bluuebunny/crossref_metadata_2025 huggingface dataset:
Desensitization of the soluble guanylyl cyclase/cGMP pathway by lipopolysaccharide in rat isolated pulmonary artery but not aorta
Authors: El‐Awady M S H , Smirnov S V , Watson M L
Published: September 2008

Background and purpose:

To investigate the function of soluble guanylyl cyclase (sGC)/3′,5′‐cyclic guanosine monophosphate (cGMP) pathway in lipopolysaccharide (LPS)‐induced changes in vascular reactivity of rat isolated pulmonary artery and aorta.

Experimental approach:

Nitric oxide (NO) production, contraction responses to endothelin‐1 (ET‐1), relaxation responses to sodium nitroprusside (SNP), 8‐pCPT‐cGMP, BAY412272 and T‐0156, SNP‐induced cGMP production and expression of sGCα1, sGCβ1and 3′,5′‐cyclic nucleotide phosphodiesterase‐5 (PDE5) proteins were measured in LPS‐treated pulmonary and aortic rings from male Wistar rats.

Key results:

In both vessels, LPS (10 μg mL−1, 20 h) increased NO production, which was inhibited by the selective inducible NOS (iNOS) inhibitor 1400W (1 μM). In the aorta, LPS decreased ET‐1‐induced contractility and this decrease was inhibited by the selective sGC inhibitor ODQ (10 μM) but not by removal of endothelium, or inhibitors of cyclooxygenase (indomethacin, 10 μM) or iNOS (1400W, 1 μM). Furthermore, aortic relaxation responses to the direct sGC activator BAY412272 were enhanced. In the pulmonary artery, SNP (1 nMto 30 μM)‐induced relaxation and cGMP production, BAY412272‐induced relaxation and sGCβ1protein expression were decreased, whereas relaxation responses to the PDE5‐specific inhibitor T‐0156 (0.1–100 nM) were enhanced. Relaxation responses to the phosphodiesterase‐resistant cGMP analogue, 8‐pCPT‐cGMP, and protein expression levels of sGCα1and PDE5 were not altered in either vessel.

Conclusion and implications:

LPS caused a selective hypocontractility of rat aorta to ET‐1 mediated mainly through NO‐independent sGC activation, whereas in the pulmonary artery, the effect of sGC activation was reduced by a decreased protein expression of sGCβ1together with increased PDE5 activity.

British Journal of Pharmacology(2008)155, 1164–1173; doi:10.1038/bjp.2008.358; published online 22 September 2008
Potential importance of alterations in hydrogen sulphide (H2S) bioavailability in diabetes
Authors: Lefer D J
Published: September 2008

Despite its long‐standing reputation as a foul smelling and toxic gas that is associated with the decay of biological matter, hydrogen sulphide (H2S) has emerged as an important regulator of cardiovascular homoeostasis. H2S promotes a number of cellular signals that regulate metabolism, cardiac function and cell survival. Endogenous H2S bioavailability is regulated by several enzymes involved in the biosynthesis of cysteine. This study by Brancaleone et al. in the current issue of the British Journal of Pharmacology provides novel insights into the impairment of H2S biosynthesis in the setting of diabetes mellitus. The authors report that enzymic H2S biosynthesis is impaired in a murine model of type 1 diabetes and the attenuation in H2S bioavailability is associated with impaired vascular reactivity. This study has profound implications for the use of pharmacological agents to augment endogenous H2S synthesis or agents that release H2S to augment the levels of this gaseous signalling molecule in cardiovascular disease.

British Journal of Pharmacology (2008) 155, 617–619; doi:fn1; published online 22 September 2008
Identification of α1L‐adrenoceptor in mice and its abolition by α1A‐adrenoceptor gene knockout
Authors: Muramatsu I , Morishima S , Suzuki F , Yoshiki H , Anisuzzaman A S M , Tanaka T , Rodrigo M C , Myagmar B E , Simpson P C
Published: September 2008

Background and purpose:

The α1L‐adrenoceptor has pharmacological properties that distinguish it from three classical α1‐adrenoceptors (α1A, α1Band α1D). The purpose of this was to identify α1L‐adrenoceptors in mice and to examine their relationship to classical α1‐adrenoceptors.

Experimental approach:

Radioligand binding and functional bioassay experiments were performed on the cerebral cortex, vas deferens and prostate of wild‐type (WT) and α1A‐, α1B‐ and α1D‐adrenoceptor gene knockout (AKO, BKO and DKO) mice.

Key results:

The radioligand [3H]‐silodosin bound to intact segments of the cerebral cortex, vas deferens and prostate of WT, BKO and DKO but not of AKO mice. The binding sites were composed of two components with high and low affinities for prazosin or RS‐17053, indicating the pharmacological profiles of α1A‐adrenoceptors and α1L‐adrenoceptors. In membrane preparations of WT mouse cortex, however, [3H]‐silodosin bound to a single population of prazosin high‐affinity sites, suggesting the presence of α1A‐adrenoceptors alone. In contrast, [3H]‐prazosin bound to two components having α1A‐adrenoceptor and α1B‐adrenoceptor profiles in intact segments of WT and DKO mouse cortices, but AKO mice lacked α1A‐adrenoceptor profiles and BKO mice lacked α1B‐adrenoceptor profiles. Noradrenaline produced contractions through α1L‐adrenoceptors with low affinity for prazosin in the vas deferens and prostate of WT, BKO and DKO mice. However, the contractions were abolished or markedly attenuated in AKO mice.

Conclusions and implications:

α1L‐Adrenoceptors were identified as binding and functional entities in WT, BKO and DKO mice but not in AKO mice, suggesting that the α1L‐adrenoceptor is one phenotype derived from the α1A‐adrenoceptor gene.

British Journal of Pharmacology(2008)155, 1224–1234; doi:10.1038/bjp.2008.360; published online 22 September 2008
The guinea‐pig tracheal potential difference as an in vivo model for the study of epithelial sodium channel function in the airways
Authors: Coote K J , Atherton H , Young A , Sugar R , Burrows R , Smith N J , Schlaeppi J‐M , Groot‐Kormelink P J , Gosling M , Danahay H
Published: September 2008

Background and purpose:

The epithelial sodium channel (ENaC) is a key regulator of airway mucosal hydration and mucus clearance. Negative regulation of airway ENaC function is predicted to be of clinical benefit in the cystic fibrosis lung. The aim of this study was to develop a small animal model to enable the direct assessment of airway ENaC function in vivo.

Experimental approach:

Tracheal potential difference (TPD) was utilized as a measure of airway epithelial ion transport in the guinea‐pig. ENaC activity in the trachea was established with a dose–response assessment to a panel of well‐characterized direct and indirect pharmacological modulators of ENaC function, delivered by intra‐tracheal (i.t.) instillation.

Key results:

The TPD in anaesthetized guinea‐pigs was attenuated by the direct ENaC blockers: amiloride, benzamil and CF552 with ED50 values of 16, 14 and 0.2 μg kg−1 (i.t.), respectively. 5‐(N‐Ethyl‐N‐isopropyl) amiloride, a structurally related compound but devoid of activity on ENaC, was without effect on the TPD. Intra‐tracheal dosing of the Kunitz‐type serine protease inhibitors aprotinin and placental bikunin, which have previously been demonstrated to inhibit proteolytic activation of ENaC, likewise potently attenuated TPD in guinea‐pigs, whereas α1‐antitrypsin and soya bean trypsin inhibitor were without effect.

Conclusions and implications:

The pharmacological sensitivity of the TPD to amiloride analogues and also to serine protease inhibitors are both consistent with that of ENaC activity in the guinea‐pig trachea. The guinea‐pig TPD therefore represents a suitable in vivo model of human airway epithelial ion transport.

British Journal of Pharmacology (2008) 155, 1025–1033; doi:10.1038/bjp.2008.363; published online 22 September 2008
An endogenous regulator of inflammation, resolvin E1, modulates osteoclast differentiation and bone resorption
Authors: Herrera B S , Ohira T , Gao L , Omori K , Yang R , Zhu M , Muscara M N , Serhan C N , Van Dyke T E , Gyurko R
Published: September 2008

Background and purpose:

The inflammation‐resolving lipid mediator resolvin E1 (RvE1) effectively stops inflammation‐induced bone loss in vivo in experimental periodontitis. It was of interest to determine whether RvE1 has direct actions on osteoclast (OC) development and bone resorption.

Experimental approach:

Primary OC cultures derived from mouse bone marrow were treated with RvE1 and analysed for OC differentiation, cell survival and bone substrate resorption. Receptor binding was measured using radiolabelled RvE1. Nuclear factor (NF)‐κB activation and Akt phosphorylation were determined with western blotting. Lipid mediator production was assessed with liquid chromatography tandem mass spectrometry.

Key results:

OC growth and resorption pit formation were markedly decreased in the presence of RvE1. OC differentiation was inhibited by RvE1 as demonstrated by decreased number of multinuclear OC, a delay in the time course of OC development and attenuation of receptor activator of NF‐κB ligand‐induced nuclear translocation of the p50 subunit of NF‐κB. OC survival and apoptosis were not altered by RvE1. Messenger RNA for both receptors of RvE1, ChemR23 and BLT1 is expressed in OC cultures. Leukotriene B4 (LTB4) competed with [3H]RvE1 binding on OC cell membrane preparations, and the LTB4 antagonist U75302 prevented RvE1 inhibition of OC growth, indicating that BLT1 mediates RvE1 actions on OC. Primary OC synthesized the RvE1 precursor 18R‐hydroxy‐eicosapentaenoic acid and LTB4. Co‐incubation of OC with peripheral blood neutrophils resulted in transcellular RvE1 biosynthesis.

Conclusions and implications:

These results indicate that RvE1 inhibits OC growth and bone resorption by interfering with OC differentiation. The bone‐sparing actions of RvE1 are in addition to inflammation resolution, a direct action in bone remodelling.

British Journal of Pharmacology (2008) 155, 1214–1223; doi:10.1038/bjp.2008.367; published online 22 September 2008
Benzylidene derivatives of andrographolide inhibit growth of breast and colon cancer cells in vitro by inducing G1 arrest and apoptosis
Authors: Jada S R , Matthews C , Saad M S , Hamzah A S , Lajis N H , Stevens M F G , Stanslas J
Published: September 2008

Background and purpose:

Andrographolide, the major phytoconstituent of Andrographis paniculata, was previously shown by us to have activity against breast cancer. This led to synthesis of new andrographolide analogues to find compounds with better activity than the parent compound. Selected benzylidene derivatives were investigated for their mechanisms of action by studying their effects on the cell cycle progression and cell death.

Experimental approach:

Microculture tetrazolium, 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) and sulphorhodamine B (SRB) assays were utilized in assessing the in vitro growth inhibition and cytotoxicity of compounds. Flow cytometry was used to analyse the cell cycle distribution of control and treated cells. CDK1 and CDK4 levels were determined by western blotting. Apoptotic cell death was assessed by fluorescence microscopy and flow cytometry.

Key results:

Compounds, in nanomolar to micromolar concentrations, exhibited growth inhibition and cytotoxicity in MCF‐7 (breast) and HCT‐116 (colon) cancer cells. In the NCI screen, 3,19‐(2‐bromobenzylidene) andrographolide (SRJ09) and 3,19‐(3‐chloro‐4‐fluorobenzylidene) andrographolide (SRJ23) showed greater cytotoxic potency and selectivity than andrographolide. SRJ09 and SRJ23 induced G1 arrest and apoptosis in MCF‐7 and HCT‐116 cells, respectively. SRJ09 downregulated CDK4 but not CDK1 level in MCF‐7 cells. Apoptosis induced by SRJ09 and SRJ23 in HCT‐116 cells was confirmed by annexin V‐FITC/PI flow cytometry analysis.

Conclusion and implications:

The new benzylidene derivatives of andrographolide are potential anticancer agents. SRJ09 emerged as the lead compound in this study, exhibiting anticancer activity by downregulating CDK4 to promote a G1 phase cell cycle arrest, coupled with induction of apoptosis.

British Journal of Pharmacology (2008) 155, 641–654; doi:10.1038/bjp.2008.368; published online 22 September 2008
Use of atorvastatin as an anti‐inflammatory treatment in Crohn's disease
Authors: Grip O , Janciauskiene S , Bredberg A
Published: September 2008

Background and purpose:

Experimental and clinical investigations have revealed that statins can downregulate both acute and chronic inflammatory processes. Whether statins express anti‐inflammatory activities in the treatment of Crohn's disease is unknown.

Experimental approach:

Ten patients were given 80 mg atorvastatin once daily for 13 weeks and then followed up for 8 weeks after the treatment. The anti‐inflammatory effects of statin were assessed by measuring levels of plasma C‐reactive protein (CRP), soluble (s) CD14, tumour necrosis factor (TNF)‐α, sTNFRI and II, CCL2 and 8 and the mucosal inflammation by faecal calprotectin. Circulating monocytes were subgrouped and their chemokine receptor expression of CCR2 and CX3CR1 were analysed.

Key results:

In 8 of 10 patients, atorvastatin treatment reduced CRP (P=0.008) and sTNFRII (P=0.064). A slight decrease in plasma levels of sCD14, TNF‐α and sTNFRI was observed in 7/10 patients and faecal calprotectin was reduced in 8/10 patients. We also observed that the treatment diminished expression of CCR2 and CX3CR1 on monocyte populations (P=0.014). At the follow‐up visit, 8 weeks after the atorvastatin treatment was terminated, CRP levels had returned to those seen before the treatment.

Conclusions and implications:

Our findings imply that atorvastatin therapy reduces inflammation in patients with Crohn's disease and, therefore, encourage further investigations of statin‐mediated protective effects in inflammatory bowel diseases.

British Journal of Pharmacology (2008) 155, 1085–1092; doi:10.1038/bjp.2008.369; published online 22 September 2008
Virodhamine relaxes the human pulmonary artery through the endothelial cannabinoid receptor and indirectly through a COX product
Authors: Kozłowska H , Baranowska M , Schlicker E , Kozłowski M , Laudañski J , Malinowska B
Published: September 2008

Background and purpose:

The endocannabinoid virodhamine is a partial agonist at the cannabinoid CB1 receptor and a full agonist at the CB2 receptor, and relaxes rat mesenteric arteries through endothelial cannabinoid receptors. Its concentration in the periphery exceeds that of the endocannabinoid anandamide. Here, we examined the influence of virodhamine on the human pulmonary artery.

Experimental approach:

Isolated human pulmonary arteries were obtained during resections for lung carcinoma. Vasorelaxant effects of virodhamine were examined on endothelium‐intact vessels precontracted with 5‐HT or KCl.

Key results:

Virodhamine, unlike WIN 55,212‐2, relaxed 5‐HT‐precontracted vessels concentration dependently. The effect of virodhamine was reduced by endothelium denudation, two antagonists of the endothelial cannabinoid receptor, cannabidiol and O‐1918, and a high concentration of the CB1 receptor antagonist rimonabant (5 μM), but only slightly attenuated by the NOS inhibitor L‐NAME and not affected by a lower concentration of rimonabant (100 nM) or by the CB2 and vanilloid receptor antagonists SR 144528 and capsazepine, respectively. The COX inhibitor indomethacin and the fatty acid amide hydrolase inhibitor URB597 and combined administration of selective blockers of small (apamin) and intermediate and large (charybdotoxin) conductance Ca2+‐activated K+ channels attenuated virodhamine‐induced relaxation. The vasorelaxant potency of virodhamine was lower in KCl‐ than in 5‐HT‐precontracted preparations.

Conclusions and implications:

Virodhamine relaxes the human pulmonary artery through the putative endothelial cannabinoid receptor and indirectly through a COX‐derived vasorelaxant prostanoid formed from the virodhamine metabolite, arachidonic acid. One or both of these mechanisms may stimulate vasorelaxant Ca2+‐activated K+ channels.

British Journal of Pharmacology (2008) 155, 1034–1042; doi:10.1038/bjp.2008.371; published online 22 September 2008
The Cystic Fibrosis Transmembrane Conductance Regulator and Chloride-Dependent Ion Fluxes of Ovine Vocal Fold Epithelium
Authors: Leydon Ciara , Fisher Kimberly V. , Lodewyck-Falciglia Danielle
Published: September 2008

Purpose

Ion-driven transepithelial water fluxes participate in maintaining superficial vocal fold hydration, which is necessary for normal voice production. The authors hypothesized that Cl
−
channels are present in vocal fold epithelial cells and that transepithelial Cl
−
fluxes can be manipulated pharmacologically.

Method

Immunohistochemical assays were used to identify cystic fibrosis transmembrane regulator Cl
−
channels in ovine vocal fold mucosae (
n
= 2). Electrophysiological responses of vocal fold mucosae (
n
= 80) to Cl
−
channel inhibitors and secretagogues were evaluated in an ovine model using a randomized controlled experimental design.

Results

Cystic fibrosis transmembrane regulator channels were localized to the plasma membranes of epithelial cells. The Cl
−
transport inhibitor, diphenylamine-2-carboxylate, elicited a 30% decrease in mean short-circuit current (I
sc
;
n
= 10). The secretagogue, isobutylmethylxanthine, yielded a 31.7% increase in mean I
sc
(
n
= 10). Another secretagogue, uridine triphosphate, elicited a 48.8% immediate and 17.3% sustained increase in mean I
sc
(
n
= 10). No sustained increases occurred following application of secretagogues to mucosae bathed in a low Cl
−
environment (
n
= 10), suggesting that responses were Cl
−
dependent.

Conclusions

The authors provide structural and functional evidence for the presence of a transepithelial pathway for Cl
−
fluxes. Pharmacological manipulation of this pathway may offer a mechanism for maintaining superficial vocal fold hydration.
The Effect of Temporal Gap Identification on Speech Perception by Users of Cochlear Implants
Authors: Sagi Elad , Kaiser Adam R. , Meyer Ted A. , Svirsky Mario A.
Published: September 2008

Purpose

This study examined the ability of listeners using cochlear implants (CIs) and listeners with normal hearing (NH) to identify silent gaps of different duration and the relation of this ability to speech understanding in CI users.

Method

Sixteen NH adults and 11 postlingually deafened adults with CIs identified synthetic vowel-like stimuli that were either continuous or contained an intervening silent gap ranging from 15 ms to 90 ms. Cumulative
d'
, an index of discriminability, was calculated for each participant. Consonant and consonant–nucleus–consonant (CNC) word identification tasks were administered to the CI group.

Results

Overall, the ability to identify stimuli with gaps of different duration was better for the NH group than for the CI group. Seven CI users had cumulative
d'
scores that were no higher than those of any NH listener, and their CNC word scores ranged from 0% to 30%. The other 4 CI users had cumulative
d'
scores within the range of the NH group, and their CNC word scores ranged from 46% to 68%. For the CI group, cumulative
d'
scores were significantly correlated with their speech testing scores.

Conclusions

The ability to identify silent gap duration may help explain individual differences in speech perception by CI users.
Low dimensional behavior of large systems of globally coupled oscillators
Authors: Ott Edward , Antonsen Thomas M.
Published: September 2008

It is shown that, in the infinite size limit, certain systems of globally coupled phase oscillators display low dimensional dynamics. In particular, we derive an explicit finite set of nonlinear ordinary differential equations for the macroscopic evolution of the systems considered. For example, an exact, closed form solution for the nonlinear time evolution of the Kuramoto problem with a Lorentzian oscillator frequency distribution function is obtained. Low dimensional behavior is also demonstrated for several prototypical extensions of the Kuramoto model, and time-delayed coupling is also considered.
Synchronization in small-world networks
Authors: Wu Ye , Shang Yun , Chen Maoyin , Zhou Changsong , Kurths Jürgen
Published: September 2008

In this paper we consider complete synchronization in small-world networks of identical Rössler oscillators. By applying a simple but effective dynamical optimization coupling scheme, we realize complete synchronization in networks with undelayed or delayed couplings, as well as ensuring that all oscillators have uniform intensities during the transition to synchronization. Further, we obtain the coupling matrix with much better synchronizability in a certain range of the probability p for adding long-range connections. Direct numerical simulations fully verify the efficiency of our mechanism.
Synchronization of complex networks through local adaptive coupling
Authors: De Lellis Pietro , di Bernardo Mario , Garofalo Franco
Published: September 2008

Two local adaptive strategies for the synchronization of complex networks are discussed in this paper. One, termed as vertex-based, uses local adaptive coupling gains at each node in the network. The other, named edge-based, associates to each edge in the network an adaptive coupling gain, determined solely on the basis of local information. The global asymptotic stability of the synchronous evolution is proven for both strategies using appropriate Lyapunov-based techniques. The effectiveness of the adaptive methodologies presented in the paper is shown via two representative examples: adaptive consensus and the adaptive synchronization of a network on N coupled Chua’s circuits.
Chaotic synchronizations of spatially extended systems as nonequilibrium phase transitions
Authors: Cencini M. , Tessone C. J. , Torcini A.
Published: September 2008

Two replicas of spatially extended chaotic systems synchronize to a common spatio-temporal chaotic state when coupled above a critical strength. As a prototype of each single spatio-temporal chaotic system a lattice of maps interacting via power-law coupling is considered. Furthermore, each unit in the one-dimensional chain is linked to the corresponding one in the replica via a local coupling. The synchronization transition is studied as a nonequilibrium phase transition, and its critical properties are analyzed at varying the spatial interaction range as well as the nonlinearity of the dynamical units composing each system. In particular, continuous and discontinuous local maps are considered. In both cases the transitions are of the second order with critical indices varying with the exponent characterizing the interaction range. For discontinuous maps it is numerically shown that the transition belongs to the anomalous directed percolation (ADP) family of universality classes, previously identified for Lévy-flight spreading of epidemic processes. For continuous maps, the critical exponents are different from those characterizing ADP, but apart from the nearest-neighbor case, the identification of the corresponding universality classes remains an open problem. Finally, to test the influence of deterministic correlations for the studied synchronization transitions, the chaotic dynamical evolutions are substituted by suitable stochastic models. In this framework and for the discontinuous case, it is possible to derive an effective Langevin description that corresponds to that proposed for ADP.
Neuronal synchrony: Peculiarity and generality
Authors: Nowotny Thomas , Huerta Ramon , Rabinovich Mikhail I.
Published: September 2008

Synchronization in neuronal systems is a new and intriguing application of dynamical systems theory. Why are neuronal systems different as a subject for synchronization? (1) Neurons in themselves are multidimensional nonlinear systems that are able to exhibit a wide variety of different activity patterns. Their “dynamical repertoire” includes regular or chaotic spiking, regular or chaotic bursting, multistability, and complex transient regimes. (2) Usually, neuronal oscillations are the result of the cooperative activity of many synaptically connected neurons (a neuronal circuit). Thus, it is necessary to consider synchronization between different neuronal circuits as well. (3) The synapses that implement the coupling between neurons are also dynamical elements and their intrinsic dynamics influences the process of synchronization or entrainment significantly. In this review we will focus on four new problems: (i) the synchronization in minimal neuronal networks with plastic synapses (synchronization with activity dependent coupling), (ii) synchronization of bursts that are generated by a group of nonsymmetrically coupled inhibitory neurons (heteroclinic synchronization), (iii) the coordination of activities of two coupled neuronal networks (partial synchronization of small composite structures), and (iv) coarse grained synchronization in larger systems (synchronization on a mesoscopic scale).
Synchronization in monkey visual cortex analyzed with an information-theoretic measure
Authors: Manyakov Nikolay V. , Van Hulle Marc M.
Published: September 2008

We apply an information-theoretic measure for phase synchrony to local field potentials recorded with a multi-electrode array implanted in area V4 of the monkey visual cortex during a reinforcement pairing experiment. We show for the first time that (1) the phase synchrony is significantly higher for the rewarded stimulus than the unrewarded one, after training the monkey; (2) just after the stimuli reversal, the difference in phase synchronization is due to the stimuli, not the reward; (3) the difference between reward and no reward is most clear in two disconnected time intervals between stimuli onset and the expected delivery of the reward; and (4) synchronous activity appears in waves running over the array, and their timing correlates well with the time intervals where the difference between reward and no reward is most prominent.
Bifurcational mechanisms of synchronization of a resonant limit cycle on a two-dimensional torus
Authors: Anishchenko V. , Nikolaev S. , Kurths J.
Published: September 2008

We study synchronization of a resonant limit cycle on a two-dimensional torus with an external harmonic signal. The regime of the resonant limit cycle is realized in a system of two coupled Van der Pol oscillators; we consider the resonances 1:1 and 1:3. We analyze the influence of coupling strength between the oscillators. We show that the resonant limit cycle can be generally synchronized on the torus through the resonance destruction followed by the locking of one and then another one of the basic frequencies. We consider the bifurcational mechanism of the synchronization effect.
External periodic driving of large systems of globally coupled phase oscillators
Authors: Antonsen T. M. , Faghih R. T. , Girvan M. , Ott E. , Platig J.
Published: September 2008

Large systems of coupled oscillators subjected to a periodic external drive occur in many situations in physics and biology. Here the simple paradigmatic case of equal strength, all-to-all sine coupling of phase oscillators subject to a sinusoidal external drive, is considered. The stationary states and their stability are determined. Using the stability information and numerical experiments, parameter space phase diagrams showing when different types of system behavior apply are constructed, and the bifurcations marking transitions between different types of behavior are delineated. The analysis is supported by results of direct numerical simulation of an ensemble of oscillators.
Synchronization, phase locking, and metachronal wave formation in ciliary chains
Authors: Niedermayer Thomas , Eckhardt Bruno , Lenz Peter
Published: September 2008

Synchronization and wave formation in one-dimensional ciliary arrays are studied analytically and numerically. We develop a simple model for ciliary motion that is complex enough to describe well the behavior of beating cilia but simple enough to study collective effects analytically. Beating cilia are described as phase oscillators moving on circular trajectories with a variable radius. This radial degree of freedom turns out to be essential for the occurrence of hydrodynamically induced synchronization of ciliary beating between neighboring cilia. The transitions to the synchronized and phase-locked state of two cilia and the formation of metachronal waves in ciliary chains with different boundary conditions are discussed.
Formation and destruction of multilayered tori in coupled map systems
Authors: Zhusubaliyev Zhanybai T. , Mosekilde Erik
Published: September 2008

The paper first illustrates how multilayered tori can arise through one or more pitchfork bifurcations of the saddle cycle on an ordinary resonance torus. The paper hereafter describes three different scenarios by which a multilayered torus can be destructed. One scenario involves a saddle-node bifurcation in which the middle layer of a three-layered torus disappears in an abrupt transition to chaos while the outer-layer manifolds and their associated saddle and unstable-focus cycles continue to exist and to control the transient dynamics. In a second scenario, the unstable focus cycles of the intermediate layers in a five-layered torus turn into unstable nodes, and closed loop connections are established between the unstable nodes and the points of the stable resonance node on the torus. Finally, a third scenario describes a transition in which homoclinic bifurcations destroy first the outer layers and thereafter also the inner layer. The paper also illustrates how the formation and destruction of multilayered tori can occur in the cluster dynamics of an ensemble of globally coupled maps. This leads to three additional scenarios for the destruction of multilayered tori.
A partial synchronization theorem
Authors: Pogromsky Alexander Yu.
Published: September 2008

When synchronization sets in, coupled systems oscillate in a coherent way. It is possible to observe also some intermediate regimes characterized by incomplete synchrony which are referred to as partial synchronization. The paper focuses on analysis of partial synchronization in networks of linearly coupled oscillators.
Variety of synchronous regimes in neuronal ensembles
Authors: Komarov M. A. , Osipov G. V. , Suykens J. A. K.
Published: September 2008

We consider a Hodgkin–Huxley-type model of oscillatory activity in neurons of the snail Helix pomatia. This model has a distinctive feature: It demonstrates multistability in oscillatory and silent modes that is typical for the thalamocortical neurons. A single neuron cell can demonstrate a variety of oscillatory activity: Regular and chaotic spiking and bursting behavior. We study collective phenomena in small and large arrays of nonidentical cells coupled by models of electrical and chemical synapses. Two single elements coupled by electrical coupling show different types of synchronous behavior, in particular in-phase and antiphase synchronous regimes. In an ensemble of three inhibitory synaptically coupled elements, the phenomenon of sequential synchronous dynamics is observed. We study the synchronization phenomena in the chain of nonidentical neurons at different oscillatory behavior coupled with electrical and chemical synapses. Various regimes of phase synchronization are observed: (i) Synchronous regular and chaotic spiking; (ii) synchronous regular and chaotic bursting; and (iii) synchronous regular and chaotic bursting with different numbers of spikes inside the bursts. We detect and study the effect of collective synchronous burst generation due to the cluster formation and the oscillatory death.
Polyrhythmic synchronization in bursting networking motifs
Authors: Shilnikov Andrey , Gordon René , Belykh Igor
Published: September 2008

We study the emergence of polyrhythmic dynamics of motifs which are the building block for small inhibitory-excitatory networks, such as central pattern generators controlling various locomotive behaviors of animals. We discover that the pacemaker determining the specific rhythm of such a network composed of realistic Hodgkin–Huxley-type neurons is identified through the order parameter, which is the ratio of the neurons’ burst durations or of duty cycles. We analyze different configurations of the motifs and describe the universal mechanisms for synergetics of the bursting patterns. We discuss also the multistability of inhibitory networks that results in polyrhythmicity of its emergent synchronous behaviors.
Onset of synchronization in complex gradient networks
Authors: Wang Xingang , Huang Liang , Guan Shuguang , Lai Ying-Cheng , Lai Choy Heng
Published: September 2008

Recently, it has been found that the synchronizability of a scale-free network can be enhanced by introducing some proper gradient in the coupling. This result has been obtained by using eigenvalue-spectrum analysis under the assumption of identical node dynamics. Here we obtain an analytic formula for the onset of synchronization by incorporating the Kuramoto model on gradient scale-free networks. Our result provides quantitative support for the enhancement of synchronization in such networks, further justifying their ubiquity in natural and in technological systems.
Network synchronizability analysis: A graph-theoretic approach
Authors: Chen Guanrong , Duan Zhisheng
Published: September 2008

This paper addresses the fundamental problem of complex network synchronizability from a graph-theoretic approach. First, the existing results are briefly reviewed. Then, the relationships between the network synchronizability and network structural parameters (e.g., average distance, degree distribution, and node betweenness centrality) are discussed. The effects of the complementary graph of a given network and some graph operations on the network synchronizability are discussed. A basic theory based on subgraphs and complementary graphs for estimating the network synchronizability is established. Several examples are given to show that adding new edges to a network can either increase or decrease the network synchronizability. To that end, some new results on the estimations of the synchronizability of coalescences are reported. Moreover, a necessary and sufficient condition for a network and its complementary network to have the same synchronizability is derived. Finally, some examples on Chua circuit networks are presented for illustration.
Microconcentrator photovoltaic cell (the m-C cell): Modeling the optimum method of capturing light in an organic fiber based photovoltaic cell
Authors: Curran Seamus , Talla Jamal , Dias Sampath , Dewald James
Published: September 2008

We propose a new architecture as an alternative method when constructing organic photovoltaics (PVs) by addressing the best method to trap resonant light within the devices using fiber optics to concentrate light in the form of a microconcentrator cell (m-C cell). Our initial effort is to address how the m-C cells manage light absorption using a mathematical model that considers all the required parameters including the incident angle, meridional plane, cross sectional area, and path length. By knowing the materials, refractive index, we are able to calculate the optical angular input to achieve maximum absorption of resonant light. We also addressed the complexity of how changing refractive indices in a multilayer device can alter the angular dependence when considering the incident input light. The consequence is that we can ensure efficient absorption of resonant light in a thin film yet without issues of transmission losses which are evident in all other thin film organic PVs.
Measurements of the steady streaming flow around oscillating spheres using three dimensional particle tracking velocimetry
Authors: Otto Florian , Riegler Emmalee K. , Voth Greg A.
Published: September 2008

Granular particles vibrated in a fluid have been found to exhibit self-organization with attractive and repulsive interactions between the particles. These interactions have been attributed to the steady streaming flow around oscillating particles. Here we examine the steady streaming flow surrounding a vertically oscillating sphere using three-dimensional particle tracking velocimetry. We present measurements of the flow with the sphere far from boundaries, close to the bottom wall of the tank, and near another oscillating sphere. For parameters of interest for granular self-organization, the flow around a single sphere far from boundaries differs significantly from an analytical calculation that has been applied to granular organization. Measured positions of the stagnation point support previously observed scaling at small amplitudes, and demonstrate how this scaling changes at large amplitudes. When the sphere is oscillated near the bottom wall, the topology of the flow changes, resulting in a larger repulsive flow region than expected. Previous experiments saw attraction in the region where the flow around a single sphere is repulsive. We conclude that advection in the streaming flow due to a single sphere cannot explain the observed granular attractive and repulsive interactions; rather, nonlinear interactions between the flows around two or more spheres must be responsible.
Echo phenomena in large systems of coupled oscillators
Authors: Ott Edward , Platig John H. , Antonsen Thomas M. , Girvan Michelle
Published: September 2008

As exemplified by the Kuramoto model, large systems of coupled oscillators may undergo a transition to phase coherence with increasing coupling strength. It is shown that below the critical coupling strength for this transition such systems may be expected to exhibit “echo” phenomena: a stimulation by two successive pulses separated by a time interval τ leads to the spontaneous formation of response pulses at a time τ,2τ,3τ,…, after the second stimulus pulse. Analysis of this phenomenon, as well as illustrative numerical experiments, are presented. The theoretical significance and potential uses of echoes in such systems are discussed.
Electrowetting on gold electrodes with microscopic three-dimensional structures for microfluidic devices
Authors: Yokomaku Hiroomi , Satoh Wataru , Fukuda Junji , Suzuki Hiroaki
Published: September 2008

To improve the performance of electrowetting-based microfluidic devices, we used micropillar structures to enhance the changes in the wettability of gold electrodes. The changes in the contact angle of a sessile drop were influenced by the diameter of the micropillars and interpillar distances. For a potential change between 0 V and −1.0 V, the change of the contact angle of the KCl sessile drop was 41° on a smooth electrode, but 88° on an electrode with micropillars with a 10 μm diameter. Furthermore, the existence of the micropillars accelerated the change of the contact angle. The gold electrodes with the micropillars were used to generate the capillary force to mobilize a liquid column in a microflow channel. Compared to a device with a smooth electrode, this device showed a fourfold increase in the flow velocity at −0.9 V. The electrodes were also used as a valve. The ability to stop an intruding solution and the switching speed was improved with the micropillar structure.
Synchronization of nonlinear systems under information constraints
Authors: Fradkov Alexander L. , Andrievsky Boris , Evans Robin J.
Published: September 2008

A brief survey of control and synchronization under information constraints (limited information capacity of the coupling channel) is given. Limit possibilities of nonlinear observer-based synchronization systems with first-order coders or full-order coders are considered in more detail. The existing and new theoretical results for multidimensional drive-response Lurie systems (linear part plus nonlinearity depending only on measurable outputs) are presented. It is shown that the upper bound of the limit synchronization error (LSE) is proportional to the upper bound of the transmission error. As a consequence, the upper and lower bounds of LSE are proportional to the maximum coupling signal rate and inversely proportional to the information transmission rate (channel capacity). The analysis is extended to networks having a “chain,” “star,” or “star-chain” topology. Adaptive chaotic synchronization under information constraints is analyzed. The results are illustrated by example: master-slave synchronization of two chaotic Chua systems coupled via a channel with limited capacity.
Energy-band structure and optical gain in strained InAs(N)/GaSb/InAs(N) quantum well lasers.
Authors: Ridene S. , Debbichi M. , Ben fredj A , Said M. , Bouchriha H.
Published: September 2008

We present a theoretical study of band structure and optical gain spectra of dilute-N InAsN/GaSb/InAsN and the similar N-free InAs/GaSb/InAs laser structures, which have a “W” band alignment. Calculations are based on a 10×10 k⋅p model incorporating valence, conduction, and nitrogen-induced bands. The two laser diodes are designed to operate at 3.3 μm at room temperature. We find that the incorporation of a few percent of nitrogen in the laser active region improves optical gain performance, which leads to a peak gain value of approximately 1000 cm−1 for a typical injection carrier concentration of 1×1012 cm−2 and a carrier transparent density of 0.54×1018 cm−3.
Microwave spectroscopy of the PBr radical in the XΣ−3 state
Authors: Okabayashi Toshiaki , Kawajiri Hideaki , Umeyama Michiaki , Ide Chihiro , Oe Sumio , Tanimoto Mitsutoshi
Published: September 2008

The microwave spectrum of the PBr radical in the XΣ−3 ground electronic state has been observed by a source modulated spectrometer. The PBr radical was generated in a free space cell by an ac∕dc glow discharge in a mixture of PBr3 with He and∕or H2. A spectrum with three spin components for each of the two isotopomers, PBr79 and PBr81, was observed. The spectrum showed hyperfine splitting caused by interactions due to both bromine and phosphorus nuclei. The molecular constants including the magnetic hyperfine and nuclear quadrupole hyperfine interaction constants were determined by analyzing the observed spectrum. The spin density of the unpaired electrons was estimated from the observed hyperfine coupling constants to be 85.4% and 16.3% on the phosphorus and bromine atoms, respectively.
Hydrodynamic effects on the disorder-to-order transitions of diblock copolymer melts
Authors: Honda Takashi , Kawakatsu Toshihiro
Published: September 2008

Dynamic self-consistent field theory and Navier–Stokes equation are coupled to study hydrodynamic effects on the disorder-to-order transition of diblock copolymer melts. Simulations are performed for different values of the viscosity and the results are compared with those without the hydrodynamic effects. The lower the viscosity is, the faster the free energy density decays. Starting from uniformly mixed initial states, body-centered-cubic spheres, hexagonally packed cylinders, and lamellar structures are obtained in the presence of the hydrodynamic effects. On the contrary, the bicontinuous double gyroid structure cannot be obtained even with the hydrodynamic effects. The scattering intensities of the domain structures are calculated to confirm these properties of the ordering of the structures.
Guiding center plasma models in three dimensions
Authors: Sugiyama Linda E.
Published: September 2008

Guiding center plasma models describe the fast charged particle gyration around magnetic field lines by an angle coordinate, defined relative to local orthogonal coordinate axes (ê1,ê2,b̂=B∕B) at each guiding center location. In three dimensions (3D), unlike uniform straight two-dimensional (2D) fields, geometrical effects make the small gyroradius expansion nonuniform in velocity phase space in first order O(ρi∕L). At second order, Hamiltonian and Lagrangian solutions may be undefined even when good magnetic flux surfaces exist; existence requires the magnetic field torsion τ=b̂⋅∇×b̂=0 and τg≡b̂⋅(∇ê1)⋅ê2=0, unless the magnetic field has a 2D symmetry, such as toroidal axisymmetry. Keeping complete 3D geometrical effects also requires the magnetic vector potential term to appear in the electric field at the same order as the electrostatic potential. These problems express properties of magnetic vector potentials, Lagrangians, and the curvature of manifolds, and have analogies to attempts to connect small scale Lagrangian theories to higher dimensional, large scale ones in the grand unification theories of physics.
Controlling spin contamination using constrained density functional theory
Authors: Schmidt J. R. , Shenvi Neil , Tully John C.
Published: September 2008

We have extended the constrained density functional theory (DFT) approach to explicitly control the magnitude of spin contamination. Unlike a restricted or restricted open-shell approach, the present method allows finer granularity, not only constraining the magnitude of the spin contamination but also allowing for the possibility of applying the constraint to a subsystem of a much larger system. This allows for the description of spin polarization where physically meaningful, while simultaneously enabling the reduction of spurious overpolarization that is present in many DFT functionals. We utilize this constraint in two particular model applications: The calculation of isotropic and anisotropic hyperfine couplings of a transition metal complex, [Mn(CN)5NO]2−, and the calculation of the diabatic dissociation curves of OF radical. In both cases, the spin contamination constraint is essential for obtaining physically meaningful, qualitatively correct, results.
Ferroelectric stripe domains in PbTiO3 thin films: Depolarization field and domain randomness
Authors: Takahashi R. , Dahl Ø. , Eberg E. , Grepstad J. K. , Tybell T.
Published: September 2008

Observation of stripe domains in PbTiO3 thin films using standard x-ray diffraction analysis at room temperature is discussed. High-quality c-axis oriented thin films of varying thickness, from 6 to 210 unit cells, were grown on buffered NH4–HF etched SrTiO3(001) and Nb:SrTiO3(001) substrates using off-axis radio frequency magnetron sputtering. High-resolution linear Qx scans reveal a superstructure around the specular Bragg peaks, consistent with the presence of ferroelectric stripe domains. For thin samples, the stripe width is found to be proportional to the square root of the film thickness, with random in-plane orientation of domains. For films with a thickness of more than ∼100 unit cells, both monodomain samples and stripe domains were observed. We present evidence for the presence of a threshold depolarization field, above which there is a monotonically decreasing relationship between the domain width and the depolarization field. Furthermore, simulations show that random variations in size of the domains affect the separation of the diffuse scattering peaks from that of the specular reflection.
Dielectric responses and multirelaxation behaviors of pure and doped CaCu3Ti4O12 ceramics
Authors: Fang Liang , Shen Mingrong , Zheng Fengang , Li Zhenya , Yang Jing
Published: September 2008

Pure and Co/Fe doped CaCu3Ti4O12 (CCTO) ceramics were prepared by solid state reaction method. The electrical properties of ceramics were found to be dependent on the type of dopant materials. A multirelaxation mechanism should be considered for the common observed (50–200 K) dielectric relaxation of CCTO ceramic. In relatively high temperature range, this relaxation followed the Arrhenius behavior with activation energy of 68 meV, which was ascribed to the Maxwell–Wagner (MW)-type relaxation associated with grains. In lower temperature range, this relaxation exhibited variable-ranger-hopping behavior due to the dipolar effects. The dielectric relaxation mechanism of Co doped CCTO ceramic was similar to that of pure CCTO ceramic, while that of Fe doped CCTO ceramic was quite different. Two dielectric relaxations were identified in the temperature range from 4 to 300 K. A dielectric relaxation at room temperature with an activation energy of 390.3 meV was attributed to the MW-type relaxation associated with grain boundaries. Another dielectric relaxation at low temperatures (100–200 K) with an activation energy of 265 meV was originated from the carrier hopping process between Fe2+ and Fe3+.