Thermochemistry of Alane Complexes for Hydrogen Storage: A Theoretical and Experimental Investigation.

Knowledge of the relative stabilities of alane (AlH(3)) complexes with electron donors is essential for identifying hydrogen storage materials for vehicular applications that can be regenerated by off-board methods; however, almost no thermodynamic data are available to make this assessment. To fill this gap, we employed the G4(MP2) method to determine heats of formation, entropies, and Gibbs free energies of formation for 38 alane complexes with NH(3-n)R(n) (R = Me, Et; n = 0-3), pyridine, pyrazine, triethylenediamine (TEDA), quinuclidine, OH(2-n)R(n) (R = Me, Et; n = 0-2), dioxane, and tetrahydrofuran (THF). Monomer, bis, and selected dimer complex geometries were considered. Using these data, we computed the thermodynamics of the key formation and dehydrogenation reactions that would occur during hydrogen delivery and alane regeneration, from which trends in complex stability were identified. These predictions were tested by synthesizing six amine-alane complexes involving trimethylamine, triethylamine, dimethylethylamine, TEDA, quinuclidine, and hexamine and obtaining upper limits of ΔG° for their formation from metallic aluminum. Combining these computational and experimental results, we establish a criterion for complex stability relevant to hydrogen storage that can be used to assess potential ligands prior to attempting synthesis of the alane complex. On the basis of this, we conclude that only a subset of the tertiary amine complexes considered and none of the ether complexes can be successfully formed by direct reaction with aluminum and regenerated in an alane-based hydrogen storage system

X-ray absorption study of Ti-activated sodium aluminum hydride

Ti K-edge x-ray absorption near edge spectroscopy (XANES) was used to explore the Ti valence and coordination in Ti-activated sodium alanate. An empirical relationship was established between the Ti valence and the Ti K-edge onset based on a set of standards. This relationship was used to estimate oxidation states of the titanium catalyst in 2 mol% and 4 mol% Ti-doped NaAlH4. These results demonstrate that the formal titanium valence is zero in doped sodium alanate and nearly invariant during hydrogen cycling. A qualitative comparison of the edge fine structure suggests that the Ti is present on the surface in the form of amorphous TiAl3.Comment: 3 pages, 4 figures, submitted to Appl. Phys. Let

Thermochemistry of Alane Complexes for Hydrogen Storage: A Theoretical and Experimental Comparison

Knowledge of the relative stabilities of alane (AlH3) complexes with electron donors is essential for identifying hydrogen storage materials for vehicular applications that can be regenerated by off-board methods; however, almost no thermodynamic data are available to make this assessment. To fill this gap, we employed the G4(MP2) method to determine heats of formation, entropies, and Gibbs free energies of formation for thirty-eight alane complexes with NH3-nRn (R = Me, Et; n = 0-3), pyridine, pyrazine, triethylenediamine (TEDA), quinuclidine, OH2-nRn (R = Me, Et; n = 0-2), dioxane, and tetrahydrofuran (THF). Monomer, bis, and selected dimer complex geometries were considered. Using these data, we computed the thermodynamics of the key formation and dehydrogenation reactions that would occur during hydrogen delivery and alane regeneration, from which trends in complex stability were identified. These predictions were tested by synthesizing six amine-alane complexes involving trimethylamine, triethylamine, dimethylethylamine, TEDA, quinuclidine, and hexamine, and obtaining upper limits of delta G for their formation from metallic aluminum. Combining these computational and experimental results, we establish a criterion for complex stability relevant to hydrogen storage that can be used to assess potential ligands prior to attempting synthesis of the alane complex. Based on this, we conclude that only a subset of the tertiary amine complexes considered and none of the ether complexes can be successfully formed by direct reaction with aluminum and regenerated in an alane-based hydrogen storage system.Comment: Accepted by the Journal of Physical Chemistry

Convergence of the Generalized Volume Averaging Method on a Convection-Diffusion Problem: A Spectral Perspective

A mixed formulation is proposed and analyzed mathematically for coupled convection-diffusion in heterogeneous medias. Transfer in solid parts driven by pure diffusion is coupled with convection-diffusion transfer in fluid parts. This study is carried out for translation-invariant geometries (general infinite cylinders) and unidirectional flows. This formulation brings to the fore a new convection-diffusion operator, the properties of which are mathematically studied: its symmetry is first shown using a suitable scalar product. It is proved to be self-adjoint with compact resolvent on a simple Hilbert space. Its spectrum is characterized as being composed of a double set of eigenvalues: one converging towards −∞ and the other towards +∞, thus resulting in a nonsectorial operator. The decomposition of the convection-diffusion problem into a generalized eigenvalue problem permits the reduction of the original three-dimensional problem into a two-dimensional one. Despite the operator being nonsectorial, a complete solution on the infinite cylinder, associated to a step change of the wall temperature at the origin, is exhibited with the help of the operator’s two sets of eigenvalues/eigenfunctions. On the computational point of view, a mixed variational formulation is naturally associated to the eigenvalue problem. Numerical illustrations are provided for axisymmetrical situations, the convergence of which is found to be consistent with the numerical discretization

Does the absence of a supportive family environment influence the outcome of a universal intervention for the prevention of depression?

To date, universal, school-based interventions have produced limited success in the long-term prevention of depression in young people. This paper examines whether family relationship support moderates the outcomes of a universal, school-based preventive intervention for depression in adolescents. It reports a secondary analysis of data from the beyondblue schools research initiative. Twenty-five matched pairs of secondary schools were randomly assigned to an intervention or control condition (N = 5633 Grade 8 students). The multi-component, school-based intervention was implemented over a 3-year period, with 2 years of follow-up in Grades 11 and 12. For those available at follow-up, small but significantly greater reductions in depressive and anxiety symptoms and improvements in emotional wellbeing were found over time for the intervention group compared to the control among those who experienced low family relationship support in Grade 8. For those who did not experience low family relationship support in Grade 8, no significant effects of the invention were found over the control condition. This pattern of results was also found for the intent-to-treat sample for measures of depression and anxiety. Previous research may have overlooked important moderating variables that influence the outcome of universal approaches to the prevention of depression. The findings raise issues of the relative costs and benefits of universal versus targeted approaches to the prevention of depression

An environmental threshold for degree of phosphorus saturation in sandy soils.

ABSTRACT soil is completely saturated with P There is critical need for a practical indicator to assess the potential by local conditions and generally reflects local surface for phosphorus (P) movement from a given site to surface waters, water criteria for P. The Netherlands has established a either via surface runoff or subsurface drainage. The degree of phosphorus saturation (DPS), which relates a measure of P already adwater quality goal for ground water of 0.15 mg total P sorbed by a soil to its P adsorption capacity, could be a good indicator , and their studies have shown that leaching of P of that soil's P release capability. Our primary objective was to find could occur especially from manure-contaminated soils a suitable analytical protocol for determining DPS and to examine S andy soils in the Suwannee River basin of northern phorus (WSP) (assessed using either deionized water Florida have little ability to adsorb P, and yet many or 0.01 M CaCl 2 ) and each method of DPS calculation; dairies in the Suwannee River basin routinely apply and (iv) examine the possibility of defining a threshold P-rich lagoon effluent onto permanent sprayfields for DPS value for Florida's sandy soils. waste disposal and nutrient recycling. Increased P loading to these sites may lead to P loss through runoff and subsurface drainage, contributing to surface water MATERIALS AND METHODS quality degradation. Improved P management of these Study Site fields requires the evaluation of soil P concentrations The Suwannee River basin was selected for this study. Many relative to the soil's ability to adsorb P. of the dairies found in the middle Suwannee River basin, Recent studies suggest that the DPS, which relates proximal to the Suwannee and Santa Fe Rivers, are situated ammonium oxalate-extractable P to the sum of oxalateatop a geomorphic zone classified as the Chiefland Limestone extractable Fe and Al (DPS Ox ), is a good indicator of a Plain. The upper surface of the aquifer system is relatively soil's potential to release P (Hooda et al., 2000). This close to the surface and layers above it are thin and unconfined concept was first introduced in the Netherlands, where (Andrews, 1992). The surficial aquifer system is largely reit has been shown that P concentrations in the soil solucharged by rainfall that percolates downward through the tion can exceed a critical concentration well before the loose surficial clastic sediments. Water naturally discharges from the aquifer through evaporation, transpiration, spring flow, and downward seepage into the underlying Floridan aqui

The pleasures and perils of inheritance

Facing death, reflecting on one’s legacies (material and ethical, personal and political) and the legal and interpersonal attempts to resolve or prevent inheritance conflicts, all bring to the fore constructions of memory and identity, intergenerational relations, and the complexities of doing and undoing family and kinship. Consequently, drawing attention to inheritance, keeping sight of it, and bringing it into play is a useful piece of the puzzle of ageing across a range of disciplines and this article provides an overview of some of the key themes in this emerging field

Work done in the margins:A comparative study of mental health literacy in pre-service teacher education in Australia and in Scotland

Ensuring pre-service teachers have strong mental health literacy is vital for progress towards an inclusive, effective education system; yet little is known about how pre-service teachers are prepared for practice with school students who present with poor mental health. The original, internationally comparative small-scale (N = 24) qualitative study reported here compared current mental health literacy provision to pre-service teacher education students in Scotland and Australia. Semi-structured telephone interviews with teacher educators who delivered mental health content divulged highly variable, often ad-hoc mental health literacy provision; a concern, given the prevalence of poor mental health affecting children and young people in schools. Thematic data analysis revealed striking commonalities among issues raised by participants from both countries, highlighting the need for urgent improvement in the provision of mental health literacy to pre-service teachers. Results suggest the possibility of strategically developing a joint Australian-Scottish mental health component suitable for delivery in both countries