In a recent work M.J. Rayson, P.R. Briddon, Phys. Rev. B 80 (2009) 205104 an implementation of filter diagonalisation with localisation constraints was shown to provide an accurate and highly ...efficient method to solve the Kohn–Sham equations using a primitive Gaussian basis for systems containing several thousand electrons. In this work, an alternative filtration algorithm is proposed, based on a rational approximation to the filtration function, to replace the kernel of this algorithm. This approach is considerably faster than the diagonalisation approach used previously and also its performance is largely independent of the filtration
temperature, aiding a more flexible approach to the construction of filtered basis sets.
Display omitted
•Solid products of the CO2 mineralization were characterized as a function of time.•A sampling technique was applied to track changes in the carbonation products.•The formation of ...hydromagnesite prior to magnesite was shown experimentally.•Transformation of hydromagnesite to magnesite strongly depends on reaction T and P.
Mineral carbonation has the potential to store billions of tonnes of CO2 safely and permanently. Enhancement of the kinetics of the formation of magnesium carbonate from magnesium-bearing silicate minerals has been the subject of numerous research studies. However, significant progress is yet to be achieved. This is, in part, due to a lack of understanding of the mechanism of the formation of magnesite in the presence of additives and under mineral carbonation conditions. In this work, an in-depth study was performed to investigate the precipitation of magnesium carbonate during single step high pressure, high temperature carbonation of thermally activated serpentine in an aqueous bicarbonate solution. Slurry samples were obtained throughout the duration of the carbonation experiments, enabling analysis of both the aqueous and solid compositions over time, providing insight into the reaction mechanism. Additionally, the effect of operating temperature on the formation of various magnesium carbonate species was examined. TGA-MS, in combination with XRD and SEM, confirmed the formation of hydromagnesite in the absence of carbon dioxide (CO2) during the reactor heat up period, owing to a reaction with the sodium bicarbonate (NaHCO3) carrier solution. Hydromagnesite was transformed to magnesite over time, with the rate of this phase transformation highly dependent on the reaction temperature. At 185°C all hydromagnesite converted to magnesite in a few minutes whereas at 120°C even after 90min hydromagnesite remained in the reactor. PHREEQC thermodynamic software was used to assess the observed formation of carbonate species. The model prediction was consistent with the experimental results obtained in this work.
Eigenproblems resulting from the use of localised basis functions (typically Gaussian or Slater type orbitals) in density functional electronic-structure calculations are often solved using direct ...linear algebra. A full implementation is presented built around an iterative method known as ‘residual minimisation—direct inversion of the iterative subspace’ (RM-DIIS) to be used to solve many similar eigenproblems in a self-consistency cycle. The method is more efficient than direct methods and exhibits superior scaling on parallel supercomputers.
A rapid and reproducible method to determine botanical composition of forage is an ecological and economic goal for range animal ecologists. Multidimensional fluorometry previously demonstrated the ...possibility of a unique optical approach for accurately determining species composition of clipped and digested plant materials. Fluorometry may be used to detect toxic plants in standing crop as well as diets by using electronic transitions in chemical structures at wavelengths between 370 and 580 nm. Grass hay (genus Pleuraphis) and 6 clipped forbs (4 species of Astragalus and 2 species of Oxytropis) were examined. The resulting spectral signatures were evaluated for differences in the blue and green regions of the visible spectrum using Principal Component Analysis (PCA). This represents the first published data using chemometrics to differentiate among fluorophores from these plant extracts. It was possible to distinguish between the grass and forbs and among forbs. Further research will be required to evaluate these same plant species in mixed diets and fecal samples.
A prominent hydrogen-related infrared absorption peak seen in many types of diamonds at 3107 cm(-1) has been the subject of investigation for many years. It is present in natural type-Ia material and ...can be introduced by heat-treating synthetic or CVD diamond. Based upon the most recent experimental data, it is thought that the defect giving rise to this vibrational mode is vacancy-related and is likely to contain nitrogen. Using first-principles simulations we present a VN3H model for the originating centre that simultaneously satisfies the different experimental observations including the strain response.
Multiple nuclei sharing a common cytoplasm are found in diverse tissues, organisms, and diseases. Yet, multinucleation remains a poorly understood biological property. Cytoplasm sharing invariably ...involves plasma membrane breaches. In contrast, we discovered cytoplasm sharing without membrane breaching in highly resorptive
rectal papillae. During a six-hour developmental window, 100 individual papillar cells assemble a multinucleate cytoplasm, allowing passage of proteins of at least 62 kDa throughout papillar tissue. Papillar cytoplasm sharing does not employ canonical mechanisms such as incomplete cytokinesis or muscle fusion pore regulators. Instead, sharing requires gap junction proteins (normally associated with transport of molecules < 1 kDa), which are positioned by membrane remodeling GTPases. Our work reveals a new role for apical membrane remodeling in converting a multicellular epithelium into a giant multinucleate cytoplasm.
•The dissolution kinetics of roasted lizardite in acid buffer solutions were studied.•An initial rapid liberation of Mg2+ followed by a very slow extraction was observed.•The extent of extraction of ...Mg depends on the particle size and solution pH.•The crackling core model (CCM) was successfully fitted to the experimental data.•Amorphous Si re-precipitation at high S/L and pH 6.1 was demonstrated.
The rate-determining step in the aqueous carbonation of serpentine minerals is the dissolution of Mg from serpentine. The dissolution rate of minerals largely depends on the pH of the solution and the size of serpentine particles. In the present work, an experimental method has been developed to study the dissolution rate of heat activated serpentine (lizardite polymorph) in a wide range of pH, solid to liquid ratio and particle size at room temperature. The results allowed us to determine the effect of these variables on the dissolution kinetics of heat activated lizardite, which represents crucial kinetic data for accurately modelling the carbonation rates of serpentinite. Additionally, amorphous Si re-precipitation at high solid to liquid (S/L) ratio and pH 6.1 was demonstrated. These provide essential data for the design and optimisation of industrial mineral carbonation processes. For the first time, the crackling core model (CCM) was applied to model the dissolution kinetics of heat activated lizardite in acidic solutions. Applying the CCM model to a wide range of particle sizes provides useful information on the mechanism of the dissolution of heat activated lizardite and the range of particle size for which the assumptions of the model are valid. Characterising serpentine particles leached under different conditions, along with analysing model parameters, provided a new insight into the mechanism of the dissolution of heat activated lizardite.
AA-stacked graphite and closely related structures, where carbon atoms are located in registry in adjacent graphene layers, are a feature of graphitic systems including twisted and folded bilayer ...graphene, and turbostratic graphite. We present the results of ab initio density functional theory calculations performed to investigate the complexes that are formed from the binding of vacancy defects across neighbouring layers in AA-stacked bilayers. As with AB stacking, the carbon atoms surrounding lattice vacancies can form interlayer structures with sp2 bonding that are lower in energy than in-plane reconstructions. The sp2 interlayer bonding of adjacent multivacancy defects in registry creates a type of stable sp2 bonded 'wormhole' or tunnel defect between the layers. We also identify a new class of 'mezzanine' structure characterised by sp3 interlayer bonding, resembling a prismatic vacancy loop. The V6 hexavacancy variant, where six sp3 carbon atoms sit midway between two carbon layers and bond to both, is substantially more stable than any other vacancy aggregate in AA-stacked layers. Our focus is on vacancy generation and aggregation in the absence of extreme temperatures or intense beams.
We have investigated the seasonal evolution of the internal tide using a yearlong mooring record in the Browse Basin on the Australian North‐West Shelf. Using a modal harmonic‐decomposition ...technique, we studied the modulation of the semi‐diurnal kinetic energy, potential energy, energy flux, group velocity and sea surface height anomaly for different internal wave modes. A very coherent and energetic, locally generated internal tide dominated the mooring record during spring‐tide periods. Relationships amongst the wave variables suggest that the interaction of multiple waves formed a standing wave pattern. To assist in explaining the seasonal variability of this standing wave pattern, we used an analytical model of internal wave generation and propagation in a double‐shelf system, representative of the area, to highlight the effects of changes in the stratification and barotropic forcing. A comparison of the low‐mode wave energy indicated that the analytical solution overestimated the observed wave energy by a factor of two and failed to detect an apparent seasonal shift in the conversion rate. We discuss potential mechanisms for this discrepancy.
Key Points
Standing internal tide formed between a double shelf break
Time‐varying stratification modifies the standing wave pattern
Analytical model overpredicts wave energy by a factor of 2
PDF
