Experimental Confirmation Of Theoretical Predictions Research Articles

Chirality Distributions for Semiconducting Single-Walled Carbon Nanotubes Determined by Photoluminescence Spectroscopy.

To realize single-walled carbon nanotube (SWCNT) chiral selective growth, elucidating the mechanism of SWCNT chirality selectivity is important. For this purpose, an accurate evaluation method for evaluating the chirality distribution of grown SWCNTs without post-growth processing or liquid-dispersion of SWCNTs is indispensable. Here, we used photoluminescence spectroscopy to directly measure the chirality distributions of individual semiconducting SWCNTs suspended on a pillar-patterned substrate. The number of chirality-assigned SWCNTs was up to 332 and 17 chirality types with the chiral angles ranging from to were detected. The growth yield of SWCNTs was confirmed to primarily depends on the chiral angle in accordance with the screw dislocation model. Furthermore, when higher-yield chiralities are selected, the chiral angle distribution with a peak corresponding to near-armchair SWCNTs is well fitted with a model that incorporates the thermodynamic effect at the SWCNT-catalyst interface into the kink growth-based kinetic model. Our quantitative and statistical data provide new insights into SWCNT growth mechanism as well as experimental confirmation of theoretical predictions.

Mapping Localized Surface Plasmons within Silver Nanocubes Using Cathodoluminescence Hyperspectral Imaging.

Localized surface plasmons within silver nanocubes less than 50 nm in size were investigated using high-resolution cathodoluminescence hyperspectral imaging. Multivariate statistical analysis of the multidimensional luminescence data set allows both the identification of distinct spectral features in the emission and the mapping of their spatial distribution. These results show a 490-nm peak emitted from the cube faces, with shorter-wavelength luminescence coming from the vertices and edges; this provides direct experimental confirmation of theoretical predictions.

Viscosity shear waves and mass drag effect in liquids

A new method based on a micromechanical sensor has been developed for the investigation of viscosity shear waves in liquids. A number of Newtonian liquids having various molecular properties were tested with the help of a miniaturized sensor oscillating in a liquid. A good experimental confirmation of theoretical predictions was obtained for relatively high viscosities η. On the contrary, a significant discrepancy between the hydrodynamic limit for η → 0, i.e. the “ideal liquid” limit, and the experimental data was observed. In addition, the data shows a discontinuity for different types of liquid molecules of variable polarity.

Achievement of high current density in Nb  Ti superconducting multifilamentary wires by introducing designed artificial pins

It is shown theoretically that a further increase in the overall critical current density of Nb  Ti multifilamentary wire is possible by introducing artificial pinning centres into Nb  Ti filaments in a specified fashion. As the first step towards experimental confirmation of theoretical predictions of the summation of individual forces, Nb  Ti monofilamentary wires were fabricated, in each of which were embedded fine filamentary Nb rods with a given diameter and spacing, to act as artificial pinning centres. These wires show higher critical current densities than have been reported so far, at fields lower than ≈ 2 T. Although the quantitative agreement between the theoretical and observed results is not yet very satisfactory, further investigation of the pinning characteristics using various artificial pins leads to a new stage where it is possible to design the wire parameters for obtaining the required characteristics of critical current density.

Rectified diffusion at megahertz frequencies

Rectified diffusion studies have in the past been generally confined to kilohertz frequency ranges where experimental confirmation of theoretical predictions can be made. However, since most of the ultrasonic devices used in medicine operate in the megahertz frequency range, it is important to extend these studies of the growth of bubbles by ultrasound to the higher range. We have modified and extended the equations associated with rectified diffusion to apply at megahertz frequencies, and have numerically solved these equations for a variety of conditions such as dissolved gas concentration, distribution of nuclei, and the frequency and intensity of the ultrasound. We have also obtained solutions for both the continuous and pulsed modes of operation. Our results indicate that bubbles can be made to grow at typical levels of exposure used in medical applications. Furthermore, at higher intensities, such as those used in studies on bean roots by Morris and Coakley [to be published in Ultrasound Med. Biol.], the times required for growth to resonance size are on the same order of magnitude as the periods associated with acoustic emissions from the root during insonification. [Work partially supported by the Office of Naval Research and the National Science Foundation.]

The thermal expansion of graphite within the layer planes

The thermal expansion of graphite within the layer planes has been investigated by X-ray diffractometer and powder diffraction techniques. Direct measurements of the a lattice dimension over the whole range of temperatures from −196° C to 3000° C have been made for the first time. Two specimens were studied, one a spectroscopic electrode material of p ≈ 0.2 and the other a highly orientated pyrolytic graphite. The variation of the coefficient of thermal expansion α a was computed from the measured variation with temperature of the a lattice dimension. It is shown that above about 400° C there is a progressive expansion of the interatomic spacings in the basal plane with α a approaching a limiting value of 1.2 × 10 −6 per °C. This provides the first experimental confirmation of theoretical prediction. Below 400° C there is an expansion with decrease in temperature. Below 0° C the rate of expansion rapidly decreases and a limiting value of the a lattice parameter is approached at − 196° C. These findings are consistent with the results of Nelson and Riley who found a minimum in the a-dimension at about 400° C. The experimental data are compared with those predicted by theory and with those obtained by other workers.

The design, contruction, and use of resistors of calculable reactance

The design, construction, and use of two-termInal resistors of calculabel reactance, covering the range 100–10 000 ohms are described. The resistors form a series of primary standards suitable for the measurement of residual inductance and are of two forms; those in the range 100–1 000 ohms consist of a single straight wire concentrically mounted withing a return conductor, while those in the range 1000–10000 ohms consist of single-layer solenoids similarly mounted. The former are suitable for measurements up to a frequency of 10000 cycles per sec. and the latter for measurements up to 3000 or 4000 cycles per sec.The inductances and capacitances of the standards are calculated as far as possible from their dimensions, although certain of the cpacitances involved were measured directly. The variation of reactance with frequency is discussed and experimental confirmation of theoretical predictions is given.Comparison measurements between the standards have been carried out using simple bridge methods, and the general consistency of the results shows that, using these standards and methods, the phase angle of any resistor in the range under discussion can be determined with an accuracy of 6 × 10−6 radian at 1000 cycles per sec. even when bridge ratios as high as 10:1 are involved. As an additional check, the values of ractance were determined in terms of the constants of high-frequency self-inductance standards, and the claculated and observed results were found to show the same consistency.