Post-perovskite CaIrO3: a conventional Slater type antiferromagnetic insulator.

To resolve the controversy of whether or not the origin of an electronic gap in antiferromagnetic post-perovskite (pPv) CaIrO3 is due to Coulomb repulsion or spin-orbit coupling, and/or both, we have performed comprehensive full potential density functional theory based calculations. A rather consistent electronic structure, which explains the origin and magnitude of the electronic gap, inter-band d-d transition energies, high thermopower and large magneto-crystalline anisotropy, is obtained with the use of a modified Becke-Johnson (mBJ) exchange potential. Fundamentally, mBJ calculations correctly capture the strong interplay of the crystal field and long range antiferromagnetic ordering of Ir spins as the mechanism that drives pPv-CaIrO3 to an insulating state. Based on our findings, we propose that pPv-CaIrO3 is a conventional Slater type antiferromagnetic insulator.

Tuning the carrier concentration using Zintl chemistry in Mg3Sb2, and its implications for thermoelectric figure-of-merit.

Zintl compounds are potential candidates for efficient thermoelectric materials, because typically they are small band gap semiconductors. In addition, such compounds allow fine tuning of the carrier concentration by chemical doping for the optimization of thermoelectric performance. Herein, such tunability is demonstrated in Mg3Sb2-based Zintl compounds via Zn(2+) doping at the Mg(2+) site of the anionic framework (Mg2Sb2)(2-), in the series Mg3-xZnxSb2 (0 ≤ x ≤ 0.1). The materials have been successfully synthesized using the spark plasma sintering (SPS) technique. X-ray diffraction (XRD) analysis confirms a single solid solution phase of Mg3-xZnxSb2 (0 ≤ x ≤ 0.1). The thermoelectric properties are characterized by the Seebeck coefficient, electrical conductivity, and thermal conductivity measurements from 323 K to 773 K. Isoelectronic Zn substitution at the Mg site presents the controlled variation in the carrier concentration for optimizing the high power factor and reduced thermal conductivity. These results lead to a substantial increase in ZT of 0.37 at 773 K for a composition with x = 0.10 which is ∼42% higher than undoped Mg3Sb2. The electronic transport data for the Mg3-xZnxSb2 (0 ≤ x ≤ 0.1) compound are analyzed using a single parabolic band model predicting that Mg2.9Zn0.1Sb2 exhibits a near-optimal carrier concentration for high ZT. The electronic structure of transport properties of these disordered Mg3-xZnxSb2 (0 ≤ x ≤ 0.1) is also studied using density functional theory and the results obtained are in good agreement with experimental results. The low cost, lightness and non-toxicity of the constituent elements make these materials ideal for mid-temperature thermoelectric applications.

Interaction of Mg with heavy metals (Cu, Cd) in T. aestivum with special reference to oxidative and proline metabolism.

Little effort has been made to understand the influence of Mg on cellular processes of plant cell during Cu and Cd toxicities. The present work demonstrates the influence of magnesium (Mg) on copper (Cu) and cadmium (Cd) toxicity on Triticum aestivum (Wheat). We measured a range of parameters related to oxidative stress in wheat exposed to Cu or Cd toxicity in media with different concentrations of Mg. Decreasing Mg concentration significantly exacerbated Cu and Cd toxicity and optimum supply of Mg improved the growth and decreased the toxicity-induced oxidative stress (a substantial decline in the amount of hydrogen peroxide (H2O2) and malondialdehyde (MDA) in root and shoot tissues). Activity of antioxidant enzymes-superoxide dismutase (SOD), ascorbae peroxidase (APX), catalase (CAT) was restored upon optimum Mg concentration in the presence of Cu and Cd toxicity. An increase in proline concentration in roots and shoots that was triggered by Cu and Cd exposure was partly reversed. This was due to decline in pyrroline-5-carboxylate synthetase (P5CS) and pyrroline-5-carboxylate reductase (P5CR) activity and enhanced proline dehydrogenase (PDH) activity. In conclusion, decreasing supply of Mg effectively exacerbated the toxicities of Cu and Cd in wheat.

Evidence of Slater-type mechanism as origin of insulating state in Sr2IrO4.

For iridates with large spatially extended 5d orbitals, it may be anticipated that distant neighbor interactions would play a crucial role in their ground state properties. From this perspective, we investigate the magnetic structure of Sr2IrO4 by including interactions beyond first and second neighbors, via supercell modeling. Adopting to first-principles scalar relativistic methods, it is found that the minimum in total energy among various magnetic structures correspond to a [Formula: see text] type antiferromagnetic ordering of the Ir ions for which the magnitude of the electronic gap, that of the Ir local moments and, the facsimile of the two-peaked structure in the optical conductivity spectra of Sr2IrO4 were found to be in good agreement with the experiments. The results unequivocally show that the origin of the electronic gap in Sr2IrO4 is due to an unconventional antiferromagnetic ordering of Ir ions, thereby classifying the system as a Slater magnet, rather than the spin-orbit coupling driven [Formula: see text] Mott insulator.

Unexplored photoluminescence from bulk and mechanically exfoliated few layers of Bi2Te3.

We report the exotic photoluminescence (PL) behaviour of 3D topological insulator Bi2Te3 single crystals grown by customized self-flux method and mechanically exfoliated few layers (18 ± 2 nm)/thin flakes obtained by standard scotch tape method from as grown Bi2Te3 crystals. The experimental PL studies on bulk single crystal and mechanically exfoliated few layers of Bi2Te3 evidenced a broad red emission in the visible region from 600-690 nm upon 375 nm excitation wavelength corresponding to optical band gap of 2 eV. These findings are in good agreement with our theoretical results obtained using the ab initio density functional theory framework. Interestingly, the observed optical band gap is several times larger than the known electronic band gap of ~0.15 eV. The experimentally observed 2 eV optical band gap in the visible region for bulk as well as for mechanically exfoliated few layers Bi2Te3 single crystals clearly rules out the quantum confinement effects in the investigated samples which are well known in the 2D systems like MoS2,WS2, WSe2, and MoSe2 for 1-3 layers.

Cooperative effects of lattice and spin-orbit coupling on the electronic structure of orthorhombic SrIrO3.

Orthorhombic SrIrO3 subjected to strain shows tunable transport properties. With underlying symmetry remaining invariant, these properties are associated with IrO6 octahedral tilting. Adopting first-principles methods, the effects of crystal field, spin-orbit coupling (SOC), and Coulomb correlations, on comparable interaction length scales, are discussed. While tilting induces a t(2g) - e(g) crystal-field splitting and band narrowing, SOC induces a partial splitting of the J(eff) bands rendering SrIrO3 a semi-metallic ground state. The SOC enhanced hybridization of Ir-O orbitals serves as an explanation as to why the critical Hubbard correlation strength increases with increasing SOC strength in SrIrO3 to induce an insulating phase.

Methamphetamine increases LPS-mediated expression of IL-8, TNF-α and IL-1ß in human macrophages through common signaling pathways.

The use of methamphetamine (MA) has increased in recent years, and is a major health concern throughout the world. The use of MA has been associated with an increased risk of acquiring HIV-1, along with an increased probability of the acquisition of various sexually transmitted infections. In order to determine the potential effects of MA exposure in the context of an infectious agent, U937 macrophages were exposed to various combinations of MA and bacterial lipopolysaccharide (LPS). Treatment with MA alone caused significant increases in the levels of TNF-α, while treatment with both MA and LPS resulted in significant increases in TNF-α, IL-1ß and the chemokine IL-8. The increases in cytokine or chemokine levels seen when cells were treated with both LPS and MA were generally greater than those increases observed when cells were treated with only LPS. Treatment with chemical inhibitors demonstrated that the signal transduction pathways including NF-kB, MAPK, and PI3-Akt were involved in mediating the increased inflammatory response. As discussed in the paper, these pathways appear to be utilized by both MA and LPS, in the induction of these inflammatory mediators. Since these pathways are involved in the induction of inflammation in response to other pathogens, this suggests that MA-exacerbated inflammation may be a common feature of infectious disease in MA abusers.

Cocaine and HIV-1 interplay in CNS: cellular and molecular mechanisms.

Although antiretrovirals are the mainstay of therapy against HIV infection, neurological complications associated with the virus continue to hamper quality of life of the infected individuals. Drugs of abuse in the infected individuals further fuel the epidemic. Epidemiological studies have demonstrated that abuse of cocaine resulted in acceleration of HIV infection and the progression of NeuroAIDS. Cocaine has not only been shown to play a crucial role in promoting virus replication, but also has diverse but often deleterious effects on various cell types of the CNS. In the neuronal system, cocaine exposure results in neuronal toxicity and also potentiates gp120-induced neurotoxicity. In the astroglia and microglia, cocaine exposure leads to up-regulation of pro-inflammatory mediators such as cytokines and chemokines. These in turn, can lead to neuroinflammation and transmission of toxic responses to the neurons. Additionally, cocaine exposure can also lead to leakiness of the blood-brain barrier that manifests as enhanced transmigraiton of leukocytes/monocytes into the CNS. Both in vitro and in vivo studies have provided valuable tools in exploring the role of cocaine in mediating HIV-associated neuropathogenesis. This review summarizes previous studies on the mechanism(s) underlying the interplay of cocaine and HIV as it relates to the CNS.

Proline improves copper tolerance in chickpea (Cicer arietinum).

The present study suggests the involvement of proline in copper tolerance of four genotypes of Cicer arietinum (chickpea). Based on the data of tolerance index and lipid peroxidation, the order for copper tolerance was as follows: RSG 888 > CSG 144 > CSG 104 > RSG 44 in the selected genotypes. The basis of differential copper tolerance in chickpea genotypes was characterized by analyzing, antioxidant enzymes (superoxide dismutase, ascorbated peroxidase and catalase), phytochelatins, copper uptake, and proline accumulation. Chickpea genotypes showed stimulated superoxide dismutase activity at all tested concentrations of copper, but H(2)O(2) decomposing enzymes especially; ascorbate peroxidase did not increase with 25 and 50 microM copper treatments. Catalase activity, however, increased at lower copper concentrations but failed to stimulate at 50 microM copper. Such divergence in responses of these enzymes minimizes their importance in protecting chickpea against copper stress. The sensitive genotypes showed greater enhancement of phytochelatins than that of tolerant genotypes. Hence, the possibility of phytochelatins in improving copper tolerance in the test plant is also excluded. Interestingly, the order of proline accumulation in the chickpea genotypes (RSG 888 > CSG 144 > CSG 104 > RSG 44) was exactly similar to the order of copper tolerance. Based on hyperaccumulation of proline in tolerant genotype (RSG 44) and the reduction and improvement of lipid peroxidation and tolerance index, respectively, by proline pretreatment, we conclude that hyperaccumulation of proline improves the copper tolerance in chickpea.