Microscopic theory of solvent mediated long range forces: influence of wetting

We show that a general density functional approach for calculating the force between two big particles immersed in a solvent of smaller ones can describe systems that exhibit fluid-fluid phase separation: the theory captures effects of strong adsorption (wetting) and of critical fluctuations in the solvent. We illustrate the approach for the Gaussian core model, a simple model of a polymer mixture in solution and find extremely attractive, long ranged solvent mediated potentials between the big particles for state points lying close to the binodal, on the side where the solvent is poor in the species which is favoured by the big particles.Comment: 7 pages, 3 figures, submitted to Europhysics Letter

Generation of defects and disorder from deeply quenching a liquid to form a solid

We show how deeply quenching a liquid to temperatures where it is linearly unstable and the crystal is the equilibrium phase often produces crystalline structures with defects and disorder. As the solid phase advances into the liquid phase, the modulations in the density distribution created behind the advancing solidification front do not necessarily have a wavelength that is the same as the equilibrium crystal lattice spacing. This is because in a deep enough quench the front propagation is governed by linear processes, but the crystal lattice spacing is determined by nonlinear terms. The wavelength mismatch can result in significant disorder behind the front that may or may not persist in the latter stage dynamics. We support these observations by presenting results from dynamical density functional theory calculations for simple one- and two-component two-dimensional systems of soft core particles.Comment: 25 pages, 11 figure

Enamel of Yalkaparidon Coheni: Representative of a Distinctive Order of Tertiary Zalambdodont Marsupials

The enamel of an incisor and a premolar of Yalkaparidon coheni was examined by scanning electron microscopy in fractured and in sectioned, polished surfaces. The enamel of both teeth demonstrated: complete, ovoid and horse-shoe shaped prisms in a Pattern 2 arrangement; a simple parallel prism course; and, enamel tubules in abundance in the premolar but restricted to the innermost enamel in the incisor. Overall, the enamel ultrastructure supports the marsupial affiliation proposed for Yalkaparidon coheni but does not unambiguously ally it with any other order of marsupials. The observation of a significant ultrastructural difference between the anterior and posterior teeth of a marsupial emphasizes the need to sample both if available. In pursuing this, we report here also the lack of tubules in the anterior teeth of the extant Tarsipes rostratus. This together with a similar absence of typical marsupial tubules from the incisor of the extinct Yalkaparidon coheni, would suggest that the wombat is not the only surviving marsupial to have experimented so extensively with this particular structural feature. It is likely that further study will demonstrate an unexpected and relative lack of tubules in the incisor enamel of other fossil Australian marsupials

Dynamic density functional study of a driven colloidal particle in polymer solutions

The Dynamic Density Functional (DDF) theory and standard Brownian dynamics simulations (BDS) are used to study the drifting effects of a colloidal particle in a polymer solution, both for ideal and interacting polymers. The structure of the stationary density distributions and the total induced current are analyzed for different drifting rates. We find good agreement with the BDS, which gives support to the assumptions of the DDF theory. The qualitative aspect of the density distribution are discussed and compared to recent results for driven colloids in one-dimensional channels and to analytical expansions for the ideal solution limit

Collective shuttling of attracting particles in asymmetric narrow channels

The rectification of a single file of attracting particles subjected to a low frequency ac drive is proposed as a working mechanism for particle shuttling in an asymmetric narrow channel. Increasing the particle attraction results in the file condensing, as signalled by the dramatic enhancement of the net particle current. Magnitude and direction of the current become extremely sensitive to the actual size of the condensate, which can then be made to shuttle between two docking stations, transporting particles in one direction, with an efficiency much larger than conventional diffusive models predict

U.S.A. visibility monitoring, trends, and regulatory programs and their relevance to Korea.

This paper describes visibility monitoring and regulatory programs in the United States, particularly within certain designated National Parks and Wilderness Areas. Government agencies responsible for the management of federal lands, in cooperation with other federal, state, and regional air quality organizations, have established a monitoring program of more than 125 sites. Recent visual documentation (scene images), optical measurements, and aerosol characterizations (mass and chemical speciation) obtained at selected monitoring sites are presented, as information on general spatial and temporal visibility trends. National regulations are described that limit the amount of additional visibility impairment from new or modified emission sources and that establish a schedule for improving existing conditions in designated areas. The relevance of the experience in developing and implementing these programs to the planning for programs to address emerging visibility problems in Korea is discussed

New insights from zinc and copper isotopic compositions of atmospheric particulate matter from two major European cities

This study reports spatial and temporal variability of Zn and Cu isotopes in atmospheric particulate matter (PM) collected in two major European cities with contrasting atmospheric pollution, Barcelona and London. We demonstrate that non-traditional stable isotopes identify source contributions of Zn and Cu and can play a major role in future air quality studies. In Barcelona, fine PM were collected at street level at sites with variable traffic density. The isotopic signatures ranged between −0.13±0.09 and −0.55±0.09‰ for d66ZnIRMM and between +0.04±0.20 and +0.33±0.15‰ for d65CuAE633. Copper isotope signatures similar to Cu sulphides and Cu/Sb ratios within the range typically found in brake wear suggest that non-exhaust emissions from vehicles are dominant. Negative Zn isotopic signatures characteristic for gaseous emissions from smelting and combustion and large enrichments of Zn and Cd suggest contribution from metallurgical industries. In London, coarse PM collected on the top of a building over 18 months display isotope signatures ranging between +0.03±0.04 and +0.49±0.02‰ for d66ZnIRMM and between +0.37±0.17 and +0.97±0.21‰ for d65CuAE633. Heavy Cu isotope signatures (up to +0.97±0.21‰) and higher enrichments and Cu/Sb ratios during winter time suggest important contribution from fossil fuel combustion. The positive d66ZnIRMM signatures are in good agreement with signatures characteristic for ore concentrates used for the production of tires and galvanised materials, suggesting non-exhaust emissions from vehicles as the main source of Zn

Australia's first fossil marsupial mole (Notoryctemorphia) resolves controversies about their evolution and palaeoenvironmental origins

Fossils of a marsupial mole (Marsupialia, Notoryctemorphia, Notoryctidae) are described from early Miocene deposits in the Riversleigh World Heritage Area, northwestern Queensland, Australia. These represent the first unequivocal fossil record of the order Notoryctemorphia, the two living species of which are among the world's most specialized and bizarre mammals, but which are also convergent on certain fossorial placental mammals (most notably chrysochlorid golden moles). The fossil remains are genuinely ‘transitional', documenting an intermediate stage in the acquisition of a number of specializations and showing that one of these—the dental morphology known as zalambdodonty—was acquired via a different evolutionary pathway than in placentals. They, thus, document a clear case of evolutionary convergence (rather than parallelism) between only distantly related and geographically isolated mammalian lineages—marsupial moles on the island continent of Australia and placental moles on most other, at least intermittently connected continents. In contrast to earlier presumptions about a relationship between the highly specialized body form of the blind, earless, burrowing marsupial moles and desert habitats, it is now clear that archaic burrowing marsupial moles were adapted to and probably originated in wet forest palaeoenvironments, preadapting them to movement through drier soils in the xeric environments of Australia that developed during the Neogene