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  • 1
    Electronic Resource
    Electronic Resource
    Adsorptive stripping voltammetry for thiomersal assay
    Amsterdam : Elsevier
    Journal of Pharmaceutical and Biomedical Analysis 12 (1994), S. 273-276 
    Details
    ISSN: 0731-7085
    Keywords: Thiomersal ; adsorptive stripping voltammetry ; contact lens solutions ; cyclic voltammetry ; differential-pulse voltammetry ; hanging mercury drop electrode
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0731-7085(94)90039-6
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Experimental design methodologies to optimize the CE separation of epinephrine enantiomers (1998)
    Springer
    Chromatographia 48 (1998), S. 395-401 
    Details
    ISSN: 1612-1112
    Keywords: Capillary electrophoresis ; Enantiomers ; Epinephrine ; Experimental designs ; Optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A capillary electrophoretic method using a chiral selector was optimized by experimental design for the enantioresolution of epinephrine enantiomers. Two β-cyclodextrins derivatives, namely heptakis-2,6-di-O-methyl-β-cyclodextrin and carboxy-methyl-β-cyclodextrin, respectively neutral and charged, were used as chiral selectors employing an uncoated capillary. By using a statistical experimental design in which all factors are varied at the same time, it was possible to optimize the method with regard to the resolution between peaks and the two migration times. A fractional factorial design and a central composite design were used. A compromise between conflicting goals, such as maximization of resolution and minimization of analysis time, was found by means of a desirability function D. Balancing these goals against each other, the most acceptable solution to the problem was found and the optimized method gave a fast separation with complete resolution between the adrenaline enantiomers. The response surfaces obtained confirmed the robustness of the method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467710
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  • 3
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    The distribution of bubble sizes during reionization (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-20
    Description: A key physical quantity during reionization is the size of H  ii regions. Previous studies found a characteristic bubble size which increases rapidly during reionization, with apparent agreement between simulations and analytic excursion set theory. Using four different methods, we critically examine this claim. In particular, we introduce the use of the watershed algorithm – widely used for void finding in galaxy surveys – which we show to be an unbiased method with the lowest dispersion and best performance on Monte Carlo realizations of a known bubble size probability density function (PDF). We find that a friends-of-friends algorithm declares most of the ionized volume to be occupied by a network of volume-filling regions connected by narrow tunnels. For methods tuned to detect the volume-filling regions, previous apparent agreement between simulations and theory is spurious, and due to a failure to correctly account for the window function of measurement schemes. The discrepancy is already obvious from visual inspection. Instead, H  ii regions in simulations are significantly larger (by factors of 10–1000 in volume) than analytic predictions. The size PDF is narrower, and evolves more slowly with time, than predicted. It becomes more sharply peaked as reionization progresses. These effects are likely caused by bubble mergers, which are inadequately modelled by analytic theory. Our results have important consequences for high-redshift 21 cm observations, the mean free path of ionizing photons, and the visibility of Lyα emitters, and point to a fundamental failure in our understanding of the characteristic scales of the reionization process.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Constraints on the star formation efficiency of galaxies during the epoch of reionization (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-27
    Description: Reionization is thought to have occurred in the redshift range of 6 〈 z 〈 9, which is now being probed by both deep galaxy surveys and CMB observations. Using halo abundance matching over the redshift range 5 〈 z 〈 8 and assuming smooth, continuous gas accretion, we develop a model for the star formation efficiency f * of dark matter haloes at z 〉 6 that matches the measured galaxy luminosity functions at these redshifts. We find that f * peaks at ~30 per cent at halo masses M ~ 10 11 –10 12 M , in qualitative agreement with its behaviour at lower redshifts. We then investigate the cosmic star formation histories and the corresponding models of reionization for a range of extrapolations to small halo masses. We use a variety of observations to further constrain the characteristics of the galaxy populations, including the escape fraction of UV photons. Our approach provides an empirically calibrated, physically motivated model for the properties of star-forming galaxies sourcing the epoch of reionization. In the case where star formation in low-mass haloes is maximally efficient, an average escape fraction ~0.1 can reproduce the optical depth reported by Planck , whereas inefficient star formation in these haloes requires either about twice as many UV photons to escape, or an escape fraction that increases towards higher redshifts. Our models also predict how future observations with James Webb Space Telescope can improve our understanding of these galaxy populations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Large fluctuations in the hydrogen-ionizing background and mean free path following the epoch of reionization (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-04
    Description: Extremely large opaque troughs in the Lyα forest have been interpreted as a sign of an extended reionization process below z ~ 6. Such features are impossible to reproduce with simple models of the intergalactic ionizing background that assume a uniform mean free path of ionizing photons. We build a self-consistent model of the ionizing background that includes fluctuations in the mean free path due to the varying strength of the ionizing background and large-scale density field. The dominant effect is the suppression of the ionizing background in large-scale voids due to ‘self-shielding’ by an enhanced number of optically thick absorbers. Our model results in a distribution of 50 Mpc  h –1 Lyα forest effective optical depths that significantly improves agreement with the observations at z ~ 5.6. Extrapolation to z ~ 5.4 and 5.8 appears promising, but matching the mean background evolution requires evolution in the absorber population beyond the scope of the present model. We also demonstrate the need for extremely large volumes (〉400 Mpc on a side) to accurately determine the incidence of rare large-scale features in the Lyα forest.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Quasar ionization front Ly{alpha} emission in an inhomogeneous intergalactic medium (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-20
    Description: The conditions within the ionization front of a quasar during reionization ( T ~ 30 000 K, neutral hydrogen fraction $x_\mathrm{H\,\small {I}}\sim 0.5$ ) are ideal for producing Lyα emission via collisional excitation of hydrogen atoms. Observations of this emission, which could subtend 10 arcmin 2 on the sky, would definitively demonstrate the presence of a neutral intergalactic medium at the observed epoch, placing valuable constraints on the progress of reionization. We find that the expected Lyα surface brightness is significantly weaker than previously determined and may be impossible to observe with current and near-future instruments. Past work calculated the Lyα emission from a quasar ionization front in a homogeneous medium with a clumping factor approximation to account for inhomogeneities. We find using 1D radiative transfer calculations that this approximation overestimates the emission by a factor of 3. Our calculations model the propagation of ionizing photons and compute the Lyα emission from quasar ionization fronts on sightlines from a hydrodynamic cosmological simulation at z = 7.1. To better understand the physical properties of the emission, we also develop an analytic model that accurately describes the results of the full radiative transfer calculation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Reionization through the lens of percolation theory (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-06
    Description: The reionization of intergalactic hydrogen has received intense theoretical scrutiny over the past two decades. Here, we approach the process formally as a percolation process and phase transition. Using semi-numeric simulations, we demonstrate that an infinitely large ionized region abruptly appears at an ionized fraction of x i 0.1 and quickly grows to encompass most of the ionized gas: by x i  ~ 0.3, nearly 90 per cent of the ionized material is part of this region. Throughout most of reionization, nearly all of the intergalactic medium is divided into just two regions, one ionized and one neutral, and both infinite in extent. We also show that the discrete ionized regions that exist before and near this transition point follow a near-power-law distribution in volume, with equal contributions to the total filling factor per logarithmic interval in size up to a sharp cutoff in volume. These qualities are generic to percolation processes, with the detailed behaviour a result of long-range correlations in the underlying density field. These insights will be crucial to understanding the distribution of ionized and neutral gas during reionization and provide precise meaning to the intuitive description of reionization as an ‘overlap’ process.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Experimental design methodologies to optimize the CE separation of epinephrine enantiomers (1998)
    Springer
    Details
    Publication Date: 1998-09-01
    Print ISSN: 0009-5893
    Electronic ISSN: 1612-1112
    Topics: Chemistry and Pharmacology
    Published by Springer
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  • 9
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    Molecular cloud properties and CO line emission in z {gtrsim} 6 galaxies (2013)
    Oxford University Press
    Details
    Publication Date: 2013-10-08
    Description: We explore molecular cloud properties and the physics of CO transition lines in z 6 Lyman-break galaxies and predict their CO fluxes using an analytic formalism built from global models of star formation in high-redshift galaxies that minimizes our reliance on local observations. Our model includes a new approach to calculating the molecular gas fraction that takes the total gas density, the star formation rate and the star formation efficiency in clouds as the principal inputs. This method agrees with chemical equilibrium calculations of the molecular fraction based on local chemistry if galaxies at z 6 have metallicities on the order of a few per cent of solar. Such low metallicities in turn imply that much of the carbon in these systems exists in ionized form rather than as CO. Moreover, we find that the higher-order CO transitions observable at high redshift with Atacama Large Millimeter Array (ALMA) will typically be sub-thermally populated but that the details depend sensitively on the presence of turbulent clumps within molecular clouds. Ultimately, we expect current facilities will only be able to observe the CO signal from reionization epoch galaxies with great difficulty. We estimate that at least ~100 h of integration time with ALMA will be required to detect the CO(6–5) transition in z  = 6 systems with rest-frame UV magnitudes of –20.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Semi-numeric simulations of helium reionization and the fluctuating radiation background (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-02
    Description: Recent He ii Lyman α forest observations within the range 2.0 z 3.2 show large fluctuations in the optical depth at z 2.7. These results point to a fluctuating He-ionizing background, which may be due to the end of helium reionization of this era. We present a fast, semi-numeric procedure to approximate detailed cosmological simulations. We compute the distribution of dark matter haloes, ionization state of helium, and density field at z  = 3, which are in broad agreement with recent simulations. Given our speed and flexibility, we investigate a range of ionizing source and active quasar prescriptions. Spanning a large area of parameter space, we find order-of-magnitude fluctuations in the He ii ionization rate in the post-reionization regime. During reionization, the fluctuations are even stronger and develop a bimodal distribution, in contrast to semi-analytic models and the hydrogen equivalent. These distributions indicate a low-level ionizing background even at significant He ii fractions.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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