Incommensurate nodes in the energy spectrum of weakly coupled antiferromagnetic Heisenberg ladders

Heisenberg ladders are investigated using the bond-mean-field theory [M.Azzouz, Phys. Rev. B 48, 6136 (1993)]. The zero inter-ladder coupling energy gap, the uniform spin susceptibility and the nuclear magnetic resonance spin-relaxation rate are calculated as a function of temperature and magnetic field. For weakly coupled ladders, the energy spectrum vanishes at incommensurate wavevectors giving rise to nodes. As a consequence, the spin susceptibility becomes linear at low temperature. Our results for the single ladder successfully compare to experiments on SrCu_2O_3 and (VO)_2P_2O_7 materials and new predictions concerning the coupling to the magnetic field are made.Comment: 4 revtex pages, 3 figures available upon reques

Viral delivery of antioxidant genes as a therapeutic strategy in experimental models of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder with no effective treatment to date. Despite its multi-factorial aetiology, oxidative stress is hypothesized to be one of the key pathogenic mechanisms. It is thus proposed that manipulation of the expression of antioxidant genes that are downregulated in the presence of mutant SOD1 may serve as a therapeutic strategy for motor neuronal protection. Lentiviral vectors expressing either PRDX3 or NRF2 genes were tested in the motor neuronal-like NSC34 cell line, and in the ALS tissue culture model, NSC34 cells expressing the human SOD1(G93A) mutation. The NSC34 SOD1(G93A) cells overexpressing either PRDX3 or NRF2 showed a significant decrease in endogenous oxidation stress levels by 40 and 50% respectively compared with controls, whereas cell survival was increased by 30% in both cases. The neuroprotective potential of those two genes was further investigated in vivo in the SOD1(G93A) ALS mouse model, by administering intramuscular injections of adenoassociated virus serotype 6 (AAV6) expressing either of the target genes at a presymptomatic stage. Despite the absence of a significant effect in survival, disease onset or progression, which can be explained by the inefficient viral delivery, the promising in vitro data suggest that a more widespread CNS delivery is needed

Interplay between field-induced and frustration-induced quantum criticalities in the frustrated two-leg Heisenberg ladder

The antiferromagnetic Heisenberg two-leg ladder in the presence of frustration and an external magnetic field is a system that is characterized by two sorts of quantum criticalities, not only one. One criticality is the consequence of intrinsic frustration, and the other one is a result of the external magnetic field. So the behaviour of each of them in the presence of the other deserves to be studied. Using the Jordan-Wigner transformation in dimensions higher than one and bond-mean-field theory we examine the interplay between the field-induced and frustration-induced quantum criticalities in this system. The present work could constitute a prototype for those systems showing multiple, perhaps sometimes competing, quantum criticalities. We calculate several physical quantities like the magnetization and spin susceptibility as functions of field and temperature.Comment: 9 pages, 8 figures, submitted to the Canadian Journal of Physic

Quantum and classical criticalities in the frustrated two-leg Heisenberg ladder

This talk was about the frustration-induced criticality in the antiferromagnetic Heisenberg model on the two-leg ladder with exchange interactions along the chains, rungs, and diagonals, and also about the effect of thermal fluctuations on this criticlity. The method used is the bond mean-field theory, which is based on the Jordan-Wigner transformation in dimensions higher than one. In this paper, we will summarize the main results presented in this talk, and report on new results about the couplings and temperature dependences of the spin susceptibility.Comment: 6 pages, 4 figures, talk presented at the Theory Canada 3 conference in 2007, submitted to the Canadian Journal of Physic

Calculation of the singlet-triplet gap of the antiferromagnetic Heisenberg Model on the ladder

The ground state energy and the singlet-triplet energy gap of the antiferromagnetic Heisenberg model on a ladder is investigated using a mean field theory and the density matrix renormalization group. Spin wave theory shows that the corrections to the local magnetization are infinite. This indicates that no long range order occurs in this system. A flux-phase state is used to calculate the energy gap as a function of the transverse coupling, $J_\perp$, in the ladder. It is found that the gap is linear in $J_\perp$ for $J_\perp\gg 1$ and goes to zero for $J_\perp\to 0$. The mean field theory agrees well with the numerical results.Comment: 11pages,6 figures (upon request) Revtex 3.0, Report#CRPS-94-0

Anisotropic two-dimensional Heisenberg model by Schwinger-boson Gutzwiller projected method

Two-dimensional Heisenberg model with anisotropic couplings in the $x$ and $y$ directions ($J_x \neq J_y$) is considered. The model is first solved in the Schwinger-boson mean-field approximation. Then the solution is Gutzwiller projected to satisfy the local constraint that there is only one boson at each site. The energy and spin-spin correlation of the obtained wavefunction are calculated for systems with up to $20 \times 20$ sites by means of the variational Monte Carlo simulation. It is shown that the antiferromagnetic long-range order remains down to the one-dimensional limit.Comment: 15 pages RevTex3.0, 4 figures, available upon request, GWRVB8-9

AAV9-mediated central nervous system-targeted gene delivery via cisterna magna route in mice

Current barriers to the use of adeno-associated virus serotype 9 (AAV9) in clinical trials for treating neurological disorders are its high expression in many off-target tissues such as liver and heart, and lack of cell specificity within the central nervous system (CNS) when using ubiquitous promoters such as human cytomegalovirus (CMV) or chicken-β-actin hybrid (CAG). To enhance targeting the transgene expression in CNS cells, self-complementary (sc) AAV9 vectors, scAAV9-GFP vectors carrying neuronal Hb9 and synapsin 1, and nonspecific CMV and CAG promoters were constructed. We demonstrate that synapsin 1 and Hb9 promoters exclusively targeted neurons in vitro, although their strengths were up to 10-fold lower than that of CMV. In vivo analyses of mouse tissue after scAAV9-GFP vector delivery via the cisterna magna revealed a significant advantage of synapsin 1 promoter over both Hb9 variants in targeting neurons throughout the brain, since Hb9 promoters were driving gene expression mainly within the motor-related areas of the brain stem. In summary, this study demonstrates that cisterna magna administration is a safe alternative to intracranial or intracerebroventricular vector delivery route using scAAV9, and introduces a novel utility of the Hb9 promoter for the targeted gene expression for both in vivo and in vitro applications

First report of Barley Yellow Dwarf Viruses (BYDVs) on dicotyledonous weed hosts in Turkey

Yellow dwarf viruses (YDVs) are economically destructive viral diseases of cereal crops, which cause the reduction of harvested yield and quality of grains. Up to now the identification of such viruses was limited to monocotyledonous Poaceae weed hosts, and was not investigated in dicotyledons. In this study, using DAS-ELISA and RT-PCR methods, 6 dicotyledonous weed species, collected from Trakya, Turkey, were examined for the presence of the YDVs pathogens BYDV-PAV, BYDV-MAV, BYDV-RMV, BYDV-SGV and CYDV-RPV. The screening tests revealed certain samples of Geranium dissectum L. and Juncus compressus Jacq. were infected with BYDV-PAV, while other samples of the same species were positive for BYDV-MAV. Additionally, RT-PCR tests of both weed species revealed cases of mixed infection by BYDV-PAV and BYDV-MAV. Transmission experiments using the aphid species Rhopalosiphum padi L. showed that BYDV-PAV was transmitted persistently from Geranium dissectum to barley cv. Barbaros seedlings. To our knowledge, this is the first report of Geranium dissectum and Juncus compressus as possible plant hosts of BYDV-PAV and BYDV-MAV in Turkey