Stochastic Feedback and the Regulation of Biological Rhythms

We propose a general approach to the question of how biological rhythms spontaneously self-regulate, based on the concept of ``stochastic feedback''. We illustrate this approach by considering the neuroautonomic regulation of the heart rate. The model generates complex dynamics and successfully accounts for key characteristics of cardiac variability, including the $1/f$ power spectrum, the functional form and scaling of the distribution of variations, and correlations in the Fourier phases. Our results suggest that in healthy systems the control mechanisms operate to drive the system away from extreme values while not allowing it to settle down to a constant output.Comment: 15 pages, latex2e using rotate and epsf, with 4 ps figures. Submitted to PR

Multiple shades of grey: Opening the black box of public sector executives' hybrid role identities

Public sector reforms of recent decades in Europe have promoted managerialism and aimed at introducing private sector thinking and practices. However, with regard to public sector executives' self-understanding, managerial role identities have not replaced bureaucratic ones; rather, components from both paradigms have combined. In this article, we introduce a bi-dimensional approach (attitudes and practices) that allows for different combinations and forms of hybridity. Empirically, we explore the role identities of public sector executives across Europe, building on survey data from over 7,000 top public officials in 19 countries (COCOPS survey). We identify country-level profiles, as well as patterns across countries, and find that administrative traditions can account for these profiles and patterns only to a limited extent. Rather, they have to be complemented by factors such as stability of the institutional environment (indicating lower shares of hybrid combinations) or extent of reform pressures (indicating higher shares of hybrid combinations)

Belief formation in a signaling game without common prior: an experiment

Using belief elicitation, the paper investigates the process of belief formation and evolution in a signaling game in which a common prior is not induced. Both prior and posterior beliefs of Receivers about Senders' types are elicited, as well as beliefs of Senders about Receivers' strategies. In the experiment, subjects often start with diffuse uniform beliefs and update them in view of observations. However, the speed of updating is influenced by the strength of initial beliefs. An interesting result is that beliefs about the prior distribution of types are updated slower than posterior beliefs, which incorporate Senders' strategies. In the medium run, for some specifications of game parameters, this leads to outcomes being significantly different from the outcomes of the game in which a common prior is induced. It is also shown that elicitation of beliefs does not considerably change the pattern of play in this game

Three-Dimensional Stochastic Estimation of Porosity Distribution: Benefits of Using Ground-Penetrating Radar Velocity Tomograms in Simulated-Annealing-Based or Bayesian Sequential Simulation Approaches

Estimation of the three-dimensional (3-D) distribution of hydrologic properties and related uncertainty is a key for improved predictions of hydrologic processes in the subsurface. However it is difficult to gain high-quality and high-density hydrologic information from the subsurface. In this regard a promising strategy is to use high-resolution geophysical data (that are relatively sensitive to variations of a hydrologic parameter of interest) to supplement direct hydrologic information from measurements in wells (e.g., logs, vertical profiles) and then generate stochastic simulations of the distribution of the hydrologic property conditioned on the hydrologic and geophysical data. In this study we develop and apply this strategy for a 3-D field experiment in the heterogeneous aquifer at the Boise Hydrogeophysical Research Site and we evaluate how much benefit the geophysical data provide. We run high-resolution 3-D conditional simulations of porosity with both simulated-annealing-based and Bayesian sequential approaches using information from multiple intersecting crosshole gound-penetrating radar (GPR) velocity tomograms and neutron porosity logs. The benefit of using GPR data is assessed by investigating their ability, when included in conditional simulation, to predict porosity log data withheld from the simulation. Results show that the use of crosshole GPR data can significantly improve the estimation of porosity spatial distribution and reduce associated uncertainty compared to using only well log measurements for the estimation. The amount of benefit depends primarily on the strength of the petrophysical relation between the GPR and porosity data, the variability of this relation throughout the investigated site, and lateral structural continuity at the site

Symbiotic Legume Nodules Employ Both Rhizobial Exo- and Endo-Hydrogenases to Recycle Hydrogen Produced by Nitrogen Fixation

BACKGROUND: In symbiotic legume nodules, endosymbiotic rhizobia (bacteroids) fix atmospheric N(2), an ATP-dependent catalytic process yielding stoichiometric ammonium and hydrogen gas (H(2)). While in most legume nodules this H(2) is quantitatively evolved, which loss drains metabolic energy, certain bacteroid strains employ uptake hydrogenase activity and thus evolve little or no H(2). Rather, endogenous H(2) is efficiently respired at the expense of O(2), driving oxidative phosphorylation, recouping ATP used for H(2) production, and increasing the efficiency of symbiotic nodule N(2) fixation. In many ensuing investigations since its discovery as a physiological process, bacteroid uptake hydrogenase activity has been presumed a single entity. METHODOLOGY/PRINCIPAL FINDINGS: Azorhizobium caulinodans, the nodule endosymbiont of Sesbania rostrata stems and roots, possesses both orthodox respiratory (exo-)hydrogenase and novel (endo-)hydrogenase activities. These two respiratory hydrogenases are structurally quite distinct and encoded by disparate, unlinked gene-sets. As shown here, in S. rostrata symbiotic nodules, haploid A. caulinodans bacteroids carrying single knockout alleles in either exo- or-endo-hydrogenase structural genes, like the wild-type parent, evolve no detectable H(2) and thus are fully competent for endogenous H(2) recycling. Whereas, nodules formed with A. caulinodans exo-, endo-hydrogenase double-mutants evolve endogenous H(2) quantitatively and thus suffer complete loss of H(2) recycling capability. More generally, from bioinformatic analyses, diazotrophic microaerophiles, including rhizobia, which respire H(2) may carry both exo- and endo-hydrogenase gene-sets. CONCLUSIONS/SIGNIFICANCE: In symbiotic S. rostrata nodules, A. caulinodans bacteroids can use either respiratory hydrogenase to recycle endogenous H(2) produced by N(2) fixation. Thus, H(2) recycling by symbiotic legume nodules may involve multiple respiratory hydrogenases

An Updated Meta-Analysis of Endothelial Nitric Oxide Synthase Gene: Three Well-Characterized Polymorphisms with Hypertension

BACKGROUND: Numerous individually underpowered association studies have been conducted on endothelial nitric oxide synthase (eNOS) genetic variants across different ethnic populations, however, the results are often irreproducible. We therefore aimed to meta-analyze three eNOS widely-evaluated polymorphisms, G894T (rs1799983) in exon 7, 4b/a in intron 4, and T-786C (rs2070744) in promoter region, in association with hypertension from both English and Chinese publications, while addressing between-study heterogeneity and publication bias. METHODS: Data were analyzed using Stata software (version 11.0), and random-effects model was applied irrespective of between-study heterogeneity, which was evaluated by subgroup and meta-regression analyses. Publication bias was weighed using the Egger's test and funnel plot. RESULTS: There were total 19284/26003 cases/controls for G894T, and 6890/6858 for 4b/a, and 5346/6392 for T-786C polymorphism. Overall comparison of allele 894T with 894G in all study populations yielded a 16% increased risk for hypertension (odds ratio [OR] = 1.16; 95% confidence interval [95% CI]: 1.07-1.27; P = 0.001), and particularly a 32% increased risk (95% CI: 1.16-1.52; P<0.0005) in Asians and a 40% increased risk (95% CI: 1.19-1.65; P<0.0005) in Chinese. Further subgroup analyses suggested that published languages accounted for the heterogeneity for G894T polymorphism. The overall OR of allele 4a versus 4b was 1.29 (95% CI: 1.13-1.46; P<0.0005) in all study populations, and this estimate was potentiated in Asians (OR = 1.42; 95% CI: 1.16-1.72; P<0.0005). For T-786C, ethnicity-stratified analyses suggested a significantly increased risk for -786C allele (OR = 1.25; 95% CI: 1.06-1.47; P = 0.007) and -786CC genotype (OR = 1.69; 95% CI: 1.20-2.38; P = 0.003) in Whites. As an aside, the aforementioned risk estimates reached significance after Bonferroni correction. Finally, meta-regression analysis on other study-level covariates failed to provide any significance for all polymorphisms. CONCLUSION: We, via a comprehensive meta-analysis, ascertained the role of eNOS G894T and 4b/a polymorphisms on hypertension in Asians, and T-786C polymorphism in Whites

Celtic pilgrimage, past and present: from historical geography to contemporary embodied practices

Perigrinatio, the Latin term for pilgrimage was at the heart of the medieval Celtic church, but was this was understood and practised not only as a journey to a shrine, but more broadly as a spiritual journey, which could lead to an isolated hermitage or peripatetic evangelistic mission. In this paper, we outline the beliefs and practices of the broad assemblage known as the Celtic church, particularly the interleaving of pilgrimage, asceticism and landscape poetics, and how these have informed continued and renewed pilgrimage practices to sites of the early Celtic church by particular denominations, ecumenical groups and those interested in broader spiritualities. These sacred mobilities are explored through vignettes of embodied-emotionalspiritual practices situated in the landscapes and faith communities of Lough Derg,Ireland and the Isle of Man. They share geographical marginality, a focus on multiple Celtic saints and an enduring belief in the immanence of God, expressed through embodied spiritual practice in the landscape. However, they differ widely in matters of institutionalised structure, regulation, discursive scripting and gendered hierarchy, reflecting situated and denominational preferences for the ascetic and aesthetic spiritual legacies of the medieval Celtic church

Kinematics of the Southern Rhodope Core Complex (North Greece)

The Southern Rhodope Core Complex is a wide metamorphic dome exhumed in the northern Aegean as a result of large-scale extension from mid-Eocene to mid-Miocene times. Its roughly triangular shape is bordered on the SW by the Jurassic and Cretaceous metamorphic units of the Serbo-Macedonian in the Chalkidiki peninsula and on the N by the eclogite bearing gneisses of the Sideroneron massif. The main foliation of metamorphic rocks is flat lying up to 100 km core complex width. Most rocks display a stretching lineation trending NEâ SW. The Kerdylion detachment zone located at the SW controlled the exhumation of the core complex from middle Eocene to mid-Oligocene. From late Oligocene to mid-Miocene exhumation is located inside the dome and is accompanied by the emplacement of the synkinematic plutons of Vrondou and Symvolon. Since late Miocene times, extensional basin sediments are deposited on top of the exhumed metamorphic and plutonic rocks and controlled by steep normal faults and flat-ramp-type structures. Evidence from Thassos Island is used to illustrate the sequence of deformation from stacking by thrusting of the metamorphic pile to ductile extension and finally to development of extensional Plio-Pleistocene sedimentary basin. Paleomagnetic data indicate that the core complex exhumation is controlled by a 30� dextral rotation of the Chalkidiki block. Extensional displacements are restored using a pole of rotation deduced from the curvature of stretching lineation trends at core complex scale. It is argued that the Rhodope Core Complex has recorded at least 120 km of extension in the North Aegean, since the last 40 My