Anderson transition and thermal effects on electron states in amorphous silicon

I discuss the properties of electron states in amorphous Si based on large scale calculations with realistic several thousand atom models. A relatively simple model for the localized to extended (Anderson) transition is reviewed. Then, the effect of thermal disorder on localized electron states is considered. It is found that under readily accessible conditions, localized (midgap or band tail) states and their conjugate energies may fluctuate dramatically. The possible importance of non-adiabatic atomic dynamics to doped or photo-excited systems is briefly discussed.Comment: Was presented at ICAMS18, Snowbird UT, August 1999. Submitted to J. of Non-Cryst. Solid

Unsupervised classification of the northwestern European seas based on satellite altimetry data

From generating metrics representative of a wide region to saving costs by reducing the density of an observational network, the reasons to split the ocean into distinct regions are many. Traditionally, this has been done somewhat arbitrarily using the bathymetry and potentially some artificial latitude–longitude boundaries. We use an ensemble of Gaussian mixture models (GMMs, unsupervised classification) to separate the complex northwestern European coastal region into classes based on sea level variability observed by satellite altimetry. To reduce the dimensionality of the data, we perform a principal component analysis on 27 years of observations and use the spatial components as input for the GMM. The number of classes or mixture components is determined by locating the maximum of the silhouette score and by testing several models. We use an ensemble approach to increase the robustness of the classification and to allow the separation into more regions than a single GMM can achieve. We also vary the number of empirical orthogonal function (EOF) maps and show that more EOFs result in a more detailed classification. With three EOFs, the area is classified into four distinct regions delimited mainly by bathymetry. Adding more EOFs results in further subdivisions that resemble oceanic fronts. To achieve a more detailed separation, we use a model focused on smaller regions, specifically the Baltic Sea, North Sea, and the Norwegian Sea

Engineering the spin polarization of one-dimensional electrons

We present results of magneto-focusing on the controlled monitoring of spin polarization within a one-dimensional (1D) channel, and its subsequent effect on modulating the spin-orbit interaction (SOI) in a 2D GaAs electron gas. We demonstrate that electrons within a 1D channel can be partially spin polarized as the effective length of the 1D channel is varied in agreement with the theoretical prediction. Such polarized 1D electrons when injected into a 2D region result in a split in the odd-focusing peaks, whereas the even peaks remain unaffected (single peak). On the other hand, the unpolarized electrons, achieved by reducing the effective length of the 1D channel, do not affect the focusing spectrum and the odd and even peaks remain as single peaks, respectively. The split in odd-focusing peaks is evidence of direct measurement of spin polarization within a 1D channel, where each sub-peak represents the population of a particular spin state. Confirmation of the spin splitting is determined by a selective modulation of the focusing peaks due to the Zeeman energy in the presence of an in-plane magnetic field. We suggest that the SOI in the 2D regime is enhanced by a stream of polarized 1D electrons. The spatial control of spin states of injected 1D electrons and the possibility of tuning the SOI may open up a new regime of spin-engineering with application in future quantum information schemes

Environment and Rural Affairs Monitoring & Modelling Programme - ERAMMP Year 1 Report 24: Welsh national natural capital accounts - Ecosystem service accounts for woodland, farmland and freshwater habitats

This report presents 7 service accounts, containing estimates of the quantity and value of services being supplied by Welsh natural capital in woodland, farmland, and freshwater broad habitats. These services include food, water, air filtration and recreation. Farmland is the largest of these three Welsh habitats, at 1,015,693 hectares, followed by woodland at 268,588 hectares (125,117 broadleaf and 143,471 coniferous), and freshwater at 42,309 hectares. The value of the stock of Welsh natural capital in woodland, farmland, and freshwater was estimated to be approximately £30.5 billion in 2014. This is a partial value and the true value is expected to be significantly higher than this figure as only 7 of the benefits received from natural capital in Wales are currently measured. Some notable examples of ecosystem services which aren’t currently measured are flood protection, hydropower, and tourism. Of the services measured, 76% of this value was attributable to intangible services not traditionally captured in GDP (recreation, pollution removal and carbon sequestration). This construction of accounts for Welsh habitats is necessary for potential future commissioning of work to exploit the many condition indicators relevant to provisioning and regulating services which come from the ongoing national monitoring programme Welsh Government has funded through the GMEP and ERAMMP programmes. These condition metrics are particularly important for assessing the underpinning resilience of ecosystems to sudden shocks. Examples include change in soil condition - increases in soil pH over time; variable trends in soil carbon - with increases in woodland and losses in Mountain, Moor and Heath habitats; and condition indicators relevant to cultural services (recreation) which show improvement in the condition of footpaths and public rights of way over time. Other condition metrics include indicators of diversity and connectivity. The accounts reported here reflect a Welsh-data focus for three habitats. A broader set of ecosystem service accounts would benefit from inclusion of other habitats such as mountain moors and heaths, and urban and coastal accounts. The potential to link to environmental monitoring, such as the new indicators developed under the Environmental and Rural Affairs Monitoring and Modelling Programme (ERAMMP) and National Survey questions should also be explored further. This will particularly benefit measures of habitat condition, which are not typically represented in the reporting of many natural capital accounts. With resource rent residual value methods in valuing many ecosystem service flows, geographical breakdowns of Natural Capital accounts, such as Welsh ecosystem service accounts, currently rely upon apportioning UK national accounts. Further development work should take place to investigate other possible valuation methodologies outlined in the System of Environmental Economic Accounting (SEEA) Experimental Ecosystem Accountin

Potential contribution of soil diversity and abundance metrics to identifying high nature value farmland (HNV)

Identifying and halting the decline of High Nature Value farmland (HNV) is seen as essential to the EU meeting its 2020 biodiversity targets. Data on HNV farmland is used to target policy instruments and monitor changes in HNV to assess policy impact and development. Initial estimates of HNV land were based on land cover data with limited spatial resolution. The EU has since taken a distributed approach, allowing countries to develop their own data and metrics to report on the presence of HNV land, and changes to it. Land cover type has been the main data used for reporting but no consistent set of data metrics have been agreed. Therefore, there is interest in both developing standardised reporting metrics and identifying land with high restoration potential to increase the area of HNV land. We explore the relationship between soil associations and broad habitats across a member state (Wales) to determine if any discernible patterns exist between soil and habitat diversity and if soils information might be useful for identifying areas with high restoration potential. We developed a set of criteria to identify soil abundance, combining soil diversity with ecological rare species approaches. The rare (< 1000 ha) and occasional (1000–10,000 ha) soils identified were associated with significantly higher levels of habitat diversity than the national average. We propose that soil diversity information could supplement habitat information in identifying areas of potential restoration interest. Two iconic areas of Wales, the Llŷn Peninsula and Conwy Valley, were compared for restoration potential. Soil diversity in both areas is higher than the national average; habitat diversity was average, or lower in the case of the Llŷn Peninsula. These areas with higher soil diversity offer greater potential for restoration to type-2 HNV. Soil diversity and habitat diversity were found to be positively correlated at a national level despite major management modification of habitats. Given this relationship it is proposed that soil diversity information offers useful metrics alongside land cover data for identifying or comparing areas with regard to potential restoration for HNV

Systematic review of economic evaluations and cost analyses of guideline implementation strategies

Objectives To appraise the quality of economic studies undertaken as part of evaluations of guideline implementation strategies; determine their resources use; and recommend methods to improve future studies. Methods Systematic review of economic studies undertaken alongside robust study designs of clinical guideline implementation strategies published (1966-1998). Studies assessed against the BMJ economic evaluations guidelines for each stage of the guideline process (guideline development, implementation and treatment). Results 235 studies were identified, 63 reported some information on cost. Only 3 studies provided evidence that their guideline was effective and efficient. 38 reported the treatment costs only, 12 implementation and treatment costs, 11 implementation costs alone, and two guideline development, implementation and treatment costs. No study gave reasonably complete information on costs. Conclusions Very few satisfactory economic evaluations of guideline implementation strategies have been performed. Current evaluations have numerous methodological defects and rarely consider all relevant costs and benefits. Future evaluations should focus on evaluating the implementation of evidence based guidelines. Keywords: Cost-effectiveness analysis, physician (or health care professional) behaviour, practice guidelines, quality improvement, systematic review.Peer reviewedAuthor versio

Morphology and acoustic artefacts of copper deposits electroplated using megasonic assisted agitation

Purpose – This study aims to understand the influence of megasonic (MS)-assisted agitation on printed circuit boards (PCBs) electroplated using copper (Cu) electrolyte solutions to improve plating efficiencies through enhanced ion transportation. Design/methodology/approach – The impact of MS-assisted agitation on topographical properties of the electroplated surfaces was studied through a design of experiments by measuring surface roughness, which is characterised by values of the parameter Ra as measured by white light phase shifting interferometry and high-resolution scanning electron microscopy. Findings – An increase in Ra from 400 to 760 nm after plating was recorded for an increase in acoustic power from 45 to 450 W. Roughening increased because of micro-bubble cavitation energy and was supported through direct imaging of the cavitation. Current thieving effect by the MS transducer induced low currents, leading to large Cu grain frosting and reduction in the board quality. Current thieving was negated in plating trials through specific placement of transducer. Wavy electroplated surfaces, due to surface acoustic waves, were also observed to reduce the uniformity of the deposit. Research limitations/implications – The formation of unstable transient cavitation and variation of the topology of the Cu surface are unwanted phenomena. Further plating studies using MS agitation are needed, along with fundamental simulations, to determine how the effects can be reduced or prevented. Practical implications – This study can help identify manufacturing settings required for high-quality MS-assisted plating and promote areas for further investigation, leading to the development of an MS plating manufacturing technique. Originality/value – This study quantifies the topographical changes to a PCB surface in response to MS agitation and evidence for deposited Cu artefacts due to acoustic effects

From chemical gardens to chemobrionics

Chemical gardens in laboratory chemistries ranging from silicates to polyoxometalates, in applications ranging from corrosion products to the hydration of Portland cement, and in natural settings ranging from hydrothermal vents in the ocean depths to brinicles beneath sea ice. In many chemical-garden experiments, the structure forms as a solid seed of a soluble ionic compound dissolves in a solution containing another reactive ion. In general any alkali silicate solution can be used due to their high solubility at high pH. The cation should not precipitate with the counterion of the metal salt used as seed. A main property of seed chemical-garden experiments is that initially, when the fluid is not moving under buoyancy or osmosis, the delivery of the inner reactant is diffusion controlled. Another experimental technique that isolates one aspect of chemical-garden formation is to produce precipitation membranes between different aqueous solutions by introducing the two solutions on either side of an inert carrier matrix. Chemical gardens may be grown upon injection of solutions into a so-called Hele-Shaw cell, a quasi-two-dimensional reactor consisting in two parallel plates separated by a small gap

Fitting the integrated Spectral Energy Distributions of Galaxies

Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting, with a special emphasis on describing the interplay between the quality of the available data, the quality of the available models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties. We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift, stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details ofdust properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The present review will be made available on an interactive, moderated web page (sedfitting.org), where the community can access and change the text. The intention is to expand the text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics & Space Scienc