1,702 research outputs found
Designing and Aligning Interprofessional Relations: Third-party ties and partnership formation in the silk industry of 18<sup>th</sup>-century Lyon
Microbial respiration, but not biomass, responded linearly to increasing light fraction organic matter input: Consequences for carbon sequestration
Rebuilding ‘lost’ soil carbon (C) is a priority in mitigating climate change and underpinning key soil functions that support ecosystem services. Microorganisms determine if fresh C input is converted into stable soil organic matter (SOM) or lost as CO2. Here we quantified if microbial biomass and respiration responded positively to addition of light fraction organic matter (LFOM, representing recent inputs of plant residue) in an infertile semi-arid agricultural soil. Field trial soil with different historical plant residue inputs [soil C content: control (tilled) = 9.6 t C ha−1 versus tilled + plant residue treatment (tilled + OM) = 18.0 t C ha−1] were incubated in the laboratory with a gradient of LFOM equivalent to 0 to 3.8 t C ha−1 (0 to 500% LFOM). Microbial biomass C significantly declined under increased rates of LFOM addition while microbial respiration increased linearly, leading to a decrease in the microbial C use efficiency. We hypothesise this was due to insufficient nutrients to form new microbial biomass as LFOM input increased the ratio of C to nitrogen, phosphorus and sulphur of soil. Increased CO2 efflux but constrained microbial growth in response to LFOM input demonstrated the difficulty for C storage in this environment
A magnetization equation for non-equilibrium spin systems
A magnetization equation for a system of spins evolving non-adiabatically and
out of equilibrium is derived without specifying the internal interactions. For
relaxation processes, this equation provides a general form of magnetization
damping. A special case of the spin-spin exchange interaction is considered.Comment: 9 pages, LATEX file; talk given at Theory Canada III, June 13-16,
2007, University of Alberta, Edmonton; to appear in Canadian Journal of
Physic
Entanglement in quantum computers described by the XXZ model with defects
We investigate how to generate maximally entangled states in systems
characterized by the Hamiltonian of the XXZ model with defects. Some proposed
quantum computers are described by such model. We show how the defects can be
used to obtain EPR states and W states when one or two excitations are
considered.Comment: 4 pages, 1 figur
Occlusion of Sulfate-based Diblock Copolymer Nanoparticles within Calcite: Effect of Varying the Surface Density of Anionic Stabilizer Chains
Polymerization-induced self-assembly (PISA) offers a highly versatile and efficient route to a wide range of organic nanoparticles. In this article, we demonstrate for the first time that poly(ammonium 2-sulfatoethyl methacrylate)-poly(benzyl methacrylate) [PSEM–PBzMA] diblock copolymer nanoparticles can be prepared with either a high or low PSEM stabilizer surface density using either RAFT dispersion polymerization in a 2:1 v/v ethanol/water mixture or RAFT aqueous emulsion polymerization, respectively. We then use these model nanoparticles to gain new insight into a key topic in materials chemistry: the occlusion of organic additives into inorganic crystals. Substantial differences are observed for the extent of occlusion of these two types of anionic nanoparticles into calcite (CaCO3), which serves as a suitable model host crystal. A low PSEM stabilizer surface density leads to uniform nanoparticle occlusion within calcite at up to 7.5% w/w (16% v/v), while minimal occlusion occurs when using nanoparticles with a high PSEM stabilizer surface density. This counter-intuitive observation suggests that an optimum anionic surface density is required for efficient occlusion, which provides a hitherto unexpected design rule for the incorporation of nanoparticles within crystals
Structure of Si(114) determined by global optimization methods
In this article we report the results of global structural optimization of
the Si(114) surface, which is a stable high-index orientation of silicon. We
use two independent procedures recently developed for the determination of
surface reconstructions, the parallel-tempering Monte Carlo method and the
genetic algorithm. These procedures, coupled with the use of a highly-optimized
interatomic potential for silicon, lead to finding a set of possible models for
Si(114), whose energies are recalculated with ab-initio density functional
methods. The most stable structure obtained here without experimental input
coincides with the structure determined from scanning tunneling microscopy
experiments and density functional calculations by Erwin, Baski and Whitman
[Phys. Rev. Lett. 77, 687 (1996)].Comment: 19 pages, 5 figure
Finding the reconstructions of semiconductor surfaces via a genetic algorithm
In this article we show that the reconstructions of semiconductor surfaces
can be determined using a genetic procedure. Coupled with highly optimized
interatomic potentials, the present approach represents an efficient tool for
finding and sorting good structural candidates for further electronic structure
calculations and comparison with scanning tunnelling microscope (STM) images.
We illustrate the method for the case of Si(105), and build a database of
structures that includes the previously found low-energy models, as well as a
number of novel configurations.Comment: 4 figures, 1 tabl
Transient elastohydrodynamic lubrication analysis of a novel metal-on-metal hip prosthesis with a non-spherical femoral bearing surface
Effective lubrication performance of metal-on-metal hip implants only requires optimum conformity within the main loaded area, while it is advantageous to increase the clearance in the equatorial region. Such a varying clearance can be achieved by using non-spherical bearing surfaces for either acetabular or femoral components. An elastohydrodynamic lubrication model of a novel metal-on-metal hip prosthesis using a non-spherical femoral bearing surface against a spherical cup was solved under loading and motion conditions specified by ISO standard. A full numerical methodology of considering the geometric variation in the rotating non-spherical head in elastohydrodynamic lubrication solution was presented, which is applicable to all non-spherical head designs. The lubrication performance of a hip prosthesis using a specific non-spherical femoral head, Alpharabola, was analysed and compared with those of spherical bearing surfaces and a non-spherical Alpharabola cup investigated in previous studies. The sensitivity of the lubrication performance to the anteversion angle of the Alpharabola head was also investigated. Results showed that the non-spherical head introduced a large squeeze-film action and also led to a large variation in clearance within the loaded area. With the same equatorial clearance, the lubrication performance of the metal-on-metal hip prosthesis using an Alpharabola head was better than that of the conventional spherical bearings but worse than that of the metal-on-metal hip prosthesis using an Alpharabola cup. The reduction in the lubrication performance caused by the initial anteversion angle of the non-spherical head was small, compared with the improvement resulted from the non-spherical geometry
Alterations in Cortical Thickness and White Matter Integrity in Mild Cognitive Impairment Measured by Whole-Brain Cortical Thickness Mapping and Diffusion Tensor Imaging
Enhancement of pair correlation in a one-dimensional hybridization model
We propose an integrable model of one-dimensional (1D) interacting electrons
coupled with the local orbitals arrayed periodically in the chain. Since the
local orbitals are introduced in a way that double occupation is forbidden, the
model keeps the main feature of the periodic Anderson model with an interacting
host. For the attractive interaction, it is found that the local orbitals
enhance the effective mass of the Cooper-pair-like singlets and also the pair
correlation in the ground state. However, the persistent current is depressed
in this case. For the repulsive interaction case, the Hamiltonian is
non-Hermitian but allows Cooper pair solutions with small momenta, which are
induced by the hybridization between the extended state and the local orbitals.Comment: 11 page revtex, no figur
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