CMB dipoles and other low-order multipoles in the quasispherical Szekeres model

Several authors have previously shown that a Gpc-scale void based on the spherically symmetric Lemaıˆtre-Tolman-Bondi (LTB) model can provide a good fit to certain cosmological data, including the SNIa data, but it is only consistent with the observed CMB dipole if we are located very close to the center, in violation of the Copernican principle. In this work we investigate the more general quasispherical Szekeres model, which does not include spherical symmetry, in order to determine whether this option may be less constricting. We find that the observer is still constrained to a small region, but it is not as geometrically ''special'' as the center of a LTB void. Furthermore, whereas the quadrupole and octupole near the center of a LTB void are necessarily small, certain Szekeres models can include a significant quadrupole while still being consistent with the observed dipole, hinting that Szekeres models may be able to give an explanation for the observed quadrupole/octupole anomalies

FDIONIC18 Interactions and stabilisation of acetone, sulfur dioxide and water with 1-octyl-3-methylimidazolium tetrafluoroborate at low temperatures

The interactions between three small molecules, water (H2O) , sulfur dioxide (SO2) and acetone ( (CH3)2CO ) with the ionic liquid (IL) 1-octyl-3-methylimidazolium tetrafluoroborate, [OMIM][BF4], have been determined using line of sight temperature programmed desorption (LOSTPD) from a gold surface. Multilayers of the IL were deposited by physical vapour deposition with multilayers of the small molecular species (adsorbed from the gas phase) at 90 K. LOSTPD was then carried out with the small molecular species desorbing first from the mixed multilayer, followed at higher temperatures by desorption of the IL from the gold surface. The IL had a high activation energy for desorption of 126(6) kJ mol-1 . Pure acetone showed a desorption activation energy of 38(2) kJ mol-1, which increased to 45 - 61 kJ mol-1 when it was pre-adsorbed below an overlying porous layer of the ionic liquid at 90 K. The stabilised acetone is thought to be associated with pores containing ionic moieties. Destabilised acetone was also observed and thought to originate from pores containing octyl chains. The quantity of stabilised acetone scaled with the amount of IL, being ≈ 1.1 molecules per IL ion pair. SO2 and H2O were co-adsorbed with the IL at 90 K leading to an intimate mixture of the two. For pure SO2 the desorption energy was 32(2) kJ mol-1, which increased to 40 - 50 kJ mol-1 for relative concentrations up to 6 SO2 molecules per IL ion pair. For pure water the activation energies were 49(5) kJ mol-1 and 43(1) kJ mol-1 for amorphous and crystalline ice respectively. When co-adsorbed with the IL the stabilisation energies were 42 - 49 kJ mol-1, but up to 505 water molecules per IL ion pair could be stabilised to some degree. The desorption mechanisms and the reasons for these interactions are discussed

Thin film structural analysis using variable-period x-ray standing waves

Variable-period x-ray standing wave (VPXSW) studies have been carried out using 3 keV x rays and photoelectron detection. Two model surfaces have been used, a native SiO2 layer (20 Å thick) on bulk silicon, and a purpose-built multilayer surface comprising a chloroform/water marker layer (12 Å thick) on an ionic liquid spacer layer (211 Å thick) deposited on a SiO2/Si substrate at 90 K. By using photoelectron detection, both chemical and elemental sensitivity were achieved. The surfaces were modeled using dynamic x-ray scattering for x-ray intensity, and attenuation of photoelectrons transmitted through the layers, to produce simulations which accurately reproduced the experimental VPXSW measurements. VPXSW measurements made using the substrate, spacer layer, and marker layer photoelectron signatures produced consistent structural values. This work demonstrates that VPXSW can be used to determine chemically specific layer thicknesses within thick (≲300Å) surface structures composed of the light elements B, C, N, O, F, and Cl with an accuracy of 10 to 15 Å, perpendicular to the surface

Biofilm assists recognition of avian trackways in Late Pleistocene coastal aeolianites, South Africa

Fourteen fossil avian tracksites have been identified in Late Pleistocene aeolianite deposits on the Cape south coast of SouthAfrica. One of these sites is unusual because of the preferential adherence of organic material (biofilm) to the natural cast tracks. This has enabled the recognition and identification of two ~6 m long, approximately parallel trackways that would otherwise not have been noticed. The trackways are visible from a distance of over 100 metres and contain 20 and 14 individual tracks, respectively. Up to 50 avian tracks are evident at this site. As the biofilm layer continues to thicken, the trackways become increasingly visible. Avian trackways of this length are globally rare.We propose that the biofilm adheres to sections with higher relief on a sedimentary surface, and that an understanding of this mode of preservation can be useful to more easily identify trackways in areas of comparable geological setting.JN