On the rise and fall of networked societies

We review recent results on the dynamics of social networks which suggest that the interplay between the network formation process and volatility may lead to the occurrence of discontinuous phase transitions and phase coexistence in a large class of models. We then investigate the effects of negative links -- links inhibiting local growth of the network -- and of a geographical distribution of the agents in such models. We show, by extensive numerical simulations, that both effects enhance this phenomenology, i.e. it increases the size of the coexistence region.Comment: 6 pages, 4 figures, Proceedings of Granada Workshop 200

Phenomenological Models of Socio-Economic Network Dynamics

We study a general set of models of social network evolution and dynamics. The models consist of both a dynamics on the network and evolution of the network. Links are formed preferentially between 'similar' nodes, where the similarity is defined by the particular process taking place on the network. The interplay between the two processes produces phase transitions and hysteresis, as seen using numerical simulations for three specific processes. We obtain analytic results using mean field approximations, and for a particular case we derive an exact solution for the network. In common with real-world social networks, we find coexistence of high and low connectivity phases and history dependence.Comment: 11 pages, 8 figure

Series Expansion Calculation of Persistence Exponents

We consider an arbitrary Gaussian Stationary Process X(T) with known correlator C(T), sampled at discrete times T_n = n \Delta T. The probability that (n+1) consecutive values of X have the same sign decays as P_n \sim \exp(-\theta_D T_n). We calculate the discrete persistence exponent \theta_D as a series expansion in the correlator C(\Delta T) up to 14th order, and extrapolate to \Delta T = 0 using constrained Pad\'e approximants to obtain the continuum persistence exponent \theta. For the diffusion equation our results are in exceptionally good agreement with recent numerical estimates.Comment: 5 pages; 5 page appendix containing series coefficient

Persistence of a Continuous Stochastic Process with Discrete-Time Sampling: Non-Markov Processes

We consider the problem of `discrete-time persistence', which deals with the zero-crossings of a continuous stochastic process, X(T), measured at discrete times, T = n(\Delta T). For a Gaussian Stationary Process the persistence (no crossing) probability decays as exp(-\theta_D T) = [\rho(a)]^n for large n, where a = \exp[-(\Delta T)/2], and the discrete persistence exponent, \theta_D, is given by \theta_D = \ln(\rho)/2\ln(a). Using the `Independent Interval Approximation', we show how \theta_D varies with (\Delta T) for small (\Delta T) and conclude that experimental measurements of persistence for smooth processes, such as diffusion, are less sensitive to the effects of discrete sampling than measurements of a randomly accelerated particle or random walker. We extend the matrix method developed by us previously [Phys. Rev. E 64, 015151(R) (2001)] to determine \rho(a) for a two-dimensional random walk and the one-dimensional random acceleration problem. We also consider `alternating persistence', which corresponds to a < 0, and calculate \rho(a) for this case.Comment: 14 pages plus 8 figure

Malaria epidemiology in the Ahafo area of Ghana

<p>Abstract</p> <p>Background</p> <p><it>Plasmodium falciparum </it>malaria remains endemic in sub-Saharan Africa including Ghana. The epidemiology of malaria in special areas, such as mining areas needs to be monitored and controlled. Newmont Ghana Gold Limited is conducting mining activities in the Brong Ahafo Region of Ghana that may have an impact on the diseases such as malaria in the mining area.</p> <p>Methods</p> <p>Prior to the start of mining activities, a cross-sectional survey was conducted in 2006/2007 to determine malaria epidemiology, including malaria parasitaemia and anaemia among children < 5 years and monthly malaria transmission in a mining area of Ghana.</p> <p>Results</p> <p>A total of 1,671 households with a child less than five years were selected. About 50% of the household heads were males. The prevalence of any malaria parasitaemia was 22.8% (95% CI 20.8 - 24.9). <it>Plasmodium falciparum </it>represented 98.1% (95% CI 96.2 - 99.2) of parasitaemia. The geometric mean <it>P. falciparum </it>asexual parasite count was 1,602 (95% CI 1,140 - 2,252) and 1,195 (95% CI 985 - 1,449) among children < 24 months and ≥ 24 months respectively. Health insurance membership (OR 0.60, 95% CI 0.45 - 0.80, p = 0.001) and the least poor (OR 0.57, 95% CI 0.37 - 0.90, p = 0.001) were protected against malaria parasitaemia. The prevalence of anaemia was high among children < 24 months compared to children ≥ 24 months (44.1% (95% CI 40.0 - 48.3) and 23.8% (95% CI 21.2 - 26.5) respectively. About 69% (95% CI 66.3 - 70.9) of households own at least one ITN. The highest EIRs were record in May 2007 (669 <it>ib/p/m</it>) and June 2007 (826 <it>ib/p/m</it>). The EIR of <it>Anopheles gambiae </it>were generally higher than <it>Anopheles funestus</it>.</p> <p>Conclusion</p> <p>The baseline malaria epidemiology suggests a high malaria transmission in the mining area prior to the start of mining activities. Efforts at controlling malaria in this mining area have been intensified but could be enhanced with increased resources and partnerships between the government and the private sector.</p

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Dynamic networks and behavior: separating selection from influence.

A current problem in the analysis of behavioral dynamics, given a simultaneously evolving social network, is the difficulty of separating effects of partner selection from effects of social influence. In this paper we present a recently developed family of statistical models that enables researchers to separate the two effects in a statistically adequate manner. To illustrate our method we make use of a three-wave panel measured in the years 1995-1997 at a school in the West of Scotland. We are able to assess the strength of selection and influence mechanisms associated with friendship networks of substance-using adolescents

Epigenetics and developmental programming of welfare and production traits in farm animals

The concept that postnatal health and development can be influenced by events that occur in utero originated from epidemiological studies in humans supported by numerous mechanistic (including epigenetic) studies in a variety of model species. Referred to as the ‘developmental origins of health and disease’ or ‘DOHaD’ hypothesis, the primary focus of large-animal studies until quite recently had been biomedical. Attention has since turned towards traits of commercial importance in farm animals. Herein we review the evidence that prenatal risk factors, including suboptimal parental nutrition, gestational stress, exposure to environmental chemicals and advanced breeding technologies, can determine traits such as postnatal growth, feed efficiency, milk yield, carcass composition, animal welfare and reproductive potential. We consider the role of epigenetic and cytoplasmic mechanisms of inheritance, and discuss implications for livestock production and future research endeavours. We conclude that although the concept is proven for several traits, issues relating to effect size, and hence commercial importance, remain. Studies have also invariably been conducted under controlled experimental conditions, frequently assessing single risk factors, thereby limiting their translational value for livestock production. We propose concerted international research efforts that consider multiple, concurrent stressors to better represent effects of contemporary animal production systems