Easy collective polarization switching in ferroelectrics

The actual mechanism of polarization switching in ferroelectrics remains a puzzle for many decades, since the usually estimated barrier for nucleation and growth is insurmountable ("paradox of the coercive field"). To analyze the mechanisms of the nucleation we consider the exactly solvable case of a ferroelectric film with a "dead" layer at the interface with electrodes. The classical nucleation is easier in this case but still impossible, since the calculated barrier is huge. We have found that the {\em interaction} between the nuclei is, however, long range, hence one has to study an {\em ensemble} of the nuclei. We show that there are the ensembles of small (embryonic) nuclei that grow {\em without the barrier}. We submit that the interaction between nuclei is the key point for solving the paradox.Comment: 5 pages, REVTeX 3.1 with one eps-figure. Corrected discussion of single stripe and cylindrical nuclei, and their interaction. The estimate for equilibrium density of embryonic nuclei is added. To appear in Phys. Rev. Letter

A large containment capsule for nuclear reactor irradiation of explosive materials

Large containment capsule for nuclear reactor irradiation of explosive material

Mean Field Theory of Polynuclear Surface Growth

We study statistical properties of a continuum model of polynuclear surface growth on an infinite substrate. We develop a self-consistent mean-field theory which is solved to deduce the growth velocity and the extremal behavior of the coverage. Numerical simulations show that this theory gives an improved approximation for the coverage compare to the previous linear recursion relations approach. Furthermore, these two approximations provide useful upper and lower bounds for a number of characteristics including the coverage, growth velocity, and the roughness exponent.Comment: revtex, 7 pages, 4 fig

Exact results for nucleation-and-growth in one dimension

We study statistical properties of the Kolmogorov-Avrami-Johnson-Mehl nucleation-and-growth model in one dimension. We obtain exact results for the gap density as well as the island distribution. When all nucleation events occur simultaneously, the island distribution has discontinuous derivatives on the rays x_n(t)=nt, n=1,2,3... We introduce an accelerated growth mechanism where the velocity increases linearly with the island size. We solve for the inter-island gap density and show that the system reaches complete coverage in a finite time and that the near-critical behavior of the system is robust, i.e., it is insensitive to details such as the nucleation mechanism.Comment: 9 pages, revtex, also available from http://arnold.uchicago.edu/~ebn

Co-firing of biomass with coals Part 1. Thermogravimetric kinetic analysis of combustion of fir (abies bornmulleriana) wood

The chemical composition and reactivity of fir (Abies bornmulleriana) wood under non-isothermal thermogravimetric (TG) conditions were studied. Oxidation of the wood sample at temperatures near 600 A degrees C caused the loss of aliphatics from the structure of the wood and created a char heavily containing C-O functionalities and of highly aromatic character. On-line FTIR recordings of the combustion of wood indicated the oxidation of carbonaceous and hydrogen content of the wood and release of some hydrocarbons due to pyrolysis reactions that occurred during combustion of the wood. TG analysis was used to study combustion of fir wood. Non-isothermal TG data were used to evaluate the kinetics of the combustion of this carbonaceous material. The article reports application of Ozawa-Flynn-Wall model to deal with non-isothermal TG data for the evaluation of the activation energy corresponding to the combustion of the fir wood. The average activation energy related to fir wood combustion was 128.9 kJ/mol, and the average reaction order for the combustion of wood was calculated as 0.30

Invasive Allele Spread under Preemptive Competition

We study a discrete spatial model for invasive allele spread in which two alleles compete preemptively, initially only the "residents" (weaker competitors) being present. We find that the spread of the advantageous mutation is well described by homogeneous nucleation; in particular, in large systems the time-dependent global density of the resident allele is well approximated by Avrami's law.Comment: Computer Simulation Studies in Condensed Matter Physics XVIII, edited by D.P. Landau, S.P. Lewis, and H.-B. Schuttler, (Springer, Heidelberg, Berlin, in press

Computational Methods to Study Kinetics of DNA Replication

New technologies such as DNA combing have led to the availability of large quanti-ties of data that describe the state of DNA while undergoing replication in S phase. In this chapter, we describe methods used to extract various parameters of replica-tion — fork velocity, origin initiation rate, fork density, numbers of potential and utilized origins — from such data. We first present a version of the technique that applies to “ideal ” data. We then show how to deal with a number of real-world complications, such as the asynchrony of starting times of a population of cells, the finite length of fragments used in the analysis, and the finite amount of DNA in a chromosome. Key words: DNA replication, replication fork velocity, origin initiation

Energy and Historic Buildings: Toward evidence-based policy reform

This research informs the intersection of climate and heritage policy development by examining the history of US energy policy as it relates to historic buildings, emerging policy tools to reduce greenhouse gas emissions, and the implications of a changing legislative landscape on historic buildings through the case of New York City. This study employs a multi-method approach, including a review of US energy codes; discourse analysis of government records, energy studies, and reports related to historic buildings and energy; select research into energy-related heritage policy at the municipal level; and geospatial and statistical methods to analyze policy implications in the case study of New York City. Historic buildings have long been afforded exemptions from energy code compliance in the US, and these waivers are widespread. Contemporary operating energy and greenhouse gas data, as well as energy justice findings about who these waivers privilege, challenge these exemptions and signal a need for significant policy reform in light of climate change. This study questions longstanding rhetoric about historic buildings being inherently green and supports the need for more evidence-based research to undergird heritage policy reform that is equitable and climate-responsive

A kinetic study of the formation of smectic phases in novel liquid crystal ionogens

A multi-rate non-isothermal kinetic analysis of the isotropic-melt to liquid crystalline phase transition of novel liquid crystalline ionogenic copolymers, LCIs, the 10-(4-methoxyazobenzene-4′-oxy)decyl methacrylate]-co-2-(acrylamido-2-methyl-1-propanesulfonic acid)s, 10-MeOAzB/AMPS, copolymers, has been performed by means of calorimetric experiments. An analytical methodology which includes the study of the phase transition rate parameter, the determination of the activation energies by using Kissinger and Flynn-Wall-Ozawa models, and the study of the phase transition kinetics by the use of the Avrami theory, has been applied. The formation of the mesophases from the isotropic state occurred close to thermodynamic equilibrium. The results evidence the presence of several individual processes in the formation of liquid crystalline phases from the melt and a strong dependence of phase transition rates and activation energies with acid contents. A decrease in the phase transition rate, related to a decrease in the overall change of the transition entropy, has been observed. The final inhibition of the liquid crystal (LC) behaviour is ascribed to an exponential increase in the activation energy of the phase transition, promoted by strong acid aggregation. An optimum composition of the 10-MeOAzB/AMPS copolymers to achieve the dual characteristics of LCIs (ionogenic and liquid crystalline behaviour) requires acid concentrations capable of promoting structure-forming effects on the LC phases and the evolution of phase separated morphologies

Analytical and computational study of magnetization switching in kinetic Ising systems with demagnetizing fields

An important aspect of real ferromagnetic particles is the demagnetizing field resulting from magnetostatic dipole-dipole interaction, which causes large particles to break up into domains. Sufficiently small particles, however, remain single-domain in equilibrium. This makes such small particles of particular interest as materials for high-density magnetic recording media. In this paper we use analytic arguments and Monte Carlo simulations to study the effect of the demagnetizing field on the dynamics of magnetization switching in two-dimensional, single-domain, kinetic Ising systems. For systems in the ``Stochastic Region,'' where magnetization switching is on average effected by the nucleation and growth of fewer than two well-defined critical droplets, the simulation results can be explained by the dynamics of a simple model in which the free energy is a function only of magnetization. In the ``Multi-Droplet Region,'' a generalization of Avrami's Law involving a magnetization-dependent effective magnetic field gives good agreement with our simulations.Comment: 29 pages, REVTeX 3.0, 10 figures, 2 more figures by request. Submitted Phys. Rev.