2,522 research outputs found
The Writings of General Lu: Religion and Rule in Khalkha Mongolia at the Turn of the 20th Century
Knudsen gas provides nanobubble stability
We provide a model for the remarkable stability of surface nanobubbles to
bulk dissolution. The key to the solution is that the gas in a nanobubble is of
Knudsen type. This leads to the generation of a bulk liquid flow which
effectively forces the diffusive gas to remain local. Our model predicts the
presence of a vertical water jet immediately above a nanobubble, with an
estimated speed of , in good agreement with our
experimental atomic force microscopy measurement of . In
addition, our model also predicts an upper bound for the size of nanobubbles,
which is consistent with the available experimental data
Surface bubble nucleation phase space
Recent research has revealed several different techniques for nanoscopic gas
nucleation on submerged surfaces, with findings seemingly in contradiction with
each other. In response to this, we have systematically investigated the
occurrence of surface nanobubbles on a hydrophobised silicon substrate for
various different liquid temperatures and gas concentrations, which we
controlled independently. We found that nanobubbles occupy a distinct region of
this phase space, occurring for gas concentrations of approximately 100-110%.
Below the nanobubble phase we did not detect any gaseous formations on the
substrate, whereas micropancakes (micron wide, nanometer high gaseous domains)
were found at higher temperatures and gas concentrations. We moreover find that
supersaturation of dissolved gases is not a requirement for nucleation of
bubbles.Comment: 4 pages, 4 figure
Calculation of the Phase Behavior of Lipids
The self-assembly of monoacyl lipids in solution is studied employing a model
in which the lipid's hydrocarbon tail is described within the Rotational
Isomeric State framework and is attached to a simple hydrophilic head.
Mean-field theory is employed, and the necessary partition function of a single
lipid is obtained via a partial enumeration over a large sample of molecular
conformations. The influence of the lipid architecture on the transition
between the lamellar and inverted-hexagonal phases is calculated, and
qualitative agreement with experiment is found.Comment: to appear in Phys.Rev.
Fossil pollen and spores as a tool for reconstructing ancient solar-ultraviolet irradiance received by plants : an assessment of prospects and challenges using proxy-system modelling
Ultraviolet-B radiation (UV-B, 280-315 nm) constitutes less than 1% of the total solar radiation that reaches the Earth's surface but has a disproportional impact on biological and ecological processes from the individual to the ecosystem level. Absorption of UV-B by ozone is also one of the primary heat sources to the stratosphere, so variations in UV-B have important relationships to the Earth's radiation budget. Yet despite its importance for understanding atmospheric and ecological processes, there is limited understanding about the changes in UV-B radiation in the geological past. This is because systematic measurements of total ozone and surface UV-B only exist since the 1970s, so biological or geochemical proxies from sediment archives are needed to reconstruct UV-B irradiance received at the Earth surface beyond the experimental record. Recent developments have shown that the quantification of UV-B-absorbing compounds in pollen and spores have the potential to provide a continuous record of the solar-ultraviolet radiation received by plants. There is increasing interest in developing this proxy in palaeoclimatic and palaeoecological research. However, differences in interpretation exist between palaeoecologists, who are beginning to apply the proxy under various geological settings, and UV-B ecologists, who question whether a causal dose-response relationship of pollen and spore chemistry to UV-B irradiance has really been established. Here, we use a proxy-system modelling approach to systematically assess components of the pollen-and spore-based UV-B-irradiance proxy to ask how these differences can be resolved. We identify key unknowns and uncertainties in making inferences about past UV-B irradiance, from the pollen sensor, the sedimentary archive, and through the laboratory and experimental procedures in order to target priority areas of future work. We argue that an interdisciplinary approach, modifying methods used by plant ecologists studying contemporary responses to solar-UV-B radiation specifically to suit the needs of palaeoecological analyses, provides a way forward in developing the most reliable reconstructions for the UV-B irradiance received by plants across a range of timescales.Peer reviewe
Spin- and angle-resolved photoemission studies of the electronic structure of Si(110)"16x2" surfaces
The electronic structure of Si(110)"16 x 2" double-domain, single-domain and
1 x 1 surfaces have been investigated using spin- and angle-resolved
photoemission at sample temperatures of 77 K and 300 K. Angle-resolved
photoemission was conducted using horizontally- and vertically-polarised 60 eV
and 80 eV photons. Band-dispersion maps revealed four surface states ( to
) which were assigned to silicon dangling bonds on the basis of measured
binding energies and photoemission intensity changes between horizontal and
vertical light polarisations. Three surface states (, and ),
observed in the Si(110)"16 x 2" reconstruction, were assigned to Si adatoms and
Si atoms present at the edges of the corrugated terrace structure. Only one of
the four surface states, , was observed in both the Si(110)"16 x 2" and 1
x 1 band maps and consequently attributed to the pervasive Si zigzag chains
that are components of both the Si(110)"16 x 2" and 1 x 1 surfaces. A state in
the bulk-band region was attributed to an in-plane bond. All data were
consistent with the adatom-buckling model of the Si(110)"16 x 2" surface.
Whilst room temperature measurements of and were statistically
compatible with zero, measurements of the enantiomorphic A-type and
B-type Si(110)"16 x 2" surfaces gave small average polarisations of around
1.5\% that were opposite in sign. Further measurements at 77 K on A-type
Si(110)"16 x 2" surface gave a smaller value of +0.3\%. An upper limit of
may thus be taken for the longitudinal polarisation.Comment: Main paper: 12 pages and 11 figures. Supplemental information: 5
pages and 2 figure
Lead(II) chloride ionic liquids and organic/inorganic hybrid materials - a study of chloroplumbate(II) speciation
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