The kinetics of surfactant desorption at the air–solution interface

The kinetics of desorption of the anionic surfactant sodium dodecylbenzene sulfonate at the air–solution interface have been studied using neutron reflectivity (NR). The experimental arrangement incorporates a novel flow cell in which the subphase can be exchanged (diluted) using a laminar flow whilst the surface region remains unaltered. The kinetics of the desorption is relatively slow and occurs over many tens of minutes compared with the dilution timescale of approximately 10–30 minutes. A detailed mathematical model, in which the rate of the desorption is determined by transport through a near-surface diffusion layer into a diluted bulk solution below, is developed and provides a good description of the timedependent adsorption data.\ud \ud A key parameter of the model is the ratio of the depth of the diffusion layer, Hc , to the depth of the fluid, Hf, and we find that this is related to the reduced Péclet number, Pe*, for the system, via Hc/Hf, = C/Pe* 1/ 2 . Although from a highly idealised experimental arrangement, the results provide an important insight into the ‘rinse mechanism’, which is applicable to a wide variety of domestic and industrial circumstances

Editors' Review and Introduction: Learning Grammatical Structures: Developmental, Cross‐Species, and Computational Approaches

Human languages all have a grammar, that is, rules that determine how symbols in a language can be combined to create complex meaningful expressions. Despite decades of research, the evolutionary, developmental, cognitive, and computational bases of grammatical abilities are still not fully understood. “Artificial Grammar Learning” (AGL) studies provide important insights into how rules and structured sequences are learned, the relevance of these processes to language in humans, and whether the cognitive systems involved are shared with other animals. AGL tasks can be used to study how human adults, infants, animals, or machines learn artificial grammars of various sorts, consisting of rules defined typically over syllables, sounds, or visual items. In this introduction, we distill some lessons from the nine other papers in this special issue, which review the advances made from this growing body of literature. We provide a critical synthesis, identify the questions that remain open, and recognize the challenges that lie ahead. A key observation across the disciplines is that the limits of human, animal, and machine capabilities have yet to be found. Thus, this interdisciplinary area of research firmly rooted in the cognitive sciences has unearthed exciting new questions and venues for research, along the way fostering impactful collaborations between traditionally disconnected disciplines that are breaking scientific ground

Polyhedral units and network connectivity in calcium aluminosilicate glasses from high-energy x-ray diffraction

Structure factors for Cax/2AlxSi1-xO2 glasses (x=0,0.25,0.5,0.67) extended to a wave vector of magnitude Q= 40 1/A have been obtained by high-energy x-ray diffraction. For the first time, it is possible to resolve the contributions of Si-O, Al-O and Ca-O coordination polyhedra to the experimental atomic pair distribution functions (PDF). It has been found that both Si and Al are four-fold coordinated and so participate in a continuous tetrahedral network at low values of x. The number of network breaking defects in the form of non-bridging oxygens (NBO's) increases slowly with x until x=0.5 (NBO's ~ 10% at x=0.5). By x=0.67 the network breaking defects become significant as evidenced by the significant drop in the average coordination number of Si. By contrast, Al-O tetrahedra remain free of NBO's and fully integrated in the Al/Si-O network for all values of x. Calcium maintains a rather uniform coordination sphere of approximately 5 oxygen atoms for all values of x. The results suggest that not only Si/Al-O tetrahedra but Ca-O polyhedra, too, play a role in determining the glassy structure

Four-body continuum-discretized coupled-channels calculations using a transformed harmonic oscillator basis

The scattering of a weakly bound three-body system by a target is discussed. A transformed harmonic oscillator basis is used to provide an appropriate discrete and finite basis for treating the continuum part of the spectrum of the projectile. The continuum-discretized coupled channels framework is used for the scattering calculations. The formalism is applied to different reactions, 6He+12C at 229.8 MeV, 6He+64Zn at 10 and 13.6 MeV, and 6He+208Pb at 22 MeV, induced by the Borromean nucleus 6He. Both the Coulomb and nuclear interactions with a target are taken into account.Comment: Published in Phys. Rev.

Testing 6,8^{6,8}He density distributions by calculations of total reaction cross-sections of 6,8^{6,8}He+28^{28}Si

Calculations of the $^{6,8}$He + $^{28}$Si total reaction cross sections at intermediate energies are performed on the basis of the Glauber-Sitenko microscopic optical-limit model. The target-nucleus density distribution is taken from the electron-nucleus scattering data, and the $^{6,8}$He densities are used as they are derived in different models. The results of the calculations are compared with the existing experimental data. The effects of the density tails of the projectile nuclei as well as the role of shell admixtures and short-range correlations are analyzed.Comment: 10 pages, 5 figures. Submitted to the International Journal of Modern Physics

Configuration Mixing within the Energy Density Functional Formalism: Removing Spurious Contributions from Non-Diagonal Energy Kernels

Multi-reference calculations along the lines of the Generator Coordinate Method or the restoration of broken symmetries within the nuclear Energy Density Functional (EDF) framework are becoming a standard tool in nuclear structure physics. These calculations rely on the extension of a single-reference energy functional, of the Gogny or the Skyrme types, to non-diagonal energy kernels. There is no rigorous constructive framework for this extension so far. The commonly accepted way proceeds by formal analogy with the expressions obtained when applying the generalized Wick theorem to the non-diagonal matrix element of a Hamilton operator between two product states. It is pointed out that this procedure is ill-defined when extended to EDF calculations as the generalized Wick theorem is taken outside of its range of applicability. In particular, such a procedure is responsible for the appearance of spurious divergences and steps in multi-reference EDF energies, as was recently observed in calculations restoring particle number or angular momentum. In the present work, we give a formal analysis of the origin of this problem for calculations with and without pairing, i.e. constructing the density matrices from either Slater determinants or quasi-particle vacua. We propose a correction to energy kernels that removes the divergences and steps, and which is applicable to calculations based on any symmetry restoration or generator coordinate. The method is formally illustrated for particle number restoration and is specified to configuration mixing calculations based on Slater determinants.Comment: 27 pages, 1 figure, accepted for publication in PR

Trace formula for dielectric cavities II: Regular, pseudo-integrable, and chaotic examples

Dielectric resonators are open systems particularly interesting due to their wide range of applications in optics and photonics. In a recent paper [PRE, vol. 78, 056202 (2008)] the trace formula for both the smooth and the oscillating parts of the resonance density was proposed and checked for the circular cavity. The present paper deals with numerous shapes which would be integrable (square, rectangle, and ellipse), pseudo-integrable (pentagon) and chaotic (stadium), if the cavities were closed (billiard case). A good agreement is found between the theoretical predictions, the numerical simulations, and experiments based on organic micro-lasers.Comment: 18 pages, 32 figure

High real-space resolution measurement of the local structure of Ga_1-xIn_xAs using x-ray diffraction

High real-space resolution atomic pair distribution functions (PDF)s from the alloy series Ga_1-xIn_xAs have been obtained using high-energy x-ray diffraction. The first peak in the PDF is resolved as a doublet due to the presence of two nearest neighbor bond lengths, Ga-As and In-As, as previously observed using XAFS. The widths of nearest, and higher, neighbor pairs are analyzed by separating the strain broadening from the thermal motion. The strain broadening is five times larger for distant atomic neighbors as compared to nearest neighbors. The results are in agreement with model calculations.Comment: 4 pages, 5 figure

New Discrete Basis for Nuclear Structure Studies

A complete discrete set of spherical single-particle wave functions for studies of weakly-bound many-body systems is proposed. The new basis is obtained by means of a local-scale point transformation of the spherical harmonic oscillator wave functions. Unlike the harmonic oscillator states, the new wave functions decay exponentially at large distances. Using the new basis, characteristics of weakly-bound orbitals are analyzed and the ground state properties of some spherical doubly-magic nuclei are studied. The basis of the transformed harmonic oscillator is a significant improvement over the harmonic oscillator basis, especially in studies of exotic nuclei where the coupling to the particle continuum is important.Comment: 13 pages, RevTex, 6 p.s. figures, submitted to Phys. Rev.