Spectral Analysis and the Dynamic Response of Complex Networks

The eigenvalues and eigenvectors of the connectivity matrix of complex networks contain information about its topology and its collective behavior. In particular, the spectral density $\rho(\lambda)$ of this matrix reveals important network characteristics: random networks follow Wigner's semicircular law whereas scale-free networks exhibit a triangular distribution. In this paper we show that the spectral density of hierarchical networks follow a very different pattern, which can be used as a fingerprint of modularity. Of particular importance is the value $\rho(0)$, related to the homeostatic response of the network: it is maximum for random and scale free networks but very small for hierarchical modular networks. It is also large for an actual biological protein-protein interaction network, demonstrating that the current leading model for such networks is not adequate.Comment: 4 pages 14 figure

A High-Resolution Spectroscopic Search for the Remaining Donor for Tycho's Supernova

In this paper, we report on our analysis using Hubble Space Telescope astrometry and Keck-I HIRES spectroscopy of the central six stars of Tycho's supernova remnant (SN 1572). With these data, we measured the proper motions, radial velocities, rotational velocities, and chemical abundances of these objects. Regarding the chemical abundances, we do not confirm the unusu- ally high [Ni/Fe] ratio previously reported for Tycho-G. Rather, we find that for all metrics in all stars, none exhibit the characteristics expected from traditional SN Ia single-degenerate-scenario calculations. The only possible exception is Tycho-B, a rare, metal-poor A-type star; however, we are unable to find a suitable scenario for it. Thus, we suggest that SN 1572 cannot be explained by the standard single-degenerate model.Comment: 34 pages, 11 Figures, revised and resubmitted to Ap

A research and evaluation capacity building model in Western Australia

Evaluation of public health programs, services and policies is increasingly required to demonstrate effectiveness. Funding constraints necessitate that existing programs, services and policies be evaluated and their findings disseminated. Evidence-informed practice and policy is also desirable to maximise investments in public health. Partnerships between public health researchers, service providers and policymakers can help address evaluation knowledge and skills gaps. The Western Australian Sexual Health and Blood-borne Virus Applied Research and Evaluation Network (SiREN) aims to build research and evaluation capacity in the sexual health and blood-borne virus sector in Western Australia (WA). Partners’ perspectives of the SiREN model after 2 years were explored. Qualitative written responses from service providers, policymakers and researchers about the SiREN model were analysed thematically. Service providers reported that participation in SiREN prompted them to consider evaluation earlier in the planning process and increased their appreciation of the value of evaluation. Policymakers noted benefits of the model in generating local evidence and highlighting local issues of importance for consideration at a national level. Researchers identified challenges communicating the services available through SiREN and the time investment needed to develop effective collaborative partnerships. Stronger engagement between public health researchers, service providers and policymakers through collaborative partnerships has the potential to improve evidence generation and evidence translation. These outcomes require long-term funding and commitment from all partners to develop and maintain partnerships. Ongoing monitoring and evaluation can ensure the partnership remains responsive to the needs of key stakeholders. The findings are applicable to many sectors

Efficiency of Scale-Free Networks: Error and Attack Tolerance

The concept of network efficiency, recently proposed to characterize the properties of small-world networks, is here used to study the effects of errors and attacks on scale-free networks. Two different kinds of scale-free networks, i.e. networks with power law P(k), are considered: 1) scale-free networks with no local clustering produced by the Barabasi-Albert model and 2) scale-free networks with high clustering properties as in the model by Klemm and Eguiluz, and their properties are compared to the properties of random graphs (exponential graphs). By using as mathematical measures the global and the local efficiency we investigate the effects of errors and attacks both on the global and the local properties of the network. We show that the global efficiency is a better measure than the characteristic path length to describe the response of complex networks to external factors. We find that, at variance with random graphs, scale-free networks display, both on a global and on a local scale, a high degree of error tolerance and an extreme vulnerability to attacks. In fact, the global and the local efficiency are unaffected by the failure of some randomly chosen nodes, though they are extremely sensititive to the removal of the few nodes which play a crucial role in maintaining the network's connectivity.Comment: 23 pages, 10 figure

A high-resolution spectroscopic search for the remaining donor for Tycho'S supernova

In this paper, we report on our analysis using Hubble Space Telescope astrometry and Keck-I HIRES spectroscopy of the central six stars of Tycho's supernova remnant (SN 1572). With these data, we measured the proper motions, radial velocities, rotationa

Variable structure control with chattering reduction of a generalized T-S model

In this paper, a fuzzy logic controller (FLC) based variable structure control (VSC) is presented. The main objective is to obtain an improved performance of highly non-linear unstable systems. New functions for chattering reduction and error convergence without sacrificing invariant properties are proposed. The main feature of the proposed method is that the switching function is added as an additional fuzzy variable and will be introduced in the premise part of the fuzzy rules; together with the state variables. In this work, a tuning of the well known weighting parameters approach is proposed to optimize local and global approximation and modelling capability of the Takagi-Sugeno (T-S) fuzzy model to improve the choice of the performance index and minimize it. The main problem encountered is that the T-S identification method can not be applied when the membership functions are overlapped by pairs. This in turn restricts the application of the T-S method because this type of membership function has been widely used in control applications. The approach developed here can be considered as a generalized version of the T-S method. An inverted pendulum mounted on a cart is chosen to evaluate the robustness, effectiveness, accuracy and remarkable performance of the proposed estimation approach in comparison with the original T-S model. Simulation results indicate the potential, simplicity and generality of the estimation method and the robustness of the chattering reduction algorithm. In this paper, we prove that the proposed estimation algorithm converge the very fast, thereby making it very practical to use. The application of the proposed FLC-VSC shows that both alleviation of chattering and robust performance are achieved

An Emerging Class of Bright, Fast-evolving Supernovae with Low-mass Ejecta

A recent analysis of supernova (SN) 2002bj revealed that it was an apparently unique type Ib SN. It showed a high peak luminosity, with absolute magnitude M_R -18.5, but an extremely fast-evolving light curve. It had a rise time of <7 days followed by a decline of 0.25 mag per day in B-band, and showed evidence for very low mass of ejecta (<0.15 M_Sun). Here we discuss two additional historical events, SN 1885A and SN 1939B, showing similarly fast light curves and low ejected masses. We discuss the low mass of ejecta inferred from our analysis of the SN 1885A remnant in M31, and present for the first time the spectrum of SN 1939B. The old environments of both SN 1885A (in the bulge of M31) and SN 1939B (in an elliptical galaxy with no traces of star formation activity), strongly support old white dwarf progenitors for these SNe. We find no clear evidence for helium in the spectrum of SN 1939B, as might be expected from a helium-shell detonation on a white dwarf, suggested to be the origin of SN 2002bj. Finally, the discovery of all the observed fast-evolving SNe in nearby galaxies suggests that the rate of these peculiar SNe is at least 1-2 % of all SNe.Comment: Additional analysis included. ApJ, in pres

Urbanization comprehensively impairs biological rhythms in coral holobionts

Coral reefs are in global decline due to climate change and anthropogenic influences (Hughes et al., Conservation Biology, 27: 261–269, 2013). Near coastal cities or other densely populated areas, coral reefs face a range of additional challenges. While considerable progress has been made in understanding coral responses to acute individual stressors (Dominoni et al., Nature Ecology & Evolution, 4: 502–511, 2020), the impacts of chronic exposure to varying combinations of sensory pollutants are largely unknown. To investigate the impacts of urban proximity on corals, we conducted a year-long in-natura study—incorporating sampling at diel, monthly, and seasonal time points—in which we compared corals from an urban area to corals from a proximal non-urban area. Here we reveal that despite appearing relatively healthy, natural biorhythms and environmental sensory systems were extensively disturbed in corals from the urban environment. Transcriptomic data indicated poor symbiont performance, disturbance to gametogenic cycles, and loss or shifted seasonality of vital biological processes. Altered seasonality patterns were also observed in the microbiomes of the urban coral population, signifying the impact of urbanization on the holobiont, rather than the coral host alone. These results should raise alarm regarding the largely unknown long-term impacts of sensory pollution on the resilience and survival of coral reefs close to coastal communities

Detection of circumstellar material in a normal Type Ia Supernova

Type Ia supernovae are thought to be thermonuclear explosions of accreting white dwarfs that reach a critical mass limit. Despite their importance as cosmological distance indicators, the nature of their progenitors has remained controversial. Here we report the detection of circumstellar material in a normal Type Ia supernova. The expansion velocities, densities and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. The relatively low expansion velocities appear to favor a progenitor system where a white dwarf accretes material from a companion star which is in the red-giant phase at the time of explosion.Comment: 25 pages, 7 figures. Accepted for publication in Science. Full resolution version at http://www.hq.eso.org/~fpatat/science/sn06X/preprint.pdf . The original paper can be found at http://www.sciencemag.org/cgi/content/abstract/114300

A High-Resolution Spectrum of the Extremely Metal-Rich Bulge G-Dwarf OGLE-2006-BLG-265

We present an R=45,000 Keck spectrum of the microlensed Galactic bulge G-dwarf OGLE-2006-BLG-265, which has a high (~60) signal-to-noise ratio despite its short (15 min) exposure time because the source was magnified by A~135. While it is very metal-rich ([Fe/H]=0.56), the higher temperature of this star compared with the luminous red giants usually measured in the bulge gives its spectrum many unblended atomic lines. We measure the abundances of 17 elements, including the first abundances for S and Cu in a bulge star. The [alpha/Fe] ratios are subsolar, while the odd-Z elements are slightly supersolar, trends that are also seen in the more metal-rich stars in the bulge and the local Galactic disk. Because the star is a dwarf, the [O/Fe], [Na/Fe], and [Al/Fe] ratios cannot be attributed to internal mixing, as is sometimes claimed for giants. Similar high-resolution spectra could be obtained for about a dozen bulge dwarf stars per year by means of well-designed target-of-opportunity observations.Comment: 5 pages, 2 figures, submitted to ApJ Letter