The substantive and practical significance of citation impact differences between institutions: Guidelines for the analysis of percentiles using effect sizes and confidence intervals

In our chapter we address the statistical analysis of percentiles: How should the citation impact of institutions be compared? In educational and psychological testing, percentiles are already used widely as a standard to evaluate an individual's test scores - intelligence tests for example - by comparing them with the percentiles of a calibrated sample. Percentiles, or percentile rank classes, are also a very suitable method for bibliometrics to normalize citations of publications in terms of the subject category and the publication year and, unlike the mean-based indicators (the relative citation rates), percentiles are scarcely affected by skewed distributions of citations. The percentile of a certain publication provides information about the citation impact this publication has achieved in comparison to other similar publications in the same subject category and publication year. Analyses of percentiles, however, have not always been presented in the most effective and meaningful way. New APA guidelines (American Psychological Association, 2010) suggest a lesser emphasis on significance tests and a greater emphasis on the substantive and practical significance of findings. Drawing on work by Cumming (2012) we show how examinations of effect sizes (e.g. Cohen's d statistic) and confidence intervals can lead to a clear understanding of citation impact differences

Six Steps to a Healthier Ambient Ozone Policy

EPA appears likely to tighten the ambient ozone standard, even as many areas of the country are having great difficulties meeting the current standard. This paper offers an analysis of potential regulatory, administrative, and legislative initiatives for reducing the costs of meeting ozone standards. The detailed analysis of these initiatives is organized into six steps: (i) acknowledge mistakes and adapt to new knowledge; (ii) rehabilitate EPA's Title I Program; (iii) build on the best ideas; (iv) clarify and change the Clean Air Act; (v) educate the public; and (vi) fund research. EPA can go a long way to make its programs more efficient and effective without changes in the Clean Air Act; indeed, a number of its current initiatives show promise. But it must do more. Congress can help, too, by giving EPA the statutory guidance and freedom it needs to improve the program.

Spectropolarimetric analysis of an active region filament. I. Magnetic and dynamical properties from single component inversions

The determination of the magnetic filed vector in solar filaments is possible by interpreting the Hanle and Zeeman effects in suitable chromospheric spectral lines like those of the He I multiplet at 10830 A. We study the vector magnetic field of an active region filament (NOAA 12087). Spectropolarimetric data of this active region was acquired with the GRIS instrument at the GREGOR telescope and studied simultaneously in the chromosphere with the He I 10830 A multiplet and in the photosphere with the Si I 10827 A line. As it is usual from previous studies, only a single component model is used to infer the magnetic properties of the filament. The results are put into a solar context with the help of the Solar Dynamic Observatory images. Some results clearly point out that a more complex inversion had to be done. Firstly, the Stokes $V$ map of He I does not show any clear signature of the presence of the filament. Secondly, the local azimuth map follows the same pattern than Stokes $V$ as if the polarity of Stokes $V$ were conditioning the inference to very different magnetic field even with similar linear polarization signals. This indication suggests that the Stokes $V$ could be dominated by the below magnetic field coming from the active region, and not, from the filament itself. Those and more evidences will be analyzed in depth and a more complex inversion will be attempted in the second part of this series.Comment: 18 pages, 19 figures, accepted for publication in A&

The impact of Early Dark Energy on non-linear structure formation

We study non-linear structure formation in high-resolution simulations of Early Dark Energy (EDE) cosmologies and compare their evolution with the standard LCDM model. Extensions of the spherical top-hat collapse model predict that the virial overdensity and linear threshold density for collapse should be modified in EDE model, yielding significant modifications in the expected halo mass function. Here we present numerical simulations that directly test these expectations. Interestingly, we find that the Sheth & Tormen formalism for estimating the abundance of dark matter halos continues to work very well in its standard form for the Early Dark Energy cosmologies, contrary to analytic predictions. The residuals are even slightly smaller than for LCDM. We also study the virial relationship between mass and dark matter velocity dispersion in different dark energy cosmologies, finding excellent agreement with the normalization for Lambda as calibrated by Evrard et al.(2008). The earlier growth of structure in EDE models relative to LCDM produces large differences in the mass functions at high redshift. This could be measured directly by counting groups as a function of the line-of-sight velocity dispersion, skirting the ambiguous problem of assigning a mass to the halo. Using dark matter substructures as a proxy for member galaxies, we demonstrate that even with 3-5 members sufficiently accurate measurements of the halo velocity dispersion function are possible. Finally, we determine the concentration-mass relationship for our EDE cosmologies. Consistent with the earlier formation time, the EDE halos show higher concentrations at a given halo mass. We find that the magnitude of the difference in concentration is well described by the prescription of Eke et al.(2001) for estimating halo concentrations.Comment: 17 pages,17 figure

A New Measurement of the Temperature Density Relation of the IGM From Voigt Profile Fitting

We decompose the Lyman-{\alpha} (Ly{\alpha}) forest of an extensive sample of 74 high signal-to-noise ratio and high-resolution quasar spectra into a collection of Voigt profiles. Absorbers located near caustics in the peculiar velocity field have the smallest Doppler parameters, resulting in a low-$b$ cutoff in the $b$-$N_{\text{HI}}$ set by the thermal state of intergalactic medium (IGM). We fit this cutoff as a function of redshift over the range $2.0\leq z \leq 3.4$, which allows us to measure the evolution of the IGM temperature-density ($T= T_0 (\rho/ \rho_0)^{\gamma-1}$) relation parameters $T_0$ and $\gamma$. We calibrate our measurements against Ly$\alpha$ forest simulations, using 21 different thermal models of the IGM at each redshift, also allowing for different values of the IGM pressure smoothing scale. We adopt a forward-modeling approach and self-consistently apply the same algorithms to both data and simulations, propagating both statistical and modeling uncertainties via Monte Carlo. The redshift evolution of $T_0$ shows a suggestive peak at $z=2.8$, while our evolution of $\gamma$ is consistent with $\gamma\simeq 1.4$ and disfavors inverted temperature-density relations. Our measured evolution of $T_0$ and $\gamma$ are generally in good agreement with previous determinations in the literature. Both the peak in the evolution of $T_0$ at $z = 2.8$, as well as the high temperatures $T_0\simeq 15000-20000\,$K that we observe at $2.4 < z < 3.4$, strongly suggest that a significant episode of heating occurred after the end of HI reionization, which was most likely the cosmic reionization of HeII.Comment: Accepted for publication in ApJ, 23 pages, 26 figures, machine readable tables available onlin