Ecological flow analysis of network collapse II: Indicators of ecosystem level vulnerability

Using donor-controlled, bottom-up equations to describe network collapse we systematically investigate the impact each species has on the survival or extinction of other species. Short of extinction, one can determine the integrated losses experienced by the ecosystem. These losses are aggregated into system level indicators, such as entropy, average gain/loss, average time to extinction, etc. The methodology is applied to 18 ecological flow networks available in the literature. We calculate the correlations between various indicators and determine high positive correlation between: number of nodes & maximal trophic level; connectedness & average entropy losses; number of nodes & average number of extinct nodes; and, maximum trophic level & evenness of links. A high negative correlation was found between: number of nodes & connectedness; connectedness & maximal trophic level; maximum tropic level & average entropy loss; and, connectedness & evenness of flows. Lastly, a low correlation was found between: average number of extinct compartments & evenness of flows; number of nodes & evenness of stocks; and, evenness of flows & evenness of stocks

Ecological flow analysis of network collapse I: New methodology to investigate network collapse dynamics

This research builds on standard ecological network analysis techniques in order to investigate the impact of removing species (nodes) on the remaining of the network species. The flow network is expressed as a system of dynamical equations such that the removal of one node has time-forward impacts on the remaining nodes. The approach allows one to determine the gain or loss experienced by each other compartment in the model and the time for such impact to occur. The general methodology is demonstrated on the Cone Spring Ecosystem. These results indicate that collapse of certain species exert more control on the overall network organization. We also investigate model sensitivity to determine discount rate robustness and discuss further research

Spectra of Heavy Quarkonia in a Magnetized-Hot Medium in the Framework of Fractional Non-relativistic Quark Model

In the fractional nonrelativistic potential model, the decomposition of heavy quarkonium in a hot magnetized medium is investigated. The analytical solution of the fractional radial Schrodinger equation for the hot-magnetized interaction potential is displayed by using the conformable fractional Nikiforov-Uvarov method. Analytical expressions for the energy eigenvalues and the radial wave function are obtained for arbitrary quantum numbers. Next, we study the charmonium and bottmonium binding energies for different magnetic field values in the thermal medium. The effect of the fractional parameter on the decomposition temperature is also analyzed for charmonium and bottomonium in the presence of hot magnetized media. We conclude that the dissociation of heavy quarkonium in the fractional nonrelativistic potential model is more practical than the classical nonrelativistic potential model.Comment: 13 pages, 4 figures. arXiv admin note: substantial text overlap with arXiv:2104.0054

A Systems Approach To Assess Trade Dependencies in U.S. Food–Energy–Water Nexus

We present a network model of the United States (U.S.) interstate food transfers to analyze the trade dependency with respect to participating regions and embodied irrigation impacts from a food–energy–water (FEW) nexus perspective. To this end, we utilize systems analysis methods including the pointwise mutual information (PMI) measure to provide an indication of interdependencies by estimating probability of trade between states. PMI compares observed trade with a benchmark of what is statistically expected given the structure and flow in the network. This helps assess whether dependencies arising from empirically observed trade occur due to chance or preferential attachment. The implications of PMI values are demonstrated by using Texas as an example, the largest importer in the U.S. grain transfer network. We find that strong dependencies exist not only just with states (Kansas, Oklahoma, Nebraska) providing high volume of transfer to Texas but also with states that have comparatively lower trade (New Mexico). This is due to New Mexico’s reliance on Texas as an important revenue source compared to its other connections. For Texas, import interdependencies arise from geographical proximity to trade. As these states primarily rely on the commonly shared High Plains aquifer for irrigation, overreliance poses a risk for water shortage for food supply in Texas. PMI values also indicate the capacity to trade more (the states are less reliant on each other than expected), and therefore provide an indication of where the trade could be shifted to avoid groundwater scarcity. However, some of the identified states rely on GHG emission intensive fossil fuels such as diesel and gasoline for irrigation, highlighting a potential tradeoff between crop water footprint and switching to lower emissions pumping fuels

Magnetic-field-induced collapse of charge-ordered nanoclusters and the Colossal Magnetoresistance effect in Nd(0.3)Sr(0.3)MnO(3)

We report synchrotron x-ray scattering studies of charge/orbitally ordered (COO) nanoclusters in Nd$_{0.7}$Sr$_{0.3}$MnO$_3$. We find that the COO nanoclusters are strongly suppressed in an applied magnetic field, and that their decreasing concentration follows the field-induced decrease of the sample electrical resistivity. The COO nanoclusters, however, do not completely disappear in the conducting state, suggesting that this state is inhomogeneous and contains an admixture of an insulating phase. Similar results were also obtained for the zero-field insulator-metal transition that occurs as temperature is reduced. These observations suggest that these correlated lattice distortions play a key role in the Colossal Magnetoresistance effect in this prototypical manganite.Comment: 5 pages, 3 embedded eps figures; to appear in PRB Rapid Commumication

A Brief History of AGN

Astronomers knew early in the twentieth century that some galaxies have emission-line nuclei. However, even the systematic study by Seyfert (1943) was not enough to launch active galactic nuclei (AGN) as a major topic of astronomy. The advances in radio astronomy in the 1950s revealed a new universe of energetic phenomena, and inevitably led to the discovery of quasars. These discoveries demanded the attention of observers and theorists, and AGN have been a subject of intense effort ever since. Only a year after the recognition of the redshifts of 3C 273 and 3C 48 in 1963, the idea of energy production by accretion onto a black hole was advanced. However, acceptance of this idea came slowly, encouraged by the discovery of black hole X-ray sources in our Galaxy and, more recently, supermassive black holes in the center of the Milky Way and other galaxies. Many questions remain as to the formation and fueling of the hole, the geometry of the central regions, the detailed emission mechanisms, the production of jets, and other aspects. The study of AGN will remain a vigorous part of astronomy for the foreseeable future.Comment: 37 pages, no figures. Uses aaspp4.sty. To be published in Publications of the Astronomical Society of the Pacific, 1999 Jun

Noise Probe of the Dynamic Phase Separation in La2/3Ca1/3MnO3

Giant Random Telegraph Noise (RTN) in the resistance fluctuation of a macroscopic film of perovskite-type manganese oxide La2/3Ca1/3MnO3 has been observed at various temperatures ranging from 4K to 170K, well below the Curie temperature (TC = 210K). The amplitudes of the two-level-fluctuations (TLF) vary from 0.01% to 0.2%. We use a statistical analysis of the life-times of the TLF to gain insight into the microscopic electronic and magnetic state of this manganite. At low temperature (below 30K) The TLF is well described by a thermally activated two-level model. An estimate of the energy difference between the two states is inferred. At higher temperature (between 60K and 170K) we observed critical effects of the temperature on the life-times of the TLF. We discuss this peculiar temperature dependence in terms of a sharp change in the free energy functional of the fluctuators. We attribute the origin of the RTN to be a dynamic mixed-phase percolative conduction process, where manganese clusters switch back and forth between two phases that differ in their conductivity and magnetization.Comment: 15 pages, PDF only, Phys. Rev. Lett. (in press