Half metallicity in a zigzag double-walled nanotube nanodot : an ab initio prediction

Ab initio density functional calculations were performed to study finite-length zigzag (7, 0) @ (16, 0) double-walled carbon nanotubes (DWCNTs) with H-termination at the open ends. We find that such a DWCNT nanodot displays a very large magnetic moment at the zigzag edges and the ground state displays symmetric anti-ferromagnetic coupling. When an external electric field is applied along the direction of tube axis, a gap is opened for one spin channel, whereas another spin channel remains metallic, i.e. half metallicity occurs. Our results suggest an important new avenue for the development of CNT-based spintronic materials with enhanced properties. © 2008 Elsevier B.V. All rights reserved.

Dots versus antidots : computational exploration of structure, magnetism, and half-metallicity in boron-nitride nanostructures

Triangle-shaped nanohole, nanodot, and lattice antidot structures in hexagonal boron-nitride (h-BN) monolayer sheets are characterized with density functional theory calculations utilizing the local spin density approximation. We find that such structures may exhibit very large magnetic moments and associated spin splitting. N-terminated nanodots and antidots show strong spin anisotropy around the Fermi level, that is, half-metallicity. While B-terminated nanodots are shown to lack magnetism due to edge reconstruction, B-terminated nanoholes can retain magnetic character due to the enhanced structural stability of the surrounding two-dimensional matrix. In spite of significant lattice contraction due to the presence of multiple holes, antidot super lattices are predicted to be stable, exhibiting amplified magnetism as well as greatly enhanced half-metallicity. Collectively, the results indicate new opportunities for designing h-BN-based nanoscale devices with potential applications in the areas of spintronics, light emission, and photocatalysis. © 2009 American Chemical Society.

Direct current electric potential in an anisotropic half-space with vertical contact containing a conductive 3D body

Detailed studies of anomalous conductors in otherwise homogeneous media have been modelled. Vertical contacts form common geometries in galvanic studies when describing geological formations with different electrical conductivities on either side. However, previous studies of vertical discontinuities have been mainly concerned with isotropic environments. In this paper, we deal with the effect on the electric potentials, such as mise-`a-la-masse anomalies, due to a conductor near a vertical contact between two anisotropic regions. We also demonstrate the interactive effects when the conductive body is placed across the vertical contact. This problem is normally very difficult to solve by the traditional numerical methods. The integral equations for the electric potential in anisotropic half-spaces are established. Green’s function is obtained using the reflection and transmission image method in which five images are needed to fit the boundary conditions on the vertical interface and the air-earth surface. The effects of the anisotropy of the environments and the conductive body on the electric potential are illustrated with the aid of several numerical examples.

Enough energy to get half way to the moon

A proposal to abandon Melbourne's Supreme Court for a new high-tech facility prompted quite an outcry of dismay when it was reported in the Melbourne press earlier this year, and has highlighted sustainability issues in relation to heritage buildings in Victoria.

Half the burden of fragility fractures in the community occur in women without osteoporosis. When is fracture prevention cost-effective?

To determine the age- and BMD-specific burden of fractures in the community and the cost-effectiveness of targeted drug therapy, we studied a demographically well-categorized population with a single main health provider. Of 1224 women over 50 years of age sustaining fractures during 2 years, the distribution of all fractures was 11%, 20%, 33%, and 36% in those aged 50–59, 60–69, 70–79, and 80+ years, respectively. Osteoporosis (T score < −2.5) was present in 20%, 46%, 59%, and 69% in the respective age groups. Based on this sample and census data for the whole country, treating all women over 50 years of age in Australia with a drug that halves fracture risk in osteoporotic women and reduces fractures in those without osteoporosis by 20%, was estimated to prevent 18,000 or 36% of the 50,000 fractures per year at a total cost of $573 million (AUD). Screening using a bone mineral density of T score of −2.5 as a cutoff, misses 80%, 54%, 41%, and 31% of fractures in women in the respective age groups. An analysis of cost per averted fracture by age group suggests that treating women in the 50- to 59-year age group with osteoporosis alone costs $156,400 per averted fracture. However, in women aged over 80 years, the cost per averted fracture is $28,500. We infer that treating all women over 50 years of age is not feasible. Using osteoporosis and age (>60 years) as criteria for intervention reduces the population burden of fractures by 28% and is cost-effective but solutions to the prevention of the remaining 72% of fragility fractures remain unavailable.