Vibrational dynamics of solid poly(ethylene oxide)

Molecular dynamics (MD) simulations of crystalline poly(ethylene oxide) (PEO) have been carried out in order to study its vibrational properties. The vibrational density of states has been calculated using a normal mode analysis (NMA) and also through the velocity autocorrelation function of the atoms. Results agree well with experimental spectroscopic data. System size effects in the crystalline state, studied through a comparison between results for 16 unit cells and that for one unit cell has shown important differences in the features below 100 cm^-1. Effects of interchain interactions are examined by a comparison of the spectra in the condensed state to that obtained for an isolated oligomer of ethylene oxide. Calculations of the local character of the modes indicate the presence of collective excitations for frequencies lower than 100 cm^-1, in which around 8 to 12 successive atoms of the polymer backbone participate. The backbone twisting of helical chains about their long axes is dominant in these low frequency modes.Comment: 19 pages, 7 figures (Phys.Rev.B submitted on 28.11.2002) Revised versio

Hope for the Best, Prepare for the Worst: Response of Tall Steel Buildings to the ShakeOut Scenario Earthquake

This work represents an effort to develop one plausible realization of the effects of the scenario event on tall steel moment-frame buildings. We have used the simulated ground motions with three-dimensional nonlinear finite element models of three buildings in the 20-story class to simulate structural responses at 784 analysis sites spaced at approximately 4 km throughout the San Fernando Valley, the San Gabriel Valley, and the Los Angeles Basin. Based on the simulation results and available information on the number and distribution of steel buildings, the recommended damage scenario for the ShakeOut drill was 5% of the estimated 150 steel moment-frame structures in the 10–30 story range collapsing, 10% red-tagged, 15% with damage serious enough to cause loss of life, and 20% with visible damage requiring building closure

Entropy production, energy loss and currents in adiabatically rocked thermal ratchets

We study the nature of currents, input energy and entropy production in different types of adiabatically rocked ratchets using the method of stochastic energetics. The currents exhibit a peak as a function of noise strength. We show that there is no underlying resonance or synchronisation phenomena in the dynamics of the particle with these current peaks. This follows from the analysis of energy loss in the medium. We also show that the maxima seen in current as well as the total entropy production are not directly correlated.Comment: 6 pages, 7 figures Minor corrections are mad

Structure, Conduct and Performance of Value Chain in Seaweed farming in India

Among the three types of technologies available in the fisheries sector in India, seaweed farming, initially promoted as a livelihood option, has emerged as the one area which probably has the maximum potential for up-scaling. This paper has examined the structure, conduct and performance of the value chain in seaweed farming in India inquiring into the production, institutional, marketing, social and community relationships in small-scale seaweed farming in the Ramanathapuram district of Tamil Nadu and the concept of self-help groups (SHG) as an increasingly workable option for coastal resources management. The value chain analysis of the sector has substantially proved that committed and synergistic production, marketing and institutional arrangements enabled by corporate leadership, offers considerable savings in transaction costs. The SHG model has also shown strong gender orientation in the initial years of seaweed culture in the district contributing to strong structural foundations to the movement. The seaweed sector in the coastal India has all the potential to rise from the low-income conditions normally associated with basic livelihood activities to higher levels of employment-income-consumption relationships.Agricultural and Food Policy,

Mitochondrial Molecular Adaptations and Life History Strategies Coevolve in Plants

Messenger RNA secondary structure prevents mutations at functionally important sites. Mutations at exposed sites would cause micro-adaptations, niche-specialization, and therefore, can be thought to promote K-strategists. Exposing, rather than protecting, conserved sites, is also potentially adaptive because they probably promote macro-adaptive changes. This presumably fits r-strategists: their population dynamics tolerate decreased survival. We found that helix-forming tendencies are greater at evolutionary conserved sites of plant mitochondrial mRNAs than at evolutionary variable sites in a majority (73%) of species–gene combinations. K-strategists preferentially protect conserved sites in short genes, r-strategists protect them most in larger genes. This adaptive scenario resembles our earlier findings in chloroplast genes. Protection levels at various codon positions also display disparity with respect to life history strategies of the plants. Conserved site protection increases overall mRNA folding stabilities for some genes, while decreases it for some others. This contrast exists between homologous genes of r- and K- strategists. Such compensating interactions between variability, mRNA size, codon position, and secondary structure factors within r- and K-strategists are most likely, molecular adaptations of plants belonging to the two extreme life history strategies. Our results suggest coevolution between molecular and ecological adaptive strategies

Estimation of phase noise in oscillators with colored noise sources

In this letter we study the design of algorithms for estimation of phase noise (PN) with colored noise sources. A soft-input maximum a posteriori PN estimator and a modified soft-input extended Kalman smoother are proposed. The performance of the proposed algorithms are compared against those studied in the literature, in terms of mean square error of PN estimation, and symbol error rate of the considered communication system. The comparisons show that considerable performance gains can be achieved by designing estimators that employ correct knowledge of the PN statistics