Flow patterns generated by oblate medusan jellyfish: field measurements and laboratory analyses

Flow patterns generated by medusan swimmers such as jellyfish are known to differ according the morphology of the various animal species. Oblate medusae have been previously observed to generate vortex ring structures during the propulsive cycle. Owing to the inherent physical coupling between locomotor and feeding structures in these animals, the dynamics of vortex ring formation must be robustly tuned to facilitate effective functioning of both systems. To understand how this is achieved, we employed dye visualization techniques on scyphomedusae (Aurelia aurita) observed swimming in their natural marine habitat. The flow created during each propulsive cycle consists of a toroidal starting vortex formed during the power swimming stroke, followed by a stopping vortex of opposite rotational sense generated during the recovery stroke. These two vortices merge in a laterally oriented vortex superstructure that induces flow both toward the subumbrellar feeding surfaces and downstream. The lateral vortex motif discovered here appears to be critical to the dual function of the medusa bell as a flow source for feeding and propulsion. Furthermore, vortices in the animal wake have a greater volume and closer spacing than predicted by prevailing models of medusan swimming. These effects are shown to be advantageous for feeding and swimming performance, and are an important consequence of vortex interactions that have been previously neglected

Two Notions Of Safety

Timothy Williamson (1992, 224–5) and Ernest Sosa (1996) have ar- gued that knowledge requires one to be safe from error. Something is said to be safe from happening iff it does not happen at “close” worlds. I expand here on a puzzle noted by John Hawthorne (2004, 56n) that suggests the need for two notions of closeness. Counterfac- tual closeness is a matter of what could in fact have happened, given the specific circumstances at hand. The notion is involved in the semantics for counterfactuals and is the one epistemologists have typically assumed. Normalized closeness is rather a matter of what could typically have happened, that is, what would go on in a class of normal alternatives to actuality, irrespectively of whether or not they could have happened in the circumstances at hand

Time Evolution of Decay Spectrum in K^0, K^0 bar -> pi^+ pi^- e^+ e^-

We consider the decay K^0 (K^0 bar) -> pi^+ pi^- e^+ e^- of a neutral K meson prepared in a state of strangeness +1 (-1). The time evolution of the state produces remarkable time-dependent effects in the angular distribution of the pi^+ pi^- e^+ e^- system. These effects are correlated with the time-dependence of the photon polarization in the radiative decay K^0 (K^0 bar) -> pi^+ pi^- gamma. We study, in particular, the CP-odd, T-odd term in the distribution d Gamma / d phi of the angle between the pi^+ pi^- and the e^+ e^- planes. We also give the spectrum in the case that the decaying meson is an incoherent mixture of K^0 and K^0 bar, and discuss the case of K_S regeneration in a K_L beam.Comment: 16 pages, 8 figures, minor typos corrected, to appear in Phys. Lett.

A mechanophysical phase transition provides a dramatic example of colour polymorphism: the tribochromism of a substituted tri(methylene)tetrahydrofuran-2-one

BACKGROUND: Derivatives of fulgides have been shown to have interesting photochromic properties. We have synthesised a number of such derivatives and have found, in some cases, that crystals can be made to change colour on crushing, a phenomenon we have termed "tribochromism". We have studied a number of derivatives by X-ray crystallography, to see if the colour is linked to molecular structure or crystal packing, or both, and our structural results have been supported by calculation of molecular and lattice energies. RESULTS: A number of 5-dicyanomethylene-4-diphenylmethylene-3-disubstitutedmethylene-tetrahydrofuran-2-one compounds have been prepared and structurally characterised. The compounds are obtained as yellow or dark red crystals, or, in one case, both. In two cases where yellow crystals were obtained, we found that crushing the crystals gave a deep red powder. Structure determinations, including those of the one compound which gave both coloured forms, depending on crystallisation conditions, showed that the yellow crystals contained molecules in which the structure comprised a folded conformation at the diphenylmethylene site, whilst the red crystals contained molecules in a twisted conformation at this site. Lattice energy and molecular conformation energies were calculated for all molecules, and showed that the conformational energy of the molecule in structure IIIa (yellow) is marginally higher, and the conformation thus less stable, than that of the molecule in structure IIIb (red). However, the van der Waals energy for crystal structure IIIa, is slightly stronger than that of structure IIIb - which may be viewed as a hint of a metastable packing preference for IIIa, overcome by the contribution of a more stabilising Coulomb energy to the overall more favourable lattice energy of structure IIIb. CONCLUSIONS: Our studies have shown that the crystal colour is correlated with one of two molecular conformations which are different in energy, but that the less stable conformation can be stabilised by its host crystal lattice. Graphical abstractGraphical representation of the structural and colour change in the tribochromic compound (III)

Improved Synthesis of 2,6,6-trimethyl-1-cyclohexene-1-acetaldehyde, a Key Intermediate for Drimane-related Sesquiterpenes.

The titel compound is conveniently prepared in 65% overall yield by a two step synthesis starting from he commercially available β-ionone

Devilish details : fine-tuning survey techniques for ephemeral sites

The Rural Life in Protohistoric Italy project investigates small surface scatters from the Bronze and Iron Age, found during field walking surveys in Calabria, Italy. In this article we argue that detailed, multidisciplinary investigations of such ephemeral sites are crucial for our understanding of protohistoric rural society and land use. We illustrate our methodology of integrated surface recordings, geophysical methods, small test pits and laboratory studies with the case study of the Late Bronze Age site T231. The implications of this case study for regional settlement models are discussed

Alkylation of ketones by use of solid KOH in dimethyl sulfoxide

A mixture of solid KOH in dimethyl sulfoxide has a strong basicity, but only a low nucleophilicity and is used for methylation of ketones. With this simple and inexpensive reagent complete methylation with yields up to 90% can be achieved

Stokes Vector of Photon in the Decays B^0 -> rho^0 gamma and B^0 -> K^* gamma

We consider a model for the decay Bbar^0 -> rho^0 gamma in which the short-distance amplitude determined by the Hamiltonian describing b -> d gamma is combined with a typical long-distance contribution Bbar^0 -> D^+ D^- -> rho^0 gamma. The latter possesses a significant dynamical phase which induces a CP-violating asymmetry A_CP, as well as an important modification of the Stokes vector of the photon. The components S_1 and S_3 of the Stokes vector S = (S_1, S_2, S_3) can be measured in the decay Bbar^0 -> rho^0 gamma^* -> pi^+ pi^- e^+ e^- where they produce a characteristic effect in the angular distribution d Gamma / d phi, phi being the angle between the pi^+ pi^- and e^+ e^- planes. A similar analysis is carried out for the decays Bbar^0 -> Kbar^* gamma and Bbar^0 -> Kbar^* gamma^* -> pi^+ K^- e^+ e^-Comment: 13 pages, 8 figures; v2: Some clarifying remarks added, together with additional references. Minor typos corrected. No change in result

Coformer Replacement as an Indicator for Thermodynamic Instability of Cocrystals: Competitive Transformation of Caffeine:Dicarboxylic Acid

yesThe thermodynamic stability of caffeine (CA) cocrystals with dicarboxylic acids (DAs) as coformers was investigated in the presence of a range of structurally related dicarboxylic acids (SRDs). Two experimental conditions (slurry and dry-grinding) were studied for mixing the cocrystal and the SRD additive. The additives oxalic, malonic and glutaric acid led to the replacement of the acid coformer for certain cocrystals. Interestingly, a change in stoichiometry was observed for the CA:maleic acid system. A stability order among the cocrystals was established depending on their tendency to replace the coformer. To understand the factors controlling the relative stabilities, lattice energies were calculated using dispersion corrected Density Functional Theory (DFT). Gibbs free energy changes were calculated from experimental solubilities. The observed stability order corroborated well with lattice energy and Gibbs free energy computations