Polyyne Ring Nucleus Growth Model for Single-Layer Carbon Nanotubes

We propose, based on recent experimental results, a polyyne ring nucleus (PRN) growth model for the synthesis of single-layer nanotubes (SLN's). The PRN model assumes that (i) the critical nuclei are the planar carbon polyyne rings that are observed to be most stable for sizes in the range C10 to C40; (ii) ComCn clusters (possibly charged) play the role of a catalyst by serving to add C2 or other gas phase species into the growing tube; (iii) promoters such as S, Bi, and Pb serve to modify the rates for these processes by stabilizing the ring structure. We suggest experiments to test and amplify this PRN model, including a flow tube arrangement that might be useful for synthesizing more uniform SLN's

How to Kneel on the Earth

How to Kneel on the Earth by Michelle A. Kian

Classifying multispectral data by neural networks

Several energy functions for synthesizing neural networks are tested on 2-D synthetic data and on Landsat-4 Thematic Mapper data. These new energy functions, designed specifically for minimizing misclassification error, in some cases yield significant improvements in classification accuracy over the standard least mean squares energy function. In addition to operating on networks with one output unit per class, a new energy function is tested for binary encoded outputs, which result in smaller network sizes. The Thematic Mapper data (four bands were used) is classified on a single pixel basis, to provide a starting benchmark against which further improvements will be measured. Improvements are underway to make use of both subpixel and superpixel (i.e. contextual or neighborhood) information in tile processing. For single pixel classification, the best neural network result is 78.7 percent, compared with 71.7 percent for a classical nearest neighbor classifier. The 78.7 percent result also improves on several earlier neural network results on this data

Capture-zone scaling in island nucleation: phenomenological theory of an example of universal fluctuation behavior

In studies of island nucleation and growth, the distribution of capture zones, essentially proximity cells, can give more insight than island-size distributions. In contrast to the complicated expressions, ad hoc or derived from rate equations, usually used, we find the capture-zone distribution can be described by a simple expression generalizing the Wigner surmise from random matrix theory that accounts for the distribution of spacings in a host of fluctuation phenomena. Furthermore, its single adjustable parameter can be simply related to the critical nucleus of growth models and the substrate dimensionality. We compare with extensive published kinetic Monte Carlo data and limited experimental data. A phenomenological theory sheds light on the result.Comment: 5 pages, 4 figures, originally submitted to Phys. Rev. Lett. on Dec. 15, 2006; revised version v2 tightens and focuses the presentation, emphasizes the importance of universal features of fluctuations, corrects an error for d=1, replaces 2 of the figure

Cell size distribution in a random tessellation of space governed by the Kolmogorov-Johnson-Mehl-Avrami model: Grain size distribution in crystallization

The space subdivision in cells resulting from a process of random nucleation and growth is a subject of interest in many scientific fields. In this paper, we deduce the expected value and variance of these distributions while assuming that the space subdivision process is in accordance with the premises of the Kolmogorov-Johnson-Mehl-Avrami model. We have not imposed restrictions on the time dependency of nucleation and growth rates. We have also developed an approximate analytical cell size probability density function. Finally, we have applied our approach to the distributions resulting from solid phase crystallization under isochronal heating conditions

Spectral signatures of photosynthesis II: coevolution with other stars and the atmosphere on extrasolar worlds

As photosynthesis on Earth produces the primary signatures of life that can be detected astronomically at the global scale, a strong focus of the search for extrasolar life will be photosynthesis, particularly photosynthesis that has evolved with a different parent star. We take planetary atmospheric compositions simulated by Segura, et al. (2003, 2005) for Earth-like planets around observed F2V and K2V stars, modeled M1V and M5V stars, and around the active M4.5V star AD Leo; our scenarios use Earth's atmospheric composition as well as very low O2 content in case anoxygenic photosynthesis dominates. We calculate the incident spectral photon flux densities at the surface of the planet and under water. We identify bands of available photosynthetically relevant radiation and find that photosynthetic pigments on planets around F2V stars may peak in absorbance in the blue, K2V in the red-orange, and M stars in the NIR, in bands at 0.93-1.1 microns, 1.1-1.4 microns, 1.5-1.8 microns, and 1.8-2.5 microns. In addition, we calculate wavelength restrictions for underwater organisms and depths of water at which they would be protected from UV flares in the early life of M stars. We estimate the potential productivity for both surface and underwater photosynthesis, for both oxygenic and anoxygenic photosynthesis, and for hypothetical photosynthesis in which longer wavelength, multi-photosystem series are used.Comment: 59 pages, 4 figures, 4 tables, forthcoming in Astrobiology ~March 200

An Improved Web Design to Support Online Investment Decisions

The rise of the Internet opens up new possibilities and creates new challenges for investors. The possibilities include ease of use, cheaper trading costs, and greatly improved access to information. The challenges include information overload and a temptation to overtrade. The present paper discusses how brokerage firms can improve their web site designs in order to meet these challenges and opportunities and to better facilitate the needs of individual investors. Specifically, the paper discusses how an objectoriented information representation system can be used to enable both investor-specific information, such as risktolerance level, investment time horizon, and tax status, and more general information from the financial markets themselves, such as company P/E levels, to be integrated into a consistent web presentation that will facilitate the investor’s making more intelligent investment decisions. Such an information representation system would be structured hierarchically, with the investor-specific information at the top of the hierarchy, driving the application of market-level, then industry-level, and, at the bottom of the hierarchy, company-specific information. Finally, the paper discusses the feasibility of implementing such a system and some of the promises and pitfalls that may arise from its implementation