Low-power photothermal self-oscillation of bimetallic nanowires

We investigate the nonlinear mechanics of a bimetallic, optically absorbing SiN-Nb nanowire in the presence of incident laser light and a reflecting Si mirror. Situated in a standing wave of optical intensity and subject to photothermal forces, the nanowire undergoes self-induced oscillations at low incident light thresholds of $<1\, \rm{\mu W}$ due to engineered strong temperature-position ($T$-$z$) coupling. Along with inducing self-oscillation, laser light causes large changes to the mechanical resonant frequency $\omega_0$ and equilibrium position $z_0$ that cannot be neglected. We present experimental results and a theoretical model for the motion under laser illumination. In the model, we solve the governing nonlinear differential equations by perturbative means to show that self-oscillation amplitude is set by the competing effects of direct $T$-$z$ coupling and $2\omega_0$ parametric excitation due to $T$-$\omega_0$ coupling. We then study the linearized equations of motion to show that the optimal thermal time constant $\tau$ for photothermal feedback is $\tau \to \infty$ rather than the widely reported $\omega_0 \tau = 1$. Lastly, we demonstrate photothermal quality factor ($Q$) enhancement of driven motion as a means to counteract air damping. Understanding photothermal effects on micromechanical devices, as well as nonlinear aspects of optics-based motion detection, can enable new device applications as oscillators or other electronic elements with smaller device footprints and less stringent ambient vacuum requirements.Comment: New references adde

Fluctuations and oscillations in a simple epidemic model

We show that the simplest stochastic epidemiological models with spatial correlations exhibit two types of oscillatory behaviour in the endemic phase. In a large parameter range, the oscillations are due to resonant amplification of stochastic fluctuations, a general mechanism first reported for predator-prey dynamics. In a narrow range of parameters that includes many infectious diseases which confer long lasting immunity the oscillations persist for infinite populations. This effect is apparent in simulations of the stochastic process in systems of variable size, and can be understood from the phase diagram of the deterministic pair approximation equations. The two mechanisms combined play a central role in explaining the ubiquity of oscillatory behaviour in real data and in simulation results of epidemic and other related models.Comment: acknowledgments added; a typo in the discussion that follows Eq. (3) is corrected

Pulsive feedback control for stabilizing unstable periodic orbits in a nonlinear oscillator with a non-symmetric potential

We examine a strange chaotic attractor and its unstable periodic orbits in case of one degree of freedom nonlinear oscillator with non symmetric potential. We propose an efficient method of chaos control stabilizing these orbits by a pulsive feedback technique. Discrete set of pulses enable us to transfer the system from one periodic state to another.Comment: 11 pages, 4 figure

Overwinter fasting and re-feeding in rainbow trout: plasma growth hormone and cortisol levels in relation to energy mobilization

This study investigated the roles of cortisol and growth hormone during a period of fasting in overwintering salmonid fish. Indices of carbohydrate (plasma glucose, liver glycogen), lipid (plasma free fatty acids) and protein metabolism (plasma protein, total plasma amino acids) were determined, together with plasma growth hormone (GH), cortisol and somatolactin levels (SL) at intervals in three groups of rainbow trout (continuously fed; fasted for 9 weeks then fed; fasted for 17 weeks). In fasted fish, a decline in body weight and condition factor was accompanied by reduced plasma glucose and hepatic glycogen and increased plasma FFA. No consistent elevation of plasma GH occurred until after 8 weeks of fasting when plasma GH levels increased nine-fold. No changes were observed in plasma total protein and AA until between weeks 13 and 17 when both were reduced significantly. When previously fasted fish resumed feeding, plasma glucose and FFA, and hepatic glycogen levels rapidly returned to control values and weight gain resumed. No significant changes in plasma cortisol levels, related to feeding regime, were evident at any point during the study and there was no evidence that SL played an active role in the response to fasting. The results suggest that overwinter fasting may not represent a significant nutritional stressor to rainbow trout and that energy mobilisation during fasting may be achieved without the involvement of GH, cortisol or SL

Benevolent characteristics promote cooperative behaviour among humans

Cooperation is fundamental to the evolution of human society. We regularly observe cooperative behaviour in everyday life and in controlled experiments with anonymous people, even though standard economic models predict that they should deviate from the collective interest and act so as to maximise their own individual payoff. However, there is typically heterogeneity across subjects: some may cooperate, while others may not. Since individual factors promoting cooperation could be used by institutions to indirectly prime cooperation, this heterogeneity raises the important question of who these cooperators are. We have conducted a series of experiments to study whether benevolence, defined as a unilateral act of paying a cost to increase the welfare of someone else beyond one's own, is related to cooperation in a subsequent one-shot anonymous Prisoner's dilemma. Contrary to the predictions of the widely used inequity aversion models, we find that benevolence does exist and a large majority of people behave this way. We also find benevolence to be correlated with cooperative behaviour. Finally, we show a causal link between benevolence and cooperation: priming people to think positively about benevolent behaviour makes them significantly more cooperative than priming them to think malevolently. Thus benevolent people exist and cooperate more

HALOGAS observations of NGC 5023 and UGC 2082: Modeling of non-cylindrically symmetric gas distributions in edge-on galaxies

In recent years it has become clear that the vertical structure of disk galaxies is a key ingredient for understanding galaxy evolution. In particular, the presence and structure of extra-planar gas has been a focus of research. The Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) survey aims to provide a census on the rate of cold neutral gas accretion in nearby galaxies as well as a statistically significant set of galaxies that can be investigated for their extra-planar gas properties. In order to better understand the the vertical structure of the neutral hydrogen in the two edge-on HALOGAS galaxies NGC 5023 and UGC 2082 we construct detailed tilted ring models. The addition of distortions resembling arcs or spiral arms significantly improves the fit of the models to these galaxies. In the case of UGC 2082 no vertical gradient in rotational velocity is required in either symmetric models nor non-symmetric models to match the observations. The best fitting model features two arcs of large vertical extent that may be due to accretion. In the case of NGC 5023 a vertical gradient is required in symmetric models (dV/dz =$-14.9\pm3.8$ km s$^{-1}$ kpc$^{-1}$) and its magnitude is significantly lowered when non-symmetric models are considered (dV/dz =$-9.4\pm3.8$ km s$^{-1}$ kpc$^{-1}$). Additionally it is shown that the underlying disk of NGC 5023 can be made symmetric, in all parameters except the warp, in non-symmetric models. In comparison to the "classical" modeling these models fit the data significantly better with a limited addition of free parameters.Comment: 27 Pages, 22 Figures. Accepted for publication in MNRA

Indirect reciprocity and the evolution of prejudicial groups

Prejudicial attitudes are widely seen between human groups, with significant consequences. Actions taken in light of prejudice result in discrimination, and can contribute to societal division and hostile behaviours. We define a new class of group, the prejudicial group, with membership based on a common prejudicial attitude towards the out-group. It is assumed that prejudice acts as a phenotypic tag, enabling groups to form and identify themselves on this basis. Using computational simulation, we study the evolution of prejudicial groups, where members interact through indirect reciprocity. We observe how cooperation and prejudice coevolve, with cooperation being directed in-group. We also consider the co-evolution of these variables when out-group interaction and global learning are immutable, emulating the possible pluralism of a society. Diversity through three factors is found to be influential, namely out-group interaction, out-group learning and number of sub-populations. Additionally populations with greater in-group interaction promote both cooperation and prejudice, while global rather than local learning promotes cooperation and reduces prejudice. The results also demonstrate that prejudice is not dependent on sophisticated human cognition and is easily manifested in simple agents with limited intelligence, having potential implications for future autonomous systems and human-machine interaction

Cost effectiveness of school-located influenza vaccination programs for elementary and secondary school children.

BackgroundStudies have noted variations in the cost-effectiveness of school-located influenza vaccination (SLIV), but little is known about how SLIV's cost-effectiveness may vary by targeted age group (e.g., elementary or secondary school students), or vaccine consent process (paper-based or web-based). Further, SLIV's cost-effectiveness may be impacted by its spillover effect on practice-based vaccination; prior studies have not addressed this issue.MethodsWe performed a cost-effectiveness analysis on two SLIV programs in upstate New York in 2015-2016: (a) elementary school SLIV using a stepped wedge design with schools as clusters (24 suburban and 18 urban schools) and (b) secondary school SLIV using a cluster randomized trial (16 suburban and 4 urban schools). The cost-per-additionally-vaccinated child (i.e., incremental cost-effectiveness ratio (ICER)) was estimated by dividing the incremental SLIV intervention cost by the incremental effectiveness (i.e., the additional number of vaccinated students in intervention schools compared to control schools). We performed deterministic analyses, one-way sensitivity analyses, and probabilistic analyses.ResultsThe overall effectiveness measure (proportion of children vaccinated) was 5.7 and 5.5 percentage points higher, respectively, in intervention elementary (52.8%) and secondary schools (48.2%) than grade-matched control schools. SLIV programs vaccinated a small proportion of children in intervention elementary (5.2%) and secondary schools (2.5%). In elementary and secondary schools, the ICER excluding vaccine purchase was $85.71 and$86.51 per-additionally-vaccinated-child, respectively. When additionally accounting for observed spillover impact on practice-based vaccination, the ICER decreased to $80.53 in elementary schools -- decreasing substantially in secondary schools. (to$53.40). These estimates were higher than the published practice-based vaccination cost (median = $25.50, mean =$45.48). Also, these estimates were higher than our 2009-2011 urban SLIV program mean costs ($65) due to additional costs for use of a new web-based consent system ($12.97 per-additionally-vaccinated-child) and higher project coordination costs in 2015-2016. One-way sensitivity analyses showed that ICER estimates were most sensitive to the SLIV effectiveness.ConclusionsSLIV raises vaccination rates and may increase practice-based vaccination in primary care practices. While these SLIV programs are effective, to be as cost-effective as practice-based vaccination our SLIV programs would need to vaccinate more students and/or lower the costs for consent systems and project coordination.Trial registrationClinicalTrials.gov NCT02227186 (August 25, 2014), updated NCT03137667 (May 2, 2017)

A GBT Survey of the HALOGAS Galaxies and Their Environments I: Revealing the full extent of HI around NGC891, NGC925, NGC4414 & NGC4565

We present initial results from a deep neutral hydrogen (HI) survey of the HALOGAS galaxy sample, which includes the spiral galaxies NGC891, NGC925, NGC4414, and NGC4565, performed with the Robert C. Byrd Green Bank Telescope (GBT). The resulting observations cover at least four deg$^2$ around these galaxies with an average 5$\sigma$ detection limit of 1.2$\times$10$^{18}$ cm$^{-2}$ over a velocity range of 20 km s$^{-1}$ and angular scale of 9.1$'$. In addition to detecting the same total flux as the GBT data, the spatial distribution of the GBT and original Westerbork Synthesis Radio Telescope (WSRT) data match well at equal spatial resolutions. The HI mass fraction below HI column densities of 10$^{19}$ cm$^{-2}$ is, on average, 2\%. We discuss the possible origins of low column density HI of nearby spiral galaxies. The absence of a considerable amount of newly detected HI by the GBT indicates these galaxies do not have significant extended diffuse HI structures, and suggests future surveys planned with the SKA and its precursors must go \textit{at least} as deep as 10$^{17}$ cm$^{-2}$ in column density to significantly increase the probability of detecting HI associated with the cosmic web and/or cold mode accretion.Comment: Accepted for publication in The Astrophysical Journal; 28 pages, 15 figure