Surface energy and surface proton order of the ice Ih basal and prism surfaces

Density-functional theory (DFT) is used to examine the basal and prism surfaces of ice Ih. Similar surface energies are obtained for the two surfaces; however, in each case a strong dependence of the surface energy on surface proton order is identified. This dependence, which can be as much as 50% of the absolute surface energy, is significantly larger than the bulk dependence (< 1%) on proton order, suggesting that the thermodynamic ground state of the ice surface will remain proton ordered well above the bulk order-disorder temperature of about 72 K. On the basal surface this suggestion is supported by Monte Carlo simulations with an empirical potential and solution of a 2D Ising model with nearest neighbor interactions taken from DFT. Order parameters that define the surface energy of each surface in terms of nearest neighbor interactions between dangling OH bonds (those which point out of the surface into vacuum) have been identified and are discussed. Overall, these results suggest that proton order-disorder effects have a profound impact on the stability of ice surfaces and will most likely have an effect on ice surface reactivity as well as ice crystal growth and morphology. S Supplementary data are available from stacks.iop.org/JPhysCM/22/074209/mmedia

Surface Energy and Surface Proton Order of Ice Ih

Ice Ih is comprised of orientationally disordered water molecules giving rise to positional disorder of the hydrogen atoms in the hydrogen bonded network of the lattice. Here we arrive at a first principles determination of the surface energy of ice Ih and suggest that the surface of ice is significantly more proton ordered than the bulk. We predict that the proton order-disorder transition, which occurs in the bulk at similar to 72 K, will not occur at the surface at any temperature below surface melting. An order parameter which defines the surface energy of ice Ih surfaces is also identified.

Maximum Outage Capacity in Dense Indoor Femtocell Networks with Joint Energy and Spectrum Utilization

We consider a multiple femtocell deployment in a small area which shares spectrum with the underlaid macrocell. We design a joint energy and radio spectrum scheme which aims not only for co-existence with the macrocell, but also for an energy-efficient implementation of the multi-femtocells. Particularly, aggregate energy usage on dense femtocell channels is formulated taking into account the cost of both the spectrum and energy usage. We investigate an energy-and-spectral efficient approach to balance between the two costs by varying the number of active sub-channels and their energy. The proposed scheme is addressed by deriving closed-form expressions for the interference towards the macrocell and the outage capacity. Analytically, discrete regions under which the most promising outage capacity is achieved by the same size of active sub-channels are introduced. Through a joint optimization of the sub-channels and their energy, properties can be found for the maximum outage capacity under realistic constraints. Using asymptotic and numerical analysis, it can be noticed that in a dense femtocell deployment, the optimum utilization of the energy and the spectrum to maximize the outage capacity converges towards a round-robin scheduling approach for a very small outage threshold. This is the inverse of the traditional greedy approach. © 2012 IEEE.

Recent contribution of sediments and fluids to the mantle's volatile budget

Subduction modifies the cycling of Earth's volatile elements. Fluid-rich sediments and hydrated oceanic lithosphere enter the convecting mantle at subduction zones. Some of the sediments and volatile components are released from the subducting slab, promote mantle melting and are returned to the surface by volcanism. The remainder continue into the deeper mantle. Quantification of the fate of these volatiles requires an understanding of both the nature and timing of fluid release and mantle melting(1). Here we analyse the trace element and isotopic geochemistry of fragments of upper mantle rocks that were transported to the surface by volcanic eruptions above the Batan Island subduction zone, Philippines. We find that the mantle fragments exhibit extreme disequilibrium between their U-Th-Ra isotopic ratios, which we interpret to result from the interaction of wet sediment melts and slab-derived fluids with rocks in the overlying mantle wedge. We infer that wet sediments were delivered from the slab to the mantle wedge between 8,000 and 10,000 years ago, whereas aqueous fluids were delivered separately much later. We estimate that about 625 ppm of water is retained in the wedge. A significant volume of water could therefore be delivered to the mantle transition zone at the base of the upper mantle, or even to the deeper mantle.

Scotland, Renewable Energy and the Independence Debate: Will Head or Heart Rule the Roost?

Political support for renewable energy development, especially offshore renewables, is particularly conspicuous in Scotland and is a centrepiece of SNP policy. However, this is built on something of a paradox because, put simply, without the subsidies paid by electricity consumers in the rest of the UK, the Scottish Government's ambitious targets for renewable energy would be politically unachievable. We argue in this paper that if Scotland does move towards independence, then there could be little reason for the UK to continue paying (much) of the subsidies since the resulting renewable generation would no longer contribute towards UK renewable energy targets. We suggest that the potential scenarios, and their implications, needs to be far better considered in the arguments around the Scottish constitutional position and the broader aims of UK energy policy.

Biogas reforming using renewable wind energy and induction heating

While the benefits of renewable energy are well known and used to influence government policy there are a number of problems which arise from having significant quantities of renewable energies on an electricity grid. The most notable problem stems from their intermittent nature which is often out of phase with the demands of the end users. This requires the development of either efficient energy storage systems, e.g. battery technology, compressed air storage etc. or through the creation of demand side management units which can utilise power quickly for manufacturing operations. Herein a system performing the conversion of synthetic biogas to synthesis gas using wind power and an induction heating system is shown. This approach demonstrates the feasibility of such techniques for stabilising the electricity grid while also providing a robust means of energy storage. This exemplar is also applicable to the production of hydrogen from the steam reforming of natural gas.

Complexity of concern: Social acceptance of wind energy and the inevitability of dissensus

This presentation will explore the  role that social acceptance of onshore wind can play in understanding and progressing the low carbon transition in Europe. Although this is commonly perceived as arising simply from the overall level of renewable energy generated (and ‘dirty’ energy displaced), its significance goes well beyond this as it helps us understand some of the key issues facing the electricity sector as a social-technical system.  As such it is not only a matter of delivering the necessary infrastructure, but requires the long term mediation of complex multi-governmental arrangements involving a very wide range of actors. The interests of these actors engage hugely different timescales, geographic scales of concern and rationalities that make the arena of social acceptance a cauldron of complexity, mediating between overlapping and incompatible concerns. The presentation will briefly review the nature of some of these relationships and discuss what this means for how we conceive and act on the social acceptance of wind, and what this means for the long term low carbon transition

Intelligent Computing for Sustainable Energy and Environment (ICSEE 2012)

No Abstract available

Varieties of resource nationalism in sub-Saharan Africa’s energy and minerals markets

This article examines resource nationalism in sub-Saharan Africa's energy and minerals markets. It does so by exploring economic and political developments in three cases: Nigeria as an example of a petro-state established by means of expropriation in the wake of decolonisation; South Africa, a mature mining industry shaped by its settler colonial history; and Mozambique, a new and therefore highly-dependent entrant into the league of significant natural gas producers. Extractive industries have played a controversial role in sub-Saharan Africa due in particular to the prevalence of the resource curse. Nevertheless, energy exports will continue to play an important role in fuelling economic growth and, potentially, also development as new deposits of natural gas and oil are discovered across the region. Resource nationalism has, moreover, increasingly constrained operations of the traditionally dominant Western energy companies, in particular as competition from state-owned energy companies in sub-Saharan Africa and from emerging powers such as China is increasing.

Energy and energy flux in axisymmetric slow and fast waves

Aims: We aim to calculate the kinetic, magnetic, thermal, and total energy densities and the flux of energy in axisymmetric sausage modes. The resulting equations should contain as few parameters as possible to facilitate applicability for different observations. 

Methods: The background equilibrium is a one-dimensional cylindrical flux tube model with a piecewise constant radial density profile. This enables us to use linearised magnetohydrodynamic equations to calculate the energy densities and the flux of energy for axisymmetric sausage modes. 

Results: The equations used to calculate the energy densities and the flux of energy in axisymmetric sausage modes depend on the radius of the flux tube, the equilibrium sound and Alfvén speeds, the density of the plasma, the period and phase speed of the wave, and the radial or longitudinal components of the Lagrangian displacement at the flux tube boundary. Approximate relations for limiting cases of propagating slow and fast sausage modes are also obtained. We also obtained the dispersive first-order correction term to the phase speed for both the fundamental slow body mode under coronal conditions and the slow surface mode under photospheric conditions.