Quantum Monte Carlo Study on Magnetization Processes

A quantum Monte Carlo method combining update of the loop algorithm with the global flip of the world line is proposed as an efficient method to study the magnetization process in an external field, which has been difficult because of inefficiency of the update of the total magnetization. The method is demonstrated in the one dimensional antiferromagnetic Heisenberg model and the trimer model. We attempted various other Monte Carlo algorithms to study systems in the external field and compared their efficiency.Comment: 5 pages, 9 figures; added references for section 1, corrected typo

Cinnamtannin B1: a small compound having antidiabetes properties

Type 2 diabetes mellitus is a chronic metabolic disease that results from defects in insulin secretion and insulin receptor kinase. Investigation of novel small active molecule that can potentiate insulin action or having a similar action as insulin is important in the treatment of diabetes. World ethnobotanical information on medicinal plants reports almost 800 plants used in the treatment of diabetes mellitus. However, only a small number of them have been studied thoroughly. Recent study conducted on Cinnamomum reported that it has a great activity in activating insulin receptor kinase and inhibiting insulin receptor phosphatase leading to increased insulin sensitivity and function as a mimetic for insulin. Our study was designed to investigate insulin-mimetic activity of cinnamtannin B1 isolated from Cinnamomum zeylanicum on adipocyte cells. The insulin-mimetic activity of cinnamtannin B1 was evaluated by monitoring preadipocytes differentiation, glucose uptake and phosphorylation of insulin receptor -subunit in 3T3-L1 adipocytes. To determine whether cinnamtannin B1 able to promote differentiation of preadipocytes, we cultured 3T3-L1 preadipocytes in the presence of cinnamtannin B1, or combination of cinnamtannin B1 and insulin, and then cell proliferation was measured at several points during the course of growth. Investigation of role of cinnamtannin B1 on tyrosine posphorylation of insulin receptor of 3T3-L1 cells was done by immunoprecipitation of cells lysate with anti-insulin receptor -subunit antibody and the immunocomplex samples were subjected to SDS-PAGE, transferred to nitrocellulose membranes, and immunoblotted with monoclonal anti- phosphotyrosine antibody. Evaluation of glucose uptake by adipocyte cells after treatment with cinnamtannin B1 was carried out by analyzing of radioactive glucose uptake with liquid scintillation counter. Based on these experiments, it was found that, a mixture cinnamtannin B1 with differentiation cocktail was able to induce differentiation of preadipocytes cells. Cinnamtannin B1 was found to active to stimulate phosphorylation of insulin receptor -subunit by positively exhibited phosphorylation at 170-kDa. The mixture of cinnamtannin B1 was also able to stimulate glucose uptake from a basal value. The results demonstrated that activity of cinnamtannin B1 on adipocyte cells was found to mimicking insulin action. It acted directly on insulin receptor -subunit by activation of PI3-kinase that stimulates glucose transporter-4 (GLUT-4) translocation. Stimulation of GLUT4 translocation therefore stimulates glucose uptake lead to glucose disposal process in adipocytes. Based on the work that has been carried out, it was suggested that cinnamtannin B1 could be one of the potential lead drug compound in the treatment of type 2 diabetes

Bis{μ-2-[bis­(pyridin-2-yl)methyl­idene]hydrazinecarbothio­amidato}bis­[bromido­copper(II)] methanol disolvate

In the centrosymmetric binuclear title compound, [Cu2Br2(C12H10N5S)2]·2CH3OH, the CuII ion adopts a slightly dis­torted square-pyramidal coordination geometry. The hydrazine carbothio­amide moiety and one of the pyridyl rings together adopt an almost planar arrangement, with a maximum deviation of 0.052 (4) Å for the C atom of the thio­urea moiety. There are two mol­ecules of methanol solvent per complex in the asymmetric unit. The nonconventional intra­molecular C—H⋯Br hydrogen bonds make the mol­ecule more rigid, whereas the conventional N—H⋯N and O—H⋯Br inter­molecular hydrogen-bonding inter­actions, supported with N—H⋯π inter­actions, establish a supra­molecular linkage among the mol­ecules in the crystal. An intermolecular C—H⋯O inter­action is also present

Quantum spin chains in a magnetic field

We demonstrate that the ``worm'' algorithm allows very effective and precise quantum Monte Carlo (QMC) simulations of spin systems in a magnetic field, and its auto-correlation time is rather insensitive to the value of H at low temperature. Magnetization curves for the $s=1/2$ and $s=1$ chains are presented and compared with existing Bethe ansatz and exact diagonalization results. From the Green function analysis we deduce the magnon spectra in the s=1 system, and directly establish the "relativistic" form E(p)=(\Delta ^2 +v^2 p^2)^{1/2} of the dispersion law.Comment: 6 pages, 8 figures; removed discussion of spin-2 case - will be published later in a separate pape

Cinnamtannin B1: a small compound having antidiabetes properties

Type 2 diabetes mellitus is a chronic metabolic disease that results from defects in insulin secretion and insulin receptor kinase. Investigation of novel small active molecule that can potentiate insulin action or having a similar action as insulin is important in the treatment of diabetes. World ethnobotanical information on medicinal plants reports almost 800 plants used in the treatment of diabetes mellitus. However, only a small number of them have been studied thoroughly. Recent study conducted on Cinnamomum reported that it has a great activity in activating insulin receptor kinase and inhibiting insulin receptor phosphatase leading to increased insulin sensitivity and function as a mimetic for insulin. Our study was designed to investigate insulin-mimetic activity of cinnamtannin B1 isolated from Cinnamomum zeylanicum on adipocyte cells. The insulin-mimetic activity of cinnamtannin B1 was evaluated by monitoring preadipocytes differentiation, glucose uptake and phosphorylation of insulin receptor β-subunit in 3T3-L1 adipocytes. To determine whether cinnamtannin B1 able to promote differentiation of preadipocytes, we cultured 3T3-L1 preadipocytes in the presence of cinnamtannin B1, or combination of cinnamtannin B1 and insulin, and then cell proliferation was measured at several points during the course of growth. Investigation of role of cinnamtannin B1 on tyrosine posphorylation of insulin receptor of 3T3-L1 cells was done by immunoprecipitation of cells lysate with anti-insulin receptor β-subunit antibody and the immunocomplex samples were subjected to SDS-PAGE, transferred to nitrocelluose membranes, and immunoblotted with monoclonal anti-phosphotyrosine antibody. Evaluation of glucose uptake by adipocyte cells after treatment with cinnamtannin B1 was carried out by analyzing of radioactive glucose uptake with liquid scintillation counter. Based on these experiments, it was found that, a mixture cinnamtannin B1 with differentiation cocktail was able to induce differentiation of preadipocytes cells. Cinnamtannin B1 was found to active to stimulate phosphorylation of insulin receptor β-subunit by positively exhibited phosphorylation at 170-kDa. The mixture of cinnamtannin B1 was also able to stimulate glucose uptake from a basal value. The results demonstrated that activity of cinnamtannin B1 on adipocyte cells was found to mimicking insulin action. It acted directly on insulin receptor β-subunit by activation of PI3-kinase that stimulates glucose transporter-4 (GLUT-4) translocation. Stimulation of GLUT4 translocation therefore stimulates glucose uptake lead to glucose disposal process in adipocytes. Based on the work that has been carried out, it was suggested that cinnamtannin B1 could be one of the Annals of Medicine & Healthcare Research Page 452 potential lead drug compound in the treatment of type 2 diabetes

Magnetization plateaus in spin chains: ``Haldane gap'' for half-integer spins

We discuss zero-temperature quantum spin chains in a uniform magnetic field, with axial symmetry. For integer or half-integer spin, $S$, the magnetization curve can have plateaus and we argue that the magnetization per site $m$ is topologically quantized as $q (S - m)= integer$ at the plateaus, where $q$ is the period of the groundstate. We also discuss conditions for the presence of the plateau at those quantized values. For $S=3/2$ and $m=1/2$, we study several models and find two distinct types of massive phases at the plateau. One of them is argued to be a ``Haldane gap phase'' for half-integer $S$.Comment: Revised version, to appear in Phys. Rev. Lett. (no changes in main conclusions); 5 pages, REVTEX with 2 figures in ep

Magnetic order in ferromagnetically coupled spin ladders

A model of coupled antiferromagnetic spin-1/2 Heisenberg ladders is studied with numerical techniques. In the case of ferromagnetic interladder coupling we find that the dynamic and static structure factor has a peak at $(\pi,\pi/2)$ where the first (second) direction is along (transversal) to the ladders. Besides, we suggest that the intensity of this peak and the spin-spin correlation at the maximum distance along the ladder direction remain finite in the bulk limit for strong enough interladder coupling. We discuss the relevance of these results for magnetic compounds containing ladders coupled in a trellis lattice and for the stripe scenario in high-T$_c$ superconducting cuprates.Comment: 6 pages, 7 psfigs- Final version to be published in Phys. Rev.

Collective excitations in ferrimagnetic Heisenberg ladders

We study ground-state properties and the low-lying excitations of Heisenberg spin ladders composed of two ferrimagnetic chains with alternating site spins $(S_1>S_2)$ by using the bosonic Dyson-Maleev formalism and Lanczos numerical techniques. The emphasis is on properties of the ferrimagnetic phase which is stable for antiferromagnetic interchain couplings $J_{\perp}\geq 0$. There are two basic implications of the underlying lattice structure: (i) the spin-wave excitations form folded acoustic and optical branches in the extended Brillouin zone and (ii) the ground state parameters (such as the on-site magnetizations and spin-stiffness constant) show a crossover behavior in the weak-coupling region $0<J_{\perp}<1$. The above peculiarities of the ladder ferrimagnetic state are studied up to second order in the quasiparticle interaction and by a numerical diagonalization of ladders containing up to N=12 rungs. The presented results for the ground-state parameters and the excitation spectrum can be used in studies on the low-temperature thermodynamics of ferrimagnetic ladders.Comment: 9 pages, 9 figure

Phase diagrams of spin ladders with ferromagnetic legs

The low-temperature properties of the spin S=1/2 ladder with anisotropic ferromagnetic legs are studied using the continuum limit bosonization approach. The weak-coupling ground state phase diagram of the model is obtained for a wide range of coupling constants and several unconventional gapless ''spin-liquid'' phases are shown to exist for ferromagnetic coupling. The behavior of the ladder system in the vicinity of the ferromagnetic instability point is discussed in detail.Comment: 11 pages, 4 figure