968 research outputs found
The development of visually guided stepping
Adults use vision during stepping and walking to fine-tune foot placement. However, the developmental profile of visually guided stepping is unclear. We asked (1) whether children use online vision to fine-tune precise steps and (2) whether preci- sion stepping develops as part of broader visuomotor development, alongside other fundamental motor skills like reaching. With 6-(N = 11), 7-(N = 11), 8-(N = 11)-year-olds and adults (N = 15), we manipulated visual input during steps and reaches. Using motion capture, we measured step and reach error, and postural stability. We expected (1) both steps and reaches would be visually guided (2) with similar developmental profiles (3) foot placement biases that promote stability, and (4) correlations between postural stability and step error. Children used vision to fine-tune both steps and reaches. At all ages, foot placement was biased (albeit not in the predicted directions). Contrary to our predictions, step error was not correlated with postural stability. By 8 years, children’s step and reach error were adult-like. Despite similar visual control mechanisms, stepping and reaching had different developmental profiles: step error reduced with age whilst reach error was lower and stable with age. We argue that the development of both visually guided and non-visually guided action is limb-specific
Anomalous Stark Shifts in Single Vertically Coupled Pairs of InGaAs Quantum Dots
Vertically coupled Stranski Krastanow QDs are predicted to exhibit strong
tunnelling interactions that lead to the formation of hybridised states. We
report the results of investigations into single pairs of coupled QDs in the
presence of an electric field that is able to bring individual carrier levels
into resonance and to investigate the Stark shift properties of the excitons
present. Pronounced changes in the Stark shift behaviour of exciton features
are identified and attributed to the significant redistribution of the carrier
wavefunctions as resonance between two QDs is achieved. At low electric fields
coherent tunnelling between the two QD ground states is identified from the
change in sign of the permanent dipole moment and dramatic increase of the
electron polarisability, and at higher electric fields a distortion of the
Stark shift is attributed to a coherent tunnelling effect between the ground
state of the upper QD and the excited state of the lower QD.Comment: Conference paper for QD2004 3 figure
Evidence for the rapid direct control both in vivo and in vitro of the efficiency of oxidative phosphorylation by 3,5,3′-tri-iodo-l-thyronine in rats
Donut and dynamic polarization effects in proton channeling through carbon nanotubes
We investigate the angular and spatial distributions of protons of the energy
of 0.223 MeV after channeling through an (11,~9) single-wall carbon nanotube of
the length of 0.2 m. The proton incident angle is varied between 0 and 10
mrad, being close to the critical angle for channeling. We show that, as the
proton incident angle increases and approaches the critical angle for
channeling, a ring-like structure is developed in the angular distribution -
donut effect. We demonstrate that it is the rainbow effect. When the proton
incident angle is between zero and a half of the critical angle for channeling,
the image force affects considerably the number and positions of the maxima of
the angular and spatial distributions. However, when the proton incident angle
is close to the critical angle for channeling, its influence on the angular and
spatial distributions is reduced strongly. We demonstrate that the increase of
the proton incident angle can lead to a significant rearrangement of the
propagating protons within the nanotube. This effect may be used to locate
atomic impurities in nanotubes as well as for creating nanosized proton beams
to be used in materials science, biology and medicine.Comment: 17 pages, 14 figure
Az ingázás térbeli jellegzetességeinek változása az Észak-Dunántúlon, különös tekintettel Győr munkaügyi vonzáskörzetére
A tanulmányban megvizsgáljuk a KSH által 2001-ben Ă©s 2011-ben elvĂ©gzett nĂ©pszámlálás ingázásra vonatkozĂł fĹ‘bb adatainak Ă©s a kĂ©t felvĂ©tel összehasonlĂtása során tapasztalt eltĂ©rĂ©sek terĂĽleti konzekvenciáit. A vizsgálat cĂ©lja elsĹ‘sorban az volt, hogy GyĹ‘r körĂ© szervezĹ‘dĹ‘ ingázĂł, munkaĂĽgyi vonzásterek jellegzetessĂ©geit megismerjĂĽk. EzĂ©rt az országos szintű vizsgálatok mellett rĂ©szletesebben koncentráltunk az Ă©szak-DunántĂşlra, melynek központrendszerĂ©t tártuk fel, s mĂ©g rĂ©szletesebben vizsgáltuk ezen belĂĽl GyĹ‘r, s a városkörnyĂ©ki tĂ©r jellegzetessĂ©geit
Channeling of charge carrier plasmons in carbon nanotubes
Ab initio calculations of the loss function of potassium-intercalated and electron-loaded bundles of single-walled carbon nanotubes yield a channeled-charge-carrier plasmon without perpendicular dispersion. Experimentally, we probe the momentum-dependent loss function of thin bundles consisting of only a few potassium-intercalated single-walled carbon nanotubes by angle-resolved electron-energy-loss spectroscopy and confirm this intrinsic channeling. The charge-carrier-plasmon energy is via in situ intercalation and is tunable in the near-visible infrared-energy range from 0.85 to 1.15 eV
Tailoring Organic-Organic Poly(vinylpyrrolidone) Microparticles and Fibers with Multiwalled Carbon Nanotubes for Reinforced Composites
Polymeric-based microparticles and fibers are tailorable for a wide range of common industrial and biomedical applications, while multiwalled carbon nanotubes (MWCNTs) are among the most useful macromolecules based on their outstanding electronic, mechanical, and optical properties at the nanoscale. If one combines these nanostructures with various polymeric precursors, their range of potential applications becomes even greater. One of the simplest and most affordable methods for fabricating micro- and nanostructures is electrospinning. Herein we demonstrate how MWCNTs may be used to produce tailor-made organic-organic poly(vinylpyrrolidone) (PVP) microparticles and fibers via electrospinning by studying their structural, vibrational, rheological, and mechanical properties' dependence on their solvent (ethanol (EtOH) or dimethylformamide (DMF)) and resulting morphology. Specifically, we find clear differences in morphologies from perfectly spherical and isolated microparticles to fibers mats, or a combination of fibers with entangled beads, with solvent type and concentration. On the basis of our findings, we propose that the mechanism governing the shape and size of the particles is a competition between the solvent's surface tension, dielectric constant, and viscoelastic properties. We show, based on both our experimental results and density functional theory (DFT) calculations, that OH functionalization of the MWCNTs is essential for achieving high PVP coverages and promoting the stability of the resulting PVP/MWCNT nanocomposite. Finally, by fabricating PVP/MWCNT fiber mats, we demonstrate that low concentrations (0.01-0.1 wt %) of MWCNTs led to a qualitative improvement (â250%) in the resulting mechanical properties, i.e., a reinforced composite. These results show how by controlling the solvent's dielectric constant, surface tension, and polymer concentration, one may produce tailor-made polymeric nanomaterials in combination with other organic/inorganic nanoparticles, i.e., silver, gold, or carbon allotropes, for next-generation applications
Energy levels and magneto-optical transitions in parabolic quantum dots with spin-orbit coupling
We report on the electronic properties of few interacting electrons confined
in a parabolic quantum dot based on a theoretical approach developed to
investigate the influence of Bychkov-Rashba spin-orbit (SO) interaction on such
a system. We note that the spin-orbit coupling profoundly influences the energy
spectrum of interacting electrons in a quantum dot. Here we present accurate
results for the energy levels and optical-absorption spectra for parabolic
quantum dots containing upto four interacting electrons, in the presence of
spin-orbit coupling and under the influence of an externally applied,
perpendicular magnetic field. We have described in detail about a very accurate
numerical scheme to evaluate these quantities. We have evaluated the effects of
SO coupling on the Fock-Darwin spectra for quantum dots made out of three
different semiconductor systems, InAs, InSb, and GaAs.Comment: expanded version of cond-mat/0501642 to be published in Phys. Rev.
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