Self-assembly of two-dimensional binary quasicrystals: A possible route to a DNA quasicrystal

We use Monte Carlo simulations and free-energy techniques to show that binary solutions of penta- and hexavalent two-dimensional patchy particles can form thermodynamically stable quasicrystals even at very narrow patch widths, provided their patch interactions are chosen in an appropriate way. Such patchy particles can be thought of as a coarse-grained representation of DNA multi-arm `star' motifs, which can be chosen to bond with one another very specifically by tuning the DNA sequences of the protruding arms. We explore several possible design strategies and conclude that DNA star tiles that are designed to interact with one another in a specific but not overly constrained way could potentially be used to construct soft quasicrystals in experiment. We verify that such star tiles can form stable dodecagonal motifs using oxDNA, a realistic coarse-grained model of DNA

Isotope effects in liquid water probed by transmission mode x ray absorption spectroscopy at the oxygen K edge

The effects of isotope substitution in liquid water are probed by x ray absorption spectroscopy at the O K edge as measured in transmission mode. Confirming earlier x ray Raman scattering experiments, the D2O spectrum is found to be blue shifted with respect to H2O, and the D2O spectrum to be less broadened. Following the earlier interpretations of UV and x ray Raman spectra, the shift is related to the difference in ground state zero point energies between D2O and H2O, while the difference in broadening is related to the difference in ground state vibrational zero point distributions. We demonstrate that the transmission mode measurements allow for determining the spectral shapes with unprecedented accuracy. Owing in addition to the increased spectral resolution and signal to noise ratio compared to the earlier measurements, the new data enable the stringent determination of blue shift and broadening in the O K edge x ray absorption spectrum of liquid water upon isotope substitution. The results are compared to UV absorption data, and it is discussed to which extent they reflect the differences in zero point energies and vibrational zero point distributions in the ground states of the liquids. The influence of the shape of the final state potential, inclusion of the Franck Condon structure, and differences between liquid H2O and D2O resulting from different hydrogen bond environments in the liquids are addressed. The differences between the O K edge absorption spectra of water from our transmission mode measurements and from the state of the art x ray Raman scattering experiments are discussed in addition. The experimentally extracted values of blue shift and broadening are proposed to serve as a test for calculations of ground state zero point energies and vibrational zero point distributions in liquid H2O and D2O. This clearly motivates the need for new calculations of the O K edge x ray absorption spectrum of liquid wate

A high frequency optical trap for atoms using Hermite-Gaussian beams

We present an experimental method to create a single high frequency optical trap for atoms based on an elongated Hermite-Gaussian TEM01 mode beam. This trap results in confinement strength similar to that which may be obtained in an optical lattice. We discuss an optical setup to produce the trapping beam and then detail a method to load a Bose-Einstein Condensate (BEC) into a TEM01 trap. Using this method, we have succeeded in producing individual highly confined lower dimensional condensates.Comment: 9 pages, 5 figure

Temperature dependent soft x ray absorption spectroscopy of liquids

A novel sample holder is introduced which allows for temperature dependent soft x ray absorption spectroscopy of liquids in transmission mode. The setup is based on sample cells with x ray transmissive silicon nitride windows. A cooling circuit allows for temperature regulation of the sample liquid between amp; 8722;10 amp; 9702;C and 50 amp; 9702;C. The setup enables to record soft x ray absorption spectra of liquids in transmission mode with a temperature resolution of 0.5K and better. Reliability and reproducibility of the spectra are demonstrated by investigating the characteristic temperature induced changes in the oxygen K edge x ray absorption spectrum of liquid water. These are compared to the corresponding changes in the oxygen K edge spectra from x ray Raman scatterin

Rods are less fragile than spheres: Structural relaxation in dense liquids composed of anisotropic particles

We perform extensive molecular dynamics simulations of dense liquids composed of bidisperse dimer- and ellipse-shaped particles in 2D that interact via repulsive contact forces. We measure the structural relaxation times obtained from the long-time decay of the self-part of the intermediate scattering function for the translational and rotational degrees of freedom (DOF) as a function of packing fraction \phi, temperature T, and aspect ratio \alpha. We are able to collapse the \phi and T-dependent structural relaxation times for disks, and dimers and ellipses over a wide range of \alpha, onto a universal scaling function {\cal F}_{\pm}(|\phi-\phi_0|,T,\alpha), which is similar to that employed in previous studies of dense liquids composed of purely repulsive spherical particles in 3D. {\cal F_{\pm}} for both the translational and rotational DOF are characterized by the \alpha-dependent scaling exponents \mu and \delta and packing fraction \phi_0(\alpha) that signals the crossover in the scaling form {\cal F}_{\pm} from hard-particle dynamics to super-Arrhenius behavior for each aspect ratio. We find that the fragility at \phi_0, m(\phi_0), decreases monotonically with increasing aspect ratio for both ellipses and dimers. Moreover, the results for the slow dynamics of dense liquids composed of dimer- and ellipse-shaped particles are qualitatively the same, despite the fact that zero-temperature static packings of dimers are isostatic, while static packings of ellipses are hypostatic.Comment: 10 pages, 17 figures, and 1 tabl

Soft Sphere Packings at Finite Pressure but Unstable to Shear

When are athermal soft sphere packings jammed ? Any experimentally relevant definition must at the very least require a jammed packing to resist shear. We demonstrate that widely used (numerical) protocols in which particles are compressed together, can and do produce packings which are unstable to shear - and that the probability of generating such packings reaches one near jamming. We introduce a new protocol that, by allowing the system to explore different box shapes as it equilibrates, generates truly jammed packings with strictly positive shear moduli G. For these packings, the scaling of the average of G is consistent with earlier results, while the probability distribution P(G) exhibits novel and rich scalingComment: 5 pages, 6 figures. Resubmitted to Physical Review Letters after a few change

Temperature dependence of density profiles for a cloud of non-interacting fermions moving inside a harmonic trap in one dimension

We extend to finite temperature a Green's function method that was previously proposed to evaluate ground-state properties of mesoscopic clouds of non-interacting fermions moving under harmonic confinement in one dimension. By calculations of the particle and kinetic energy density profiles we illustrate the role of thermal excitations in smoothing out the quantum shell structure of the cloud and in spreading the particle spill-out from quantum tunnel at the edges. We also discuss the approach of the exact density profiles to the predictions of a semiclassical model often used in the theory of confined atomic gases at finite temperature.Comment: 7 pages, 4 figure

The IIASA Energy Access Tool (Energy-ENACT)

Researchers from the Energy Program at the International Institute for Applied Systems Analysis (IIASA), building on work carried out within the framework of the Global Energy Assessment (GEA), have developed an interactive web-based scenario analysis tool that permits assessment of different policies for achieving universal access to modern energy by 2030. This software, known as the IIASA Energy-ENACT tool, is designed to assist national and regional policy makers and analysts in their strategic policy planning processes. The tool extends work undertaken for the GEA and, as such, is built on an extensive set of energy access scenarios to visualise costs and benefits of specific policy choices and their impacts. This document serves as an introduction to the Energy-ENACT tool and as a brief manual for the typical user