3,745 research outputs found
Unusual structural tuning of magnetism in cuprate perovskites
Understanding the structural underpinnings of magnetism is of great
fundamental and practical interest. Se_{1-x}Te_{x}CuO_{3} alloys are model
systems for the study of this question, as composition-induced structural
changes control their magnetic interactions. Our work reveals that this
structural tuning is associated with the position of the supposedly dummy atoms
Se and Te relative to the super-exchange (SE) Cu--O--Cu paths, and not with the
SE angles as previously thought. We use density functional theory,
tight-binding, and exact diagonalization methods to unveil the cause of this
surprising effect and hint at new ways of engineering magnetic interactions in
solids.Comment: 4 pages, with 4 postscript figures embedded. Uses REVTEX4 and
graphicx macro
Metal nanoring and tube formation on carbon nanotubes
The structural and electronic properties of aluminum covered single wall
carbon nanotubes (SWNT) are studied from first-principles for a large number of
coverage. Aluminum-aluminum interaction that is stronger than aluminum-tube
interaction, prevents uniform metal coverage, and hence gives rise to the
clustering. However, a stable aluminum ring and aluminum nanotube with well
defined patterns can also form around the semiconducting SWNT and lead to
metallization. The persistent current in the Al nanoring is discussed to show
that a high magnetic field can be induced at the center of SWNT.Comment: Submitted to Physical Review
Changes of micronutrients, dry weight and plant development in canola (Brassica napus L.) cultivars under salt stress
This study was carried out to determine the effects of salt stress on the growth, dry weights and micronutrient contents of canola (Brassica napus L.) cultivars grown in greenhouse conditions. 12 canola cultivars (Marinca, Kosa, Spok, Semu DNK207 NA, Tower, Liraspa, Star, Tobin, Helios, Semu 209/81, Regent and Lirawell) were exposed to salinity treatments (150 mM NaCl and control). Shoot, leaf and root dry weights of all the cultivars at 45-day-old plants were determined. Micronutrient contents (Fe, Mn, Cu and Zn) of the leaves, stems and roots were also analyzed. Salinity stress negatively affected the canola cultivars and the extent of effects varied depending on the salt tolerance of the cultivars. Generally, salinity reduced the plant growth and dry weights. Fe, Mn, Cu and Zn concentrations were high in the roots when compared with those in the leaves and shoots in the salt applied samples. It was observed that, micronutrient contents showed some variation in the different plant parts of the canola cultivars as a result of salt applications to the growing media. Iron (Fe), manganese (Mn) and copper (Cu) content increased in all the plant parts with salt applications except for some cultivars. On the other hand, when mean data of the cultivars were considered, it could be said that zinc (Zn) content of the leaves was not significantly affected by the salt stress.Key words: Canola, Brassica napus, dry weight, micronutrient accumulation, salt stress
Effect of salinity stress on plant fresh weight and nutrient composition of some Canola (Brassica napus L.) cultivars
Soil salinity is a major limitation to crop production in many areas of the world. A pot experiment was carried out with rapeseed cultivars in order to investigate the effects of salinity stress on plant development and nutrient composition. For the salinity studies, 150 mM NaCl concentration was applied to12 rapseed cultivars (Marinca, Kosa, Spok, Semu DNK207 NA, Tower, Liraspa, Star, Tobin, Helios, Semu 209/81, Regent and Lirawell) under the greenhouse conditions. All the cultivars were harvested after 45 days from planting. Green plants parts were weighted. Harvested rapeseed plants were separated into root, shoot and leaf parts for nutrient (K+, Na+, K+/Na+, Ca2+ and Cl-) analysis. As shown in this study, salinity stress affected negatively all the canola cultivars investigated. Generally, salinity reduced the green partsâ weight. K+, Ca2+ and K+/Na+ contents in plants decreased by salt stress, but Na+ and Cl- content in the roots, shoots and leaves of all the cultivars significantly increased. In the salt treatment, the K+ and Ca2+ concentrations were the highest in the leaf samples as compared to root and shoot samples. Furthermore, the highest concentration of Na+ and Cl- was observed in the leaf and shoot. Under salinity, Regent and Lirawell cultivars retained the highest K+ and Ca2+ content in leaves, with respect to the K+ content. The effect of NaCl treatment on the canola cultivarsâ growth was not considerable.Key words: Canola cultivars, green plant parts, nutrient content, salt stress
Exceptional CO2 capture in a hierarchically porous carbon with simultaneous high surface area and pore volume
A new type of hierarchically porous carbon (HPC) structures of simultaneously high surface area and high pore volume has been synthesised from carefully controlled carbonization of in-house optimised metalâorganic frameworks (MOFs). Changes in synthesis conditions lead to millimetre-sized MOF-5 crystals in a high yield. Subsequent carbonization of the MOFs yield HPCs with simultaneously high surface area, up to 2734 m2 gâ1, and exceptionally high total pore volume, up to 5.53 cm3 gâ1. In the HPCs, micropores are mostly retained and meso- and macro- pores are generated from defects in the individual crystals, which is made possible by structural inheritance from the MOF precursor. The resulting HPCs show a significant amount of CO2 adsorption, over 27 mmol gâ1 (119 wt%) at 30 bar and 27 °C, which is one of the highest values reported in the literature for porous carbons. The findings are comparatively analysed with the literature. The results show great potential for the development of high capacity carbon-based sorbents for effective pre-combustion CO2 capture and other gas and energy storage applications
Strong short-range magnetic order in a frustrated FCC lattice and its possible role in the iron structural transformation
We investigate magnetic properties of a frustrated Heisenberg antiferromagnet
with a face-centered cubic (FCC) lattice and exchange interactions between the
nearest- and next-nearest neighbours, J1 and J2. In a collinear phase with the
wave vector Q = (pi,pi,pi) the equations of the self-consistent spin-wave
theory for the sublattice magnetization and the average short range order
parameter are obtained and numerically solved. The dependence of the Neel
temperature T_N on the ratio J2/J1 is obtained. It is shown, that at strong
enough frustration there is a wide temperature region above T_N with strong
short range magnetic order. Application of this result to description of
structural phase transition between alpha and gamma-phase of Fe is considered
Multi-phonon scattering and Ti-induced hydrogen dynamics in sodium alanate
We use ab initio methods and neutron inelastic scattering (NIS) to study the
structure, energetics, and dynamics of pure and Ti-doped sodium alanate
(NaAlH_4), focusing on the possibility of substitutional Ti doping. The NIS
spectrum is found to exhibit surprisingly strong and sharp two-phonon features.
The calculations reveal that substitutional Ti doping is energetically
possible. Ti prefers to substitute for Na and is a powerful hydrogen attractor
that facilitates multiple Al--H bond breaking. Our results hint at new ways of
improving the hydrogen dynamics and storage capacity of the alanates.Comment: 5 pages, with 4 postscript figures embedded. Uses REVTEX4 and
graphicx macro
- âŠ