bluuebunny/crossref_metadata_2025_split huggingface dataset:
ON THE GENERALITY OF THE UNFOLDED CHUA'S CIRCUIT
Authors: WU CHAI WAH , CHUA LEON O. 
Published: October 2004

In this paper, we study the generality of Chua's oscillator by deriving a class of vector fields that Chua's oscillator is equivalent to. For the class of vector fields with a scalar nonlinearity, we prove that under certain conditions, two such vector fields are topologically conjugate if the Jacobian matrices at each point have the same eigenvalues and the equilibrium points are matched up. We show how these conditions are related to the complete state observability of a corresponding linear system. These results are used to show that the n-dimensional Chua's oscillator is topologically conjugate to almost every vector field in this class. We comment on the special case when the vector field is piecewise-linear and in particular when the vector field is 2-segment piecewise-linear. These results are illustrated by transforming several systems studied in the literature into equivalent Chua's oscillators. We also extend some of these results to the case of several scalar nonlinearities. As a corollary we prove that almost all piecewise-linear vector fields with parallel boundary planes are topologically conjugate if the boundary planes and equilibrium points are the same and the eigenvalues in corresponding regions are the same. We also give a dual result of topological conjugacy.
AN EXPERIMENTAL STUDY OF A POPULATION OF RELAXATION OSCILLATORS WITH A PHASE-REPELLING MEAN-FIELD COUPLING
Authors: BRAILOVE ADAM A. , LINSAY PAUL S. 
Published: October 2004

The dynamical behavior of a system of coupled relaxation oscillators is studied experimentally. A population of up to 15 coupled electronic op-amp relaxation oscillators is used as a prototype for the real collections of limit-cycle oscillators frequently found in many physical, biological, and technological systems. The oscillators interact via an all-to-all or mean-field coupling. The rarely studied case of antiferromagnetic interactions, in which oscillators tend to repel each other in phase, is considered. The behavior of the system is significantly different from the predictions of the limited theory that is currently available. The novel behavior observed includes the existence of numerous distinguishable phase-locked states and an exponential distribution of the duration of transients. The critical coupling strength necessary for the oscillator system to completely phase-lock is measured. A simple geometrical model of the dynamics of the system during the transient is presented as a means of understanding the exponential distribution of transient lengths. In addition, a phase-response oscillator model is shown to exhibit similar transient behavior.
VISUALIZING RELATIVE EQUILIBRIA AND BIFURCATIONS BY PAINTING HAMILTONIANS ON PERSONAL COMPUTERS
Authors: PASCUA P. , RUBIO J.L. , VIARTOLA A. , FERRER S. 
Published: October 2004

In this paper, we present a graphical tool running on a PC for studies of integrable systems of one degree of freedom with several parameters, in particular for perturbed Hamiltonian systems with symmetries whose orbit space is the two-dimensional sphere S2 after they are reduced by normalization. The pioneering work was performed by Coffey et al. [1990], who developed a graphical method on a Connection Machine in order to paint the Hamiltonian function ℋ* over phase space, instead of numerical integrations of the corresponding differential equations. We have pursued their idea and the procedure proposed here renders pictures at the rate of one picture per minute. For research or teaching activities, the above mentioned method may be used in two directions: (a) in the stability analysis of equilibria and their bifurcations in parameter space; (b) for the specification of initial conditions and the corresponding qualitative long term global dynamics, in order to make proper choices for numerical studies of the full problem. As examples of how to interact with the program, and of the different role played by physical and dynamical parameters, we consider the dynamics of the Laplace–Runge–Lenz vector in two perturbed Keplerian systems of recent interest: the generalized Van der Waals effect in the hydrogen atom, and Harrington’s model for triple stellar systems.
DIMENSIONAL ANALYSIS OF THE ELECTRICAL ACTIVITY IN FIBRILLATING ISOLATED HEARTS
Authors: CASALEGGIO A. , CORANA A. , RANJAN R. , THAKOR N.V. 
Published: October 2004

The dynamical behavior of the electrophysiological response at the epicardium of isolated Langendorff-perfused rabbit heart during different induced arrhythmic conditions is studied with the use of the correlation dimension D2 and Lyapunov exponents. Different conditions are investigated: normal sinus rhythm (NSR), normal sinus rhythm after ischemia (NSRI), and ventricular fibrillation with and without perfusion (VFWP and VF, respectively). Both single lead and simultaneous recordings from four leads are analyzed. The correlation dimensions during VF and VFWP are significantly higher than during NSR or NSRI, although low-dimensional attractors could not be clearly observed in VF and VFWP. Our conclusions are (a) that isolated hearts behave periodically during NSR, probably because the heart does not have to cope with time-varying demands either from the nervous system or from the metabolism; (b) during NSRI, spatially different regions of the heart show periodicities or chaotic behavior with low-dimensions, possibly due to electrophysiological inhomogeneity of the heart tissue; (c) during VF and VFWP, an intrinsic change in the dynamics seems to occur, and the heart behaves as a high-dimensional system, wherein VFWP signals show a greater spatial homogeneity than do VF signals. We propose a possible interpretation of the results in terms of the synchronization of cells by a pacemaker and desynchronization as a result of malignant arrhythmias.
EFFECTS OF LOCAL ISCHEMIA AND TRANSIENT CONDUCTION BLOCKS ON THE INDUCTION OF CARDIAC REENTRIES
Authors: BARDOU ALAIN , ACHOUR SOUMEYA , AUGER PIERRE , CHASSÉ JEAN-LUC 
Published: October 2004

The present work is aimed at investigating the effects of ischemia and transient blocks on induction of ventricular fibrillation. Electrophysiologic effects of local ischemia induced by minor myocardial infarction (variation of the dispersion of refractory periods as well as conduction velocity) on initiation of reentry mechanisms were studied by means of computer simulations based on a cellular automata model of propagation of activation wave through a ventricular surface element. A local ischemic area was simulated, showing that altered refractoriness can facilitate initiation of reentry phenomena. The probability of reentries is a function of the size of ischemic zone and of the spatial rate of dispersion of refractory periods. Our results show that the dispersion of refractoriness is an important parameter in triggering cardiac reentries. Above a threshold value of dispersion, even very small ischemic zones can induce spiral waves. We also study the effects of transient conduction blocks on reentries. The role of transient blocks in the triggering of reentries is investigated by use of a two-dimensional set of discretely coupled cells described by the Van Capelle and Durrer model. We study the effect of the size and of the time duration of the transient block on the induction of spiral waves. For each block size, we determine a time window in which spiral waves are initiated.
FRACTAL EVOLUTION IN DETERMINISTIC AND RANDOM MODELS
Authors: FUSSY SIEGFRIED , GRÖSSING GERHARD , SCHWABL HERBERT 
Published: October 2004

One-dimensional coupled map lattices or quantum cellular automata with any additionally implemented temporal feedback operations (involving some memory of the system’s states) and a normalization procedure after each time step exhibit a universal dynamic property called fractal evolution [Fussy & Grössing, 1994]. It is characterized by a power-law behavior of a system’s order parameter with regard to a resolution-like parameter which controls the deviation from an undisturbed (i.e., feedback-less) system’s evolution and provides a dynamically invariant measure for the emerging spatiotemporal patterns. By comparison with another, simpler model without memory, where the patterns are generated randomly, the underlying principles of fractal evolution are studied. It is shown that our system evolving entirely deterministically, exhibits properties occurring usually only in random models, where the global measures, up to a certain degree, are calculable. Other properties like the fractal evolution exponent remain in general computationally irreducible due to the self-referential feedback dynamics. A specific model with an approximate estimation of the fractal evolution exponent is discussed. The stability of fractal evolution with respect to the dependence of pattern formation on the systems variables is also analyzed.
ON THE QUESTION OF DISSIPATION AND PARAMETRIC EXCITATION IN CHAOTIC NONAUTONOMOUS RESONATORS
Authors: SARAFIAN G. , KAPLAN B. Z. 
Published: October 2004

Three categories of second order resonators are treated in this work: A. Nonautonomous driven resonators whose reactors are nonlinear and resistances are positive. (The resonators are similar to the RL Diode circuit). B. Nonautonomous driven resonators whose reactors are linear (and maintained constant in time) and whose dissipation is due to a nonlinear resistor which consists of a negative resistance part. C. Autonomous resonators whose reactors are parametrically excited. (The reactances of the resonators of category C are made directly periodically time varied). The introduction of category C is mainly for auxiliary purposes, in order to bridge difficulties that occur in comparing resonators of categories A and B. Resonators of both categories A and B demonstrate similar dynamic behaviors, since both are capable in certain circumstances of exhibiting bifurcation phenomena and chaos. This demonstrated similarity is puzzling. This is due to the fact that the resonators of category A are fully dissipative, while the resonators of category B should exhibit negative dissipation for part of their movement. This negative dissipation in resonators of category B is essential for enabling them to exhibit chaotic behavior. A first step in resolving the puzzle is made by recalling the fact that parametrically pumping reactances in resonators of category C may induce an effective negative resistance in their circuit, and as a result they are somewhat similar to resonators of category B. A complete resolution of the puzzle should, however, include yet another step, where one shows that members of categories A and C possess affinity. A great part of the work is, therefore, devoted to demonstrating that resonators of categories A and C are related in exhibiting similarity in their dynamic features. (This happens although the reactances of resonators of category A are maintained constant in time, while the resonators of category C are periodically time varied). One of the objectives is to convince the reader that some of the dynamic interactions occurring in resonators of category A are “parametric"-like in nature. Hence, an association between categories A and C is demonstrated.
Effect of altitude on thrombopoietin and the platelet count in healthy volunteers
Authors: Hartmann Sabine , Huch Renate , Breymann Christian , Krafft Alexander 
Published: October 2004

SummaryAlthough there is evidence that altitude increases the platelet count, its effect on the platelet precursor stimulating factor, thrombopoietin (TPO), is unclear. Unlike erythropoietin, TPO appears largely unresponsive to exogenous signals. In a study in 16 healthy volunteers,we report the effects of altitude exposure at between 1000 and 1822 m for 1 or 2 weeks on TPO, the platelet count (+ indices), erythropoietin, hemoglobin, hematocrit and erythrocytes (+ indices).There were significant post-expo-sure increases in TPO (57.9 vs 37.1 U/l; P = 0.0006), platelet count (219.1 vs 208.0 x 103/ml; P = 0.031) and erythropoietin (16.1 vs 9.9 U/l; P = 0.0032).There was a positive correlation between the increases in TPO and platelet count (r = 0.52, P = 0.043). Hemoglobin and hematocrit remained unchanged. Our results provide clear evidence for a relationship, presumably driven by hypoxia, between altitude exposure,TPO production and the platelet count.
Temporal changes in pulmonary expression of key procoagulant molecules in rabbits with endotoxin-induced acute lung injury: elevated expression levels of protease-activated receptors
Authors: Jesmin Subrina , Matsuda Naoyuki , Sakuma Ichiro , Kobayashi Shigeaki , Sakuraya Fumika , Hattori Yuichi , Gando Satoshi 
Published: October 2004

SummaryRecently a new concept has emerged implicating thrombin signaling as the “bridge” that connects tissue damage to hemostatic and inflammatory responses. In view of this concept, we hypothesized that induction of protease-activated receptor (PAR) expression may play a critical role in endotoxin-induced tissue injury through the cellular actions of thrombin. Thus, in this study, temporal changes in expression of key precoagulant molecules, including PARs, in lungs from rabbits rendered endotoxemic by 100 μg/kg lipopolysaccharide (LPS) were examined with measurements of variables reflecting acute lung injury (ALI). ALI induction by LPS was confirmed by blood gas derangement, lung vascular hyperpermeability, and histopathological changes, and was characterized by the deposition of fibrin in the alveolar spaces, bronchioles and vessels. Plasminogen activator inhibitor-1 (PAI-1) and tissue factor (TF) were highly expressed in lungs after LPS injection. While the peaks in levels of PAI-1 and TF were comparable (12∼13-fold from control), their expression time-courses were different: PAI-1 exhibited a bell-shaped expression pattern and peak at 6 h, whereas TF level reached maximum at 10 h. Of note, LPS induced a rapid and significant increase in levels of PAR-1 compared to control, with a peak level at 1 h (3.3-fold). Although declining thereafter, it remained significantly higher than the control level throughout the study period. Expressions of PAR-2, -3, and -4 were also increased by LPS with different time courses from PAR-1 expression. Immunofluorescence staining for PAR-1 were localized in blood vessels, bronchial epithelium, and alveolar pneumocytes after LPS. These results suggest that the increased expression levels of PARs, in addition to PAI-1 and TF, may, in part, underlie the development of ALI occurring during endotoxemia.
Strenuous, acute exercise suppresses polymorphonuclear leukocyte respiratory burst under adherence to surface-adherent platelets in men
Authors: Wang Jong-Shyan 
Published: October 2004

SummaryInteraction between polymorphonuclear leukocyte (PMN) and platelets is important in the pathogenesis of thrombosis and inflammation. This study investigates how strenuous, acute exercise affects PMN oxidative burst activity under adherence to surface-adherent platelets. Thirty sedentary healthy men exercised strenuously (up to maximal oxygen consumption) on a bicycle ergometer. Before and immediately after exercise, the kinetics of oxidant production, phosphorylation of various protein kinase C (PKC) isoforms, and translocation of p47phox in PMNs under adherence to surface-adherent platelets were measured using fluorescence microscopy combined with computerized image analysis. Analytical results can be summarized as follows: (i) either treating the platelet with P-selectin (CD62P) and glycoprotein IIb/IIIa (CD41) antibodies or treating the PMN with β2-integrin (CD18) and Mac-1 (CD11b) antibodies and PKCζpseudosubstrate effectively inhibits platelet-promoted oxidant production of PMN; (ii) PMNs adhesion to surface-adherent platelets is associated with a higher amount of phospho-PKCζand a larger ratio of membrane to cytosolic p47phox than suspended PMNs; (iii) strenuous, acute exercise decreases platelet-promoted oxidant production of PMN and is accompanied by suppressed phosphorylation of PKCζ, translocation of p47phox, and inhibition of PKCζpseudosubstrate to oxidant production; (iv) no significant changes occur in PKCα/βII and δ phosphorylation of adherent PMNs following this exercise. Therefore, we conclude that strenuous, acute exercise suppresses platelet-promoted oxidative burst of PMN, possibly by reducing phosphorylation of PKCζand translocation of the cytosolic p47phox to the plasma membrane, thus inhibiting the assembly and activation of NADPH oxidase in PMN.
Neutrophils stimulated by apolipoprotein(a) generate fragments that are stronger inhibitors of plasmin formation than apo(a)
Authors: Lamanuzzi Leila , Mtairag El Mostafa , Pepe Gabriella , Anglés-Cano Eduardo 
Published: October 2004

SummaryApolipoprotein(a), the plasminogen-like component of lipoprotein(a), is transformed into fragments by polymorphonuclear neutrophils (PMNs) elastase. Since stimulated PMNs express urokinase-type plasminogen activator (uPA), we sought to investigate the relevance of apo(a) fragmentation on plasminogen activation by neutrophils. Freshly isolated human PMNs stimulated by a 10 kringle recombinant apo(a), r-apo(a), activate plasminogen in a specific and saturable manner (Km = 476 ± 42 nM, Vmax = 896 ± 18 pmol min-1). This activation is prevented by amiloride, an inhibitor of u-PA, and ɛ-aminocaproic acid, ɛ-ACA, a lysine analogue that blocks plasminogen binding to PMNs. Stimulation of PMNs by apo(a) results in the formation of elastase-derived apo(a) fragments. These fragments produce a concentration-dependent decrease in the formation of plasmin. Addition of elastase inhibitors to PMNs prevented degradation of apo(a) and partially restored the formation of plasmin. In a similar manner, isolated r-apo(a) fragments were able to produce a 100% decrease in plasmin generation as compared to intact r-apo(a). These data indicate that apo(a) fragments produce a more pronounced inhibition in the generation of cellbound plasmin by uPA than the parent apo(a). These effects of apo(a) and its fragments were neutralised by a monoclonal antibody directed against the lysine-binding site of apo(a). This mechanism may be of biological relevance to the effects of Lp(a) in conditions where PMNs accumulate and release elastase, i.e. thrombus lysis and inflammatory lesions.
Over-the-counter vitamin K1-containing multivitamin supplements disrupt warfarin anticoagulation in vitamin K1-depleted patients
Authors: Kurnik Daniel , Loebstein Ronen , Rabinovitz Hadas , Austerweil Naomi , Almog Shlomo , Halkin Hillel 
Published: October 2004

SummaryMost multivitamin supplements contain far less vitamin K1 than thought to affect warfarin anticoagulation. Having described 3 patients with multivitamin-warfarin interactions, we hypothesized that vitamin K1–depleted patients are sensitive to even small increments. Therefore, we compared the effect of a vitamin K1-containing multivitamin on warfarin anticoagulation between patients with low versus normal vitamin K1 status. We screened 102 warfarin-treated patients and recruited nine with “low” (< 1.5 mcg/L, 10th percentile) (group 1) and 7 with “normal” (>4.5 mcg/L, median) (group 2) total vitamin K1 plasma levels (vitamin K1 + vitamin K1 2,3-epoxide). Patients received one multivitamin tablet containing 25 mcg of vitamin K1 daily, for 4 weeks (period 1). A predefined algorithm was used to adjust warfarin doses if the INR was outside the therapeutic range. Patients requiring warfarin increments were then switched to 4 weeks of a vitamin K1-free multivitamin supplement (period 2). During period 1, subtherapeutic INRs occurred in 9/9 and 1/7 patients in group 1 and 2, respectively (p <0.001). In group 1, INR decreased by a median of 0.51 (p <0.01), and warfarin dose had to be raised by 5.3% (p <0.01), whereas INR and warfarin dose did not change significantly in group 2. During period 2 (7 patients), there were trends towards decreased total vitamin K1 and rising INRs associated with significantly lower warfarin doses. We conclude that vitamin K1-containing multivitamins reduce INR in patients with low vitamin K1 status. Our study suggests that vitamin Kdepleted patients are sensitive to even small changes in vitamin K1 intake.
A role for the thiol isomerase protein ERP5 in platelet function
Authors: Jordan Peter A. , Stevens Joanne M. , Hubbard Gary P. , Barrett Natasha E. , Sage Tanya , Authi Kalwant S. , Gibbins Jonathan M. 
Published: October 2004

AbstractFormation and rearrangement of disulfide bonds during the correct folding of nascent proteins is modulated by a family of enzymes known as thiol isomerases, which include protein disulfide isomerase (PDI), endoplasmic reticulum protein 5 (ERP5), and ERP57. Recent evidence supports an alternative role for this family of proteins on the surface of cells, where they are involved in receptor remodeling and recognition. In platelets, blocking PDI with inhibitory antibodies inhibits a number of platelet activation pathways, including aggregation, secretion, and fibrinogen binding. Analysis of human platelet membrane fractions identified the presence of the thiol isomerase protein ERP5. Further study showed that ERP5 is resident mainly on platelet intracellular membranes, although it is rapidly recruited to the cell surface in response to a range of platelet agonists. Blocking cell-surface ERP5 using inhibitory antibodies leads to a decrease in platelet aggregation in response to agonists, and a decrease in fibrinogen binding and P-selectin exposure. It is possible that this is based on the disruption of integrin function, as we observed that ERP5 becomes physically associated with the integrin β3 subunit during platelet stimulation. These results provide new insights into the involvement of thiol isomerases and regulation of platelet activation.
A novel apoptosis pathway activated by the carboxyl terminus of p21
Authors: Dong Chen , Li Qing , Lyu Shu-chen , Krensky Alan M. , Clayberger Carol 
Published: October 2004

AbstractDelivery of biologically active peptides into cells may help elucidate intracellular signal transduction pathways, identify additional in vivo functions, and develop new therapeutics. Although p21 was first identified as a major regulator of cell cycle progression, it is now clear that p21 subserves multiple functions. The amino terminus of p21 interacts with cyclins and cyclin-dependent kinases, while the carboxyl terminus interacts with proliferating cell nuclear antigen (PCNA), growth arrest and DNA damage–inducible gene 45 (GADD45), calmodulin, SET, and CCAAT/enhancer binding protein-α (C/EBP-α). A chimeric peptide, p21-IRS, consisting of the carboxyl terminal domain of p21 conjugated to a pentapeptide (RYIRS) rapidly enters lymphoid cells and activates apoptosis. In the present study, we investigate the molecular events involved in p21-activated apoptosis. Comparison of p21-IRS with other known proapoptotic agents demonstrates that p21-IRS activates a novel apoptotic pathway: mitochondria are central to the process, but caspases and a decrease in Δψm are not involved. Targeting the p21 peptide to specific cell populations may allow development of novel therapies to eliminate aberrant cells in human diseases.