Impact of time varying interaction: Formation and annihilation of extreme events in dynamical systems.

This study investigates the emergence of extreme events in two different coupled systems: the FitzHugh-Nagumo neuron model and the forced Liénard system, both based on time-varying interactions. The time-varying coupling function between the systems determines the duration and frequency of their interaction. Extreme events in the coupled system arise as a result of the influence of time-varying interactions within various parameter regions. We specifically focus on elucidating how the transition point between extreme events and regular events shifts in response to the duration of interaction time between the systems. By selecting the appropriate interaction time, we can effectively mitigate extreme events, which is highly advantageous for controlling undesired fluctuations in engineering applications. Furthermore, we extend our investigation to networks of oscillators, where the interactions among network elements are also time dependent. The proposed approach for coupled systems holds wide applicability to oscillator networks.

Different routes to large-intensity pulses in Zeeman laser model.

In this study, we report a rich variety of large-intensity pulses exhibited by a Zeeman laser model. The instabilities in the system occur via three different dynamical processes, such as quasiperiodic intermittency, Pomeau-Manneville intermittency, and the breakdown of quasiperiodic motion to chaos followed by an interior crisis. This Zeeman laser model is more capable of exploring the major possible types of instabilities when changing a specific system's parameter in a particular range. We exemplified distinct dynamical transitions of the Zeeman laser model. The statistical measures reveal the appearance of the low probability of large-intensity pulses above the qualifier threshold value. Moreover, they seem to follow an exponential decay that shows a Poisson-like distribution. The impact of noise and time delay effects have been analyzed near the transition point of the system.

Transition to hyperchaos and rare large-intensity pulses in Zeeman laser.

A discontinuous transition to hyperchaos is observed at discrete critical parameters in the Zeeman laser model for three well known nonlinear sources of instabilities, namely, quasiperiodic breakdown to chaos followed by interior crisis, quasiperiodic intermittency, and Pomeau-Manneville intermittency. Hyperchaos appears with a sudden expansion of the attractor of the system at a critical parameter for each case and it coincides with triggering of occasional and recurrent large-intensity pulses. The transition to hyperchaos from a periodic orbit via Pomeau-Manneville intermittency shows hysteresis at the critical point, while no hysteresis is recorded during the other two processes. The recurrent large-intensity pulses show characteristic features of extremes with their height larger than a threshold and the probability of a rare occurrence. The phenomenon is robust to weak noise although the critical parameter of transition to hyperchaos shifts with noise strength. This phenomenon appears as common in many low dimensional systems as reported earlier by Chowdhury et al. [Phys. Rep. 966, 1-52 (2022)], there the emergent large-intensity events or extreme events dynamics have been recognized simply as chaotic in nature although the temporal dynamics shows occasional large deviations from the original chaotic state in many examples. We need a new metric, in the future, that would be able to classify such significantly different dynamics and distinguish from chaos.

Transition to hyperchaos: Sudden expansion of attractor and intermittent large-amplitude events in dynamical systems.

Hyperchaos is distinguished from chaos by the presence of at least two positive Lyapunov exponents instead of just one in dynamical systems. A general scenario is presented here that shows emergence of hyperchaos with a sudden large expansion of the attractor of continuous dynamical systems at a critical parameter when the temporal dynamics shows intermittent large-amplitude spiking or bursting events. The distribution of local maxima of the temporal dynamics is non-Gaussian with a tail, confirming a rare occurrence of the large-amplitude events. We exemplify our results on the sudden emergence of hyperchaos in three paradigmatic models, namely, a coupled Hindmarsh-Rose model, three coupled Duffing oscillators, and a hyperchaotic model.

Instabilities in quasiperiodic motion lead to intermittent large-intensity events in Zeeman laser.

We report intermittent large-intensity pulses that originate in Zeeman laser due to instabilities in quasiperiodic motion, one route follows torus-doubling to chaos and another goes via quasiperiodic intermittency in response to variation in system parameters. The quasiperiodic breakdown route to chaos via torus-doubling is well known; however, the laser model shows intermittent large-intensity pulses for parameter variation beyond the chaotic regime. During quasiperiodic intermittency, the temporal evolution of the laser shows intermittent chaotic bursting episodes intermediate to the quasiperiodic motion instead of periodic motion as usually seen during the Pomeau-Manneville intermittency. The intermittent bursting appears as occasional large-intensity events. In particular, this quasiperiodic intermittency has not been given much attention so far from the dynamical system perspective, in general. In both cases, the infrequent and recurrent large events show non-Gaussian probability distribution of event height extended beyond a significant threshold with a decaying probability confirming rare occurrence of large-intensity pulses.

Chaos in fractional system with extreme events.

Understanding extreme events attracts scientists due to substantial impacts. In this work, we study the emergence of extreme events in a fractional system derived from a Liénard-type oscillator. The effect of fractional-order derivative on the extreme events has been investigated for both commensurate and incommensurate fractional orders. Especially, such a system displays multistability and coexistence of multiple extreme events.

Routes to extreme events in dynamical systems: Dynamical and statistical characteristics.

Intermittent large amplitude events are seen in the temporal evolution of a state variable of many dynamical systems. Such intermittent large events suddenly start appearing in dynamical systems at a critical value of a system parameter and continues for a range of parameter values. Three important processes of instabilities, namely, interior crisis, Pomeau-Manneville intermittency, and the breakdown of quasiperiodic motion, are most common as observed in many systems that lead to such occasional and rare transitions to large amplitude spiking events. We characterize these occasional large events as extreme events if they are larger than a statistically defined significant height. We present two exemplary systems, a single system and a coupled system, to illustrate how the instabilities work to originate extreme events and they manifest as non-trivial dynamical events. We illustrate the dynamical and statistical properties of such events.

Linking genotype to phenotype in a changing ocean: inferring the genomic architecture of a blue mussel stress response with genome-wide association.

A key component to understanding the evolutionary response to a changing climate is linking underlying genetic variation to phenotypic variation in stress response. Here, we use a genome-wide association approach (GWAS) to understand the genetic architecture of calcification rates under simulated climate stress. We take advantage of the genomic gradient across the blue mussel hybrid zone (Mytilus edulis and Mytilus trossulus) in the Gulf of Maine (GOM) to link genetic variation with variance in calcification rates in response to simulated climate change. Falling calcium carbonate saturation states are predicted to negatively impact many marine organisms that build calcium carbonate shells - like blue mussels. We sampled wild mussels and measured net calcification phenotypes after exposing mussels to a 'climate change' common garden, where we raised temperature by 3°C, decreased pH by 0.2 units and limited food supply by filtering out planktonic particles >5 µm, compared to ambient GOM conditions in the summer. This climate change exposure greatly increased phenotypic variation in net calcification rates compared to ambient conditions. We then used regression models to link the phenotypic variation with over 170 000 single nucleotide polymorphism loci (SNPs) generated by genotype by sequencing to identify genomic locations associated with calcification phenotype, and estimate heritability and architecture of the trait. We identified at least one of potentially 2-10 genomic regions responsible for 30% of the phenotypic variation in calcification rates that are potential targets of natural selection by climate change. Our simulations suggest a power of 13.7% with our study's average effective sample size of 118 individuals and rare alleles, but a power of >90% when effective sample size is 900.

Heterogeneity and concordance in locus-specific differentiation and introgression between species of towhees.

The maintenance or breakdown of reproductive isolation is an observable outcome of secondary contact between species. In cases where hybrids beyond the F1 are formed, the representation of each species' ancestry can vary dramatically among genomic regions. This genomic heterogeneity in ancestry and introgression can offer insight into evolutionary processes, particularly if introgression is compared in multiple hybrid zones. Similarly, considerable heterogeneity exists across the genome in the extent to which populations and species have diverged, reflecting the combined effects of different evolutionary processes on genetic variation. We studied hybridization across two hybrid zones of two phenotypically well-differentiated bird species in Mexico (Pipilo maculatus and P. ocai), to investigate genomic heterogeneity in differentiation and introgression. Using genotyping-by-sequencing (GBS) and hierarchical Bayesian models, we genotyped 460 birds at over 41 000 single nucleotide polymorphism (SNP) loci. We identified loci exhibiting extreme introgression relative to the genome-wide expectation using a Bayesian genomic cline model. We also estimated locus-specific FST and identified loci with exceptionally high genetic divergence between the parental species. We found some concordance of locus-specific introgression in the two independent hybrid zones (6-20% of extreme loci shared across zones), reflecting areas of the genome that experience similar gene flow when the species interact. Additionally, heterogeneity in introgression and divergence across the genome revealed another subset of loci under the influence of locally specific factors. These results are consistent with a history in which reproductive isolation has been influenced by a common set of loci in both hybrid zones, but where local environmental and stochastic factors also lead to genomic differentiation.

Extreme events in the forced Liénard system.

We observe extremely large amplitude intermittent spikings in a dynamical variable of a periodically forced Liénard-type oscillator and characterize them as extreme events, which are rare, but recurrent and larger in amplitude than a threshold. The extreme events occur via two processes, an interior crisis and intermittency. The probability of occurrence of the events shows a long-tail distribution in both the cases. We provide evidence of the extreme events in an experiment using an electronic analog circuit of the Liénard oscillator that shows good agreement with our numerical results.

Palivizumab use in preterm neonates.

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis in infants. Palivizumab is an immunoprophylactic agent for RSV prevention in preterm infants and those with neonatal chronic lung disease. This study examines its use across neonatal units in Ireland. A questionnaire was administered to one Consultant Neonatologist or Paediatrician in each of the 20 maternity centres in Ireland about their guidelines for Palivizumab administration. There is variation in administration of Palivizumab with little consistency found between protocols reported in terms of age and presence of chronic lung disease. Ten centres have in house protocols, 3 centres use the American Academy of Paediatrics (AAP) guidelines, 2 centres prefer the UK Joint Committee on Vaccination and Immunisation (JCVI) guidelines and 3 centres do not have a set protocol. Four participants felt its use has impacted on hospital admissions and 61% believe its use is cost effective. The budgetary implication for immunoprophylaxis with Palivizumab in Ireland is estimated at 1.5 to 2 million euros annually. Given current pharmacoeconomic constraints there is a need to implement a national protocol on RSV immunoprophylaxis.

Genetic differentiation among recently diverged delphinid taxa determined using AFLP markers.

In the mid-1990s, a new common dolphin species (Delphinus capensis) was defined in the northeast Pacific using morphological characters and mitochondrial DNA (mtDNA) sequences. This species is sympatric with a second species, Delphinus delphis; morphological differences between the two are slight and it is clear they are closely related. Does the phenotypic distinction result from only a few important genes or from large differences between their nuclear genomes? We used amplified fragment length polymorphism (AFLP) markers to broadly survey the nuclear genomes of these two species to examine the levels of nuclear divergence and genetic diversity between them. Furthermore, to create an evolutionary context in which to compare the level of interspecific divergence found between the two Delphinus taxa, we also examined two distinct morphotypes of the bottlenose dolphin (Tursiops truncatus). A nonmetric multidimensional scaling analysis clearly differentiated both Delphinus species, indicating that significant nuclear genetic differentiation has arisen between the species despite their morphological similarity. However, the AFLP data indicated that the two T. truncatus morphotypes exhibit greater divergence than D. capensis and D. delphis, suggesting that they too should be considered different species.

Preliminary characterisation of an in vitro paradigm for the study of the delayed effects of organophosphorus compounds: hen embryo brain spheroids.

Organophosphate induced delayed neuropathy (OPIDN) has been studied extensively but the mechanisms of toxicity remain unclear. It is generally accepted that the inhibition and ageing (dealkylation) of the B-esterase neuropathy target esterase (NTE) is integral to axonal loss. At present, the only way of detecting compounds that induce OPIDN is the hen test, an animal model. In this study, we preliminary validated hen embryo brain spheroids (HEBS) for the study of organophosphate (OP) toxicity. Hen brain spheroids have been characterised previously, although they have never been fully optimised for OP testing. We optimised the levels of acetylcholine esterase (AChE) and neuropathy target esterase by adapting the culture technique and using chemically defined media. Spheroid cultures were maintained for 35 days and viability and enzyme levels were monitored over this time. Levels of AChE and NTE in this system remained stable over the 35 day period. Using transmission electron microscopy, we have shown synaptogenesis within HEBS earlier than previously suggested in spheroid culture. These studies indicate that HEBS may be useful for the study of OP-induced toxicity and that the long-term stability of the cultures makes it an ideal candidate for studying OPIDN.

Myocardial protection during ventricular fibrillation by reduction of proton-driven sarcolemmal sodium influx.

Although the inhibition of proton-driven sarcolemmal sodium influx ameliorates ischemic injury in the quiescent myocardium, the effects when ventricular fibrillation is present are largely unknown. We used an isolated rat heart model to investigate whether inhibition of the sodium-hydrogen exchanger isoform-1 (with the benzoylguanidine derivatives HOE-694 and cariporide) with or without concomitant inhibition of the sodium-bicarbonate co-transporter (with perfusate buffered with N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid [HEPES]) during ischemia and ventricular fibrillation could ameliorate functional myocardial abnormalities presumed to limit cardiac resuscitability. Ischemic contracture, which typically develops during ventricular fibrillation, was ameliorated by HOE-694 when either a bicarbonate-buffered (20 +/- 7 mm Hg vs 15 +/- 5 mm Hg, P <.05) or a HEPES-buffered (14 +/- 5 mm Hg vs 10 +/- 3 mm Hg, P <.04) perfusate was used. Maximal amelioration occurred when cariporide and HEPES-buffered perfusate were used simultaneously (25 +/- 14 mm Hg vs 11 +/- 3 mm Hg, P <.01), and this was accompanied by lesser leftward shifts of the end-diastolic pressure-volume curves after defibrillation. Intramyocardial sodium increases of 76% during ischemia and ventricular fibrillation (P <.05) were ameliorated by the sodium-influx-limiting interventions. Thus interventions limiting sarcolemmal sodium influx during ischemia and ventricular fibrillation may facilitate successful resuscitation from ventricular fibrillation.

Induction of rat pancreatic glutathione S-transferase and quinone reductase activities by a mixture of glucosinolate breakdown derivatives found in Brussels sprouts.

The chemoprotective effects of cruciferous vegetables against cancer has been linked to the induction of detoxification enzymes, including the phase II enzymes, glutathione S-transferases (GST) and quinone reductase (QR). Four glucosinolate breakdown products found in Brussels sprouts and previously shown individually to affect detoxification enzymes--(1-cyano-2-hydroxy-3-butene (Crambene), indole-3-carbinol (I3C), phenylethyl isothiocyanate (PEITC) and 1-isothiocyanato-3-(methylsulfinyl)-propane (IBN) were administered to male F344 rats by oesophageal intubation for 7 days both as a mixture and individually to assess the effect of these compounds on GST and QR activity in the pancreas, an organ previously shown to be affected by cruciferous diets. The doses of each compound in the mixture (50 mg Crambene/kg, 56 mg I3C/kg, 0.1 mg PEITC/kg and 38 mg IBN/kg) were chosen to represent the relative proportions of the parent glucosinolate for each compound in Brussels sprouts and shown to be below the toxic threshold for all the compounds. In rats receiving the mixture, pancreatic QR and GST activities were elevated 31- and 1.7-fold, respectively, while glutathione (GSH) was elevated threefold. On an individual basis, Crambene alone caused a 21-fold elevation of QR and 1.5-fold elevation of GST activities, while pancreatic GSH was elevated by both Crambene and PEITC 2.6- and twofold, respectively. No other significant effects of individual components were found. When the mixture was administered at 60% of the original dose, pancreatic QR and GST activities were elevated 12- and 1.4-fold, respectively, and pancreatic GSH was elevated 1.5-fold. At 20% of the original dose, pancreatic GSH was unaffected and QR and GST activities were elevated 2.7- and 1.3-fold, respectively. The results of these studies suggest that a diet rich in cruciferous vegetables may produce phase 11 enzyme induction in the pancreas, and that Crambene may be the most active component.

Surviving social assistance: 12-month prevalence of depression in sole-support parents receiving social assistance.

BACKGROUND: Although it is generally recognized that poverty and depression can coexist among single parents receiving social assistance, there is insufficient research on this topic. The goals of this study therefore were to investigate the prevalence, correlates and health care expenditures associated with depression among sole-support parents receiving social assistance. METHODS: Sole-support parents who had applied for social assistance in 2 regions of southwestern Ontario were included in the study. Depression was diagnosed with the 1994 University of Michigan Composite International Diagnostic Interview short forms. RESULTS: The 12-month prevalence rate of depressive disorder among the parents interviewed was 45.4% (345/760). A total of 247 (32.5%) had major depressive disorder alone, 19 (2.5%) had dysthymia, and 79 (10.4%) had both major depressive disorder and dysthymia ("double depression"). Those with major depressive disorder, particularly double depression, had significantly higher rates of coexisting psychiatric disorder than those without depressive disorders. Parents with depression reported higher rates of developmental delay and behaviour problems in their children than parents without depression. Expenditures for health care services were higher for parents with depression and for their children than for parents without depressive disorder and their children. INTERPRETATION: Single parents receiving social assistance have high rates of depression. Such parents with depression also have higher rates of other psychiatric disorders and higher expenditures for health care services, and their children have higher rates of developmental delay and behaviour problems.

A comparison of the individual and collective effects of four glucosinolate breakdown products from brussels sprouts on induction of detoxification enzymes.

Four glucosinolate derivatives were evaluated individually and as a mixture for their effects on hepatic P4501A (CYP1A), glutathione S-transferase (GST), quinone reductase (QR), glutathione reductase (G-Rd), and GSH levels. Doses of the derivatives were chosen to represent their relative abundance in Brussels sprouts. Adult male F344 rats received either corn oil (vehicle); one of the agents: indole-3-carbinol (I3C, 56 mg/kg), iberin (38 mg/kg), phenylethylisothiocyanate (PEITC, 0.1 mg/kg), or cyanohydroxybutene (crambene, 50 mg/kg); or all of the agents at the doses shown (as a mixture) given by gavage daily for 7 days. The mixture and I3C caused an 11- and 9.4-fold induction of CYP1A, respectively. Crambene and I3C each caused a 1.4-fold increase in GST, while the mixture caused a 2.5-fold increase. Crambene and I3C caused a 2.5- and 1.9-fold increase in QR, respectively. The mixture caused a 6.2-fold increase. Crambene, PEITC, and the mixture caused a 1.8-, 1.6-, and 2.0-fold increase in hepatic GSH levels, respectively. Crambene, I3C, iberin, and the mixture caused 1.3-, 1.4-, 1.2-, and 1.7-fold increases in G-Rd, respectively. In a second study the mixture was given at 60 and 20% of the original dose. CYP 1A, QR, G-Rd, and GST elevations were dose-dependent; GSH levels were not elevated. It is concluded that I3C and crambene are responsible for the majority of enzyme increases seen. A synergistic effect of I3C and crambene was evident on induction of GST and QR, but not on GSH, G-Rd, or P4501A.

Effect of environmental enrichment and housing density on immune system reactivity to acute exercise stress.

Positive stress has been described in the literature but not well characterized experimentally. This experiment was designed to test the hypothesis that environmental enrichment and housing density in C57BL/6 female mice modulate immune responses to acute exercise stress. A 2 x 2 x 2 factorial design was used where enrichment (enrich), nonenriched (nonenrich), group housed (group), individually housed (ind), and stress (stress) or no stress (nonstress) acted as the independent variables. Enrichment involved a 7-week exposure to in-cage running wheels and a variety of cage objects. Ninety minutes after treadmill exercise stress at 25 m/min, 4 degrees slope, for 30 min (or no exercise stress) mice were sacrificed, and splenocyte blastogenesis to the T-cell mitogen concanavalin A (Con A), splenic T-cell subset enumeration, and percent live/dead splenic cells by flow cytometry were evaluated. Results showed significant interaction effects for mitogen responses, percent Ly2+ subset, and percent live/dead splenocyte responses. Proliferation to Con A was higher in nonenrich group-housed animals than other groups. Percent live/dead cell analysis revealed a significant housing x stress interaction with fewer percent live and higher percent metabolically stressed splenocytes obtained from ind-stressed mice than other groups. These data suggest that enrichment and housing density are important factors influencing immune responses in the basal state, and in response to exercise stress.