Estimating the distribution of dynamic invariants: illustrated with an application to human photo-plethysmographic time series

Dynamic invariants are often estimated from experimental time series with the aim of differentiating between different physical states in the underlying system. The most popular schemes for estimating dynamic invariants are capable of estimating confidence intervals, however, such confidence intervals do not reflect variability in the underlying dynamics. We propose a surrogate based method to estimate the expected distribution of values under the null hypothesis that the underlying deterministic dynamics are stationary. We demonstrate the application of this method by considering four recordings of human pulse waveforms in differing physiological states and show that correlation dimension and entropy are insufficient to differentiate between these states. In contrast, algorithmic complexity can clearly differentiate between all four rhythms

Modulation of Thermoelectric Power of Individual Carbon Nanotubes

Thermoelectric power (TEP) of individual single walled carbon nanotubes (SWNTs) has been measured at mesoscopic scales using a microfabricated heater and thermometers. Gate electric field dependent TEP-modulation has been observed. The measured TEP of SWNTs is well correlated to the electrical conductance across the SWNT according to the Mott formula. At low temperatures, strong modulations of TEP were observed in the single electron conduction limit. In addition, semiconducting SWNTs exhibit large values of TEP due to the Schottky barriers at SWNT-metal junctions.Comment: to be published in Phys. Rev. Let

Dynamical modeling of collective behavior from pigeon flight data: flock cohesion and dispersion

Several models of flocking have been promoted based on simulations with qualitatively naturalistic behavior. In this paper we provide the first direct application of computational modeling methods to infer flocking behavior from experimental field data. We show that this approach is able to infer general rules for interaction, or lack of interaction, among members of a flock or, more generally, any community. Using experimental field measurements of homing pigeons in flight we demonstrate the existence of a basic distance dependent attraction/repulsion relationship and show that this rule is sufficient to explain collective behavior observed in nature. Positional data of individuals over time are used as input data to a computational algorithm capable of building complex nonlinear functions that can represent the system behavior. Topological nearest neighbor interactions are considered to characterize the components within this model. The efficacy of this method is demonstrated with simulated noisy data generated from the classical (two dimensional) Vicsek model. When applied to experimental data from homing pigeon flights we show that the more complex three dimensional models are capable of predicting and simulating trajectories, as well as exhibiting realistic collective dynamics. The simulations of the reconstructed models are used to extract properties of the collective behavior in pigeons, and how it is affected by changing the initial conditions of the system. Our results demonstrate that this approach may be applied to construct models capable of simulating trajectories and collective dynamics using experimental field measurements of herd movement. From these models, the behavior of the individual agents (animals) may be inferred

Gravitational Waves Probe the Coalescence Rate of Massive Black Hole Binaries

We calculate the expected nHz--$\mu$Hz gravitational wave (GW) spectrum from coalescing Massive Black Hole (MBH) binaries resulting from mergers of their host galaxies. We consider detection of this spectrum by precision pulsar timing and a future Pulsar Timing Array. The spectrum depends on the merger rate of massive galaxies, the demographics of MBHs at low and high redshift, and the dynamics of MBH binaries. We apply recent theoretical and observational work on all of these fronts. The spectrum has a characteristic strain $h_c(f)~10^{-15} (f/yr^{-1})^{-2/3}$, just below the detection limit from recent analysis of precision pulsar timing measurements. However, the amplitude of the spectrum is still very uncertain owing to approximations in the theoretical formulation of the model, to our lack of knowledge of the merger rate and MBH population at high redshift, and to the dynamical problem of removing enough angular momentum from the MBH binary to reach a GW-dominated regime.Comment: 31 Pages, 8 Figures, small changes to match the published versio

Transgenic analysis of the atrialnatriuretic factor (ANF) promoter: Nkx2-5 and GATA-4 binding sites are required for atrial specific expression of ANF

AbstractThe atrial natriuretic factor (ANF) gene is initially expressed throughout the myocardial layer of the heart, but during subsequent development, expression becomes limited to the atrial chambers. Mouse knockout and mammalian cell culture studies have shown that the ANF gene is regulated by combinatorial interactions between Nkx2-5, GATA-4, Tbx5, and SRF; however, the molecular mechanisms leading to chamber-specific expression are currently unknown. We have isolated the Xenopus ANF promoter in order to examine the temporal and spatial regulation of the ANF gene in vivo using transgenic embryos. The mammalian and Xenopus ANF promoters show remarkable sequence similarity, including an Nkx2-5 binding site (NKE), two GATA sites, a T-box binding site (TBE), and two SRF binding sites (SREs). Our transgenic studies show that mutation of either SRE, the TBE or the distal GATA element, strongly reduces expression from the ANF promoter. However, mutations of the NKE, the proximal GATA, or both elements together, result in relatively minor reductions in transgene expression within the myocardium. Surprisingly, mutation of these elements results in ectopic ANF promoter activity in the kidneys, facial muscles, and aortic arch artery-associated muscles, and causes persistent expression in the ventricle and outflow tract of the heart. We propose that the NKE and proximal GATA elements serve as crucial binding sites for assembly of a repressor complex that is required for atrial-specific expression of the ANF gene

Free Speech in the College Community

Robert O\u27Neil has written the book he was destined to write: Free Speech in the College Community. The former President of the University of Virginia and the University of Wisconsin, O\u27Neil is a distinguished lawyer and First Amendment scholar who has long been active in disputes involving student speech and academic freedom. He has parlayed those credentials into a book that is both creative and accessible. For both lawyers and non lawyers interested in campus speech issues, there is no better text available

QSO's from Galaxy Collisions with Naked Black Holes

In the now well established conventional view (see Rees [1] and references therein), quasi-stellar objects (QSOs) and related active galactic nuclei (AGN) phenomena are explained as the result of accretion of plasma onto giant black holes which are postulated to form via gravitational collapse of the high density regions in the centers of massive host galaxies. This model is supported by a wide variety of indirect evidence and seems quite likely to apply at least to some observed AGN phenomena. However, one surprising set of new Hubble Space Telescope (HST) observations [2-4] directly challenges the conventional model, and the well known evolution of the QSO population raises some additional, though not widely recognized, difficulties. We propose here an alternative possibility: the Universe contains a substantial independent population of super-massive black holes, and QSO's are a phenomenon that occurs due to their collisions with galaxies or gas clouds in the intergalactic medium (IGM). This hypothesis would naturally explain why the QSO population declines very rapidly towards low redshift, as well as the new HST data.Comment: plain TeX file, no figures, submitted to Natur

Spatial accessibility and social inclusion: The impact of Portugal's last health reform

Health policies seek to promote access to health care and should provide appropriate geographical accessibility to each demographical functional group. The dispersal demand of health‐careservices and the provision for such services atfixed locations contribute to the growth of inequality intheir access. Therefore, the optimal distribution of health facilities over the space/area can lead toaccessibility improvements and to the mitigation of the social exclusion of the groups considered mostvulnerable. Requiring for such, the use of planning practices joined with accessibility measures. However,the capacities of Geographic Information Systems in determining and evaluating spatial accessibility inhealth system planning have not yet been fully exploited. This paper focuses on health‐care services planningbased on accessibility measures grounded on the network analysis. The case study hinges on mainlandPortugal. Different scenarios were developed to measure and compare impact on the population'saccessibility. It distinguishes itself from other studies of accessibility measures by integrating network data ina spatial accessibility measure: the enhanced two‐stepfloating catchment area. The convenient location forhealth‐care facilities can increase the accessibility standards of the population and consequently reducethe economic and social costs incurred. Recently, the Portuguese government implemented a reform thataimed to improve, namely, the access and equity in meeting with the most urgent patients. It envisaged,in terms of equity, the allocation of 89 emergency network points that ensured more than 90% of thepopulation be within 30 min from any one point in the network. Consequently, several emergency serviceswere closed, namely, in rural areas. This reform highlighted the need to improve the quality of the emergencycare, accessibility to each care facility, and equity in their access. Hence, accessibility measures becomean efficient decision‐making tool, despite its absence in effective practice planning. According to anapplication of this type of measure, it was possible to verify which levels of accessibility were decreased,including the most disadvantaged people, with a larger time of dislocation of 12 min between 2001 and 2011