Radially restricted linear energy transfer for high-energy protons: A new analytical approach

Radially restricted linear energy transfer (LET) is a basic physical parameter relevant to radiation biology and radiation protection. In this report a convenient method is presented for the analytical computation of this quantity without the need for complicated simulation. The method uses the energy-re-stricted LETL, as recently redefined in a 1993 ICRU draft document and supplements it by a relatively simple term that represents the energy of fast rays lost within distancer from the track core. The method provides a better fit than other models and is valid over the entire range of radial distance from track center to the maximum radial distance traveled by the most energetic secondary electrons.L r computed by this approach differs only a few percent from the values Contribution to the international symposium on heavy ions research: space, radiation protection and therapy, 21–24 March 1994, Sophia-Antipolis, Franc

Distance, Growth Factor, and Dark Energy Constraints from Photometric Baryon Acoustic Oscillation and Weak Lensing Measurements

Baryon acoustic oscillations (BAOs) and weak lensing (WL) are complementary probes of cosmology. We explore the distance and growth factor measurements from photometric BAO and WL techniques and investigate the roles of the distance and growth factor in constraining dark energy. We find for WL that the growth factor has a great impact on dark energy constraints but is much less powerful than the distance. Dark energy constraints from WL are concentrated in considerably fewer distance eigenmodes than those from BAO, with the largest contributions from modes that are sensitive to the absolute distance. Both techniques have some well determined distance eigenmodes that are not very sensitive to the dark energy equation of state parameters w_0 and w_a, suggesting that they can accommodate additional parameters for dark energy and for the control of systematic uncertainties. A joint analysis of BAO and WL is far more powerful than either technique alone, and the resulting constraints on the distance and growth factor will be useful for distinguishing dark energy and modified gravity models. The Large Synoptic Survey Telescope (LSST) will yield both WL and angular BAO over a sample of several billion galaxies. Joint LSST BAO and WL can yield 0.5% level precision on ten comoving distances evenly spaced in log(1+z) between redshift 0.3 and 3 with cosmic microwave background priors from Planck. In addition, since the angular diameter distance, which directly affects the observables, is linked to the comoving distance solely by the curvature radius in the Friedmann-Robertson-Walker metric solution, LSST can achieve a pure metric constraint of 0.017 on the mean curvature parameter Omega_k of the universe simultaneously with the constraints on the comoving distances.Comment: 15 pages, 9 figures, details and references added, ApJ accepte

Catastrophic photometric redshift errors: weak lensing survey requirements

We study the sensitivity of weak lensing surveys to the effects of catastrophic redshift errors - cases where the true redshift is misestimated by a significant amount. To compute the biases in cosmological parameters, we adopt an efficient linearized analysis where the redshift errors are directly related to shifts in the weak lensing convergence power spectra. We estimate the number Nspec of unbiased spectroscopic redshifts needed to determine the catastrophic error rate well enough that biases in cosmological parameters are below statistical errors of weak lensing tomography. While the straightforward estimate of Nspec is ~10^6 we find that using only the photometric redshifts with z<=2.5 leads to a drastic reduction in Nspec to ~30,000 while negligibly increasing statistical errors in dark energy parameters. Therefore, the size of spectroscopic survey needed to control catastrophic errors is similar to that previously deemed necessary to constrain the core of the z_s-z_p distribution. We also study the efficacy of the recent proposal to measure redshift errors by cross-correlation between the photo-z and spectroscopic samples. We find that this method requires ~10% a priori knowledge of the bias and stochasticity of the outlier population, and is also easily confounded by lensing magnification bias. The cross-correlation method is therefore unlikely to supplant the need for a complete spectroscopic redshift survey of the source population.Comment: 14 pages, 3 figure

The Coyote Universe I: Precision Determination of the Nonlinear Matter Power Spectrum

Near-future cosmological observations targeted at investigations of dark energy pose stringent requirements on the accuracy of theoretical predictions for the clustering of matter. Currently, N-body simulations comprise the only viable approach to this problem. In this paper we demonstrate that N-body simulations can indeed be sufficiently controlled to fulfill these requirements for the needs of ongoing and near-future weak lensing surveys. By performing a large suite of cosmological simulation comparison and convergence tests we show that results for the nonlinear matter power spectrum can be obtained at 1% accuracy out to k~1 h/Mpc. The key components of these high accuracy simulations are: precise initial conditions, very large simulation volumes, sufficient mass resolution, and accurate time stepping. This paper is the first in a series of three, with the final aim to provide a high-accuracy prediction scheme for the nonlinear matter power spectrum.Comment: 18 pages, 22 figures, minor changes to address referee repor

Self calibration of photometric redshift scatter in weak lensing surveys

Photo-z errors, especially catastrophic errors, are a major uncertainty for precision weak lensing cosmology. We find that the shear-(galaxy number) density and density-density cross correlation measurements between photo-z bins, available from the same lensing surveys, contain valuable information for self-calibration of the scattering probabilities between the true-z and photo-z bins. The self-calibration technique we propose does not rely on cosmological priors nor parameterization of the photo-z probability distribution function, and preserves all of the cosmological information available from shear-shear measurement. We estimate the calibration accuracy through the Fisher matrix formalism. We find that, for advanced lensing surveys such as the planned stage IV surveys, the rate of photo-z outliers can be determined with statistical uncertainties of 0.01-1% for $z<2$ galaxies. Among the several sources of calibration error that we identify and investigate, the {\it galaxy distribution bias} is likely the most dominant systematic error, whereby photo-z outliers have different redshift distributions and/or bias than non-outliers from the same bin. This bias affects all photo-z calibration techniques based on correlation measurements. Galaxy bias variations of $O(0.1)$ produce biases in photo-z outlier rates similar to the statistical errors of our method, so this galaxy distribution bias may bias the reconstructed scatters at several-$\sigma$ level, but is unlikely to completely invalidate the self-calibration technique.Comment: v2: 19 pages, 10 figures. Added one figure. Expanded discussions. Accepted to MNRA

Using the DPSIR framework for transdisciplinary training and knowledge elicitation in the Gulf of Thailand

No abstract available

Imprints of dynamical dark energy on weak-lensing measurements

We show that simple models of scalar-field dark energy leave a generic enhancement in the weak-lensing power spectrum when compared to the LCDM prediction. In particular, we calculate the linear-scale enhancement in the convergence (or cosmic-shear) power spectrum for two best-fit models of scalar-field dark energy, namely, the Ratra-Peebles and SUGRA-type quintessence. Our calculations are based on linear perturbation theory, using gauge-invariant variables with carefully defined adiabatic initial conditions. We find that geometric effects enhance the lensing power spectrum on a broad range of scales, whilst the clustering of dark energy gives rise to additional power on large scales. The dark-energy power spectrum for these models are also explicitly obtained. On degree scales, the total enhancement may be as large as 30-40% for sources at redshift ~1. We argue that there are realistic prospects for detecting such an enhancement using the next generation of large telescopes.Comment: 10 pages, 8 figures, replacement matches version published in MNRA

The role of host PrP in Transmissible Spongiform Encephalopathies

AbstractPrP has a central role in the Transmissible Spongiform Encephalopathies (TSEs), and mutations and polymorphisms in host PrP can profoundly alter the host's susceptibility to a TSE agent. However, precisely how host PrP influences the outcome of disease has not been established. To investigate this we have produced by gene targeting a series of inbred lines of transgenic mice expressing different PrP genes. This allows us to study directly the influence of the host PrP gene in TSEs. We have examined the role of glycosylation, point mutations, polymorphisms and PrP from different species on host susceptibility and the disease process both within the murine species and across species barriers

Constraining Cosmology with High Convergence Regions in Weak Lensing Surveys

We propose to use a simple observable, the fractional area of "hot spots" in weak gravitational lensing mass maps which are detected with high significance, to determine background cosmological parameters. Because these high-convergence regions are directly related to the physical nonlinear structures of the universe, they derive cosmological information mainly from the nonlinear regime of density fluctuations. We show that in combination with future cosmic microwave background anisotropy measurements, this method can place constraints on cosmological parameters that are comparable to those from the redshift distribution of galaxy cluster abundances. The main advantage of the statistic proposed in this paper is that projection effects, normally the main source of uncertainty when determining the presence and the mass of a galaxy cluster, here serve as a source of information.Comment: 14 pages, 4 figures, accepted for publication in Astrophysical Journa

Weak lensing power spectra for precision cosmology: Multiple-deflection, reduced shear and lensing bias corrections

It is usually assumed that the ellipticity power spectrum measured in weak lensing observations can be expressed as an integral over the underlying matter power spectrum. This is true at second order in the gravitational potential. We extend the standard calculation, constructing all corrections to fourth order in the gravitational potential. There are four types of corrections: corrections to the lensing shear due to multiple-deflections; corrections due to the fact that shape distortions probe the reduced shear $\gamma/(1-\kappa)$ rather than the shear itself; corrections associated with the non-linear conversion of reduced shear to mean ellipticity; and corrections due to the fact that observational galaxy selection and shear measurement is based on galaxy brightnesses and sizes which have been (de)magnified by lensing. We show how the previously considered corrections to the shear power spectrum correspond to terms in our analysis, and highlight new terms that were not previously identified. All correction terms are given explicitly as integrals over the matter power spectrum, bispectrum, and trispectrum, and are numerically evaluated for the case of sources at z=1. We find agreement with previous works for the ${\mathcal O}(\Phi^3)$ terms. We find that for ambitious future surveys, the ${\mathcal O}(\Phi^4)$ terms affect the power spectrum at the ~ 1-5 $\sigma$ level; they will thus need to be accounted for, but are unlikely to represent a serious difficulty for weak lensing as a cosmological probe.Comment: 14 pages, 3 figures; matches A & A accepted versio