2,036 research outputs found
The rich circumstellar chemistry of SMP LMC 11
Carbon-rich evolved stars from the asymptotic giant branch to the planetary nebula phase are characterized by a rich and complex carbon chemistry in their circumstellar envelopes. A peculiar object is the preplanetary nebula SMP LMC 11, whose Spitzer Infrared Spectrograph spectrum shows remarkable and diverse molecular absorption bands. To study howthe molecular composition in this object compares to our current understanding of circumstellar carbon chemistry, we modeled this molecular absorption. We find high abundances for a number of molecules, perhaps most notably benzene. We also confirm the presence of propyne (CH3C2H) in this spectrum. Of all the cyanopolyynes, only HC3N is evident; we can detect at best a marginal presence of HCN. From comparisons to various chemical models, we can conclude that SMP LMC 11 must have an unusual circumstellar environment (a torus rather than an outflow)
The secret world of shrimps: polarisation vision at its best
Animal vision spans a great range of complexity, with systems evolving to
detect variations in optical intensity, distribution, colour, and polarisation.
Polarisation vision systems studied to date detect one to four channels of
linear polarisation, combining them in opponent pairs to provide
intensity-independent operation. Circular polarisation vision has never been
seen, and is widely believed to play no part in animal vision. Polarisation is
fully measured via Stokes' parameters--obtained by combined linear and circular
polarisation measurements. Optimal polarisation vision is the ability to see
Stokes' parameters: here we show that the crustacean \emph{Gonodactylus
smithii} measures the exact components required. This vision provides optimal
contrast-enhancement, and precise determination of polarisation with no
confusion-states or neutral-points--significant advantages. We emphasise that
linear and circular polarisation vision are not different modalities--both are
necessary for optimal polarisation vision, regardless of the presence of
strongly linear or circularly polarised features in the animal's environment.Comment: 10 pages, 6 figures, 2 table
Reviews
The following publications have been reviewed by the mentioned authors;Welsh Crafts by Mary Eirwen Jones, reviewed by Roy NashA Source Book of Picture Making by Henry Pluckrose, reviewed by R. HartApproaches to Drawing by Leo Walmsley, reviewed by John EgglestonMoulded and Slip Cast Pottery and Ceramics by David Cowley, reviewed by Michael PaffardPainting by John Lancaster, reviewed by R. N. MacGregorDesign Resource Sheets by R. N. Billington and J. R. Jeffrey, reviewed by Dick SuttonEnamelling on Metal, Oppi. Intracht, reviewed by J. N. AtkinsProcesses by Jack Bainbridge, reviewed by Michael SayerArtists and People by Su Braden, reviewed by Roy ShawMake Your Own Musical Instrument by Stuart Dalby, reviewed by Eric DecorteDesign in General Education by John Harahan, reviewed by Bernard AylwardPainting Without a Brush by Roy Sparkes, reviewed by John LancasterBuilding Craft Equipment by A. Jay and Carol W. Abrams, reviewed by S. R. BlundellPyrography by Berhand Havez and Jean-Claude Varlet, reviewed by Paul Kin
Influence of Nanoparticle Size and Shape on Oligomer Formation of an Amyloidogenic Peptide
Understanding the influence of macromolecular crowding and nanoparticles on
the formation of in-register -sheets, the primary structural component
of amyloid fibrils, is a first step towards describing \emph{in vivo} protein
aggregation and interactions between synthetic materials and proteins. Using
all atom molecular simulations in implicit solvent we illustrate the effects of
nanoparticle size, shape, and volume fraction on oligomer formation of an
amyloidogenic peptide from the transthyretin protein. Surprisingly, we find
that inert spherical crowding particles destabilize in-register -sheets
formed by dimers while stabilizing -sheets comprised of trimers and
tetramers. As the radius of the nanoparticle increases crowding effects
decrease, implying smaller crowding particles have the largest influence on the
earliest amyloid species. We explain these results using a theory based on the
depletion effect. Finally, we show that spherocylindrical crowders destabilize
the ordered -sheet dimer to a greater extent than spherical crowders,
which underscores the influence of nanoparticle shape on protein aggregation
The future of sovereignty in multilevel governance Europe: a constructivist reading
Multilevel governance presents a depiction of contemporary structures in EU Europe as consisting of overlapping authorities and competing competencies. By focusing on emerging non-anarchical structures in the international system, hence moving beyond the conventional hierarchy/anarchy dichotomy to distinguish domestic and international arenas, this seems a radical transformation of the familiar Westphalian system and to undermine state sovereignty. Paradoxically, however, the principle of sovereignty proves to be resilient despite its alleged empirical decline. This article argues that social constructivism can explain the paradox, by considering sovereign statehood as a process-dependent institutional fact, and by showing that multilevel governance can feed into this process
Effective Lagrangian Approach to the Theory of Eta Photoproduction in the Region
We investigate eta photoproduction in the resonance region
within the effective Lagrangian approach (ELA), wherein leading contributions
to the amplitude at the tree level are taken into account. These include the
nucleon Born terms and the leading -channel vector meson exchanges as the
non-resonant pieces. In addition, we consider five resonance contributions in
the - and - channel; besides the dominant , these are:
and . The amplitudes for the
and the photoproduction near threshold have significant
differences, even as they share common contributions, such as those of the
nucleon Born terms. Among these differences, the contribution to the
photoproduction of the -channel excitation of the is the most
significant. We find the off-shell properties of the spin-3/2 resonances to be
important in determining the background contributions. Fitting our effective
amplitude to the available data base allows us to extract the quantity
, characteristic of the
photoexcitation of the resonance and its decay into the
-nucleon channel, of interest to precise tests of hadron models. At the
photon point, we determine it to be from
the old data base, and from a
combination of old data base and new Bates data. We obtain the helicity
amplitude for to be from the old data base, and from the combination of the old data base and new Bates
data, compared with the results of the analysis of pion photoproduction
yielding , in the same units.Comment: 43 pages, RevTeX, 9 figures available upon request, to appear in
Phys. Rev.
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