Electronic band structure and carrier effective mass in calcium aluminates

First-principles electronic band structure investigations of five compounds of the CaO-Al2O3 family, 3CaO.Al2O3, 12CaO.7Al2O3, CaO.Al2O3, CaO.2Al2O3 and CaO.6Al2O3, as well as CaO and alpha-, theta- and kappa-Al2O3 are performed. We find that the conduction band in the complex oxides is formed from the oxygen antibonding p-states and, although the band gap in Al2O3 is almost twice larger than in CaO, the s-states of both cations. Such a hybrid nature of the conduction band leads to isotropic electron effective masses which are nearly the same for all compounds investigated. This insensitivity of the effective mass to variations in the composition and structure suggests that upon a proper degenerate doping, both amorphous and crystalline phases of the materials will possess mobile extra electrons

The Shadow Side of Teaching Classroom as Organization

Classroom as organization (CAO) is an approach at the extreme end of an experiential learning intensity continuum (Sleeth & Brown, 1984). While proponents suggest they would never go back to a teacher-centered classroom, CAO has not become widely adopted since its initial description by Cohen (1976). We argue this is, in part, because of shadow elements that may discourage faculty in both initial adoption and persistence in the journey from novice to master. This article reports the authors reflexive process related to the shadow elements they encountered as early adopters of the CAO methodology. The paper begins with a brief background on CAO, followed by a discussion of shadow elements that manifest at the student and faculty levels. We include our recommendations for practice

Outsourcing business services and the role of central administrative offices

In this paper, I study whether there is any evidence that the market scale surrounding a central administrative office (CAO), which includes corporate headquarters, influences a firm's cost-effectiveness in procuring business services. By linking plant-level data from the 1992 Annual Survey of Manufactures with CAO information from the Survey of Auxiliary Establishments, I examine manufacturing plants' practice of outsourcing services in relation to the size of the local service market surrounding the plant and that surrounding the plant's CAO. I found statistically significant evidence that the greater the size of local market surrounding a CAO, the higher the plant's probability of relying on the CAO for outsourcing advertising, bookkeeping and accounting, and legal services. These results are found even after controlling for the size of the local market surrounding a plant and plant characteristics.Contracting out ; Unemployment

Enhancement of microalgae anaerobic digestion by thermo-alkaline pretreatment with lime (CaO)

The aim of this study was to evaluate for the first time the effect of a thermo-alkaline pretreatment with lime (CaO) on microalgae anaerobic digestion. The pretreatment was carried out by adding different CaO doses (4 and 10%) at different temperatures (room temperature (25 °C), 55 and 72 °C). The exposure time was 4 days for pretreatments at 25 °C, and 24 h for pretreatments at 55 and 72 °C. Following, a biochemical methane potential test was conducted with pretreated and untreated microalgae. According to the results, the pretreatment enhanced proteins solubilisation by 32.4% and carbohydrates solubilisation by 31.4% with the highest lime dose and temperature (10% CaO and 72 °C). Furthermore, anaerobic digestion kinetics were improved in all cases (from 0.08 to 0.14 day- 1 for untreated and pretreated microalgae, respectively). The maximum biochemical methane potential increase (25%) was achieved with 10% CaO at 72 °C, in accordance with the highest biomass solubilisation. Thus, lime pretreatment appears as a potential strategy to improve microalgae anaerobic digestion.Peer ReviewedPostprint (author's final draft

Oxidative coupling of methane over Ba/CaO catalysts: a comparison with Li/MgO

A comparison has been made of the behaviour in the oxidative coupling of methane of a Ba/CaO catalyst with that of a Li/MgO material. Doping of CaO with BaCO3 resulted in a catalyst which is more active at lower reaction temperatures than is BaCO3. The active oxygen entity in the case of Ba/CaO is probably an O2−2 species. Ba/CaO is more stable but less selective than is Li/MgO. The effect of residence time was studied for both Ba/CaO and Li/MgO. The direct oxidation of methyl radicals to give carbon monoxide and carbon dioxide plays a more important role in the case of Ba/CaO than is the case with Li /MgO

Energy storage for a lunar base by the reversible chemical reaction: CaO+H2O reversible reaction Ca(OH)2

A thermochemical solar energy storage concept involving the reversible reaction CaO + H2O yields Ca(OH)2 is proposed as a power system element for a lunar base. The operation and components of such a system are described. The CaO/H2O system is capable of generating electric power during both the day and night. The specific energy (energy to mass ratio) of the system was estimated to be 155 W-hr/kg. Mass of the required amount of CaO is neglected since it is obtained from lunar soil. Potential technical problems, such as reactor design and lunar soil processing, are reviewed

Highly efficient CO2 capture with simultaneous iron and CaO recycling for the iron and steel industry

An efficient CO2 capture process has been developed by integrating calcium looping (CaL) and waste recycling technologies into iron and steel production. A key advantage of such a process is that CO2 capture is accompanied by simultaneous iron and CaO recycling from waste steel slag. High-purity CaO-based CO2 sorbents, with CaO content as high as 90 wt%, were prepared easily via acid extraction of steel slag using acetic acid. The steel slag-derived CO2 sorbents exhibited better CO2 reactivity and slower (linear) deactivation than commercial CaO during calcium looping cycles. Importantly, the recycling efficiency of iron from steel slag with an acid extraction is improved significantly due to a simultaneous increase in the recovery of iron-rich materials and the iron content of the materials recovered. High-quality iron ore with iron content of 55.1–70.6% has been recovered from waste slag in this study. Although costing nearly six times as much as naturally derived CaO in the purchase of feedstock, the final cost of the steel slag-derived, CaO-based sorbent developed is compensated by the byproducts recovered, i.e., high-purity CaO, high-quality iron ore, and acetone. This could reduce the cost of the steel slag-derived CO2 sorbent to 57.7 € t−1, appreciably lower than that of the naturally derived CaO. The proposed integrated CO2 capture process using steel slag-derived, CaO-based CO2 sorbents developed appears to be cost-effective and promising for CO2 abatement from the iron and steel industry

Finite element analysis of non-isothermal multiphase porous media in dynamics

This work presents a mathematical and a numerical model for the analysis of the thermo-hydro-mechanical (THM) behavior of multiphase deformable porous materials in dynamics. The fully coupled governing equations are developed within the Hybrid Mixture Theory. To analyze the THM behavior of soil structures in the low frequency domain, e.g. under earthquake excitation, the u-p-T formulation is advocated by neglecting the relative acceleration of the fluids and their convective terms. The standard Bubnov-Galerkin method is applied to the governing equations for the spatial discretization, whereas the generalized Newmark scheme is used for the time discretization. The final non-linear and coupled system of algebraic equations is solved by the Newton method within the monolithic approach. The formulation and the implemented solution procedure are validated through the comparison with other finite element solutions or analytical solutions