5,764 research outputs found
Sturdier DNA nanotubes via ligation
DNA nanotubes are crystalline self-assemblies of DNA tiles ~10 nm in diameter that readily grow tens of micrometers in length. Easy assembly,
programmability, and stiffness make them interesting for many applications, but DNA nanotubes begin to melt at temperatures below 40 °C,
break open when deposited on mica or scanned by AFM, and disintegrate in deionized water. These weaknesses can be traced to the presence
of discontinuities in the phosphate backbone, called nicks. The nanotubes studied here have five nicks, one in the core of a tile and one at
each corner. We report the successful ligation of all four corner nicks by T4 DNA ligase. Although ligation does not change the nanotubes’
stiffness, ligated nanotubes withstand temperatures over 70 °C, resist breaking during AFM, and are stable in pure water for over a month.
Ligated DNA nanotubes are thus physically and chemically sturdy enough to withstand the manipulations necessary for many technological
applications
Unsteady flow around a Rectangular Cylinder
This paper describes an investigation into the unsteady flow behaviour around a rectangular cylinder using particle image velocimetry (PIV). Instantaneous and average velocity fields were obtained from PIV images. Analysis of the structures observed in the instantaneous velocity fields reveals the presence of small scale (Kelvin-Helmholtz) vortex structures in the shear layer that separates at the leading edge of the rectangular cylinder, and evidence of von Karman vortex shedding was observed in the wake region
Distributional fixed point equations for island nucleation in one dimension: a retrospective approach for capture zone scaling
The distributions of inter-island gaps and captures zones for islands
nucleated on a one-dimensional substrate during submonolayer deposition are
considered using a novel retrospective view. This provides an alternative
perspective on why scaling occurs in this continuously evolving system.
Distributional fixed point equations for the gaps are derived both with and
without a mean field approximation for nearest neighbour gap size correlation.
Solutions to the equations show that correct consideration of fragmentation
bias justifies the mean field approach which can be extended to provide
closed-from equations for the capture zones. Our results compare favourably to
Monte Carlo data for both point and extended islands using a range of critical
island size . We also find satisfactory agreement with theoretical
models based on more traditional fragmentation theory approaches.Comment: 9 pages, 7 figures and 1 tabl
Measures of gravitational entropy I. Self-similar spacetimes
We examine the possibility that the gravitational contribution to the entropy
of a system can be identified with some measure of the Weyl curvature. In this
paper we consider homothetically self-similar spacetimes. These are believed to
play an important role in describing the asymptotic properties of more general
models. By exploiting their symmetry properties we are able to impose
significant restrictions on measures of the Weyl curvature which could reflect
the gravitational entropy of a system. In particular, we are able to show, by
way of a more general relation, that the most widely used "dimensionless"
scalar is \textit{not} a candidate for this measure along homothetic
trajectories.Comment: revtex, minor clarifications, to appear in Physical Review
Strong cosmic censorship and Misner spacetime
Misner spacetime is among the simplest solutions of Einstein's equation that exhibits a Cauchy horizon with a smooth extension beyond it. Besides violating strong cosmic censorship, this extension contains closed timelike curves. We analyze the stability of the Cauchy horizon and prove that neighboring spacetimes in one parameter families of solutions through Misner's in pure gravity, gravity coupled to a scalar field, or Einstein-Maxwell theory end at the Cauchy horizon developing a curvature singularity.publishedVersionFil: Denaro, Pedro Ignacio Esteban. Universidad Nacional de Córdoba. Facultad de Matemática, AstronomÃa y FÃsica; Argentina.Fil: Denaro, Pedro Ignacio Esteban. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Instituto de FÃsica Enrique Gaviola; Argentina.Fil: Dotti, Gustavo Daniel. Universidad Nacional de Córdoba. Facultad de Matemática, AstronomÃa y FÃsica; Argentina.Fil: Dotti, Gustavo Daniel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Instituto de FÃsica Enrique Gaviola; Argentina.Otras Ciencias FÃsica
Uniform and fast switching of window-size smectic A liquid crystal panels utilising the field gradient generated at the fringes of patterned electrodes
A method to enable smectic A (SmA) liquid crystal (LC) devices to switch uniformly and hence fast from the clear state to a scattered state is presented. It will allow the reduction of the switching time for a SmA LC panel of 1x1 m2 changing from a clear state to a fully scattered state by more than three orders to a few tens of milliseconds. Experimental results presented here reveal that SmA LC scattering initiates from the nucleated LC defects at the field gradient of the applied electric field usually along the edges of the panel electrode and grows laterally to spread over a panel, which takes a long time if the panel size is large. By patterning the electrodes in use, it is possible to create a large number of field gradient sites near the electrode discontinuities, resulting in a uniform and fast switching over the whole panel and the higher the pattern density the shorter the panel switching time. For the SmA LC panels used here, the ITO transparent electrodes are patterned by laser ablation and photolithography, respectively. It is shown that the defect nucleation time is much shorter than the growth time of the scattered region, hence it is possible to use the density of the field gradient sites to control the uniformity and switching time of a panel. Furthermore, the patterned SmA panels have a lower switching voltage than that of the non-patterned ones in general.The authors would like to thank the UK Engineering and Physical Sciences Research Council (EPSRC) for the support through the Platform Grant for Liquid Crystal Photonics (EP/F00897X/1) and Dr Anthony Davey for providing the organic SmA LC and Dow Corning Corp. for providing the siloxane-based SmA LC used in this study. The authors would also like to thank Dr Stuart Speakman for the helpful discussions.This is the final version of the article. It first appeared from Taylor & Francis via http://dx.doi.org/10.1080/02678292.2016.114201
Computation of molecular Hartree–Fock Wigner intracules
The computation of molecular Wigner intracules from Hartree–Fock wave functions using Gaussian basis functions is described. The Wigner intracule is a new type of intracule that contains information about both the relative position and momentum of the electrons. Two methods for evaluating the required integrals are presented. The first approach uses quadrature while the second requires summation of an infinite series.This research was partly supported by the Engineering
and Physical Sciences Research Council through a project
studentship (GR/R81121) to D.P.O. and an Advanced Research
Fellowship (GR/R77636) to N.A.B
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Forecasting Urban Residential Stock Turnover Dynamics using System Dynamics and Bayesian Model Averaging
Knowing the size of the building stock is perhaps the most basic determinant in assessing energy use in buildings. However, official statistics on urban residential stock for many countries are piecemeal at best. Previous studies estimating stock size an
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Applying Bayesian model averaging to characterise urban residential stock turnover dynamics
Building stock is a key determinant in building energy modelling and policy analysis. However, official statistics on total floor area of urban residential stock in China only exist up to 2006. Previous studies estimating Chinese urban residential stock size and energy use made various questionable methodological assumptions and only produced deterministic results. This paper presents a Bayesian approach to characterise the stock turnover dynamics and estimate stock size uncertainties. Firstly, a probabilistic dynamic model is developed to describe the building aging and demolition process governed by a hazard function specified by a parametric survival model. Secondly, with each of five candidate parametric survival models, the dynamic model is simulated through Markov Chain Monte Carlo (MCMC) to obtain posterior distributions of model-specific parameters, estimate marginal likelihood, and make predictions on stock size. Finally, Bayesian Model Averaging (BMA) is applied to create a model ensemble that combines the model-specific posterior predictive distributions of the stock evolution pathway in proportion to posterior model probabilities. This Bayesian modelling framework, and its results in the form of probability distributions of annual total stock and age-specific substocks, can provide a solid basis for further modelling and analysis of policy trade-offs across embodied-versus-operational energy consumption and carbon emissions of buildings in the context of sectorwide transition towards decarbonising buildings
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