A Quantum Approach of Meso-Magnet Dynamics with Spin Transfer Torque

We present a theory of magnetization dynamics driven by spin-polarized current in terms of the quantum master equation. In the spin coherent state representation, the master equation becomes a Fokker-Planck equation, which naturally includes the spin transfer and quantum fluctuation. The current electron scattering state is correlated to the magnet quantum states, giving rise to quantum correction to the electron transport properties in the usual semiclassical theory. In the large spin limit, the magnetization dynamics is shown to obey the Hamilton-Jacobi equation or the Hamiltonian canonical equations.Comment: 7 pages, expanded version with 2 figures and appendix par

Exact asymptotics of monomer-dimer model on rectangular semi-infinite lattices

By using the asymptotic theory of Pemantle and Wilson, exact asymptotic expansions of the free energy of the monomer-dimer model on rectangular $n \times \infty$ lattices in terms of dimer density are obtained for small values of $n$, at both high and low dimer density limits. In the high dimer density limit, the theoretical results confirm the dependence of the free energy on the parity of $n$, a result obtained previously by computational methods. In the low dimer density limit, the free energy on a cylinder $n \times \infty$ lattice strip has exactly the same first $n$ terms in the series expansion as that of infinite $\infty \times \infty$ lattice.Comment: 9 pages, 6 table

Four-state rock-paper-scissors games on constrained Newman-Watts networks

We study the cyclic dominance of three species in two-dimensional constrained Newman-Watts networks with a four-state variant of the rock-paper-scissors game. By limiting the maximal connection distance $R_{max}$ in Newman-Watts networks with the long-rang connection probability $p$, we depict more realistically the stochastic interactions among species within ecosystems. When we fix mobility and vary the value of $p$ or $R_{max}$, the Monte Carlo simulations show that the spiral waves grow in size, and the system becomes unstable and biodiversity is lost with increasing $p$ or $R_{max}$. These results are similar to recent results of Reichenbach \textit{et al.} [Nature (London) \textbf{448}, 1046 (2007)], in which they increase the mobility only without including long-range interactions. We compared extinctions with or without long-range connections and computed spatial correlation functions and correlation length. We conclude that long-range connections could improve the mobility of species, drastically changing their crossover to extinction and making the system more unstable.Comment: 6 pages, 7 figure

Feminist Perspective of Cross-gender Power Relation in Caryl Churchill's Top Girls

Top Girls, one of Caryl Churchill's most popular plays, describes the lives of six female characters coming from different centuries. Each of them has their own story to tell, as they have all been victimized by the patriarchal system in the century when they live and have resisted the system with different strategies. They either employ roles that are traditionally reserved for men or they adopt the archetypically feminine qualities. Despite their resistance and success, they find themselves unhappy and unsatisfied over their achievements. Thus this raises the question of the effectiveness of the feminist movement

Interplay between spin density wave and π\pi phase shifted superconductivity in the Fe pnictide superconductors

We explore if the phase separation or coexistence of the spin density wave (SDW) and superconductivity (SC) states has any relation to the incommensurability of the SDW in the Fe pnictide superconductors. A systematic method of determining the phase separation or coexistence was employed by computing the anisotropy coefficient $\beta$ from the the 4th order terms of the Ginzburg--Landau (GL) expansion of the free energy close to the tricritical/tetracritical point. It was complemented by the self-consistent numerical iterations of the gap equations to map out the boundaries between the phase separation and coexistence of the SDW and SC phases, and between commensurate (C) and incommensurate (IC) SDW in the temperature--doping plane. Our principal results for the sign reversed $s$-wave pairing SC, in terms of the multicritical temperature, $T_c$, the phase separation/coexistence boundary between the SDW and SC, $T^*$, and the boundary between C/IC SDW, $T_M^*$, are: (a) IC-SDW and SC coexist for $T_c < T^*$ and phase separate otherwise, (b) SDW takes the C form for $T_c>T_M^*$ and IC form for $T_c<T_M^*$, and (c) the thermodynamic first order phase transition intervenes in between the C-SDW and IC-SDW boundary for large $T_M^0$, where $T_M^0$ is the SDW transition temperature at zero doping, $T^*=0.35 ~T_M^0$ and $T_M^*=0.56\ T_M^0$. The intervention makes the phase diagram more complicated than previously reported. By contrast no coexistence was found for the equal sign pairing SC. These results will be compared with the experimental reports in the Fe pnictide superconductors.Comment: 9 pages, 4 figures, Submitted to Phys.Rev.

Numerical study of the random field Ising model at zero and positive temperature

In this paper the three dimensional random field Ising model is studied at both zero temperature and positive temperature. Critical exponents are extracted at zero temperature by finite size scaling analysis of large discontinuities in the bond energy. The heat capacity exponent $\alpha$ is found to be near zero. The ground states are determined for a range of external field and disorder strength near the zero temperature critical point and the scaling of ground state tilings of the field-disorder plane is discussed. At positive temperature the specific heat and the susceptibility are obtained using the Wang-Landau algorithm. It is found that sharp peaks are present in these physical quantities for some realizations of systems sized $16^3$ and larger. These sharp peaks result from flipping large domains and correspond to large discontinuities in ground state bond energies. Finally, zero temperature and positive temperature spin configurations near the critical line are found to be highly correlated suggesting a strong version of the zero temperature fixed point hypothesis.Comment: 11 pages, 14 figure