Problems in the coupling of eye and hand in the sequential movements of children with developmental coordination disorder

Background: Shifting gaze and attention ahead of the hand is a natural component in the performance of skilled manual actions. Very few studies have examined the precise co-ordination between the eye and hand in children with Developmental Coordination Disorder (DCD). Methods This study directly assessed the maturity of eye-hand co-ordination in children with DCD. A double-step pointing task was used to investigate the coupling of the eye and hand in 7-year-old children with and without DCD. Sequential targets were presented on a computer screen, and eye and hand movements were recorded simultaneously. Results There were no differences between typically developing (TD) and DCD groups when completing fast single-target tasks. There were very few differences in the completion of the first movement in the double-step tasks, but differences did occur during the second sequential movement. One factor appeared to be the propensity for the DCD children to delay their hand movement until some period after the eye had landed on the target. This resulted in a marked increase in eye-hand lead during the second movement, disrupting the close coupling and leading to a slower and less accurate hand movement among children with DCD. Conclusions In contrast to skilled adults, both groups of children preferred to foveate the target prior to initiating a hand movement if time allowed. The TD children, however, were more able to reduce this foveation period and shift towards a feedforward mode of control for hand movements. The children with DCD persevered with a look-then-move strategy, which led to an increase in error. For the group of DCD children in this study, there was no evidence of a problem in speed or accuracy of simple movements, but there was a difficulty in concatenating the sequential shifts of gaze and hand required for the completion of everyday tasks or typical assessment items.

The art of conversation is coordination: common ground and the coupling of eye movements during dialogue

When two people discuss something they can see in front of them, what is the relationship between their eye movements? We recorded the gaze of pairs of subjects engaged in live, spontaneous dialogue. Cross-recurrence analysis revealed a coupling between the eye movements of the two conversants. In the first study, we found their eye movements were coupled across several seconds. In the second, we found that this coupling increased if they both heard the same background information prior to their conversation. These results provide a direct quantification of joint attention during unscripted conversation and show that it is influenced by knowledge in the common ground.

Time-dependent orientation coupling in equilibrium polymer melts

The motion in concentrated polymer systems is described by either the Rouse or the reptation model, which both assume that the relaxation of each polymer chain is independent of the surrounding chains. This, however, is in contradiction with several experiments. In this Letter, we propose a universal description of orientation coupling in polymer melts in terms of the time-dependent coupling parameter κ(t). We use molecular dynamics simulations to show that the coupling parameter increases with time, reaching about 50% at long times, independently of the chain length or blend composition. This leads to predictions of component dynamics in mixtures of different molecular weights from the knowledge of monodisperse dynamics for unentangled melts. Finally, we demonstrate that entanglements do not play a significant role in the observed coupling. © 2010 The American Physical Society

Coupling aerosol surface and bulk chemistry with a kinetic double layer model (K2-SUB): oxidation of oleic acid by ozone

We present a kinetic double layer model coupling aerosol surface and bulk chemistry (K2-SUB) based on the PRA framework of gas-particle interactions (Poschl-Rudich-Ammann, 2007). K2-SUB is applied to a popular model system of atmospheric heterogeneous chemistry: the interaction of ozone with oleic acid. We show that our modelling approach allows de-convoluting surface and bulk processes, which has been a controversial topic and remains an important challenge for the understanding and description of atmospheric aerosol transformation. In particular, we demonstrate how a detailed treatment of adsorption and reaction at the surface can be coupled to a description of bulk reaction and transport that is consistent with traditional resistor model formulations. From literature data we have derived a consistent set of kinetic parameters that characterise mass transport and chemical reaction of ozone at the surface and in the bulk of oleic acid droplets. Due to the wide range of rate coefficients reported from different experimental studies, the exact proportions between surface and bulk reaction rates remain uncertain. Nevertheless, the model results suggest an important role of chemical reaction in the bulk and an approximate upper limit of similar to 10(-11) cm(2) s(-1) for the surface reaction rate coefficient. Sensitivity studies show that the surface accommodation coefficient of the gas-phase reactant has a strong non-linear influence on both surface and bulk chemical reactions. We suggest that K2-SUB may be used to design, interpret and analyse future experiments for better discrimination between surface and bulk processes in the oleic acid-ozone system as well as in other heterogeneous reaction systems of atmospheric relevance.

Palladium-coated nickel nanoclusters: new Hiyama cross-coupling catalysts

The advantages of bimetallic nanoparticles as C - C coupling catalysts are discussed, and a simple, bottom- up synthesis method of core - shell Ni - Pd clusters is presented. This method combines electrochemical and 'wet chemical' techniques, and enables the preparation of highly monodispersed structured bimetallic nanoclusters. The double- anode electrochemical cell is described in detail. The core - shell Ni - Pd clusters were then applied as catalysts in the Hiyama cross- coupling reaction between phenyltrimethoxysilane and various haloaryls. Good product yields were obtained with a variety of iodo- and bromoaryls. We found that, for a fixed amount of Pd atoms, the core - shell clusters outperform both the monometallic Pd clusters and the alloy bimetallic Ni - Pd ones. THF is an excellent solvent for this process, with less than 2% homocoupling by-product. The roles of the stabiliser and the solvent are discussed.

The impact of finer-resolution air-sea coupling on the intraseasonal oscillation of the Indian monsoon

The new HadKPP atmosphere–ocean coupled model is described and then used to determine the effects of sub-daily air–sea coupling and fine near-surface ocean vertical resolution on the representation of the Northern Hemisphere summer intra-seasonal oscillation. HadKPP comprises the Hadley Centre atmospheric model coupled to the K Profile Parameterization ocean-boundary-layer model. Four 30-member ensembles were performed that varied in oceanic vertical resolution between 1 m and 10 m and in coupling frequency between 3 h and 24 h. The 10 m, 24 h ensemble exhibited roughly 60% of the observed 30–50 day variability in sea-surface temperatures and rainfall and very weak northward propagation. Enhancing either only the vertical resolution or only the coupling frequency produced modest improvements in variability and only a standing intra-seasonal oscillation. Only the 1 m, 3 h configuration generated organized, northward-propagating convection similar to observations. Sub-daily surface forcing produced stronger upper-ocean temperature anomalies in quadrature with anomalous convection, which likely affected lower-atmospheric stability ahead of the convection, causing propagation. Well-resolved air–sea coupling did not improve the eastward propagation of the boreal summer intra-seasonal oscillation in this model. Upper-ocean vertical mixing and diurnal variability in coupled models must be improved to accurately resolve and simulate tropical sub-seasonal variability. In HadKPP, the mere presence of air–sea coupling was not sufficient to generate an intra-seasonal oscillation resembling observations.

Coupling cancellation based multiuser detector for asynchronous DS/CDMA

A three-shot multiuser detector is proposed for the reverse link of asynchronous DS/CDMA systems. By taking advantage of the preceding (already reconstructed) bit and the matched filter output for the following two bits, the coupling between temporally adjacent bits (TABs, which always exists for asynchronous systems) is cancelled in a three step fashion. The obtained detector has several useful advantages over existing schemes.

Astigmatism in tapered slot antennas

A series of scale model measurements of transverse electromagnetic mode tapered slot antennas are presented. They show that the beam launched by this type of antenna is astigmatic. It is shown how an off-axis spherical mirror can be used to correct this astigmatism to allow efficient coupling to quasi-optical systems. A millimetre wave antenna and mirror combination is described and, with the aid of solid state noise diodes, the coupling of the launched beam to a quasi-optical spectrometer is shown to be in good agreement with that predicted by the scale model measurements.

Assessment of the RE(OH)3 Ising magnetic materials as possible candidates for the study of transverse-field-induced quantum phase transitions

The LiHoxY1−xF4 Ising magnetic material subject to a magnetic field perpendicular to the Ho3+ Ising direction has shown over the past 20 years to be a host of very interesting thermodynamic and magnetic phenomena. Unfortunately, the availability of other magnetic materials other than LiHoxY1−xF4 that may be described by a transverse-field Ising model remains very much limited. It is in this context that we use here a mean-field theory to investigate the suitability of the Ho(OH)3, Dy(OH)3, and Tb(OH)3 insulating hexagonal dipolar Ising-type ferromagnets for the study of the quantum phase transition induced by a magnetic field, Bx, applied perpendicular to the Ising spin direction. Experimentally, the zero-field critical (Curie) temperatures are known to be Tc≈2.54, 3.48, and 3.72 K, for Ho(OH)3, Dy(OH)3, and Tb(OH)3, respectively. From our calculations we estimate the critical transverse field, Bxc, to destroy ferromagnetic order at zero temperature to be Bxc=4.35, 5.03, and 54.81 T for Ho(OH)3, Dy(OH)3, and Tb(OH)3, respectively. We find that Ho(OH)3, similarly to LiHoF4, can be quantitatively described by an effective S=1/2 transverse-field Ising model. This is not the case for Dy(OH)3 due to the strong admixing between the ground doublet and first excited doublet induced by the dipolar interactions. Furthermore, we find that the paramagnetic (PM) to ferromagnetic (FM) transition in Dy(OH)3 becomes first order for strong Bx and low temperatures. Hence, the PM to FM zero-temperature transition in Dy(OH)3 may be first order and not quantum critical. We investigate the effect of competing antiferromagnetic nearest-neighbor exchange and applied magnetic field, Bz, along the Ising spin direction ẑ on the first-order transition in Dy(OH)3. We conclude from these preliminary calculations that Ho(OH)3 and Dy(OH)3 and their Y3+ diamagnetically diluted variants, HoxY1−x(OH)3 and DyxY1−x(OH)3, are potentially interesting systems to study transverse-field-induced quantum fluctuations effects in hard axis (Ising-type) magnetic materials.

Induced random fields in the LiHoxY1-xF4 quantum ising magnet in a transverse magnetic field

The LiHoxY1-xF4 magnetic material in a transverse magnetic field Bxx̂ perpendicular to the Ising spin direction has long been used to study tunable quantum phase transitions in a random disordered system. We show that the Bx-induced magnetization along the x̂ direction, combined with the local random dilution-induced destruction of crystalline symmetries, generates, via the predominant dipolar interactions between Ho3+ ions, random fields along the Ising ẑ direction. This identifies LiHoxY1-xF4 in Bx as a new random field Ising system. The random fields explain the rapid decrease of the critical temperature in the diluted ferromagnetic regime and the smearing of the nonlinear susceptibility at the spin-glass transition with increasing Bx and render the Bx-induced quantum criticality in LiHoxY1-xF4 likely inaccessible.

Magnetic coupling in trinuclear partial cubane copper(II) complexes with a hydroxo bridging core and peripheral phenoxo bridges from NNO donor Schiff base ligands

Three new trinuclear copper(II) complexes, [(CuL1)(3)(mu(3)-OH)](ClO4)(2)center dot 3.75H(2)O (1), [(CuL2)(3)(mu(3)-OH)](ClO4)(2) (2) and [(CuL3)(3)(mu(3)-OH)](BF4)(2)center dot 0.5CH(3)CN (3) have been synthesized from three tridentate Schiff bases HL1, HL2, and HL3 (HL1 = 2-[(2-amino-ethylimino)-methyl]-phenol, HL2 = 2-[(2-methylamino-ethylimino)-methyl]-phenol and HL3 = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol). The complexes are characterized by single-crystal X-ray diffraction analyses, IR, UV-vis and EPR spectroscopy, and variable-temperature magnetic measurements. All the compounds contain a partial cubane [Cu3O4] core consisting of the trinuclear unit [(CuL)(3)(mu(3)-OH)](2+) together with perchlorate or fluoroborate anions. In each of the complexes, the three copper atoms are five-coordinated with a distorted square-pyramidal geometry except in complex 1, in which one of the Cu-II ions of the trinuclear unit is six-coordinate being in addition weakly coordinated to one of the perchlorate anions. Variable-temperature magnetic measurements and EPR spectra indicate an antiferromagnetic exchange coupling between the CuII ions of complexes 1 and 2, while this turned out to be ferromagnetic for complex 3. Experimental values have been fitted according to an isotropic exchange Hamiltonian. Calculations based on Density Functional Theory have also been performed in order to estimate the exchange coupling constants in these three complexes. Both sets of values indicate similar trends and specially calculated J values establish a magneto-structural correlation between them and the Cu-O-Cu bond angle, in that the coupling is more ferromagnetic for smaller bond angle values.

Mono-aqua-bridged dinuclear complexes of Cu(II) containing NNO donor Schiff base ligand: Hydrogen-bond-mediated exchange coupling

Two new mono-aqua-bridged dinuclear Cu(II) complexes of tridentate NNO Schiff bases, [Cu-2(mu-H2O)L-2(1)(H2O)(2)](BF4)(2)center dot 2H(2)O (1) and [Cu-2(mu-H2O)L-2(2)(H2O)(2)](BF4)(2)center dot 2H(2)O (2) where HL1 = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol and HL2 =2-[(2-dimethylamino-ethylimino)-methyl]-phenol were synthesized. Both the complexes were characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. For both the complexes each Cu(II) ion is in a square-pyramidal environment being bonded to three atoms from the tridentate NNO Schiff base and a terminal H2O molecule in the equatorial plane; a second H2O ligand acts as a bridge between the two Cu(II) centres through the axial positions. Hydrogen bonds between the terminal H2O ligand and the Schiff base of the adjacent centre complete the intra-dimer linkages. Variable-temperature (4-300 K) magnetic susceptibility measurement shows the presence of significant antiferromagnetic coupling for both the complexes (J = -12.2 and -12.5 cm(-1), respectively, for 1 and 2), mediated mainly through the intra-dimer H-bonds.

Coupling thin layer electrochemistry with epifluorescence microscopy: an expedient way of investigating electrofluorochromism of organic dyes

The first example of thin layer electrochemistry coupled to epifluorescence microscopy in the total internal reflectance mode is described and applied to the investigation of electrochemically modulated fluorescence of an organic dye (chloromethoxytetrazine) in solution. This technique allows to generate full redox switch of fluorescence when converting reversibly the dye into its anion radical, as well as to record the spectral features of the electrogenerated species. Recording simultaneously fluorescence intensity and lifetime along with coulombic charge as a function of the electrode potential will lead to a deep insight into the redox quenching mechanism.