Modality effects in vocabulary acquisition

It is unknown whether modality affects the efficiency with which humans learn novel word forms and their meanings, with previous studies reporting both written and auditory advantages. The current study implements controls whose absence in previous work likely offers explanation for such contradictory findings. In two novel word learning experiments, participants were trained and tested on pseudoword - novel object pairs, with controls on: modality of test, modality of meaning, duration of exposure and transparency of word form. In both experiments word forms were presented in either their written or spoken form, each paired with a pictorial meaning (novel object). Following a 20-minute filler task, participants were tested on their ability to identify the picture-word form pairs on which they were trained. A between subjects design generated four participant groups per experiment 1) written training, written test; 2) written training, spoken test; 3) spoken training, written test; 4) spoken training, spoken test. In Experiment 1 the written stimulus was presented for a time period equal to the duration of the spoken form. Results showed that when the duration of exposure was equal, participants displayed a written training benefit. Given words can be read faster than the time taken for the spoken form to unfold, in Experiment 2 the written form was presented for 300 ms, sufficient time to read the word yet 65% shorter than the duration of the spoken form. No modality effect was observed under these conditions, when exposure to the word form was equivalent. These results demonstrate, at least for proficient readers, that when exposure to the word form is controlled across modalities the efficiency with which word form-meaning associations are learnt does not differ. Our results therefore suggest that, although we typically begin as aural-only word learners, we ultimately converge on developing learning mechanisms that learn equally efficiently from both written and spoken materials

Ultrafast electron dynamics at water covered alkali adatoms adsorbed on Cu(111)

Here we report on the ultrafast electron dynamics of the alkalis Na, K, and Cs coadsorbed with D2O on Cu(111) surfaces, which we investigated with femtosecond time-resolved two-photon photoemission. The well known transient electronic binding energy stabilization in bare adsorbed alkalis is enhanced by the presence of water which acts as a solvent and increases the transient energy gain. We observe for all adsorbed alkalis a transient binding energy stabilization of 100–300 meV. The stabilization rates range from 1 to 2 eV ps-1. Here the heavier alkali exhibits a slower stabilization which we explain by their weaker static alkali–water interaction observed in thermal desorption spectroscopy. The population dynamics at low water coverage is described by a single exponential. With increasing water coverage the behavior becomes non-exponential suggesting an additional excited state due to electron solvatio

Determination of the electron's solvation site on D₂O/Cu(111) using Xe overlayers and femtosecond photoelectron spectroscopy

We investigate the binding site of solvated electrons in amorphous D2O clusters and D2O wetting layers adsorbed on Cu(111) by means of two-photon photoelectron (2PPE) spectroscopy. On the basis of different interactions of bulk- or surface-bound solvated electrons with rare gas atoms, titration experiments using Xe overlayers reveal the location of the electron solvation sites. In the case of flat clusters with a height of 2-4 bilayers adsorbed on Cu(111), solvated electrons are found to reside at the ice - vacuum interface, whereas a bulk character is determined for solvated electrons in wetting layers. Furthermore, time-resolved experiments are performed to determine the origin of the transition between these different solvation sites with increasing D2O coverage. We employ an empirical model calculation to analyse the rate of electron transfer back to the substrate and the energetic stabilization of the solvated electrons, which allows further insight into the binding site for clusters. We find that the solvated electrons reside at the edges of the clusters. Therefore, we attribute the transition from surface- to bulk-solvation to the coalescence of the clusters to a closed ice film occurring at a nominal coverage of 2-3 BL, while the distance of the binding sites to the metal-ice interface is maintained

Multi-wavelength modeling of the spatially resolved debris disk of HD 107146

(abridged) We aim to constrain the location, composition, and dynamical state of planetesimal populations and dust around the young, sun-like (G2V) star HD 107146}. We consider coronagraphic observations obtained with the Advanced Camera for Surveys (HST/ACS) onboard the HST in broad V and broad I filters, a resolved 1.3mm map obtained with the Combined Array for Research in Millimeter-Wave Astronomy (CARMA), Spitzer/IRS low resolution spectra, and the spectral energy distribution (SED) of the object at wavelengths ranging from 3.5micron to 3.1mm. We complement these data with new coronagraphic high resolution observations of the debris disk using the Near Infrared Camera and Multi-Object Spectrometer (HST/NICMOS) aboard the HST in the F110W filter. The SED and images of the disk in scattered light as well as in thermal reemission are combined in our modeling using a parameterized model for the disk density distribution and optical properties of the dust. A detailed analytical model of the debris disk around HD 107146 is presented that allows us to reproduce the almost entire set of spatially resolved and unresolved multi-wavelength observations. Considering the variety of complementary observational data, we are able to break the degeneracies produced by modeling SED data alone. We find the disk to be an extended ring with a peak surface density at 131AU. Furthermore, we find evidence for an additional, inner disk probably composed of small grains released at the inner edge of the outer disk and moving inwards due to Poynting-Robertson drag. A birth ring scenario (i.e., a more or less broad ring of planetesimals creating the dust disk trough collisions) is found to be the most likely explanation of the ringlike shape of the disk.Comment: 15 pages, 9 figures, accepted for publication in A&

Ultrafast Exciton Formation at the ZnO(101¯0) Surface

We study the ultrafast quasiparticle dynamics in and below the ZnO conduction band using femtosecond time-resolved two-photon photoelectron spectroscopy. Above band gap excitation causes hot electron relaxation by electron-phonon scattering down to the Fermi level EF followed by ultrafast (200 fs) formation of a surface exciton (SX). Transient screening of the Coulomb interaction reduces the SX formation probability at high excitation densities near the Mott limit. Located just below the surface, the SX are stable with regard to hydrogen-induced work function modifications and thus the ideal prerequisite for resonant energy transfer applications

Wavelets: mathematics and applications

The notion of wavelets is defined. It is briefly described {\it what} are wavelets, {\it how} to use them, {\it when} we do need them, {\it why} they are preferred and {\it where} they have been applied. Then one proceeds to the multiresolution analysis and fast wavelet transform as a standard procedure for dealing with discrete wavelets. It is shown which specific features of signals (functions) can be revealed by this analysis, but can not be found by other methods (e.g., by the Fourier expansion). Finally, some examples of practical application are given (in particular, to analysis of multiparticle production}. Rigorous proofs of mathematical statements are omitted, and the reader is referred to the corresponding literature.Comment: 16 pages, 5 figures, Latex, Phys. Atom. Nuc

Life at high Deborah number

In many biological systems, microorganisms swim through complex polymeric fluids, and usually deform the medium at a rate faster than the inverse fluid relaxation time. We address the basic properties of such life at high Deborah number analytically by considering the small-amplitude swimming of a body in an arbitrary complex fluid. Using asymptotic analysis and differential geometry, we show that for a given swimming gait, the time-averaged leading-order swimming kinematics of the body can be expressed as an integral equation on the solution to a series of simpler Newtonian problems. We then use our results to demonstrate that Purcell's scallop theorem, which states that time-reversible body motion cannot be used for locomotion in a Newtonian fluid, breaks down in polymeric fluid environments

Invertebrate communities on historical shipwrecks in the western Atlantic : relation to islands

Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 566 (2017): 17-29, doi:10.3354/meps12058.Shipwrecks can be considered island-like habitats on the seafloor. We investigated the fauna of eight historical shipwrecks off the east coast of the U.S. to assess whether species distribution patterns on the shipwrecks fit models from classical island theory. Invertebrates on the shipwrecks included both sessile (sponges, anemones, hydroids) and motile (crustaceans, echinoderms) species. Invertebrate communities were significantly different among wrecks. The size and distance between wrecks influenced the biotic communities, much like on terrestrial islands. However, while wreck size influenced species richness (alpha diversity), distance to the nearest wreck influenced community composition (beta diversity). Alpha and beta diversity on the shipwrecks were thus influenced by different abiotic factors. We found no evidence of either nested patterns or non-random co-occurrence of morphotypes, suggesting that the taxa on a given shipwreck were randomly selected from the available taxon pool. Species present on the shipwrecks generally had one of two reproductive modes: most motile or solitary sessile species had long-duration planktotrophic larvae, while most encrusting or colonial sessile species had short-duration lecithotrophic larvae and underwent asexual reproduction by budding as adults. Short-duration larvae may recruit to their natal shipwreck, allowing them to build up dense populations and dominate the wreck surfaces. A high degree of dominance was indeed observed on the wrecks, with up to 80% of the fauna being accounted for by the most common species alone. By comparing the shipwreck communities to known patterns of succession in shallow water, we hypothesize that the shipwrecks are in a stage of mid-succession.This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-0829517. Funding for this project was supplied by the Bureau of Ocean Energy Management (BOEM), under contract to CSA Ocean Sciences, Inc. (contract M10PC00100) in partnership with the National Oceanographic 377 Partnership Program

Propulsion in a viscoelastic fluid

Flagella beating in complex fluids are significantly influenced by viscoelastic stresses. Relevant examples include the ciliary transport of respiratory airway mucus and the motion of spermatozoa in the mucus-filled female reproductive tract. We consider the simplest model of such propulsion and transport in a complex fluid, a waving sheet of small amplitude free to move in a polymeric fluid with a single relaxation time. We show that, compared to self-propulsion in a Newtonian fluid occurring at a velocity U_N, the sheet swims (or transports fluid) with velocity U / U_N = [1+De^2 (eta_s)/(eta) ]/[1+De^2], where eta_s is the viscosity of the Newtonian solvent, eta is the zero-shear-rate viscosity of the polymeric fluid, and De is the Deborah number for the wave motion, product of the wave frequency by the fluid relaxation time. Similar expressions are derived for the rate of work of the sheet and the mechanical efficiency of the motion. These results are shown to be independent of the particular nonlinear constitutive equations chosen for the fluid, and are valid for both waves of tangential and normal motion. The generalization to more than one relaxation time is also provided. In stark contrast with the Newtonian case, these calculations suggest that transport and locomotion in a non-Newtonian fluid can be conveniently tuned without having to modify the waving gait of the sheet but instead by passively modulating the material properties of the liquid.Comment: 21 pages, 1 figur

The dust, planetesimals and planets of HD 38529

HD 38529 is a post-main sequence G8III/IV star (3.5 Gyr old) with a planetary system consisting of at least two planets having Msin(i) of 0.8 MJup and 12.2 MJup, semimajor axes of 0.13 AU and 3.74 AU, and eccentricities of 0.25 and 0.35, respectively. Spitzer observations show that HD 38529 has an excess emission above the stellar photosphere, with a signal-to-noise ratio (S/N) at 70 micron of 4.7, a small excess at 33 micron (S/N=2.6) and no excess <30 micron. We discuss the distribution of the potential dust-producing planetesimals from the study of the dynamical perturbations of the two known planets, considering in particular the effect of secular resonances. We identify three dynamically stable niches at 0.4-0.8 AU, 20-50 AU and beyond 60 AU. We model the spectral energy distribution of HD 38529 to find out which of these niches show signs of harboring dust-producing plantesimals. The secular analysis, together with the SED modeling resuls, suggest that the planetesimals responsible for most of the dust emission are likely located within 20-50 AU, a configuration that resembles that of the Jovian planets + Kuiper Belt in our Solar System. Finally, we place upper limits (8E-6 lunar masses of 10 micron particles) to the amount of dust that could be located in the dynamically stable region that exists between the two planets (0.25--0.75 AU).Comment: 23 pages, including 1 table and 5 figures. Accepted for publication in Ap