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
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
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
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
Uniqueness of static decompositions
We classify static manifolds which admit more than one static decomposition
whenever a condition on the curvature is fullfilled. For this, we take a
standard static vector field and analyze its associated one parameter family of
projections onto the base. We show that the base itself is a static manifold
and the warping function satisfies severe restrictions, leading us to our
classification results. Moreover, we show that certain condition on the
lightlike sectional curvature ensures the uniqueness of static decomposition
for Lorentzian manifolds.Comment: 14 page
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
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
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
Integration of the Friedmann equation for universes of arbitrary complexity
An explicit and complete set of constants of the motion are constructed
algorithmically for Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) models
consisting of an arbitrary number of non-interacting species. The inheritance
of constants of the motion from simpler models as more species are added is
stressed. It is then argued that all FLRW models admit what amounts to a unique
candidate for a gravitational epoch function (a dimensionless scalar invariant
derivable from the Riemann tensor without differentiation which is monotone
throughout the evolution of the universe). The same relations that lead to the
construction of constants of the motion allow an explicit evaluation of this
function. In the simplest of all models, the CDM model, it is shown
that the epoch function exists for all models with , but for
almost no models with .Comment: Final form to appear in Physical Review D1
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