Photoluminescence and population analysis of single-walled carbon nanotubes produced by CVD and pulsed-laser vaporization methods

Band gap photoluminescence (PL) behaviors of single-walled carbon nanotubes (SWNTs) grown by the methods of chemical vapor deposition and pulsed-laser vaporization are investigated over the wide diameter range (≈0.8–1.4 nm). The peak intensity of the PL signals strongly depends on chirality and the ‘(2n + m) family type’ of SWNTs. Based on the PL results, a population analysis of these SWNTs is conducted by combining the calculated PL yields for each (n, m) tube. The results are directly compared with the histograms of diameter distributions estimated by the transmission electron microscope (TEM) observations to check the validity of the analysis.     

Transverse-Mode Control of VCSELs With Convex Mirror

We propose the transverse-mode control of vertical-cavity surface-emitting lasers (VCSELs) with a convex mirror. A possibility of improvements on single-mode output power and higher-order mode suppression is presented by optimizing a convex mirror.     

Low-density attack revisited

The low-density attack proposed by Lagarias and Odlyzko is a powerful algorithm against the subset sum problem. The improvement algorithm due to Coster et al. would solve almost all the problems of density <0.9408... in the asymptotical sense. On the other hand, the subset sum problem itself is known as an NP-hard problem, and a lot of efforts have been paid to establish public-key cryptosystems based on the problem. In these cryptosystems, densities of the subset sum problems should be higher than 0.9408... in order to avoid the low-density attack. For example, the Chor-Rivest cryptosystem adopted subset sum problems with relatively high densities. In this paper, we further improve the low-density attack by incorporating an idea that integral lattice points can be covered with polynomially many spheres of shorter radius and of lower dimension. As a result, the success probability of our attack can be higher than that of Coster et al.’s attack for fixed dimensions. The density bound is also improved for fixed dimensions. Moreover, we numerically show that our improved low-density attack makes the success probability higher in case of low Hamming weight solution, such as the Chor-Rivest cryptosystem, if we assume SVP oracle calls.      

X-Ray Tube Voltage Dependence of Wiener Spectra of Screen Structure Mottle Recorded on Front and Back Emulsions

A low-speed screen/film system was used to investigate structure mottle, i.e., the density fluctuation of an x-ray film due to inhomogeneous screen structure. The tube voltage dependence of the Wiener spectra of the structure mottle was separately determined for front and back film emulsions. The Wiener spectral values of the structure mottle of the front emulsion were greater than those of the back emulsion at lower tube voltages. The spectral values of the structure mottle of the front emulsion decreased with tube voltage, while those of the back emulsion increased. We explain these phenomena by the behavior of the Wiener spectra of the relative spatial fluctuation of fluorescence intensity due to following reasons: (1) spatial thickness fluctuation of the screen produces a relative spatial fluctuation of x-ray energy absorbed in the screen, and (2) as the distance between the emulsion of the film and the average position of the x-ray absorption in the screen lengthens, the number of random scattering and absorption of light photons increase.Presented at the International Commission for Optics Topical Meeting, Kyoto, 1994.     

A simple synthesis of 5-methoxyindole and 5-methoxy-2-oxindole

1-Methoxy- and 1-hydroxy-2-oxindoles rearranged in acidic solution to 5-substituted 2-aminophenylacetic acid derivatives which were cyclized to the corresponding 2-oxindoles with heating. The synthesis of 5-methoxyindole from 5-methoxy-2-oxindole was also described.