4,459 research outputs found

    New Mexico

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    New Mexico

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    The Harbor of Love

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    https://digitalcommons.library.umaine.edu/mmb-vp/1407/thumbnail.jp

    Optical data of meteoritic nano-diamonds from far-ultraviolet to far-infrared wavelengths

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    We have used different spectroscopic techniques to obtain a consistent quantitative absorption spectrum of a sample of meteoritic nano-diamonds in the wavelength range from the vacuum ultraviolet (0.12 μ\mum) to the far infrared (100 μ\mum). The nano-diamonds have been isolated by a chemical treatment from the Allende meteorite (Braatz et al.2000). Electron energy loss spectroscopy (EELS) extends the optical measurements to higher energies and allows the derivation of the optical constants (n & k) by Kramers-Kronig analysis. The results can be used to restrain observations and to improve current models of the environment where the nano-diamonds are expected to have formed. We also show that the amount of nano-diamond which can be present in space is higher than previously estimated by Lewis et al. (1989).Comment: 11 pages, 7 figure

    Calibration of optimal execution of financial transactions in the presence of transient market impact

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    Trading large volumes of a financial asset in order driven markets requires the use of algorithmic execution dividing the volume in many transactions in order to minimize costs due to market impact. A proper design of an optimal execution strategy strongly depends on a careful modeling of market impact, i.e. how the price reacts to trades. In this paper we consider a recently introduced market impact model (Bouchaud et al., 2004), which has the property of describing both the volume and the temporal dependence of price change due to trading. We show how this model can be used to describe price impact also in aggregated trade time or in real time. We then solve analytically and calibrate with real data the optimal execution problem both for risk neutral and for risk averse investors and we derive an efficient frontier of optimal execution. When we include spread costs the problem must be solved numerically and we show that the introduction of such costs regularizes the solution.Comment: 31 pages, 8 figure

    The WiggleZ Dark Energy Survey: Survey Design and First Data Release

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    The WiggleZ Dark Energy Survey is a survey of 240,000 emission line galaxies in the distant universe, measured with the AAOmega spectrograph on the 3.9-m Anglo-Australian Telescope (AAT). The target galaxies are selected using ultraviolet photometry from the GALEX satellite, with a flux limit of NUV<22.8 mag. The redshift range containing 90% of the galaxies is 0.2<z<1.0. The primary aim of the survey is to precisely measure the scale of baryon acoustic oscillations (BAO) imprinted on the spatial distribution of these galaxies at look-back times of 4-8 Gyrs. Detailed forecasts indicate the survey will measure the BAO scale to better than 2% and the tangential and radial acoustic wave scales to approximately 3% and 5%, respectively. This paper provides a detailed description of the survey and its design, as well as the spectroscopic observations, data reduction, and redshift measurement techniques employed. It also presents an analysis of the properties of the target galaxies, including emission line diagnostics which show that they are mostly extreme starburst galaxies, and Hubble Space Telescope images, which show they contain a high fraction of interacting or distorted systems. In conjunction with this paper, we make a public data release of data for the first 100,000 galaxies measured for the project.Comment: Accepted by MNRAS; this has some figures in low resolution format. Full resolution PDF version (7MB) available at http://www.physics.uq.edu.au/people/mjd/pub/wigglez1.pdf The WiggleZ home page is at http://wigglez.swin.edu.au

    Substrate-Assisted Catalysis Unifies Two Families of Chitinolytic Enzymes

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    Hen egg-white lysozyme has long been the paradigm for enzymatic glycosyl hydrolysis with retention of configuration, with a protonated carboxylic acid and a deprotonated carboxylate participating in general acid-base catalysis. In marked contrast, the retaining chitin degrading enzymes from glycosyl hydrolase families 18 and 20 all have a single glutamic acid as the catalytic acid but lack a nucleophile on the enzyme. Both families have a catalytic (βα)8-barrel domain in common. X-ray structures of three different chitinolytic enzymes complexed with substrates or inhibitors identify a retaining mechanism involving a protein acid and the carbonyl oxygen atom of the substrate’s C2 N-acetyl group as the nucleophile. These studies unambiguously demonstrate the distortion of the sugar ring toward a sofa conformation, long postulated as being close to that of the transition state in glycosyl hydrolysis.

    The 6dF galaxy survey: cosmological constraints from the velocity power spectrum

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    We present scale-dependent measurements of the normalized growth rate of structure fσ8(k, z = 0) using only the peculiar motions of galaxies. We use data from the 6-degree Field Galaxy Survey velocity sample together with a newly compiled sample of low-redshift (z 300 h−1 Mpc, which represents one of the largest scale growth rate measurement to date. We find no evidence for a scale-dependence in the growth rate, or any statistically significant variation from the growth rate as predicted by the Planck cosmology. Bringing all the scales together, we determine the normalized growth rate at z = 0 to ∼15 per cent in a manner independent of galaxy bias and in excellent agreement with the constraint from the measurements of redshift-space distortions from 6-degree Field Galaxy Survey. We pay particular attention to systematic errors. We point out that the intrinsic scatter present in Fundamental Plane and Tully–Fisher relations is only Gaussian in logarithmic distance units; wrongly assuming it is Gaussian in linear (velocity) units can bias cosmological constraints. We also analytically marginalize over zero-point errors in distance indicators, validate the accuracy of all our constraints using numerical simulations, and demonstrate how to combine different (correlated) velocity surveys using a matrix ‘hyperparameter’ analysis. Current and forthcoming peculiar velocity surveys will allow us to understand in detail the growth of structure in the low-redshift universe, providing strong constraints on the nature of dark energy
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