Cooperative hunting in a discrete predator-prey system

We propose and investigate a discrete-time predator-prey system with cooperative hunting in the predator population. The model is constructed from the classical Nicholson-Bailey host-parasitoid system with density dependent growth rate. A sufficient condition based on the model parameters for which both populations can coexist is derived, namely that the predator's maximal reproductive number exceeds one. We study existence of interior steady states and their stability in certain parameter regimes. It is shown that the system behaves asymptotically similar to the model with no cooperative hunting if the degree of cooperation is small. Large cooperative hunting, however, may promote persistence of the predator for which the predator would otherwise go extinct if there were no cooperation

Dimensional crossover of thermal conductance in graphene nanoribbons: A first-principles approach

First-principles density-functional calculations are performed to investigate the thermal transport properties in graphene nanoribbons (GNRs). The dimensional crossover of thermal conductance from one to two dimensions (2D) is clearly demonstrated with increasing ribbon width. The thermal conductance of GNRs in a few nanometer width already exhibits an approximate low-temperature dependence of $T^{1.5}$, like that of 2D graphene sheet which is attributed to the quadratic nature of dispersion relation for the out-of-plane acoustic phonon modes. Using a zone-folding method, we heuristically derive the dimensional crossover of thermal conductance with the increase of ribbon width. Combining our calculations with the experimental phonon mean-free path, some typical values of thermal conductivity at room temperature are estimated for GNRs and for 2D graphene sheet, respectively. Our findings clarify the issue of low-temperature dependence of thermal transport in GNRs and suggest a calibration range of thermal conductivity for experimental measurements in graphene-based materials.Comment: 18 pages, 4 figure

A Note on Normal Forms of Quantum States and Separability

We study the normal form of multipartite density matrices. It is shown that the correlation matrix (CM) separability criterion can be improved from the normal form we obtained under filtering transformations. Based on CM criterion the entanglement witness is further constructed in terms of local orthogonal observables for both bipartite and multipartite systems.Comment: 8 page

Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides

The complex interdigitated phases have greatly frustrated attempts to document the basic features of the superconductivity in the alkali metal intercalated iron chalcogenides. Here, using elastic neutron scattering, energy-dispersive x-ray spectroscopy, and resistivity measurements, we elucidate the relations of these phases in Rb$_{1-\delta}$Fe$_y$Se$_{2-z}$S$_z$. We find: i) the iron content is crucial in stabilizing the stripe antiferromagnetic (AF) phase with rhombic iron vacancy order ($y\approx1.5$), the block AF phase with $\sqrt{5}\times \sqrt{5}$ iron vacancy order ($y\approx1.6$), and the iron vacancy-free phase ($y\approx2$); ii) the superconducting phase ($z=0$) evolves into a metallic phase ($z>1.5$) with sulfur substitution due to the progressive decrease of the electronic correlation strength. Both the stripe AF phase and the block AF phase are Mott insulators. Our data suggest that there are miscibility gaps between these three phases. The existence of the miscibility gaps in the iron content is the key to understanding the relationship between these complicated phases.Comment: 7 pages, 6 figure

Optimal measurements to access classical correlations of two-qubit states

We analyze the optimal measurements accessing classical correlations in arbitrary two-qubit states. Two-qubit states can be transformed into the canonical forms via local unitary operations. For the canonical forms, we investigate the probability distribution of the optimal measurements. The probability distribution of the optimal measurement is found to be centralized in the vicinity of a specific von Neumann measurement, which we call the maximal-correlation-direction measurement (MCDM). We prove that for the states with zero-discord and maximally mixed marginals, the MCDM is the very optimal measurement. Furthermore, we give an upper bound of quantum discord based on the MCDM, and investigate its performance for approximating the quantum discord.Comment: 8 pages, 3 figures, version accepted by Phys. Rev.

AN EXPLORATORY ECONOMETRIC ANALYSIS OF SHARED ELECTRONIC BANKING NETWORK ADOPTION

What are the determinants of early interorganizational system (IOS) adoption? This paper focuses on a specific kind of IOS -- shared electronic banking networks -- and employs an economic approach that views adoption and diffusion in terms of cost and benefit. We attempt to identify firm characteristics that are likely to influence the perceived business value of network membership and develop specific hypotheses that can be tested empirically using historical data in a realistic setting. We undertake an exploratory econometric analysis of the adoption of Yankee 24, a large shared electronic banking network in the northeastern United States. Using Bass' analytical diffusion model, we categorize Yankee 24 network members into earlier and later adopters. Probit models are estimated to assess the impact of explanatory variables on shared electronic banking network adoption. The number of branch offices operated by a bank, its total demand deposits, and the proportion of its total deposits accounted for by demand deposits are found to be important predictors of earlier adoption. We find that the number of branch offices operated by a bank, a proxy for the size of its proprietary network, has a negative impact on early adoption, which contradicts the common wisdom that a large firm size is a prerequisite for adoption of technological innovations.Information Systems Working Papers Serie

GROWTH PATTERNS AND REGIME CHANGE IN NATIONALLY SHARED ELECTRONIC BANKING NETWORKS: AN ECONOMETRIC ANALYSIS OF CIRRUS AND PLUS

Does adoption of shared electronic banking network technology in the financial services industry exhibit S-curve growth patterns as other technologies do? This paper examines this issue in the context of an econometric analysis of the national networks, CIRRUS and PLUS. When the size of the CIRRUS and PLUS networks grew into the range of market saturation, network operators decided in favor of "duality", a move to share their assets, while maintaining separate corporate identities. This research offers empirical evidence that it may be necessary to formulate more sophisticated models to describe the process of adoption and diffusion of an innovation in the presence of market competitionInformation Systems Working Papers Serie