60 research outputs found

    Discrete breathers in honeycomb Fermi-Pasta-Ulam lattices

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    We consider the two-dimensional Fermi-Pasta-Ulam lattice with hexagonal honeycomb symmetry, which is a Hamiltonian system describing the evolution of a scalar-valued quantity subject to nearest neighbour interactions. Using multiple-scale analysis we reduce the governing lattice equations to a nonlinear Schrodinger (NLS) equation coupled to a second equation for an accompanying slow mode. Two cases in which the latter equation can be solved and so the system decoupled are considered in more detail: firstly, in the case of a symmetric potential, we derive the form of moving breathers. We find an ellipticity criterion for the wavenumbers of the carrier wave, together with asymptotic estimates for the breather energy. The minimum energy threshold depends on the wavenumber of the breather. We find that this threshold is locally maximised by stationary breathers. Secondly, for an asymmetric potential we find stationary breathers, which, even with a quadratic nonlinearity generate no second harmonic component in the breather. Plots of all our findings show clear hexagonal symmetry as we would expect from our lattice structure. Finally, we compare the properties of stationary breathers in the square, triangular and honeycomb lattices

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    Not AvailableThe increasing prevalence of environmental pollution, especially soil contamination with heavy metals has led to their uptake in the human food chains through plant parts. Accumulation and magnification of heavy metals in human tissues through consumption of herbal remedies can cause hazardous impacts on health. Therefore, chemical profiling of nine heavy metals (Mn, Cr, Pb, Fe, Cd, Co, Zn, Ni and Hg) was undertaken in stem and leaf samples of ten medicinal plants (Acacia nilotica, Bacopa monnieri, Commiphora wightii, Ficus religiosa, Glycyrrhiza glabra, Hemidesmus indicus, Salvadora oleoides, Terminalia bellirica, Terminalia chebula and Withania somnifera) collected from environmentally diverse regions of Haryana and Rajasthan states in North-Western India. Concentration of all heavy metals, except Cr, was within permissible limits in the tested stem and leaf samples. Leaf samples had consistently more Cr compared to respective stem samples with highest concentration in leaf samples of Bacopa monnieri (13.19 ± 0.0480 ppm) and stem samples of Withania somnifera (4.93 ± 0.0185 ppm) both collected from Bahadurgarh (heavy industrial area), Haryana. This amount was beyond the permissible limit of 2.0 ppm defined by WHO for raw herbal material. Other two most perilous metals Pb (2.64 ± 0.0260) and Cd (0.04 ± 0.0274) were also recorded in Bahadurgarh region, although below permissible limits. Concentration of Hg remained below detectable levels in all the leaf and stem samples tested. These results suggested that cultivation of medicinal plants and other dietary herbs should be curtailed near environmentally polluted especially industrial areas for avoidance of health hazards.Not Availabl

    On PAR with Young People: Learnings from the SARUA Project

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    The Student Action Research for University Access (SARUA) is a participatory action research project between groups of senior high school students, their schoolteachers and university staff. During the eight years of its activities in at least 17 high schools in the greater metropolitan area of Brisbane significant learnings have developed about working with students on projects that affect their own lives. This paper problematises aspects of partnerships and collaboration between two diverse cultures of the university and the school and discusses the benefits of such collaboration, some of the challenges faced and the responsibilities of the university partners in facilitating action research with young people
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