Vector chiral states in low-dimensional quantum spin systems

A class of exact spin ground states with nonzero averages of vector spin chirality, $$, is presented. It is obtained by applying non-uniform O(2) rotations of spin operators in the XY plane on the SU(2)-invariant Affleck-Kennedy-Lieb-Tasaki (AKLT) states and their parent Hamiltonians. Excitation energies of the new ground states are studied with the use of single-mode approximation in one dimension for S=1. The excitation gap remains robust. Construction of chiral AKLT states is shown to be possible in higher dimensions. We also present a general idea to produce vector chirality-condensed ground states as non-uniform O(2) rotations of the non-chiral parent states. Dzyaloshinskii-Moriya interaction is shown to imply non-zero spin chirality.Comment: 4 pages, 1 figur

Coupling of phonons and spin waves in triangular antiferromagnet

We investigate the influence of the spin-phonon coupling in the triangular antiferromagnet where the coupling is of the exchange-striction type. The magnon dispersion is shown to be modified significantly at wave vector (2pi,0) and its symmetry-related points, exhibiting a roton-like minimum and an eventual instability in the dispersion. Various correlation functions such as equal-time phonon correlation, spin-spin correlation, and local magnetization are calculated in the presence of the coupling.Comment: 6 pages, 5 figures; references added, minor text revisions, submitted to PR

Role of Intracellular Free Calcium in the Obesity and Insulin Resistance Associated with Dominant Agouti Mutations

Several dominant mutations at the agouti locus in the mouse cause a syndrome of adult-onset obesity, hyperinsulinemia, and insulin resistance. Although ectopic overexpression of the agouti gene is directly responsible for the disease in these mutations, the precise mechanism is unclear. Intracellular Ca2+ ([Ca2+]i) appears to have a role in mediating insulin signal transduction, and altered handling of [Ca2+]i homeostasis and flux is observed in obese and insulin resistant animals and humans. Data reported here demonstrate that mice carrying the dominant agouti mutation, viable yellow (Avy), exhibit an elevation of [Ca2+]i and Ca2+ influx rate in insulin-sensitive type I skeletal muscle. The degree of elevation in [Ca2+]i is highly correlated with the degree of expression of agouti gene and the elevation of body weight. Moreover, recombinant agouti protein directly induced a sustained increase in [Ca2+]i in cultured myocytes and adipocytes; this effect is substantially inhibited by Ca2+ channel blockade. Ca2+channel blockade was also effective in reducing fat pad mass and fatty acid synthase (FAS) mRNA levels and activity in adipocytes of transgenic mice expressing the agouti gene in a ubiquitous manner. These results are consistent with previous reports in which recombinant agouti protein directly stimulates FAS mRNA levels and activity and triglyceride content in cultured adipocytes in a Ca2+ dependent manner. Accordingly, altered [Ca2+]i metabolism appears to be involved in development of obesity syndrome in Avy mice, and this defect in Ca2+ signaling may cause activation of FAS either directly or indirectly and subsequent de novo lipogenesis, contributing accumulation of fat depot in these mice

Nitrogen doping of carbon nanoelectrodes for enhanced control of DNA translocation dynamics

Controlling the dynamics of DNA translocation is a central issue in the emerging nanopore-based DNA sequencing. To address the potential of heteroatom doping of carbon nanostructures to achieve this goal, herein we carry out atomistic molecular dynamics simulations for single-stranded DNAs translocating between two pristine or doped carbon nanotube (CNT) electrodes. Specifically, we consider the substitutional nitrogen doping of capped CNT (capCNT) electrodes and perform two types of molecular dynamics simulations for the entrapped and translocating single-stranded DNAs. We find that the substitutional nitrogen doping of capCNTs stabilizes the edge-on nucleobase configurations rather than the original face-on ones and slows down the DNA translocation speed by establishing hydrogen bonds between the N dopant atoms and nucleobases. Due to the enhanced interactions between DNAs and N-doped capCNTs, the duration time of nucleobases within the nanogap was extended by up to ~ 290 % and the fluctuation of the nucleobases was reduced by up to ~ 70 %. Given the possibility to be combined with extrinsic light or gate voltage modulation methods, the current work demonstrates that the substitutional nitrogen doping is a promising direction for the control of DNA translocation dynamics through a nanopore or nanogap based of carbon nanomaterials.Comment: 11 pages, 4 figure