Anomalous impurity effect on magnetization in frustrated one-dimensional ferro- and ferrimagnets

Significant decrease of spontaneous magnetization in frustrated one-dimensional ferro- and ferrimagnets due to non-magnetic impurities is predicted. Using the density-matrix renormalization group method and the exact diagonalization method, we confirm that the total spin can vanish due to a single impurity in finite chains. Introducing the picture of magnetic domain inversion, we numerically investigate the impurity-density dependence of magnetization. In particular, we show that even with an infinitesimal density of impurities the magnetization in the ground state is reduced by about 40% from that of the corresponding pure system. Conditions for the materials which may show this anomalous impurity effect are formulated.Comment: 4 pages, 6 figure

A study of density modulation index in the inner heliospheric solar wind during solar cycle 23

The ratio of the rms electron density fluctuations to the background density in the solar wind (density modulation index, $\epsilon_{N} \equiv \Delta{N}/N$) is of vital importance in understanding several problems in heliospheric physics related to solar wind turbulence. In this paper, we have investigated the behavior of $\epsilon_{N}$ in the inner-heliosphere from 0.26 to 0.82 AU. The density fluctuations $\Delta{N}$ have been deduced using extensive ground-based observations of interplanetary scintillation (IPS) at 327 MHz, which probe spatial scales of a few hundred km. The background densities ($N$) have been derived using near-Earth observations from the Advanced Composition Explorer ($\it{ACE}$). Our analysis reveals that $0.001 \lesssim \epsilon_{N} \lesssim 0.02$ and does not vary appreciably with heliocentric distance. We also find that $\epsilon_{N}$ declines by 8% from 1998 to 2008. We discuss the impact of these findings on problems ranging from our understanding of Forbush decreases to the behavior of the solar wind dynamic pressure over the recent peculiar solar minimum at the end of cycle 23..Comment: 13 Pages, 8 Figures, Accepted for publication in Ap

Thermally-induced magnetic phases in an Ising spin Kondo lattice model on a kagome lattice at 1/3-filling

Numerical investigation on the thermodynamic properties of an Ising spin Kondo lattice model on a kagome lattice is reported. By using Monte Carlo simulation, we investigated the magnetic phases at 1/3-filling. We identified two successive transitions from high-temperature paramagnetic state to a Kosterlitz-Thouless-like phase in an intermediate temperature range and to a partially disordered phase at a lower temperature. The partially disordered state is characterized by coexistence of antiferromagnetic hexagons and paramagnetic sites with period $\sqrt3 \times \sqrt3$. We compare the results with those for the triangular lattice case.Comment: 4 pages, 2 figure

Online Intelligent Controllers for an Enzyme Recovery Plant: Design Methodology and Performance

This paper focuses on the development of intelligent controllers for use in a process of enzyme recovery from pineapple rind. The proteolytic enzyme bromelain (EC 3.4.22.4) is precipitated with alcohol at low temperature in a fed-batch jacketed tank. Temperature control is crucial to avoid irreversible protein denaturation. Fuzzy or neural controllers offer a way of implementing solutions that cover dynamic and nonlinear processes. The design methodology and a comparative study on the performance of fuzzy-PI, neurofuzzy, and neural network intelligent controllers are presented. To tune the fuzzy PI Mamdani controller, various universes of discourse, rule bases, and membership function support sets were tested. A neurofuzzy inference system (ANFIS), based on Takagi-Sugeno rules, and a model predictive controller, based on neural modeling, were developed and tested as well. Using a Fieldbus network architecture, a coolant variable speed pump was driven by the controllers. The experimental results show the effectiveness of fuzzy controllers in comparison to the neural predictive control. The fuzzy PI controller exhibited a reduced error parameter (ITAE), lower power consumption, and better recovery of enzyme activity

Anomalous magnetic phase in an undistorted pyrochlore oxide Cd2Os2O7 induced by geometrical frustration

We report on the muon spin rotation/relaxation study of a pyrochlore oxide, Cd2Os2O7, which exhibits a metal-insulator (MI) transition at T_{MI}~225 K without structural phase transition. It reveals strong spin fluctuation (>10^8/s) below the MI transition, suggesting a predominant role of geometrical spin frustration amongst Os^{5+} ions. Meanwhile, upon further cooling, a static spin density wave discontinuously develops below T_{SDW}~150 K. These observations strongly suggest the occurrence of an anomalous magnetic transition and associated change in the local spin dynamics in undistorted pyrochlore antiferromagnet.Comment: 5 pages, 4 figure

A characterization of compact complex tori via automorphism groups

We show that a compact Kaehler manifold X is a complex torus if both the continuous part and discrete part of some automorphism group G of X are infinite groups, unless X is bimeromorphic to a non-trivial G-equivariant fibration. Some applications to dynamics are given.Comment: title changed, to appear in Math. An