Polymer Reptation in Disordered Media

The effect of ambient disorders and sequence heterogeneities on the reptation of a long polymer is studied with the aid of a disordered tube model. The dynamics of a random heteropolymer is found to be much slower than that of a homopolymer due to collective pinning effects. The asymptotic properties belong to the universality class of a directed path in (1+1)-dimensional random media.Comment: 4 pages, to appear in PRL; text, figures and related (p)reprints also available at http://matisse.ucsd.edu/~hwa/pub.htm

Greenhouse Gas Policy and Canadian Agriculture

To meet its commitment to the Kyoto Protocol (KP), Canada must reduce its current annual GHG emissions (694 MT CO2 equivalent) by 240 MT CO2. Canada’s agricultural industries have the potential to generate a carbon sink of 10 MT CO2 (Government of Canada, 2003). The purpose of this article is to consider the manner in which Canadian agricultural policy has responded to Canada’s KP commitment and the likelihood that Canadian agriculture will participate significantly in carbon emission trading.Agricultural and Food Policy, Environmental Economics and Policy,

LogConcDEAD: An R Package for Maximum Likelihood Estimation of a Multivariate Log-Concave Density

In this article we introduce the R package LogConcDEAD (Log-concave density estimation in arbitrary dimensions). Its main function is to compute the nonparametric maximum likelihood estimator of a log-concave density. Functions for plotting, sampling from the density estimate and evaluating the density estimate are provided. All of the functions available in the package are illustrated using simple, reproducible examples with simulated data.

LogConcDEAD: An R package for maximum likelihood estimation of a multivariate log-concave density

In this document we introduce the R package LogConcDEAD (Log-concave density estimation in arbitrary dimensions). Its main function is to compute the nonparametric maximum likelihood estimator of a log-concave density. Functions for plotting, sampling from the density estimate and evaluating the density estimate are provided. All of the functions available in the package are illustrated using simple, reproducible examples with simulated data

Polymer Adsorption on Disordered Substrate

We analyze the recently proposed "pattern-matching" phase of a Gaussian random heteropolymer adsorbed on a disordered substrate [S. Srebnik, A.K. Chakraborty and E.I. Shakhnovich, Phys. Rev. Lett. 77, 3157 (1996)]. By mapping the problem to that of a directed homopolymer in higher-dimensional random media, we show that the pattern-matching phase is asymptotically weakly unstable, and the large scale properties of the system are given by that of an adsorbed homopolymer.Comment: 5 pages, RevTeX, text also available at http://matisse.ucsd.edu/~hw

Phase Transition of DNA-Linked Gold Nanoparticle

Melting and hybridization of DNA-capped gold nanoparticle networks are investigated with optical absorption spectroscopy. Single-stranded, 12-base DNA-capped gold nanoparticles are linked with complementary, single-stranded, 24-base linker DNA to form particle networks. Compared to free DNA, a sharp melting transition is seen in these networked DNA-nanoparticle systems. The sharpness is explained by percolation transition phenomena.Comment: 9 pages, 4 figures, submitte

Dynamical Properties of a Growing Surface on a Random Substrate

The dynamics of the discrete Gaussian model for the surface of a crystal deposited on a disordered substrate is investigated by Monte Carlo simulations. The mobility of the growing surface was studied as a function of a small driving force $F$ and temperature $T$. A continuous transition is found from high-temperature phase characterized by linear response to a low-temperature phase with nonlinear, temperature dependent response. In the simulated regime of driving force the numerical results are in general agreement with recent dynamic renormalization group predictions.Comment: 10 pages, latex, 3 figures, to appear in Phys. Rev. E (RC