Sub-surface damage issues for effective fabrication of large optics

A new ultra precision large optics grinding machine, BoX®has been developed at Cranfield University. BoX®islocated at the UK's Ultra Precision Surfaces laboratory at the OpTIC Technium. This machine offers a rapidand economic solution for grinding large off-axis aspherical and free-form optical components.This paper presents an analysis of subsurface damage assessments of optical ground materials produced usingdiamond resin bonded grinding wheels. The specific materials used, Zerodur®and ULE®are currently understudy for making extremely large telescope (ELT) segmented mirrors such as in the E-ELT project.The grinding experiments have been conducted on the BoX®grinding machine using wheels with grits sizes of76 μm, 46 μm and 25 μm. Grinding process data was collected using a Kistler dynamometer platform. Thehighest material removal rate (187.5 mm3/s) used ensures that a 1 metre diameter optic can be ground in lessthan 10 hours. The surface roughness and surface profile were measured using a Form Talysurf. The subsurfacedamage was revealed using a sub aperture polishing process in combination with an etching technique.These results are compared with the targeted form accuracy of 1 μm p-v over a 1 metre part, surface roughnessof 50-150 nm RMS and subsurface damage in the range of 2-5 μm. This process stage was validated on a 400mm ULE®blank and a 1 metre hexagonal Z

Solvent mediated interactions between model colloids and interfaces: A microscopic approach

We determine the solvent mediated contribution to the effective potentials for model colloidal or nano- particles dispersed in a binary solvent that exhibits fluid-fluid phase separation. Using a simple density functional theory we calculate the density profiles of both solvent species in the presence of the `colloids', which are treated as external potentials, and determine the solvent mediated (SM) potentials. Specifically, we calculate SM potentials between (i) two colloids, (ii) a colloid and a planar fluid-fluid interface, and (iii) a colloid and a planar wall with an adsorbed wetting film. We consider three different types of colloidal particles: colloid A which prefers the bulk solvent phase rich in species 2, colloid C which prefers the solvent phase rich in species 1, and `neutral' colloid B which has no strong preference for either phase, i.e. the free energies to insert the colloid into either of the coexisting bulk phases are almost equal. When a colloid which has a preference for one of the two solvent phases is inserted into the disfavored phase at statepoints close to coexistence a thick adsorbed `wetting' film of the preferred phase may form around the colloids. The presence of the adsorbed film has a profound influence on the form of the SM potentials.Comment: 17 Pages, 13 Figures. Accepted for publication in Journal of Chemical Physic

Economic and regulatory approaches to improve the environmental performance of buildings in South Africa

In the past, economic instruments for environmental purposes were strongly resisted by industry, government and the public. As such, they were used only in exceptional circumstances. More recently, there has been a realisation that economic instruments can be a powerful complement to direct regulations. Consequently, economic instruments are playing an increasingly important role in the environmental management of buildings. The activities of the construction industry are driven by economic forces, so using market mechanisms is a logical strategy to pursue the objectives of sustainable construction. Perhaps the question is not whether economic mechanisms should be employed to improve environmental building performance, but rather how this should be achieved.This article suggests that it can be achieved by using the economic instrument of ecolabelling to create market competition for improved building performance. Ecolabelling has traditionally been associated with household products, but has more recently been applied to a wider range of products, including buildings and building materials. The basis for building ecolabels is provided by the results of building environmental assessments, which evaluate building per formance. In developed countries, these assessments have stimulated market demand for ‘green’ building developments. Building environmental assessment methods have used the concept of ecolabelling to provide consumers with an additional benchmark in renting or purchasing buildings.Yet, it is unknown whether the South African building market will be similarly responsive to ‘green’ market incentives. In South Africa, where the majority of the population are struggling to satisfy their basic needs, and lack proper education, the environmental ‘ethos’ of the general public has not developed to an extent where environmental issues are seen as a serious priority.Building environmental assessment methods in South Africa are evolving from ‘green’ evaluations that were pragmatically developed to respond to immediate needs, to the measurement of ‘sustainability’. Ecolabels can now reflect the performance of building development in terms of all aspects of sustainability, including socio economic, technical and environmental dimensions of sustainable construction. This has been made possible by the development of a unique South African building environmental assessment method that measures sustainability, namely the “Sustainable Buildings Assessment Technique.”Although much has been written about economic mechanisms, practical guidance on how to implement these mechanisms in building developments is scarce. This article outlines some of the opportunities and constraints associated with market driven and environmental performance in buildings. The limitations of economic approaches in South Africa include a lack of environ mental awareness, misconceptions of ‘green’ buildings, building industry constraints and the market dependence of voluntary assessment protocols. Regulatory approaches are not without their own limitations, the most significant of which is the acute shortage of resources in South African environmental authorities, a factor that is likely to restrict the effectiveness of regulatory approaches.The article goes on to examine the particular problems associated with developing world markets (such as South Africa’s). Furthermore, the relationship between regulatory, ‘command and control’ approaches and economic, market driven approaches is discussed. It is concluded that the ideals of sustain able construction can best be achieved by using regulatory approaches in conjunction with economic instruments

Macrophage podosomes assemble at the leading lamella by growth and fragmentation

Podosomes are actin- and fimbrin-containing adhesions at the leading edge of macrophages. In cells transfected with β-actin–ECFP and L-fimbrin–EYFP, quantitative four-dimensional microscopy of podosome assembly shows that new adhesions arise at the cell periphery by one of two mechanisms; de novo podosome assembly, or fission of a precursor podosome into daughter podosomes. The large podosome cluster precursor also appears to be an adhesion structure; it contains actin, fimbrin, integrin, and is in close apposition to the substratum. Microtubule inhibitors paclitaxel and demecolcine inhibit the turnover and polarized formation of podosomes, but not the turnover rate of actin in these structures. Because daughter podosomes and podosome cluster precursors are preferentially located at the leading edge, they may play a critical role in continually generating new sites of cell adhesion

The effects of pre- and postnatal depression in fathers: a natural experiment comparing the effects of exposure to depression on offspring.

BACKGROUND: Depression in fathers in the postnatal period is associated with an increased risk of behavioural problems in their offspring, particularly for boys. The aim of this study was to examine for differential effects of depression in fathers on children's subsequent psychological functioning via a natural experiment comparing prenatal and postnatal exposure. METHODS: In a longitudinal population cohort study (the Avon Longitudinal Study of Parents and Children (ALSPAC)) we examined the associations between depression in fathers measured in the prenatal and postnatal period (measured using the Edinburgh Postnatal Depression Scale), and later behavioural/emotional and psychiatric problems in their children, assessed at ages 3(1/2) and 7 years. RESULTS: Children whose fathers were depressed in both the prenatal and postnatal periods had the highest risks of subsequent psychopathology, measured by total problems at age 3(1/2) years (Odds Ratio 3.55; 95% confidence interval 2.07, 6.08) and psychiatric diagnosis at age 7 years (OR 2.54; 1.19, 5.41). Few differences emerged when prenatal and postnatal depression exposure were directly compared, but when compared to fathers who were not depressed, boys whose fathers had postnatal depression only had higher rates of conduct problems aged 3(1/2) years (OR 2.14; 1.22, 3.72) whereas sons of the prenatal group did not (OR 1.41; .75, 2.65). These associations changed little when controlling for maternal depression and other potential confounding factors. CONCLUSIONS: The findings of this study suggest that the increased risk of later conduct problems, seen particularly in the sons of depressed fathers, maybe partly mediated through environmental means. In addition, children whose fathers are more chronically depressed appear to be at a higher risk of emotional and behavioural problems. Efforts to identify the precise mechanisms by which transmission of risk may occur should be encouraged to enable the development of focused interventions to mitigate risks for young children

On the dynamics of WKB wave functions whose phase are weak KAM solutions of H-J equation

In the framework of toroidal Pseudodifferential operators on the flat torus $\Bbb T^n := (\Bbb R / 2\pi \Bbb Z)^n$ we begin by proving the closure under composition for the class of Weyl operators $\mathrm{Op}^w_\hbar(b)$ with simbols $b \in S^m (\mathbb{T}^n \times \mathbb{R}^n)$. Subsequently, we consider $\mathrm{Op}^w_\hbar(H)$ when $H=\frac{1}{2} |\eta|^2 + V(x)$ where $V \in C^\infty (\Bbb T^n;\Bbb R)$ and we exhibit the toroidal version of the equation for the Wigner transform of the solution of the Schr\"odinger equation. Moreover, we prove the convergence (in a weak sense) of the Wigner transform of the solution of the Schr\"odinger equation to the solution of the Liouville equation on $\Bbb T^n \times \Bbb R^n$ written in the measure sense. These results are applied to the study of some WKB type wave functions in the Sobolev space $H^{1} (\mathbb{T}^n; \Bbb C)$ with phase functions in the class of Lipschitz continuous weak KAM solutions (of positive and negative type) of the Hamilton-Jacobi equation $\frac{1}{2} |P+ \nabla_x v_\pm (P,x)|^2 + V(x) = \bar{H}(P)$ for $P \in \ell \Bbb Z^n$ with $\ell >0$, and to the study of the backward and forward time propagation of the related Wigner measures supported on the graph of $P+ \nabla_x v_\pm$

The Signature of Primordial Grain Growth in the Polarized Light of the AU Mic Debris Disk

We have used the Hubble Space Telescope/ACS coronagraph to make polarization maps of the AU Mic debris disk. The fractional linear polarization rises monotonically from about 0.05 to 0.4 between 20 and 80 AU. The polarization is perpendicular to the disk, indicating that the scattered light originates from micron sized grains in an optically thin disk. Disk models, which simultaneously fit the surface brightness and polarization, show that the inner disk (< 40-50 AU) is depleted of micron-sized dust by a factor of more than 300, which means that the disk is collision dominated. The grains have high maximum linear polarization and strong forward scattering. Spherical grains composed of conventional materials cannot reproduce these optical properties. A Mie/Maxwell-Garnett analysis implicates highly porous (91-94%) particles. In the inner Solar System, porous particles form in cometary dust, where the sublimation of ices leaves a "bird's nest" of refractory organic and silicate material. In AU Mic, the grain porosity may be primordial, because the dust "birth ring" lies beyond the ice sublimation point. The observed porosities span the range of values implied by laboratory studies of particle coagulation by ballistic cluster-cluster aggregation. To avoid compactification, the upper size limit for the parent bodies is in the decimeter range, in agreement with theoretical predictions based on collisional lifetime arguments. Consequently, AU Mic may exhibit the signature of the primordial agglomeration process whereby interstellar grains first assembled to form macroscopic objects.Comment: 12 pages, 8 figures, ApJ, in pres