Ionizing radiation fluctuations and large-scale structure in the Lyman-alpha forest

We investigate the large-scale inhomogeneities of the hydrogen ionizing radiation field in the Universe at redshift z=3. Using a raytracing algorithm, we simulate a model in which quasars are the dominant sources of radiation. We make use of large scale N-body simulations of a LambdaCDM universe, and include such effects as finite quasar lifetimes and output on the lightcone, which affects the shape of quasar light echoes. We create Lya forest spectra that would be generated in the presence of such a fluctuating radiation field, finding that the power spectrum of the Lya forest can be suppressed by as much as 15 % for modes with k=0.05-1 Mpc/h. This relatively small effect may have consequences for high precision measurements of the Lya power spectrum on larger scales than have yet been published. We also investigate another radiation field probe, the cross-correlation of quasar positions and the Lya forest. For both quasar lifetimes which we simulate (10^7 yr and 10^8 yr), we expect to see a strong decrease in the Lya absorption close to other quasars (the ``foreground'' proximity effect). We then use data from the Sloan Digital Sky Survey First Data Release to make an observational determination of this statistic. We find no sign of our predicted lack of absorption, but instead increased absorption close to quasars. If the bursts of radiation from quasars last on average < 10^6 yr, then we would not expect to be able to see the foreground effect. However, the strength of the absorption itself seems to be indicative of rare objects, and hence much longer total times of emission per quasar. Variability of quasars in bursts with timescales > 10^4yr and < 10^6 yr could reconcile these two facts.Comment: Submitted to ApJ, 21 pages, 17 postscript figures, emulateapj.st

Creating tissue with intervertebral disc-like characteristics using gdf5 functionalized silk scaffolds and human mesenchymal stromal cells

For years, researchers have searched for a suitable biomaterial to regenerate the intervertebral disc (IVD). A promising candidate is silk, as there have been several approaches in the past where silk fibroin was used to repair the IVD’s nucleus pulposus (NP) and annulus fibrosus (AF). However, to date, nobody has attempted to recreate IVD tissue with dimensions and cell densities comparable to a human IVD using silk and human mesenchymal stromal cells (MSC). Therefore, silk scaffolds were produced from Bombyx mori yarn. To mimic the AF, the yarn was embroidered into a ring-like structure or patch. To mimic the NP, fibre-additive manufacturing was applied to create highly porous constructs. Half of the NP scaffolds were functionalized with the growth differentiation factor 5 (GDF5). The scaffolds were seeded with MSCs from five human donors in a density of one-third of the density found in the human IVD and cultured for 7, 14 or 21 days in transforming growth factor β1 (TGF-β1)-enriched medium. All scaffolds were biocompatible as cell numbers increased by a factor 4-5. Furthermore, the scaffolds generally showed an anabolic phenotype, which was positively influenced by GDF5, and tissue-like characteristics were promoted based on the scaffolds’ morphology. In conclusion, the here proposed silk scaffolds showed IVD-like characteristics with a size and cell density comparable to human IVD tissue

Generating Individual Patient Preferences for the Treatment of Osteoarthritis Using Adaptive Choice-Based Conjoint (ACBC) Analysis.

INTRODUCTION: To explore how adaptive choice-based conjoint (ACBC) analysis could contribute to shared decision-making in the treatment of individual patients with osteoarthritis (OA). METHODS: In-depth case study of three individuals randomly selected from patients with OA participating in an ACBC analysis exercise. Eleven members of a research users' group participated in developing an ACBC task on medication preferences for OA. Individual medication priorities are illustrated by the detailed analysis of ACBC output from three randomly selected patients from the main sample. RESULTS: The case study analysis illustrates individual preferences. Participant 1's priority was avoidance of the four high-risk side effects of medication, which accounted for 90% of the importance of all attributes, while the remaining attributes (expected benefit; way of taking medication; frequency; availability) accounted only for 10% of the total influence. Participant 3 was similar to participant 1 but would accept a high risk of one of the side effects if the medication were available by prescription. In contrast, participant 2's priority was the avoidance of Internet purchase of medication; this attribute (availability) accounted for 52% of the importance of all attributes. CONCLUSIONS: Individual patients have preferences that likely lead to different medication choices. ACBC has the potential as a tool for physicians to identify individual patient preferences as a practical basis for concordant prescribing for OA in clinical practice. Future research needs to establish whether accurate knowledge of individual patient preferences for treatment attributes and levels translates into concordant behavior in clinical practice

Constraining quasar host halo masses with the strength of nearby Lyman-alpha forest absorption

Using cosmological hydrodynamic simulations we measure the mean transmitted flux in the Lyman alpha forest for quasar sightlines that pass near a foreground quasar. We find that the trend of absorption with pixel-quasar separation distance can be fitted using a simple power law form including the usual correlation function parameters r_{0} and \gamma so that ( = \sum exp(-tau_eff*(1+(r/r_{0})^(-\gamma)))). From the simulations we find the relation between r_{0} and quasar mass and formulate this as a way to estimate quasar host dark matter halo masses, quantifying uncertainties due to cosmological and IGM parameters, and redshift errors. With this method, we examine data for ~3000 quasars from the Sloan Digital Sky Survey (SDSS) Data Release 3, assuming that the effect of ionizing radiation from quasars (the so-called transverse proximity effect) is unimportant (no evidence for it is seen in the data.) We find that the best fit host halo mass for SDSS quasars with mean redshift z=3 and absolute G band magnitude -27.5 is log10(M/M_sun) = 12.48^{+0.53}_{-0.89}. We also use the Lyman-Break Galaxy (LBG) and Lyman alpha forest data of Adelberger et al in a similar fashion to constrain the halo mass of LBGs to be log10(M/M_sun) = 11.13^{+0.39}_{-0.55}, a factor of ~20 lower than the bright quasars. In addition, we study the redshift distortions of the Lyman alpha forest around quasars, using the simulations. We use the quadrupole to monopole ratio of the quasar-Lyman alpha forest correlation function as a measure of the squashing effect. We find that this does not have a measurable dependence on halo mass, but may be useful for constraining cosmic geometry.Comment: 10 pages, 11 figures, submitted to MNRA

Preface: Special Issue on Environmental Impact of Nature‐Based Tourism.

Tourism is growing rapidly throughout the world, including nature‐based tourism, but natural habitats are shrinking. How do we avoid damaging what is left as an increasing number of visitors wish to experience nature or enjoy adventure or relaxation in natural surroundings? This issue explores various environmental impact factors, from the physical effects of trampling through the disturbance of wildlife to the attitudes of visitors and how well‐run tourism ventures might modify their behavior

Recovering the Primordial Density Fluctuations: A comparison of methods

We present a comparative study of six different methods for reversing the gravitational evolution of a cosmological density field to recover the primordial fluctuations: linear theory, the Gaussianization mapping scheme, two different quasi-linear dynamical schemes based on the Zel'dovich approximation, a Hybrid dynamical-Gaussianization method and the Path Interchange Zel'dovich Approximation (PIZA). The final evolved density field from an N-body simulation constitutes our test case. We use a variety of statistical measures to compare the initial density field recovered from it to the true initial density field, using each of the six different schemes. These include point-by-point comparisons of the density fields in real space, the individual modes in Fourier space, as well as global statistical properties such as the genus, the PDF of the density, and the distribution of peak heights and their shapes. We find linear theory to be the most inaccurate of all the schemes. The Gaussianization scheme is the least accurate after linear theory. The two quasi-linear dynamical schemes are more accurate than Gaussianization, although they break down quite drastically when used outside their range of validity - the quasi-linear regime. The complementary beneficial aspects of the dynamical and the Gaussianization schemes are combined in the Hybrid method. We find this Hybrid scheme to be more accurate and robust than either Gaussianization or the dynamical method alone. The PIZA scheme performs substantially better than the others in all point-by-point comparisons. However, it produces an oversmoothed initial density field, with a smaller number of peaks than expected, but recovers the PDF of the initial density with impressive accuracy on scales as small as 3Mpc/h.Comment: 39 pages, including 13 Figures, submitted to Ap

Association patterns and foraging behaviour in natural and artificial guppy shoals

Animal groups are often nonrandom assemblages of individuals that tend to be assorted by factors such as sex, body size, relatedness and familiarity. Laboratory studies using fish have shown that familiarity among shoal members confers a number of benefits to individuals, such as increased foraging success. However, it is unclear whether fish in natural shoals obtain these benefits through association with familiars. We investigated whether naturally occurring shoals of guppies, Poecilia reticulata, are more adept at learning a novel foraging task than artificial (in which we selected shoal members randomly) shoals. We used social network analysis to compare the structures of natural and artificial shoals and examined whether shoal organization predicts patterns of foraging behaviour. Fish in natural shoals benefited from increased success in the novel foraging task compared with fish in artificial shoals. Individuals in natural shoals showed a reduced latency to approach the novel feeder, followed more and formed smaller subgroups compared to artificial shoals. Our findings show that fish in natural shoals do gain foraging benefits and that this may be facilitated by a reduced perception of risk among familiarized individuals and/or enhanced social learning mediated by following other individuals and small group sizes. Although the structure of shoals was stable over time, we found no direct relationship between shoal social structure and patterns of foraging behaviour

Evolution of the Cluster Mass and Correlation Functions in LCDM Cosmology

The evolution of the cluster mass function and the cluster correlation function from z = 0 to z = 3 are determined using 10^6 clusters obtained from high-resolution simulations of the current best-fit LCDM cosmology (\Omega_m = 0.27, \sigma_8 = 0.84, h = 0.7). The results provide predictions for comparisons with future observations of high redshift clusters. A comparison of the predicted mass function of low redshift clusters with observations from early Sloan Digital Sky Survey data, and the predicted abundance of massive distant clusters with observational results, favor a slightly larger amplitude of mass fluctuations (\sigma_8 = 0.9) and lower density parameter (\Omega_m = 0.2); these values are consistent within 1-\sigma with the current observational and model uncertainties. The cluster correlation function strength increases with redshift for a given mass limit; the clusters were more strongly correlated in the past, due to their increasing bias with redshift - the bias reaches b = 100 at z = 2 for M > 5 x 10^13 h^-1 M_sun. The richness-dependent cluster correlation function, represented by the correlation scale versus cluster mean separation relation, R0-d, is generally consistent with observations. This relation can be approximated as R_0 = 1.7 d^0.6 h^-1 Mpc for d = 20 - 60 h^-1 Mpc. The R0-d relation exhibits surprisingly little evolution with redshift for z < 2; this can provide a new test of the current LCDM model when compared with future observations of high redshift clusters.Comment: 20 pages, 9 figures, accepted for publication in Ap