Our goal was to investigate auditory and speech perception abilities of children with and without reading disability (RD) and associations between auditory, speech perception, reading, and spelling skills. Participants were 9-year-old, Finnish-speaking children with RD (N = 30) and typically reading children (N = 30). Results showed significant group differences between the groups in phoneme duration discrimination but not in perception of amplitude modulation and rise time. Correlations among rise time discrimination, phoneme duration, and spelling accuracy were found for children with RD. Those children with poor rise time discrimination were also poor in phoneme duration discrimination and in spelling. Results suggest that auditory processing abilities could, at least in some children, affect speech perception skills, which in turn would lead to phonological processing deficits and dyslexia.

Laser ablation has been used to grow silicon nanowires with an average diameter of 6.7 nm ± 2.7 nm surrounded by an amorphous SiOx sheath of 1–2 nm. This paper reports the imaging, chemical and structural analysis of these wires. Due to the growth temperature and the presence of calcium impurities and trace oxygen, two distinct types of wires are found. They appear to grow by two different processes. One requires a metal catalyst, the other is catalyzed by oxygen.

In situ resistivity and thermoelectric power (S) have been used to study the nature of the adsorption of hydrogen in bundles of single-walled carbon nanotubes for H2 pressure P <1 atm and temperatures 77 K<T<500 K. Isothermal plots of S vs. Δρ/ρ0 are found to exhibit linear behavior as a function of gas coverage, consistent with a physisorption process. Studies of S, ρ at T = 500 K as a function of pressure exhibit a plateau at a pressure P~40 Torr, the same pressure where the H % measurements suggest the highest binding energy sites are being saturated. The effects of H2 exposure at 500 K on the thermoelectric transport properties are fully reversible.

We report (6 wt %) storage of H2 at T=77 K in processed bundles of single-walled carbon nanotubes at P=2 atmospheres. The hydrogen storage isotherms are completely reversible. D2 isotherms confirm this anomalous low-pressure adsorption and further reveal the effects of quantum mechanical zero point motion. We propose that our post-synthesis treatment of the sample not only improves access for hydrogen to the central pores within individual nanotubes, but also may create a roughened tube surface with an enhanced binding energy for hydrogen. Such an enhancement is needed to understand the strong adsorption at low pressure. We obtain an experimental isosteric heat qst=125 ± 5 meV for processed SWNT materials.

This paper develops a method to deduce the dielectric function of nanostructures smaller than the chosen wavelength of light. It modifies the Maxwell - Garnett Effective Medium Theory equations to calculate the dielectric function of a metal embedded inside a dielectric. Specifically, reflection and transmission measurements of an array of bismuth nanowires in an anodized porous alumina template are used to calculate the frequency - dependent di-electric function of the nanowires. The spectra are taken using Fourier transform infrared spectroscopy covering the 500 to 4000 cm−1 frequency range. These data are used to determine the real and imaginary parts of the dielectric function of the composite materials. Next, the percentage of the total volume occupied by either Bi or air in the porous alumina (the “filling factor”) was found by scanning electron microscopy. The modified Maxwell-Garnett (M-G) equations specify how to use the filling factor and the dielectric function of the composite material to calculate the dielectric function of the alumina. Finally, the modified M-G equations are used a second time to calculate the dielectric function of Bi nanowires using the dielectric function of alumina, the dielectric function of the filled template, and the filling factor. The resulting dielectric function of Bi nanowires is then compared to theoretical predictions.

The Z-contrast scanning transmission electron microscopy (STEM) imaging technique has been used to study dopant atoms and catalyst particles in single wall carbon nanotubes (SWNT). Iodine and bromine have been doped respectively in arc-grown SWNTs. We have directly observed the dopant sites and distributions. Both dopants appear to be incorporated linearly within the SWNT bundles. SWNT were also grown by pulsed laser ablation with mixed Ni and Co catalyst, and the size and distribution of catalytic particles was studied. By using Z-contrast imaging, we found that the size distribution of the catalyst particles varied over a large range, but even the smallest were larger than the diameter of an individual SWNT. Furthermore, electron energy loss spectroscopy (EELS) is used to determine the composition of individual nanocatalyst particles, and were found to consist of a uniform alloy of Co and Ni.

A resonant Raman study of single-wall carbon nanotubes (SWNT) using several laser lines between 0.94 and 3.05 eV is presented. A detailed lineshape analysis shows that the bands associated with the nanotube radial breathing mode are composed of a sum of individual peaks whose relative intensities depend strongly on the laser energy, in agreement with prior work. On the other hand, the shape of the Raman bands associated with the tangential C–C stretching motions in the 1500–1600 cm−1 range does not depend significantly on the laser energy for laser excitation energies in the ranges 0.94–1.59 eV and 2.41–3.05 eV. However, new C–C stretching modes are observed in the spectra collected using laser excitations with energies close to 1.9 eV. The new results are discussed in terms of the difference between the 1D electronic density of states for the semiconducting and metallic carbon nanotubes.

High temperature heat treatment of single wall carbon nanotube bundles in flowing H2 was used to produce a significant fraction (∼40%) of diameter-doubled, or coalesced tubes with a mean diameter corresponding to that of ∼(20, 20) tubes. At three laser excitation wavelengths (514.5, 647, and 1064 nm), a reduction in the Raman scattering intensity of the strong radial and tangential modes was observed in the H2-treated sample, consistent with the reduced fraction of tubes in the sample after coalescence. However, using 488 nm excitation, little or no change is observed in the Raman spectrum after the H2 treatment, suggesting that this excitation wavelength couples only to chiral symmetry tubes. Using the 647 nm excitation, the effect of H2 treatment on the tangential band is quite unique, and a significant change in the shape of the tangential band was observed. Our lineshape analysis, and other results reported in this issue, suggest that this unique change of shape is due to lost scattering intensity from metallic tubes partially compensated by tangential mode scattering from the coalesced tubes. The normally prominent radial breathing mode band, which would be expected at ∼90 cm−1 for ∼(20, 20) tubes was not observed, indicating that these larger diameter tubes do not exhibit strong resonant scattering, at least at any of the wavelengths used in this study.

We have subjected single-walled carbon nanotube materials (SWNTM's) to a variety of organic functionalization reactions. These reactions include radioactive photolabeling studies using diradical and nitrene sources, and treatment with dichlorocarbene and Birch reduction conditions. All of the reactions provide evidence for chemical attachment to the SWNTM's, but because of the impure nature of the staring materials, we are unable to ascertain the site of reaction. In the case of dichlorocarbene we are able to show the presence of chlorine in the SWNT bundles, but as a result of the large amount of amorphous carbon that is attached to the tube walls, we cannot distinguish between attachment of dichlorocarbene to the walls of the SWNT's and reaction with the amorphous carbon.

Results of the temperature dependence of the thermoelectric power and fourprobe resistance of single wall carbon nanotube mats are presented. The data are interpreted in terms of the response of a percolating network of metallic nanotube bundles. To the best of our knowledge, the work represents the first systematic study of the transport properties of a series of samples prepared using different transition metal-Y growth catalysts. Although x-ray diffraction and Raman scattering data indicate these samples are nominally the same, we find that the identity of the catalyst has a pronounced effect on the electrical transport properties. The data are interpreted qualitatively in terms of a dilute Kondo system involving the coupling of the the localized magnetic moments of impurity atoms (derived from the catalyst), and the conduction electron spins in the nanotube walls.

Background. The possibility that monoaminergic neurotransmission is altered in pathological gambling was examined.

Methods. Monoamines and their metabolites were measured in CSF obtained at level L4–5 from ten pathological gamblers and seven controls.

Results. A decrease in dopamine and an increase in 3,4-dihydroxyphenylacetic acid and homovanilic acid was found. Noradrenaline and its metabolite 3-methoxy-4-hydroxyphenylglycol was also increased but 5-hydroxytryptamine and 5-hydroxyindoleacetic acid were unchanged.

Conclusion. It is suggested that the function of the dopaminergic system, possibly mediating positive and negative reward, and the noradrenergic system, possibly mediating selective attention, is changed in pathological gambling.

Room temperature Raman scattering spectra are reported for the type II superconductors MxBaySi46 (M-Na, K) which were recently shown to exhibit Tc's ∼ 3.5 K. The spectra are compared to those of other Si46-clathrates which exhibit normal metallic behavior down to 2K. Thirteen of the twenty first-order Raman frequencies predicted by group theory have been detected, and the frequencies are found to be sensitive to the particular dopants. The Raman linewidths observed for the MxBaySi46 system are comparable to those observed for Na8Si46 and K7Si46. The data, taken collectively, suggest that the line broadening in the metallic Si-clathrates is due to important contributions from both the electron-phonon interaction as well as to a random filling of the Si cages.

Oriented films of layered Se-carbon compounds are grown on Ni substrates in evacuated sealed quartz tubes. Results of X-ray diffraction, Raman scattering and the c-axis electrical transport studies are reported. A discussion of possible models for the carbon -Se interaction is presented.

Using a CO2 laser to drive the pyrolysis of W(CO)6 and O2, we have synthesized nanocrystalline WO3-x particles. These nanopowders are found to exhibit a narrow size distribution with an average particle size produced in the range 5 to 10 nm, depending on the experimental conditions. Typical production rates are ∼ 2 g/h. Results from a Raman scattering study on WO3 nanopowder samples annealed in O2 indicate that a smaller particle size appears to stabilize the low-T ferroelectric phase ( < -40 °C) at room temperature.

Using both XRD and HRTEM lattice imaging, we have shown that CO2 laser pyrolysis (LP) produces nanoscale transition metal carbide and nitride catalysts, including cubic Mo2C, Mo2N, and W2N, which possess highly crystalline structures in their as-synthesized form In contrast, LP-produced W2C in its hexagonal phase is disordered. Clear lattice expansion, induced by the small crystallite size of the nanoparticles has been observed for LP-produced Mo2C particles, which have a typical crystallite size of 2 nm. No carbon coating was observed in HRTEM for LP-produced Mo2C particles. Furthermore, Mo=N and Mo=C bonding in Mo2N and Mo2C, respectively, were identified by an XPS measurement, which also reveals the presence of a thin oxide layer formed on the particle surface during the passivation process. Finally, the average crystallite sizes determined from HRTEM and XRD are in good agreement, indicating that the line broadening observed in XRD is due to the small crystallite size of the nanoparticles.

Nanoscale and well dispersed catalyst particles offer a large number of advantages: no diffusion resistance, easy accessibility to reactants, and a large number of active sites. In coal liquefaction, highly dispersed catalysts are especially needed because the catalyst particles are only able to influence reactions within their immediate vicinity.

Nanocrystalline powders of 2H-MoS2 and 2H-WS2 with average particle size 5 and 9 nm, respectively, have been produced using C02laser pyrolysis. Typical production rate for these nanoparticles is 2g/hr. Particle size, crystallite size, and the structural phase were determined using X-ray diffraction(XRD), transmission electron microscopy(TEM), and Raman scattering. Particle size effects may have been observed in the Raman-active modes (WS2 and MoS2) and in the band-edge excitons (MoS2).

We report the optical properties of C60 determined from the variable angle ellipsometry and near normal incidence reflection / transmission (R.T) experiments, and of M6C60 from the R, T experiments. The measurements were performed on thin films (d∼1000 Å) of C60 and M6C60 deposited on both Si(100) and suprasil substrates. The onset for strong absorption across the HOMO-LUMO gap in CgQ is measured to be -2.3 eV, slightly larger than the gap values obtained from the x-ray photoelectron spectroscopy (XPS) and electron-energy-loss spectroscopy (EELS) experiments. The observed peak positions in ε2(ω) for M6C60 and C60 compares well with the recent band structure calculations and suggests that the M6C60 compounds exhibit only a weak hybridization between the C60 and M states.