Antiferromagnetic Spin Ladders with Odd and Even number of Chains

We construct frustrated antiferromagnetic spin ladders with m chains for which the exact ground state can be determined in a particular parameter regime. The excitation spectrum is shown rigorously to be gapless ( with gap ) for odd ( even ) m. In a general parameter regime, the four-chain and periodic ladders are studied using a mean-field theory based on the bond operator formalism for spin $S=1/2$. The excitation spectrum and the spin-gap are calculated in both the cases. The spin-gap of the frustrated ladder system has a larger magnitude than in the case of non-frustrated ladders. For the frustrated periodic ladder, the spin-gap vanishes at a critical value of the interladder coupling strength which is larger than the critical value in the case of non-frustrated periodic ladder.Comment: 22 pages, LaTeX, 6 figures available upon request, submitted to Phys. Rev.

Exact ground and excited states of frustrated antiferromagnets on the CaV_4O_9 lattice

The experimental observation of a spin-gap in the antiferromagnetic spin-1/2 compound $CaV_4O_9$ has been attributed to the formation of a plaquette resonating-valence-bond (PRVB) state in the underlying 1/5-depleted square lattice. We construct a spin-1/2 model on the 1/5-depleted lattice for which the PRVB state can be shown to be the exact ground state in a particular parameter regime. In a subspace of this parameter regime, the first excited state can be calculated exactly. In a different parameter regime, the dimer state is shown to be the exact ground state.Comment: 13 pages, LaTeX, 4 figures, to appear in Phys. Rev.

Spin dynamics of a one-dimensional spin-1/2 fully anisotropic Ising-like antiferromagnet in a transverse magnetic field

We consider the one-dimensional Ising-like fully anisotropic S=1/2 Heisenberg antiferromagnetic Hamiltonian and study the dynamics of domain wall excitations in the presence of transverse magnetic field $h_x$. We obtain dynamical spin correlation functions along the magnetic field $S^{xx}(q,\omega)$ and perpendicular to it $S^{yy}(q,\omega)$. It is shown that the line shapes of $S^{xx}(q,\omega)$ and $S^{yy}(q,\omega)$ are purely symmetric at the zone-boundary. It is observed in $S^{yy}(q,\omega)$ for $\pi/2<q<\pi$ that the spectral weight moves toward low energy side with the increase of $h_x$. This model is applicable to study the spin dynamics of CsCoCl$_3$ in the presence of weak interchain interactions.Comment: 19 pages, LaTeX, 12 eps figure

Domain-wall excitations in the one-dimensional spin-1/2 fully anisotropic ising-like antiferromagnet

We consider S = &#189; the Ising-like, fully anisotropic Heisenberg antiferromagnetic Hamiltonian in one dimension and study the dynamics of domain-wall excitations using perturbation theory. It is shown that the domain walls can form bound states. The transverse correlation function S xx (q, &#969; ) is calculated in first-order perturbation theory and the zone-centre lineshape is found to be asymmetric towards lower energy. A comparison of the results with earlier theories as well as experimental results on CsCoCl3 and CsCoBr3 is made

Anti-inflammatory activity of root of Alpinia galanga willd

Objective: The objective of the study is to evaluate the acute and chronic anti-inflammatory activities of root extract of Alpinia galanga in rodents. Materials and Methods: The study was carried out using albino rats of either sex (150-200 g). An extract of the root of A. galanga was prepared using absolute alcohol and distillation in a Soxhlet apparatus. The acute anti-inflammatory effects of this extract were evaluated using carrageenan-, bradykinin-, and 5-HT-induced rat paw edema. The chronic anti-inflammatory effects were evaluated using formaldehyde-induced rat paw edema. Results and Analysis: Inhibition of inflammation was seen to be 32.22% in carrageenan-induced, 37.70% in 5-HT-induced, and 35.21% in bradykinin-induced anti-inflammatory models. In chronic inflammatory model, a progressive inhibition of 34.73% (3 rd day), 37.50% (5 th day), 38.83% (7 th day), 44.66% (9 th day), 49.59% (11 th day), and 55.75% (13 th day) was observed with study compound. The efficacy was comparable with the standard drugs. Conclusion: It can be thus concluded that A. galanga has anti-inflammatory properties and probably acts by blocking histaminic and serotonin pathways. It may be an effective alternative to NASAIDs and corticosteroid in inflammatory disorders