Denaturation transition of stretched DNA

We generalize the Poland-Scheraga model to consider DNA denaturation in the presence of an external stretching force. We demonstrate the existence of a force-induced DNA denaturation transition and obtain the temperature-force phase diagram. The transition is determined by the loop exponent $c$ for which we find the new value $c=4\nu-1/2$ such that the transition is second order with $c=1.85<2$ in $d=3$. We show that a finite stretching force $F$ destabilizes DNA, corresponding to a lower melting temperature $T(F)$, in agreement with single-molecule DNA stretching experiments.Comment: 5 pages, 3 figure

Influences of physical oceanographic processes on chlorophyll distributions in coastal and estuarine waters of the South Atlantic Bight

Coastal and estuarine waters of the South Atlantic Bight are highly productive, with primary production of 600-700 gC/m2/y. While controls and fate of this production are conceptually well understood, the importance of meteorology and physical circulation processes on phytoplankton has not received equivalent attention. Here, we describe the effects of wind stress and tidal currents on temporal and spatial distributions of phytoplankton biomass represented as chlorophyll a (chl a). Moored instruments were deployed and shipboard sampling was conducted in the North Edisto estuary (South Carolina) and adjacent inner shelf waters during four, two-week field studies in May and August 1993, and June and September 1994. Local wind regimes induced upwelling- and downwelling-favorable conditions which strengthened or reduced vertical density stratification in the coastal frontal zone, respectively, and shifted the location of the front. Chl a in shelf waters was more or less homogenous independent of the wind regime, while chl a on the estuary delta was generally vertically stratified. Within the estuary, chl a concentrations were positively correlated with the alongshore component of wind stress; chl a was not correlated with the weaker cross-shelf component of wind stress. Highest chl a occurred during strong downwelling-favorable events. The quick response time to wind forcing (6-12 hrs) implied a direct effect on chl a distributions and not a stimulation of growth processes. The source of the elevated chl a in response to wind forcing was apparently resuspension of settled and epibenthic algal cells. Tidal currents also influenced the vertical distribution and concentration of chl a. Time series sampling on the estuary delta showed that, with increasing velocity of ebb and flood tide currents, the relative contributions of pennate and centric diatoms with attached detritus and sand grains also increased, indicating that tidal resuspension of settled and epibenthic microalgae also occurred. Vertical stratification of chl a (highest concentrations near the bottom) began to degrade upon mixing by tidal currents with velocities as low as 10 cm/sec. Homogenization of 5-7 m water columns was fully achieved at velocities of 20-30 cm/sec. The data document the direct and comparatively immediate (timescales of minuteshours) impact of tidal and wind energy on concentrations and distribution patterns of phytoplankton in coastal and estuarine waters of the South Atlantic Bight

Rolling quantum dice with a superconducting qubit

One of the key challenges in quantum information is coherently manipulating the quantum state. However, it is an outstanding question whether control can be realized with low error. Only gates from the Clifford group -- containing $\pi$, $\pi/2$, and Hadamard gates -- have been characterized with high accuracy. Here, we show how the Platonic solids enable implementing and characterizing larger gate sets. We find that all gates can be implemented with low error. The results fundamentally imply arbitrary manipulation of the quantum state can be realized with high precision, providing new practical possibilities for designing efficient quantum algorithms.Comment: 8 pages, 4 figures, including supplementary materia

Unzipping Kinetics of Double-Stranded DNA in a Nanopore

We studied the unzipping kinetics of single molecules of double-stranded DNA by pulling one of their two strands through a narrow protein pore. PCR analysis yielded the first direct proof of DNA unzipping in such a system. The time to unzip each molecule was inferred from the ionic current signature of DNA traversal. The distribution of times to unzip under various experimental conditions fit a simple kinetic model. Using this model, we estimated the enthalpy barriers to unzipping and the effective charge of a nucleotide in the pore, which was considerably smaller than previously assumed.Comment: 10 pages, 5 figures, Accepted: Physics Review Letter

Logic gates at the surface code threshold: Superconducting qubits poised for fault-tolerant quantum computing

A quantum computer can solve hard problems - such as prime factoring, database searching, and quantum simulation - at the cost of needing to protect fragile quantum states from error. Quantum error correction provides this protection, by distributing a logical state among many physical qubits via quantum entanglement. Superconductivity is an appealing platform, as it allows for constructing large quantum circuits, and is compatible with microfabrication. For superconducting qubits the surface code is a natural choice for error correction, as it uses only nearest-neighbour coupling and rapidly-cycled entangling gates. The gate fidelity requirements are modest: The per-step fidelity threshold is only about 99%. Here, we demonstrate a universal set of logic gates in a superconducting multi-qubit processor, achieving an average single-qubit gate fidelity of 99.92% and a two-qubit gate fidelity up to 99.4%. This places Josephson quantum computing at the fault-tolerant threshold for surface code error correction. Our quantum processor is a first step towards the surface code, using five qubits arranged in a linear array with nearest-neighbour coupling. As a further demonstration, we construct a five-qubit Greenberger-Horne-Zeilinger (GHZ) state using the complete circuit and full set of gates. The results demonstrate that Josephson quantum computing is a high-fidelity technology, with a clear path to scaling up to large-scale, fault-tolerant quantum circuits.Comment: 15 pages, 13 figures, including supplementary materia

Dallas with balls: televized sport, soap opera and male and female pleasures

Two of the most popular of television genres, soap opera and sports coverage have been very much differentiated along gender lines in terms of their audiences. Soap opera has been regarded very much as a 'gynocentric' genre with a large female viewing audience while the audiences for television sport have been predominantly male. Gender differentiation between the genres has had implications for the popular image of each. Soap opera has been perceived as inferior; as mere fantasy and escapism for women while television sports has been perceived as a legitimate, even edifying experience for men. In this article the authors challenge the view that soap opera and television sport are radically different and argue that they are, in fact, very similar in a number of significant ways. They suggest that both genres invoke similar structures of feeling and sensibility in their respective audiences and that television sport is a 'male soap opera'. They consider the ways in which the viewing context of each genre is related to domestic life and leisure, the ways in which the textual structure and conventions of each genre invoke emotional identification, and finally, the ways in which both genres re-affirm gender identities

Spectral signatures of many-body localization with interacting photons

Statistical mechanics is founded on the assumption that a system can reach thermal equilibrium, regardless of the starting state. Interactions between particles facilitate thermalization, but, can interacting systems always equilibrate regardless of parameter values\,? The energy spectrum of a system can answer this question and reveal the nature of the underlying phases. However, most experimental techniques only indirectly probe the many-body energy spectrum. Using a chain of nine superconducting qubits, we implement a novel technique for directly resolving the energy levels of interacting photons. We benchmark this method by capturing the intricate energy spectrum predicted for 2D electrons in a magnetic field, the Hofstadter butterfly. By increasing disorder, the spatial extent of energy eigenstates at the edge of the energy band shrink, suggesting the formation of a mobility edge. At strong disorder, the energy levels cease to repel one another and their statistics approaches a Poisson distribution - the hallmark of transition from the thermalized to the many-body localized phase. Our work introduces a new many-body spectroscopy technique to study quantum phases of matter