems. The existence and its associated existing regions are given for the 1-hom orbit and the 1-per orbit, respectively, and bifurcation surfaces of the two-fold periodic orbit are also obtained. At last, these bifurcation results are applied to the fine heteroclinic loop for the planar system, which leads to some new and interesting results.
Blowout bifurcation of chaotic saddles
Directory of Open Access Journals (Sweden)
Tomasz Kapitaniak
1999-01-01
Full Text Available Chaotic saddles are nonattracting dynamical invariant sets that can lead to a variety of physical phenomena. We describe the blowout bifurcation of chaotic saddles located in the symmetric invariant manifold of coupled systems and discuss dynamical phenomena associated with this bifurcation.
Neural Excitability and Singular Bifurcations.
De Maesschalck, Peter; Wechselberger, Martin
2015-12-01
We discuss the notion of excitability in 2D slow/fast neural models from a geometric singular perturbation theory point of view. We focus on the inherent singular nature of slow/fast neural models and define excitability via singular bifurcations. In particular, we show that type I excitability is associated with a novel singular Bogdanov-Takens/SNIC bifurcation while type II excitability is associated with a singular Andronov-Hopf bifurcation. In both cases, canards play an important role in the understanding of the unfolding of these singular bifurcation structures. We also explain the transition between the two excitability types and highlight all bifurcations involved, thus providing a complete analysis of excitability based on geometric singular perturbation theory.
Continuum Hamiltonian Hopf Bifurcation II
Hagstrom, G I
2013-01-01
Building on the development of [MOR13], bifurcation of unstable modes that emerge from continuous spectra in a class of infinite-dimensional noncanonical Hamiltonian systems is investigated. Of main interest is a bifurcation termed the continuum Hamiltonian Hopf (CHH) bifurcation, which is an infinite-dimensional analog of the usual Hamiltonian Hopf (HH) bifurcation. Necessary notions pertaining to spectra, structural stability, signature of the continuous spectra, and normal forms are described. The theory developed is applicable to a wide class of 2+1 noncanonical Hamiltonian matter models, but the specific example of the Vlasov-Poisson system linearized about homogeneous (spatially independent) equilibria is treated in detail. For this example, structural (in)stability is established in an appropriate functional analytic setting, and two kinds of bifurcations are considered, one at infinite and one at finite wavenumber. After defining and describing the notion of dynamical accessibility, Kre\\u{i}n-like the...
New trends in Brunner's relation: dielectric levels
Trouiller, Yorick; Didiergeorges, Anne; Fanget, Gilles L.; Laviron, Cyrille; Comboure, Corinne; Quere, Yves
1999-07-01
The goal of this paper is to understand the optical phenomena at dielectric levels. The purpose is also to quantify the impact of dielectric and resist thickness variations on the CD range with and without Bottom Anti Reflective COating (BARC). First we will show how all dielectric levels can be reduced to the stack metal/oxide/BARC/resist, and what are the contributions to resists and dielectric thickness range for each levels. Then a simple model will be developed to understand CD variation in this tack: by extending the Perot/Fabry model to the dielectric levels, developed by Brunner for the gate level, we can obtain a simple relation between the CD variation and all parameters. Experimentally CD variation for Damascene line level on 0.18micrometers technology has been measured depending on oxide thickness and resist thickness and can confirm this model. UV5 resist, AR2 BARC from Shipley and Top ARC from JSR have been used for these experiments. The main conclusions are: (1) Depending on your dielectric deposition and CMP processes, if resist thickness is controlled, a standard BARC process used for the gate is adapted to remove oxide thickness variation influence providing the optimized resist thickness is used. (2) If both resist thickness and dielectric thickness are uncontrolled, a more absorbent BARC is required.
Volkenstein, M V; Livshits, M A
1989-01-01
The interrelations of physics and biology are discussed. It is shown that Darwin can be considered as one of the founders of the important field of contemporary physics called physics of dissipative structures or synergetics. The theories of gradual and punctual evolution are presented. The contradiction between these theories can be solved on the basis of molecular theory of evolution and on the basis of the phenomenological physical treatment. The general physical properties of living systems, considered as open systems being far from equilibrium, are listed and simple non-linear mathematical models describing gradual and punctual speciation are suggested. The usual pictures which present these two kinds of speciation can possess physico-mathematical sense. Punctuated speciation means bifurcation, a kind of non-equilibrium phase transition.
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...
Ergodicity-breaking bifurcations and tunneling in hyperbolic transport models
Giona, M.; Brasiello, A.; Crescitelli, S.
2015-11-01
One of the main differences between parabolic transport, associated with Langevin equations driven by Wiener processes, and hyperbolic models related to generalized Kac equations driven by Poisson processes, is the occurrence in the latter of multiple stable invariant densities (Frobenius multiplicity) in certain regions of the parameter space. This phenomenon is associated with the occurrence in linear hyperbolic balance equations of a typical bifurcation, referred to as the ergodicity-breaking bifurcation, the properties of which are thoroughly analyzed.
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 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...
Cross-talk induces bifurcations in nonlinear models of synaptic plasticity.
Elliott, Terry
2012-02-01
Linear models of synaptic plasticity provide a useful starting-point for examining the dynamics of neuronal development and learning, but their inherent problems are well known. Models of synaptic plasticity that embrace the demands of biological realism are therefore typically nonlinear. Viewed from a more abstract perspective, nonlinear models of synaptic plasticity are a subset of nonlinear dynamical systems. As such, they may therefore exhibit bifurcations under the variation of control parameters, including noise and errors in synaptic updates. One source of noise or error is the cross-talk that occurs during otherwise Hebbian plasticity. Under cross-talk, stimulation of a set of synapses can induce or modify plasticity in adjacent, unstimulated synapses. Here, we analyze two nonlinear models of developmental synaptic plasticity and a model of independent component analysis in the presence of a simple model of cross-talk. We show that cross-talk does indeed induce bifurcations in these models, entirely destroying their ability to acquire either developmentally or learning-related patterns of fixed points. Importantly, the critical level of cross-talk required to induce bifurcations in these models is very sensitive to the statistics of the afferents' activities and the number of afferents synapsing on a postsynaptic cell. In particular, the critical level can be made arbitrarily small. Because bifurcations are inevitable in nonlinear models, our results likely apply to many nonlinear models of synaptic plasticity, although the precise details vary by model. Hence, many nonlinear models of synaptic plasticity are potentially fatally compromised by the toxic influence of cross-talk and other sources of noise and errors more generally. We conclude by arguing that biologically realistic models of synaptic plasticity must be robust against noise-induced bifurcations and that biological systems may have evolved strategies to circumvent their possible dangers.
Bifurcation Adds Flavor to Basketball
Min, Byeong June
2016-01-01
We report an emergence of bifurcation in basketball, a single-particle system governed by Newtonian mechanics. When shooting the basketball, the obvious control parameters are the launch speed and the launch angle. We propose to use the three-dimensional velocity phase-space volume associated with the given launch parameters to quantify the difficulty of the shooting. The optimal launch angle that maximizes the associated phase-space volume undergoes a bifurcation as the launch speed is increased, if the shooter is farther than a critical distance away from the hoop. Thus, the bifurcation makes it very important to control the launch speed accurately. If the air resistance is removed, the bifurcation disappears and the phase-space volume distribution becomes dispersionless and shrinks in magnitude.
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).
Qiu, B.; Chen, S.
2010-12-01
Satellite altimeter sea surface height (SSH) data from the past 17 years are used to investigate the interannual-to-decadal changes in the bifurcation of the North Equatorial Current (NEC) along the Philippine coast. The NEC bifurcation latitude migrated quasi-decadally between 10N and 15N with northerly bifurcations observed in late 1992, 1997-98 and 2003-04, and southerly bifurcations in 1999-2000 and 2008-09. The observed NEC bifurcation latitude can be approximated well by the SSH anomalies in the 12-14N and 127-130E box east of the mean NEC bifurcation point. Using a 1.5-layer reduced-gravity model forced by the ECMWF reanalysis wind stress data, we find that the SSH anomalies in this box can be simulated favorably to serve as a proxy for the observed NEC bifurcation. With the availability of the long-term reanalysis wind stress data, this allows us to lengthen the NEC bifurcation time series back to 1962. Although quasi-decadal variability was prominent in the last two decades, the NEC bifurcation was dominated by changes with a 3~5-yr period during the 1980s and had low variance prior to the 1970s. These inter-decadal modulations in the characteristics of the NEC bifurcation reflect similar inter-decadal modulations in the wind forcing field over the western tropical North Pacific Ocean. Although the NEC bifurcation on the interannual and longer timescales is in general related to the Nino-3.4 index with a positive (negative) index corresponding to a northerly (southerly) bifurcation, the exact location of bifurcation is determined by wind forcing in the 12-14N band that contains variability not fully representable by the Nino-3.4 index.
Kolokolov, Yury; Monovskaya, Anna
The paper completes the cycle of the research devoted to the development of the experimental bifurcation analysis (not computer simulations) in order to answer the following questions: whether qualitative changes occur in the dynamics of local climate systems in a centennial timescale?; how to analyze such qualitative changes with daily resolution for local and regional space-scales?; how to establish one-to-one daily correspondence between the dynamics evolution and economic consequences for productions? To answer the questions, the unconventional conceptual model to describe the local climate dynamics was proposed and verified in the previous parts. That model (HDS-model) originates from the hysteresis regulator with double synchronization and has a variable structure due to competition between the amplitude quantization and the time quantization. The main advantage of the HDS-model is connected with the possibility to describe “internally” (on the basis of the self-regulation) the specific causal effects observed in the dynamics of local climate systems instead of “external” description of three states of the hysteresis behavior of climate systems (upper, lower and transient states). As a result, the evolution of the local climate dynamics is based on the bifurcation diagrams built by processing the data of meteorological observations, where the strange effects of the essential interannual daily variability of annual temperature variation are taken into account and explained. It opens the novel possibilities to analyze the local climate dynamics taking into account the observed resultant of all internal and external influences on each local climate system. In particular, the paper presents the viewpoint on how to estimate economic damages caused by climate-related hazards through the bifurcation analysis. That viewpoint includes the following ideas: practically each local climate system is characterized by its own time pattern of the natural qualitative
Coronary bifurcation stenting: insights from in vitro and virtual bench testing.
Mortier, Peter; De Beule, Matthieu; Dubini, Gabriele; Hikichi, Yutaka; Murasato, Yoshinobu; Ormiston, John A
2010-12-01
The various techniques and devices that have been proposed for the treatment of coronary bifurcation lesions have differing levels of complexity and each has one or more limitations. Two highly complementary ex vivo methods are available to study the treatment of bifurcation lesions: in vitro and virtual bench testing. Both methods can be used to develop, evaluate and optimise bifurcation stenting techniques and dedicated devices. The basics, the evolution, the advantages and limitations of both methods are discussed in this paper. Subsequently, a literature overview of the main insights gained from ex vivo testing in the field of bifurcation stenting is given.
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.
Regularizations of two-fold bifurcations in planar piecewise smooth systems using blowup
DEFF Research Database (Denmark)
Kristiansen, Kristian Uldall; Hogan, S. J.
2015-01-01
rigorously how singular canards can persist and how the bifurcation of pseudo-equilibria is related to bifurcations of equilibria in the regularized system. We also show that PWS limit cycles are connected to Hopf bifurcations of the regularization. In addition, we show how regularization can create another...... type of limit cycle that does not appear to be present in the original PWS system. For both types of limit cycle, we show that the criticality of the Hopf bifurcation that gives rise to periodic orbits is strongly dependent on the precise form of the regularization. Finally, we analyse the limit cycles...
Ng, Yan Cheng; Namgung, Bumseok; Tien, Sim Leng; Leo, Hwa Liang; Kim, Sangho
2016-08-01
Heterogeneous distribution of red blood cells (RBCs) in downstream vessels of arteriolar bifurcations can be promoted by an asymmetric formation of cell-free layer (CFL) in upstream vessels. Consequently, the CFL widths in subsequent downstream vessels become an important determinant for tissue oxygenation (O2) and vascular tone change by varying nitric oxide (NO) availability. To extend our previous understanding on the formation of CFL in arteriolar bifurcations, this study investigated the formation of CFL widths from 2 to 6 vessel-diameter (2D-6D) downstream of arteriolar bifurcations in the rat cremaster muscle (D = 51.5 ± 1.3 μm). As the CFL widths are highly influenced by RBC aggregation, the degree of aggregation was adjusted to simulate levels seen during physiological and pathological states. Our in vivo experimental results showed that the asymmetry of CFL widths persists along downstream vessels up to 6D from the bifurcating point. Moreover, elevated levels of RBC aggregation appeared to retard the recovery of CFL width symmetry. The required length of complete symmetry recovery was estimated to be greater than 11D under reduced flow conditions, which is relatively longer than interbifurcation distances of arterioles for vessel diameter of ∼50 μm. In addition, our numerical prediction showed that the persistent asymmetry of CFL widths could potentially result in a heterogeneous vasoactivity over the entire arteriolar network in such abnormal flow conditions.
Controlling hopf bifurcations: Discrete-time systems
Directory of Open Access Journals (Sweden)
Guanrong Chen
2000-01-01
Full Text Available Bifurcation control has attracted increasing attention in recent years. A simple and unified state-feedback methodology is developed in this paper for Hopf bifurcation control for discrete-time systems. The control task can be either shifting an existing Hopf bifurcation or creating a new Hopf bifurcation. Some computer simulations are included to illustrate the methodology and to verify the theoretical results.
Thermodynamic geometry and critical aspects of bifurcations.
Mihara, A
2016-07-01
This work presents an exploratory study of the critical aspects of some well-known bifurcations in the context of thermodynamic geometry. For each bifurcation its normal form is regarded as a geodesic equation of some model analogous to a thermodynamic system. From this hypothesis it is possible to calculate the corresponding metric and curvature and analyze the critical behavior of the bifurcation.
Solution and transcritical bifurcation of Burgers equation
Institute of Scientific and Technical Information of China (English)
Tang Jia-Shi; Zhao Ming-Hua; Han Feng; Zhang Liang
2011-01-01
Burgers equation is reduced into a first-order ordinary differential equation by using travelling wave transformation and it has typical bifurcation characteristics. We can obtain many exact solutions of the Burgers equation, discuss its transcritical bifurcation and control dynamical behaviours by extending the stable region. The transcritical bifurcation exists in the (2 + 1)-dimensional Burgers equation.
Morphodynamics of a Bifurcation on the Wax Lake Delta, LA
Slingerland, R. L.; Best, J.; Parsons, D. R.; Edmonds, D. A.
2009-12-01
To better predict the dynamical behavior of fine-grained deltaic distributary networks, we collected integrated morphological, flow, and sediment transport data from a third-order bifurcation (BIF) on the Wax Lake Delta, LA, during July 15-20, 2009. Theory and numerical modeling predicts that over a range of channel aspect ratios, friction factors, and Shields numbers, three functions exist that relate the discharge ratio of the bifurcate arms at equilibrium conditions to the Shields number. One function predicts symmetrical configurations, while the other two predict asymmetrical discharges. To test the theoretical predictions we employed high-resolution multibeam echo sounding (MBES) and acoustic Doppler velocity profiling to map the bifurcation. The arms of the BIF are asymmetric in planform, depth (west arm/east arm = 4.2/3.1 m), discharge (335/140 cumecs), and bedload transport, with two-thirds of the dunes revealed on the MBES survey entering the western bifurcate channel. The bed consists of fine sand (D50 = 0.125 mm) sculpted into dunes, which in these 4 m water depths average 7 meters long and 0.52 m high and provide a form friction factor of about 0.028. Measured cross-sectional mean velocity of the main channel during the survey was ~ 0.23 m/s, which for sand-bed systems yields a low Shields number of θ = 0.093. For this θ theory predicts a stable equilibrium bifurcate discharge ratio of 4.5, which compares unfavorably with the observed value of 2.4. As there is no indication from 30 years of aerial photography that this BIF is morphologically unstable, either the bifurcation is maintained by the higher discharges of the spring flood or the theoretical envelope of stable bifurcation configurations requires re-evaluation.
Bifurcations of optimal vector fields
Kiseleva, T.; Wagener, F.
2015-01-01
We study the structure of the solution set of a class of infinite-horizon dynamic programming problems with one-dimensional state spaces, as well as their bifurcations, as problem parameters are varied. The solutions are represented as the integral curves of a multivalued optimal vector field on sta
NEW BIFURCATION PATTERNS IN ELEMENTARY BIFURCATION PROBLEMS WITH SINGLE-SIDE CONSTRAINT
Institute of Scientific and Technical Information of China (English)
吴志强; 陈予恕
2001-01-01
Bifurcations with constraints are open problems appeared in research on periodic bifurcations of nonlinear dynamical systems, but the present singularity theory doesn't contain any analytical methods and results about it. As the complement to singularity theory and the first step to study on constrained bifurcations, here are given the transition sets and persistent perturbed bifurcation diagrams of 10 elementary bifurcation of codimension no more than three.
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.
ROBUST CONTROL OF PERIODIC BIFURCATION SOLUTIONS
Institute of Scientific and Technical Information of China (English)
梁建术; 陈予恕; 梁以德
2004-01-01
The topological bifurcation diagrams and the coefficients of bifurcation equation were obtained by C-L method.According to obtained bifurcation diagrams and combining control theory,the method of robust control of periodic bifurcation was presented,which differs from generic methods of bifurcation control.It can make the existing motion pattern into the goal motion pattern.Because the method does not make strict requirement about parametric values of the controller,it is convenient to design and make it.Numerical simulations verify validity of the method.
Insight into Phenomena of Symmetry Breaking Bifurcation
Institute of Scientific and Technical Information of China (English)
FANG Tong; ZHANG Ying
2008-01-01
@@ We show that symmetry-breaking (SB) bifurcation is just a transition of different forms of symmetry, while still preserving system's symmetry. SB bifurcation always associates with a periodic saddle-node bifurcation, identifiable by a zero maximum of the top Lyapunov exponent of the system. In addition, we show a significant phase portrait of a newly born periodic saddle and its stable and unstable invariant manifolds, together with their neighbouring flow pattern of Poincaré mapping points just after the periodic saddle-node bifurcation, thus gaining an insight into the mechanism of SB bifurcation.
Escape statistics for parameter sweeps through bifurcations.
Miller, Nicholas J; Shaw, Steven W
2012-04-01
We consider the dynamics of systems undergoing parameter sweeps through bifurcation points in the presence of noise. Of interest here are local codimension-one bifurcations that result in large excursions away from an operating point that is transitioning from stable to unstable during the sweep, since information about these "escape events" can be used for system identification, sensing, and other applications. The analysis is based on stochastic normal forms for the dynamic saddle-node and subcritical pitchfork bifurcations with a time-varying bifurcation parameter and additive noise. The results include formulation and numerical solution for the distribution of escape events in the general case and analytical approximations for delayed bifurcations for which escape occurs well beyond the corresponding quasistatic bifurcation points. These bifurcations result in amplitude jumps encountered during parameter sweeps and are particularly relevant to nano- and microelectromechanical systems, for which noise can play a significant role.
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.
On noise induced Poincaré-Andronov-Hopf bifurcation.
Samanta, Himadri S; Bhattacharjee, Jayanta K; Bhattacharyay, Arijit; Chakraborty, Sagar
2014-12-01
It has been numerically seen that noise introduces stable well-defined oscillatory state in a system with unstable limit cycles resulting from subcritical Poincaré-Andronov-Hopf (or simply Hopf) bifurcation. This phenomenon is analogous to the well known stochastic resonance in the sense that it effectively converts noise into useful energy. Herein, we clearly explain how noise induced imperfection in the bifurcation is a generic reason for such a phenomenon to occur and provide explicit analytical calculations in order to explain the typical square-root dependence of the oscillations' amplitude on the noise level below a certain threshold value. Also, we argue that the noise can bring forth oscillations in average sense even in the absence of a limit cycle. Thus, we bring forward the inherent general mechanism of the noise induced Hopf bifurcation naturally realisable across disciplines.
On noise induced Poincaré–Andronov–Hopf bifurcation
Energy Technology Data Exchange (ETDEWEB)
Samanta, Himadri S., E-mail: hss@umd.edu [Biophysics Program, Institute For Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States); Bhattacharjee, Jayanta K., E-mail: director@hri.res.in [Harish-Chandra Research Institute, Allahabad (India); Bhattacharyay, Arijit, E-mail: a.bhattacharyay@iiserpune.ac.in [Indian Institute of Science Education and Research, Pune (India); Chakraborty, Sagar, E-mail: sagarc@iitk.ac.in [Department of Physics, Indian Institute of Technology Kanpur, Uttar Pradesh 208016 (India); Mechanics and Applied Mathematics Group, Indian Institute of Technology Kanpur, Uttar Pradesh 208016 (India)
2014-12-01
It has been numerically seen that noise introduces stable well-defined oscillatory state in a system with unstable limit cycles resulting from subcritical Poincaré–Andronov–Hopf (or simply Hopf) bifurcation. This phenomenon is analogous to the well known stochastic resonance in the sense that it effectively converts noise into useful energy. Herein, we clearly explain how noise induced imperfection in the bifurcation is a generic reason for such a phenomenon to occur and provide explicit analytical calculations in order to explain the typical square-root dependence of the oscillations' amplitude on the noise level below a certain threshold value. Also, we argue that the noise can bring forth oscillations in average sense even in the absence of a limit cycle. Thus, we bring forward the inherent general mechanism of the noise induced Hopf bifurcation naturally realisable across disciplines.
The Branching Bifurcation of Adaptive Dynamics
Della Rossa, Fabio; Dercole, Fabio; Landi, Pietro
2015-06-01
We unfold the bifurcation involving the loss of evolutionary stability of an equilibrium of the canonical equation of Adaptive Dynamics (AD). The equation deterministically describes the expected long-term evolution of inheritable traits — phenotypes or strategies — of coevolving populations, in the limit of rare and small mutations. In the vicinity of a stable equilibrium of the AD canonical equation, a mutant type can invade and coexist with the present — resident — types, whereas the fittest always win far from equilibrium. After coexistence, residents and mutants effectively diversify, according to the enlarged canonical equation, only if natural selection favors outer rather than intermediate traits — the equilibrium being evolutionarily unstable, rather than stable. Though the conditions for evolutionary branching — the joint effect of resident-mutant coexistence and evolutionary instability — have been known for long, the unfolding of the bifurcation has remained a missing tile of AD, the reason being related to the nonsmoothness of the mutant invasion fitness after branching. In this paper, we develop a methodology that allows the approximation of the invasion fitness after branching in terms of the expansion of the (smooth) fitness before branching. We then derive a canonical model for the branching bifurcation and perform its unfolding around the loss of evolutionary stability. We cast our analysis in the simplest (but classical) setting of asexual, unstructured populations living in an isolated, homogeneous, and constant abiotic environment; individual traits are one-dimensional; intra- as well as inter-specific ecological interactions are described in the vicinity of a stationary regime.
Transport Bifurcation Induced by Sheared Toroidal Flow in Tokamak Plasmas
Highcock, E G; Parra, F I; Schekochihin, A A; Roach, C M; Cowley, S C
2011-01-01
First-principles numerical simulations are used to describe a transport bifurcation in a differentially rotating tokamak plasma. Such a bifurcation is more probable in a region of zero magnetic shear, where the component of the sheared toroidal flow that is perpendicular to the magnetic field has the strongest suppressing effect on the turbulence, than one of finite magnetic shear. Where the magnetic shear is zero, there are no growing linear eigenmodes at any finite value of flow shear. However, subcritical turbulence can be sustained, owing to the transient growth of modes driven by the ion temperature gradient (ITG) and the parallel velocity gradient (PVG). Nonetheless, in a parameter space containing a wide range of temperature gradients and velocity shears, there is a sizeable window where all turbulence is suppressed. Combined with the relatively low transport of momentum by collisional (neoclassical) mechanisms, this produces the conditions for a bifurcation from low to high temperature and velocity gr...
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.
Level of Work Related Stress among Teachers in Elementary Schools
Directory of Open Access Journals (Sweden)
Teuta Agai–Demjaha
2015-07-01
CONCLUSION: Our findings confirm that the majority of interviewed teachers perceived their work-related stress as high or very high. In terms of the relationship between the level of teachers’ stress and certain demographic and job characteristics, according to our results, the level of work-related stress has shown significantly high relation to gender, age, levels of grades taught as well as working experience, and significant relation to the level of education.
Bifurcation analysis of a forest-grassland ecosystem
Russo, Lucia; Spiliotis, Konstantinos G.
2016-06-01
The nonlinear analysis of a forest-grassland ecosystem is performed as the main system parameters are changed. The model consists of a couple of nonlinear ordinary differential equations which include dynamically the human perceptions of forest/grassland value. The system displays multiple steady states corresponding to different forest densities as well as periodic regimes characterized by oscillations in time. We performed the bifurcation analysis of the system as the parameter relative to the human opinions influence is changed. We found that the main mechanisms which regulate the transitions occurring between different states or the appearance of new steady and dynamic regimes are transcritical, saddle/node and Hopf bifurcations.
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
AIMS: Randomized trials of coronary bifurcation stenting have shown better outcomes from a simple (provisional) strategy rather than a complex (planned two-stent) strategy in terms of short-term efficacy and safety. Here, we report the 5-year all-cause mortality based on pooled patient-level data...
Bifurcations analysis of oscillating hypercycles.
Guillamon, Antoni; Fontich, Ernest; Sardanyés, Josep
2015-12-21
We investigate the dynamics and transitions to extinction of hypercycles governed by periodic orbits. For a large enough number of hypercycle species (n>4) the existence of a stable periodic orbit has been previously described, showing an apparent coincidence of the vanishing of the periodic orbit with the value of the replication quality factor Q where two unstable (non-zero) equilibrium points collide (named QSS). It has also been reported that, for values below QSS, the system goes to extinction. In this paper, we use a suitable Poincaré map associated to the hypercycle system to analyze the dynamics in the bistability regime, where both oscillatory dynamics and extinction are possible. The stable periodic orbit is identified, together with an unstable periodic orbit. In particular, we are able to unveil the vanishing mechanism of the oscillatory dynamics: a saddle-node bifurcation of periodic orbits as the replication quality factor, Q, undergoes a critical fidelity threshold, QPO. The identified bifurcation involves the asymptotic extinction of all hypercycle members, since the attractor placed at the origin becomes globally stable for values Qbifurcation, these extinction dynamics display a periodic remnant that provides the system with an oscillating delayed transition. Surprisingly, we found that the value of QPO is slightly higher than QSS, thus identifying a gap in the parameter space where the oscillatory dynamics has vanished while the unstable equilibrium points are still present. We also identified a degenerate bifurcation of the unstable periodic orbits for Q=1.
Inversion of hematocrit partition at microfluidic bifurcations.
Shen, Zaiyi; Coupier, Gwennou; Kaoui, Badr; Polack, Benoît; Harting, Jens; Misbah, Chaouqi; Podgorski, Thomas
2016-05-01
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 (ϕ0) partition depends strongly on RBC deformability, as long as ϕ0<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 ϕ0, 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 properties. These parameters can lead to unexpected behaviors with consequences on the microcirculatory function and oxygen delivery in healthy and pathological conditions.
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...
Impact of local flow haemodynamics on atherosclerosis in coronary artery bifurcations.
Antoniadis, Antonios P; Giannopoulos, Andreas A; Wentzel, Jolanda J; Joner, Michael; Giannoglou, George D; Virmani, Renu; Chatzizisis, Yiannis S
2015-01-01
Coronary artery bifurcations are susceptible to atherosclerosis as a result of the unique local flow patterns and the subsequent endothelial shear stress (ESS) environment that are conducive to the development of plaques. Along the lateral walls of the main vessel and side branches, a distinct flow pattern is observed with local low and oscillatory ESS, while high ESS develops at the flow divider (carina). Histopathologic studies have shown that the distribution of plaque at bifurcation regions is related to the local ESS patterns. The local ESS profile also influences the outcome of percutaneous coronary interventions in bifurcation lesions. A variety of invasive and non-invasive imaging modalities have enabled 3D reconstruction of coronary bifurcations and thereby detailed local ESS assessment by computational fluid dynamics. Highly effective strategies for treatment and ultimately prevention of atherosclerosis in coronary bifurcations are anticipated with the use of advanced imaging and computational fluid dynamic techniques.
Xiao, Min; Zheng, Wei Xing; Jiang, Guoping; Cao, Jinde
2015-12-01
In this paper, a fractional-order recurrent neural network is proposed and several topics related to the dynamics of such a network are investigated, such as the stability, Hopf bifurcations, and undamped oscillations. The stability domain of the trivial steady state is completely characterized with respect to network parameters and orders of the commensurate-order neural network. Based on the stability analysis, the critical values of the fractional order are identified, where Hopf bifurcations occur and a family of oscillations bifurcate from the trivial steady state. Then, the parametric range of undamped oscillations is also estimated and the frequency and amplitude of oscillations are determined analytically and numerically for such commensurate-order networks. Meanwhile, it is shown that the incommensurate-order neural network can also exhibit a Hopf bifurcation as the network parameter passes through a critical value which can be determined exactly. The frequency and amplitude of bifurcated oscillations are determined.
Backward bifurcations, turning points and rich dynamics in simple disease models.
Zhang, Wenjing; Wahl, Lindi M; Yu, Pei
2016-10-01
In this paper, dynamical systems theory and bifurcation theory are applied to investigate the rich dynamical behaviours observed in three simple disease models. The 2- and 3-dimensional models we investigate have arisen in previous investigations of epidemiology, in-host disease, and autoimmunity. These closely related models display interesting dynamical behaviors including bistability, recurrence, and regular oscillations, each of which has possible clinical or public health implications. In this contribution we elucidate the key role of backward bifurcations in the parameter regimes leading to the behaviors of interest. We demonstrate that backward bifurcations with varied positions of turning points facilitate the appearance of Hopf bifurcations, and the varied dynamical behaviors are then determined by the properties of the Hopf bifurcation(s), including their location and direction. A Maple program developed earlier is implemented to determine the stability of limit cycles bifurcating from the Hopf bifurcation. Numerical simulations are presented to illustrate phenomena of interest such as bistability, recurrence and oscillation. We also discuss the physical motivations for the models and the clinical implications of the resulting dynamics.
Hopf and steady state bifurcation analysis in a ratio-dependent predator-prey model
Zhang, Lai; Liu, Jia; Banerjee, Malay
2017-03-01
In this paper, we perform spatiotemporal bifurcation analysis in a ratio-dependent predator-prey model and derive explicit conditions for the existence of non-constant steady states that emerge through steady state bifurcation from related constant steady states. These explicit conditions are numerically verified in details and further compared to those conditions ensuring Turing instability. We find that (1) Turing domain is identical to the parametric domain where there exists only steady state bifurcation, which implies that Turing patterns are stable non-constant steady states, but the opposite is not necessarily true; (2) In non-Turing domain, steady state bifurcation and Hopf bifurcation act in concert to determine the emergent spatial patterns, that is, non-constant steady state emerges through steady state bifurcation but it may be unstable if the destabilising effect of Hopf bifurcation counteracts the stabilising effect of diffusion, leading to non-stationary spatial patterns; (3) Coupling diffusion into an ODE model can significantly enrich population dynamics by inducing alternative non-constant steady states (four different states are observed, two stable and two unstable), in particular when diffusion interacts with different types of bifurcation; (4) Diffusion can promote species coexistence by saving species which otherwise goes to extinction in the absence of diffusion.
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.
STOCHASTIC HOPF BIFURCATION IN QUASI-INTEGRABLE-HAMILTONIAN SYSTEMS
Institute of Scientific and Technical Information of China (English)
GAN Chunbiao
2004-01-01
A new procedure is developed to study the stochastic Hopf bifurcation in quasiintegrable-Hamiltonian systems under the Gaussian white noise excitation. Firstly, the singular boundaries of the first-class and their asymptotic stable conditions in probability are given for the averaged Ito differential equations about all the sub-system's energy levels with respect to the stochastic averaging method. Secondly, the stochastic Hopf bifurcation for the coupled sub-systems are discussed by defining a suitable bounded torus region in the space of the energy levels and employing the theory of the torus region when the singular boundaries turn into the unstable ones. Lastly, a quasi-integrableHamiltonian system with two degrees of freedom is studied in detail to illustrate the above procedure.Moreover, simulations by the Monte-Carlo method are performed for the illustrative example to verify the proposed procedure. It is shown that the attenuation motions and the stochastic Hopf bifurcation of two oscillators and the stochastic Hopf bifurcation of a single oscillator may occur in the system for some system's parameters. Therefore, one can see that the numerical results are consistent with the theoretical predictions.
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.
Energy Technology Data Exchange (ETDEWEB)
Fujimura, Kaoru [ed.] [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
1995-01-01
This is the abstracts of the Mini-Symposium on Stability and Bifurcation in Fluid Motions held on September 9-10, 1994 at the Tokai Establishment of JAERI and the Tokai Kaikan. Sixteen talks were given on various important subjects related with stability and bifurcation phenomena in fluids. All of them are theoretical and numerical analyses involving linear stability analysis, weakly nonlinear analysis, bifurcation analysis, and direct computation of nonlinearly equilibrium solutions. (author).
A theory of biological relativity: no privileged level of causation.
Noble, Denis
2012-02-06
Must higher level biological processes always be derivable from lower level data and mechanisms, as assumed by the idea that an organism is completely defined by its genome? Or are higher level properties necessarily also causes of lower level behaviour, involving actions and interactions both ways? This article uses modelling of the heart, and its experimental basis, to show that downward causation is necessary and that this form of causation can be represented as the influences of initial and boundary conditions on the solutions of the differential equations used to represent the lower level processes. These insights are then generalized. A priori, there is no privileged level of causation. The relations between this form of 'biological relativity' and forms of relativity in physics are discussed. Biological relativity can be seen as an extension of the relativity principle by avoiding the assumption that there is a privileged scale at which biological functions are determined.
Bifurcation of Pacific North Equatorial Current at the surface
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The grid altimetry data between 1993 and 2006 near the Philippines were analyzed by the method of Empirical Orthogonal Function (EOF) to study the variation of bifurcation of the North Equatorial Current at the surface of the Pacific. The relatively short-term signals with periods of about 6 months, 4 months, 3 months and 2 months are found besides seasonal and interannual variations mentioned in previous studies. Local wind stress curl plays an important role in controlling variation of bifurcation latitude except in the interannual timescale. The bifurcation latitude is about 13.3°N in annual mean state and it lies at the northernmost position (14.0°N) in January, at the southernmost position (12.5°N) in July. The amplitude of variation of bifurcation latitude in a year is 1.5°, which can mainly be explained as the contributions of the signals with periods of about 1 year (1.2°) and 0.5 year (0.3°).
Local and Global Bifurcations With Nonhyperbolic Equilibria
Institute of Scientific and Technical Information of China (English)
孙建华; 罗定军
1994-01-01
The normal forms of coupling functions governing local and global bifurcations are studied for a generic (d+1) -parameter family of three-dimensional systems with a heteroclinic orbit connecting a hyperbolic saddle and a nonhyperbolic equilibrium occurring in the saddle-node,transcritical and pitchfork bifurcations,respectively.Singularity theory and a version of Melnikov function are used in this paper.
Perturbed bifurcations in the BCS gap equation
DEFF Research Database (Denmark)
Spathis, P. N.; Sørensen, Mads Peter; Lazarides, Nickos
1992-01-01
. The transitions from d- or s- to mixed s- and d-wave solutions result from pitchfork bifurcations. In the case of slightly different pairing strength in the x and y directions, perturbed pitchfork bifurcations emerge, leading to a dramatic change in the physical properties of the superconducting state....
BIFURCATION IN PRESCRIBED MEAN CURVATURE PROBLEM
Institute of Scientific and Technical Information of China (English)
马力
2002-01-01
This paper discusses the existence problem in the study of some partial differential equations. The author gets some bifurcation on the prescribed mean curvature problem on the unit ball, the scalar curvature problem on the n-sphere, and some field equations. The author gives some natural conditions such that the standard bifurcation or Thom-Mather theory can be used.
School Management Related Knowledge Levels of Primary School Teachers
Ugurlu, Celal Teyyar
2013-01-01
The knowledge levels of the teachers affect the qualifications of operations and transactions in schools. School management related knowledge of the teachers is an essential tool to reach the targets of the school. The objective of this study was to determine the school management related knowledge levels of the teachers. Qualitative and…
Inter-level relations in computer science, biology, and psychology
Boogerd, Fred; Bruggeman, Frank; Jonker, Catholijn; Looren de Jong, Huib; Tamminga, Allard; Treur, Jan; Westerhoff, Hans; Wijngaards, Wouter
2002-01-01
Investigations into inter-level relations in computer science, biology and psychology call for an *empirical* turn in the philosophy of mind. Rather than concentrate on *a priori* discussions of inter-level relations between “completed” sciences, a case is made for the actual study of the way inter-
Crisis bifurcations in plane Poiseuille flow.
Zammert, Stefan; Eckhardt, Bruno
2015-04-01
Many shear flows follow a route to turbulence that has striking similarities to bifurcation scenarios in low-dimensional dynamical systems. Among the bifurcations that appear, crisis bifurcations are important because they cause global transitions between open and closed attractors, or indicate drastic increases in the range of the state space that is covered by the dynamics. We here study exterior and interior crisis bifurcations in direct numerical simulations of transitional plane Poiseuille flow in a mirror-symmetric subspace. We trace the state space dynamics from the appearance of the first three-dimensional exact coherent structures to the transition from an attractor to a chaotic saddle in an exterior crisis. For intermediate Reynolds numbers, the attractor undergoes several interior crises, in which new states appear and intermittent behavior can be observed. The bifurcations contribute to increasing the complexity of the dynamics and to a more dense coverage of state space.
Twisted and Nontwisted Bifurcations Induced by Diffusion
Lin, X B
1996-01-01
We discuss a diffusively perturbed predator-prey system. Freedman and Wolkowicz showed that the corresponding ODE can have a periodic solution that bifurcates from a homoclinic loop. When the diffusion coefficients are large, this solution represents a stable, spatially homogeneous time-periodic solution of the PDE. We show that when the diffusion coefficients become small, the spatially homogeneous periodic solution becomes unstable and bifurcates into spatially nonhomogeneous periodic solutions. The nature of the bifurcation is determined by the twistedness of an equilibrium/homoclinic bifurcation that occurs as the diffusion coefficients decrease. In the nontwisted case two spatially nonhomogeneous simple periodic solutions of equal period are generated, while in the twisted case a unique spatially nonhomogeneous double periodic solution is generated through period-doubling. Key Words: Reaction-diffusion equations; predator-prey systems; homoclinic bifurcations; periodic solutions.
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.
Transport Bifurcation in Plasma Interchange Turbulence
Li, Bo
2016-10-01
Transport bifurcation and mean shear flow generation in plasma interchange turbulence are explored with self-consistent two-fluid simulations in a flux-driven system with both closed and open field line regions. The nonlinear evolution of interchange modes shows the presence of two confinement regimes characterized by the low and high mean flow shear. By increasing the input heat flux above a certain threshold, large-amplitude oscillations in the turbulent and mean flow energy are induced. Both clockwise and counter-clockwise types of oscillations are found before the transition to the second regime. The fluctuation energy is decisively transferred to the mean flows by large-amplitude Reynolds power as turbulent intensity increases. Consequently, a transition to the second regime occurs, in which strong mean shear flows are generated in the plasma edge. The peak of the spectrum shifts to higher wavenumbers as the large-scale turbulent eddies are suppressed by the mean shear flow. The transition back to the first regime is then triggered by decreasing the input heat flux to a level much lower than the threshold for the forward transition, showing strong hysteresis. During the back transition, the mean flow decreases as the energy transfer process is reversed. This transport bifurcation, based on a field-line-averaged 2D model, has also been reproduced in our recent 3D simulations of resistive interchange turbulence, in which the ion and electron temperatures are separated and the parallel current is involved. Supported by the MOST of China Grant No. 2013GB112006, US DOE Contract No. DE-FC02-08ER54966, US DOE by LLNL under Contract DE-AC52-07NA2734.
Bifurcation structure of the C-type period-doubling transition
DEFF Research Database (Denmark)
Laugesen, Jakob Lund; Mosekilde, Erik; Zhusubaliyev, Zhanybai T.
2012-01-01
(Arneodo et al. (1983) [15]). Using the Rössler system as an example, we present a detailed analysis of the bifurcation structure associated with the forcing of a three-dimensional period-doubling system. We explain how this structure is related to the recently discovered phenomenon of multi-layered tori...... and discuss different bifurcation scenarios that transform a resonance torus into a period-doubled ergodic torus. Similar bifurcation phenomena have recently been observed in a biologically relevant model of kidney blood flow regulation in response to fluctuations in arterial pressure....
Bifurcations of a large scale circulation in a quasi-bidimensional turbulent flow
Michel, Guillaume; Pétrélis, François; Fauve, Stephan
2016-01-01
We report the experimental study of the bifurcations of a large-scale circulation that is formed over a turbulent flow generated by a spatially periodic forcing. After shortly describing how the flow becomes turbulent through a sequence of symmetry breaking bifurcations, we focus our study on the transitions that occur within the turbulent regime. They are related to changes in the shape of the probability density function (PDF) of the amplitude of the large scale flow. We discuss the nature of these bifurcations and how to model the shape of the PDF.
Guo, Junru; Liu, Yulong; Song, Jun; Bao, Xianwen; Li, Yan; Chen, Shaoyang; Yang, Jinkun
2015-12-01
The equatorial Current in the North Pacific (NEC) is an upper layer westward ocean current, which flows to the west boundary of the ocean, east of the Philippines, and bifurcates into the northerly Kuroshio and the main body of the southerly Mindanao current. Thus, NEC is both the south branch of the Subtropical Circulation and the north branch of the Tropical Circulation. The junction of the two branches extends to the west boundary to connect the bifurcation points forming the bifurcation line. The position of the North Pacific Equatorial Current bifurcation line of the surface determines the exchange between and the distribution of subtropical and tropical circulations, thus affecting the local or global climate. A new identification method to track the line and the bifurcation channel was used in this study, focusing on the climatological characteristics of the western boundary of the North Equatorial Current bifurcation line. The long-term average NEC west boundary bifurcation line shifts northwards with depth. In terms of seasonal variation, the average position of the western boundary of the bifurcation line is southernmost in June and northernmost in December, while in terms of interannual variation, from spring to winter in the years when ENSO is developing, the position of the west boundary bifurcation line of NEC is relatively to the north (south) in EI Niño (La Niña) years as compared to normal years.
Hero's journey in bifurcation diagram
Monteiro, L. H. A.; Mustaro, P. N.
2012-06-01
The hero's journey is a narrative structure identified by several authors in comparative studies on folklore and mythology. This storytelling template presents the stages of inner metamorphosis undergone by the protagonist after being called to an adventure. In a simplified version, this journey is divided into three acts separated by two crucial moments. Here we propose a discrete-time dynamical system for representing the protagonist's evolution. The suffering along the journey is taken as the control parameter of this system. The bifurcation diagram exhibits stationary, periodic and chaotic behaviors. In this diagram, there are transition from fixed point to chaos and transition from limit cycle to fixed point. We found that the values of the control parameter corresponding to these two transitions are in quantitative agreement with the two critical moments of the three-act hero's journey identified in 10 movies appearing in the list of the 200 worldwide highest-grossing films.
Institute of Scientific and Technical Information of China (English)
CUI Deng-lan; LI Yang-cheng
2007-01-01
Based on the contact equivalent relation of smooth map-germs in singularity theory, the stability of equivariant bifurcation problems with two types of state variables and their unfoldings in the presence of parameter symmetry is discussed. Some basic results are obtained. Transversality condition is used to characterize the stability of equavariant bifurcation problems.
Barman, Prasenjit; Faponle, Abayomi S; Vardhaman, Anil Kumar; Angelone, Davide; Löhr, Anna-Maria; Browne, Wesley R; Comba, Peter; Sastri, Chivukula V; de Visser, Sam P
2016-01-01
Reaction bifurcation processes are often encountered in the oxidation of substrates by enzymes and generally lead to a mixture of products. One particular bifurcation process that is common in biology relates to electron transfer versus oxygen atom transfer by high-valent iron(IV)-oxo complexes, whi
Equilibrium-torus bifurcation in nonsmooth systems
DEFF Research Database (Denmark)
Zhusubahyev, Z.T.; Mosekilde, Erik
2008-01-01
Considering a set of two coupled nonautonomous differential equations with discontinuous right-hand sides describing the behavior of a DC/DC power converter, we discuss a border-collision bifurcation that can lead to the birth of a two-dimensional invariant torus from a stable node equilibrium...... linear approximation to our system in the neighbourhood of the border. We determine the functional relationships between the parameters of the normal form map and the actual system and illustrate how the normal form theory can predict the bifurcation behaviour along the border-collision equilibrium......-torus bifurcation curve....
Attractivity and bifurcation for nonautonomous dynamical systems
Rasmussen, Martin
2007-01-01
Although, bifurcation theory of equations with autonomous and periodic time dependence is a major object of research in the study of dynamical systems since decades, the notion of a nonautonomous bifurcation is not yet established. In this book, two different approaches are developed which are based on special definitions of local attractivity and repulsivity. It is shown that these notions lead to nonautonomous Morse decompositions, which are useful to describe the global asymptotic behavior of systems on compact phase spaces. Furthermore, methods from the qualitative theory for linear and nonlinear systems are derived, and nonautonomous counterparts of the classical one-dimensional autonomous bifurcation patterns are developed.
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.
EFFECTS OF CONSTANT EXCITATION ON LOCAL BIFURCATION
Institute of Scientific and Technical Information of China (English)
WU Zhi-qiang; CHEN Yu-shu
2006-01-01
The effects of the constant excitation on the local bifurcation of the periodic solutions in the 1:2 internal resonant systems were analyzed based on the singularity theory. It is shown that the constant excitation make influence only when there exist some nonlinear terms, in the oscillator with lower frequency. Besides acting as main bifurcation parameter, the constant excitation, together with coefficients of some nonlinear terms,may change the values of unfolding parameters and the type of the bifurcation. Under the non-degenerate cases, the effect of the third order terms can be neglected.
Angiopoietin-related growth factor level in preeclampsia
2012-01-01
Abstract Aim. Angiopoietin-related growth factor (AGF) is associated with angiogenesis but it can also affect glucose and energy metabolism. The aim of this study was to determine AGF levels in preeclampsia. Method. The study included 32 women with preeclampsia (preeclampsia group) and 32 non-preeclamptic, healthy, third trimester pregnant women (Control group). We analyzed serum levels of AGF and other biochemical and anthropometric markers in all subjects. Results. Serum AGF levels were sig...
Bifurcations and Crises in a Shape Memory Oscillator
Directory of Open Access Journals (Sweden)
Luciano G. Machado
2004-01-01
Full Text Available The remarkable properties of shape memory alloys have been motivating the interest in applications in different areas varying from biomedical to aerospace hardware. The dynamical response of systems composed by shape memory actuators presents nonlinear characteristics and a very rich behavior, showing periodic, quasi-periodic and chaotic responses. This contribution analyses some aspects related to bifurcation phenomenon in a shape memory oscillator where the restitution force is described by a polynomial constitutive model. The term bifurcation is used to describe qualitative changes that occur in the orbit structure of a system, as a consequence of parameter changes, being related to chaos. Numerical simulations show that the response of the shape memory oscillator presents period doubling cascades, direct and reverse, and crises.
Relation between blood lead levels and childhood anemia in India.
Jain, Nitin B; Laden, Francine; Guller, Ulrich; Shankar, Anoop; Kazani, Shamsah; Garshick, Eric
2005-05-15
Lead pollution is a substantial problem in developing countries such as India. The US Centers for Disease Control and Prevention has defined an elevated blood lead level in children as > or = 10 microg/dl, on the basis of neurologic toxicity. The US Environmental Protection Agency suggests a threshold lead level of 20-40 microg/dl for risk of childhood anemia, but there is little information relating lead levels anemia. Therefore, the authors examined the association between lead levels as low as 10 mug/dl and anemia in Indian children under 3 years of age. Anemia was divided into categories of mild (hemoglobin level 10-10.9 g/dl), moderate (hemoglobin level 8-9.9 g/dl), and severe (hemoglobin level Lead levels lead levels > or = 10-19.9 microg/dl and 97 (9%) had levels > or = 20 microg/dl. After adjustment for child's age, duration of breastfeeding, standard of living, parent's education, father's occupation, maternal anemia, and number of children in the immediate family, children with lead levels > or = 10 microg/dl were 1.3 (95% confidence interval: 1.0, 1.7) times as likely to have moderate anemia as children with lead levels anemia was 1.7 (95% confidence interval: 1.1, 2.6). Health agencies in India should note the association of elevated blood lead levels with anemia and make further efforts to curb lead pollution and childhood anemia.
Bifurcation of non-negative solutions for an elliptic system
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
In the paper,we consider a nonlinear elliptic system coming from the predator-prey model with diffusion.Predator growth-rate is treated as bifurcation parameter.The range of parameter is found for which there exists nontrivial solution via the theory of bifurcation from infinity,local bifurcation and global bifurcation.
BIFURCATION OF PERIODIC ORBITS OF A THREE-DIMENSIONAL SYSTEM
Institute of Scientific and Technical Information of China (English)
LIU XUANLIANG; HAN MAOAN
2005-01-01
Consider a three-dimensional system having an invariant surface. By using bifurcation techniques and analyzing the solutions of bifurcation equations, the authors study the spacial bifurcation phenomena of a k multiple closed orbit in the invariant surface.The sufficient conditions of the existence of many closed orbits bifurcate from the k multiple closed orbit are obtained.
Institute of Scientific and Technical Information of China (English)
WV Xiao-Bo; MO Juan; YANG Ming-Hao; ZHENG Qiao-Hua; GU Hua-Guang; HEN Wei
2008-01-01
@@ Two different bifurcation scenarios, one is novel and the other is relatively simpler, in the transition procedures of neural firing patterns are studied in biological experiments on a neural pacemaker by adjusting two parameters. The experimental observations are simulated with a relevant theoretical model neuron. The deterministic non-periodic firing pattern lying within the novel bifurcation scenario is suggested to be a new case of chaos, which has not been observed in previous neurodynamical experiments.
Singular analysis of two-dimensional bifurcation system
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
Bifurcation properties of two-dimensional bifurcation system are studied in this paper.Universal unfolding and transition sets of the bifurcation equations are obtained.The whole parametric plane is divided into several different persistent regions according to the type of motion,and the different qualitative bifurcation diagrams in different persistent regions are given.The bifurcation properties of the two-dimensional bifurcation system are compared with its reduced one-dimensional system.It is found that the system which is reduced to one dimension has lost many bifurcation properties.
Iridium-related deep levels in n-type silicon
Bollmann, J; Weber, J
2000-01-01
Iridium-related deep levels in n-type silicon were studied by deep level transient spectroscopy (DLTS). Two different sets of samples were used which differ in the Ir-doping process. Stable Ir isotopes were introduced in the melt during the floating-zone growth process. Other samples were implanted with radioactive mercury isotopes, which decay via gold and platinum to iridium or osmium. In these samples an identification of Ir-related levels from the known half-life of the isotopes is possible. Two dominant levels at E/sub c/-0.28 eV and E /sub c/-0.57 eV are assigned to isolated substitutional Ir. Two other levels at E/sub c/-0.17 eV and E/sub c/-0.45 eV are identified as iridium-hydrogen complexes containing one or two hydrogen atoms, respectively. (16 refs).
The Bifurcation Behavior of CO Coupling Reactor
Institute of Scientific and Technical Information of China (English)
徐艳; 马新宾; 许根慧
2005-01-01
The bifurcation behavior of the CO coupling reactor was examined based on the one-dimensional pseudohomogeneous axial dispersion dynamic model. The method of finite difference was used for solving the boundary value problem; the continuation technique and the direct method were applied to determine the bifurcation diagram.The effects of dimensionless adiabatic temperature rise, Damkoehler number, activation energy, heat transfer coefficient and feed ratio on the bifurcation behavior were investigated. It was shown that there existed static bifurcation and the oscillations did not occur in the reactor. The result also revealed that the reactor exhibited at most 1-3-1 multiplilicity patterns within the range of practical possible parameters and the measures, such as weakening the axial dispersion of reactor, enhancing heat transfer, decreasing the concentration of ethyl nitrite, were efficient for avoiding the possible risk of multiple steady states.
Bifurcation and synchronization of synaptically coupled FHN models with time delay
Energy Technology Data Exchange (ETDEWEB)
Wang Qingyun [School of Science, Beijing University of Aeronautics and Astronautics, Beijing 100083 (China); Inner College of Mongolia Finance and Economics, Huhhot 010051 (China); Lu Qishao [School of Science, Beijing University of Aeronautics and Astronautics, Beijing 100083 (China); Chen Guanrong [Department of Electronic Engineering, City University of Hong Kong, Hong Kong (China); Feng Zhaosheng [Department of Mathematics, University of Texas - Pan American, Edinburg, TX 78441 (United States)], E-mail: zsfeng@utpa.edu; Duan Lixia [School of Science, Beijing University of Aeronautics and Astronautics, Beijing 100083 (China)
2009-01-30
This paper presents an investigation of dynamics of the coupled nonidentical FHN models with synaptic connection, which can exhibit rich bifurcation behavior with variation of the coupling strength. With the time delay being introduced, the coupled neurons may display a transition from the original chaotic motions to periodic ones, which is accompanied by complex bifurcation scenario. At the same time, synchronization of the coupled neurons is studied in terms of their mean frequencies. We also find that the small time delay can induce new period windows with the coupling strength increasing. Moreover, it is found that synchronization of the coupled neurons can be achieved in some parameter ranges and related to their bifurcation transition. Bifurcation diagrams are obtained numerically or analytically from the mathematical model and the parameter regions of different behavior are clarified.
Cavitated Bifurcation for Incompressible Hyperelastic Material
Institute of Scientific and Technical Information of China (English)
任九生; 程昌钧
2002-01-01
The spherical cavitated bifurcation for a hyperelastic solid sphere made of the incompressible Valanis-Landel material under boundary dead-loading is examined. The analytic solution for the bifurcation problem is obtained. The catastrophe and concentration of stresses are discussed. The stability of solutions is discussed through the energy comparison.And the growth of a pre-existing micro-void is also observed.
Institute of Scientific and Technical Information of China (English)
JIA Bing; GU Hua-Guang; LI Yu-Ye
2011-01-01
@@ Excitability is an essential characteristic of excitable media such as nervous and cardiac systems.Different types of neuronal excitability are related to different bifurcation structures.We simulate the coherence resonance effect near a saddle-node and homoclinic bifurcation corresponding to type-I excitability in a theoretical neuron model,and recognize the obvious features of the corresponding firing pattern.Similar firing patterns are discovered in rat hippocampal CA1 pyramidal neurons.The results are not only helpful for understanding the dynamics of the saddle-node bifurcation and type-I excitability in a realistic nervous system,but also provide a practical indicator to identify types of excitability and bifurcation.%Excitability is an essential characteristic of excitable media such as nervous and cardiac systems. Different types of neuronal excitability are related to different bifurcation structures. We simulate the coherence resonance effect near a saddle-node and homoclinic bifurcation corresponding to type-I excitability in a theoretical neuron model, and recognize the obvious features of the corresponding firing pattern. Similar firing patterns are discovered in rat hippocampal CA1 pyramidal neurons. The results are not only helpful for understanding the dynamics of the saddle-node bifurcation and type-I excitability in a realistic nervous system, but also provide a practical indicator to identify types of excitability and bifurcation.
Bifurcations and Chaos in Duffing Equation
Institute of Scientific and Technical Information of China (English)
2007-01-01
The Duffing equation with even-odd asymmetrical nonlinear-restoring force and one external forcing is investigated. The conditions of existence of primary resonance, second-order, third-order subharmonics, m-order subharmonics and chaos are given by using the second-averaging method, the Melnikov method and bifurcation theory. Numerical simulations including bifurcation diagram, bifurcation surfaces and phase portraits show the consistence with the theoretical analysis. The numerical results also exhibit new dynamical behaviors including onset of chaos, chaos suddenly disappearing to periodic orbit, cascades of inverse period-doubling bifurcations, period-doubling bifurcation, symmetry period-doubling bifurcations of period-3 orbit, symmetry-breaking of periodic orbits, interleaving occurrence of chaotic behaviors and period-one orbit, a great abundance of periodic windows in transient chaotic regions with interior crises and boundary crisis and varied chaotic attractors. Our results show that many dynamical behaviors are strictly departure from the behaviors of the Duffing equation with odd-nonlinear restoring force.
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 ...
Crystalline undulator radiation and sub-harmonic bifurcation of system
Institute of Scientific and Technical Information of China (English)
Luo Xiao-Hua; He Wei; Wu Mu-Ying; Shao Ming-Zhu; Luo Shi-Yu
2013-01-01
Looking for new light sources,especially short wavelength laser light sources has attracted widespread attention.This paper analytically describes the radiation of a crystalline undulator field by the sine-squared potential.In the classical mechanics and the dipole approximation,the motion equation of a particle is reduced to a generalized pendulum equation with a damping term and a forcing term.The bifurcation behavior of periodic orbits is analyzed by using the Melnikov method and the numerical method,and the stability of the system is discussed.The results show that,in principle,the stability of the system relates to its parameters,and only by adjusting these parameters appropriately can the occurrence of bifurcation be avoided or suppressed.
STABILITY, BIFURCATIONS AND CHAOS IN UNEMPLOYMENT NON-LINEAR DYNAMICS
Directory of Open Access Journals (Sweden)
Pagliari Carmen
2013-07-01
Full Text Available The traditional analysis of unemployment in relation to real output dynamics is based on some empirical evidences deducted from Okun’s studies. In particular the so called Okun’s Law is expressed in a linear mathematical formulation, which cannot explain the fluctuation of the variables involved. Linearity is an heavy limit for macroeconomic analysis and especially for every economic growth study which would consider the unemployment rate among the endogenous variables. This paper deals with an introductive study about the role of non-linearity in the investigation of unemployment dynamics. The main idea is the existence of a non-linear relation between the unemployment rate and the gap of GDP growth rate from its trend. The macroeconomic motivation of this idea moves from the consideration of two concatenate effects caused by a variation of the unemployment rate on the real output growth rate. These two effects are concatenate because there is a first effect that generates a secondary one on the same variable. When the unemployment rate changes, the first effect is the variation in the level of production in consequence of the variation in the level of such an important factor as labour force; the secondary effect is a consecutive variation in the level of production caused by the variation in the aggregate demand in consequence of the change of the individual disposal income originated by the previous variation of production itself. In this paper the analysis of unemployment dynamics is carried out by the use of the logistic map and the conditions for the existence of bifurcations (cycles are determined. The study also allows to find the range of variability of some characteristic parameters that might be avoided for not having an absolute unpredictability of unemployment dynamics (deterministic chaos: unpredictability is equivalent to uncontrollability because of the total absence of information about the future value of the variable to
Explaining trends and variability in coastal relative sea level
Frederikse, Thomas; Riva, Riccardo
2016-04-01
Comprehensive understanding of trends and variability in coastal mean sea level is vital for protecting shores under a changing climate. To understand the behavior of coastal relative sea level (RSL), it is crucial to identify all relevant processes. We combine data from various geophysical models and observations to determine whether the trends and decadal variability observed in relative sea level at tide gauges can be explained by the sum of all known contributors. A key contributor to RSL is vertical land motion, which is caused by glacial isostatic adjustment (GIA), solid earth response to surface loading, tectonics, and local effects. We explicitly model low-frequency loading effects to correct GPS records, which leads to a more consistent trend than only using GIA models. Secondly, we create sea level fingerprints based on estimates of ice melt and changes in land hydrology, which provide the RSL contribution due to large-scale mass transport. Since coastal areas are often located on shallow continental shelves, steric effects will generally be small, and a large fraction of the decadal sea level variability will have a remote steric origin. Therefore, we determine a relation between coastal sea level and deep sea steric variability. For the period 1950-2012, we find that for many locations, including the European coast, the observed and modeled RSL time series agree well on decadal and secular scales.
Salt marsh stability modelled in relation to sea level rise
DEFF Research Database (Denmark)
Bartholdy, Jesper; Bartholdy, Anders; Kroon, Aart
2010-01-01
Accretion on a natural backbarrier salt marsh was modeled as a function of high tide level, initial salt marsh level and distance to the source. Calibration of the model was based on up to ca 80 year old marker horizons, supplemented by 210Pb/137Cs datings and subsequent measurements of clay...... rise, the marsh at the specific location will eventually drown, whereas - with a sea level rise below this level – it will grow towards the top of the rising tidal frame. The short term variation of salt marsh accretion was found to correlate well with variations in the North Atlantic Oscillation...... - relatively quickly grow above the level of the highest astronomical tide, whereas this - in practice - will never happen for the latter....
Forecasting Bifurcations from Large Perturbation Recoveries in Feedback Ecosystems.
D'Souza, Kiran; Epureanu, Bogdan I; Pascual, Mercedes
2015-01-01
Forecasting bifurcations such as critical transitions is an active research area of relevance to the management and preservation of ecological systems. In particular, anticipating the distance to critical transitions remains a challenge, together with predicting the state of the system after these transitions are breached. In this work, a new model-less method is presented that addresses both these issues based on monitoring recoveries from large perturbations. The approach uses data from recoveries of the system from at least two separate parameter values before the critical point, to predict both the bifurcation and the post-bifurcation dynamics. The proposed method is demonstrated, and its performance evaluated under different levels of measurement noise, with two ecological models that have been used extensively in previous studies of tipping points and alternative steady states. The first one considers the dynamics of vegetation under grazing; the second, those of macrophyte and phytoplankton in shallow lakes. Applications of the method to more complex situations are discussed together with the kinds of empirical data needed for its implementation.
MECHANICAL HEART-VALVE PROSTHESES - SOUND LEVEL AND RELATED COMPLAINTS
LAURENS, RRP; WIT, HP; EBELS, T
1992-01-01
In a randomised study, we investigated the sound production of mechanical heart valve prostheses and the complaints related to this sound. The CarboMedics, Bjork-Shiley monostrut and StJude Medical prostheses were compared. A-weighted levels of the pulse-like sound produced by the prosthesis were me
Loop-level KLT, BCJ and EYM amplitude relations
He, Song
2016-01-01
In this letter, we extend the tree-level Kawai--Lewellen--Tye (KLT) and Bern--Carrasco--Johansson (BCJ) amplitude relations to loop integrands of gauge theory and gravity. By rearranging the propagators of gauge and gravity loop integrands, we propose the first manifestly gauge- and diffeomorphism invariant formulation of their double-copy relations. The one-loop KLT formula expresses gravity integrands in terms of more basic gauge invariant building blocks for gauge-theory amplitudes, dubbed partial integrands. The latter obey a one-loop analogue of the BCJ relations, and both KLT and BCJ relations are universal to bosons and fermions in any number of spacetime dimensions and independent on the amount of supersymmetry. Also, one-loop integrands of Einstein--Yang--Mills (EYM) theory are related to partial integrands of pure gauge theories. Finally, we briefly report on preliminary two-loop evidence that the KLT formula can be extended to any loop order.
Gaudreault, Mathieu; Drolet, François; Viñals, Jorge
2010-11-01
Analytical expressions for pitchfork and Hopf bifurcation thresholds are given for a nonlinear stochastic differential delay equation with feedback. Our results assume that the delay time τ is small compared to other characteristic time scales, not a significant limitation close to the bifurcation line. A pitchfork bifurcation line is found, the location of which depends on the conditional average , where x(t) is the dynamical variable. This conditional probability incorporates the combined effect of fluctuation correlations and delayed feedback. We also find a Hopf bifurcation line which is obtained by a multiple scale expansion around the oscillatory solution near threshold. We solve the Fokker-Planck equation associated with the slowly varying amplitudes and use it to determine the threshold location. In both cases, the predicted bifurcation lines are in excellent agreement with a direct numerical integration of the governing equations. Contrary to the known case involving no delayed feedback, we show that the stochastic bifurcation lines are shifted relative to the deterministic limit and hence that the interaction between fluctuation correlations and delay affect the stability of the solutions of the model equation studied.
Pitchfork and Hopf bifurcation thresholds in stochastic equations with delayed feedback.
Gaudreault, Mathieu; Lépine, Françoise; Viñals, Jorge
2009-12-01
The bifurcation diagram of a model stochastic differential equation with delayed feedback is presented. We are motivated by recent research on stochastic effects in models of transcriptional gene regulation. We start from the normal form for a pitchfork bifurcation, and add multiplicative or parametric noise and linear delayed feedback. The latter is sufficient to originate a Hopf bifurcation in that region of parameters in which there is a sufficiently strong negative feedback. We find a sharp bifurcation in parameter space, and define the threshold as the point in which the stationary distribution function p(x) changes from a delta function at the trivial state x=0 to p(x) approximately x(alpha) at small x (with alpha=-1 exactly at threshold). We find that the bifurcation threshold is shifted by fluctuations relative to the deterministic limit by an amount that scales linearly with the noise intensity. Analytic calculations of the bifurcation threshold are also presented in the limit of small delay tau-->0 that compare quite favorably with the numerical solutions even for moderate values of tau .
Relative sea-level changes during the Holocene in Bangladesh
Rashid, Towhida; Suzuki, S.; Sato, Hiroshi; Monsur, M. H.; Saha, S. K.
2013-03-01
This paper presents a reconstruction of the Holocene paleo-environment in the central part of Bangladesh in relation to relative sea-level changes 200 km north of the present coastline. Lithofacies characteristics, mangal peat, diatoms and paleophysiographical evidence were considered to reconstruct the past position and C-14 ages were used to determine the time of formation of the relative sea level during the Holocene. With standard reference datum, the required m.s.l. at the surface of five sections was calculated. The relative sea-level (RSL) curve suggests that Bangladesh experienced two mid-Holocene RSL transgressions punctuated by regressions. The curve shows an RSL highstand at approximately 7500 cal BP, although the height of this highstand could not be determined because the transgressive phase was observed in a bioturbated sand flat facies. The curve shows a regression of approximately 6500 cal BP, and the RSL was considerably lower, perhaps 1-2 m, than the present m.s.l. The abundant marine diatoms and mangrove pollens indicate the highest RSL transgression in Bangladesh at approximately 6000 cal BP, being at least 4.5 to 5 m higher than the modern m.s.l. After this phase, the relative sea level started to fall, and consequently, a freshwater peat developed at approximately 5980-5700 cal BP. The abundant mangrove pollens in the salt-marsh succession shows the regression at approximately 5500 cal BP, when it was 1-2 m higher than the modern sea level. The curve indicates that at approximately 5000 cal BP and onwards, the RSL started to fall towards its present position, and the present shoreline of Bangladesh was established at approximately 1500 cal BP and has not noticeably migrated inland since.
SOUND LABOR RELATIONS AT ENTERPRISE LEVEL IN THAILAND
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Vichai Thosuwonchinda
2016-07-01
Full Text Available The objective of this research was to study the pattern of sound labor relations in Thailand in order to reduce conflicts between employers and workers and create cooperation. The research was based on a qualitative approach, using in-depth interview with 10 stakeholder groups of Thai industrial relations system. They were employees of non unionized companies at the shop floor level, employees of non unionized companies at the supervisor level, trade union leaders at the company level, trade union leaders at the national level, employers of non-unionized companies, employers’ organization leaders, and human resource managers, members of tripartite bodies, government officials and labor academics. The findings were presented in a model identifying 5 characteristics that enhance sound relations in Thailand, i.e. recognition between employer and workers, good communication, trust, data revealing and workers’ participation. It was suggested that all parties, employers, workers and the government should take part in the promotion of sound labor relations. The employer have to acknowledge labor union with a positive attitude, have good communication with workers , create trust with workers, disclose information, create culture of mutual benefits as well as accept sincerely the system that include workers’ participation. Workers need a strong labor union, good and sincere representatives for clear communication, trust, mutual benefits and seek conflict solutions with employer by win-win strategy. The government has a supporting role in adjusting the existing laws in the appropriate way, by creating policy for sound labor relations, and putting the idea of sound labor relations into practice.
Parameterized center manifold for unfolding bifurcations with an eigenvalue +1 in n-dimensional maps
Wen, Guilin; Yin, Shan; Xu, Huidong; Zhang, Sijin; Lv, Zengyao
2016-10-01
For the fold bifurcation with an eigenvalue +1, there are three types of potential solutions from saddle-node bifurcation, transcritical bifurcation and pitchfork bifurcation. In the existing analysis methods for high maps, there is a problem that for the fold bifurcation, saddle-node bifurcation and transcritical bifurcation cannot be distinguished by the center manifold without bifurcation parameter. In this paper, a parameterized center manifold has been derived to unfold the solutions of the fold bifurcation with an eigenvalue +1, which is used to reduce a general n-dimensional map to one-dimensional map. On the basis of the reduced map, the conditions of the fold bifurcations including saddle-node bifurcation, transcritical bifurcation and pitchfork bifurcation are established for general maps, respectively. We show the applications of the proposed bifurcation conditions by three four-dimensional map examples to distinguish saddle-node bifurcation, transcritical bifurcation and pitchfork bifurcation.
Multiparameter bifurcations and mixed-mode oscillations in Q-switched CO2 lasers.
Doedel, Eusebius J; Pando L, Carlos L
2014-05-01
We study the origin of mixed-mode oscillations and related bifurcations in a fully molecular laser model that describes CO2 monomode lasers with a slow saturable absorber. Our study indicates that the presence of isolas of periodic mixed-mode oscillations, as the pump parameter and the cavity-frequency detuning change, is inherent to Q-switched CO2 monomode lasers. We compare this model, known as the dual four-level model, to the more conventional 3:2 model and to a CO2 laser model for fast saturable absorbers. In these models, we find similarities as well as qualitative differences, such as the different nature of the homoclinic tangency to a relevant unstable periodic orbit, where the Gavrilov-Shilnikov theory and its extensions may hold. We also show that there are isolas of periodic mixed-mode oscillations in a model for CO2 lasers with modulated losses, as the pump parameter varies. The coarse-grained bifurcation diagrams of the periodic mixed-mode oscillations in these models suggest that these oscillations belong to similar classes.
Salt marsh stability modelled in relation to sea level rise
Bartholdy, Jesper; Bartholdy, Anders T.; Kroon, Aart
2010-05-01
Accretion on a natural backbarrier salt marsh was modeled as a function of high tide level, initial salt marsh level and distance to the source. Calibration of the model was based on up to ca 80 year old marker horizons, supplemented by 210Pb/137Cs datings and subsequent measurements of clay thickness. Autocompaction was incorporated in the model, and shown to play a major role for the translation of accretion rates measured as length per unit time to accumulation rates measured as mass per area per unit time. This is important, even for shallow salt marsh deposits for which it is demonstrated that mass depth down core can be directly related to the bulk dry density of the surface layer by means of a logarithmic function. The results allow for an evaluation of the use of marker horizons in the topmost layers and show that it is important to know the level of the marker in relation to the salt marsh base. In general, deeper located markers will indicate successively smaller accretion rates with the same sediment input. Thus, stability analysis made on the basis of newly established marker horizons will be biased and indicate salt marsh stabilities far above the correct level. Running the model with a constant sea level revealed that balance between the inner and the outer salt marsh deposition can not be achieved within a reasonable time scale. Likewise it is shown that only one specific sea level rise provides equilibrium for a given location on the salt marsh. With a higher sea level rise, the marsh at the specific location will eventually drown, whereas - with a sea level rise below this level - it will grow towards the top of the rising tidal frame. The short term variation of salt marsh accretion was found to correlate well with variations in the North Atlantic Oscillation - the NAO winter index. Comparisons between the geomorphological development of wind tide affected salt marshes, like those present on the Danish North Sea coasts, and primary astronomically
Asymptotic Bifurcation Solutions for Perturbed Kuramoto-Sivashinsky Equation
Institute of Scientific and Technical Information of China (English)
HUANG Qiong-Wei; TANG Jia-Shi
2011-01-01
Stability and dynamic bifurcation in the perturbed Kuramoto-Sivashinsky (KS) equation with Dirichlet boundary condition are investigated by using central manifold reduction procedure.The result shows, as the bifurcation parameter crosses a critical value, the system undergoes a pitchfork bifurcation to produce two asymptotically stable solutions.Furthermore, when the distance from bifurcation is of comparable order ∈2 (｜∈｜ (≤) 1), the first two terms in e-expansions for the new asymptotic bifurcation solutions are derived by multiscale expansion method.Such information is useful to the bifurcation control.
Local bifurcation analysis of a four-dimensional hyperchaotic system
Institute of Scientific and Technical Information of China (English)
Wu Wen-Juan; Chen Zeng-Qiang; Yuan Zhu-Zhi
2008-01-01
Local bifurcation phenomena in a four-dimensional continuous hyperchaotic system, which has rich and complex dynamical behaviours, are analysed. The local bifurcations of the system are investigated by utilizing the bifurcation theory and the centre manifold theorem, and thus the conditions of the existence of pitchfork bifurcation and Hopf bifurcation are derived in detail. Numerical simulations are presented to verify the theoretical analysis, and they show some interesting dynamics, including stable periodic orbits emerging from the new fixed points generated by pitchfork bifurcation, coexistence of a stable limit cycle and a chaotic attractor, as well as chaos within quite a wide parameter region.
Secondary flow behavior in a double bifurcation
Leong, Fong Yew; Smith, Kenneth A.; Wang, Chi-Hwa
2009-04-01
Secondary flows in the form of multivortex structures can occur in bifurcation models as the result of upstream influence. Results from numerical modeling of steady inspiratory flows indicate that, for the case of a symmetric planar double bifurcation, four counter-rotating vortices develop in each of the grand daughter branches. In this paper, experimental visualization and verification is provided by particle image velocimetry measurements on a modified single bifurcation model. A splitter plate was positioned in the mother tube so that secondary vorticity was introduced into the fluid core. The axial velocity profile before the bifurcation junction resembles the M-shaped velocity profile commonly observed in bifurcated tube flows. The result of this manipulation is the development of a physically observable four-vortex configuration in the cross sections of the daughter branches, thus demonstrating the strong influence of upstream secondary vorticity. Through numerical visualization of vortex lines, it is shown that secondary vorticity is amplified by the extension of vortex lines due to secondary flow within the daughter tube. Order-of-magnitude arguments have been applied to the vorticity transport equation; and key dimensionless parameters have been obtained, accounting for curvature effects. Results indicate that the secondary vorticity goes through a maximum with increasing downstream distance, as a result of the interplay between vortex stretching and viscous effects.
Institute of Scientific and Technical Information of China (English)
GUO Rui-zhi; LI Yang-cheng
2005-01-01
Based on the left-right equivalent relation of smooth map-germs in singularity theory, the unfoldings of multiparameter equivariant bifurcation problems with respect to leftright equivalence are discussed. The state variables of such an equivariant bifurcation problem were divided into two groups, in which the first can vary independently, while the others depend on the first in the varying process. By applying related methods and techniques in the unfolding theory of smooth map-germs, the necessary and sufficient condition for an unfolding of a multiparameter equivariant bifurcation problem with two groups of state variables to be versal is obtained.
Mangrove sedimentation and response to relative sea-level rise
Woodroffe, CD; Rogers, K.; Mckee, Karen L.; Lovelock, CE; Mendelssohn, IA; Saintilan, N.
2016-01-01
Mangroves occur on upper intertidal shorelines in the tropics and subtropics. Complex hydrodynamic and salinity conditions influence mangrove distributions, primarily related to elevation and hydroperiod; this review considers how these adjust through time. Accumulation rates of allochthonous and autochthonous sediment, both inorganic and organic, vary between and within different settings. Abundant terrigenous sediment can form dynamic mudbanks; tides redistribute sediment, contrasting with mangrove peat in sediment-starved carbonate settings. Sediments underlying mangroves sequester carbon, but also contain paleoenvironmental records of adjustments to past sea-level changes. Radiometric dating indicates long-term sedimentation, whereas Surface Elevation Table-Marker Horizon measurements (SET-MH) provide shorter perspectives, indicating shallow subsurface processes of root growth and substrate autocompaction. Many tropical deltas also experience deep subsidence, which augments relative sea-level rise. The persistence of mangroves implies an ability to cope with moderately high rates of relative sea-level rise. However, many human pressures threaten mangroves, resulting in continuing decline in their extent throughout the tropics.
Mangrove Sedimentation and Response to Relative Sea-Level Rise
Woodroffe, C. D.; Rogers, K.; McKee, K. L.; Lovelock, C. E.; Mendelssohn, I. A.; Saintilan, N.
2016-01-01
Mangroves occur on upper intertidal shorelines in the tropics and subtropics. Complex hydrodynamic and salinity conditions, related primarily to elevation and hydroperiod, influence mangrove distributions; this review considers how these distributions change over time. Accumulation rates of allochthonous and autochthonous sediment, both inorganic and organic, vary between and within different settings. Abundant terrigenous sediment can form dynamic mudbanks, and tides redistribute sediment, contrasting with mangrove peat in sediment-starved carbonate settings. Sediments underlying mangroves sequester carbon but also contain paleoenvironmental records of adjustments to past sea-level changes. Radiometric dating indicates long-term sedimentation, whereas measurements made using surface elevation tables and marker horizons provide shorter perspectives, indicating shallow subsurface processes of root growth and substrate autocompaction. Many tropical deltas also experience deep subsidence, which augments relative sea-level rise. The persistence of mangroves implies an ability to cope with moderately high rates of relative sea-level rise. However, many human pressures threaten mangroves, resulting in a continuing decline in their extent throughout the tropics. *
Alternate Pacing of Border-Collision Period-Doubling Bifurcations.
Zhao, Xiaopeng; Schaeffer, David G
2007-11-01
Unlike classical bifurcations, border-collision bifurcations occur when, for example, a fixed point of a continuous, piecewise C1 map crosses a boundary in state space. Although classical bifurcations have been much studied, border-collision bifurcations are not well understood. This paper considers a particular class of border-collision bifurcations, i.e., border-collision period-doubling bifurcations. We apply a subharmonic perturbation to the bifurcation parameter, which is also known as alternate pacing, and we investigate the response under such pacing near the original bifurcation point. The resulting behavior is characterized quantitatively by a gain, which is the ratio of the response amplitude to the applied perturbation amplitude. The gain in a border-collision period-doubling bifurcation has a qualitatively different dependence on parameters from that of a classical period-doubling bifurcation. Perhaps surprisingly, the differences are more readily apparent if the gain is plotted vs. the perturbation amplitude (with the bifurcation parameter fixed) than if plotted vs. the bifurcation parameter (with the perturbation amplitude fixed). When this observation is exploited, the gain under alternate pacing provides a useful experimental tool to identify a border-collision period-doubling bifurcation.
Stochastic bifurcations in a prototypical thermoacoustic system.
Gopalakrishnan, E A; Tony, J; Sreelekha, E; Sujith, R I
2016-08-01
We study the influence of noise in a prototypical thermoacoustic system, which represents a nonlinear self-excited bistable oscillator. We analyze the time series of unsteady pressure obtained from a horizontal Rijke tube and a mathematical model to identify the effect of noise. We report the occurrence of stochastic bifurcations in a thermoacoustic system by tracking the changes in the stationary amplitude distribution. We observe a complete suppression of a bistable zone in the presence of high intensity noise. We find that the complete suppression of the bistable zone corresponds to the nonexistence of phenomenological (P) bifurcations. This is a study in thermoacoustics to identify the parameter regimes pertinent to P bifurcation using the stationary amplitude distribution obtained by solving the Fokker-Planck equation.
Stochastic bifurcations in a prototypical thermoacoustic system
Gopalakrishnan, E. A.; Tony, J.; Sreelekha, E.; Sujith, R. I.
2016-08-01
We study the influence of noise in a prototypical thermoacoustic system, which represents a nonlinear self-excited bistable oscillator. We analyze the time series of unsteady pressure obtained from a horizontal Rijke tube and a mathematical model to identify the effect of noise. We report the occurrence of stochastic bifurcations in a thermoacoustic system by tracking the changes in the stationary amplitude distribution. We observe a complete suppression of a bistable zone in the presence of high intensity noise. We find that the complete suppression of the bistable zone corresponds to the nonexistence of phenomenological (P) bifurcations. This is a study in thermoacoustics to identify the parameter regimes pertinent to P bifurcation using the stationary amplitude distribution obtained by solving the Fokker-Planck equation.
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.
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.
A model for the nonautonomous Hopf bifurcation
Anagnostopoulou, V.; Jäger, T.; Keller, G.
2015-07-01
Inspired by an example of Grebogi et al (1984 Physica D 13 261-8), we study a class of model systems which exhibit the full two-step scenario for the nonautonomous Hopf bifurcation, as proposed by Arnold (1998 Random Dynamical Systems (Berlin: Springer)). The specific structure of these models allows a rigorous and thorough analysis of the bifurcation pattern. In particular, we show the existence of an invariant ‘generalised torus’ splitting off a previously stable central manifold after the second bifurcation point. The scenario is described in two different settings. First, we consider deterministically forced models, which can be treated as continuous skew product systems on a compact product space. Secondly, we treat randomly forced systems, which lead to skew products over a measure-preserving base transformation. In the random case, a semiuniform ergodic theorem for random dynamical systems is required, to make up for the lack of compactness.
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 ...
Multiple Discourse Relations on the Sentential Level in Japanese
Mori, Y
1996-01-01
In the German government (BMBF) funded project Verbmobil, a semantic formalism Language for Underspecified Discourse Representation Structures (LUD) is used which describes several DRSs and allows for underspecification. Dealing with Japanese poses challenging problems. In this paper, a treatment of multiple discourse relation constructions on the sentential level is shown, which are common in Japanese but cause a problem for the formalism,. The problem is to distinguish discourse relations which take the widest scope compared with other scope-taking elements on the one hand and to have them underspecified among each other on the other hand. We also state a semantic constraint on the resolution of multiple discourse relations which seems to prevail over the syntactic c-command constraint.
Congenital pseudoarthrosis of the clavicle with bifurcation
Directory of Open Access Journals (Sweden)
Narender Kumar Magu
2014-01-01
Full Text Available Congenital pseudoarthrosis of clavicle is a rare clinical entity. It usually presents as a swelling in the clavicular region at birth or soon after birth. Fitzwilliam′s original description of 60 subtypes of congenital pseudoarthrosis of clavicle have addressed several anatomical variants, e.g. association with cervical rib and abnormally vertical and elevated upper ribs. However, congenital pseudoarthrosis of clavicle associated with bifurcation is an atypical anatomic variant. To the best of our knowledge, this variant has never been mentioned in the literature. In the present report, we have described this subtype of symptomatic congenital pseudoarthrosis of the clavicle with bifurcation and its possible management.
Heteroclinic Bifurcation of Strongly Nonlinear Oscillator
Institute of Scientific and Technical Information of China (English)
ZHANG Qi-Chang; WANG Wei; LI Wei-Yi
2008-01-01
Analytical prediction of heteroclinic bifurcation of the strongly nonlinear oscillator is presented by using the extended normal form method.We consider the approximate periodic solution of the system subject to the quintic nonlinearity by introducing the undetermined fundamental frequency.For the occurrence of heteroclinicity,the bifurcation criterion is accomplished.It depends on the contact of the limit cycle with the saddle equilibrium.As is illustrated,the explicit application shows that the new results coincide very well with the results of numerical simulation when disturbing parameter is of arbitrary magnitude.PACS: 82.40.Bj,47.20.Ky,02.30.Hq
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.
Basin bifurcation in quasiperiodically forced systems
Energy Technology Data Exchange (ETDEWEB)
Feudel, U.; Witt, A.; Grebogi, C. [Institut fuer Physik, Universitaet Potsdam, Am Neuen Palais, PF 601553, D-14415, Potsdam (Germany); Lai, Y. [Departments of Physics and Astronomy and of Mathematics, The University of Kansas, Lawrence, Kansas 66045 (United States); Grebogi, C. [Institute for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States)
1998-09-01
In this paper we study quasiperiodically forced systems exhibiting fractal and Wada basin boundaries. Specifically, by utilizing a class of representative systems, we analyze the dynamical origin of such basin boundaries and we characterize them. Furthermore, we find that basin boundaries in a quasiperiodically driven system can undergo a unique type of bifurcation in which isolated {open_quotes}islands{close_quotes} of basins of attraction are created as a system parameter changes. The mechanism for this type of basin boundary bifurcation is elucidated. {copyright} {ital 1998} {ital The American Physical Society}
The dynamo bifurcation in rotating spherical shells
Morin, Vincent; 10.1142/S021797920906378X
2010-01-01
We investigate the nature of the dynamo bifurcation in a configuration applicable to the Earth's liquid outer core, i.e. in a rotating spherical shell with thermally driven motions. We show that the nature of the bifurcation, which can be either supercritical or subcritical or even take the form of isola (or detached lobes) strongly depends on the parameters. This dependence is described in a range of parameters numerically accessible (which unfortunately remains remote from geophysical application), and we show how the magnetic Prandtl number and the Ekman number control these transitions.
Splitting rivers at their seams: bifurcations and avulsion
Kleinhans, M.G.; Ferguson, R.I.; Lane, S.N.; Hardy, R.J.
2012-01-01
River bifurcations are critical but poorly understood elements of many geomorphological systems. They are integralelements of alluvial fans, braided rivers, fluvial lowland plains, and deltas and control the partitioning of water and sediment throughthese systems. Bifurcations are commonly unstable
Homoclinic Bifurcation Properties near Eight－figure Homoclinic Orbit
Institute of Scientific and Technical Information of China (English)
邹永魁; 佘彦
2002-01-01
In this paper paper we investigate the homoclinic bifurcation properties near an eight-figure homoclinic orbit of co-dimension two of a planar dynamical system.The corresponding local bifurcation diagram is also illustrated by numerical computation.
Border Collision Bifurcations in Two Dimensional Piecewise Smooth Maps
Banerjee, S; Banerjee, Soumitro; Grebogi, Celso
1999-01-01
Recent investigations on the bifurcations in switching circuits have shown that many atypical bifurcations can occur in piecewise smooth maps which can not be classified among the generic cases like saddle-node, pitchfork or Hopf bifurcations occurring in smooth maps. In this paper we first present experimental results to establish the theoretical problem: the development of a theory and classification of the new type of bifurcations resulting from border collision. We then present a systematic analysis of such bifurcations by deriving a normal form --- the piecewise linear approximation in the neighborhood of the border. We show that there can be eleven qualitatively different types of border collision bifurcations depending on the parameters of the normal form, and these are classified under six cases. We present a partitioning of the parameter space of the normal form showing the regions where different types of bifurcations occur. This theoretical framework will help in explaining bifurcations in all syst...
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.
An Experimental Investigation of the Aeroacoustics of a Two-Dimensional Bifurcated Supersonic Inlet
LI, S.-M.; HANUSKA, C. A.; NG, W. F.
2001-11-01
An experiment was conducted on a two-dimensional bifurcated, supersonic inlet to investigate the aeroacoustics at take-off and landing conditions. A 104·1 mm (4·1 in) diameter turbofan simulator was coupled to the inlet to generate the noise typical of a turbofan engine. Aerodynamic and acoustic data were obtained in an anechoic chamber under ground-static conditions (i.e., no forward flight effect). Results showed that varying the distance between the trailing edge of the bifurcated ramp of the inlet and the fan face had negligible effect on the total noise level. Thus, one can have a large freedom to design the bifurcated ramp mechanically and aerodynamically, with minimum impact on the aeroacoustics. However, the effect of inlet guide vanes' (IGV) axial spacing to the fan face has a first order effect on the aeroacoustics for the bifurcated 2-D inlet. As much as 5 dB reduction in the overall sound pressure level and as much as 15 dB reduction in the blade passing frequency tone were observed when the IGV was moved from 0·8 chord of rotor blade upstream of the fan face to 2·0 chord of the blade upstream. The wake profile similarity of the IGV was also found in the flow environment of the 2-D bifurcated inlet, i.e., the IGV wakes followed the usual Gauss' function.
Degree of myopia in relation to intelligence and educational level.
Teasdale, T W; Fuchs, J; Goldschmidt, E
1988-12-10
Intelligence test scores and educational levels were compared for 5943 myopic and 9891 non-myopic 18-year-old men being drafted for military service in Denmark. The former were grouped by degree of myopia, in the range -0.25 diopters (D) to -7.75 D, according to the power of correcting lenses required. Myopes of all degrees had significantly higher test scores and educational levels than non-myopes. However, the relation of these two variables to degree of myopia was not linear; for both variables there were no significant differences among myopia groups in the range -2.0 to -7.75 D. Whereas factors associated with intelligence and education seem to be important in triggering the onset of myopia, they seem to be much less important in determining the degree to which myopia progresses.
Stochastic calculus application to dynamic bifurcations and threshold crossings
Jansons, K M; Jansons, Kalvis M.
1997-01-01
For the dynamic pitchfork bifurcation in the presence of white noise, the statistics of the last time at zero are calculated as a function of the noise level and the rate of change of the parameter. The threshold crossing problem used, for example, to model the firing of a single cortical neuron is considered, concentrating on quantities that may be experimentally measurable but have so far received little attention. Expressions for the statistics of pre-threshold excursions, occupation density and last crossing time of zero are compared with results from numerical generation of paths.
Two degenerate boundary equilibrium bifurcations in planar Filippov systems
Dercole, F.; Della Rossa, F.; Colombo, A.; Kuznetsov, Yuri
2011-01-01
We contribute to the analysis of codimension-two bifurcations in discontinuous systems by studying all equilibrium bifurcations of 2D Filippov systems that involve a sliding limit cycle. There are only two such local bifurcations: (1) a degenerate boundary focus, which we call the homoclinic boundar
CLASSIFICATION OF BIFURCATIONS FOR NONLINEAR DYNAMICAL PROBLEMS WITH CONSTRAINTS
Institute of Scientific and Technical Information of China (English)
吴志强; 陈予恕
2002-01-01
Bifurcation of periodic solutions widely existed in nonlinear dynamical systems isa kind of constrained one in intrinsic quality because its amplitude is always non-negative.Classification of the bifurcations with the type of constraint was discussed. All its six typesof transition sets are derived, in which three types are newly found and a method isproposed for analyzing the constrained bifurcation.
Chaos and reverse bifurcation in a RCL circuit
Cascais, J.; Dilão, R.; da Costa, A. Noronha
1983-01-01
The bifurcation diagram and attractor of a driven non-linear oscillator are directly obtained. The system exhibits not only period doubling, chaotic band merging and noise-free windows like the logistic map, but also reverse flip bifurcations, i.e. period halving. A negative schwartzian derivative map is found also possessing reverse bifurcations.
Comments on the Bifurcation Structure of 1D Maps
DEFF Research Database (Denmark)
Belykh, V.N.; Mosekilde, Erik
1997-01-01
-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...
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).
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.
Townsend, Jacob C; Steinberg, Daniel H; Nielsen, Christopher D; Todoran, Thomas M; Patel, Chetan P; Leonardi, Robert A; Wolf, Bethany J; Brilakis, Emmanouil S; Shunk, Kendrick A; Goldstein, James A; Kern, Morton J; Powers, Eric R
2013-08-01
Atherosclerosis has been shown to develop preferentially at sites of coronary bifurcation, yet culprit lesions resulting in ST-elevation myocardial infarction do not occur more frequently at these sites. We hypothesized that these findings can be explained by similarities in intracoronary lipid and that lipid and lipid core plaque would be found with similar frequency in coronary bifurcation and nonbifurcation segments. One hundred seventy bifurcations were identified, 156 of which had comparative nonbifurcation segments proximal and/or distal to the bifurcation. We compared lipid deposition at bifurcation and nonbifurcation segments in coronary arteries using near-infrared spectroscopy (NIRS), a novel method for the in vivo detection of coronary lipid. Any NIRS signal for the presence of lipid was found with similar frequency in bifurcation and nonbifurcation segments (79% vs 74%, p = NS). Lipid core burden index, a measure of total lipid quantity indexed to segment length, was similar across bifurcation segments as well as their proximal and distal controls (lipid core burden index 66.3 ± 106, 67.1 ± 116, and 66.6 ± 104, p = NS). Lipid core plaque, identified as a high-intensity focal NIRS signal, was found in 21% of bifurcation segments, and 20% of distal nonbifurcation segments (p = NS). In conclusion, coronary bifurcations do not appear to have higher levels of intracoronary lipid or lipid core plaque than their comparative nonbifurcation regions.
Bifurcation of Fredholm Maps II; The Dimension of the Set of Bifurcation Points
Pejsachowicz, Jacobo
2010-01-01
We obtain an estimate for the covering dimension of the set of bifurcation points for solutions of nonlinear elliptic boundary value problems from the principal symbol of the linearization of the problem along the trivial branch of solutions.
Tarnopolski, Mariusz
2013-01-01
This paper presents bifurcation and generalized bifurcation diagrams for a rotational model of an oblate satellite. Special attention is paid to parameter values describing one of Saturn's moons, Hyperion. For various oblateness the largest Lyapunov Characteristic Exponent (LCE) is plotted. The largest LCE in the initial condition as well as in the mixed parameter-initial condition space exhibits a fractal structure, for which the fractal dimension was calculated. It results from the bifurcation diagrams of which most of the parameter values for preselected initial conditions lead to chaotic rotation. The First Recurrence Time (FRT) diagram provides an explanation of the birth of chaos and the existence of quasi-periodic windows occuring in the bifurcation diagrams.
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 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...
Bifurcations in dynamical systems with parametric excitation
Fatimah, Siti
2002-01-01
This thesis is a collection of studies on coupled nonconservative oscillator systems which contain an oscillator with parametric excitation. The emphasis this study will, on the one hand, be on the bifurcations of the simple solutions such as fixed points and periodic orbits, and on the other hand o
[Longitudinal stent deformation during bifurcation lesion treatment].
Mami, Z; Monsegu, J
2014-12-01
Longitudinal stent deformation is defined as a compression of stent length after its implantation. It's a rare complication but dangerous seen with several stents. We reported a case of longitudinal stent deformation during bifurcation lesion treatment with a Promus Element(®) and we perform a short review of this complication.
On the direction of pitchfork bifurcation
Directory of Open Access Journals (Sweden)
Xiaojie Hou
2007-02-01
Full Text Available We present an algorithm for computing the direction of pitchfork bifurcation for two-point boundary value problems. The formula is rather involved, but its computational evaluation is quite feasible. As an application, we obtain a multiplicity result.
Moment of inertia, backbending, and molecular bifurcation.
Tyng, Vivian; Kellman, Michael E
2007-07-28
We predict an anomaly in highly excited bending spectra of acetylene with high vibrational angular momentum. We interpret this in terms of a vibrational shape effect with moment of inertia backbending, induced by a sequence of bifurcations with a transition from "local" to "orthogonal" modes.
The recognition of equivariant bifurcation problems
Institute of Scientific and Technical Information of China (English)
李养成
1996-01-01
The orbit of an equivariant bifurcation problem with multiparameter is characterized under the action of the group of unipotent equivalences. When the unipotent tangent space is invariant under unipotent equivalences, the recognition problem can be solved by just using linear algebra. Sufficient conditions for a subspace to be intrinsic subspace under unipotent equivalences are given.
Bifurcation structure of successive torus doubling
Energy Technology Data Exchange (ETDEWEB)
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.
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...
Hyperhomocysteinemia in ulcerative colitis is related to folate levels
Institute of Scientific and Technical Information of China (English)
Petros Zezos; Georgia Papaioannou; Nikolaos Nikolaidis; Themistoclis Vasiliadis; Olga Giouleme; Nikolaos Evgenidis
2005-01-01
AIM: To study the prevalence and clinical significance of hyperhomocysteinemia (hHcys), an independent factor for arterial and venous thrombosis, in a group of patients with ulcerative colitis (UC).METHODS: Fasting homocysteine (Hcys), folate, and vitamin B12 serum levels were measured in 40 UC patients and 50 healthy controls. Clinical data regarding UC were gathered.RESULTS: Median serum Hcys levels in UC patients were similar to those in controls (12.26 μmol/L vs 12.32 μmol/L), but the prevalence of hHcys was higher in UC patients than in controls (30% vs 10%, P= 0.028). UC significantly increased the risk of hHcys (adjusted odds ratio: 4.125;95% CI: 1.26-13.44). Multivariate regression analysis showed that male sex, folate and vitamin B12 deficiency or lower serum values were significant independent predictors of higher Hcys levels in UC patients (r2 = 0.4; P＜0.001).CONCLUSION: hHcys is common in UC patients and it is related to folate and vitamin B12 deficiency or lower serum values. It would be reasonable for patients with UC to receive folate and vitamin B complex supplements as a prophylactic measure.
BIFURCATION OF A SHAFT WITH HYSTERETIC-TYPE INTERNAL FRICTION FORCE OF MATERIAL
Institute of Scientific and Technical Information of China (English)
丁千; 陈予恕
2003-01-01
The bifurcation of a shaft with hysteretic internal friction of material was analysed. Firstly, the differential motion equation in complex form was deduced using Hamilton principle. Then averaged equations in primary resonances were obtained using the averaging method. The stability of steady-state responses was also determined. Lastly, the bifurcations of both normal motion (synchronous whirl) and self-excited motion (nonsynchronous whirl) were investigated using the method of singularity. The study shows that by a rather large disturbance, the stability of the shaft can be lost through Hopf bifurcation in case the stability condition is not satisfied. The averaged self-excited response appears as a type of unsymmetrical bifurcation with high orders of co-dimension. The second Hopf bifurcation, which corresponds to double amplitude-modulated response, can occur as the speed of the shaft increases. Balancing the shaft carefully to decrease its unbalance level and increasing the external damping are two effective methods to avoid the appearance of the self-sustained whirl induced by the hysteretic internal friction of material.
Directory of Open Access Journals (Sweden)
William H Barnett
Full Text Available The dynamics of individual neurons are crucial for producing functional activity in neuronal networks. An open question is how temporal characteristics can be controlled in bursting activity and in transient neuronal responses to synaptic input. Bifurcation theory provides a framework to discover generic mechanisms addressing this question. We present a family of mechanisms organized around a global codimension-2 bifurcation. The cornerstone bifurcation is located at the intersection of the border between bursting and spiking and the border between bursting and silence. These borders correspond to the blue sky catastrophe bifurcation and the saddle-node bifurcation on an invariant circle (SNIC curves, respectively. The cornerstone bifurcation satisfies the conditions for both the blue sky catastrophe and SNIC. The burst duration and interburst interval increase as the inverse of the square root of the difference between the corresponding bifurcation parameter and its bifurcation value. For a given set of burst duration and interburst interval, one can find the parameter values supporting these temporal characteristics. The cornerstone bifurcation also determines the responses of silent and spiking neurons. In a silent neuron with parameters close to the SNIC, a pulse of current triggers a single burst. In a spiking neuron with parameters close to the blue sky catastrophe, a pulse of current temporarily silences the neuron. These responses are stereotypical: the durations of the transient intervals-the duration of the burst and the duration of latency to spiking-are governed by the inverse-square-root laws. The mechanisms described here could be used to coordinate neuromuscular control in central pattern generators. As proof of principle, we construct small networks that control metachronal-wave motor pattern exhibited in locomotion. This pattern is determined by the phase relations of bursting neurons in a simple central pattern generator
The 'Sphere': A Dedicated Bifurcation Aneurysm Flow-Diverter Device.
Peach, Thomas; Cornhill, J Frederick; Nguyen, Anh; Riina, Howard; Ventikos, Yiannis
2014-01-01
We present flow-based results from the early stage design cycle, based on computational modeling, of a prototype flow-diverter device, known as the 'Sphere', intended to treat bifurcation aneurysms of the cerebral vasculature. The device is available in a range of diameters and geometries and is constructed from a single loop of NITINOL(®) wire. The 'Sphere' reduces aneurysm inflow by means of a high-density, patterned, elliptical surface that partially occludes the aneurysm neck. The device is secured in the healthy parent vessel by two armatures in the shape of open loops, resulting in negligible disruption of parent or daughter vessel flow. The device is virtually deployed in six anatomically accurate bifurcation aneurysms: three located at the Basilar tip and three located at the terminus bifurcation of the Internal Carotid artery (at the meeting of the middle cerebral and anterior cerebral arteries). Both steady state and transient flow simulations reveal that the device presents with a range of aneurysm inflow reductions, with mean flow reductions falling in the range of 30.6-71.8% across the different geometries. A significant difference is noted between steady state and transient simulations in one geometry, where a zone of flow recirculation is not captured in the steady state simulation. Across all six aneurysms, the device reduces the WSS magnitude within the aneurysm sac, resulting in a hemodynamic environment closer to that of a healthy vessel. We conclude from extensive CFD analysis that the 'Sphere' device offers very significant levels of flow reduction in a number of anatomically accurate aneurysm sizes and locations, with many advantages compared to current clinical cylindrical flow-diverter designs. Analysis of the device's mechanical properties and deployability will follow in future publications.
BIFURCATION ANALYSIS OF EQUILIBRIUM POINT IN TWO NODE POWER SYSTEM
Directory of Open Access Journals (Sweden)
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.
Structural and diffusional brain abnormality related to relatively low level alcohol consumption.
Sasaki, Hiroki; Abe, Osamu; Yamasue, Hidenori; Fukuda, Rin; Yamada, Haruyasu; Takei, Kunio; Suga, Motomu; Takao, Hidemasa; Kasai, Kiyoto; Aoki, Shigeki; Ohtomo, Kuni
2009-06-01
Chronic excessive alcohol intake results in alcohol-related brain damage. Many previous reports have documented alcohol-related global or local brain shrinkage or diffusional abnormalities among alcoholics and heavy to moderate drinkers; however, the influence of relatively low levels of alcohol consumption on brain structural or diffusional abnormality is unclear. We investigated structural or diffusional abnormalities related to lifetime alcohol consumption (LAC) using voxel-based morphometry (VBM) among Japanese non-alcohol-dependent individuals (114 males, 97 females). High-resolution three-dimensional magnetic resonance images and diffusion tensor imaging were acquired in all subjects. The collected images were normalized, segmented, and smoothed using SPM 5. Gray matter volume (GMV) and white matter volume (WMV) were normalized for each total intracranial volume (TIV), and partial correlation coefficients were estimated between normalized GMV or WMV and lifetime alcohol consumption (LAC) adjusted for age. To investigate regional GMV or WMV abnormalities related to LAC, multiple regression analyses were performed among regional GMV or WMV and LAC, age, and TIV. To investigate subtle regional abnormalities, multiple regression analyses were performed among fractional anisotropy (FA) or mean diffusivity (MD), and LAC and age. No LAC-related global or regional GMV or WMV abnormality or LAC-related regional FA abnormality was found among male or female subjects. Significant LAC-related MD increase was found in the right amygdala among female subjects only. The current results suggest female brain vulnerability to alcohol, and a relation between subtle abnormality in the right amygdala and alcohol misuse.
Transport bifurcation induced by sheared toroidal flow in tokamak plasmasa)
Highcock, E. G.; Barnes, M.; Parra, F. I.; Schekochihin, A. A.; Roach, C. M.; Cowley, S. C.
2011-10-01
First-principles numerical simulations are used to describe a transport bifurcation in a differentially rotating tokamak plasma. Such a bifurcation is more probable in a region of zero magnetic shear than one of finite magnetic shear, because in the former case the component of the sheared toroidal flow that is perpendicular to the magnetic field has the strongest suppressing effect on the turbulence. In the zero-magnetic-shear regime, there are no growing linear eigenmodes at any finite value of flow shear. However, subcritical turbulence can be sustained, owing to the existence of modes, driven by the ion temperature gradient and the parallel velocity gradient, which grow transiently. Nonetheless, in a parameter space containing a wide range of temperature gradients and velocity shears, there is a sizeable window where all turbulence is suppressed. Combined with the relatively low transport of momentum by collisional (neoclassical) mechanisms, this produces the conditions for a bifurcation from low to high temperature and velocity gradients. A parametric model is constructed which accurately describes the combined effect of the temperature gradient and the flow gradient over a wide range of their values. Using this parametric model, it is shown that in the reduced-transport state, heat is transported almost neoclassically, while momentum transport is dominated by subcritical parallel-velocity-gradient-driven turbulence. It is further shown that for any given input of torque, there is an optimum input of heat which maximises the temperature gradient. The parametric model describes both the behaviour of the subcritical turbulence (which cannot be modelled by the quasi-linear methods used in current transport codes) and the complicated effect of the flow shear on the transport stiffness. It may prove useful for transport modelling of tokamaks with sheared flows.
Static and dynamic bifurcations in magnetoelastic ribbons (abstract)
Savage, H. T.; Adler, Charles; Antman, Stuart S.; Melamud, M.
1987-04-01
The ΔE effect in certain field annealed amorphous ribbon is now about 10, i.e., Young's modulus E, can be reversibly changed by a factor of 9 with the application of a field of less than 1 Oe. We have reported the field-induced buckling of a vertically oriented ribbon. The ribbon buckles under its own weight due to the reduction of E with field H. Critical buckling values of H were found to be in good agreement with the eigenvalues of the linearized version of the operator describing the process. Here we present: (a) holographic data where the gradient in the fringe spacing obtained from the hologram of the straight and buckled states is a measure of the curvature; and (b) a rigorous mathematical formalism for extracting from experiment the nonlinear constitutive relation between the curvature θ'(s) and the bending couple m(s) where s is the distance along the ribbon. This process must be carried out (with H as a parameter) from H=0, to values of H somewhat above the anisotropy field, to effect a complete description of the magnetoelastic behavior. In dynamic experiments where the ribbon is driven by H=H0+h sin ωt we observe a subharmonic bifurcation (parametric resonance) when ω is about twice the half-wavelength elastic resonance frequency and h exceeds a threshold value governed by the magnitude of ∂E/∂H. Other, more complicated bifurcations are seen as h is increased further. We show the nonlinear equation of motion with damping to explain the bifurcation structure.
Bharadvaj, B K; Mabon, R F; Giddens, D P
1982-01-01
The evidence for hypothesizing a relationship between hemodynamics and atherogenesis as well as the motivation for selecting the carotid bifurcation for extensive fluid dynamic studies has been discussed in Part I of this two-paper sequence. Part II deals with velocity measurements within the bifurcation model described by Fig. 1 and Table 1 of the previous paper. A plexiglass model conforming to the dimensions of the average carotid bifurcation was machined and employed for velocity measurements with a laser-Doppler anemometer (LDA). The objective of this phase of the study was to obtain quantitative information on the velocity field and to estimate levels and directions of wall shear stress in the region of the bifurcation.
Analysis of Bifurcation and Nonlinear Control for Chaos in Gear Transmission System
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Wang Jingyue
2013-07-01
Full Text Available In order to study the bifurcation characteristics and control chaotic vibration of the gear transmission system. The complex dynamics characters of gear transmission system are studied. The dynamical equation and the state equation of gear transmission system are established according to Newton's rule. The route to chaos of the system is studied by the bifurcation diagram, phase portrait, time course diagram and Poincaré map. A method of controlling chaos by nonlinear feedback controller is developed to guide chaotic motions towards regular motions. Numerical simulation shows that with the increase of meshing stiffness, gear transmission system will be from the periodic motion to chaotic motion by doubling bifurcation, the effectiveness and feasibility of the strategy to get rid of chaos by stabilizing the related unstable periodic orbit.
Bifurcation and neck formation as a precursor to ductile fracture during high rate extension
Energy Technology Data Exchange (ETDEWEB)
Freund, L.B.; Soerensen, N.J. [Brown Univ., Providence, RI (United States)
1997-12-31
A block of ductile material, typically a segment of a plate or shell, being deformed homogeneously in simple plane strain extension commonly undergoes a bifurcation in deformation mode to nonuniform straining in the advanced stages of plastic flow. The focus here is on the influence of material inertia on the bifurcation process, particularly on the formation of diffuse necks as precursors to dynamic ductile fracture. The issue is considered from two points of view, first within the context of the theory of bifurcation of rate-independent, incrementally linear materials and then in terms of the complete numerical solution of a boundary value problem for an elastic-viscoplastic material. It is found that inertia favors the formation of relatively short wavelength necks as observed in shaped charge break-up and dynamic fragmentation.
The bifurcation threshold value of the chaos detection system for a weak signal
Institute of Scientific and Technical Information of China (English)
李月; 杨宝俊; 杜立志; 袁野
2003-01-01
Recently, it has become an important problem to confirm the bifurcation threshold value of a chaos detectionsystem for a weak signal in the fields of chaos detection. It is directly related to whether the results of chaos detectionare correct or not. In this paper, the discrimination system for the dynamic behaviour of a chaos detection system fora weak signal is established by using the theory of linear differential equation with periodic coefficients and computingthe Lyapunov exponents of the chaos detection system; and then, the movement state of the chaos detection system isdefined. The simulation experiments show that this method can exactly confirm the bifurcation threshold value of thechaos detection system.
Bilman, Els M; Kleef, Ellen van; Mela, David J; Hulshof, Toine; van Trijp, Hans C M
2012-12-01
The aim of this study was to explore (a) whether and how consumers may (over-) interpret satiety claims, and (b) whether and to what extent consumers recognize that personal efforts are required to realize possible satiety-related or weight loss benefits. Following means-end chain theory, we explored for a number of satiety claims the extent of inference-making to higher-level benefits than actually stated in the claim, using internet-based questions and tasks. Respondents (N=1504) in U.K., France, Italy and Germany participated in the study. The majority of these respondents correctly interpret satiety-related claims; i.e. they largely limit their interpretation to what was actually stated. They do not expect a "magic bullet" effect, but understand that personal efforts are required to translate product attributes into potential weight control benefits. Less-restrained eaters were at lower risk for over-interpreting satiety-related claims, whilst respondents with a stronger belief that their weight is something that they can control accept more personal responsibility, and better understand that personal efforts are required to be effective in weight control. Overall, these results indicate there is likely to be a relatively low level of consumer misinterpretation of satiety-related claims on food products.
Han, Xiujing; Chen, Zhenyang; Bi, Qinsheng
2016-02-01
We propose a simple one-dimensional non-autonomous map, in which some novel bursting patterns (e.g., "fold/double inverse flip" bursting, "fold/multiple inverse flip" bursting, and "fold/a cascade of inverse flip" bursting) can be observed. Typically, these bursting patterns exhibit complex structures containing a chain of inverse period-doubling bifurcations. The active states related to these bursting can be period-2(n) (n = 1, 2, 3,…) attractors or chaotic attractors, which may evolve to quiescence by a chain of inverse period-doubling bifurcations when the slow excitation decreases through period-doubling bifurcation points of the map. This accounts for the complex inverse period-doubling bifurcation structures observed in bursting patterns. Our findings enrich the possible routes to bursting as well as the underlying mechanisms of bursting.
Institute of Scientific and Technical Information of China (English)
Ma Shao-Juan; Xu Wei; Li Wei; Fang Tong
2006-01-01
The Chebyshev polynomial approximation is applied to investigate the stochastic period-doubling bifurcation and chaos problems of a stochastic Duffing-van der Pol system with bounded random parameter of exponential probability density function subjected to a harmonic excitation. Firstly the stochastic system is reduced into its equivalent deterministic one, and then the responses of stochastic system can be obtained by numerical methods. Nonlinear dynamical behaviour related to stochastic period-doubling bifurcation and chaos in the stochastic system is explored. Numerical simulations show that similar to its counterpart in deterministic nonlinear system of stochastic period-doubling bifurcation and chaos may occur in the stochastic Duffing-van der Pol system even for weak intensity of random parameter.Simply increasing the intensity of the random parameter may result in the period-doubling bifurcation which is absent from the deterministic system.
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...... of a microwave-driven Josephson junction confirm the theory. Results should be of interest in parametric-amplification studies....
Sex differences in intracranial arterial bifurcations
DEFF Research Database (Denmark)
Lindekleiv, Haakon M; Valen-Sendstad, Kristian; Morgan, Michael K
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....... The 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....
Sex differences in intracranial arterial bifurcations
DEFF Research Database (Denmark)
Lindekleiv, Haakon M; Valen-Sendstad, Kristian; Morgan, Michael K;
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....... The 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....
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....
The relation between oxygen saturation level and retionopathy of prematurity
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Mohammad Gharavi Fard
2016-03-01
Full Text Available Introduction: Oxygen therapy used for preterm infant disease might be associated with oxygen toxicity or oxidative stress. The exact oxygen concentration to control and maintain the arterial oxygen saturation balance is not certainly clear. We aimed to compare the efficacy of higher or lower oxygen saturations on the development of severe retinopathy of prematurity which is a major cause of blindness in preterm neonates. Methods: PubMed was searched for obtaining the relevant articles. A total of seven articles were included after studying the titles, abstracts, and the full text of retrieved articles at initial search. Inclusion criteria were all the English language human clinical randomized controlled trials with no time limitation, which studied the efficacy of low versus high oxygen saturation measured by pulse oximetry in preterm infants.Result: It can be suggested that lower limits of oxygen saturations have higher efficacy at postmesetural age of ≤28 weeks in preterm neonates. This relation has been demonstrated in five large clinical trials including three Boost trials, COT, and Support.Discussion: Applying higher concentrations of oxygen supplementations at mesentural age ≥32 weeks reduced the development of retinopathy of prematurity. Lower concentrations of oxygen saturation decreased the incidence and the development of retinopathy of prematurity in preterm neonates while applied soon after the birth.Conclusions: Targeting levels of oxygen saturation in the low or high range should be performed cautiously with attention to the postmesentural age in preterm infants at the time of starting the procedures.
Codimension two bifurcation of a vibro-bounce system
Institute of Scientific and Technical Information of China (English)
Guanwei Luo; Yandong Chu; Yanlong Zhang; Jianhua Xie
2005-01-01
A three-degree-of-freedom vibro-bounce system is considered. The disturbed map of period one single-impact motion is derived analytically. A center manifold theorem dimensional one, and the normal form map associated with Hopf-flip bifurcation is obtained. Dynamical behavior of the system, near the point of codimension two bifurcation, is investigated by using qualitative analysis and numerical simulation. It is found that near the point of Hopf-flip bifurcation there exists not only Hopf bifurcation of period one singleimpact motion, but also Hopf bifurcation of period two double-impact motion. The results from simulation show that there exists an interesting torus doubling bifurcation near the codimension two bifurcation. The torus doubling bifurcation makes the quasi-periodic attractor associated with period one single-impact motion transform to the other quasi-periodic attractor represented by two attracting closed circles. The torus bifurcation is qualitatively different from the typical torus doubling bifurcation occurring in the vibro-impact systems. Different routes from period one single-impact motion to chaos are observed by numerical simulation.
Bifurcations and safe regions in open Hamiltonians
Energy Technology Data Exchange (ETDEWEB)
Barrio, R; Serrano, S [GME, Dpto Matematica Aplicada and IUMA, Universidad de Zaragoza, E-50009 Zaragoza (Spain); Blesa, F [GME, Dpto Fisica Aplicada, Universidad de Zaragoza, E-50009 Zaragoza (Spain)], E-mail: rbarrio@unizar.es, E-mail: fblesa@unizar.es, E-mail: sserrano@unizar.es
2009-05-15
By using different recent state-of-the-art numerical techniques, such as the OFLI2 chaos indicator and a systematic search of symmetric periodic orbits, we get an insight into the dynamics of open Hamiltonians. We have found that this kind of system has safe bounded regular regions inside the escape region that have significant size and that can be located with precision. Therefore, it is possible to find regions of nonzero measure with stable periodic or quasi-periodic orbits far from the last KAM tori and far from the escape energy. This finding has been possible after a careful combination of a precise 'skeleton' of periodic orbits and a 2D plate of the OFLI2 chaos indicator to locate saddle-node bifurcations and the regular regions near them. Besides, these two techniques permit one to classify the different kinds of orbits that appear in Hamiltonian systems with escapes and provide information about the bifurcations of the families of periodic orbits, obtaining special cases of bifurcations for the different symmetries of the systems. Moreover, the skeleton of periodic orbits also gives the organizing set of the escape basin's geometry. As a paradigmatic example, we study in detail the Henon-Heiles Hamiltonian, and more briefly the Barbanis potential and a galactic Hamiltonian.
Bifurcations and safe regions in open Hamiltonians
Barrio, R.; Blesa, F.; Serrano, S.
2009-05-01
By using different recent state-of-the-art numerical techniques, such as the OFLI2 chaos indicator and a systematic search of symmetric periodic orbits, we get an insight into the dynamics of open Hamiltonians. We have found that this kind of system has safe bounded regular regions inside the escape region that have significant size and that can be located with precision. Therefore, it is possible to find regions of nonzero measure with stable periodic or quasi-periodic orbits far from the last KAM tori and far from the escape energy. This finding has been possible after a careful combination of a precise 'skeleton' of periodic orbits and a 2D plate of the OFLI2 chaos indicator to locate saddle-node bifurcations and the regular regions near them. Besides, these two techniques permit one to classify the different kinds of orbits that appear in Hamiltonian systems with escapes and provide information about the bifurcations of the families of periodic orbits, obtaining special cases of bifurcations for the different symmetries of the systems. Moreover, the skeleton of periodic orbits also gives the organizing set of the escape basin's geometry. As a paradigmatic example, we study in detail the Hénon-Heiles Hamiltonian, and more briefly the Barbanis potential and a galactic Hamiltonian.
CONTROL OF A SADDLE NODE BIFURCATION IN A POWER SYSTEM USING A PID CONTROLLER
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J. Alvarez
2003-04-01
Full Text Available In this work, we present the elimination of a saddle-node bifurcation in a basic power system using a PIDcontroller. In addition, a stability analysis of the rotor angle and its frequency, which are directly related tovoltage collapse problem, is presented.
(r,s)-STABILITY OF UNFOLDING OF Γ-EQUIVARIANT BIFURCATION PROBLEM
Institute of Scientific and Technical Information of China (English)
Liu Hengxing; Zhang Dunmu
2005-01-01
In this paper,the Γ-equivariant (s, t)-equivalence relation and Γ-equivariant infinitesimally (r, s)-stability of Γ-equivariant bifurcation problem are defined. The criterion for Γ-equivariant infinitesimally (r, s)-stability is proven when Γ is a compact finite Lie group . Transversality condition is used to characterize the stability.
Bifurcation analysis of 3D ocean flows using a parallel fully-implicit ocean model
Thies, J.; Wubs, F.W.; Dijkstra, H.A.
2009-01-01
To understand the physics and dynamics of the ocean circulation, techniques of numerical bifurcation theory such as continuation methods have proved to be useful. Up to now these techniques have been applied to models with relatively few degrees of freedom such as multi-layer quasi-geostrophic and s
Bifurcations of the Lagrangian orbits from the classical to the curved 3-body problem
Diacu, Florin
2016-11-01
We consider the 3-body problem of celestial mechanics in Euclidean, elliptic, and hyperbolic spaces and study how the Lagrangian (equilateral) relative equilibria bifurcate when the Gaussian curvature varies. We thus prove the existence of new classes of orbits. In particular, we find some families of isosceles triangles, which occur in elliptic space.
Resonances and bifurcations in systems with elliptical equipotentials
Marchesiello, Antonella
2012-01-01
We present a general analysis of the orbit structure of 2D potentials with self-similar elliptical equipotentials by applying the method of Lie transform normalization. We study the most relevant resonances and related bifurcations. We find that the 1:1 resonance is associated only to the appearance of the loops and leads to the destabilization of either one or the other normal modes, depending on the ellipticity of equipotentials. Inclined orbits are never present and may appear only when the equipotentials are heavily deformed. The 1:2 resonance determines the appearance of bananas and anti-banana orbits: the first family is stable and always appears at a lower energy than the second, which is unstable. The bifurcation sequence also produces the variations in the stability character of the major axis orbit and is modified only by very large deformations of the equipotentials. Higher-order resonances appear at intermediate or higher energies and can be described with good accuracy.
Consequences of entropy bifurcation in non-Maxwellian astrophysical environments
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M. P. Leubner
2008-07-01
Full Text Available Non-extensive systems, accounting for long-range interactions and correlations, are fundamentally related to non-Maxwellian distributions where a duality of equilibria appears in two families, the non-extensive thermodynamic equilibria and the kinetic equilibria. Both states emerge out of particular entropy generalization leading to a class of probability distributions, where bifurcation into two stationary states is naturally introduced by finite positive or negative values of the involved entropic index kappa. The limiting Boltzmann-Gibbs-Shannon state (BGS, neglecting any kind of interactions within the system, is subject to infinite entropic index and thus characterized by self-duality. Fundamental consequences of non-extensive entropy bifurcation, manifest in different astrophysical environments, as particular core-halo patterns of solar wind velocity distributions, the probability distributions of the differences of the fluctuations in plasma turbulence as well as the structure of density distributions in stellar gravitational equilibrium are discussed. In all cases a lower entropy core is accompanied by a higher entropy halo state as compared to the standard BGS solution. Data analysis and comparison with high resolution observations significantly support the theoretical requirement of non-extensive entropy generalization when dealing with systems subject to long-range interactions and correlations.
Bifurcation property and persistence of configurations for parallel mechanisms
Institute of Scientific and Technical Information of China (English)
王玉新; 王仪明; 刘学深
2003-01-01
The configuration of parallel mechanisms at the singularity position is uncertain. How to control the mechanism through the singularity position with a given configuration is one of the key problems of the robot controlling. In this paper the bifurcation property and persistence of configurations at the singularity position is investigated for 3-DOF parallel mechanisms. The dimension of the bifurcation equations is reduced by Liapunov-Schmidt reduction method. According to the strong equivalence condition, the normal form which is consistent with the bifurcation condition of the original equation is selected. Through universal unfolding of the bifurcation equation, the influences of the disturbance factors, such as the influence of length of the input component on the configuration persistence at the bifurcation position, are analyzed. Using this method we can obtain the bifurcation curve in which the configuration will be held when the mechanism passes through the singularity position. Therefore, the configuration is under control in this way.
Simplest Normal Forms of Generalized Neimark-Sacker Bifurcation
Institute of Scientific and Technical Information of China (English)
DING Yumei; ZHANG Qichang
2009-01-01
The normal forms of generalized Neimark-Sacker bifurcation are extensively studied using normal form theory of dynamic system. It is well known that if the normal forms of the generalized Neimark-Sacker bifurcation are expressed in polar coordinates, then all odd order terms must, in general, remain in the normal forms. In this paper, five theorems are presented to show that the conventional Neimark-Sacker bifurcation can be further simpli-fied. The simplest normal forms of generalized Neimark-Sacker bifurcation are calculated. Based on the conven-tional normal form, using appropriate nonlinear transformations, it is found that the generalized Neimark-Sacker bifurcation has at most two nonlinear terms remaining in the amplitude equations of the simplest normal forms up to any order. There are two kinds of simplest normal forms. Their algebraic expression formulas of the simplest nor-mal forms in terms of the coefficients of the generalized Neimark-Sacker bifurcation systems are given.
Bifurcation structure of a model of bursting pancreatic cells
DEFF Research Database (Denmark)
Mosekilde, Erik; Lading, B.; Yanchuk, S.;
2001-01-01
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 transition from this structure to the so-called period-adding structure is found to involve a subcritical period-doubling bifurcation and the emergence of type-III intermittency. The period-adding transition itself is not smooth but consists of a saddle-node bifurcation in which (n + 1)-spike bursting...... behavior is born, slightly overlapping with a subcritical period-doubling bifurcation in which n-spike bursting behavior loses its stability....
Codimension 2 reversible heteroclinic bifurcations with inclination flips
Institute of Scientific and Technical Information of China (English)
XU YanCong; ZHU DeMing; DENG GuiFeng
2009-01-01
In this paper,the heteroclinic bifurcation problem with real eigenvalues and two inclination-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.
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.
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.
Global Bifurcation of a Novel Computer Virus Propagation Model
Directory of Open Access Journals (Sweden)
Jianguo Ren
2014-01-01
Full Text Available In a recent paper by J. Ren et al. (2012, a novel computer virus propagation model under the effect of the antivirus ability in a real network is established. The analysis there only partially uncovers the dynamics behaviors of virus spread over the network in the case where around bifurcation is local. In the present paper, by mathematical analysis, it is further shown that, under appropriate parameter values, the model may undergo a global B-T bifurcation, and the curves of saddle-node bifurcation, Hopf bifurcation, and homoclinic bifurcation are obtained to illustrate the qualitative behaviors of virus propagation. On this basis, a collection of policies is recommended to prohibit the virus prevalence. To our knowledge, this is the first time the global bifurcation has been explored for the computer virus propagation. Theoretical results and corresponding suggestions may help us suppress or eliminate virus propagation in the network.
Characterization of static bifurcations for n-dimensional flows in the frequency domain
Institute of Scientific and Technical Information of China (English)
Li ZENG; Yi ZHAO
2006-01-01
In this paper n-dimensional flows (described by continuous-time system) with static bifurcations are considered with the aim of classification of different elementary bifurcations using the frequency domain formalism. Based on frequency domain approach, we prove some criterions for the saddle-node bifurcation, transcritical bifurcation and pitchfork bifurcation, and give an example to illustrate the efficiency of the result obtained.
Bifurcation analysis in single-species population model with delay
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
A single-species population model is investigated in this paper.Firstly,we study the existence of Hopf bifurcation at the positive equilibrium.Furthermore,an explicit algorithm for determining the direction of the Hopf bifurcation and stability of the bifurcation periodic solutions are derived by using the normal form and the center manifold theory.At last,numerical simulations to support the analytical conclusions are carried out.
BIFURCATIONS OF TRAVELLING WAVE SOLUTIONS IN VARIANT BOUSSINESQ EQUATIONS
Institute of Scientific and Technical Information of China (English)
YUAN Yu-bo; PU Dong-mei; LI Shu-min
2006-01-01
The bifurcations of solitary waves and kink waves for variant Boussinesq equations are studied by using the bifurcation theory of planar dynamical systems. The bifurcation sets and the numbers of solitary waves and kink waves for the variant Boussinesq equations are presented. Several types explicit formulas of solitary waves solutions and kink waves solutions are obtained. In the end, several formulas of periodic wave solutions are presented.
Nonlinear physical systems spectral analysis, stability and bifurcations
Kirillov, Oleg N
2013-01-01
Bringing together 18 chapters written by leading experts in dynamical systems, operator theory, partial differential equations, and solid and fluid mechanics, this book presents state-of-the-art approaches to a wide spectrum of new and challenging stability problems.Nonlinear Physical Systems: Spectral Analysis, Stability and Bifurcations focuses on problems of spectral analysis, stability and bifurcations arising in the nonlinear partial differential equations of modern physics. Bifurcations and stability of solitary waves, geometrical optics stability analysis in hydro- and magnetohydrodynam
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.
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
Bifurcations in two coupled Rössler systems
DEFF Research Database (Denmark)
Rasmussen, J; Mosekilde, Erik; Reick, C.
1996-01-01
The paper presents a detailed bifurcation analysis of two symmetrically coupled Rössler systems. The symmetry in the coupling does not allow any one direction to become preferred, and the coupled system is therefore an example of a dissipative system that cannot be considered as effectively one......-dimensional. The results are presented in terms of one- and two-parmeter bifurcation diagrams. A particularly interesting finding is the replacement of some of the period-doubling bifurcations by torus bifurcations. By virtue of this replacement, instead of a Feigenbaum transition to chaos a transition via torus...
Diffusion-driven instability and Hopf bifurcation in Brusselator system
Institute of Scientific and Technical Information of China (English)
LI Bo; WANG Ming-xin
2008-01-01
The Hopf bifurcation for the Brusselator ordinary-differential-equation (ODE)model and the corresponding partial-differential-equation(PDE)model are investigated by using the Hopf bifurcation theorem.The stability of the Hopf bifurcation periodic solution is di8cu88ed by applying the normal form theory and the center manifold theorem.When parameters satisfy some conditions,the spatial homogenous equilibrium solution and the spatial homogenous periodic solution become unstable.Our results show that if parameters are properly chosen,Hopf bifurcation does not occur for the ODE system,but occurs for the PDE system.
Sequences of gluing bifurcations in an analog electronic circuit
Energy Technology Data Exchange (ETDEWEB)
Akhtanov, Sayat N.; Zhanabaev, Zeinulla Zh. [Physico-Technical Department, Al Farabi Kazakh National University, Al Farabi Av. 71, Almaty, 050038 Kazakhstan (Kazakhstan); Zaks, Michael A., E-mail: zaks@math.hu-berlin.de [Institute of Mathematics, Humboldt University, Rudower Chaussee 25, D-12489 Berlin (Germany)
2013-10-01
We report on the experimental investigation of gluing bifurcations in the analog electronic circuit which models a dynamical system of the third order: Lorenz equations with an additional quadratic nonlinearity. Variation of one of the resistances in the circuit changes the coefficient at this nonlinearity and replaces the Lorenz route to chaos by a different scenario which leads, through the sequence of homoclinic bifurcations, from periodic oscillations of the voltage to the irregular ones. Every single bifurcation “glues” in the phase space two stable periodic orbits and creates a new one, with the doubled length: a sequence of such bifurcations results in the birth of the chaotic attractor.
Hopf bifurcation for tumor-immune competition systems with delay
Directory of Open Access Journals (Sweden)
Ping Bi
2014-01-01
Full Text Available In this article, a immune response system with delay is considered, which consists of two-dimensional nonlinear differential equations. The main purpose of this paper is to explore the Hopf bifurcation of a immune response system with delay. The general formula of the direction, the estimation formula of period and stability of bifurcated periodic solution are also given. Especially, the conditions of the global existence of periodic solutions bifurcating from Hopf bifurcations are given. Numerical simulations are carried out to illustrate the the theoretical analysis and the obtained results.
High-codimensional static bifurcations of strongly nonlinear oscillator
Institute of Scientific and Technical Information of China (English)
Zhang Qi-Chang; Wang Wei; Liu Fu-Hao
2008-01-01
The static bifurcation of the parametrically excited strongly nonlinear oscillator is studied.We consider the averaged equations of a system subject to Duffing-van der Pol and quintic strong nonlinearity by introducing the undetermined fundamental frequency into the computation in the complex normal form.To discuss the static bifurcation,the bifurcation problem is described as a 3-codimensional unfolding with Z2 symmetry on the basis of singularity theory.The transition set and bifurcation diagrams for the singularity are presented,while the stability of the zero solution is studied by using the eigenvalues in various parameter regions.
Oscillatory Activities in Regulatory Biological Networks and Hopf Bifurcation
Institute of Scientific and Technical Information of China (English)
YAN Shi-Wei; WANG Qi; XIE Bai-Song; ZHANG Feng-Shou
2007-01-01
Exploiting the nonlinear dynamics in the negative feedback loop, we propose a statistical signal-response model to describe the different oscillatory behaviour in a biological network motif. By choosing the delay as a bifurcation parameter, we discuss the existence of Hopf bifurcation and the stability of the periodic solutions of model equations with the centre manifold theorem and the normal form theory. It is shown that a periodic solution is born in a Hopf bifurcation beyond a critical time delay, and thus the bifurcation phenomenon may be important to elucidate the mechanism of oscillatory activities in regulatory biological networks.
Bifurcation and stability for a nonlinear parabolic partial differential equation
Chafee, N.
1973-01-01
Theorems are developed to support bifurcation and stability of nonlinear parabolic partial differential equations in the solution of the asymptotic behavior of functions with certain specified properties.
Cancer risk in relation to serum copper levels.
Coates, R J; Weiss, N S; Daling, J R; Rettmer, R L; Warnick, G R
1989-08-01
A nested, matched case-control study was conducted to assess the relationship between serum levels of copper and the subsequent risk of cancer. One hundred thirty-three cases of cancer were identified during 1974-1984 among 5000 members of a northwest Washington State employee cohort from whom serum specimens had been previously obtained and stored. Two hundred forty-one controls were selected at random from the cohort and were matched to the cases on the basis of age, sex, race, and date of blood draw. Serum copper levels were measured by atomic absorption spectrometry. Risk of a subsequent diagnosis of cancer was positively associated with serum copper levels, but only among those cases diagnosed within 4 years of the time the serum specimens were collected. Among cases diagnosed more than 4 years after specimen collection, there was no consistent association between serum copper levels and risk. Adjustment for age, sex, race, occupational status, cigarette smoking, family history of cancer, alcohol consumption, and, among females, use of exogenous hormones had no appreciable effect on these relationships. The findings suggest that the presence of cancer may increase serum copper levels several years prior to its diagnosis. They are less supportive of the hypothesis that serum copper levels affect cancer risk.
Burzotta, Francesco; Cook, Brian; Iaizzo, Paul A; Singh, Jasvindar; Louvard, Yves; Latib, Azeem
2015-01-01
The Visible Heart® Laboratory is an original experimental laboratory in which harvested animal hearts are resuscitated and connected to a support machine in order to beat outside the animal body. Resuscitated animal hearts may be exposed to various types of endovascular intervention under full, multimodality inspection. This unique experimental setting allows the performance of percutaneous coronary intervention (PCI) in a setting which resembles a standard catheterisation laboratory set-up, and contemporaneously allows unique multimodality imaging. For these reasons, the performance of PCI on bifurcations in the Visible Heart® Laboratory may improve the knowledge of the dynamic stent deformations and stent-vessel wall interactions associated with the different steps of the various techniques for bifurcation stenting. Furthermore, the collected images may also serve as a novel educative resource for physicians. The performance of bifurcation stenting in the Visible Heart® Laboratory is a promising experimental setting to gain novel information regarding any existing or future PCI technique to treat coronary bifurcations.
The Structure and Bifurcation of Atmospheric Motions
Institute of Scientific and Technical Information of China (English)
刘式适; 刘式达; 付遵涛; 辛国君; 梁福明
2004-01-01
The 3-D spiral structure resulting from the balance between the pressure gradient force, Coriolis force, and viscous force is a common atmospheric motion pattern. If the nonlinear advective terms are considered, this typical pattern can be bifurcated. It is shown that the surface low pressure with convergent cyclonic vorticity and surface high pressure with divergent anticyclonic vorticity are all stable under certain conditions. The anomalous structure with convergent anticyclonic vorticity is always unstable. But the anomalous weak high pressure structure with convergent cyclonic vorticity can exist, and this denotes the cyclone's dying out.
Uniformity pattern and related criteria for two-level factorials
Institute of Scientific and Technical Information of China (English)
FANG; Kaitai; QIN; Hong
2005-01-01
In this paper,the study of projection properties of two-level factorials in view of geometry is reported.The concept of uniformity pattern is defined.Based on this new concept,criteria of uniformity resolution and minimum projection uniformity are proposed for comparing two-level factorials.Relationship between minimum projection uniformity and other criteria such as minimum aberration,generalized minimum aberration and orthogonality is made explict.This close relationship raises the hope of improving the connection between uniform design theory and factorial design theory.Our results provide a justification of orthogonality,minimum aberration,and generalized minimum aberration from a natural geometrical interpretation.
Human brain mercury levels related to exposure to amalgam fillings.
Ertaş, E; Aksoy, A; Turla, A; Karaarslan, E S; Karaarslan, B; Aydın, A; Eken, A
2014-08-01
The safety of dental amalgam as the primary material in dental restoration treatments has been debated since its introduction. It is widely accepted that amalgam restorations continuously release elemental mercury (Hg) vapor, which is inhaled and absorbed by the body and distributed to tissues, including the brain. The aim of the present study was to investigate whether the presence of amalgam fillings is correlated with brain Hg level. The Hg levels in the parietal lobes of the brains of 32 cadavers were analyzed with an atomic absorption spectrometer with the mercury hydride system. A total of 32 brain samples were tested; of these, 10 were from cadavers with amalgam fillings, while 22 of them were amalgam free. Hg was detected in 60.0% (6 of 10) of the samples in the amalgam group and in 36.3% (8 of 22) in the amalgam-free group. The average Hg level of the amalgam group was 0.97 ± 0.83 µg/g (minimum: 0.3 µg/g and maximum: 2.34 µg/g), and in the amalgam-free group, it was 1.06 ± 0.57 µg/g (minimum: 0.17 µg/g and maximum: 1.76 µg/g). The results of the present study showed no correlation between the presence of amalgam fillings and brain Hg level.
Decreased relative brain tissue levels of inositol in fetal hydrocephalus.
Kok, R.D.; Steegers-Theunissen, R.P.M.; Eskes, T.K.A.B.; Heerschap, A.; Berg, P.P. van den
2003-01-01
OBJECTIVE: Inositol seems to play a role in the development of the central nervous system. In this study, the brain tissue level of inositol in fetal hydrocephalus was compared with that of healthy control subjects. STUDY DESIGN: Proton magnetic resonance spectroscopy was used to examine the inosito
SERUM FIBRINOGEN LEVELS AND ITS RELATION TO DIABETIC RETINOPATHY
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Adil Majeed
2015-11-01
Full Text Available BACKGROUND Elevation of plasma fibrinogen is thought to be one of the major risk factors associated with increase in blood viscosity in patients with diabetic retinopathy. Diabetic retinopathy being a microangiopathy, the study was done with the aim to assess the relationship between serum fibrinogen levels in patients with and without diabetic retinopathy. MATERIALS AND METHODS This study was conducted at Government Medical College, Srinagar, in which 101 diabetic patients with and without retinopathy were evaluated. These patients were classified into two groups: 1 Patients with diabetic retinopathy, which included 50 patients. 2 Patients without diabetic retinopathy, which included 51 patients. Each patient was subjected to a comprehensive ocular examination and the results were recorded and analyzed in detail. RESULTS Our study which was prospective, non-randomized hospital based study was undertaken for the period of 18 months to see the association between fibrinogen levels in the blood and the development of diabetic retinopathy. Our study included 101 patients with type-2 diabetes. Among this Group-1 included 50 patients with diabetic retinopathy and Group-2 included 51 patients without diabetic retinopathy. In our study, total number of female patients were 65 (64.35% and males were 36 (35.64%. The mean age for males and females was 57.5 and 54.6 years respectively. Mean duration of diabetes in patients with retinopathy and without retinopathy was 10.9 and 5.7 years respectively. It was observed in our study that most of the patients with diabetic retinopathy had compromised visual acuity in one or both eyes, i.e., Vn>6/60. We found that out of 50 patients with diabetic retinopathy, 36 (72% patients were having raised serum fibrinogen levels, while as out of 51 patients without diabetic retinopathy 17 (33.33% patients were having raised serum fibrinogen levels, and mean serum fibrinogen levels in patients with and without retinopathy
Woodruff, D Cary; Fowler, Denver W
2012-07-01
Within Diplodocoidea (Dinosauria: Sauropoda), phylogenetic position of the three subclades Rebbachisauridae, Dicraeosauridae, and Diplodocidae is strongly influenced by a relatively small number of characters. Neural spine bifurcation, especially within the cervical vertebrae, is considered to be a derived character, with taxa that lack this feature regarded as relatively basal. Our analysis of dorsal and cervical vertebrae from small-sized diplodocoids (representing at least 18 individuals) reveals that neural spine bifurcation is less well developed or absent in smaller specimens. New preparation of the roughly 200-cm long diplodocid juvenile Sauriermuseum Aathal 0009 reveals simple nonbifurcated cervical neural spines, strongly reminiscent of more basal sauropods such as Omeisaurus. An identical pattern of ontogenetically linked bifurcation has also been observed in several specimens of the basal macronarian Camarasaurus, suggesting that this is characteristic of several clades of Sauropoda. We suggest that neural spine bifurcation performs a biomechanical function related to horizontal positioning of the neck that may become significant only at the onset of a larger body size, hence, its apparent absence or weaker development in smaller specimens. These results have significant implications for the taxonomy and phylogenetic position of taxa described from specimens of small body size. On the basis of shallow bifurcation of its cervical and dorsal neural spines, the small diplodocid Suuwassea is more parsimoniously interpreted as an immature specimen of an already recognized diplodocid taxon. Our findings emphasize the view that nonmature dinosaurs often exhibit morphologies more similar to their ancestral state and may therefore occupy a more basal position in phylogenetic analyses than would mature specimens of the same species. In light of this, we stress the need for phylogenetic reanalysis of sauropod clades where vital characters may be ontogenetically
Quaternions in University-Level Physics Considering Special Relativity
Horn, M E
2003-01-01
As an expansion of complex numbers, the quaternions show close relations to numerous physically fundamental concepts. In spite of that, the didactic potential provided by quaternion interrelationships in formulating physical laws are hardly regarded in the current physics curriculum. In particular, many approaches emerge that are useful in conveying the unity of seemingly distinct theories in a didactically convincing manner. This will be exemplified with the help of special relativity. The diverse examples of spatial and space-time rotations are merged into a didactic whole by introducing quaternion transformations and comparing them to the representation using rotation matrices common in physics books.
Relating indoor NO 2 levels to infant personal exposures
Harlos, David P.; Marbury, Marian; Samet, Jonathan; Spengler, John D.
We report here the results of a field survey of personal nitrogen dioxide exposure (PNO 2) of infants and simultaneous indoor NO 2 levels from various points throughout the infants' homes. Personal nitrogen dioxide levels can be predicted by average room NO 2 concentrations when appropriately weighted by infant presence in the room. Bedroom NO 2 concentration alone presents an alternative predictor which is more suitable for use in large scale surveys. Because of the typical infant's peculiar time-location patterns, they receive most of their NO 2 exposures in bedrooms (65 %)and living rooms (32 %), while the kitchen (5 %) and outdoor environments (> 2%)contribute only a small fraction of daily exposure. Average NO 2 exposure during cooking periods can be predicted using passive samplers placed directly over stoves and hours of stove use time.
Ecological public goods games: cooperation and bifurcation.
Hauert, Christoph; Wakano, Joe Yuichiro; Doebeli, Michael
2008-03-01
The Public Goods Game is one of the most popular models for studying the origin and maintenance of cooperation. In its simplest form, this evolutionary game has two regimes: defection goes to fixation if the multiplication factor r is smaller than the interaction group size N, whereas cooperation goes to fixation if the multiplication factor r is larger than the interaction group size N. Hauert et al. [Hauert, C., Holmes, M., Doebeli, M., 2006a. Evolutionary games and population dynamics: Maintenance of cooperation in public goods games. Proc. R. Soc. Lond. B 273, 2565-2570] have introduced the Ecological Public Goods Game by viewing the payoffs from the evolutionary game as birth rates in a population dynamic model. This results in a feedback between ecological and evolutionary dynamics: if defectors are prevalent, birth rates are low and population densities decline, which leads to smaller interaction groups for the Public Goods game, and hence to dominance of cooperators, with a concomitant increase in birth rates and population densities. This feedback can lead to stable co-existence between cooperators and defectors. Here we provide a detailed analysis of the dynamics of the Ecological Public Goods Game, showing that the model exhibits various types of bifurcations, including supercritical Hopf bifurcations, which result in stable limit cycles, and hence in oscillatory co-existence of cooperators and defectors. These results show that including population dynamics in evolutionary games can have important consequences for the evolutionary dynamics of cooperation.
Bifurcation analysis of a delay reaction-diffusion malware propagation model with feedback control
Zhu, Linhe; Zhao, Hongyong; Wang, Xiaoming
2015-05-01
With the rapid development of network information technology, information networks security has become a very critical issue in our work and daily life. This paper attempts to develop a delay reaction-diffusion model with a state feedback controller to describe the process of malware propagation in mobile wireless sensor networks (MWSNs). By analyzing the stability and Hopf bifurcation, we show that the state feedback method can successfully be used to control unstable steady states or periodic oscillations. Moreover, formulas for determining the properties of the bifurcating periodic oscillations are derived by applying the normal form method and center manifold theorem. Finally, we conduct extensive simulations on large-scale MWSNs to evaluate the proposed model. Numerical evidences show that the linear term of the controller is enough to delay the onset of the Hopf bifurcation and the properties of the bifurcation can be regulated to achieve some desirable behaviors by choosing the appropriate higher terms of the controller. Furthermore, we obtain that the spatial-temporal dynamic characteristics of malware propagation are closely related to the rate constant for nodes leaving the infective class for recovered class and the mobile behavior of nodes.
Hypercrater Bifurcations, Attractor Coexistence, and Unfolding in a 5D Model of Economic Dynamics
Directory of Open Access Journals (Sweden)
Toichiro Asada
2011-01-01
Full Text Available Complex dynamical features are explored in a discrete interregional macrodynamic model proposed by Asada et al., using numerical methods. The model is five-dimensional with four parameters. The results demonstrate patterns of dynamical behaviour, such as bifurcation processes and coexistence of attractors, generated by high-dimensional discrete systems. In three cases of two-dimensional parameter subspaces the stability of equilibrium region is determined and its boundaries, the flip and Neimark-Hopf bifurcation curves, are identified by means of necessary coefficient criteria. In the first case closed invariant curves (CICs are found to occur through 5D-crater-type bifurcations, and for certain ranges of parameter values a stable equilibrium coexists with an unstable CIC associated with the subcritical bifurcation, as well as with an outer stable CIC. A remarkable feature of the second case is the coexistence of two attracting CICs outside the stability region. In both these cases the related hysteresis effects are illustrated by numerical simulations. In the third case a remarkable feature is the apparent unfolding of an attracting CIC before it evolves to a chaotic attractor. Examples of CICs and chaotic attractors are given in subspaces of phase space.
Vance, William; Ross, John
1988-05-01
We study experimentally continuous transitions from quasiperiodic to periodic states for a time-periodically forced chemical oscillator. The chemical reaction is the hydration of 2,3-epoxy-1-propanol, and is carried out in a continuous stirred tank reactor (CSTR). Periodic oscillatory states are observed to arise in the autonomous system through supercritical Hopf bifurcations as either the total flow rate or the cooling coil temperature is changed. Under conditions of oscillation for the autonomous system, small-amplitude periodic variation of the total flow rate generates an attracting two-torus from the stable limit cycle. From the experiments we determine the structure of the toroidal flow, stroboscopic phase portraits, and circle maps as a function of the forcing amplitude and period. A continuous transition from the quasiperiodic to a periodic state, in which the two-torus contracts to a closed curve (Neimark-Sacker torus bifurcation), is observed as the forcing amplitude is increased at a constant forcing period, or as the forcing period is changed at a constant moderate forcing amplitude. Qualitative theoretical predictions compare well with the experimental observations. This paper presents the first experimental observation of a Neimark-Sacker torus bifurcation in a forced chemical oscillator system, and relates the bifurcation diagram of the unforced system to that of the forced system.
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.
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.
Hopf Bifurcations of a Chemostat System with Bi-parameters
Institute of Scientific and Technical Information of China (English)
李晓月; 千美华; 杨建平; 黄启昌
2004-01-01
We study a chemostat system with two parameters, S0-initial density and D-flow-speed of the solution. At first, a generalization of the traditional Hopf bifurcation theorem is given. Then, an existence theorem for the Hopf bifurcation of the chemostat system is presented.
Influence of perturbations on period-doubling bifurcation
DEFF Research Database (Denmark)
Svensmark, Henrik; Samuelsen, Mogens Rugholm
1987-01-01
The influence of noise and resonant perturbation on a dynamical system in the vicinity of a period-doubling bifurcation is investigated. It is found that the qualitative dynamics can be revealed by simple considerations of the Poincaré map. These considerations lead to a shift of the bifurcation...
Splitting rivers at their seams: bifurcations and avulsion
Kleinhans, M.G.; Ferguson, R.I.; Lane, S.N.; Hardy, R.J.
2012-01-01
River bifurcations are critical but poorly understood elements of many geomorphological systems. They are integral elements of alluvial fans, braided rivers, fluvial lowland plains, and deltas and control the partitioning of water and sediment through these systems. Bifurcations are commonly unstabl
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.
THE UNFOLDING OF EQUIVARIANT BIFURCATION PROBLEMS WITH PARAMETERS SYMMETRY
Institute of Scientific and Technical Information of China (English)
高守平; 李养成
2004-01-01
In this paper versal unfolding theorem of multiparameter equivariant bifurcation problem with parameter symmetry is given. The necessary and sufficient condition that unfolding of multiparameter equivariant bifurcation problem with parameter symmetry factors through another is given. The corresponding results in [1]-[6] are generalized.
Effects of Hard Limits on Bifurcation, Chaos and Stability
Institute of Scientific and Technical Information of China (English)
Rui-qi Wang; Ji-cai Huang
2004-01-01
An SMIB model in the power systems,especially that concering the effects of hard limits on bifurcations, chaos and stability is studied.Parameter conditions for bifurcations and chaos in the absence of hard limits are compared with those in the presence of hard limits.It has been proved that hard limits can affect system stability.We find that (1)hard limits can change unstable equilibrium into stable one;(2)hard limits can change stability of limit cycles induced by Hopf bifurcation;(3)persistence of hard limits can stabilize divergent trajectory to a stable equilibrium or limit cycle;(4)Hopf bifurcation occurs before SN bifurcation,so the system collapse can be controlled before Hopf bifurcation occurs.We also find that suitable limiting values of hard limits can enlarge the feasibility region.These results are based on theoretical analysis and numerical simulations, such as condition for SNB and Hopf bifurcation,bifurcation diagram,trajectories,Lyapunov exponent,Floquet multipliers,dimension of attractor and so on.
Homoclinic Bifurcation of Orbit Flip with Resonant Principal Eigenvalues
Institute of Scientific and Technical Information of China (English)
Tian Si ZHANG; De Ming ZHU
2006-01-01
Codimension-3 bifurcations of an orbit-flip homoclinic orbit with resonant principal eigenvalues are studied for a four-dimensional system. The existence, number, co-existence and non-coexistence of 1-homoclinic orbit, 1-periodic orbit, 2n-homoclinic orbit and 2n-periodic orbit are obtained. The bifurcation surfaces and existence regions are also given.
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.
Verification of bifurcation diagrams for polynomial-like equations
Korman, Philip; Li, Yi; Ouyang, Tiancheng
2008-03-01
The results of our recent paper [P. Korman, Y. Li, T. Ouyang, Computing the location and the direction of bifurcation, Math. Res. Lett. 12 (2005) 933-944] appear to be sufficient to justify computer-generated bifurcation diagram for any autonomous two-point Dirichlet problem. Here we apply our results to polynomial-like nonlinearities.
The Persistence of a Slow Manifold with Bifurcation
DEFF Research Database (Denmark)
Kristiansen, Kristian Uldall; Palmer, P.; Robert, M.
2012-01-01
his paper considers the persistence of a slow manifold with bifurcation in a slow-fast two degree of freedom Hamiltonian system. In particular, we consider a system with a supercritical pitchfork bifurcation in the fast space which is unfolded by the slow coordinate. The model system is motivated...
Intermittency and Jakobson's theorem near saddle-node bifurcations
Homburg, A.J.; Young, T.
2007-01-01
Abstract. We discuss one parameter families of unimodal maps, with negative Schwarzian derivative, unfolding a saddle-node bifurcation. We show that there is a parameter set of positive but not full Lebesgue density at the bifurcation, for which the maps exhibit absolutely continuous invariant measu
Coarse-grained numerical bifurcation analysis of lattice Boltzmann models
Leemput, P. Van; Lust, K.W.A.; Kevrekidis, I.G.
2005-01-01
In this paper we study the coarse-grained bifurcation analysis approach proposed by I.G. Kevrekidis and collaborators in PNAS [C. Theodoropoulos, Y.H. Qian, I.G. Kevrekidis, "Coarse" stability and bifurcation analysis using time-steppers: a reaction-diffusion example, Proc. Natl. Acad. Sci. 97 (18)
Analysis of Vehicle Steering and Driving Bifurcation Characteristics
Directory of Open Access Journals (Sweden)
Xianbin Wang
2015-01-01
Full Text Available The typical method of vehicle steering bifurcation analysis is based on the nonlinear autonomous vehicle model deriving from the classic two degrees of freedom (2DOF linear vehicle model. This method usually neglects the driving effect on steering bifurcation characteristics. However, in the steering and driving combined conditions, the tyre under different driving conditions can provide different lateral force. The steering bifurcation mechanism without the driving effect is not able to fully reveal the vehicle steering and driving bifurcation characteristics. Aiming at the aforementioned problem, this paper analyzed the vehicle steering and driving bifurcation characteristics with the consideration of driving effect. Based on the 5DOF vehicle system dynamics model with the consideration of driving effect, the 7DOF autonomous system model was established. The vehicle steering and driving bifurcation dynamic characteristics were analyzed with different driving mode and driving torque. Taking the front-wheel-drive system as an example, the dynamic evolution process of steering and driving bifurcation was analyzed by phase space, system state variables, power spectral density, and Lyapunov index. The numerical recognition results of chaos were also provided. The research results show that the driving mode and driving torque have the obvious effect on steering and driving bifurcation characteristics.
Bifurcation behaviours of peak current controlled PFC boost converter
Institute of Scientific and Technical Information of China (English)
Ren Hai-Peng; Liu Ding
2005-01-01
Bifurcation behaviours of the peak current controlled power-factor-correction (PFC) boost converter, including fast-scale instability and low-frequency bifurcation, are investigated in this paper. Conventionally, the PFC converter is analysed in continuous conduction mode (CCM). This prevents us from recognizing the overall dynamics of the converter. It has been pointed out that the discontinuous conduction mode (DCM) can occur in the PFC boost converter, especially in the light load condition. Therefore, the DCM model is employed to analyse the PFC converter to cover the possible DCM operation. By this way, the low-frequency bifurcation diagram is derived, which makes the route from period-double bifurcation to chaos clear. The bifurcation diagrams versus the load resistance and the output capacitance also indicate the stable operation boundary of the converter, which is useful for converter design.
Bifurcations of emerging patterns in the presence of additive noise.
Agez, Gonzague; Clerc, Marcel G; Louvergneaux, Eric; Rojas, René G
2013-04-01
A universal description of the effects of additive noise on super- and subcritical spatial bifurcations in one-dimensional systems is theoretically, numerically, and experimentally studied. The probability density of the critical spatial mode amplitude is derived. From this generalized Rayleigh distribution we predict the shape of noisy bifurcations by means of the most probable value of the critical mode amplitude. Comparisons with numerical simulations are in quite good agreement for cubic or quintic amplitude equations accounting for stochastic supercritical bifurcation and for cubic-quintic amplitude equation accounting for stochastic subcritical bifurcation. Experimental results obtained in a one-dimensional Kerr-like slice subjected to optical feedback confirm the analytical expression prediction for the supercritical bifurcation shape.
Bifurcation of transition paths induced by coupled bistable systems
Tian, Chengzhe; Mitarai, Namiko
2016-06-01
We discuss the transition paths in a coupled bistable system consisting of interacting multiple identical bistable motifs. We propose a simple model of coupled bistable gene circuits as an example and show that its transition paths are bifurcating. We then derive a criterion to predict the bifurcation of transition paths in a generalized coupled bistable system. We confirm the validity of the theory for the example system by numerical simulation. We also demonstrate in the example system that, if the steady states of individual gene circuits are not changed by the coupling, the bifurcation pattern is not dependent on the number of gene circuits. We further show that the transition rate exponentially decreases with the number of gene circuits when the transition path does not bifurcate, while a bifurcation facilitates the transition by lowering the quasi-potential energy barrier.
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.
Streamline topologies and their bifurcations for mixed convective peristaltic flow
Directory of Open Access Journals (Sweden)
Z. Asghar
2015-09-01
Full Text Available In this work our focus is on streamlines patterns and their bifurcations for mixed convective peristaltic flow of Newtonian fluid with heat transfer. The flow is considered in a two dimensional symmetric channel and the governing equations are simplified under widely taken assumptions of large wavelength and low Reynolds number in a wave frame of reference. In order to study the streamlines patterns, a system of nonlinear autonomous differential equations are established and dynamical systems approach is used to discuss the local bifurcations and their topological changes. We have discussed all types of bifurcations and their topological changes are presented graphically. We found that the vortices contract along the vertical direction whereas they expand along horizontal direction. A global bifurcations diagram is used to summarize the bifurcations. The trapping and backward flow regions are mainly affected by increasing Grashof number and constant heat source parameter in such a way that trapping region increases whereas backward flow region shrinks.
Bifurcations and Stability Boundary of a Power System
Institute of Scientific and Technical Information of China (English)
Ying-hui Gao
2004-01-01
A single-axis ux decay model including an excitation control model proposed in [12,14,16] is studied. As the bifurcation parameter P m (input power to the generator) varies, the system exhibits dynamics emerging from static and dynamic bifurcations which link with system collapse. We show that the equilibrium point of the system undergoes three bifurcations: one saddle-node bifurcation and two Hopf bifurcations. The state variables dominating system collapse are different for different critical points, and the excitative control may play an important role in delaying system from collapsing. Simulations are presented to illustrate the dynamical behavior associated with the power system stability and collapse. Moreover, by computing the local quadratic approximation of the 5-dimensional stable manifold at an order 5 saddle point, an analytical expression for the approximate stability boundary is worked out.
Buckel, Wolfgang; Thauer, Rudolf K
2013-02-01
The review describes four flavin-containing cytoplasmatic multienzyme complexes from anaerobic bacteria and archaea that catalyze the reduction of the low potential ferredoxin by electron donors with higher potentials, such as NAD(P)H or H(2) at ≤ 100 kPa. These endergonic reactions are driven by concomitant oxidation of the same donor with higher potential acceptors such as crotonyl-CoA, NAD(+) or heterodisulfide (CoM-S-S-CoB). The process called flavin-based electron bifurcation (FBEB) can be regarded as a third mode of energy conservation in addition to substrate level phosphorylation (SLP) and electron transport phosphorylation (ETP). FBEB has been detected in the clostridial butyryl-CoA dehydrogenase/electron transferring flavoprotein complex (BcdA-EtfBC), the multisubunit [FeFe]hydrogenase from Thermotoga maritima (HydABC) and from acetogenic bacteria, the [NiFe]hydrogenase/heterodisulfide reductase (MvhADG-HdrABC) from methanogenic archaea, and the transhydrogenase (NfnAB) from many Gram positive and Gram negative bacteria and from anaerobic archaea. The Bcd/EtfBC complex that catalyzes electron bifurcation from NADH to the low potential ferredoxin and to the high potential crotonyl-CoA has already been studied in some detail. The bifurcating protein most likely is EtfBC, which in each subunit (βγ) contains one FAD. In analogy to the bifurcating complex III of the mitochondrial respiratory chain and with the help of the structure of the human ETF, we propose a conformational change by which γ-FADH(-) in EtfBC approaches β-FAD to enable the bifurcating one-electron transfer. The ferredoxin reduced in one of the four electron bifurcating reactions can regenerate H(2) or NADPH, reduce CO(2) in acetogenic bacteria and methanogenic archaea, or is converted to ΔμH(+)/Na(+) by the membrane-associated enzyme complexes Rnf and Ech, whereby NADH and H(2) are recycled, respectively. The mainly bacterial Rnf complexes couple ferredoxin oxidation by NAD(+) with
Ecological consequences of global bifurcations in some food chain models.
van Voorn, George A K; Kooi, Bob W; Boer, Martin P
2010-08-01
Food chain models of ordinary differential equations (ode's) are often used in ecology to gain insight in the dynamics of populations of species, and the interactions of these species with each other and their environment. One powerful analysis technique is bifurcation analysis, focusing on the changes in long-term (asymptotic) behaviour under parameter variation. For the detection of local bifurcations there exists standardised software, but until quite recently most software did not include any capabilities for the detection and continuation of global bifurcations. We focus here on the occurrence of global bifurcations in four food chain models, and discuss the implications of their occurrence. In two stoichiometric models (one piecewise continuous, one smooth) there exists a homoclinic bifurcation, that results in the disappearance of a limit cycle attractor. Instead, a stable positive equilibrium becomes the global attractor. The models are also capable of bistability. In two three-dimensional models a Shil'nikov homoclinic bifurcation functions as the organising centre of chaos, while tangencies of homoclinic cycle-to-cycle connections 'cut' the chaotic attractors, which is associated with boundary crises. In one model this leads to extinction of the top predator, while in the other model hysteresis occurs. The types of ecological events occurring because of a global bifurcation will be categorized. Global bifurcations are always catastrophic, leading to the disappearance or merging of attractors. However, there is no 1-on-1 coupling between global bifurcation type and the possible ecological consequences. This only emphasizes the importance of including global bifurcations in the analysis of food chain models.
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
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.
Bifurcations and Patterns in Nonlinear Dissipative Systems
Energy Technology Data Exchange (ETDEWEB)
Guenter Ahlers
2005-05-27
This project consists of experimental investigations of heat transport, pattern formation, and bifurcation phenomena in non-linear non-equilibrium fluid-mechanical systems. These issues are studies in Rayleigh-B\\'enard convection, using both pure and multicomponent fluids. They are of fundamental scientific interest, but also play an important role in engineering, materials science, ecology, meteorology, geophysics, and astrophysics. For instance, various forms of convection are important in such diverse phenomena as crystal growth from a melt with or without impurities, energy production in solar ponds, flow in the earth's mantle and outer core, geo-thermal stratifications, and various oceanographic and atmospheric phenomena. Our work utilizes computer-enhanced shadowgraph imaging of flow patterns, sophisticated digital image analysis, and high-resolution heat transport measurements.
Civan, Adem
2015-01-01
This research was carried out to determine the self-esteem and life quality levels of disabled and non-disabled tennis sportsmen; and also to set forth the relation between their self-esteem and life quality levels. The research group consists of total 44 sportsmen including 22 disabled tennis sportsmen (n[subscript (female)]=9, n[subscript…
Directory of Open Access Journals (Sweden)
G. Vilalta
2008-05-01
section of the arteries as a result of lipid deposit in the inner layer of the vessel. Thepresent paper studies the influence of the blood viscosity in the flow at the carotid bifurcation through the numericalmodeling. The study was carried out for three stenosis levels, (SS=30, 60 and 75 % and five viscosity values, (3,5 cP, 7 cP,20 cP, 35 cP, 50 cP.The results obtained show a significant reduction in the blood flow for viscosities increasing up to 7cP. For greater viscosities values the system flow remains constant, which is consistent with the medical practice.Key words: Fluid dynamic, polymer addition, finite element formulation, carotid bifurcation.
Synchronization and Bifurcation of General Complex Dynamical Networks
Institute of Scientific and Technical Information of China (English)
SUN Wei-Gang; XU Cong-Xiang; LI Chang-Pin; FANG Jin-Qing
2007-01-01
In the present paper, synchronization and bifurcation of general complex dynamical networks are investigated. We mainly focus on networks with a somewhat general coupling matrix, i.e., the sum of each row equals a nonzero constant u. We derive a result that the networks can reach a new synchronous state, which is not the asymptotic limit set determined by the node equation. At the synchronous state, the networks appear bifurcation if we regard the constant u as a bifurcation parameter. Numerical examples are given to illustrate our derived conclusions.
Systematic experimental exploration of bifurcations with noninvasive control.
Barton, D A W; Sieber, J
2013-05-01
We present a general method for systematically investigating the dynamics and bifurcations of a physical nonlinear experiment. In particular, we show how the odd-number limitation inherent in popular noninvasive control schemes, such as (Pyragas) time-delayed or washout-filtered feedback control, can be overcome for tracking equilibria or forced periodic orbits in experiments. To demonstrate the use of our noninvasive control, we trace out experimentally the resonance surface of a periodically forced mechanical nonlinear oscillator near the onset of instability, around two saddle-node bifurcations (folds) and a cusp bifurcation.
Bifurcation control in the Burgers-KdV equation
Energy Technology Data Exchange (ETDEWEB)
Maccari, Attilio [Technical Institute ' G. Cardano' , Piazza della Resistenza 1, 00015 Monterotondo (Rome) (Italy)], E-mail: solitone@yahoo.it
2008-03-15
We consider the bifurcation control for the forced Burgers-KdV equation by means of delay feedback linear terms. We use a perturbation method in order to find amplitude and phase modulation equations as well as external force-response and frequency-response curves. We observe in the resonance response a saddle-node bifurcation that leads to jump and hysteresis phenomena. We compare the uncontrolled and controlled systems and demonstrate that control terms can delay or remove the occurrence of the saddle-node bifurcation and reduce the amplitude peak of the resonant response.
Bifurcation of limit cycles from quartic isochronous systems
Directory of Open Access Journals (Sweden)
Linping Peng
2014-04-01
Full Text Available This article concerns the bifurcation of limit cycles for a quartic system with an isochronous center. By using the averaging theory, it shows that under any small quartic homogeneous perturbations, at most two limit cycles bifurcate from the period annulus of the considered system, and this upper bound can be reached. In addition, we study a family of perturbed isochronous systems and prove that there are at most three limit cycles bifurcating from the period annulus of the unperturbed one, and the upper bound is sharp.
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.
{ital {Delta}I}=4 Bifurcation in Identical Superdeformed Bands
Energy Technology Data Exchange (ETDEWEB)
Haslip, D.; Flibotte, S.; Gervais, G.; Nieminen, J.; Svensson, C.; Waddington, J.; Wilson, J. [Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1 (CANADA); de France, G. [Centre de Recherches Nucleaires et ULP, F-67037 Strasbourg Cedex 2 (France); Devlin, M.; LaFosse, D.; Lerma, F.; Sarantites, D. [Chemistry Department, Washington University, St. Louis, Missouri 63130 (United States); Galindo-Uribarri, A. [AECL, Chalk River Laboratories, Chalk River, Ontario, K0J 1J0 (CANADA); Hackman, G. [Argonne National Laboratory, Argonne, Illinois 60439 (United States); Lee, I.; Macchiavelli, A.; MacLeod, R. [Nuclear Science Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States); Mullins, S. [Department of Nuclear Physics, RSPhysSE, ANU, Canberra, ACT 0200 (Australia)
1997-05-01
{Delta}I=4 bifurcation has been observed in two superdeformed bands, the newly discovered yrast superdeformed band of {sup 148}Eu, and a previously known excited band in {sup 148}Gd. Both of these bands have moments of inertia that are identical to the yrast band of {sup 149}Gd, the first superdeformed band in which this bifurcation was observed. This first observation of {Delta}I=4 bifurcation in identical superdeformed bands provides a crucial test of recent models. {copyright} {ital 1997} {ital The American Physical Society}
Multi-Stream Inflation: Bifurcations and Recombinations in the Multiverse
Wang, Yi
2010-01-01
In this Letter, we briefly review the multi-stream inflation scenario, and discuss its implications in the string theory landscape and the inflationary multiverse. In multi-stream inflation, the inflation trajectory encounters bifurcations. If these bifurcations are in the observable stage of inflation, then interesting observational effects can take place, such as domain fences, non-Gaussianities, features and asymmetries in the CMB. On the other hand, if the bifurcation takes place in the eternal stage of inflation, it provides an alternative creation mechanism of bubbles universes in eternal inflation, as well as a mechanism to locally terminate eternal inflation, which reduces the measure of eternal inflation.
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.
Seasonal variability of the bifurcation of the North Equatorial Current
Institute of Scientific and Technical Information of China (English)
JU Qiang-chang; JIANG Song; TIAN Ji-wei; KONG Ling-hai; NI Guo-xi
2013-01-01
Seasonal variability of the bifurcation of the North Equatorial Current (NEC) is studied by constructing the analytic solution for the time-dependent horizontal linear shallow water quasi-geostrophic equations.Using the Florida State University wind data from 1961 through 1992,we find that the bifurcation latitude of the NEC changes with seasons.Furthermore,it is shown that the NEC bifurcation is at its southernmost latitude (12.7°N) in June and the northernmost latitude (14.4° N) in November.
Delay Induced Hopf Bifurcation of Small-World Networks
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
In this paper, the stability and the Hopf bifurcation of small-world networks with time delay are studied. By analyzing the change of delay, we obtain several sufficient conditions on stable and unstable properties. When the delay passes a critical value, a Hopf bifurcation may appear. Furthermore, the direction and the stability of bifurcating periodic solutions are investigated by the normal form theory and the center manifold reduction. At last, by numerical simulations, we further illustrate the effectiveness of theorems in this paper.
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.
Computational simulations in coronary bifurcations: Paving the future of interventional planning.
Collet, Carlos; Serruys, Patrick W
2016-06-01
Anatomical evaluation is of paramount importance in the treatment of bifurcation lesions. Left main coronary artery bifurcation geometry differs from left anterior descending artery/diagonal and circumflex artery/obtuse marginal bifurcations. Individualized approach with pre-procedural planning has the potential to improve outcomes after bifurcation treatment.
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.
Evolution of Relational Database to Object-Relational Database in Abstract Level
Yugopuspito, Pujianto; Araki, Keijiro
1999-01-01
Relational Database is a mature database with a rigorous specification and is broadly applicable. The deficient in data representation has been known since the software application changed to object oriented. An effort should be taken to encounter the connection between existing Relational Database with a new software application that is object oriented. In a case where a complete migration is not the choice of solution since the existing Relational Database should be preserved, then an Objec...
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.
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.
20 CFR 663.840 - How is the level of needs-related payments determined?
2010-04-01
... 20 Employees' Benefits 3 2010-04-01 2010-04-01 false How is the level of needs-related payments determined? 663.840 Section 663.840 Employees' Benefits EMPLOYMENT AND TRAINING ADMINISTRATION, DEPARTMENT OF... Services § 663.840 How is the level of needs-related payments determined? (a) The payment level for...
Tensor methods for parameter estimation and bifurcation analysis of stochastic reaction networks.
Liao, Shuohao; Vejchodský, Tomáš; Erban, Radek
2015-07-06
Stochastic modelling of gene regulatory networks provides an indispensable tool for understanding how random events at the molecular level influence cellular functions. A common challenge of stochastic models is to calibrate a large number of model parameters against the experimental data. Another difficulty is to study how the behaviour of a stochastic model depends on its parameters, i.e. whether a change in model parameters can lead to a significant qualitative change in model behaviour (bifurcation). In this paper, tensor-structured parametric analysis (TPA) is developed to address these computational challenges. It is based on recently proposed low-parametric tensor-structured representations of classical matrices and vectors. This approach enables simultaneous computation of the model properties for all parameter values within a parameter space. The TPA is illustrated by studying the parameter estimation, robustness, sensitivity and bifurcation structure in stochastic models of biochemical networks. A Matlab implementation of the TPA is available at http://www.stobifan.org.
"Virtual" in-vivo bench test for bifurcation stenting with "StentBoost".
Agostoni, Pierfrancesco; Verheye, Stefan; Vermeersch, Paul; Cornelis, Kristoff; Van Langenhove, Glenn
2009-04-01
"StentBoost" is a new angiographic technique that allows improved angiographic visualization of stents deployed in coronary arteries, by enhancing the X-ray focus of the region where the stent is placed. Using this technique we were able to assess the deformation and the expansion of a stent deployed to treat a bifurcation lesion between the mid-left anterior descending (LAD) artery and a big second diagonal branch, during sequential inflations of: (1) the stent per se in the LAD, (2) the ostium of the diagonal branch through the stent struts, (3) the stent again with a non compliant balloon, and (4) both branches with the kissing balloon technique. "StentBoost" guided our clinical and angiographic decision-making process and allowed us to create a "virtual" bench test of the stent deployed at the level of the bifurcation treated.
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.
Classification of boundary equilibrium bifurcations in planar Filippov systems.
Glendinning, Paul
2016-01-01
If a family of piecewise smooth systems depending on a real parameter is defined on two different regions of the plane separated by a switching surface, then a boundary equilibrium bifurcation occurs if a stationary point of one of the systems intersects the switching surface at a critical value of the parameter. We derive the leading order terms of a normal form for boundary equilibrium bifurcations of planar systems. This makes it straightforward to derive a complete classification of the bifurcations that can occur. We are thus able to confirm classic results of Filippov [Differential Equations with Discontinuous Right Hand Sides (Kluwer, Dordrecht, 1988)] using different and more transparent methods, and explain why the 'missing' cases of Hogan et al. [Piecewise Smooth Dynamical Systems: The Case of the Missing Boundary Equilibrium Bifurcations (University of Bristol, 2015)] are the only cases omitted in more recent work.
Bifurcation of Periodic Orbits and Chaos in Duffing Equation
Institute of Scientific and Technical Information of China (English)
Mei-xiang Cai; Jian-ping Yang
2006-01-01
Duffing equation with fifth nonlinear-restoring force, one external forcing and a phase shift is investigated. The conditions of existences for primary resonance, second-order, third-order subharmonics, morder subharmonics and chaos are given by using second-averaging method, Melnikov methods and bifurcation theory. Numerical simulations including bifurcation diagrams, bifurcation surfaces, phase portraits, not only show the consistence with the theoretical analysis, but also exhibit the new dynamical behaviors. We show the onset of chaos, chaos suddenly disappearing to period orbit, one-band and double-band chaos, period-doubling bifurcations from period 1, 2, and 3 orbits, period-windows (period-2, 3 and 5) in chaotic regions.
Bifurcations of double homoclinic flip orbits with resonant eigenvalues
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Concerns double homoclinic loops with orbit flips and two resonant eigenvalues in a four-dimensional system. We use the solution of a normal form system to construct a singular map in some neighborhood of the equilibrium, and the solution of a linear variational system to construct a regular map in some neighborhood of the double culation gives explicitly an expression of the associated successor function. By a delicate analysis of the bifurcation equation, we obtain the condition that the original double homoclinic loops are kept, and prove the existence and the existence regions of the large 1-homoclinic orbit bifurcation surface, 2-fold large 1-periodic orbit bifurcation surface,large 2-homoclinic orbit bifurcation surface and their approximate expressions. We also locate the large periodic orbits and large homoclinic orbits and their number.
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 APPLIED TO CHIRAL SYMMETRY-BREAKING
ATKINSON, D
1990-01-01
Chiral symmetry breaking in quantum electrodynamics and quantum chromodynamics is considered as a problem in bifurcation theory. Inequalities and positivity play key roles, as they do in much of the work of Andre Martin.
Bifurcation behaviors of catalytic combustion in a micro-channel
Institute of Scientific and Technical Information of China (English)
Wen Zeng; Maozhao Xie; Hongan Maa; Wei Xua
2008-01-01
Bifurcation analysis of ignition and extinction of catalytic combustion in a short micro-channel is carried out with the laminar flow model incorporated as the flow model. The square of transverse Thiele modulus and the realdence time are used as bifurcation parameters. The influences of different parameters on ignition and extinction behavior are investigated. It is shown that all these parameters have great effects on the bifurcation behaviors of ignition and extinction in the short micro-channel. The effects of flow models on bifurcation behaviors of combustion are also analyzed. The results show that in comparison with the fiat velocity profile model, for the case of the laminar flow model, the temperatures of ignition and extinction of combustion ate higher and the unsteady multiple solution region is larger.
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.
Energy Technology Data Exchange (ETDEWEB)
Lanchares, V. [Departamento de Matematicas y Computacion, Universidad de La Rioja, 26004 Logrono (Spain); Inarrea, M.; Salas, J.P. [Area de Fisica Aplicada, Universidad de La Rioja, 26004 Logrono (Spain)
1997-09-01
In a classical model, the dynamics of the hydrogen atom subjected to a circularly polarized microwave field and a magnetic field is shown to belong to the family of so-called biparametric quadratic Hamiltonians. The energy-level structure is studied in terms of the parametric bifurcations. {copyright} {ital 1997} {ital The American Physical Society}
Wilhelm, Miriam M.
2011-01-01
A growing research stream has expanded the level of analysis beyond single buyer-supplier relations to the network, including supplier-supplier relations. These supplier-supplier relations may constitute a missing link between the traditional analysis of the dyadic and the network level of analysis
Institute of Scientific and Technical Information of China (English)
Liu Su-Hua; Tang Jia-Shi; Qin Jin-Qi; Yin Xiao-Bo
2008-01-01
Bifurcation characteristics of the Langford system in a general form are systematically analysed,and nonlinear controls of periodic solutions changing into invariant tori in this system are achieved.Analytical relationship between control gain and bifurcation parameter is obtained.Bifurcation diagrams are drawn,showing the results of control for secondary Hopf bifurcation and sequences of bifurcations route to chaos.Numerical simulations of quasi-periodic tori validate analytic predictions.
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.
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....
Subcritical dynamo bifurcation in the Taylor-Green flow.
Ponty, Y; Laval, J-P; Dubrulle, B; Daviaud, F; Pinton, J-F
2007-11-30
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.
BIFURCATIONS OF ROUGH 3-POINT-LOOP WITH HIGHER DIMENSIONS
Institute of Scientific and Technical Information of China (English)
金银来; 朱德明; 郑庆玉
2003-01-01
The authors study the bifurcation problems of rough heteroclinic loop connecting threesaddle points for the case β1 ＞ 1, β2 ＞ 1, β3 ＜ 1 and β1β2β3 ＜ 1. The existence, number, co-existence and incoexistence of 2-point-loop, 1-homoclinic orbit and 1-periodic orbit are studied.Meanwhile, the bifurcation surfaces and existence regions are given.
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.
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 analysis for the Lugiato-Lefever equation
Godey, Cyril
2016-01-01
The Lugiato-Lefever equation is a cubic nonlinear Schr\\"odinger equation, including damping, detuning and driving, which arises as a model in nonlinear optics. We study the existence of stationary waves which are found as solutions of a four-dimensional reversible dynamical system in which the evolutionary variable is the space variable. Relying upon tools from bifurcation theory and normal forms theory, we discuss the codimension 1 bifurcations. We prove the existence of various types of ste...
Dissection of a non-bifurcating cervical carotid artery.
Nas, Omer Fatih; Karakullukcuoglu, Zeynel; Hakyemez, Bahattin; Erdogan, Cuneyt
2016-06-01
A non-bifurcating cervical carotid artery is a rare anomaly in the population. Radiologic diagnosis of pathologies seen together with this anomaly can be challenging. Despite not being diagnostic all the time, digital subtraction angiography is accepted as the gold standard method for the diagnosis of dissection. We present a case of a non-bifurcating cervical carotid artery and concomitant dissection, which presented to the hospital with trauma and ischemic findings.
Bifurcations and chaos control in discrete small-world networks
Institute of Scientific and Technical Information of China (English)
Li Ning; Sun Hai-Yi; Zhang Qing-Ling
2012-01-01
An impulsive delayed feedback control strategy to control period-doubling bifurcations and chaos is proposed.The control method is then applied to a discrete small-world network model.Qualitative analyses and simulations show that under a generic condition,the bifurcations and the chaos can be delayed or eliminated completely.In addition,the periodic orbits embedded in the chaotic attractor can be stabilized.
Subcritical Hopf bifurcations in low-density jets
Zhu, Yuanhang; Gupta, Vikrant; Li, Larry K. B.
2016-11-01
Low-density jets are known to bifurcate from a steady state (a fixed point) to self-excited oscillations (a periodic limit cycle) when the Reynolds number increases above a critical value corresponding to the Hopf point, ReH . In the literature, this Hopf bifurcation is often considered to be supercritical because the self-excited oscillations appear only when Re > ReH . However, we find that under some conditions, there exists a hysteretic bistable region at ReSN ReSN denotes a saddle-node bifurcation point. This shows that the Hopf bifurcation can also be subcritical, which has three main implications. First, low-density jets could be triggered into self-excited oscillations even when Re < ReH . Second, in the modeling of low-density jets, the subcritical or supercritical nature of the Hopf bifurcation should be taken into account because the former is caused by cubic nonlinearity whereas the latter is caused by square nonlinearity. Third, the response of the system to external forcing and noise depends on its proximity to the bistable region. Therefore, when investigating the forced response of low-density jets, it is important to consider whether the Hopf bifurcation is subcritical or supercritical.
Bifurcation magnetic resonance in films magnetized along hard magnetization axis
Energy Technology Data Exchange (ETDEWEB)
Vasilevskaya, Tatiana M., E-mail: t_vasilevs@mail.ru [Ulyanovsk State University, Leo Tolstoy 42, 432017 Ulyanovsk (Russian Federation); Sementsov, Dmitriy I.; Shutyi, Anatoliy M. [Ulyanovsk State University, Leo Tolstoy 42, 432017 Ulyanovsk (Russian Federation)
2012-09-15
We study low-frequency ferromagnetic resonance in a thin film magnetized along the hard magnetization axis performing an analysis of magnetization precession dynamics equations and numerical simulation. Two types of films are considered: polycrystalline uniaxial films and single-crystal films with cubic magnetic anisotropy. An additional (bifurcation) resonance initiated by the bistability, i.e. appearance of two closely spaced equilibrium magnetization states is registered. The modification of dynamic modes provoked by variation of the frequency, amplitude, and magnetic bias value of the ac field is studied. Both steady and chaotic magnetization precession modes are registered in the bifurcation resonance range. - Highlights: Black-Right-Pointing-Pointer An additional bifurcation resonance arises in a case of a thin film magnetized along HMA. Black-Right-Pointing-Pointer Bifurcation resonance occurs due to the presence of two closely spaced equilibrium magnetization states. Black-Right-Pointing-Pointer Both regular and chaotic precession modes are realized within bifurcation resonance range. Black-Right-Pointing-Pointer Appearance of dynamic bistability is typical for bifurcation resonance.
Makarenko, A. V.
2016-10-01
A new class of bifurcations is defined in discrete dynamical systems, and methods for their diagnostics and the analysis of their properties are presented. The TQ-bifurcations considered are implemented in discrete mappings and are related to the qualitative rearrangement of the shape of trajectories in an extended space of states. Within the demonstration of the main capabilities of the toolkit, an analysis is carried out of a logistic mapping in a domain to the right of the period-doubling limit point. Five critical values of the parameter are found for which the geometric structure of the trajectories of the mapping experiences a qualitative rearrangement. In addition, an analysis is carried out of the so-called "trace map," which arises in the problems of quantum-mechanical description of various properties of discrete crystalline and quasicrystalline lattices.
Bifurcations in models of a society of reasonable contrarians and conformists.
Bagnoli, Franco; Rechtman, Raúl
2015-10-01
We study models of a society composed of a mixture of conformist and reasonable contrarian agents that at any instant hold one of two opinions. Conformists tend to agree with the average opinion of their neighbors and reasonable contrarians tend to disagree, but revert to a conformist behavior in the presence of an overwhelming majority, in line with psychological experiments. The model is studied in the mean-field approximation and on small-world and scale-free networks. In the mean-field approximation, a large fraction of conformists triggers a polarization of the opinions, a pitchfork bifurcation, while a majority of reasonable contrarians leads to coherent oscillations, with an alternation of period-doubling and pitchfork bifurcations up to chaos. Similar scenarios are obtained by changing the fraction of long-range rewiring and the parameter of scale-free networks related to the average connectivity.
Bifurcation threshold of the delayed van der Pol oscillator under stochastic modulation.
Gaudreault, Mathieu; Drolet, François; Viñals, Jorge
2012-05-01
We obtain the location of the Hopf bifurcation threshold for a modified van der Pol oscillator, parametrically driven by a stochastic source and including delayed feedback in both position and velocity. We introduce a multiple scale expansion near threshold, and we solve the resulting Fokker-Planck equation associated with the evolution at the slowest time scale. The analytical results are compared with a direct numerical integration of the model equation. Delay modifies the Hopf frequency at threshold and leads to a stochastic bifurcation that is shifted relative to the deterministic limit by an amount that depends on the delay time, the amplitude of the feedback terms, and the intensity of the noise. Interestingly, stochasticity generally increases the region of stability of the limit cycle.
The bifurcation threshold value of the chaos detection system for a weak signal
Institute of Scientific and Technical Information of China (English)
李月; 杨宝俊; 杜立志; 袁野
2003-01-01
Recently, it has become an important problem to confirm the bifurcation threshold value of a chaos detection system for a weak signal in the fields of chaos detection. It is directly related to whether the results of chaos detection are correct or not. In this paper, the discrimination system for the dynamic behaviour of a chaos detection system for a weak signal is established by using the theory of linear differential equation with periodic coefficients and computing the Lyapunov exponents of the chaos detection system; and then, the movement state of the chaos detection system is defined. The simulation experiments show that this method can exactly confirm the bifurcation threshold value of the chaos detection system.
Bifurcation analysis of the behavior of partially wetting liquids on a rotating cylinder
Lin, Te-Sheng; Tseluiko, Dmitri; Thiele, Uwe
2015-01-01
We discuss the behavior of partially wetting liquids on a rotating cylinder using the model of Thiele [J. Fluid Mech. 671, 121-136 (2011)] that takes into account the effects of gravity, viscosity, rotation, surface tension and wettability. Such a system can be considered as a prototype for many other systems where the interplay of spatial heterogeneity and a lateral driving force in the proximity of a first- or second-order phase transition results in intricate behaviour. So does a partially wetting drop on a rotating cylinder undergo a depinning transition as the rotation speed is increased, whereas for ideally wetting liquids the behavior changes monotonically. We analyze in detail the transition in the bifurcation behavior for partially wetting liquids as the wettability of the liquid decreases, and, in particular, how the global bifurcation related to the depinning of drops is created when increasing the contact angle. We employ various numerical continuation techniques that allow us to track stable/unst...
Bifurcations in models of a society of reasonable contrarians and conformists
Bagnoli, Franco
2015-01-01
We study models of a society composed of a mixture of conformist and reasonable contrarian agents that at any instant hold one of two opinions. Conformists tend to agree with the average opinion of their neighbors and reasonable contrarians to disagree, but revert to a conformist behavior in the presence of an overwhelming majority, in line with psychological experiments. The model is studied in the mean field approximation and on small-world and scale-free networks. In the mean field approximation, a large fraction of conformists triggers a polarization of the opinions, a pitchfork bifurcation, while a majority of reasonable contrarians leads to coherent oscillations, with an alternation of period-doubling and pitchfork bifurcations up to chaos. Similar scenarios are obtained by changing the fraction of long-range rewiring and the parameter of scale-free networks related to the average connectivity.
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...
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...
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...
Généreux, Philippe; Kumsars, Indulis; Lesiak, Maciej; Kini, Annapoorna; Fontos, Géza; Slagboom, Ton; Ungi, Imre; Metzger, D. Christopher; Wykrzykowska, Joanna J.; Stella, Pieter R.; Bartorelli, Antonio L.; Fearon, William F.; Lefèvre, Thierry; Feldman, Robert L.; Lasalle, Laura; Francese, Dominic P.; Onuma, Yoshinobu; Grundeken, Maik J.; Garcia-Garcia, Hector M.; Laak, Linda L.; Cutlip, Donald E.; Kaplan, Aaron V.; Serruys, Patrick W.; Leon, Martin B.
2015-01-01
Background Bifurcation lesions are frequent among patients with symptomatic coronary disease treated by percutaneous coronary intervention. Current evidence recommends a conservative (provisional) approach when treating the side branch (SB). Objectives The TRYTON (Prospective, Single Blind, Randomiz
It's All Relative: Different Levels of Relational Similarity Used in Children's Comparisons
Paik, Jae H.; Mix, Kelly S.
2008-01-01
Using a sticker search task, Gentner and Rattermann ("Perspectives on thought and language: Interrelations in development" (Gelman & Byrnes, Eds.), pp. 225-227, 1991) found that the ability to ignore surface features and match objects in terms of relative size emerged around 5 years of age. However, because spatial position covaried with relative…
Hannah, Samuel D; Shedden, Judith M; Brooks, Lee R; Grundy, John G
2016-11-01
In this paper, we use behavioural methods and event-related potentials (ERPs) to explore the relations between informational and instantiated features, as well as the relation between feature abstraction and rule type. Participants are trained to categorize two species of fictitious animals and then identify perceptually novel exemplars. Critically, two groups are given a perfectly predictive counting rule that, according to Hannah and Brooks (2009. Featuring familiarity: How a familiar feature instantiation influences categorization. Canadian Journal of Experimental Psychology/Revue Canadienne de Psychologie Expérimentale, 63, 263-275. Retrieved from http://doi.org/10.1037/a0017919), should orient them to using abstract informational features when categorizing the novel transfer items. A third group is taught a feature list rule, which should orient them to using detailed instantiated features. One counting-rule group were taught their rule before any exposure to the actual stimuli, and the other immediately after training, having learned the instantiations first. The feature-list group were also taught their rule after training. The ERP results suggest that at test, the two counting-rule groups processed items differently, despite their identical rule. This not only supports the distinction that informational and instantiated features are qualitatively different feature representations, but also implies that rules can readily operate over concrete inputs, in contradiction to traditional approaches that assume that rules necessarily act on abstract inputs.
Croes, Kim; De Coster, Sam; De Galan, Sandra; Morrens, Bert; Loots, Ilse; Van de Mieroop, Els; Nelen, Vera; Sioen, Isabelle; Bruckers, Liesbeth; Nawrot, Tim; Colles, Ann; Den Hond, Elly; Schoeters, Greet; van Larebeke, Nicolas; Baeyens, Willy; Gao, Yue
2014-03-01
Due to possible health risks, quantification of mercury accumulation in humans was included in the Flemish biomonitoring programmes FLEHS I (2002-2006) and FLEHS II (2007-2011). The general objective of FLEHS I was to assess regional exposure levels in order to link possible differences in these internal exposure levels to different types of local environmental pressure. Therefore, Hg and MMHg (methylmercury) were only measured in pooled blood samples per region and per age class. In FLEHS II, mercury concentrations were measured in hair of each participant. About 200 adolescents and 250 mothers (reference group) and two times 200 adolescents (2 hotspots) were screened. The main objectives of the FLEHS II study were: (1) to determine reference levels of mercury in hair for Flanders; (2) to assess relations between mercury exposure and possible sources like fish consumption; (3) to assess dose-effect relations between mercury exposure and health effect markers. The results showed that mercury concentrations in the Flemish population were rather low compared to other studies. Mercury levels in the Flemish populations were strongly related to the age of the participants and consumption of fish. Significant negative associations were observed between mercury in hair and asthma, having received breast feeding as a newborn, age at menarche in girls, allergy for animals and free testosterone levels. Significant correlations were also observed between mercury in hair and genes JAK2, ARID4A, Hist1HA4L (boys) and HLAdrb5, PIAS2, MANN1B1, GIT and ABCA1 (girls).
Sánchez Sanz, Julia; Getto, Philipp
2016-07-01
With the aim of applying numerical methods, we develop a formalism for physiologically structured population models in a new generality that includes consumer-resource, cannibalism and trophic models. The dynamics at the population level are formulated as a system of Volterra functional equations coupled to ODE. For this general class, we develop numerical methods to continue equilibria with respect to a parameter, detect transcritical and saddle-node bifurcations and compute curves in parameter planes along which these bifurcations occur. The methods combine curve continuation, ODE solvers and test functions. Finally, we apply the methods to the above models using existing data for Daphnia magna consuming Algae and for Perca fluviatilis feeding on Daphnia magna. In particular, we validate the methods by deriving expressions for equilibria and bifurcations with respect to which we compute errors, and by comparing the obtained curves with curves that were computed earlier with other methods. We also present new curves to show how the methods can easily be applied to derive new biological insight. Schemes of algorithms are included.
Bifurcation analysis and stability design for aircraft longitudinal motion with high angle of attack
Directory of Open Access Journals (Sweden)
Xin Qi
2015-02-01
Full Text Available Bifurcation analysis and stability design for aircraft longitudinal motion are investigated when the nonlinearity in flight dynamics takes place severely at high angle of attack regime. To predict the special nonlinear flight phenomena, bifurcation theory and continuation method are employed to systematically analyze the nonlinear motions. With the refinement of the flight dynamics for F-8 Crusader longitudinal motion, a framework is derived to identify the stationary bifurcation and dynamic bifurcation for high-dimensional system. Case study shows that the F-8 longitudinal motion undergoes saddle node bifurcation, Hopf bifurcation, Zero-Hopf bifurcation and branch point bifurcation under certain conditions. Moreover, the Hopf bifurcation renders series of multiple frequency pitch oscillation phenomena, which deteriorate the flight control stability severely. To relieve the adverse effects of these phenomena, a stabilization control based on gain scheduling and polynomial fitting for F-8 longitudinal motion is presented to enlarge the flight envelope. Simulation results validate the effectiveness of the proposed scheme.
Predicting the onset of period-doubling bifurcations in noisy cardiac systems.
Quail, Thomas; Shrier, Alvin; Glass, Leon
2015-07-28
Biological, physical, and social systems often display qualitative changes in dynamics. Developing early warning signals to predict the onset of these transitions is an important goal. The current work is motivated by transitions of cardiac rhythms, where the appearance of alternating features in the timing of cardiac events is often a precursor to the initiation of serious cardiac arrhythmias. We treat embryonic chick cardiac cells with a potassium channel blocker, which leads to the initiation of alternating rhythms. We associate this transition with a mathematical instability, called a period-doubling bifurcation, in a model of the cardiac cells. Period-doubling bifurcations have been linked to the onset of abnormal alternating cardiac rhythms, which have been implicated in cardiac arrhythmias such as T-wave alternans and various tachycardias. Theory predicts that in the neighborhood of the transition, the system's dynamics slow down, leading to noise amplification and the manifestation of oscillations in the autocorrelation function. Examining the aggregates' interbeat intervals, we observe the oscillations in the autocorrelation function and noise amplification preceding the bifurcation. We analyze plots--termed return maps--that relate the current interbeat interval with the following interbeat interval. Based on these plots, we develop a quantitative measure using the slope of the return map to assess how close the system is to the bifurcation. Furthermore, the slope of the return map and the lag-1 autocorrelation coefficient are equal. Our results suggest that the slope and the lag-1 autocorrelation coefficient represent quantitative measures to predict the onset of abnormal alternating cardiac rhythms.
Energy Technology Data Exchange (ETDEWEB)
Suarez-Antola, Roberto, E-mail: roberto.suarez@miem.gub.u, E-mail: rsuarez@ucu.edu.u [Universidad Catolica del Uruguay, Montevideo (Uruguay). Fac. de Ingenieria y Tecnologias. Dept. de Matematica; Ministerio de Industria, Energia y Mineria, Montevideo (Uruguay). Direccion General de Secretaria
2011-07-01
One of the goals of nuclear power systems design and operation is to restrict the possible states of certain critical subsystems to remain inside a certain bounded set of admissible states and state variations. In the framework of an analytic or numerical modeling process of a BWR power plant, this could imply first to find a suitable approximation to the solution manifold of the differential equations describing the stability behavior, and then a classification of the different solution types concerning their relation with the operational safety of the power plant. Inertial manifold theory gives a foundation for the construction and use of reduced order models (ROM's) of reactor dynamics to discover and characterize meaningful bifurcations that may pass unnoticed during digital simulations done with full scale computer codes of the nuclear power plant. The March-Leuba's BWR ROM is generalized and used to exemplify the analytical approach developed here. A nonlinear integral-differential equation in the logarithmic power is derived. Introducing a KBM Ansatz, a coupled set of two nonlinear ordinary differential equations is obtained. Analytical formulae are derived for the frequency of oscillation and the parameters that determine the stability of the steady states, including sub- and supercritical PAH bifurcations. A Bautin's bifurcation scenario seems possible on the power-flow plane: near the boundary of stability, a region where stable steady states are surrounded by unstable limit cycles surrounded at their turn by stable limit cycles. The analytical results are compared with recent digital simulations and applications of semi-analytical bifurcation theory done with reduced order models of BWR. (author)
Remigius, W. Dheelibun; Sarkar, Sunetra; Gupta, Sayan
2017-03-01
Use of heavy gases in centrifugal compressors for enhanced oil extraction have made the impellers susceptible to failures through acousto-elastic instabilities. This study focusses on understanding the dynamical behavior of such systems by considering the effects of the bounded fluid housed in a casing on a rotating disc. First, a mathematical model is developed that incorporates the interaction between the rotating impeller - modelled as a flexible disc - and the bounded compressible fluid medium in which it is immersed. The nonlinear effects arising due to large deformations of the disc have been included in the formulation so as to capture the post flutter behavior. A bifurcation analysis is carried out with the disc rotational speed as the bifurcation parameter to investigate the dynamical behavior of the coupled system and estimate the stability boundaries. Parametric studies reveal that the relative strengths of the various dissipation mechanisms in the coupled system play a significant role that affect the bifurcation route and the post flutter behavior in the acousto-elastic system.
Dong, Jingliang; Wong, Kelvin K L; Tu, Jiyuan
2013-04-01
The study of cardiovascular models was presented in this paper based on medical image reconstruction and computational fluid dynamics. Our aim is to provide a reality platform for the purpose of flow analysis and virtual intervention outcome predication for vascular diseases. By connecting two porous mediums with transient permeability at the downstream of the carotid bifurcation branches, a downstream peripheral impedance model was developed, and the effect of the downstream vascular bed impedance can be taken into consideration. After verifying its accuracy with a healthy carotid bifurcation, this model was implemented in a diseased carotid bifurcation analysis. On the basis of time-averaged wall shear stress, oscillatory shear index, and the relative residence time, fractions of abnormal luminal surface were highlighted, and the atherosclerosis was assessed from a hemodynamic point of view. The effect of the atherosclerosis on the transient flow division between the two branches because of the existence of plaque was also analysed. This work demonstrated that the proposed downstream peripheral vascular impedance model can be used for computational modelling when the outlets boundary conditions are not available, and successfully presented the potential of using medical imaging and numerical simulation to provide existing clinical prerequisites for diagnosis and therapeutic treatment.
Periodic Solutions of the Forced Pendulum: Exchange of Stability and Bifurcations
Katriel, Guy
2002-06-01
We study the T-periodic solutions of the forced pendulum equation u″+cu‧+a sin(u)=λf(t), where f satisfies f(t+{T}/{2})=-f(t). We prove that this equation always has at least two geometrically distinct T-periodic solutions u0 and u1. We then investigate the dependence of the set of T-periodic solutions on the forcing strength λ. We prove that under some restriction on the parameters a,c, the periodic solutions found before can be smoothly parameterized by λ, and that there are some λ-intervals for which u0(λ), u1(λ) are the only T-periodic solutions up to geometrical equivalence, but there are other λ-intervals in which additional T-periodic solutions bifurcate off the branches u0(λ), u1(λ). We characterize the global structure of the bifurcating branches. Related to this bifurcation phenomenon is the phenomenon of 'exchange of stability' - in some λ-intervals u0(λ) is dynamically stable and u1(λ) is unstable, while in other λ-intervals the reverse is true, a phenomenon which has important consequences for the dynamics of the forced pendulum, as we show by both theoretical analysis and numerical simulation.
Lykov, Kirill; Li, Xuejin; Lei, Huan; Pivkin, Igor V; Karniadakis, George Em
2015-08-01
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.
Nonequilibrium Chemical Patterns and Their Bifurcations
Lee, Kyoung Jin
Stationary and dynamic patterns that arise in reaction-diffusion systems are investigated in laboratory experiments. Our study reveals several new types of pattern that have not been observed in previous studies. The new patterns are observed in a ferrocyanide-iodate-sulfite (FIS) system, and they include stationary lamellae, self -replicating spots, and repulsive waves. All are large amplitude patterns that are initiated by a finite amplitude perturbation. Our simulation results on a four-species FIS reaction diffusion model as well as several recent studies on other models by other researchers reveal similar patterns and pattern forming instabilities. The stationary lamellae form through transverse front instability and front repulsion, whereas the much studied small amplitude Turing structures form spontaneously at the onset of the Turing instability. The mechanism of self-replicating spots, which undergo a life-like process of birth through replication and death through overcrowding, is explained heuristically and rigorously by the Ising-Bloch front bifurcation recently studied by Meron and co-workers. The repulsive excitable waves are different from conventional excitable waves in that they do not collide and annihilate. Our earlier study investigates Turing patterns in chlorite-iodide-malonic acid (CIMA) system. We demonstrate that Turing patterns can form in a CIMA system even without the presence of a large molecule, the starch color indicator, which in a popular model plays a crucial role in Turing pattern formation. We speculate that the polyacrylamide gel used in our study plays a similar role to that of the starch indicator. The morphological transition of a Turing structure in a CIMA system was also investigated by changing the thickness of the gel medium.
NONLINEAR DYNAMICAL ANALYSIS OF BIFURCATION AND CONFLUENCE OF THE PACIFIC WESTERN BOUNDARY CURRENTS
Institute of Scientific and Technical Information of China (English)
NI Guo-xi; JIANG Song; JU Qiang-chang; KONG Ling-hai
2012-01-01
In this paper,we analyze the bifurcation and the confluence of the Pacific western boundary currents by an analytical approach.Applying the conservation law,the geostrophie balance relation and the Bernoulli integral to a reduced gravity model,we get a quantitative relation for the outflow and the inflow,and establish the related formulae for the width and the veering angle of offshore currents under the inflow condition.Furthermore,a comparison between the volume transport based on the observation data and the analytical value for the Pacific western boundary currents is presented,which validates the theoretical analysis.
Hong, Mei; Zhang, Ren; Li, Ming; Wang, Shuo; Zeng, Wenhua; Wang, Zhengxin
2016-04-01
Despite much previous effort, the establishment of an accurate model of the western Pacific subtropical high (WPSH) and analysis of its chaotic behavior has proved to be difficult. Based on a phase-space technique, a nonlinear dynamical model of the WPSH ridge line and summer monsoon factors is constructed here from 50 years of data. Using a genetic algorithm, model inversion and parameter optimization are performed. The Lyapunov spectrum, phase portraits, time history, and Poincaré surface of section of the model are analyzed and an initial-value sensitivity test is performed, showing that the model and data have similar phase portraits and that the model is robust. Based on equilibrium stability criteria, four types of equilibria of the model are analyzed. Bifurcations and catastrophes of the equilibria are studied and related to the physical mechanism and actual weather phenomena. The results show that the onset and enhancement of the Somali low-level jet and the latent heat flux of the Indian monsoon are among the most important reasons for the appearance and maintenance of the double-ridge phenomenon. Violent breakout and enhancement of the Mascarene cold high will cause the WPSH to jump northward, resulting in the "empty plum" phenomenon. In the context of bifurcation and catastrophe in the dynamical system, the influence of the factors considered here on the WPSH has theoretical and practical significance. This work also opens the way to new lines of research on the interaction between the WPSH and the summer monsoon system.
Bifurcations of a singular prey-predator economic model with time delay and stage structure
Energy Technology Data Exchange (ETDEWEB)
Zhang Xue [Institute of Systems Science, Northeastern University, Shenyang, Liaoning 110004 (China); Key Laboratory of Integrated Automation of Process Industry (Northeastern Univ.), Ministry of Education, Shenyang, Liaoning 110004 (China)], E-mail: zhangxueer@gmail.com; Zhang Qingling [Institute of Systems Science, Northeastern University, Shenyang, Liaoning 110004 (China); Key Laboratory of Integrated Automation of Process Industry (Northeastern Univ.), Ministry of Education, Shenyang, Liaoning 110004 (China)], E-mail: qlzhang@mail.neu.edu.cn; Liu Chao [Institute of Systems Science, Northeastern University, Shenyang, Liaoning 110004 (China); Key Laboratory of Integrated Automation of Process Industry (Northeastern Univ.), Ministry of Education, Shenyang, Liaoning 110004 (China); Xiang Zhongyi [Department of Mathematics, Hubei University for Nationalities, Enshi, Hubei 445000 (China)
2009-11-15
This paper studies a singular prey-predator economic model with time delay and stage structure. Compared with other researches on dynamics of prey-predator population, this model is described by differential-algebraic equations due to economic factor. For zero economic profit, this model exhibits three bifurcational phenomena: transcritical bifurcation, Hopf bifurcation and singular induced bifurcation. For positive economic profit, the model undergoes a saddle-node bifurcation at critical value of positive economic profit, and the increase of delay destabilizes the positive equilibrium point of the system and bifurcates into small amplitude periodic solution. Finally, by using Matlab software, numerical simulations illustrate the effectiveness of the results.
Coronary bifurcation angle from 3-D predicts clinical outcomes after stenting bifurcation lesions
Institute of Scientific and Technical Information of China (English)
CHEN Shao-liang; DING Shi-qing; Tak W Kwan; Teguh Santoso; ZHANG Jun-jie; YE Fei; XU Ya-wei; FU Qiang; KAN Jing; Chitprapai Paiboon; ZHOU Yong
2012-01-01
Background The predictive value of bifurcation angle (BA) for worse events after stenting bifurcation lesions remains to be unknown.The present study was to investigate the dynamic change of BA and clinical relevance for patients with coronary bifurcation lesions treated by drug-eluting stent (DES).Methods BA was calculated by 3-D quantitative coronary analysis from 347 patients in DKCRUSH-Ⅱ study.Primary endpoint was the occurrence of composite major adverse cardiac events (MACE) at 12-month,including cardiac death,myocardial infarction (MI) and target vessel revascularization (TVR).Secondary end points were the rate of binary restenosis and stent thrombosis at 12-month.Results Stenting was associated with the reduction of distal BA.The cut-off value of distal BAfor predicting MACE was 60° Distal BA in ＜60° group had less reduction after stenting ((-1.96±13.58)° vs.(-12.12±23.58)°,P ＜0.001 ); two-stent technique was associated with significant reduction of distal BA (△(-4.05±14.20)°),compared to single stent group (△+1.55±11.73,P=0.003); the target lesion revascularization (TLR),TVR and MACE rate was higher in one-stent group (16.5％,19.0％ and 21.5％),compared to two-stent group (3.8％,P=0.002; 7.5％,P=0.016; and 9.8％,P=0.024),respectively.Among patients in ≥60° group,there were no significant differences in distal BA,stent thrombosis (ST),MI,MACE,death,TLR,TVR between one- and two-stent groups; after stenting procedure,there was only slight change of distal BA in left anterior descending (LAD)-Ieft circumflex (LCX) subgroup (from (88.54±21.33)° at baseline to (82.44±31.72)° post-stenting),compared to either LAD-diagonal branch (Di),or LCX-obtuse marginal branch (OM),or RCA distal (RCAd) (all P ＜0.001 ).Conclusion Two-stent technique was associated with significant reduction of distal BA.DK crush stenting had reduced rate of MACE in patients in ＜60° group,compared to one-stent technique.
Inverse bifurcation analysis: application to simple gene systems
Directory of Open Access Journals (Sweden)
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.
Directory of Open Access Journals (Sweden)
Omid Arjmandi-Tash
2012-12-01
Full Text Available Introduction: Atherosclerosis is a focal disease that susceptibly forms near bifurcations, anastomotic joints, side branches, and curved vessels along the arterial tree. In this study, pulsatile blood flow in a bifurcation model with a non-planar branch is investigated. Methods: Wall shear stress (WSS distributions along generating lines on vessels for different bifurcation angles are calculated during the pulse cycle. Results: The WSS at the outer side of the bifurcation plane vanishes especially for higher bifurcation angles but by increasing the bifurcation angle low WSS region squeezes. At the systolic phase there is a high possibility of formation of a separation region at the outer side of bifurcation plane for all the cases. WSS peaks exist on the inner side of bifurcation plane near the entry section of daughter vessels and these peaks drop as bifurcation angle is increased. Conclusion: It was found that non-planarity of the daughter vessel lowers the minimum WSS at the outer side of the bifurcation and increases the maximum WSS at the inner side. So it seems that the formation of atherosclerotic plaques at bifurcation region in direction of non-planar daughter vessel is more risky.
Fluid dynamics in airway bifurcations: II. Secondary currents.
Martonen, T B; Guan, X; Schreck, R M
2001-04-01
As the second component of a systematic investigation on flows in bifurcations reported in this journal, this work focused on secondary currents. The first article addressed primary flows and the third discusses localized conditions (both in this issue). Secondary flow patterns were studied in two lung bifurcation models (Schreck, 1972) using FIDAP with the Cray T90 supercomputer. The currents were examined at different prescribed distances distal to the carina. Effects of inlet conditions, Reynolds numbers, and diameter ratios and orientations of airways were addressed. The secondary currents caused by the presence of the carina and inclination of the daughter tubes exhibited symmetric, multivortex patterns. The intensities of the secondary currents became stronger for larger Reynolds numbers and larger angles of bifurcation.
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.
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...
Bifurcations in the optimal elastic foundation for a buckling column
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Rayneau-Kirkhope, Daniel, E-mail: ppxdr@nottingham.ac.u [School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD (United Kingdom); Farr, Robert [Unilever R and D, Olivier van Noortlaan 120, AT3133, Vlaardingen (Netherlands); London Institute for Mathematical Sciences, 22 South Audley Street, Mayfair, London (United Kingdom); Ding, K. [Department of Physics, Fudan University, Shanghai, 200433 (China); Mao, Yong [School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD (United Kingdom)
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.
Adaptive Control of Electromagnetic Suspension System by HOPF Bifurcation
Directory of Open Access Journals (Sweden)
Aming Hao
2013-01-01
Full Text Available EMS-type maglev system is essentially nonlinear and unstable. It is complicated to design a stable controller for maglev system which is under large-scale disturbance and parameter variance. Theory analysis expresses that this phenomenon corresponds to a HOPF bifurcation in mathematical model. An adaptive control law which adjusts the PID control parameters is given in this paper according to HOPF bifurcation theory. Through identification of the levitated mass, the controller adjusts the feedback coefficient to make the system far from the HOPF bifurcation point and maintain the stability of the maglev system. Simulation result indicates that adjusting proportion gain parameter using this method can extend the state stability range of maglev system and avoid the self-excited vibration efficiently.
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.
Bifurcations and transitions to chaos in an inverted pendulum
Kim, Sang-Yoon; Hu, Bambi
1998-09-01
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 pendulum by varying the amplitude and frequency of the vertical oscillation. It is found that the inverted state stabilizes via alternating ``reverse'' subcritical pitchfork and period-doubling bifurcations, while it destabilizes via alternating ``normal'' supercritical period-doubling and pitchfork bifrucations. An infinite sequence of period-doubling bifurcations, leading to chaos, follows each destabilization of the inverted state. The critical behaviors in the period-doubling cascades are also discussed.
Rosette Central Configurations, Degenerate central configurations and bifurcations
Lei, Jinzhi
2009-01-01
In this paper we find a class of new degenerate central configurations and bifurcations in the Newtonian $n$-body problem. In particular we analyze the Rosette central configurations, namely a coplanar configuration where $n$ particles of mass $m_1$ lie at the vertices of a regular $n$-gon, $n$ particles of mass $m_2$ lie at the vertices of another $n$-gon concentric with the first, but rotated of an angle $\\pi/n$, and an additional particle of mass $m_0$ lies at the center of mass of the system. This system admits two mass parameters $\\mu=m_0/m_1$ and $\\ep=m_2/m_1$. We show that, as $\\mu$ varies, if $n> 3$, there is a degenerate central configuration and a bifurcation for every $\\ep>0$, while if $n=3$ there is a bifurcations only for some values of $\\epsilon$.
Bifurcation of learning and structure formation in neuronal maps
DEFF Research Database (Denmark)
Marschler, Christian; Faust-Ellsässer, Carmen; Starke, Jens
2014-01-01
Most learning processes in neuronal networks happen on a much longer time scale than that of the underlying neuronal dynamics. It is therefore useful to analyze slowly varying macroscopic order parameters to explore a network's learning ability. We study the synaptic learning process giving rise...... to map formation in the laminar nucleus of the barn owl's auditory system. Using equation-free methods, we perform a bifurcation analysis of spatio-temporal structure formation in the associated synaptic-weight matrix. This enables us to analyze learning as a bifurcation process and follow the unstable...... states as well. A simple time translation of the learning window function shifts the bifurcation point of structure formation and goes along with traveling waves in the map, without changing the animal's sound localization performance....
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.
Garnier, Simon; Combe, Maud; Jost, Christian; Theraulaz, Guy
2013-01-01
Interactions between individuals and the structure of their environment play a crucial role in shaping self-organized collective behaviors. Recent studies have shown that ants crossing asymmetrical bifurcations in a network of galleries tend to follow the branch that deviates the least from their incoming direction. At the collective level, the combination of this tendency and the pheromone-based recruitment results in a greater likelihood of selecting the shortest path between the colony's nest and a food source in a network containing asymmetrical bifurcations. It was not clear however what the origin of this behavioral bias is. Here we propose that it results from a simple interaction between the behavior of the ants and the geometry of the network, and that it does not require the ability to measure the angle of the bifurcation. We tested this hypothesis using groups of ant-like robots whose perceptual and cognitive abilities can be fully specified. We programmed them only to lay down and follow light trails, avoid obstacles and move according to a correlated random walk, but not to use more sophisticated orientation methods. We recorded the behavior of the robots in networks of galleries presenting either only symmetrical bifurcations or a combination of symmetrical and asymmetrical bifurcations. Individual robots displayed the same pattern of branch choice as individual ants when crossing a bifurcation, suggesting that ants do not actually measure the geometry of the bifurcations when travelling along a pheromone trail. Finally at the collective level, the group of robots was more likely to select one of the possible shorter paths between two designated areas when moving in an asymmetrical network, as observed in ants. This study reveals the importance of the shape of trail networks for foraging in ants and emphasizes the underestimated role of the geometrical properties of transportation networks in general.
Directory of Open Access Journals (Sweden)
Simon Garnier
Full Text Available Interactions between individuals and the structure of their environment play a crucial role in shaping self-organized collective behaviors. Recent studies have shown that ants crossing asymmetrical bifurcations in a network of galleries tend to follow the branch that deviates the least from their incoming direction. At the collective level, the combination of this tendency and the pheromone-based recruitment results in a greater likelihood of selecting the shortest path between the colony's nest and a food source in a network containing asymmetrical bifurcations. It was not clear however what the origin of this behavioral bias is. Here we propose that it results from a simple interaction between the behavior of the ants and the geometry of the network, and that it does not require the ability to measure the angle of the bifurcation. We tested this hypothesis using groups of ant-like robots whose perceptual and cognitive abilities can be fully specified. We programmed them only to lay down and follow light trails, avoid obstacles and move according to a correlated random walk, but not to use more sophisticated orientation methods. We recorded the behavior of the robots in networks of galleries presenting either only symmetrical bifurcations or a combination of symmetrical and asymmetrical bifurcations. Individual robots displayed the same pattern of branch choice as individual ants when crossing a bifurcation, suggesting that ants do not actually measure the geometry of the bifurcations when travelling along a pheromone trail. Finally at the collective level, the group of robots was more likely to select one of the possible shorter paths between two designated areas when moving in an asymmetrical network, as observed in ants. This study reveals the importance of the shape of trail networks for foraging in ants and emphasizes the underestimated role of the geometrical properties of transportation networks in general.
Post-Treatment Hemodynamics of a Basilar Aneurysm and Bifurcation
Energy Technology Data Exchange (ETDEWEB)
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.
Directory of Open Access Journals (Sweden)
Peter Etim Ekanem
2015-09-01
Full Text Available Background: The tibial and common peroneal nerves are dorsal and ventral divisions of the ventral rami of L4 to S3 of the lumbosacral plexus that join to form the sciatic nerve. The two nerves are structurally separate and supply the posterior compartment of the thigh, the leg and the foot. The point of bifurcation or separation of the sciatic nerve into tibial and common peroneal nerve varies. The common site is at the junction of the middle and lower third of the back of the thigh, near the apex of the popliteal fossa, but division may occur at any point above this. It may also rarely occur below it. The variations in the bifurcation of the sciatic nerve have clinical implications. They may result in nerve injury during deep intramuscular injections in the gluteal region, sciatica, piriformis syndrome etc. This study is to report the variations of the bifurcation in the sciatic nerve found in the cadaveres from Ethiopia, and discuss the clinical implications of such variations. Conclusion: We conclude from this study that the bifurcation of the sciatic nerve could occur high up in the gluteal region in relation to the piriformis muscle and may present clinical challenges in patient management
Directory of Open Access Journals (Sweden)
Zhonghua Sun
2013-01-01
Full Text Available The aim of this study is to investigate the relationship between intraluminal appearances of coronary plaques and left coronary bifurcation angle and plaque components using coronary CT virtual intravascular endoscopy (VIE. Fifty patients suspected of coronary artery disease undergoing coronary CT angiography were included in the study. The left bifurcation angle in patients with diseased left coronary artery which was measured as 94.3° ± 16.5 is significantly larger than that in patients with normal left coronary artery, which was measured as 76.5° ± 15.9 (P<0.001. Irregular VIE appearances were found in 10 out of 11 patients with mixed plaques in the left anterior descending (LAD and left circumflex (LCx, while, in 29 patients with calcified plaques in the LAD and LCx, irregular VIE appearances were only noticed in 5 patients. Using 80° as a cut-off value to determine coronary artery disease, smooth VIE appearances were found in 95% of patients (18/19 with left bifurcation angle of less than 80°, while irregular VIE appearances were observed in nearly 50% of patients (15/31 with left bifurcation angle of more than 80°. This preliminary study shows that VIE appearances of the coronary lumen are directly related to the types of plaques.
Cellular instability in rapid directional solidification - Bifurcation theory
Braun, R. J.; Davis, S. H.
1992-01-01
Merchant and Davis performed a linear stability analysis on a model for the directional solidification of a dilute binary alloy valid for all speeds. The analysis revealed that nonequilibrium segregation effects modify the Mullins and Sekerka cellular mode, whereas attachment kinetics has no effect on these cells. In this paper, the nonlinear stability of the steady cellular mode is analyzed. A Landau equation is obtained that determines the amplitude of the cells. The Landau coefficient here depends on both nonequilibrium segregation effects and attachment kinetics. This equation gives the ranges of parameters for subcritical bifurcation (jump transition) or supercritical bifurcation (smooth transition) to cells.
Bifurcation method for solving multiple positive solutions to Henon equation
Institute of Scientific and Technical Information of China (English)
2008-01-01
Three algorithms based on the bifurcation method are applied to solving the D4 symmetric positive solutions to the boundary value problem of Henon equation. Taking r in Henon equation as a bi- furcation parameter, the D4-Σd(D4-Σ1, D4-Σ2) symmetry-breaking bifurcation points on the branch of the D4 symmetric positive solutions are found via the extended systems. Finally, Σd(Σ1, Σ2) sym- metric positive solutions are computed by the branch switching method based on the Liapunov-Schmidt reduction.
Universal fractional map and cascade of bifurcations type attractors.
Edelman, M
2013-09-01
We modified the way in which the Universal Map is obtained in the regular dynamics to derive the Universal α-Family of Maps depending on a single parameter α>0, which is the order of the fractional derivative in the nonlinear fractional differential equation describing a system experiencing periodic kicks. We consider two particular α-families corresponding to the Standard and Logistic Maps. For fractional αbifurcations from regular to chaotic motion in regular dynamics corresponding fractional systems demonstrate a new type of attractors--cascade of bifurcations type trajectories.
Bifurcation analysis of nephron pressure and flow regulation
DEFF Research Database (Denmark)
Barfred, Mikael; Mosekilde, Erik; Holstein-Rathlou, N.-H.
1996-01-01
One- and two-dimensional continuation techniques are applied to study the bifurcation structure of a model of renal flow and pressure control. Integrating the main physiological mechanisms by which the individual nephron regulates the incoming blood flow, the model describes the interaction between...... the tubuloglomerular feedback and the response of the afferent arteriole. It is shown how a Hopf bifurcation leads the system to perform self-sustained oscillations if the feedback gain becomes sufficiently strong, and how a further increase of this parameter produces a folded structure of overlapping period...
Communication: Mode bifurcation of droplet motion under stationary laser irradiation.
Takabatake, Fumi; Yoshikawa, Kenichi; Ichikawa, Masatoshi
2014-08-01
The self-propelled motion of a mm-sized oil droplet floating on water, induced by a local temperature gradient generated by CW laser irradiation is reported. The circular droplet exhibits two types of regular periodic motion, reciprocal and circular, around the laser spot under suitable laser power. With an increase in laser power, a mode bifurcation from rectilinear reciprocal motion to circular motion is caused. The essential aspects of this mode bifurcation are discussed in terms of spontaneous symmetry-breaking under temperature-induced interfacial instability, and are theoretically reproduced with simple coupled differential equations.
Bogdanov-Takens bifurcation in a predator-prey model
Liu, Zhihua; Magal, Pierre; Xiao, Dongmei
2016-12-01
In this paper, we investigate a class of predator-prey model with age structure and discuss whether the model can undergo Bogdanov-Takens bifurcation. The analysis is based on the normal form theory and the center manifold theory for semilinear equations with non-dense domain combined with integrated semigroup theory. Qualitative analysis indicates that there exist some parameter values such that this predator-prey model has an unique positive equilibrium which is Bogdanov-Takens singularity. Moreover, it is shown that under suitable small perturbation, the system undergoes the Bogdanov-Takens bifurcation in a small neighborhood of this positive equilibrium.
An Approach to Robust Control of the Hopf Bifurcation
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Giacomo Innocenti
2011-01-01
Full Text Available The paper illustrates a novel approach to modify the Hopf bifurcation nature via a nonlinear state feedback control, which leaves the equilibrium properties unchanged. This result is achieved by recurring to linear and nonlinear transformations, which lead the system to locally assume the ordinary differential equation representation. Third-order models are considered, since they can be seen as proper representatives of a larger class of systems. The explicit relationship between the control input and the Hopf bifurcation nature is obtained via a frequency approach, that does not need the computation of the center manifold.
Inflation, bifurcations of nonlinear curvature Lagrangians and dark energy
Mielke, Eckehard W; Schunck, Franz E
2008-01-01
A possible equivalence of scalar dark matter, the inflaton, and modified gravity is analyzed. After a conformal mapping, the dependence of the effective Lagrangian on the curvature is not only singular but also bifurcates into several almost Einsteinian spaces, distinguished only by a different effective gravitational strength and cosmological constant. A swallow tail catastrophe in the bifurcation set indicates the possibility for the coexistence of different Einsteinian domains in our Universe. This `triple unification' may shed new light on the nature and large scale distribution not only of dark matter but also on `dark energy', regarded as an effective cosmological constant, and inflation.
Discretizing the transcritical and pitchfork bifurcations – conjugacy results
Lóczi, Lajos
2015-01-07
© 2015 Taylor & Francis. We present two case studies in one-dimensional dynamics concerning the discretization of transcritical (TC) and pitchfork (PF) bifurcations. In the vicinity of a TC or PF bifurcation point and under some natural assumptions on the one-step discretization method of order (Formula presented.) , we show that the time- (Formula presented.) exact and the step-size- (Formula presented.) discretized dynamics are topologically equivalent by constructing a two-parameter family of conjugacies in each case. As a main result, we prove that the constructed conjugacy maps are (Formula presented.) -close to the identity and these estimates are optimal.
Virtual bench testing to study coronary bifurcation stenting.
Migliavacca, Francesco; Chiastra, Claudio; Chatzizisis, Yiannis S; Dubini, Gabriele
2015-01-01
Virtual bench testing is a numerical methodology which has been applied to the study of coronary interventions. It exploits the amazing growth of computer performance for scientific calculation and makes it possible to simulate very different and complex multiphysics environments and processes, including coronary bifurcation stenting. The quality of prediction from any computer model is very sensitive to the quality of the input data and assumptions. This also holds true in stent virtual bench testing. This paper reviews the state of the art in the field of bifurcation stenting modelling and identifies the current advantages and limitations of this methodology.
Energy Technology Data Exchange (ETDEWEB)
HCTT CHE
2009-12-16
The purpose of this document is to provide a suggested approach, based on input from pediatric stakeholders, to communicating pediatric-related information on pandemic influenza at the community level in a step-by-step manner.
LOCAL STABILITY AND BIFURCATION IN A THREE—UNIT DELAYED NEURAL NETWORK
Institute of Scientific and Technical Information of China (English)
LINYiping; LIJibin; 等
2003-01-01
A system of three-unit networks with coupled cells is investigated.The general formula for bifurcation direction of Hopf bifurcation is calculated and the estimate formula of period of the periodic solution is given.
BIFURCATION OF PERIODIC SOLUTION IN A THREE-UNIT NEURAL NETWORK WITH DELAY
Institute of Scientific and Technical Information of China (English)
林怡平; ROLAND LEMMERT; PETER VOLKMANN
2001-01-01
A system of three-unit networks with no self-connection is investigated, the general formula for bifurcation direction of Hopf bifurcation is calculated, and the estimation formula of the period for periodic solution is given.
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.
BIFURCATION OF LIMIT CYCLES FROM A DOUBLE HOMOCLINIC LOOP WITH A ROUGH SADDLE
Institute of Scientific and Technical Information of China (English)
HAN MAOAN; BI PING
2004-01-01
This paper concerns with the bifurcation of limit cycles from a double bomoclinic loop under multiple parameter perturbations for general planar systems. The existence conditions of 4 homoclinic bifurcation curves and small and large limit cycles are especially investigated.
42 CFR 433.67 - Limitations on level of FFP for permissible provider-related donations.
2010-10-01
... 42 Public Health 4 2010-10-01 2010-10-01 false Limitations on level of FFP for permissible... General Administrative Requirements State Financial Participation § 433.67 Limitations on level of FFP for... the amount of bona fide provider-related donations that a State may receive without a reduction in...
Policy-level interventions and work-related psychosocial risk management in the European Union
Leka, S.; Jain, A.; Zwetsloot, G.I.J.M.; Cox, T.
2010-01-01
There exists a substantial degree of diversity across strategies to prevent and manage work- related psychosocial risks and their associated health effects. Whereas it is common to distinguish between organizational and individual interventions, the important level of policy- level interventions has
Yokus, Tuba
2015-01-01
This study aims to examine the relation between pre-service music teachers' psychological resilience and academic achievement levels and to determine what variables influence their psychological resilience levels. The study sample consisted of students enrolled in a music education program in the 2013-2014 academic year (N = 333). In respect with…
The Impact of Pathological Levels of Internet-Related Anxiety on Internet Usage
Brosnan, Mark; Joiner, Richard; Gavin, Jeff; Crook, Charles; Maras, Pam; Guiller, Jane; Scott, Adrian J.
2012-01-01
This article compares the use of the Internet during the first year of university education of students who have pathological levels of Internet anxiety with those who do not. Two hundred and sixteen first year psychology students (females 184, males 32) were surveyed for their levels of Internet-related anxiety, from which 12 (5.6%) were…
Some electrical and optical properties of nickel-related deep levels in silicon. [Si:Ni
Energy Technology Data Exchange (ETDEWEB)
Bartos, J. (Inst. of Physics, Slovak Academy of Sciences, Bratislava (Czechoslovakia)); Tesar, L. (Tesla Roznow, Roznov p. Radhostem (Czechoslovakia))
1990-12-16
Silicon wafers with p-n junctions are contaminated by nickel and the temperature behaviour of the reverse current of these p-n junctions is investigated. Nickel-related deep energy levels are studied by DLTS measurement. The dominant energy level of Ni is at E{sub v} + 0.31 eV. The illumination and annealing sensitivity of this level is also observed. An attempt is made to explain qualitatively this phenomenon. (orig.).
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.
Hopf Bifurcation of a Differential-Algebraic Bioeconomic Model with Time Delay
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Xiaojian Zhou
2012-01-01
Full Text Available We investigate the dynamics of a differential-algebraic bioeconomic model with two time delays. Regarding time delay as a bifurcation parameter, we show that a sequence of Hopf bifurcations occur at the positive equilibrium as the delay increases. Using the theories of normal form and center manifold, we also give the explicit algorithm for determining the direction of the Hopf bifurcations and the stability of the bifurcating periodic solutions. Numerical tests are provided to verify our theoretical analysis.
Kramers-Kronig relation in a Doppler-broadenedΛ-type three-level system
Institute of Scientific and Technical Information of China (English)
王梦; 庞兆广; 王如泉; 左战春; 芦小刚; 白金海; 裴丽娅; 缪兴绪; 高艳磊; 吴令安; 傅盘铭; 杨世平
2015-01-01
We measure the absorption and dispersion in a Doppler-broadenedΛ-type three level system by resonant stimulated Raman spectroscopy with homodyne detection. Through studying the dressed state energies of the system, it is found that the absorption and dispersion satisfy the Kramers–Kronig relation. The absorption and dispersion spectra calculated by employing this relation agree well with our experimental observations.
Liu, Yonggang; Peltier, W. Richard; Yang, Jun; Vettoretti, Guido; Wang, Yuwei
2016-07-01
The hard snowball Earth bifurcation point is determined by the level of atmospheric carbon dioxide concentration (pCO2) below which complete glaciation of the planet would occur. In previous studies, the bifurcation point was determined based on the assumption that the extent of continental glaciation could be neglected and the results thereby obtained suggested that very low values of pCO2 would be required (~100 ppmv). Here, we deduce the upper bound on the bifurcation point using the coupled atmosphere-ocean climate model of the NCAR that is referred to as the Community Climate System Model version 3 by assuming that the continents are fully covered by ice sheets prior to executing the transition into the hard snowball state. The thickness of the ice sheet is assumed to be that obtained by an ice-sheet model coupled to an energy balance model for a soft snowball Earth. We find that the hard snowball Earth bifurcation point is in the ranges of 600-630 and 300-320 ppmv for the 720 and 570 Ma continental configurations, respectively. These critical points are between 10 and 3 times higher than their respective values when ice sheets are completely neglected. We also find that when the ice sheets are thinner than those assumed above, the climate is colder and the bifurcation point is larger. The key process that causes the excess cooling when continental ice sheets are thin is shown to be associated with the fact that atmospheric heat transport from the adjacent oceans to the ice sheet-covered continents is enhanced in such conditions. Feedbacks from sea-ice expansion and reduced water vapor concentration further cool the oceanic regions strongly.
Stability of the Bifurcation Solutions for a Predator-Prey Model
Institute of Scientific and Technical Information of China (English)
孟义杰; 王一夫
2003-01-01
The bifurcation solution of the nonnegative steady-state of a reaction-diffusion system was investigated. The combination of the sturm-type eigenvalue and the theorem of bifurcation was used to study the local coexistence solutions, and obtain the stability of bifurcation solutions. The system model describes predator-prey interaction in an unstirred chemostat.
Stability and Hopf Bifurcation of a Predator-Prey Model with Distributed Delays and Competition Term
Directory of Open Access Journals (Sweden)
Lv-Zhou Zheng
2014-01-01
Full Text Available A class of predator-prey system with distributed delays and competition term is considered. By considering the time delay as bifurcation parameter, we analyze the stability and the Hopf bifurcation of the predator-prey system. According to the theorem of Hopf bifurcation, some sufficient conditions are obtained for the local stability of the positive equilibrium point.
Quasi-periodic Bifurcations of Invariant Circles in Low-dimensional Dissipative Dynamical Systems
Vitolo, Renato; Broer, Henk; Simo, Carles
2011-01-01
This paper first summarizes the theory of quasi-periodic bifurcations for dissipative dynamical systems. Then it presents algorithms for the computation and continuation of invariant circles and of their bifurcations. Finally several applications are given for quasiperiodic bifurcations of Hopf, sad
STABILITY AND BIFURCATION OF A HUMAN RESPIRATORY SYSTEM MODEL WITH TIME DELAY
Institute of Scientific and Technical Information of China (English)
沈启宏; 魏俊杰
2004-01-01
The stability and bifurcation of the trivial solution in the two-dimensional differential equation of a model describing human respiratory system with time delay were investigated. Formulas about the stability of bifurcating periodic solution and the direction of Hopf bifurcation were exhibited by applying the normal form theory and the center manifold theorem. Furthermore, numerical simulation was carried out.
Anna, Bluszcz
2016-01-01
Nowadays methods of measurement and assessment of the level of sustained development at the international, national and regional level are a current research problem, which requires multi-dimensional analysis. The relative assessment of the sustainability level of the European Union member states and the comparative analysis of the position of Poland relative to other countries was the aim of the conducted studies in the article. EU member states were treated as objects in the multi-dimensional space. Dimensions of space were specified by ten diagnostic variables describing the sustainability level of UE countries in three dimensions, i.e., social, economic and environmental. Because the compiled statistical data were expressed in different units of measure, taxonomic methods were used for building an aggregated measure to assess the level of sustainable development of EU member states, which through normalisation of variables enabled the comparative analysis between countries. Methodology of studies consisted of eight stages, which included, among others: defining data matrices, calculating the variability coefficient for all variables, which variability coefficient was under 10 %, division of variables into stimulants and destimulants, selection of the method of variable normalisation, developing matrices of normalised data, selection of the formula and calculating the aggregated indicator of the relative level of sustainable development of the EU countries, calculating partial development indicators for three studies dimensions: social, economic and environmental and the classification of the EU countries according to the relative level of sustainable development. Statistical date were collected based on the Polish Central Statistical Office publication.
2008-01-01
The International Public Relations Association (IPRA) in their Gold Paper No.7 (1990:6) recognises two schools of thought about education and training for public relations : one that it is preparation for a technician level post and the other that it is preparation for management. These two approaches broadly represent that of public relations education in the USA and that in Europe, respectively. These two different approaches differ markedly. South African tertiary education utilises both o...
Relation between workplace accidents and the levels of carboxyhemoglobin in motorcycle taxi drivers
Directory of Open Access Journals (Sweden)
Luiz Almeida da Silva
2013-09-01
Full Text Available OBJECTIVE: to investigate the relation between workplace accidents and the levels of carboxyhemoglobin found in motorcycle taxi drivers. METHOD: correlational, quantitative study involving 111 workers and data obtained in July 2012 through a questionnaire to characterize the participants and blood collection to measure carboxyhemoglobin levels. RESULT: 28.8% had suffered workplace accidents; 27.6% had fractured the lower limbs and significant symptoms of carbon monoxide exposure were verified in smokers. The carboxyhemoglobin levels were higher among smokers and victims of workplace accidents. CONCLUSION: motorcycle taxi drivers had increased levels of carboxyhemoglobin, possibly due to the exposure to carbon monoxide; these levels are also increased among smokers and victims of workplace accidents. The study provides advances in the knowledge about occupational health and environmental science, and also shows that carboxyhemoglobin can be an indicator of exposure to environmental pollutants for those working outdoors, which can be related to workplace accidents.
Bifurcation Analysis of Spiral Growth Processes in Plants
DEFF Research Database (Denmark)
Andersen, C.A.; Ernstsen, C.N.; Mosekilde, Erik
1999-01-01
In order to examine the significance of different assumptions about the range of the inhibitory forces, we have performed a series of bifurcation analyses of a simple model that can explain the formation of helical structures in phyllotaxis. Computer simulations are used to illustrate the role...
Streamline topology: Patterns in fluid flows and their bifurcations
DEFF Research Database (Denmark)
Brøns, Morten
2007-01-01
Using dynamical systems theory, we consider structures such as vortices and separation in the streamline patterns of fluid flows. Bifurcation of patterns under variation of external parameters is studied using simplifying normal form transformations. Flows away from boundaries, flows close to fixed...
Efficient computation of bifurcation diagrams via adaptive ROMs
Energy Technology Data Exchange (ETDEWEB)
Terragni, F [Gregorio Millán Institute for Fluid Dynamics, Nanoscience and Industrial Mathematics, Universidad Carlos III de Madrid, E-28911 Leganés (Spain); Vega, J M, E-mail: fterragn@ing.uc3m.es [E.T.S.I. Aeronáuticos, Universidad Politécnica de Madrid, E-28040 Madrid (Spain)
2014-08-01
Various ideas concerning model reduction based on proper orthogonal decomposition are discussed, exploited, and suited to the approximation of complex bifurcations in some dissipative systems. The observation that the most energetic modes involved in these low dimensional descriptions depend only weakly on the actual values of the problem parameters is firstly highlighted and used to develop a simple strategy to capture the transitions occurring over a given bifurcation parameter span. Flexibility of the approach is stressed by means of some numerical experiments. A significant improvement is obtained by introducing a truncation error estimate to detect when the approximation fails. Thus, the considered modes are suitably updated on demand, as the bifurcation parameter is varied, in order to account for possible changes in the phase space of the system that might be missed. A further extension of the method to more complex (quasi-periodic and chaotic) attractors is finally outlined by implementing a control of truncation instabilities, which leads to a general, adaptive reduced order model for the construction of bifurcation diagrams. Illustration of the ideas and methods in the complex Ginzburg–Landau equation (a paradigm of laminar flows on a bounded domain) evidences a fairly good computational efficiency. (paper)
Shells, orbit bifurcations and symmetry restorations in Fermi systems
Magner, A G; Arita, K
2016-01-01
The periodic-orbit theory based on the improved stationary-phase method within the phase-space path integral approach is presented for the semiclassical description of the nuclear shell structure, concerning the main topics of the fruitful activity of V. G. Solovjov. We apply this theory to study bifurcations and symmetry breaking phenomena in a radial power-law potential which is close to the realistic Woods-Saxon one up to about the Fermi energy. Using the realistic parametrization of nuclear shapes we explain the origin of the double-humped fission barrier and the asymmetry in the fission isomer shapes by the bifurcations of periodic orbits. The semiclassical origin of the oblate-prolate shape asymmetry and tetrahedral shapes is also suggested within the improved periodic-orbit approach. The enhancement of shell structures at some surface diffuseness and deformation parameters of such shapes are explained by existence of the simple local bifurcations and new non-local bridge-orbit bifurcations in integrabl...
Existence and bifurcation of integral manifolds with applications
Institute of Scientific and Technical Information of China (English)
HAN; Mao'an; CHEN; Xianfeng
2005-01-01
In this paper a bifurcation theorem on the existence of integral manifolds is obtained by using contracting principle. As an application, sufficient conditions for a higher dimensional system to have an integral manifold are given. Especially the existence and uniqueness of a 3-dimensional invariant torus appearing in a 4-dimensional autonomous system with singularity of codimension two are proved.
Homoclinic Bifurcation for Boussinesq Equation with Even Constraint
Institute of Scientific and Technical Information of China (English)
DAI Zheng-De; JIANG Mu-Rong; DAI Qing-Yun; LI Shao-Lin
2006-01-01
@@ The exact homoclinic orbits and periodic soliton solution for the Boussinesq equation are shown. The equilibrium solution u0 = -1/6 is a unique bifurcation point. The homoclinic orbits and solitons will be interchanged with the solution varying from one side of-1/6 to the other side. The solution structure can be understood in general.
BIFURCATION ANALYSIS OF A MITOTIC MODEL OF FROG EGGS
Institute of Scientific and Technical Information of China (English)
吕金虎; 张子范; 张锁春
2003-01-01
The mitotic model of frog eggs established by Borisuk and Tyson is qualitatively analyzed. The existence and stability of its steady states are further discussed. Furthermore, the bifurcation of above model is further investigated by using theoretical analysis and numerical simulations. At the same time, the numerical results of Tyson are verified by theoretical analysis.
THE UNIQUENESS OF BIFURCATION TO SEPARATRIX LOOPS IN SUPERCRITICAL CASES
Institute of Scientific and Technical Information of China (English)
SUNJIANHUA
1994-01-01
In paper[4] the existence of bifurcation to separatrix loops in supercritical cases on the plane is studied.This note is a continuation of [4].The author proves the uniqueness of limit cycles in a neighb-orhood of the separatrix loop,and the results strengthen the relevant conclusions in[1-6].
A recent bifurcation in Arctic sea-ice cover
Livina, Valerie N
2012-01-01
There is ongoing debate over whether Arctic sea-ice has already passed a 'tipping point', or whether it will do so in future, with several recent studies arguing that the loss of summer sea ice does not involve a bifurcation because it is highly reversible in models. Recently developed methods can detect and sometimes forewarn of bifurcations in time-series data, hence we applied them to satellite data for Arctic sea-ice cover. Here we show that a new low ice cover state has appeared from 2007 onwards, which is distinct from the normal state of seasonal sea ice variation, suggesting a bifurcation has occurred from one attractor to two. There was no robust early warning signal of critical slowing down prior to this bifurcation, consistent with it representing the appearance of a new ice cover state rather than the loss of stability of the existing state. The new low ice cover state has been sampled predominantly in summer-autumn and seasonal forcing combined with internal climate variability are likely respons...
A recent bifurcation in Arctic sea-ice cover
Directory of Open Access Journals (Sweden)
V. N. Livina
2012-07-01
Full Text Available There is ongoing debate over whether Arctic sea-ice has already passed a "tipping point", or whether it will do so in future, with several recent studies arguing that the loss of summer sea ice does not involve a bifurcation because it is highly reversible in models. Recently developed methods can detect and sometimes forewarn of bifurcations in time-series data, hence we applied them to satellite data for Arctic sea-ice cover. Here we show that a new low ice cover state has appeared from 2007 onwards, which is distinct from the normal state of seasonal sea ice variation, suggesting a bifurcation has occurred from one attractor to two. There was no robust early warning signal of critical slowing down prior to this bifurcation, consistent with it representing the appearance of a new ice cover state rather than the loss of stability of the existing state. The new low ice cover state has been sampled predominantly in summer-autumn and seasonal forcing combined with internal climate variability are likely responsible for triggering recent transitions between the two ice cover states. However, all early warning indicators show destabilization of the summer-autumn sea-ice since 2007. This suggests the new low ice cover state may be a transient feature and further abrupt changes in summer-autumn Arctic sea-ice cover could lie ahead; either reversion to the normal state or a yet larger ice loss.
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.
Evidence and control of bifurcations in a respiratory system
Energy Technology Data Exchange (ETDEWEB)
Goldin, Matías A., E-mail: mgoldin@df.uba.ar; Mindlin, Gabriel B. [Laboratorio de Sistemas Dinámicos, IFIBA y Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 1, Ciudad Universitaria, Buenos Aires (Argentina)
2013-12-15
We studied the pressure patterns used by domestic canaries in the production of birdsong. Acoustically different sound elements (“syllables”) were generated by qualitatively different pressure gestures. We found that some ubiquitous transitions between syllables can be interpreted as bifurcations of a low dimensional dynamical system. We interpreted these results as evidence supporting a model in which different timescales interact nonlinearly.
Nonlinear aeroelastic analysis of airfoils: bifurcation and chaos
Lee, B. H. K.; Price, S. J.; Wong, Y. S.
1999-04-01
Different types of structural and aerodynamic nonlinearities commonly encountered in aeronautical engineering are discussed. The equations of motion of a two-dimensional airfoil oscillating in pitch and plunge are derived for a structural nonlinearity using subsonic aerodynamics theory. Three classical nonlinearities, namely, cubic, freeplay and hysteresis are investigated in some detail. The governing equations are reduced to a set of ordinary differential equations suitable for numerical simulations and analytical investigation of the system stability. The onset of Hopf-bifurcation, and amplitudes and frequencies of limit cycle oscillations are investigated, with examples given for a cubic hardening spring. For various geometries of the freeplay, bifurcations and chaos are discussed via the phase plane, Poincaré maps, and Lyapunov spectrum. The route to chaos is investigated from bifurcation diagrams, and for the freeplay nonlinearity it is shown that frequency doubling is the most commonly observed route. Examples of aerodynamic nonlinearities arising from transonic flow and dynamic stall are discussed, and special attention is paid to numerical simulation results for dynamic stall using a time-synthesized method for the unsteady aerodynamics. The assumption of uniform flow is usually not met in practice since perturbations in velocities are encountered in flight. Longitudinal atmospheric turbulence is introduced to show its effect on both the flutter boundary and the onset of Hopf-bifurcation for a cubic restoring force.
Numerical computation of bifurcations in large equilibrium systems in MATLAB.
Bindel, David; Friedman, Mark; Govaerts, Willy; Hughes, Jeremy; Kuznetsov, Yuri
2014-01-01
The Continuation of Invariant Subspaces (CIS) algorithm produces a smoothly-varying basis for an invariant subspace R(s) of a parameter-dependent matrix A(s). We have incorporated the CIS algorithm into Cl_matcont, a Matlab package for the study of dynamical systems and their bifurcations. Using sub
Bifurcation of Vortex Density Current in Trapped Bose Condensates
Institute of Scientific and Technical Information of China (English)
XU Tao; ZHANG ShengLi
2002-01-01
Vortex density current in the Gross-Pitaevskii theory is studied. It is shown that the inner structure of the topological vortices can be classified by Brouwer degrees and Hopf indices of φ-mapping. The dynamical equations of vortex density current have been given. The bifurcation behavior at the critical points of the current is discussed in detail.
Experimental bifurcation analysis of an impact oscillator – Determining stability
DEFF Research Database (Denmark)
Bureau, Emil; Schilder, Frank; Elmegård, Michael
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. A...
A reversible bifurcation analysis of the inverted pendulum
Broer, H.W.; Hoveijn, I.; Noort, M. van
1998-01-01
The inverted pendulum with a periodic parametric forcing is considered as a bifurcation problem in the reversible setting. Parameters are given by the size of the forcing and the frequency ratio. Normal form theory provides an integrable approximation of the Poincare map generated by a planar vector
Forcing an entire bifurcation diagram: Case studies in chemical oscillators
Kevrekidis, I. G.; Aris, R.; Schmidt, L. D.
1986-12-01
We study the finite amplitude periodic forcing of chemical oscillators. In particular, we examine systems that, when autonomous, (i.e. for zero forcing amplitude) exhibit a single stable oscillation. Using one of the system parameters as a forcing variable by varying it periodically, we show through extensive numerical work how the bifurcation diagram of the autonomous system with respect to this parameter affects the qualitative response of the full forced system. As the forcing variable oscillates around its midpoint, its instantaneous values may cross points (such as Hopf bifurcation poiints) of the autonomous bifurcation diagram so that the characterization of the system as a simple forced oscillator is no longer valid. Such a neighboring Hopf bifurcation of the unforced system is found to set the scene for the interaction of resonance horns and the loss of tori in the full forced system as the amplitude of the forcing grows. Our test case presented here is the Continuous Stirred Tank Reactor (CSTR) with periodically forced coolant temperature.
Bifurcation Analysis and Chaos Control in a Discrete Epidemic System
Directory of Open Access Journals (Sweden)
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.
Bifurcations of Eigenvalues of Gyroscopic Systems with Parameters Near Stability Boundaries
DEFF Research Database (Denmark)
Seyranian, Alexander P.; Kliem, Wolfhard
1999-01-01
. It is shown that the bifurcation (splitting) of double eigenvalues is closely related to the stability, flutter and divergence boundaries in the parameter space. Normal vectors to these boundaries are derived using only information at a boundary point: eigenvalues, eigenvectors and generalized eigenvectors......The paper deals with stability problems of linear gyroscopic systems with finite or infinite degrees of freedom, where the system matrices or operators depend smoothly on several real parameters. Explicit formulae for the behavior of eigenvalues under a change of parameters are obtained...
Institute of Scientific and Technical Information of China (English)
Li Yangcheng; He Wei
2008-01-01
For the unfolding of equivariant bifurcation problems with two types of state variables in the presence of parameter symmetry, the versa[ unfolding theorem with re-spect to left-right equivalence is obtained by using the related methods and techniques in the singularity theory of smooth map-germs. The corresponding results in [4, 9] can be considered as its special cases. A relationship between the versal unfolding w.r.t, left-right equivalence and the versal deformation w.r.t, contact equivalence is established.
Increased deoxythymidine triphosphate levels is a feature of relative cognitive decline
DEFF Research Database (Denmark)
Madsen, Claus Desler; Frederiksen, Jane H; Olsen, Maria Nathalie Angleys;
2015-01-01
Mitochondrial bioenergetics, mitochondrial reactive oxygen species (ROS) and cellular levels of nucleotides have been hypothesized as early indicators of Alzheimer's disease (AD). Utilizing relative decline of cognitive ability as a predictor of AD risk, we evaluated the correlation between change...... of deoxythymidine-triphosphate (dTTP) (20%), but not mitochondrial bioenergetics parameters measured in this study or mitochondrial ROS. Levels of dTTP in PBMCs are indicators of relative cognitive change suggesting a role of deoxyribonucleotides in the etiology of AD....... of deoxyribonucleotide triphosphates were measured in peripheral blood mononuclear cells (PBMCs) from a total of 103 selected participants displaying the most pronounced relative cognitive decline and relative cognitive improvement. We show that relative cognitive decline is associated with higher PBMC content...
Dynamics and bifurcations of a coupled column-pendulum oscillator
Mustafa, G.; Ertas, A.
1995-05-01
This study deals with the dynamics of a large flexible column with a tip mass-pendulum arrangement. The system is a conceptualization of a vibration-absorbing device for flexible structures with tip appendages. The bifurcation diagrams of the averaged system indicate that the system loses stability via two distinct routes; one leading to a saddle-node bifurcation, and the other to the Hopf bifurcation, indicating the existence of an invariant torus. Under the change of forcing amplitude, these bifurcations coalesce. This phenomenon has important global ramifications, in the sense that the periodic modulations associated with the Hopf bifurcation tend to have an infinite period, a strong indicator of existence of homoclinic orbits. The system also possesses isolated solutions (the so-called "isolas") that form isolated loops bounded away from zero. As the forcing amplitude is varied, the isolas appear, disappear or coalesce with the regular solution branches. The response curves indicate that the column amplitude shows saturation and the pendulum acts as a vibration absorber. However, there is also a frequency range over which a reverse flow of energy occurs, where the pendulum shows reduced amplitude at the cost of large amplitudes of the column. The experimental dynamics shows that the periodic motion gives rise to a quasi-periodic response, confirming the existence of tori. Within the quasi-periodic region, there are windows containing intricate webs of mode-locked periodic responses. An increase in the force amplitude causes the tori to break up, a phenomenon similar to the onset of turbulence in hydrodynamics.
Relative and absolute level populations in beam-foil-excited neutral helium
Davidson, J.
1975-01-01
Relative and absolute populations of 19 levels in beam-foil-excited neutral helium at 0.275 MeV have been measured. The singlet angular-momentum sequences show dependences on principal quantum number consistent with n to the -3rd power, but the triplet sequences do not. Singlet and triplet angular-momentum sequences show similar dependences on level excitation energy. Excitation functions for six representative levels were measured in the range from 0.160 to 0.500 MeV. The absolute level populations increase with energy, whereas the neutral fraction of the beam decreases with energy. Further, the P angular-momentum levels are found to be overpopulated with respect to the S and D levels. The overpopulation decreases with increasing principal quantum number.
Dual-earner families' stress levels and personal and life-style-related variables.
Sund, K; Ostwald, S K
1985-01-01
This study investigated personal and life-style-related variables and stress levels in dual-earner families in the preschool stage of family development. The sample was composed of 92 families receiving child day care through a major day care provider in the Upper Midwest. The Family Inventory of Life Events and Changes was used to measure the family stress level. The majority of dual-earner families in this sample were experiencing a moderate level of family stress based on national stress level norms calculated for families in the preschool stage of development. Parental age and age of children were statistically related to the family stress level. Life-style-related variables statistically significant in this study were amount of income and satisfaction with income level, satisfaction with child care, and flexibility in vacation scheduling. Parents who could easily schedule vacations during the same time period had significantly lower family stress levels than parents who had difficulty scheduling vacations together, p less than .003. Additionally, parents who reported being forced to take separate vacations because of their work schedules had statistically higher scores on family stress than parents who had never had to take separate vacations because of work schedules, p less than .002.
Pankow, James F
2010-04-13
This study examines the sensitivity in predicted levels of atmospheric organic particulate matter (M(o), microg m(-3)) as those levels may potentially be affected by changes in relative humidity and temperature. In a given system, for each partitioning compound, f(g) and f(p) represent the gaseous and particulate fractions (f(g) + f(p) = 1). Sensitivity in the M(o) levels becomes dampened as the compounds contributing significantly to M(o) are increasingly found in the particle phase (f(p) --> 1). Thus, although local maxima in sensitivity can be encountered as M(o) levels increase, because as M(o) increases each f(p) --> 1, then increasing M(o) levels generally tend to reduce sensitivity in M(o) levels to changes in relative humidity and temperature. Experiments designed to elucidate the potential magnitudes of the effects of relative humidity and temperature on M(o) levels must be carried out at M(o) levels that are relevant for the ambient atmosphere: The f(p) values for the important partitioning compounds must not be elevated above ambient-relevant values. Systems in which M(o) levels are low (e.g., 1-2 microg m(-3)) and/or composed of unaged secondary organic aerosol are the ones most likely to show sensitivity to changing relative humidity and temperature. Results from two published chamber studies are examined in the above regard: [Warren B, et al. (2009) Atmos Environ 43:1789-1795] and [Prisle NL, et al. (2010) Geophys Res Lett 37:L01802].
Postglacial relative sea level change at Fildes Peninsula, King George Island (West Antarctic
Directory of Open Access Journals (Sweden)
K. V. Polishchuk
2016-01-01
Full Text Available Analysis and integration of data obtained in our field and laboratory investigations of 2008–2012 together with results of previous paleogeographic studies were conducted to reveal parameters and factors of the post-glacial changes in the relative sea-level on the Fildes Peninsula and the King George Island. Results of dating of organic material taken from cross-sections of Quaternary deposits, data on morphology of marine landforms as well as on bottom sediments in lakes were used to construct a curve of changes in the relative sea-level.Our research has shown that the rapid rise of relative sea level in the area (since the beginning of the Holocene decelerated about 8000 years BP, achieving its maximum about 7000 years BP. This was followed by the fall of relative sea-level (the land elevation by 18–20 m in total, and it was characterized by relatively high rate of fall during periods of 6000– 5000 years BP, 4000–2500 years BP, and during the last 1500 years; the rate decreased in 5000–4000 years BP and 2500– 1600 years BP. The changes in relative sea level in this region were determined by the following factors: the eustatic component of the global changes in sea-level and, possibly, oscillations in the global sea level of another nature; local parameters of the Last glacial maximum; a course of the Peninsula deglaciation; regional physical characteristics of the Earth's crust and the mantle substances; local tectonic processes, including the isostatic rebound. Since the beginning of the Holocene up to about 7000 years BP, the main contribution to changes of the relative sea-level in this area was made by the global eustatic factor. The subsequent fall of the relative sea-level (elevation of the Peninsula surface proceeded under condition of reduced role of the eustatic factor and predominance of other factors.
Généreux, Philippe; Kini, Annapoorna; Lesiak, Maciej; Kumsars, Indulis; Fontos, Géza; Slagboom, Ton; Ungi, Imre; Metzger, D. Christopher; Wykrzykowska, Joanna J.; Stella, Pieter R.; Bartorelli, Antonio L.; Fearon, William F.; Lefèvre, Thierry; Feldman, Robert L.; Tarantini, Giuseppe; Bettinger, Nicolas; Minalu Ayele, Girma; LaSalle, Laura; Francese, Dominic P.; Onuma, Yoshinobu; Grundeken, Maik J.; Garcia-Garcia, Hector M.; Laak, Linda L.; Cutlip, Donald E.; Kaplan, Aaron V.; Serruys, Patrick W.; Leon, Martin B.
2016-01-01
Objectives: To examine the benefit of the Tryton dedicated side branch (SB) stent compared with provisional stenting in the treatment of complex bifurcation lesions involving large SBs. Background: The TRYTON Trial was designed to evaluate the utility of a dedicated SB stent to treat true bifurcatio
BIFURCATION IN A TWO-DIMENSIONAL NEURAL NETWORK MODEL WITH DELAY
Institute of Scientific and Technical Information of China (English)
WEI Jun-jie; ZHANG Chun-rui; LI Xiu-ling
2005-01-01
A kind of 2-dimensional neural network model with delay is considered. By analyzing the distribution of the roots of the characteristic equation associated with the model, a bifurcation diagram was drawn in an appropriate parameter plane. It is found that a line is a pitchfork bifurcation curve. Further more, the stability of each fixed point and existence of Hopf bifurcation were obtained. Finally, the direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions were determined by using the normal form method and centre manifold theory.
Institute of Scientific and Technical Information of China (English)
LuoGuanwei; XieJianhua
2003-01-01
A two-degrees-of-freedom vibratory system with a clearance or gap is under consideration based on the Poincard map. Stability and local bifurcation of the period-one doubleimpact symmetrical motion of the system are analyzed by using the equation of map. The routes from periodic impact motions to chaos, via pitchfork bifurcation, period-doubling bifurcation and grazing bifurcation, are studied by numerical simulation. Under suitable system parameter conditions, Neimark-Sacker bifurcations associated with periodic impact motion can occur in the two-degrees-of-freedom vibro-impact system.
Bifurcation of piecewise-linear nonlinear vibration system of vehicle suspension
Institute of Scientific and Technical Information of China (English)
Shun ZHONG; Yu-shu CHEN
2009-01-01
A kinetic model of the piecewise-linear nonlinear suspension system that consists of a dominant spring and an assistant spring is established.Bifurcation of the resonance solution to a suspension system with two degrees of freedom is investigated with the singularity theory.Transition sets of the system and 40 groups of bifurcation diagrams are obtained.The local bifurcation is found,and shows the overall characteristics of bifurcation.Based on the relationship between parameters and the topological bifurcation solutions,motion characteristics with different parameters are obtained.The results provides a theoretical basis for the optimal control of vehicle suspension system parameters.
The Land Subsidence and Relative Sea Level Rise in Chinese Delta Areas
Institute of Scientific and Technical Information of China (English)
YeYincan; LiuDujuan
2004-01-01
Based on some experts' research effort, the problems of land subsidence and relative sea level rise in three Chinese delta areas(Huanghe, Changjiang and Zhujiang Delta) are analyzed and discussed in this paper. The authors' opinion is that the land subsidence is mainly induced by human activity and has made the greater contributions to the relative sea level rise and become one of the geological hazards in these areas. In Tianjin and Shanghai areas where had ever existed serious land subsidence problem, due to the positive and effective control methods, the ratio of man-induced land subsidence to relative sea level rise decreased from 80% - 90% in 1960s - 1970s to less than 60% at present. But it is estimated that in the next tens of years this ratio will still be considerable. So human being must keep its eyes on this phenomenon and take more positive countermeasures to control the land subsidenee.
Deterministic and stochastic bifurcations in the Hindmarsh-Rose neuronal model.
Dtchetgnia Djeundam, S R; Yamapi, R; Kofane, T C; Aziz-Alaoui, M A
2013-09-01
We analyze the bifurcations occurring in the 3D Hindmarsh-Rose neuronal model with and without random signal. When under a sufficient stimulus, the neuron activity takes place; we observe various types of bifurcations that lead to chaotic transitions. Beside the equilibrium solutions and their stability, we also investigate the deterministic bifurcation. It appears that the neuronal activity consists of chaotic transitions between two periodic phases called bursting and spiking solutions. The stochastic bifurcation, defined as a sudden change in character of a stochastic attractor when the bifurcation parameter of the system passes through a critical value, or under certain condition as the collision of a stochastic attractor with a stochastic saddle, occurs when a random Gaussian signal is added. Our study reveals two kinds of stochastic bifurcation: the phenomenological bifurcation (P-bifurcations) and the dynamical bifurcation (D-bifurcations). The asymptotical method is used to analyze phenomenological bifurcation. We find that the neuronal activity of spiking and bursting chaos remains for finite values of the noise intensity.
Multi-Bifurcation Effect of Blood Flow by Lattice Boltzmann Method
Institute of Scientific and Technical Information of China (English)
RAO Yong; NI Yu-Shan; LIU Chao-Feng
2008-01-01
The multi-bifurcation effect of blood flow is investigated by lattice Boltzmann method at Re = 200 with six different bifurcation angles α, which are 22.5°, 25°, 28°, 30°, 33°, 35°, respectively. The velocities and ratios of average velocity at various bifurcations are discussed. It is indicated that the maximum velocity at the section near the first divider increases and shifts towards the walls of branch with the increase of α. At the first bifurcation, the average horizontal velocities increase with the increase of α. The average horizontal velocities of outer branches at the secondary bifurcation decrease at 22.5°≤α≤30° and increase at 30°≤α≤35°, whereas those of inner branches at the secondary bifurcation have the opposite variation, as the same as the above variations of the ratios of average horizontal velocities at various bifurcations. The ratios of average vertical velocities of branch at first bifurcation to that of outer branches at the secondary bifurcation increase at 22.5°≤α≤30° and decrease at 30°≤α≤35°, whereas the ratios of average vertical velocities of branch at first bifurcation to that of inner branches at the secondary bifurcation always decrease.
Periodically perturbed Hopf bifurcation of a kind of nonlinear systems%一类非线性系统的周期扰动Hopf 分支
Institute of Scientific and Technical Information of China (English)
殷红燕
2014-01-01
The influence of small periodic perturbations on a kind of nonlinear systems exhibiting Hopf bi-furcation is studied. In particular, we discuss the existence of bifurcating periodic solutions in the case that the excitation frequency and the critical natural frequency of Hopf bifurcation is resonance and subharmonic resonance. In this work, the ideas related method of averaging. It is shown that in some parameter regions the systems exhibit harmonic solution bifurcation and subharmonic solution bifurcation. Furthermore, the stability of subharmonic solutions is discussed.%研究了小周期扰动对一类存在Hopf 分支的非线性系统的影响。特别是应用平均法讨论了扰动频率与Hopf分支固有频率在共振及二阶次调和共振的情形周期解分支的存在性。表明了在某些参数区域内，系统存在调和解分支和次调和解分支，并进一步讨论了二阶次调和分支周期解的稳定性。
Kaluza-Klein Masses and Couplings: Radiative Corrections to Tree-Level Relations
Bauman, Sky
2011-01-01
The most direct experimental signature of a compactified extra dimension is the appearance of towers of Kaluza-Klein particles obeying specific mass and coupling relations. However, such masses and couplings are subject to radiative corrections. In this paper, using techniques developed in previous work, we investigate the extent to which such radiative corrections deform the expected tree-level relations between Kaluza-Klein masses and couplings. As toy models for our analysis, we investigate a flat five-dimensional scalar \\lambda\\phi^4 model and a flat five-dimensional Yukawa model involving both scalars and fermions. In each case, we identify the conditions under which the tree-level relations are stable to one-loop order, and the situations in which radiative corrections modify the algebraic forms of these relations. Such corrections to Kaluza-Klein spectra therefore have the potential to distort the apparent geometry of a large extra dimension.
HOPF BIFURCATION AND CHAOS OF FINANCIAL SYSTEM ON CONDITION OF SPECIFIC COMBINATION OF PARAMETERS
Institute of Scientific and Technical Information of China (English)
Junhai MA; Yaqiang CUI; Lixia LIU
2008-01-01
This paper studies the global bifurcation and Hopf bifurcation of one kind of complicated financial system with different parameter combinations. Conditions on which bifurcation happens, and the critical system structure when the system transforms from one kind of topological structure to another are studied as well. The criterion for identifying Hopf bifurcation under different parameter combinations is also given. The chaotic character of this system under quasi-periodic force is finally studied. The bifurcation structure graphs are given when two parameters of the combination are fixed while the other parameter varies. The presence and stability of 2 and 3 dimensional torus bifurcation are studied. All of the Lyapunov exponents of the system with different bifurcation parameters and routes leading the system to chaos with different parameter combinations are studied. It is of important theoretical and practical meaning to probe the intrinsic mechanism of such continuous complicated financial system and to find the macro control policies for such kind of system.
Hopf bifurcations in a predator-prey system with multiple delays
Energy Technology Data Exchange (ETDEWEB)
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.
Doubly twisted Neimark–Sacker bifurcation and two coexisting two-dimensional tori
Energy Technology Data Exchange (ETDEWEB)
Sekikawa, Munehisa, E-mail: sekikawa@cc.utsunomiya-u.ac.jp [Department of Mechanical and Intelligent Engineering, Utsunomiya University, Utsunomiya 321-8585 (Japan); Inaba, Naohiko [Organization for the Strategic Coordination of Research and Intellectual Properties, Meiji University, Kawasaki 214-8571 (Japan)
2016-01-08
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. - Highlights: • This study investigates a three-coupled delayed logistic map. • It generates complex quasiperiodic bifurcations. • Two periodic solution coexist in a conventional Arnol'd tongue. • Two two-tori coexist in a high-dimensional Arnol'd tongue.
The relation between leisure activities and glycemic levels from deaf adults
Directory of Open Access Journals (Sweden)
Inacia Sátiro Xavier de França
2014-01-01
Full Text Available The aim has been to check the association among leisure activities and glycemic levels from deaf adults. Transversal study made with 36 deaf adults in an Audiocomunicação school, making use of a semi-structured questionnaire. Chi-square, Fisher and Contingency Coefficient tests were made. Unfed capillary glycemic average showed up close to values considered usual, however, there are participants with risky glycemic level. Participants with altered glycemic levels totalized 11,1%. We checked association among deaf glycemic people having leisure activities, go shopping (p=0,034 and visiting relatives (p=0,012. Leisure activities may have influence over glycemic levels of deaf people, and nurses are supposed to consider stimuli and orientation of leisure activities in nurse processes, as a potential intervention to promote health of those people, and prevent implications caused by altered glycemic levels.
Matteson, M A; Linton, A D; Barnes, S J; Cleary, B L; Lichtenstein, M J
1996-02-01
Clinical observations and research studies have documented that people with Alzheimer's disease and related disorders (ADRD) appear to regress developmentally during the course of the disease. The purpose of this study was to prospectively determine the association between changes in Piaget levels of cognitive development and cognitive decline in nursing home residents in various stages of ADRD. Fifty-seven people were tested three times at yearly intervals, using the Folstein Mini-Mental State Exam to determine cognitive levels and a set of 14 Piaget tasks to determine cognitive developmental levels: 1) Formal Operations; 2) Concrete Operations; 3) Preoperational; and 4) Sensorimotor. Mean MMSE scores declined from 12.7 to 9.4, and there was a downward trend in Piaget levels over the study period. ANOVA showed significant differences (p Piaget levels, and Spearman rho analysis showed significant correlations between Piaget levels and MMSE for each year (p < 0.0005, Years 1, 2, 3). The results suggest that there is a concurrent decline in cognitive developmental levels and cognition in people in various stages of Alzheimer's disease and related disorders.
Kobtan, Abdelrahman A; El-Kalla, Ferial S; Soliman, Hanan H; Zakaria, Soha S; Goda, Mohamed A
2016-02-01
Hepatic encephalopathy is a serious complication of liver failure. Until now, the precise pathophysiologic mechanisms are not fully determined. It has been demonstrated that manganese plays an important role in the pathogenesis of hepatic encephalopathy. Therefore, we studied manganese levels in serum of cirrhotic patients with hepatic encephalopathy in relation to grading and recurrence of hepatic encephalopathy. One hundred persons were enrolled in the study, 80 cirrhotic patients with or without encephalopathy and 20 healthy controls. Hepatic encephalopathy was diagnosed clinically and by laboratory findings. Serum manganese levels were measured in all participants. The grading of hepatic encephalopathy was significantly correlated to the severity of liver dysfunction. The mean serum manganese level was significantly higher in cirrhotic patients than in controls and in cirrhotic patients with encephalopathy than in those without encephalopathy. It was also significantly higher in patients with advanced grading of hepatic encephalopathy. Serum manganese level was positively correlated to number of recurrences of encephalopathy during a 6-month follow-up period. Serum manganese levels were able to predict recurrence of hepatic encephalopathy within 6 months following the episode. Serum manganese levels are positively correlated to the modified Child-Pugh score of cirrhosis as well as grading and number of recurrences of hepatic encephalopathy. Higher manganese levels seem to be related to worsening of the condition, and its measurement may be used as a predictor of repeated recurrences.
DEFF Research Database (Denmark)
Mommersteeg, Paula M C; Kupper, Nina; Schoormans, Dounya;
2010-01-01
Chronic heart failure (CHF) is a condition with a high mortality risk. Besides traditional risk factors, poor health-related quality of life (HRQoL) is also associated with poor prognosis in CHF. Immunological functioning might serve as a biological pathway underlying this association, since pro...... and anti-inflammatory cytokines are independent predictors of prognosis. The aim of this study was to examine the association between HRQoL at inclusion (baseline) and pro and anti-inflammatory cytokine levels both at baseline and 12months, using a prospective study design. CHF outpatients completed...
Individual variation in levels of haptoglobin-related protein in children from Gabon.
Directory of Open Access Journals (Sweden)
Heather J Imrie
Full Text Available BACKGROUND: Haptoglobin related protein (Hpr is a key component of trypanosome lytic factors (TLF, a subset of high-density lipoproteins (HDL that form the first line of human defence against African trypanosomes. Hpr, like haptoglobin (Hp can bind to hemoglobin (Hb and it is the Hpr-Hb complexes which bind to these parasites allowing uptake of TLF. This unique form of innate immunity is primate-specific. To date, there have been no population studies of plasma levels of Hpr, particularly in relation to hemolysis and a high prevalence of ahaptoglobinemia as found in malaria endemic areas. METHODS AND PRINCIPAL FINDINGS: We developed a specific enzyme-linked immunosorbent assay to measure levels of plasma Hpr in Gabonese children sampled during a period of seasonal malaria transmission when acute phase responses (APR, malaria infection and associated hemolysis were prevalent. Median Hpr concentration was 0.28 mg/ml (range 0.03-1.1. This was 5-fold higher than that found in Caucasian children (0.049 mg/ml, range 0.002-0.26 with no evidence of an APR. A general linear model was used to investigate associations between Hpr levels, host polymorphisms, parasitological factors and the acute phase proteins, Hp, C-reactive protein (CRP and albumin. Levels of Hpr were associated with Hp genotype, decreased with age and were higher in females. Hpr concentration was strongly correlated with that of Hp, but not CRP. CONCLUSIONS/SIGNIFICANCE: Individual variation in Hpr levels was related to Hp level, Hp genotype, demographics, malaria status and the APR. The strong correlations between plasma levels of Hp and Hpr suggest that they are regulated by similar mechanisms. These population-based observations indicate that a more dynamic view of the relative roles of Hpr and Hpr-Hb complexes needs to be considered in understanding innate immunity to African trypanosomes and possibly other pathogens including the newly discovered Plasmodium spp of humans and
Olivieri, Giuseppe; Russo, Maria Elena; Marzocchella, Antonio; Salatino, Piero
2011-01-01
A mathematical model of an aerobic biofilm reactor is presented to investigate the bifurcational patterns and the dynamical behavior of the reactor as a function of different key operating parameters. Suspended cells and biofilm are assumed to grow according to double limiting kinetics with phenol inhibition (carbon source) and oxygen limitation. The model presented by Russo et al. is extended to embody key features of the phenomenology of the granular-supported biofilm: biofilm growth and detachment, gas-liquid oxygen transport, phenol, and oxygen uptake by both suspended and immobilized cells, and substrate diffusion into the biofilm. Steady-state conditions and stability, and local dynamic behavior have been characterized. The multiplicity of steady states and their stability depend on key operating parameter values (dilution rate, gas-liquid mass transfer coefficient, biofilm detachment rate, and inlet substrate concentration). Small changes in the operating conditions may be coupled with a drastic change of the steady-state scenario with transcritical and saddle-node bifurcations. The relevance of concentration profiles establishing within the biofilm is also addressed. When the oxygen level in the liquid phase is <10% of the saturation level, the biofilm undergoes oxygen starvation and the active biofilm fraction becomes independent of the dilution rate. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011.
A bifurcation analysis of boiling water reactor on large domain of parametric spaces
Pandey, Vikas; Singh, Suneet
2016-09-01
The boiling water reactors (BWRs) are inherently nonlinear physical system, as any other physical system. The reactivity feedback, which is caused by both moderator density and temperature, allows several effects reflecting the nonlinear behavior of the system. Stability analyses of BWR is done with a simplified, reduced order model, which couples point reactor kinetics with thermal hydraulics of the reactor core. The linear stability analysis of the BWR for steady states shows that at a critical value of bifurcation parameter (i.e. feedback gain), Hopf bifurcation occurs. These stable and unstable domains of parametric spaces cannot be predicted by linear stability analysis because the stability of system does not include only stability of the steady states. The stability of other dynamics of the system such as limit cycles must be included in study of stability. The nonlinear stability analysis (i.e. bifurcation analysis) becomes an indispensable component of stability analysis in this scenario. Hopf bifurcation, which occur with one free parameter, is studied here and it formulates birth of limit cycles. The excitation of these limit cycles makes the system bistable in the case of subcritical bifurcation whereas stable limit cycles continues in an unstable region for supercritical bifurcation. The distinction between subcritical and supercritical Hopf is done by two parameter analysis (i.e. codimension-2 bifurcation). In this scenario, Generalized Hopf bifurcation (GH) takes place, which separates sub and supercritical Hopf bifurcation. The various types of bifurcation such as limit point bifurcation of limit cycle (LPC), period doubling bifurcation of limit cycles (PD) and Neimark-Sacker bifurcation of limit cycles (NS) have been identified with the Floquet multipliers. The LPC manifests itself as the region of bistability whereas chaotic region exist because of cascading of PD. This region of bistability and chaotic solutions are drawn on the various
Grant, K. M.; Grimm, R.; Mikolajewicz, U.; Marino, G.; Ziegler, M.; Rohling, E. J.
2016-01-01
The Mediterranean basin is sensitive to global sea-level changes and African monsoon variability on orbital timescales. Both of these processes are thought to be important to the deposition of organic-rich sediment layers or 'sapropels' throughout the eastern Mediterranean, yet their relative influe
Macro-level indicators of the relations between research funding and research output
Leydesdorff, L.; Wagner, C.S.
2009-01-01
In response to the call for a science of science policy, we discuss the contribution of indicators at the macro-level of nations from a scientometric perspective. In addition to global trends such as the rise of China, one can relate percentages of world share of publications to government expenditu
Gao, Zan; Newton, Maria; Carson, Russell L.
2008-01-01
This study examines the predictive utility of students' motivation (self-efficacy and task values) to their physical activity levels and health-related physical fitness (cardiovascular fitness and muscular strength/endurance) in middle school fitness activity classes. Participants (N = 305) responded to questionnaires assessing their self-efficacy…
The Influence of Activation Level on Belief Bias in Relational Reasoning
Banks, Adrian P.
2013-01-01
A novel explanation of belief bias in relational reasoning is presented based on the role of working memory and retrieval in deductive reasoning, and the influence of prior knowledge on this process. It is proposed that belief bias is caused by the believability of a conclusion in working memory which influences its activation level, determining…
Data revisions and the statistical relation of global mean sea-level and temperature
DEFF Research Database (Denmark)
Hillebrand, Eric; Johansen, Søren; Schmith, Torben
We study the stability of the estimated statistical relation of global mean temperature and global mean sea-level with regard to data revisions. Using three different model specifications proposed in the literature, we compare coefficient estimates and forecasts using two different vintages...
Recovery during lunch breaks: Testing long-term relations with energy levels at work
Sianoja, M.; Kinnunen, U.; Bloom, J. de; Korpela, K.; Geurts, S.A.E.
2016-01-01
This study had two aims. First, we examined whether lunch break settings, activities, and recovery experiences were associated with lunchtime recovery cross-sectionally. Second, we investigated whether lunchtime recovery was related to energy levels (i.e., exhaustion and vigor) across a 12-month per
Is There a Relationship between Improving Human Relation Skills and Levels of Academic Performance?
Burns, Jolene; Byrne, Susan; Kiedaisch, Jan; Thiele, Nancy; Weber, Gwyn
This Action Research Project implemented a program for improving human relation skills intended to raise the academic performance level of students. The target population consists of kindergarten, seventh grade (regular/at-risk), and high school (regular/behavior disordered) students. Analysis of both research literature and problem evidence…
Castaldi, C.; Frenken, K.; Los, B.
2015-01-01
Castaldi C., Frenken K. and Los B. Related variety, unrelated variety and technological breakthroughs: an analysis of US state-level patenting, Regional Studies. This paper investigates how variety affects the innovation output of a region. Borrowing arguments from theories of recombinant innovation
Uric acid levels and their relation to incapacities in acute cerebrovascular disease
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Julio López Argüelles
2010-02-01
Full Text Available Background: cerebrovascular disease and ischemic cardiopathy can be considered as an epidemic and constitute the first cause of incapacities in developed countries. Multiple studies have shown the association between uric acid levels and cerebrovascular diseases. Objective: To correlate the levels of serum uric acid and incapacities in the acute phase of cerebrovascular disease. Methods: A correlational study was carried out with 217 patients with acute cerebrovascular disease. The patient’s incapacity level was measured by using the Barthel Index and those results were related with the serum uric acid levels and other variables. Results: Male patients have higher levels of uric acid (p=0, 04; r=0, 13. Age and Barthel index were p < 0,001; r = -0, 30 and uric acid levels and Barthel Index were p=0, 03; r=-0, 14. The principal predicting factors of incapacity in the acute phase of cerebrovascular disease were the high levels of uric acid, age and diabetes mellitus. Conclusions: It is shown that the highest is the level of uric acid at advanced age; the greatest is the risk of suffering from incapacity in acute phases of cerebrovascular diseases.
Testosterone levels in healthy men are related to amygdala reactivity and memory performance.
Ackermann, Sandra; Spalek, Klara; Rasch, Björn; Gschwind, Leo; Coynel, David; Fastenrath, Matthias; Papassotiropoulos, Andreas; de Quervain, Dominique J-F
2012-09-01
Testosterone is a steroid hormone thought to influence both emotional and cognitive functions. It is unknown, however, if testosterone also affects the interaction between these two domains, such as the emotional arousal-induced enhancement of memory. Healthy subjects (N=234) encoded pictures taken from the International Affective Picture System (IAPS) during functional magnetic resonance imaging (fMRI) and underwent a free recall test 10 min after memory encoding. We show that higher endogenous testosterone levels at encoding were associated with higher arousal ratings of neutral pictures in men. fMRI analysis revealed that higher testosterone levels were related to increased brain activation in the amygdala during encoding of neutral pictures. Moreover, endogenous testosterone levels were positively correlated with the number of freely recalled neutral pictures. No such relations were found in women. These findings point to a male-specific role for testosterone in enhancing memory by increasing the biological salience of incoming information.
Bifurcations and Chaos in a Discrete Predator-prey System with Holling Type-Ⅳ Functional Response
Institute of Scientific and Technical Information of China (English)
Ji-cai Huang
2005-01-01
A discrete predator-prey system with Holling type-Ⅳ functional response obtained by the Euler method is first investigated. The conditions of existence for fold bifurcation, flip bifurcation and Hopf bifurcation are derived by using the center manifold theorem and bifurcation theory. Furthermore, we give the condition for the occurrence of codimension-two bifurcation called the Bogdanov-Takens bifurcation for fixed points and present approximate expressions for saddle-node, Hopf and homoclinic bifurcation sets near the Bogdanov-Takens bifurcation point. We also show, the existence of degenerated fixed point with codimension three at least. The numerical simulations, including bifurcation diagrams, phase portraits, and computation of maximum Lyapunov exponents, not only show the consistence with the theoretical analysis but also exhibit the rich and complex dynamical behaviors such as the attracting invariant circle, period-doubling bifurcation from period-2,3,4 orbits,interior crisis, intermittency mechanic, and sudden disappearance of chaotic dynamic.
Discrete Thermodynamics of 2-level Laser - Why Not and When Yes
Zilbergleyt, B
2006-01-01
The paper explores a possible application of the discrete thermodynamics to a 2-level laser. The model accounts for the laser openness to incoming pumping power and coming out energy with the emitted light. As an open system, a laser should be in open equilibrium with thermodynamic forces, related to both energy flows. Conditions of equilibria are expressed by a logistic map with specially developed dynamic inverse pitchfork bifurcation diagrams for graphical presentation of the solutions. The graphs explicitly confirm the triggering nature of a laser where bistability is manifested by pitchfork ground and laser branches, with the relative population equilibrium values close to 1 and 0 correspondingly. Simulation was run for a 2-level laser emitting light from far infrared to short wave UV. A newly discovered feature of such a laser is the line spectrum of up and down transitions of the laser excitable dwellers, occurring between the laser and the ground pitchfork branches beyond bifurcation point. The densit...
Sorokin, A. V.; Aparicio Alcalde, M.; Bastidas, V. M.; Engelhardt, G.; Angelakis, D. G.; Brandes, T.
2016-09-01
In this work we study a one-dimensional lattice of Lipkin-Meshkov-Glick models with alternating couplings between nearest-neighbors sites, which resembles the Su-Schrieffer-Heeger model. Typical properties of the underlying models are present in our semiclassical-topological hybrid system, allowing us to investigate an interplay between semiclassical bifurcations at mean-field level and topological phases. Our results show that bifurcations of the energy landscape lead to diverse ordered quantum phases. Furthermore, the study of the quantum fluctuations around the mean-field solution reveals the existence of nontrivial topological phases. These are characterized by the emergence of localized states at the edges of a chain with free open-boundary conditions.
Alterations of serum levels of BDNF-related miRNAs in patients with depression.
Directory of Open Access Journals (Sweden)
You-Jie Li
Full Text Available Depression is a serious and potentially life-threatening mental disorder with unknown etiology. Emerging evidence shows that brain-derived neurotrophic factor (BDNF and microRNAs (miRNAs play critical roles in the etiology of depression. Here this study was aimed to identify and characterize the roles of BDNF and its putative regulatory miRNAs in depression. First, we identified that miR-182 may be a putative miRNA that regulates BDNF levels by bioinformatic studies, and characterized the effects of miR-182 on the BDNF levels using cell-based studies, side by side with miR-132 (a known miRNA that regulates BDNF expression. We showed that treatment of miR-132 and miR-182 respectively decreased the BDNF protein levels in a human neuronal cell model, supporting the regulatory roles of miR-132 and miR-182 on the BDNF expression. Furthermore, we explored the roles of miR-132 and miR-182 on the BDNF levels in depression using human subjects by assessing their serum levels. Compared with the healthy controls, patients with depression showed lower serum BDNF levels (via the enzyme-linked immunosorbent assays and higher serum miR-132 and miR-182 levels (via the real-time PCR. Finally, the Pearson's (or Spearman's correlation coefficient was calculated to study whether there was a relationship among the Self-Rating Depression Scale score, the serum BDNF levels, and serum BDNF-related miRNA levels. Our results revealed that there was a significant negative correlation between the SDS scores and the serum BDNF levels, and a positive correlation between the SDS scores and miR-132 levels. In addition, we found a reverse relationship between the serum BDNF levels and the miR-132/miR-182 levels in depression. Collectively, we provided evidence supporting that miR-182 is a putative BDNF-regulatory miRNA, and suggested that the serum BDNF and its related miRNAs may be utilized as important biomarkers in the diagnosis or as therapeutic targets of depression.
Suárez-Bagnasco, D.; Balay, G.; Cymberknop, L.; Armentano, R. L.; Negreira, C. A.
2013-03-01
Arterial behaviour in-vivo is influenced, amongst other factors, by the interaction between blood flow and the arterial wall endothelium, and the biomechanical properties of the arterial wall. This interaction plays an important role in pathogenic mechanisms of cardiovascular diseases such as atherosclerosis and arteriosclerosis. To quantify these interactions both from biomechanical and hemodynamical standpoints, a complete characterization and modelling of the arterial wall, blood flow, shear wall and circumferential wall stresses are needed. The development of a new multi-parameter measurement system (distances, pressures, flows, velocity profiles, temperature, viscosity) for an in-vitro characterization of the biomechanics and hemodynamics in arterial bifurcations (specially in carotid bifurcations) is described. This set-up represents an improvement relative to previous set-ups developed by the group FCIEN-FMED and is presently under development. Main subsystems interactions and environment-system interactions were identified and compensated to improve system's performance. Several interesting problems related with signal acquisition using a variety of sensors and some experimental results are shown and briefly discussed. Experimental data allow construction of meshes and parameter estimation of the biomechanical properties of the arterial wall, as well as boundary conditions, all suitable to be employed in CFD and FSI numerical simulation.
Fluid dynamics in airway bifurcations: III. Localized flow conditions.
Martonen, T B; Guan, X; Schreck, R M
2001-04-01
Localized flow conditions (e.g., backflows) in transition regions between parent and daughter airways of bifurcations were investigated using a computational fluid dynamics software code (FIDAP) with a Cray T90 supercomputer. The configurations of the bifurcations were based on Schreck s (1972) laboratory models. The flow intensities and spatial regions of reversed motion were simulated for different conditions. The effects of inlet velocity profiles, Reynolds numbers, and dimensions and orientations of airways were addressed. The computational results showed that backflow was increased for parabolic inlet conditions, larger Reynolds numbers, and larger daughter-to-parent diameter ratios. This article is the third in a systematic series addressed in this issue; the first addressed primary velocity patterns and the second discussed secondary currents.
Isochronous bifurcations in second-order delay differential equations
Directory of Open Access Journals (Sweden)
Andrea Bel
2014-07-01
Full Text Available In this article we consider a special type of second-order delay differential equations. More precisely, we take an equation of a conservative mechanical system in one dimension with an added term that is a function of the difference between the value of the position at time $t$ minus the position at the delayed time $t-\\tau$. For this system, we show that, under certain conditions of non-degeneration and of convergence of the periodic solutions obtained by the Homotopy Analysis Method, bifurcation branches appearing in a neighbourhood of Hopf bifurcation due to the delay are isochronous; i.e., all the emerging cycles have the same frequency.
Numerical Study on the Bifurcation of the North Equatorial Current
Institute of Scientific and Technical Information of China (English)
LIU Yulong; WANG Qi; SONG Jun; ZHU Xiande; GONG Xiaoqing; WU Fang
2011-01-01
A 1.5-layer reduced-gravity model forced by wind stress is used to study the bifurcations of the North Equatorial Current (NEC).The authors found that after removing the Ekman drift,the modelled circulations can serve well as a proxy of the SODA circulations on the σθ=25.0kgm-3 potential density surface based on available long-term reanalysis wind stress data.The modelled results show that the location of the western boundary bifurcation of the NEC depends on both zonal averaged and local zero wind stress curl latitude.The effects of the anomalous wind stress curl added in different areas are also investigated and it is found that they can change the strength of the Mindanao Eddy (ME),and then influence the interior pathway.
Model Reduction of Nonlinear Aeroelastic Systems Experiencing Hopf Bifurcation
Abdelkefi, Abdessattar
2013-06-18
In this paper, we employ the normal form to derive a reduced - order model that reproduces nonlinear dynamical behavior of aeroelastic systems that undergo Hopf bifurcation. As an example, we consider a rigid two - dimensional airfoil that is supported by nonlinear springs in the pitch and plunge directions and subjected to nonlinear aerodynamic loads. We apply the center manifold theorem on the governing equations to derive its normal form that constitutes a simplified representation of the aeroelastic sys tem near flutter onset (manifestation of Hopf bifurcation). Then, we use the normal form to identify a self - excited oscillator governed by a time - delay ordinary differential equation that approximates the dynamical behavior while reducing the dimension of the original system. Results obtained from this oscillator show a great capability to predict properly limit cycle oscillations that take place beyond and above flutter as compared with the original aeroelastic system.
Extraordinary behavioral entrainment following circadian rhythm bifurcation in mice.
Harrison, Elizabeth M; Walbeek, Thijs J; Sun, Jonathan; Johnson, Jeremy; Poonawala, Qays; Gorman, Michael R
2016-12-08
The mammalian circadian timing system uses light to synchronize endogenously generated rhythms with the environmental day. Entrainment to schedules that deviate significantly from 24 h (T24) has been viewed as unlikely because the circadian pacemaker appears capable only of small, incremental responses to brief light exposures. Challenging this view, we demonstrate that simple manipulations of light alone induce extreme plasticity in the circadian system of mice. Firstly, exposure to dim nocturnal illumination (entrainment. Continuation of dim light is unnecessary for T15/30 behavioral entrainment following bifurcation. Finally, neither dim light alone nor a shortened night is sufficient for the extraordinary entrainment observed under bifurcation. Thus, we demonstrate in a non-pharmacological, non-genetic manipulation that the circadian system is far more flexible than previously thought. These findings challenge the current conception of entrainment and its underlying principles, and reveal new potential targets for circadian interventions.
Topological bifurcations in a model society of reasonable contrarians
Bagnoli, Franco
2013-01-01
People are often divided into conformists and contrarians, the former tending to align to the majority opinion in their neighborhood and the latter tending to disagree with that majority. In practice, however, the contrarian tendency is rarely followed when there is an overwhelming majority with a given opinion, which denotes a social norm. Such reasonable contrarian behavior is often considered a mark of independent thought, and can be a useful strategy in financial markets. We present the opinion dynamics of a society of reasonable contrarian agents. The model is a cellular automaton of Ising type, with antiferromagnetic pair interactions modeling contrarianism and plaquette terms modeling social norms. We introduce the entropy of the collective variable as a way of comparing deterministic (mean-field) and probabilistic (simulations) bifurcation diagrams. In the mean field approximation the model exhibits bifurcations and a chaotic phase, interpreted as coherent oscillations of the whole society. However, i...
Diameter of basalt columns derived from fracture mechanics bifurcation analysis.
Bahr, H-A; Hofmann, M; Weiss, H-J; Bahr, U; Fischer, G; Balke, H
2009-05-01
The diameter of columnar joints forming in cooling basalt and drying starch increases with decreasing growth rate. This observation can be reproduced with a linear-elastic three-dimensional fracture mechanics bifurcation analysis, which has been done for a periodic array of hexagonal columnar joints by considering a bifurcation mode compatible with observations on drying starch. In order to be applicable to basalt columns, the analysis has been carried out with simplified stationary temperature fields. The critical diameter differs from the one derived with a two-dimensional model by a mere factor of 1/2. By taking into account the latent heat released at the solidification front, the results agree fairly well with observed column diameters.
Perturbed period-doubling bifurcation. II. Experiments on Josephson junctions
DEFF Research Database (Denmark)
Eriksen, Gert Friis; Hansen, Jørn Bindslev
1990-01-01
We present experimental results on the effect of periodic perturbations on a driven, dynamic system that is close to a period-doubling bifurcation. In the preceding article a scaling law for the change of stability of such a system was derived for the case where the perturbation frequency ωS is c......B as a function of the frequency and the amplitude of the perturbation signal ΔμB(ωS,AS) for a model system, the microwave-driven Josephson tunnel junction, and find reasonable agreement between the experimental results and the theory.......We present experimental results on the effect of periodic perturbations on a driven, dynamic system that is close to a period-doubling bifurcation. In the preceding article a scaling law for the change of stability of such a system was derived for the case where the perturbation frequency ω...
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.
Symmetry restoring bifurcation in collective decision-making.
Zabzina, Natalia; Dussutour, Audrey; Mann, Richard P; Sumpter, David J T; Nicolis, Stamatios C
2014-12-01
How social groups and organisms decide between alternative feeding sites or shelters has been extensively studied both experimentally and theoretically. One key result is the existence of a symmetry-breaking bifurcation at a critical system size, where there is a switch from evenly distributed exploitation of all options to a focussed exploitation of just one. Here we present a decision-making model in which symmetry-breaking is followed by a symmetry restoring bifurcation, whereby very large systems return to an even distribution of exploitation amongst options. The model assumes local positive feedback, coupled with a negative feedback regulating the flow toward the feeding sites. We show that the model is consistent with three different strains of the slime mold Physarum polycephalum, choosing between two feeding sites. We argue that this combination of feedbacks could allow collective foraging organisms to react flexibly in a dynamic environment.
Complex bifurcations in Bénard-Marangoni convection
Vakulenko, Sergey; Sudakov, Ivan
2016-10-01
We study the dynamics of a system defined by the Navier-Stokes equations for a non-compressible fluid with Marangoni boundary conditions in the two-dimensional case. We show that more complicated bifurcations can appear in this system for a certain nonlinear temperature profile as compared to bifurcations in the classical Rayleigh-Bénard and Bénard-Marangoni systems with simple linear vertical temperature profiles. In terms of the Bénard-Marangoni convection, the obtained mathematical results lead to our understanding of complex spatial patterns at a free liquid surface, which can be induced by a complicated profile of temperature or a chemical concentration at that surface. In addition, we discuss some possible applications of the results to turbulence theory and climate science.
Finite Element Meshes Auto-Generation for the Welted Bifurcation
Institute of Scientific and Technical Information of China (English)
YUANMei; LIYa-ping
2004-01-01
In this paper, firstly, a mathematical model for a specific kind of welted bifurcation is established, the parametric equation for the intersecting curve is resulted in. Secondly, a method for partitioning finite element meshes of the welted bifurcation is put forward, its main idea is that developing the main pipe surface and the branch pipe surface respectively, dividing meshes on each developing plane and obtaining meshes points, then transforming their plane coordinates into space coordinates. Finally, an applied program for finite element meshes auto-generation is simply introduced, which adopt ObjectARX technique and its running result can be shown in AutoCAD. The meshes generated in AutoCAD can be exported conveniently to most of finite element analysis soft wares, and the finite element computing result can satisfy the engineering precision requirement.
Binks, Oliver; Meir, Patrick; Rowland, Lucy; da Costa, Antonio Carlos Lola; Vasconcelos, Steel Silva; de Oliveira, Alex Antonio Ribeiro; Ferreira, Leandro; Christoffersen, Bradley; Nardini, Andrea; Mencuccini, Maurizio
2016-07-01
The tropics are predicted to become warmer and drier, and understanding the sensitivity of tree species to drought is important for characterizing the risk to forests of climate change. This study makes use of a long-term drought experiment in the Amazon rainforest to evaluate the role of leaf-level water relations, leaf anatomy and their plasticity in response to drought in six tree genera. The variables (osmotic potential at full turgor, turgor loss point, capacitance, elastic modulus, relative water content and saturated water content) were compared between seasons and between plots (control and through-fall exclusion) enabling a comparison between short- and long-term plasticity in traits. Leaf anatomical traits were correlated with water relation parameters to determine whether water relations differed among tissues. The key findings were: osmotic adjustment occurred in response to the long-term drought treatment; species resistant to drought stress showed less osmotic adjustment than drought-sensitive species; and water relation traits were correlated with tissue properties, especially the thickness of the abaxial epidermis and the spongy mesophyll. These findings demonstrate that cell-level water relation traits can acclimate to long-term water stress, and highlight the limitations of extrapolating the results of short-term studies to temporal scales associated with climate change.
Relation of obesity with serum 25 hydroxy vitamin D3 levels in type 2 diabetic patients
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Ahmet Cimbek
2012-01-01
Full Text Available Background: Hypovitaminosis D is associated with diabetes mellitus (DM. Aim of our study was to determine the relation of obesity with vitamin D levels in type 2 diabetic patients. Materials and Methods: We examined 101 type 2 diabetic patients and made a correlation analysis in all parameters. Then we classified our diabetics according to their body-mass indices and compared their 25 hdroxy vitamin D3 levels. Results: We found negative correlation between 25O HD and body mass index (BMI (P: <0.001, r: -0.23. When we classified our diabetics according to their body mass indices as normal, overweight and obese, and compared their 25 hydroxy vitamin D3 levels, we determined that in every BMI group 25 hydroxy vitamin D levels were not found to be significantly different. Conclusion: These results suggest that at least in a Turkish population with type 2 DM vitamin D levels are low and correlate with BMI, but when vitamin D levels are so low, as obesity worsens vitamin D levels does not lessen.
Bifurcation analysis for a free boundary problem modeling tumor growth
Escher, Joachim
2010-01-01
In this paper we deal with a free boundary problem modeling the growth of nonnecrotic tumors.The tumor is treated as an incompressible fluid, the tissue elasticity is neglected and no chemical inhibitor species are present. We re-express the mathematical model as an operator equation and by using a bifurcation argument we prove that there exist stationary solutions of the problem which are not radially symmetric.
Time-Periodic Einstein--Klein--Gordon Bifurcations of Kerr
Chodosh, Otis
2015-01-01
We construct one-parameter families of solutions to the Einstein--Klein--Gordon equations bifurcating off the Kerr solution such that the underlying family of spacetimes are each an asymptotically flat, stationary, axisymmetric, black hole spacetime, and such that the corresponding scalar fields are non-zero and time-periodic. An immediate corollary is that for these Klein--Gordon masses, the Kerr family is not asymptotically stable as a solution to the Einstein--Klein--Gordon equations.
Bifurcation of solutions of nonlinear Sturm–Liouville problems
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Gulgowski Jacek
2001-01-01
Full Text Available A global bifurcation theorem for the following nonlinear Sturm–Liouville problem is given Moreover we give various versions of existence theorems for boundary value problems The main idea of these proofs is studying properties of an unbounded connected subset of the set of all nontrivial solutions of the nonlinear spectral problem , associated with the boundary value problem , in such a way that .
Asymptotic results for bifurcating random coefficient autoregressive processes
Blandin, Vassili
2012-01-01
The purpose of this paper is to study the asymptotic behavior of the weighted least square estimators of the unknown parameters of random coefficient bifurcating autoregressive processes. Under suitable assumptions on the immigration and the inheritance, we establish the almost sure convergence of our estimators, as well as a quadratic strong law and central limit theorems. Our study mostly relies on limit theorems for vector-valued martingales.
SHAPE BIFURCATION OF AN ELASTIC WAFER DUE TO SURFACE STRESS
Institute of Scientific and Technical Information of China (English)
闫琨; 何陵辉; 刘人怀
2003-01-01
A geometrically nonlinear analysis was proposed for the deformation of a freestanding elastically isotropic wafer caused by the surface stress change on one surface. Thelink between the curvature and the change in surface stress was obtained analytically fromenergetic consideration. In contrast to the existing linear analysis, a remarkableconsequence is that, when the wafer is very thin or the surface stress difference between thetwo major surfaces is large enough, the shape of the wafer will bifurcate.
Bifurcations and Chaos in Time Delayed Piecewise Linear Dynamical Systems
Senthilkumar, D. V.; Lakshmanan, M.
2004-01-01
We reinvestigate the dynamical behavior of a first order scalar nonlinear delay differential equation with piecewise linearity and identify several interesting features in the nature of bifurcations and chaos associated with it as a function of the delay time and external forcing parameters. In particular, we point out that the fixed point solution exhibits a stability island in the two parameter space of time delay and strength of nonlinearity. Significant role played by transients in attain...
A reversible bifurcation analysis of the inverted pendulum
Broer, H. W.; Hoveijn, I.; van Noort, M.
1998-01-01
The inverted pendulum with a periodic parametric forcing is considered as a bifurcation problem in the reversible setting. Parameters are given by the size of the forcing and the frequency ratio. Normal form theory provides an integrable approximation of the Poincaré map generated by a planar vector field. Genericity of the model is studied by a perturbation analysis, where the spatial symmetry is optional. Here equivariant singularity theory is used.
A reversible bifurcation analysis of the inverted pendulum
Broer, H.W.; Hoveijn, I.; van Noort, M.
1998-01-01
The inverted pendulum with a periodic parametric forcing is considered as a bifurcation problem in the reversible setting. Parameters are given by the size of the forcing and the frequency ratio. Normal form theory provides an integrable approximation of the Poincare map generated by a planar vector field. Genericity of the model is studied by a perturbation analysis, where the spatial symmetry is optional. Here equivariant singularity theory is used.
BIFURCATIONS OF INVARIANT CURVES OF A DIFFERENCE EQUATION
Institute of Scientific and Technical Information of China (English)
贺天兰
2001-01-01
Bifurcation of the invariant curves of a difference equation is studied. The system defined by the difference equation is integrable , so the study of the invariant curves of the difference system can become the study of topological classification of the planar phase portraits defined by a planar Hamiltonian system. By strict qualitative analysis, the classification of the invariant curves in parameter space can be obtained.
Hopf and homoclinic bifurcations for near-Hamiltonian systems
Tian, Yun; Han, Maoan
2017-02-01
We study homoclinic bifurcation of limit cycles in perturbed planar Hamiltonian systems. Suppose that a homoclinic loop is defined by H =hs. Our main result is that a new method is established for computing the coefficients of the expansion of Melnikov functions at h =hs. Then by using those coefficients, more limit cycles would be found around homoclinic loops. An example is also provided to illustrate our method.
Bifurcation for non linear ordinary differential equations with singular perturbation
Directory of Open Access Journals (Sweden)
Safia Acher Spitalier
2016-10-01
Full Text Available We study a family of singularly perturbed ODEs with one parameter and compare their solutions to the ones of the corresponding reduced equations. The interesting characteristic here is that the reduced equations have more than one solution for a given set of initial conditions. Then we consider how those solutions are organized for different values of the parameter. The bifurcation associated to this situation is studied using a minimal set of tools from non standard analysis.
Ng, Yan Cheng; Namgung, Bumseok; Leo, Hwa Liang; Kim, Sangho
2016-07-26
This study examined the effect of red blood cell (RBC) aggregation on nitric oxide (NO) and oxygen (O2) distributions in the downstream vessels of arteriolar bifurcations. Particular attention was paid to the inherent formation of asymmetric cell-free layer (CFL) widths in the downstream vessels and its consequential impact on the NO/O2 bioavailability after the bifurcations. A microscopic image-based two-dimensional transient model was used to predict the NO/O2 distribution by utilizing the in vivo CFL width data obtained under non-, normal- and hyper-aggregating conditions at the pseudoshear rate of 15.6±2.0s(-1). In vivo experimental result showed that the asymmetry of CFL widths was enhanced by the elevation in RBC aggregation level. The model demonstrated that NO bioavailability was regulated by the dynamic fluctuation of the local CFL widths, which is corollary to its modulation of wall shear stress. Accordingly, the uneven distribution of NO/O2 was prominent at opposite sides of the arterioles up to six vessel-diameter (6D) away from the bifurcating point, and this was further enhanced by increasing the levels of RBC aggregation. Our findings suggested that RBC aggregation potentially augments both the formation of asymmetric CFL widths and its influence on the uneven distribution of NO/O2 in the downstream flow of an arteriolar bifurcation. The extended heterogeneity of NO/O2 downstream (2D-6D) also implied its potential propagation throughout the entire arteriolar microvasculature.
Institute of Scientific and Technical Information of China (English)
Su-deok SHON; Seung-jae LEE; Kang-guk LEE
2013-01-01
This study investigated characteristics of bifurcation and critical buckling load by shape imperfection of space truss,which were sensitive to initial conditions.The critical point and buckling load were computed by the analysis of the eigenvalues and determinants of the tangential stiffness matrix.The two-free-nodes example and star dome were selected for the case study in order to examine the nodal buckling and global buckling by the sensitivity to the eigen buckling mode and the analyses of the influence,and characteristics of the parameters as defined by the load ratio of the center node and surrounding node,as well as rise-span ratio were performed.The sensitivity to the imperfection of the initial shape of the two-free-nodes example,which occurs due 1o snapping at the critical point,resulted in bifurcation before the limit point due to the buckling mode,and the buckling load was reduced by the increase in the amount of imperfection.The two sensitive buckling patterns of the numerical model are established by investigating the displaced position of the free nodes,and the asymmetric eigenmode greatly influenced the behavior of the imperfection shape whether it was at limit point or bifurcation.Furthermore,the sensitive mode of the two-free-nodes example was similar to the in-extensional basis mechanism of a simplified model.The star dome,which was used to examine the influence among several nodes,indicated that the influence of nodal buckling was greater than that of global buckling as the rise-span ratio was higher.Besides,global buckling is occurred with reaching bifurcation point as the value of load ratio was higher,and the buckling load level was about 50％-70％ of load level at limit point.
Zhioua, M.; El Aroudi, A.; Belghith, S.; Bosque-Moncusí, J. M.; Giral, R.; Al Hosani, K.; Al-Numay, M.
A study of a DC-DC boost converter fed by a photovoltaic (PV) generator and supplying a constant voltage load is presented. The input port of the converter is controlled using fixed frequency pulse width modulation (PWM) based on the loss-free resistor (LFR) concept whose parameter is selected with the aim to force the PV generator to work at its maximum power point. Under this control strategy, it is shown that the system can exhibit complex nonlinear behaviors for certain ranges of parameter values. First, using the nonlinear models of the converter and the PV source, the dynamics of the system are explored in terms of some of its parameters such as the proportional gain of the controller and the output DC bus voltage. To present a comprehensive approach to the overall system behavior under parameter changes, a series of bifurcation diagrams are computed from the circuit-level switched model and from a simplified model both implemented in PSIM© software showing a remarkable agreement. These diagrams show that the first instability that takes place in the system period-1 orbit when a primary parameter is varied is a smooth period-doubling bifurcation and that the nonlinearity of the PV generator is irrelevant for predicting this phenomenon. Different bifurcation scenarios can take place for the resulting period-2 subharmonic regime depending on a secondary bifurcation parameter. The boundary between the desired period-1 orbit and subharmonic oscillation resulting from period-doubling in the parameter space is obtained by calculating the eigenvalues of the monodromy matrix of the simplified model. The results from this model have been validated with time-domain numerical simulation using the circuit-level switched model and also experimentally from a laboratory prototype. This study can help in selecting the parameter values of the circuit in order to delimit the region of period-1 operation of the converter which is of practical interest in PV systems.
Directory of Open Access Journals (Sweden)
Ehya Garshasbi
2010-02-01
Full Text Available Multiple sclerosis is a chronic inflammatory disease of central nervous system.Women are more susceptible to this disease. One of the obvious clinical complaints in women with multiple sclerosis specially treated with Beta Interferones is menstrual cycle irregularity. The aim of this study was to determine the prevalence of menstrual irregularities and probable changes in blood levels of related hormones (FSH, LH, PRL, TSH, T4, T3 in 58 females with definite MS treated with beta interferones versus 58 healthy women. In comparison to the control group, the patients had higher prevalence of irregular menstruation (P=0.001, oligomenorrhea (p=0.03, abnormal amount of menstrual blood flow (P=0.001, abnormal duration of menstrual flow (P=0.01 and missed period (P=0.04. Mean LH level in patients group was higher than control group (P=0.04.Hyperprolactinemia (>25.5ng/ml was more prevalent in patients group .There were not a significant difference in plasma levels of FSH and thyroid hormones between two groups. There were some relations between the type of Beta interferones and the subtype of menstrual irregularities in the patients. In conclusion, the results of this study emphasized the high rate of menstrual problem and changes of related plasma hormone levels in MS patients.
Groot Jebbink, E.; Grimme, F.A.; Goverde, P.C.; Oostayen, J.A.; Slump, C.H.; Reijnen, M.M.P.J.
2015-01-01
OBJECTIVE: Kissing stents (KS) are commonly used to treat aortoiliac occlusive disease, but patency results are often lower than those of isolated stents. The Covered Endovascular Reconstruction of the Aortic Bifurcation (CERAB) technique was recently introduced to reconstruct the aortic bifurcation
Groot Jebbink, Erik; Grimme, Frederike A.B.; Goverde, Peter C.J.M.; Oostayen, van Jacques A.; Slump, Cornelis H.; Reijnen, Michel M.P.J.
2015-01-01
Objective: Kissing stents (KS) are commonly used to treat aortoiliac occlusive disease, but patency results are often lower than those of isolated stents. The Covered Endovascular Reconstruction of the Aortic Bifurcation (CERAB) technique was recently introduced to reconstruct the aortic bifurcation
Association of hair iron levels with creativity and psychological variables related to creativity
Takeuchi, Hikaru; Taki, Yasuyuki; Sekiguchi, Atsushi; Nouchi, Rui; Kotozaki, Yuka; Nakagawa, Seishu; Miyauchi, Carlos M.; Iizuka, Kunio; Yokoyama, Ryoichi; Shinada, Takamitsu; Yamamoto, Yuki; Hanawa, Sugiko; Araki, Tsuyoshi; Hashizume, Hiroshi; Kunitoki, Keiko; Sassa, Yuko; Kawashima, Ryuta
2013-01-01
Creativity generally involves the conception of original and valuable ideas. Previous studies have suggested an association between creativity and the dopaminergic system, and that physical activity facilitates creativity. Iron plays a key role in the dopaminergic system and physical activity. Here, we newly investigated the associations between hair iron levels and creativity, dopamine-related traits and states [novelty seeking, extraversion, and vigor (motivational state)], as well as the physical activity level. In the present study, we addressed this issue by performing a hair mineral analysis to determine iron levels and a behavioral creativity test of divergent thinking and related psychological measures among young adults (254 men, 88 women; mean age 20.79 ± 2.03 years). Iron levels did not show any significant association with creativity but displayed significant positive associations with novelty seeking, extraversion, and physical activity level. These results may be partly congruent with the notion that iron plays a key role in the dopaminergic system and imply that iron is important for traits and physical activity, which facilitate creativity. Future interventional or longitudinal studies are warranted to identify any causal effects. PMID:24385960
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Noormohammad Noori
2015-06-01
Full Text Available Background: Dilated cardiomyopathy is revealed with left ventricular dilatation and systolic dysfunction. Objectives: This study aimed to compare the children with dilated cardiomyopathy and control group regarding the level of Calcitonin Gene Related Peptide (CGRP and its relationship with echocardiography findings Patients and Methods: This case-control study was conducted on 37 children with dilated cardiomyopathy and free of any clinical symptoms and 37 healthy age- and sex-matched children referring to Ali-e-Asghar and Ali Ebne Abitaleb hospitals in Zahedan, Iran. After taking history, echocardiography was performed for both groups. The data were analyzed using the SPSS statistical software and appropriate statistical tests. Results: The two groups were significantly different regarding most of the echocardiographic parameters (P < 0.05. Also, a significant difference was found between the two groups concerning the mean CGRP levels (P = 0.001. Among echocardiographic parameters, CGRP was directly related to Interventricular Septal dimension in Systole (IVSS (P = 0.022, R = 0.375. However, no significant relationship was observed between CGRP level and Ross classification. Conclusions: The findings of this study showed an increase in CGRP serum levels in the case group. Besides, a direct correlation was observed between CGRP level and IVSS.
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Bayan A. Obeidat
2012-11-01
Full Text Available Objectives: To determine the prevalence of premenstrual symptoms (PMS due to primary dysmenorrhea among a sample of university female students, and to explore possible association with vitamin D and parathyroid (PTH levels, as well as frequency of consumption of dairy products. Design: A cross-sectional study. Setting: One Jordanian university. Subjects: A total of 177 female students aged between 18 and 24 years who experienced primary dysmenorrhea participated in the study and completed a self administered questionnaire to collect information concerning demographics, menstruation- related information, associated specified premenstrual symptoms, and consumption of dairy products. Plasma 25-hydroxyvitamin vitamin D level and intact parathyroid hormone level were measured. Results: Of the 177 participants 91.5% had two or more symptoms among which fatigue, mood swings, anxiety, abdominal bloating, and depression were the most prevalent symptoms. There was no evident association between presence of symptoms and vitamin D status, PTH level or dairy products consumption. Headaches and social withdrawal were significantly lower in those women who consumed high amounts of dairy products. Conclusion: Premenstrual symptoms are very common in young women with primary dysmenorrhea. PMS has no relation to levels of vitamin D, parathyroid hormone or dairy products consumption. Headache and social withdrawal may be affected by dairy product consumption.
Rustembegovic, Avdo; Sofic, Emin; Wichart, Ildiko
2006-01-01
Weight gain is a common adverse effect associated with the use of most typical and atypical antipsychotic. Aim of this study was to investigate serum prolactin, leptin, cholesterol, triglyceride, lipoproteins, such high density lipoprotein (HDL), and low density lipoprotein (LDL) levels in patients with Parkinson's disease (PD)-related psychosis during long-term medication with atypical antipsychotic. The study population comprised 40 patients, who were divided into 4 groups: olanzapine (n=10), risperidone (n=10), seroquel (n=10) monotherapy, a group of 10 patients receiving only antiparkinson drugs and a control group of 8 healthy persons. The patients were evaluated at baseline and at the sixth and twelfth week according to the Positive and Negative Syndrome Scale (PANSS), body mass index (BMI), and fasting serum prolactin, leptin, lipids and lipoproteins levels. Treatment of patients with olanzapine caused marked increase of serum LDL, cholesterol, triglyceride, and leptin levels (p<0,02). No changes in HDL concentrations. There was positive relationship between serum leptin, lipid levels and BMI. However, treatment of patients with seroquel did not cause changes in serum prolactin, leptin, lipids, and lipoproteins levels. Our results suggest that treatment of patients with PD-related psychosis with seroquel appears to have minimal influence on serum leptin, prolactin, lipids, lipoproteins and BMI compared with olanzapine and risperidone.
Factors related to high-level mobility in male servicemembers with traumatic lower-limb loss
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Ignacio A. Gaunaurd, PhD, MSPT
2013-10-01
Full Text Available The purpose of this study was to examine the possible relationship between factors modifiable by rehabilitation interventions (rehabilitation factors, other factors related to lower-limb loss (other factors, and high-level mobility as measured by the Comprehensive High-Level Activity Mobility Predictor (CHAMP in servicemembers (SMs with traumatic lower-limb loss. One-hundred eighteen male SMs with either unilateral transtibial amputation (TTA, unilateral transfemoral amputation (TFA, or bilateral lower-limb amputation (BLLA participated. Stepwise regression analysis was used to develop separate regression models of factors predicting CHAMP score. Regression models containing both rehabilitation factors and other factors explained 81% (TTA, 36% (TFA, and 91% (BLLA of the variance in CHAMP score. Rehabilitation factors such as lower-limb strength and dynamic balance were found to be significantly related to CHAMP score and can be enhanced with the appropriate intervention. Further, the findings support the importance of salvaging the knee joint and its effect on high-level mobility capabilities. Lastly, the J-shaped energy storage and return feet were found to improve high-level mobility for SMs with TTA. These results could help guide rehabilitation and aid in developing appropriate interventions to assist in maximizing high-level mobility capabilities for SMs with traumatic lower-limb loss.
Association of serum uric acid with different levels of glucose and related factors
Institute of Scientific and Technical Information of China (English)
YUAN Hui-juan; YANG Xu-guang; SHI Xiao-yang; TIAN Rui; ZHAO Zhi-gang
2011-01-01
Background Previous studies have demonstrated that serum uric acid (UA) is an independent predictor of incident type 2 diabetes mellitus (T2DM) in general populations. This study aimed to investigate specific characteristics of UA and its relationship between UA and blood glucose and other risk factors in the Chinese population.Methods A total of 946 subjects were included in this study. UA, glucose, insulin, fractional excretion of UA (FEua),creatinine clearance rate (Ccr), hemoglobin A1c (HbA1c), fructosamine (FA), blood pressure and lipids were studied and also reexamined after the patients underwent two weeks of combined therapeutics.Results UA levels were the highest in subjects with impaired glucose regulation (IGR), followed by subjects with normoglycemia (NGT) and finally by subjects with T2DM. The level of the 2-hour postprandial insulin and the area under the curve for insulin (AUCins) showed a similar tendency. The UA levels initially increased with increasing fasting blood glucose (FBG) and postprandial blood glucose (PPBG) levels, up to 7 mmol/L and 10 mmol/L, respectively, and thereafter decreased at higher FBG and PPBG levels. Compared with subjects in the lower serum UA quartile, subjects in the upper quartile of serum UA levels had higher weights, triglyceride levels, and creatinine levels as well as lower Ccr and FEua levels. Compared with women's group, UA levels were higher, and FEua levels were lower in men's group. Sex,body mass index (BMI), mean arterial blood pressure (MAP), serum triglycerides (TG), FA and Ccr were independent correlation factors of UA. UA decreased and FEua increased after the patients underwent a combined treatment.Conclusions UA increased initially and then decreased as glucose levels increased from NGT to IGR and T2DM.Compared with NGT and T2DM, IGR subjects had higher SUA levels, which related to its high levels of insulin. Under T2DM, male gender, BMI, MAP, Ccr, TG and FA are independent correlation factors of UA
Inertial and interceptional deposition of fibers in a bifurcating airway.
Zhang, L; Asgharian, B; Anjilvel, S
1996-01-01
A computer model of a three-dimensional bifurcating airway was constructed in which the parent and daughter airways had different lengths but equal diameters. A diameter of 0.6 cm was chosen for the airways based on the third generation of Weibel's symmetric lung model. Different bifurcation angles of 60 degrees, 90 degrees, and 120 degrees were studied. Airflow fields in the airway were obtained by a finite-element method (FIDAP, Fluid Dynamics International, Evanston, IL) for Reynolds numbers of 500 and 1000, assuming uniform parent inlet velocities. The equations of motion for fiber transport in the airways were obtained, and deposition by the combined mechanisms of impaction and interception was incorporated. A computer code was developed that utilized the flow field data and calculated fiber transport in the airways using the equations of motion for fibers. Deposition efficiency was obtained by simulating a large number of fibers of various sizes. Fiber entering the daughter airways tended to orient themselves parallel to the flow. A site of enhanced deposition (or hot spot) was observed at the carina. The dominant parameter for the deposition was the fiber Stokes number. Flow Reynolds number and airway bifurcation angle were also found to affect the deposition.
Fluid dynamics in airway bifurcations: I. Primary flows.
Martonen, T B; Guan, X; Schreck, R M
2001-04-01
The subject of fluid dynamics within human airways is of great importance for the risk assessment of air pollutants (inhalation toxicology) and the targeted delivery of inhaled pharmacologic drugs (aerosol therapy). As cited herein, experimental investigations of flow patterns have been performed on airway models and casts by a number of investigators. We have simulated flow patterns in human lung bifurcations and compared the results with the experimental data of Schreck (1972). The theoretical analyses were performed using a third-party software package, FIDAP, on the Cray T90 supercomputer. This effort is part of a systematic investigation where the effects of inlet conditions, Reynolds numbers, and dimensions and orientations of airways were addressed. This article focuses on primary flows using convective motion and isovelocity contour formats to describe fluid dynamics; subsequent articles in this issue consider secondary currents (Part II) and localized conditions (Part III). The agreement between calculated and measured results, for laminar flows with either parabolic or blunt inlet conditions to the bifurcations, was very good. To our knowledge, this work is the first to present such detailed comparisons of theoretical and experimental flow patterns in airway bifurcations. The agreement suggests that the methodologies can be employed to study factors affecting airflow patterns and particle behavior in human lungs.
Affordance-controlled bifurcations of action patterns in martial arts.
Hristovski, Robert; Davids, Keith; Araújo, Duarte
2006-10-01
Effects of participant-target distance and perceived handstriking efficiency on emergent behavior in the martial art of boxing were investigated, revealing affordance-controlled nonlinear dynamical effects (i.e. bifurcations) within the participant--target system. Results established the existence of critical values of scaled distances for emergence of first time excitations and annihilations of a diverse range of boxing actions i.e. on the appearance and dissolution of jabs, hooks and uppercuts. Reasons for the action diversity were twofold: (a) topological discontinuous changes (bifurcations) in the number of possible handstrikes, i.e. motor solutions to the hitting task; (b) fine modification of probabilities of emergence of striking patterns. Exploitation of a 'strikeability' affordance available in scaled distance-to-target information by boxers led to a diversity of emergent actions through a cascade of bifurcations in the task perceptual-motor work space. Data suggested that perceived efficiency (E) of an action changed as a function of scaled distance (D) and was correlated with the probability of occurrence of action patterns (P), exhibiting the following dependence P = P(E(D)). The implication is that probability of occurrence (P) depends on efficiency (E), which in turn depends on scaled distance (D) to the target. Accordingly, scaled distance-dependent perceived efficiency seems a viable candidate for a contextual (control) parameter to describe the nonlinear dynamics of striking actions in boxing.
Bifurcation of solutions of separable parameterized equations into lines
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Yun-Qiu Shen
2010-09-01
Full Text Available Many applications give rise to separable parameterized equations of the form $A(y, muz+b(y, mu=0$, where $y in mathbb{R}^n$, $z in mathbb{R}^N$ and the parameter $mu in mathbb{R}$; here $A(y, mu$ is an $(N+n imes N$ matrix and $b(y, mu in mathbb{R}^{N+n}$. Under the assumption that $A(y,mu$ has full rank we showed in [21] that bifurcation points can be located by solving a reduced equation of the form $f(y, mu=0$. In this paper we extend that method to the case that $A(y,mu$ has rank deficiency one at the bifurcation point. At such a point the solution curve $(y,mu,z$ branches into infinitely many additional solutions, which form a straight line. A numerical method for reducing the problem to a smaller space and locating such a bifurcation point is given. Applications to equilibrium solutions of nonlinear ordinary equations and solutions of discretized partial differential equations are provided.
Numerical bifurcation analysis of the bipedal spring-mass model
Merker, Andreas; Kaiser, Dieter; Hermann, Martin
2015-01-01
The spring-mass model and its numerous extensions are currently one of the best candidates for templates of human and animal locomotion. However, with increasing complexity, their applications can become very time-consuming. In this paper, we present an approach that is based on the calculation of bifurcations in the bipedal spring-mass model for walking. Since the bifurcations limit the region of stable walking, locomotion can be studied by computing the corresponding boundaries. Originally, the model was implemented as a hybrid dynamical system. Our new approach consists of the transformation of the series of initial value problems on different intervals into a single boundary value problem. Using this technique, discontinuities can be avoided and sophisticated numerical methods for studying parametrized nonlinear boundary value problems can be applied. Thus, appropriate extended systems are used to compute transcritical and period-doubling bifurcation points as well as turning points. We show that the resulting boundary value problems can be solved by the simple shooting method with sufficient accuracy, making the application of the more extensive multiple shooting superfluous. The proposed approach is fast, robust to numerical perturbations and allows determining complete manifolds of periodic solutions of the original problem.
Bifurcation analysis of fan casing under rotating air flow excitation
Institute of Scientific and Technical Information of China (English)
温登哲; 陈予恕
2014-01-01
A fan casing model of cantilever circular thin shell is constructed based on the geometric characteristics of the thin-walled structure of aero-engine fan casing. According to Donnelly’s shell theory and Hamilton’s principle, the dynamic equations are established. The dynamic behaviors are investigated by a multiple-scale method. The effects of casing geometric parameters and motion parameters on the natural frequency of the system are studied. The transition sets and bifurcation diagrams of the system are obtained through a singularity analysis of the bifurcation equation, showing that various modes of the system such as the bifurcation and hysteresis will appear in different parameter regions. In accordance with the multiple relationship of the fan speed and stator vibration frequency, the fan speed interval with the casing vibration sudden jump is calculated. The dynamic reasons of casing cracks are investigated. The possibility of casing cracking hysteresis interval is analyzed. The results show that cracking is more likely to appear in the hysteresis interval. The research of this paper provides a theoretical basis for fan casing design and system parameter optimization.
Reverse bifurcation and fractal of the compound logistic map
Wang, Xingyuan; Liang, Qingyong
2008-07-01
The nature of the fixed points of the compound logistic map is researched and the boundary equation of the first bifurcation of the map in the parameter space is given out. Using the quantitative criterion and rule of chaotic system, the paper reveal the general features of the compound logistic map transforming from regularity to chaos, the following conclusions are shown: (1) chaotic patterns of the map may emerge out of double-periodic bifurcation and (2) the chaotic crisis phenomena and the reverse bifurcation are found. At the same time, we analyze the orbit of critical point of the compound logistic map and put forward the definition of Mandelbrot-Julia set of compound logistic map. We generalize the Welstead and Cromer's periodic scanning technology and using this technology construct a series of Mandelbrot-Julia sets of compound logistic map. We investigate the symmetry of Mandelbrot-Julia set and study the topological inflexibility of distributing of period region in the Mandelbrot set, and finds that Mandelbrot set contain abundant information of structure of Julia sets by founding the whole portray of Julia sets based on Mandelbrot set qualitatively.
Bifurcation in autonomous and nonautonomous differential equations with discontinuities
Akhmet, Marat
2017-01-01
This book is devoted to bifurcation theory for autonomous and nonautonomous differential equations with discontinuities of different types. That is, those with jumps present either in the right-hand-side or in trajectories or in the arguments of solutions of equations. The results obtained in this book can be applied to various fields such as neural networks, brain dynamics, mechanical systems, weather phenomena, population dynamics, etc. Without any doubt, bifurcation theory should be further developed to different types of differential equations. In this sense, the present book will be a leading one in this field. The reader will benefit from the recent results of the theory and will learn in the very concrete way how to apply this theory to differential equations with various types of discontinuity. Moreover, the reader will learn new ways to analyze nonautonomous bifurcation scenarios in these equations. The book will be of a big interest both for beginners and experts in the field. For the former group o...
Grant, K. M.; Grimm, R.; Mikolajewicz, U.; Marino, G.; Ziegler, M.; Rohling, E. J.
2016-05-01
The Mediterranean basin is sensitive to global sea-level changes and African monsoon variability on orbital timescales. Both of these processes are thought to be important to the deposition of organic-rich sediment layers or 'sapropels' throughout the eastern Mediterranean, yet their relative influences remain ambiguous. A related issue is that an assumed 3-kyr lag between boreal insolation maxima and sapropel mid-points remains to be tested. Here we present new geochemical and ice-volume-corrected planktonic foraminiferal stable isotope records for sapropels S1 (Holocene), S3, S4, and S5 (Marine Isotope Stage 5) in core LC21 from the southern Aegean Sea. The records have a radiometrically constrained chronology that has already been synchronised with the Red Sea relative sea-level record, and this allows detailed examination of the timing of sapropel deposition relative to insolation, sea-level, and African monsoon changes. We find that sapropel onset was near-synchronous with monsoon run-off into the eastern Mediterranean, but that insolation-sapropel/monsoon phasings were not systematic through the last glacial cycle. These latter phasings instead appear to relate to sea-level changes. We propose that persistent meltwater discharges into the North Atlantic (e.g., at glacial terminations) modified the timing of sapropel deposition by delaying the timing of peak African monsoon run-off. These observations may reconcile apparent model-data offsets with respect to the orbital pacing of the African monsoon. Our observations also imply that the previous assumption of a systematic 3-kyr lag between insolation maxima and sapropel midpoints may lead to overestimated insolation-sapropel phasings. Finally, we surmise that both sea-level rise and monsoon run-off contributed to surface-water buoyancy changes at times of sapropel deposition, and their relative influences differed per sapropel case, depending on their magnitudes. Sea-level rise was clearly important for
Evaluating the competent use of EAP linguistic features in relation to CEFRL English levels
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Mª Pilar Durán Escribano
2015-07-01
Full Text Available The purpose of this study is to analyse the competent use of EAP linguistic features (passive voice, use of nominal groups, typical verb forms, and modality, by the Technical University of Madrid engineering students, in relation to their CEFR competence levels, from A2 to C1. The results obtained with the STATGRAPHICS programme serve to identify those specific grammar structures most difficult to Spanish engineering students so that their learning may be favoured. Results calibration to CERF reference levels also renders a more complete scale of linguistic competence applied to EAP contexts.
Application of the Generalized Work Relation for an N-level Quantum System
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Junichi Ishikawa
2014-06-01
Full Text Available An efficient periodic operation to obtain the maximum work from a nonequilibrium initial state in an N–level quantum system is shown. Each cycle consists of a stabilization process followed by an isentropic restoration process. The instantaneous time limit can be taken in the stabilization process from the nonequilibrium initial state to a stable passive state. In the restoration process that preserves the passive state a minimum period is needed to satisfy the uncertainty relation between energy and time. An efficient quantum feedback control in a symmetric two–level quantum system connected to an energy source is proposed.
Baird, Bill
1986-08-01
A neural network model describing pattern recognition in the rabbit olfactory bulb is analysed to explain the changes in neural activity observed experimentally during classical Pavlovian conditioning. EEG activity recorded from an 8×8 arry of 64 electrodes directly on the surface on the bulb shows distinct spatial patterns of oscillation that correspond to the animal's recognition of different conditioned odors and change with conditioning to new odors. The model may be considered a variant of Hopfield's model of continuous analog neural dynamics. Excitatory and inhibitory cell types in the bulb and the anatomical architecture of their connection requires a nonsymmetric coupling matrix. As the mean input level rises during each breath of the animal, the system bifurcates from homogenous equilibrium to a spatially patterned oscillation. The theory of multiple Hopf bifurcations is employed to find coupled equations for the amplitudes of these unstable oscillatory modes independent of frequency. This allows a view of stored periodic attractors as fixed points of a gradient vector field and thereby recovers the more familiar dynamical systems picture of associative memory.
Numerical study of steady turbulent flow through bifurcated nozzles in continuous casting
Najjar, Fady M.; Thomas, Brian G.; Hershey, Donald E.
1995-08-01
Bifurcated nozzles are used in continuous casting of molten steel, where they influence the quality of the cast steel slabs. The present study performs two-dimensional (2-D) and three-dimensional (3-D) simulations of steady turbulent (K- ɛ) flow in bifurcated nozzles, using a finite-element (FIDAP) model, which has been verified previously with water model experiments. The effects of nozzle design and casting process operating variables on the jet characteristics exiting the nozzle are investigated. The nozzle design parameters studied include the shape, angle, height, width, and thickness of the ports and the bottom geometry. The process operating practices include inlet velocity profile and angle as well as port curvature caused by erosion or inclusion buildup. Results show that the jet angle is controlled mainly by the port angle but is steeper with larger port area and thinner walls. The degree of swirl is increased by larger or rounder ports. The effective port area, where there is no recirculation, is increased by smaller or curved ports. Flow asymmetry is more severe with skewed or angled inlet conditions or unequal port sizes. Turbulence levels in the jet are higher with higher casting speed and smaller ports.
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Asuman YAVUZYILMAZ
2007-02-01
Full Text Available Burnout manifests itself in individuals working in professions involving face-to-face contact with the public in depersonalization towards others, feelings of emotional exhaustion, and reduced feelings of personal achievement and adequacy. The objective in this study was to determine burnout and job satisfaction levels and related factors in primary health center personnel in the central part of the Turkish province of Trabzon. A total of 227 people working in central Trabzon province primary health centers participated in this cross-sectional study, a level of 90.4%. The Maslach Burnout Inventory was used to determine burnout level and the Job Satisfaction Inventory for job satisfaction. Burnout levels in health personnel were high among women (15.06±5.57, married individuals (14.80±5.65 and those dissatisfied with their working conditions (16.80±5.81; physicians (5.00±2.79, those without children (5.19±2.54, those whose spouses were not working (4.69±2.70 and smokers (4.71±3.29 had a high level of depersonalization; and married individuals were determined to have a low personal achievement level (10.24±4.14 (p=0.020, p=0.028, p=0.011, p=0.038, p=0.028, p=0.012 and p=0.010, respectively. In conclusion, gender, marital status, age, satisfaction with working conditions and income level were determined to be related to burnout and job satisfaction. [TAF Prev Med Bull 2007; 6(1.000: 41-50
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Murat TOPBAS
2007-02-01
Full Text Available Burnout manifests itself in individuals working in professions involving face-to-face contact with the public in depersonalization towards others, feelings of emotional exhaustion, and reduced feelings of personal achievement and adequacy. The objective in this study was to determine burnout and job satisfaction levels and related factors in primary health center personnel in the central part of the Turkish province of Trabzon. A total of 227 people working in central Trabzon province primary health centers participated in this cross-sectional study, a level of 90.4%. The Maslach Burnout Inventory was used to determine burnout level and the Job Satisfaction Inventory for job satisfaction. Burnout levels in health personnel were high among women (15.06±5.57, married individuals (14.80±5.65 and those dissatisfied with their working conditions (16.80±5.81; physicians (5.00±2.79, those without children (5.19±2.54, those whose spouses were not working (4.69±2.70 and smokers (4.71±3.29 had a high level of depersonalization; and married individuals were determined to have a low personal achievement level (10.24±4.14 (p=0.020, p=0.028, p=0.011, p=0.038, p=0.028, p=0.012 and p=0.010, respectively. In conclusion, gender, marital status, age, satisfaction with working conditions and income level were determined to be related to burnout and job satisfaction. [TAF Prev Med Bull. 2007; 6(1: 41-50