Curvature effects on the surface thickness and tension at the free interface of 4^4He systems

The thickness $W$ and the surface energy $\sigma_A$ at the free interface of superfluid $^4$He are studied. Results of calculations carried out by using density functionals for cylindrical and spherical systems are presented in a unified way, including a comparison with the behavior of planar slabs. It is found that for large species $W$ is independent of the geometry. The obtained values of $W$ are compared with prior theoretical results and experimental data. Experimental data favor results evaluated by adopting finite range approaches. The behavior of $\sigma_A$ and $W \sigma_A$ exhibit overshoots similar to that found previously for the central density, the trend of these observables towards their asymptotic values is examined.Comment: 35 pages, TeX, 5 figures, definitive versio

Local mean-field study of capillary condensation in silica aerogels

We apply local mean-field (i.e. density functional) theory to a lattice model of a fluid in contact with a dilute, disordered gel network. The gel structure is described by a diffusion-limited cluster aggregation model. We focus on the influence of porosity on both the hysteretic and the equilibrium behavior of the fluid as one varies the chemical potential at low temperature. We show that the shape of the hysteresis loop changes from smooth to rectangular as the porosity increases and that this change is associated to disorder-induced out-of-equilibrium phase transitions that differ on adsorption and on desorption. Our results provide insight in the behavior of $^4$He in silica aerogels.Comment: 19 figure

Structural and dynamical properties of superfluid helium: a density functional approach

We present a novel density functional for liquid 4He, properly accounting for the static response function and the phonon-roton dispersion in the uniform liquid. The functional is used to study both structural and dynamical properties of superfluid helium in various geometries. The equilibrium properties of the free surface, droplets and films at zero temperature are calculated. Our predictions agree closely to the results of ab initio Monte Carlo calculations, when available. The introduction of a phenomenological velocity dependent interaction, which accounts for backflow effects, is discussed. The spectrum of the elementary excitations of the free surface and films is studied.Comment: 37 pages, REVTeX 3.0, figures on request at [email protected]

Web-based horizon scanning: Concepts and practice

PurposeIn this review, the aim is first to define horizon scanning and then outline the general approach currently employed by many organisations using web‐based resources. It then aims to discuss the benefits and drivers of horizon scanning, to identify some organisations currently undertaking activities in the field, and explain in detail how the web‐based horizon scanning approach is implemented. The aim is then to conclude with a discussion of good practice and areas for further research.Design/methodology/approachThe basis for this review is a symposium held at the UK Defence Science and Technology Laboratory in March 2010, where groups undertaking horizon scanning activities shared practices and reviewed the state of the art. Practitioners from both public sector and private organisations attending this symposium, as well as others, were invited to contribute to the manuscript, developing this as an iterative exercise over the last year.FindingsStructured processes of web‐based horizon scanning, underpinned by strong technical understanding and principles of good practice described in the review, can add significant value to organisational decision making.Originality/valueWhile a growing number of private and public sector organisations have already embarked on the use of the web as a key information resource, no detailed explanation of the web‐based horizon scanning approach has been published. The review therefore makes an original contribution to this field, with collaborations by horizon scanning practitioners, discussing what constitutes good practice and highlighting areas where future research is needed.</jats:sec

The effect of environmental change on early Aptian ostracods faunas in the Wessex Basin, southern England

A major phase of transgression in the Wessex Basin (southern England) during the earliest Aptian resulted in the collapse of the generally fresh water Barremian environment and the initiation of the marine milieu. Cypridea-rich faunas in the Shepherd's Chine Member (Vectis Formation), were gradually replaced by faunas dominated by Sternbergella cornigera, Mantelliana mantelli and Theriosynoecum fittoni. This change is interpreted as indicating that salinities had passed from fresh-oligohaline to meso- and pliohaline and that ephemeral water bodies were replaced by more widespread, permanent, lagoonal waters. The ostracods from the highest part of the Vectis Formation appear to be heralding the major transgression that was about to engulf the Wessex Basin. The marine incursion during the obsoletus Ammonite Subzone brought with it newly formed environmental niches that were rapidly occupied by microfaunas. Several ostracod species are interpreted as euryhaline, but others appear to have been restricted to marine or near marine salinities. The earliest marine ostracod faunas were recorded from the Perna Bed Member, Isle of Wight, and include abundant Asciocythere albae and frequent to common Schuleridea derooi, Neocythere gottisi, N. bordeti and Cytherelloidea sp. Other species include rare Cythereis geometrica, C. semiaperta, Eocytheropteron stchepinskyi and Protocythere croutesensis. In addition, elsewhere in southern England, Protocythere mertensi langi, Dolocytheridea intermedia, Paranotacythere (P.) oertlii and P. (P.) atypica occur. The relationship of this earliest Aptian population with that of the Paris Basin cannot be mistaken

The Tookoonooka marine impact horizon, Australia: sedimentary and petrologic evidence

Ejecta from the large subsurface Tookoonooka impact structure have been found in the Lower Cretaceous strata of the extensive Eromanga Basin of central Australia. Observations from 31 wells spanning 400,000 km2 of the basin provide compelling evidence for the presence of a marine impact horizon of regional extent. Drill core was examined to determine the sedimentary context of the Tookoonooka impact event, the presence of ejecta, and the nature of the impact horizon. The base of the Wyandra Sandstone Member of the Cadna-owie Formation is an unconformity commonly overlain by very poorly sorted sediment with imbricated pebbles, exotic clasts, and occasional boulders. The basal Wyandra Sandstone Member is bimodal: a fine sand mode reflects an ambient sediment contribution and a coarse mode is interpreted to be impact-derived. Wells Thargomindah-1 and Eromanga-1, within four crater radii of Tookoonooka, contain distinctive clastsupported breccia-conglomerate beds at the base of the Wyandra Sandstone Member. Clasts in these beds include altered accretionary and melt impactoclasts, as well as lithic and mineral grains corresponding to the Tookoonooka target rock sequence, including basement. Petrographic evidence includes shock metamorphosed quartz and lithic grains with planar deformation features. These breccia-conglomerates are in stark contrast to the underlying, laterally persistent, unimodal Cadna-owie sediments and overlying shales deposited in an epeiric sea. The base of the Wyandra Sandstone Member is therefore interpreted to be the Tookoonooka impact horizon. The timing of the impact event is confirmed to be the Barremian-Aptian boundary, at 125 ± 1 Ma. The Wyandra Sandstone Member preserves both impact ejecta and postimpact marine sediments.Katherine A. Bron and Victor Gosti