727 research outputs found
Reliability analysis of the fatigue resistance of offshore structures
Imperial Users onl
On a conjecture of Marton
We prove a conjecture of K. Marton, widely known as the polynomial
Freiman--Ruzsa conjecture, in characteristic . The argument extends to odd
characteristic, with details to follow in a subsequent paper.Comment: 33 pages, updated version now to be submitted for publicatio
The EU and Asia within an evolving global order: what is Europe? Where is Asia?
The papers in this special edition are a very small selection from those presented at the EU-NESCA (Network of European Studies Centres in Asia) conference on "the EU and East Asia within an Evolving Global Order: Ideas, Actors and Processes" in November 2008 in Brussels. The conference was the culmination of three years of research activity involving workshops and conferences bringing together scholars from both regions primarily to discuss relations between Europe and Asia, perceptions of Europe in Asia, and the relationship between the European regional project and emerging regional forms in Asia. But although this was the last of the three major conferences organised by the consortium, it in many ways represented a starting point rather than the end; an opportunity to reflect on the conclusions of the first phase of collaboration and point towards new and continuing research agendas for the future
Accuracy tests of radiation schemes used in hot Jupiter global circulation models
The treatment of radiation transport in global circulation models (GCMs) is crucial to correctly describe Earth and exoplanet atmospheric dynamics processes. The two-stream approximation and correlated-k method are currently state-of-the-art approximations applied in both Earth and hot Jupiter GCM radiation schemes to facilitate rapid calculation of fluxes and heating rates. Their accuracy have been tested extensively for Earth-like conditions, but verification of the methods' applicability to hot Jupiter-like conditions is lacking in the literature. We are adapting the UK Met Office GCM, the Unified Model (UM), for the study of hot Jupiters, and present in this work the adaptation of the Edwards-Slingo radiation scheme based on the two-stream approximation and the correlated-k method. We discuss the calculation of absorption coefficients from high temperature line lists and highlight the large uncertainty in the pressure-broadened line widths. We compare fluxes and heating rates obtained with our adapted scheme to more accurate discrete ordinate (DO) line-by-line (LbL) calculations ignoring scattering effects. We find that, in most cases, errors stay below 10 % for both heating rates and fluxes using ~ 10 k-coefficients in each band and a diffusivity factor D = 1.66. The two-stream approximation and the correlated-k method both contribute non-negligibly to the total error. We also find that using band-averaged absorption coefficients, which have previously been used in radiative-hydrodynamical simulations of a hot Jupiter, may yield errors of ~ 100 %, and should thus be used with caution.European Community’s Seventh Framework Programme FP7/2007-2013Science & Technology Facilities Council (STFC)Royal Societ
“Cross” Supermicelles via the Hierarchical Assembly of Amphiphilic Cylindrical Triblock Comicelles
Self-assembled
“cross” architectures are well-known
in biological systems (as illustrated by chromosomes, for example);
however, comparable synthetic structures are extremely rare. Herein
we report an in depth study of the hierarchical assembly of the amphiphilic
cylindrical P–H–P triblock comicelles with polar (P)
coronal ends and a hydrophobic (H) central periphery in a selective
solvent for the terminal segments which allows access to “cross”
supermicelles under certain conditions. Well-defined P–H–P
triblock comicelles M(PFS-<i>b</i>-PtBA)-<i>b</i>-M(PFS-<i>b</i>-PDMS)-<i>b</i>-M(PFS-<i>b</i>-PtBA) (M = micelle segment, PFS = polyferrocenyldimethylsilane,
PtBA = poly(<i>tert</i>-butyl acrylate), and PDMS = polydimethylsiloxane)
were created by the living crystallization-driven self-assembly (CDSA)
method. By manipulating two factors in the supermicelles, namely the
H segment-solvent interfacial energy (through the central H segment
length, <i>L</i><sub>1</sub>) and coronal steric effects
(via the PtBA corona chain length in the P segment, <i>L</i><sub>2</sub> related to the degree of polymerization DP<sub>2</sub>) the aggregation of the triblock comicelles could be finely tuned.
This allowed a phase-diagram to be constructed that can be extended
to other triblock comicelles with different coronas on the central
or end segment where “cross” supermicelles were exclusively
formed under predicted conditions. Laser scanning confocal microscopy
(LSCM) analysis of dye-labeled “cross” supermicelles,
and block “cross” supermicelles formed by addition of
a different unimer to the arm termini, provided complementary characterization
to transmission electron microscopy (TEM) and dynamic light scattering
(DLS) and confirmed the existence of these “cross” supermicelles
as kinetically stable, micron-size colloidally stable structures in
solution
Monodisperse Cylindrical Micelles and Block Comicelles of Controlled Length in Aqueous Media
Cylindrical
block copolymer micelles have shown considerable promise
in various fields of biomedical research. However, unlike spherical
micelles and vesicles, control over their dimensions in biologically
relevant solvents has posed a key challenge that potentially limits
in depth studies and their optimization for applications. Here, we
report the preparation of cylindrical micelles of length in the wide
range of 70 nm to 1.10 μm in aqueous media with narrow length
distributions (length polydispersities <1.10). In our approach,
an amphiphilic linear-brush block copolymer, with high potential for
functionalization, was synthesized based on poly(ferrocenyldimethylsilane)-<i>b</i>-poly(allyl glycidyl ether) (PFS-<i>b</i>-PAGE)
decorated with triethylene glycol (TEG), abbreviated as PFS-<i>b</i>-(PEO-<i>g</i>-TEG). PFS-<i>b</i>-(PEO-<i>g</i>-TEG) cylindrical micelles of controlled length with low
polydispersities were prepared in <i>N</i>,<i>N</i>-dimethylformamide using small seed initiators via living crystallization-driven
self-assembly. Successful dispersion of these micelles into aqueous
media was achieved by dialysis against deionized water. Furthermore,
B–A–B amphiphilic triblock comicelles with PFS-<i>b</i>-poly(2-vinylpyridine) (P2VP) as hydrophobic “B”
blocks and hydrophilic PFS-<i>b</i>-(PEO-<i>g</i>-TEG) “A” segments were prepared and their hierarchical
self-assembly in aqueous media studied. It was found that superstructures
formed are dependent on the length of the hydrophobic blocks. Quaternization
of P2VP was shown to cause the disassembly of the superstructures,
resulting in the first examples of water-soluble cylindrical multiblock
comicelles. We also demonstrate the ability of the triblock comicelles
with quaternized terminal segments to complex DNA and, thus, to potentially
function as gene vectors
The coincidence and angular clustering of Chandra and SCUBA sources
NRC publication: N
Recommended from our members
Regional climate impacts of a possible future grand solar minimum.
This is the final published version. It first appeared at http://www.nature.com/ncomms/2015/150623/ncomms8535/full/ncomms8535.html.Any reduction in global mean near-surface temperature due to a future decline in solar activity is likely to be a small fraction of projected anthropogenic warming. However, variability in ultraviolet solar irradiance is linked to modulation of the Arctic and North Atlantic Oscillations, suggesting the potential for larger regional surface climate effects. Here, we explore possible impacts through two experiments designed to bracket uncertainty in ultraviolet irradiance in a scenario in which future solar activity decreases to Maunder Minimum-like conditions by 2050. Both experiments show regional structure in the wintertime response, resembling the North Atlantic Oscillation, with enhanced relative cooling over northern Eurasia and the eastern United States. For a high-end decline in solar ultraviolet irradiance, the impact on winter northern European surface temperatures over the late twenty-first century could be a significant fraction of the difference in climate change between plausible AR5 scenarios of greenhouse gas concentrations.This work was supported by the Joint DECC/Defra Met Office Hadley Centre Climate
Programme (GA01101) and also by the EU project SPECS funded by the European
Commission’s Seventh Framework Research Programme under the grant agreement
308378 (Met Office Hadley Centre authors), by the NERC National Centre for
Atmospheric Science (NCAS) Climate directorate (L.J.G. and A.C.M.), an ERC ACCI
grant (A.C.M) and an AXA Postdoctoral Fellowship (A.C.M.)
Uniform Toroidal Micelles via the Solution Self-Assembly of Block Copolymer-Homopolymer Blends Using a "frustrated Crystallization" Approach
Toroidal
nanostructures are of growing importance due to their
unique geometry and potential utility in materials fabrication. Although
a variety of amphiphilic block copolymers has been shown to self-assemble
into toroidal micelles, the conventional methods used are often very
slow with little control over the size of the resulting nanostructures.
Here, we report a rapid and efficient synthetic route to prepare toroidal
micelles of near uniform diameter through the cooperative coassembly
of amorphous blends of polyferrocenylsilane block copolymer and homopolymer,
where the degree of polymerization of the core-forming metalloblock
in the former is greater than for the latter. The self-assembly process
is accomplished within a few minutes, and the ring size of the toroids
can be varied between 30 and 90 nm by adjusting the mass ratio of
the block copolymer and homopolymer. The kinetic stability of the
resulting toroidal micelles can be enhanced by frustrating core crystallization
through solvent modulation and the toroids can also be readily used
as templates to fabricate circular arrays of metal nanoparticles
- …