Magneto-optical methods allow us to observe the dynamics of domain wall motion, but this is intrinsically a very noisy process. We discuss a new method allowing us to reduce the measurement noise, taking advantage of the acquisition of a whole temporal sequence of images. The resulting avalanche distributions give interesting hints as to the magnetization dynamics, but are strongly dependent on the size of the observation windows chosen. We investigate the effects of window size by studying finite-size scaling, and use this to extract the fractal dimension critical exponent 1/σν.

Transcription factor binding sites are being discovered at a rapid pace. It is now necessary to turn attention towards understanding how these sites work in combination to influence gene expression. Quantitative models that accurately predict gene expression from promoter sequence will be a crucial part of solving this problem. Here we present such a model, based on the analysis of synthetic promoter libraries in yeast (Saccharomyces cerevisiae).

As a single DNA molecule is positively supercoiled under constant tension, its extension initially increases due to a negative twist-stretch coupling. The subsequent attainment of an extension maximum has previously been assumed to be indicative of the onset of a phase transition from B- to scP-DNA. Here we show that an extension maximum in fact does not coincide with the onset of a phase transition. This transition is evidenced by a direct observation of a torque plateau using an angular optical trap.

We theoretically explore the generation of few-body analogs of fractional quantum Hall states. We consider an array of identical few-atom clusters (n=2,3,4), each cluster trapped at the node of an optical lattice. By temporally varying the amplitude and phase of the trapping lasers, one can introduce a rotating deformation at each site. We analyze protocols for coherently transferring ground-state clusters into highly correlated states, producing theoretical fidelities (probability of reaching the target state) in excess of 99%. © 2008 The American Physical Society.

We report the electrical characteristics of substrate-supported metallic single walled carbon nanotubes at temperatures up to 573 K over a range of bias voltages (Vb) for zero gate voltage in air under atmospheric pressure. Our results show a monotonic increase in resistance with temperature, with an I- Vb characteristic that is linear at high temperature but nonlinear at low temperature.

We study the metastability of the superheated Meissner state in type II superconductors with κ≫1 beyond Ginzburg-Landau theory, which is applicable only in the vicinity of the critical temperature. Within Eilenberger's semiclassical approximation, we use the local electrodynamic response of the superconductor to derive a generalized thermodynamic potential valid at any temperature. The stability analysis of this functional yields the temperature dependence of the superheating field.

Superconducting excitations-Bogoliubov quasiparticles-are the quantum mechanical mixture of negatively charged electron (-e) and positively charged hole (+e). Depending on the applied voltage bias in scanning tunneling microscope (STM) one can sample the particle and hole content of such a superconducting excitation. Recent STM experiments offer a unique insight into the inner workings of the superconducting state of superconductors. We propose a new observable quantity for STM studies that is the manifestation of the particle-hole dualism of the quasiparticles.

We investigate the membrane aspect of graphene and its impact on the electronic properties. We show that rippling generates spatially varying electrochemical potential that is proportional to the square of the local curvature. This is due to the rehybridization effects and the change in the next-neighbor hopping caused by curvature. We estimate the electrochemical- potential variation associated with the rippling observed in recent scanning tunneling microscopy (STM) to be of order 30 meV. Further we show that the charge inhomogeneity in turn stabilizes ripple formation.

Previous calculations on model systems for the cooperative binding of two NO2 molecules to carbon nanotubes using density functional theory and second order Moller-Plesset perturbation theory gave results differing by 30 kcal/mol. Quantum Monte Carlo calculations are performed to study the role of electronic correlations in these systems and resolve the discrepancy between these previous calculations. Compared to QMC binding energies, MP2 and LDA are shown to overbind, while B3LYP and BPW91 underbind.

The Gordian knot of density-functional theories for classical molecular liquids remains finding an accurate free-energy functional in terms of the densities of the atomic sites of the molecules. Following Kohn and Sham, we show how to solve this problem by considering noninteracting molecules in a set of effective potentials. This shift in perspective leads to an accurate and computationally tractable description in terms of simple three-dimensional functions.