| 26) |  |
J.-C. Wang, T. Foroud, A. L. Hinrichs, N. X. H. Le, S. Bertelsen, J. P. Budde, O. Harari, D. L. Koller, L. Wetherill, A. Agrawal, L. Almasy, A. I. Brooks, K. Bucholz, D. Dick, V. Hesselbrock,
E. O. Johnson, S. Kang, M. Kapoor, J. Kramer, S. Kuperman, P. A. F. Madden, N. Manz, N. G.
Martin, J. N. McClintick, G. W. Montgomery, J. I. Nurnberger Jr, M. Rangaswamy, J. Rice, M.
Schuckit, J. A. Tischfield, J. B. Whitfield, X. Xuei, B. Porjesz, A. C. Heath, H. .J. Edenberg,
L. J. Bierut, and A. M. Goate: "A genome wide association study of alcohol dependence symptom counts in extended pedigrees identifies C15orf53" Molecular Psychiatry ?? (2013), ???-??? Several studies have identified genes associated with alcohol-use disorders (AUDs), but the variation in each of these genes explains only a small portion of the genetic vulnerability. The goal of the present study was to perform a genome-wide association study (GWAS) in extended families from the Collaborative Study on the Genetics of Alcoholism to identify novel genes affecting risk for alcohol dependence (AD). To maximize the power of the extended family design, we used a quantitative endophenotype, measured in all individuals: number of alcohol-dependence symptoms endorsed (symptom count (SC)). Secondary analyses were performed to determine if the single nucleotide polymorphisms (SNPs) associated with SC were also associated with the dichotomous phenotype, DSM-IV AD. This family-based GWAS identified SNPs in C15orf53 that are strongly associated with DSM-IV alcohol-dependence symptom counts (P = 4.5 × 10-8, inflation-corrected P = 9.4 × 10-7). Results with DSM-IV AD in the regions of interest support our findings with SC, although the associations were less significant. Attempted replications of the most promising association results were conducted in two independent samples: nonoverlapping subjects from the Study of Addiction: Genes and Environment (SAGE) and the Australian Twin Family Study of AUDs (OZALC). Nominal association of C15orf53 with SC was observed in SAGE. The variant that showed strongest association with SC, rs12912251 and its highly correlated variants (D' = 1, r2> 0.95), have previously been associated with risk for bipolar disorder. |
| 25) |  |
S. J. Kang, M. Rangaswamy, N. Manz, J.-C. Wang, L. Wetherill, T. Hinrichs, L. Almasy, A. Brooks, D. B. Chorlian, D. Dick, V. Hesselbrock, J. Kramer, S. Kuperman, J. Nurnberger Jr, J. Rice, M. Schuckit, J. Tischfield, L.J. Bierut, H. J. Edenberg, A. Goate, T. Foroud, and B. Porjesz: "Family-based Genome-wide Association Study of Frontal Theta Oscillations Identifies Potassium Channel Gene KCNJ6" Genes, Brain and Behavior 11 (2012), 712-719  (supplemental data)Event-related oscillations (EROs) represent highly heritable neuroelectric correlates of cognitive processes that manifest deficits in alcoholics and in offspring at high risk to develop alcoholism. Theta ERO to targets in the visual oddball task has been shown to be an endophenotype for alcoholism. A family-based genomewide association study was performed for the frontal theta ERO phenotype using 634 583 autosomal single nucleotide polymorphisms (SNPs) genotyped in 1560 family members from 117 families densely affected by alcohol use disorders, recruited in the Collaborative Study on the Genetics of Alcoholism. Genome-wide significant association was found with several SNPs on chromosome 21 in KCNJ6 (a potassium inward rectifier channel; KIR3.2/GIRK2), with the most significant SNP at P = 4.7 × 10-10). The same SNPs were also associated with EROs from central and parietal electrodes, but with less significance, suggesting that the association is frontally focused. One imputed synonymous SNP in exon four, highly correlated with our top three SNPs, was significantly associated with the frontal theta ERO phenotype. These results suggest KCNJ6 or its product GIRK2 account for some of the variations in frontal theta band oscillations. GIRK2 receptor activation contributes to slow inhibitory postsynaptic potentials thatmodulate neuronal excitability, and therefore influence neuronal networks. |
| 24) |  |
C. Kamarajan, M. Rangaswamy, N. Manz, D. B. Chorlian, A. K. Pandey, B. N. Roopesh, and B. Porjesz "Topography, Power and Current Source Density of Theta Oscillations during Reward Processing as Markers for Alcohol Dependence" Human Brain Mapping" Human Brain Mapping 33 (2012), 1019-1039 Abstract: Recent studies have linked alcoholism with a dysfunctional neural reward system. Although several electrophysiological studies have explored reward processing in healthy individuals, such studies in alcohol- dependent individuals are quite rare. The present study examines theta oscillations during reward processing in abstinent alcoholics. The electroencephalogram (EEG) was recorded in 38 abstinent alcoholics and 38 healthy controls as they performed a single outcome gambling task, which involved outcomes of eitherloss or gain of an amount (10 or 50¢) that was bet. Event-related theta band (3.0–7.0 Hz) power following each outcome stimulus was computed using the S-transform method. Theta power at the time window of the outcome-related negativity (ORN) and positivity (ORP) (200–500 ms) was compared across groups and outcome conditions. Additionally, behavioral data of impulsivity and task performance were analyzed. The alcoholic group showed significantly decreased theta power during reward processing compared to controls. Current source density (CSD) maps of alcoholics revealed weaker and diffuse source activity for all conditions and weaker bilateral prefrontal sources during the Loss 50 condition when compared with controls who manifested stronger and focused midline sources. Furthermore, alcoholics exhibited increased impulsivity and risk-taking on the behavioral measures. A strong association between reduced anterior theta power and impulsive task-performance was observed. It is suggested that decreased power and weaker and diffuse CSD in alcoholics may be due to dysfunctional neural reward circuitry. The relationship among alcoholism, theta oscillations, reward processing, and impulsivity could offer clues to understand brain circuitries that mediate reward processing and inhibitory control |
| 23) |  |
M. Kapoor, J. C Wang, S. Bertelsen, K. Bucholz, J. P Budde, A. Hinrichs, A. Agrawal, A. Brooks, D. B Chorlian, D. Dick, V. Hesselbrock, T. Foroud, J. Kramer, S. Kuperman, N. Manz, J. Nurnberger Jr, B. Porjesz, J. P Rice, J. Tischfield, X. Xuei, M. Schuckit, H. J Edenberg, L. J Bierut, and A. Goate "Variants located upstream of CHRNB4 on chromosome 15q25.1 are associated with age at onset of daily smoking and habitual smoking" PLoS ONE 7 (2012), e33513 Abstract: Several genome-wide association and candidate gene studies have linked chromosome 15q24–q25.1 (a region including the CHRNA5-CHRNA3-CHRNB4 gene cluster) with alcohol dependence, nicotine dependence and smoking-related illnesses such as lung cancer and chronic obstructive pulmonary disease. To further examine the impact of these genes on thedevelopment of substance use disorders, we tested whether variants within and flanking the CHRNA5-CHRNA3-CHRNB4 gene cluster affect the transition to daily smoking (individuals who smoked cigarettes 4 or more days per week) in a cross sectional sample of adolescents and young adults from the COGA (Collaborative Study of the Genetics of Alcoholism) families. Subjects were recruited from families affected with alcoholism (either as a first or second degree relative) and the comparison families. Participants completed the SSAGA interview, a comprehensive assessment of alcohol and other substance use and related behaviors. Using the Quantitative trait disequilibrium test (QTDT) significant association was detected between age at onset of daily smoking and variants located upstream of CHRNB4. Multivariate analysis using a Cox proportional hazards model further revealed that these variants significantly predict the age at onset of habitual smoking among daily smokers. These variants were not in high linkage disequilibrium (0.28<r2<0.56) with variants that have previously been reported to affect risk for nicotine dependence and smoking related diseases in adults. The data suggests that an age-associated relationship underlies the association of SNPs in CHRNB4 with onset of chronic smoking behaviors in adolescents and young adults and may improve genetic information that will lead to better prevention and intervention for substance use disorders among adolescents and young adults. |
| 22) |  |
A. K. Pandey, C. Kamarajan, Y. Tang, D. B. Chorlian, B. N. Roopesh, N. Manz, A. Stimus, M. Rangaswamy, and B. Porjesz "Neurocognitive Deficits in Male Alcoholics: An ERP/sLORETA Analysis of the N2 Component in an Equal Probability Go/NoGo Task" Biological Psychiatry 89 (2012), 170-182 Abstract: In alcoholism research, studies concerning time-locked electrophysiological aspects of response inhibition have concentrated mainly on the P3 component of the event-related potential (ERP). The objective of the present study was to investigate the N2 component of the ERP to elucidate possible brain dysfunction related to the motor response and its inhibition using a Go/NoGo task in alcoholics. The sample consisted of 78 abstinent alcoholic males and 58 healthy male controls. The N2 peak was compared across group and task conditions. Alcoholics showed significantly reduced N2 peak amplitudes compared to normal controls for Go as well as NoGo task conditions. Control subjects showed significantly larger NoGo than Go N2 amplitudes at frontal regions, whereas alcoholics did not show any differences between task conditions at frontal regions. Standardized low resolution electromagnetic tomography analysis (sLORETA) indicated that alcoholics had significantly lower current density at the source than control subjects for the NoGo condition at bilateral anterior prefrontal regions, whereas the differences between groups during the Go trials were not statistically significant. Furthermore, NoGo current density across both groups revealed significantly more activation in bilateral anterior cingulate cortical (ACC) areas, with the maximum activation in the right cingulate regions. However, the magnitude of this difference was much less in alcoholics compared to control subjects. These findings suggest that alcoholics may have deficits in effortful processing during the motor response and its inhibition, suggestive of possible frontal lobe dysfunction. |
| 21) |  |
J. Derringer, R. F. Krueger, N. Manz, B. Porjesz, L. Almasy, E. Bookman, H. J. Edenberg, J. R. Kramer, J. A. Tischfield, GENEVA consortium, and L. J. Bierut "Non-replication of an association of SGIP1 SNPs with alcohol dependence and theta EEG power" Psychiatric Genetics 21 (2011), 265-266 (supplemental data)Abstract: A recent study in a sample of Plains Indians showed association between eight single nucleotide polymorphisms (SNPs) located in the SGIP1 gene and resting y electroencephalogram (EEG) power. This association appeared to generalize to alcohol use disorders, for which EEG power is a potential endophenotype. We analyzed a large, diverse sample for replication of the association of these implicated SGIP1 SNPs (genotyped on the Illumina 1M platform) with alcohol dependence (N = 3988) and q EEG power (N = 1066). We found no evidence of association of the earlier implicated SGIP1 SNPs with either alcohol dependence or q EEG power (all P > 0.15) in this sample. The earlier implicated SNPs located in SGIP1 gene showed no association with alcohol dependence or q EEG power in this sample of individuals with European and/or African ancestry. This failure to replicate may be the result of differences in ancestry between this sample and the original sample. |
| 20) |  |
M. Zlojutro, N. Manz, M. Rangaswamy, X. Xuei, L. Flury-Wetherill, D. Koller, L. J. Bierut, A. Goate, V. Hesselbrock, S. Kuperman, J. Nurnberger Jr., J. P. Rice, M. A. Schuckit, T. Foroud, H. J. Edenberg, B. Porjesz, and L. Almasy "Genome-wide association study of theta band event-related oscillations identifies serotonin receptor gene HTR7 influencing risk of alcohol dependence" American Journal of Medical Genetics Part B: Neuropsychiatric Genetics 156 (2011), 44-58 Abstract: Event-related brain oscillations (EROs) represent highly heritable neuroelectrical correlates of human perception and cognitive performance that exhibit marked deficits in patients with various psychiatric disorders. We report the results of the first genome-wide association study (GWAS) of an ERO endophenotype— frontal theta ERO evoked by visual oddball targets during P300 response in 1,064 unrelated individuals drawn from a study of alcohol dependence. Forty-two SNPs of the Illumina HumanHap 1M microarray were selected from the theta ERO GWAS for replication in family-based samples (N = 1,095), with four markers revealing nominally significant association. The most significant marker from the two-stage study is rs4907240 located within ARID protein 5A gene (ARID5A) on chromosome 2q11 (unadjusted, Fisher’s combined P = 3.68 × 10-6).However, the most intriguing association to emerge is with rs7916403 in serotoninreceptor geneHTR7onchromosome 10q23 (combined P = 1.53 × 10-4), implicating the serotonergic system in the neurophysiological underpinnings of theta EROs. Moreover, promising SNPs were tested for association with diagnoses of alcohol dependence (DSM-IV), revealing a significant relationship with the HTR7 polymorphism among GWAS case–controls (P=0.008). Significant recessive genetic effects were also detected for alcohol dependence in both case–control and family -based samples (P = 0.031 and 0.042, respectively), with the HTR7 risk allele corresponding to theta ERO reductions among homozygotes. These results suggest a role of the serotonergic system in the biological basis of alcohol dependence and underscore the utility of analyzing brain oscillations as a powerful approach to understanding complex genetic psychiatric disorders. |
| 19) |  |
C. Kamarajan, M. Rangaswamy, Y. Tang, D. B. Chorlian, A. K. Pandey, B. N. Roopesh, N. Manz, R. Saunders, A. T. Stimus, and B. Porjesz "Dysfunctional reward processing in male alcoholics: An ERP study during a gambling task" Journal of Psychiatric Research 44 (2010), 576-590 Objective: A dysfunctional neural reward system has been shown to be associated with alcoholism. The current study aims to examine reward processing in male alcoholics by using event-related potentials (ERPs) as well as behavioral measures of impulsivity and risk-taking. Methods: Outcome-related negativity (ORN/N2) and positivity (ORP/P3) derived from a single outcome gambling task were analyzed using a mixed model procedure. Current density was compared across groups and outcomes using standardized low resolution electromagnetic tomography (sLORETA). Behavioral scores were also compared across groups. Correlations of ERP factors with behavioral and impulsivity factors were also analyzed. Results: Alcoholics showed significantly lower amplitude than controls during all outcome conditions for the ORP component and decreased amplitude during the loss conditions for the ORN component. Within conditions, gain produced higher amplitudes than loss conditions. Topographically, both groups had an anterior focus during loss conditions and posterior maxima during gain conditions, especially for the ORN component. Decreased ORP current density at cingulate gyrus and less negative ORN current density at sensory and motor areas characterized the alcoholics. Alcoholics had higher levels of impulsivity and risk-taking features than controls. Conclusions: Deficient outcome/reward processing and increased impulsivity and risk-taking observed in alcoholics may be at least partly due to reward deficiency and/or dysfunctional reward circuitry in the brain, suggesting that alcoholism can be considered as part of the cluster of the reward deficiency syndrome (RDS). |
| 18) |  |
A. C. H. Chen, N. Manz, Y. Tang, M. Rangaswamy, L. Almasy, S. Kuperman, J. Nurnberger Jr, S. J. O'Connor, H. J. Edenberg, M. A. Schuckit, J. Tischfield, T. Foround, L. Bierut, J. Rohrbaugh, J. P. Rice, A. Goate, V. Hesselbrock, and B. Porjesz "Single Nucleotide Polymorphisms in Corticotropin Releasing Hormone Receptor 1 Gene (CRHR1) Are Associated with Quantitative Traits of Event-Related Potential and Alcohol Dependence" Alcoholism: Clinical and Experimental Research 34 (2010), 988-996 Background: Endophenotypes reflect more proximal effects of genes than diagnostic categories, hence providing a more powerful strategy in searching for genes involved in complex psychiatric disorders. There is strong evidence suggesting the P3 amplitude of the event-related potential (ERP) as an endophenotype for the risk of alcoholism and other disinhibitory disorders. Recent studies demonstrated a crucial role of corticotropin releasing hormone receptor 1 (CRHR1) in the environmental stress response and ethanol self-administration in animal models. The aim of the present study was to test the potential associations between single-nucleotide polymorphisms (SNPs) in the CRHR1 gene and the quantitative trait, P3 amplitude during the processing of visual target signals in an oddball paradigm, as well as alcohol dependence diagnosis. Methods: We analyzed a sample from the Collaborative Study on the Genetics of Alcoholism (COGA) comprising 1049 Caucasian subjects from 209 families (including 472 alcohol-dependent individuals). Quantitative transmission disequilibrium test (QTDT) and family-based association test (FBAT) were used to test the association, and false discovery rate (FDR) was applied to correct for multiple comparisons. Results: Significant associations (p < 0.05) were found between the P3 amplitude and alcohol dependence with multiple SNPs in the CRHR1 gene. Conclusions: Our results suggest that CRHR1 may be involved in modulating the P3 component of the ERP during information processing and in vulnerability to alcoholism. These findings underscore the utility of electrophysiology and the endophenotype approach in the genetic study of psychiatric disorders. |
| 17) |  |
G. Bordyugov, N. Fischer, H. Engel, N. Manz, and O. Steinbock "Anomalous dispersion in the Belousov-Zhabotinsky reaction: Experiments and modeling" Physica D: Nonlinear Phenomena 239 (2010), 766-775 Abstract: We report results on dispersion relations and instabilities of traveling waves in excitable systems. Experiments employ solutions of the 1,4-cyclohexanedione BelousovZhabotinsky reaction confined to thin capillary tubes which create a pseudo-one-dimensional system. Theoretical analyses focus on a threevariable reaction-diffusion model that is known to reproduce qualitatively many of the experimentally observed dynamics. Using continuation methods, we show that the transition from normal, monotonic to anomalous, single-overshoot dispersion curves is due to an orbit flip bifurcation of the solitary pulse homoclinics. In the case of ``wave stacking'', this anomaly induces attractive pulse interaction, slow solitary pulses, and faster wave trains. For ``wave merging'', wave trains break up in the wake of the slow solitary pulse due to an instability of wave trains at small wavelength. A third case, ``wave tracking'' is characterized by the non-existence of solitary waves but existence of periodic wave trains. The corresponding dispersion curve is a closed curve covering a finite band of wavelengths. |
| 16) |  |
C. Kamarajan, B. Porjesz, M. Rangaswamy, Y. Tang, D. B. Chorlian, A. Padmanabhapillai, R. Saunders, A. K. Pandey, B. N. Roopesh, N. Manz, A. T. Stimus, and H. Begleiter "Brain signatures of monetary loss and gain: outcome-related potentials in a single outcome gambling task" Behavioural Brain Research 197 (2009), 62-76 Abstract: This study evaluates the event-related potential (ERP) components in a single outcome gambling task that involved monetary losses and gains. The participants were 50 healthy young volunteers (25 males and 25 females). The gambling task involved valence (loss and gain) and amount (50¢ and 10¢) as outcomes. The outcome-related negativity (ORN/N2) and outcome-related positivity (ORP/P3) were analyzed and compared across conditions and gender. Monetary gain (compared to loss) and higher amount (50¢ compared to 10¢) produced higher amplitudes and shorter latencies in both ORN and ORP components. Difference wave plots showed that earlier processing (200–400 ms) is dominated by the valence (loss/gain) while later processing (after 400 ms) is marked by the amount (50¢/10¢). Functional mapping using Low Resolution Electromagnetic Tomography (LORETA) indicated that the ORN separated the loss against gain in both genders, while the ORP activity distinguished the 50¢ against 10¢ in males. This study further strengthens the view that separate brain processes/circuitry may mediate loss and gain. Although there were no gender differences in behavioral and impulsivity scores, ORN and ORP measures for different task conditions had significant correlations with behavioral scores. This gambling paradigm may potentially offer valuable indicators to study outcome processing and impulsivity in normals as well as in clinical populations. |
| 15) |  |
C. Kamarajan, M. Rangaswamy, D. B. Chorlian, N. Manz, Y. Tang, A. K. Pandey, B. N. Roopesh, A. T. Stimus, and B. Porjesz "Theta oscillations during the processing of monetary loss and gain: A perspective on gender and impulsivity" Brain Research 1235 (2008), 45-62 Abstract: Event-related oscillations (EROs) have proved to be very useful in the understanding of a variety of neurocognitive processes including reward/outcome processing. In the present study, theta power (4.0–7.0 Hz) following outcome stimuli in the time window of the N2–P3 complex (200–500 ms) was analyzed in healthy normals (20 males and 20 females) while performing a gambling task that involved monetary loss and gain. The main aim was to analyze outcome processing in terms of event-related theta power in the context of valence, amount, gender, and impulsivity. The S-transform was used for the signal processing of the ERO data in terms of time–frequency–power. Results from filtered waveforms showed a partially consistent phase-alignment of the increased theta activity corresponding to N2 and P3 components following the outcome stimuli. Gain conditions produced more theta power than loss conditions. While there was anterior involvement in both gain and loss, posterior activation was stronger during gain conditions than during loss conditions. Females exhibited posterior maxima during gain conditions while males had an anterior maxima during both loss and gain conditions. The current source density of theta activity in females involved larger areas with a bilateral frontal activity while males predominantly had a frontal midline activity. Theta power was significantly higher in females than males across all conditions. Low theta (4.0–5.5 Hz) predominantly contributed to the posterior activity during gain conditions. High theta (5.5–7.0 Hz) was more associated with impulsivity measures than low theta activity. These findings may offer valuable clues to understand outcome processing, impulsivity, and gender differences. |
| 14) |  |
O. U. Kheowan, V. A. Davydov, N. Manz, and S. C. Müller "Compensation of curvature effects by illumination" Phys. Lett. A 367 (2007), 311-315 Abstract: Front deformation of initially planar excitation waves can be observed in nonplanar media or in spatially heterogeneously illuminated systems. The deformation of propagating reaction–diffusion waves in either of these systems has been investigated earlier separately. Here we present a combination of both heterogeneous systems, which can lead to a compensation of wave deformations. Our theoretical analysis of the evolution of propagating excitation waves, based on the framework of a kinematical theory, shows that the curvature effect can be compensated by illumination. Supporting experiments were performed with the light-sensitive Belousov–Zhabotinsky system. |
| 13) |  |
N. Manz and O. Steinbock "Propagation failures, breathing pulses, and backfiring in an excitable reaction-diffusion system" Chaos 16 (2006), 037112 Abstract: We report results from experiments with a pseudo-one-dimensional Belousov-Zhabotinsky reaction that employs 1,4-cyclohexanedione as its organic substrate. This excitable system shows traveling oxidation pulses and pulse trains that can undergo complex sequences of propagation failures. Moreover, we present examples for i) breathing pulses that undergo periodic changes in speed and size and ii) backfiring pulses that near their back repeatedly generate new pulses propagating in opposite direction. |
| 12) |  |
N. Manz, B. T. Ginn, and O. Steinbock Video of an anomalous target pattern on Oliver Steinbock's Youtube channel. |
| 11) |  |
N. Manz and O. Steinbock "Dynamics of excitation pulses with attractive interaction: Kinematic analysis and chemical wave experiments" Phys. Rev. E 70 (2004), 066213 Abstract: We present a theoretical analysis of stacking and destacking wave trains in excitable reaction-diffusion systems with anomalous velocity-wavelength dependence. For linearized dispersion relations, kinematic analysis yields an analytical function that rigorously describes front trajectories. The corresponding accelerations have exactly one extremum that slowly decays with increasing pulse number. For subsequent pulses these maxima occur with a lag time equal to the inverse slope of the linearized dispersion curve. These findings are reproduced in experiments with chemical waves in the 1,4-cyclohexanedione Belousov-Zhabotinsky reaction but should be also applicable to step bunching on crystal surfaces and certain traffic phenomena. |
| 10) |  |
N. Manz and O. Steinbock Video of the drifting spiral wave shown in the image (tracking dynamics) on Oliver Steinbock's Youtube channel. Example of an annihilating spiral wave pair (tracking dynamics) on Oliver Steinbock's Youtube channel. |
| 9) |  |
N. Manz, C. T. Hamik, and O. Steinbock "Tracking Waves and Vortex Nucleation in Excitable Systems with Anomalous Dispersion" Phys. Rev. Lett. 92 (2004), 248301 Abstract: We report experimental results obtained from a chemical reaction-diffusion system in which wave propagation is limited to a finite band of wavelengths and in which no solitary pulses exist. Wave patterns increase their size through repeated annihilation events of the frontier pulse that allow the succeeding pulses to advance farther. A related type of wave dynamics involves a stable but slow frontier pulse that annihilates subsequent waves in front-to-back collisions. These so-called merging dynamics give rise to an unexpected form of spiral wave nucleation. All of these phenomena are reproduced by a simple, three-species reaction-diffusion model that reveals the importance of the underlying anomalous dispersion relation. Video of reaction-diffusion waves in a capillary tube (quasi-onedimensional) in the tracking regime of this anomalous BZ system on Oliver Steinbock's Youtube channel. Video of 2-D target pattern in the merging regime of this anomalous BZ system. Video of 2-D target pattern in the tracking regime of this anomalous BZ system. |
| 8) |  |
N. Manz, B. T Ginn, and O. Steinbock Simulation of a meandering spiral wave. |
| 7) |  |
N. Manz and S. C. Müller Abstract: For many years the Belousov–Zhabotinsky reaction has been used to explore the large variety of dynamical behavior of excitation waves. The understanding of chemical waves can be applied to other physical and biological systems. Most theoretical and experimental work has been done in planar media, whereas for nonplanar systems there exist many theoretical but only very few experimental studies. In this article we present a methodology to develop quasi-two-dimensional, nonhomogeneously curved reaction media. These systems can be used to perform experiments on chemical reaction-diffusion processes which occur, for instance, in the Belousov–Zhabotinsky reaction placed in nonplanar geometries. |
| 6) |  |
N. Manz, V. A. Davydov, S. C. Müller, and M. Bär Abstract: The dynamic behaviour of spiral waves rotating on surfaces of curved reaction–diffusion systems depends strongly on the curvature of the surface. It was shown in an earlier experiment that a spiral in a Belousov–Zhabotinsky system on a paraboloid drifts to the point of highest Gaussian curvature, as predicted numerically and analytically. Beyond this, theoretical work predicts an increase of the rotation frequency of spiral waves with an increase in the curvature of the system surface (e.g., spirals on different spherical surfaces with decreasing radii). This behaviour leads to an additional term in the function for the rotation frequency proportional to the Gaussian curvature of the system. In this Letter we combine both effects to determine the curvature dependence of the spiral rotation frequency in curved reaction–diffusion systems. On a non-homogeneously curved surface, the spiral tip (the inner end of a spiral) drifts through regions with increasing surface curvature. Measurements of the rotation frequency performed during this propagation verify the predicted effect. The experimental data are confirmed by analytical results in the framework of the kinematic theory. |
| 5) |  |
N. Manz, V. A. Davydov, V. S. Zykov, and S. C. Müller Abstract: The evolution of excitation wave fronts in a spatially modulated light-sensitive Belousov-Zhabotinsky system is investigated experimentally and theoretically. The excitation wave propagates in a thin, quasi-twodimensional reaction layer, which is illuminated through a periodical gray level mask. The light-induced differences in excitability and velocity give rise to a temporal and spatial modulation of the initially flat fronts. The experimental front evolution is described in the framework of a kinematical theory as developed earlier for nonuniformly curved systems. |
| 4) |  |
V. A. Davydov, N. Manz, O. Steinbock, and S. C. Müller Abstract: In the literature, different properties of propagating excitation waves on curved surfaces are published. Theoretical papers predicted critical properties of waves on curved surfaces. If an excitation wave propagates in a non-planar system, its geodetic curvature causes a transition from excitable to non-excitable dynamics. In this paper we present first experimental results of the transition in a weakly excitable BZ system which are in good agreement with the theoretical predictions. |
| 3) |  |
C. T. Hamik, N. Manz, and O. Steinbock Abstract: We report the formation of stable bound wave packets in a modified Belousov-Zhabotinsky reaction. These densely stacked structures arise from an attractive interaction between oxidation pulses that is not known from the classical Belousov-Zhabotinsky system. The characteristic stacking period increases with the initial concentration of bromate but decreases with cyclohexanedione. Wave stacking can also induce cascades of bunching events in which internally dense but mutually well segregated wave clusters are formed. For different initial concentrations, we observed the apparent merging of waves in front-to-back collisions. All three modes of wave dynamics are analyzed in terms of their dispersion behavior. The dispersion relations proved to be anomalous in each case and revealed the existence of an attractor which induces the formation of stable wave packets. The underlying mechanism has a pure reaction-diffusion character since wave propagation is not affected by fluid convection. At high initial concentrations of ferroin, we detected complex relaxation kinetics which indicate the presence of at least two independent species that control the recovery and hence the dispersion behavior of the medium. |
| 2) |  |
V. A. Davydov, N. Manz, O. Steinbock, V. S. Zykov, and S. C. Müller Abstract: The evolution of an excitation front propagating on a nonuniformly curved surface is considered within the framework of a kinematical model of its motion. For the case of a surface with a periodically modulated curvature an exact solution of the front shape is obtained under the assumption of sufficiently small surface deformation. The results of the theoretical consideration are compared with the experimental data obtained with a modified Belousov-Zhabotinsky reaction in a thin nonuniformly curved layer. |
| 1) |  |
N. Manz, S. C. Müller, and O. Steinbock Video of reaction-diffusion waves in a capillary tube (quasi-onedimensional) in the stacking regime of this anomalous BZ system. Video of reaction-diffusion waves in a capillary tube (quasi-onedimensional) in the merging regime of this anomalous BZ system. |
