The metallicity of gamma-ray burst environments from high energy observations

Gamma-ray bursts (GRBs) and their early afterglows ionise their circumburst material. Only high-energy spectroscopy therefore, allows examination of the matter close to the burst itself. Soft X-ray absorption allows an estimate to be made of the total column density in metals. The detection of the X-ray afterglow can also be used to place a limit on the total gas column along the line of sight based on the Compton scattering opacity. Such a limit would enable, for the first time, the determination of lower limits on the metallicity in the circumburst environments of GRBs. In this paper, we determine the limits that can be placed on the total gas column density in the vicinities of GRBs based on the Compton scattering. We simulate the effects of Compton scattering on a collimated beam of high energy photons passing through a shell of high column density material to determine the expected lightcurves, luminosities, and spectra. We compare these predictions to observations, and determine what limits can realistically be placed on the total gas column density. The smearing out of pulses in the lightcurve from Compton scattering is not likely to be observable, and its absence does not place strong constraints on the Compton depth for GRBs. However, the distribution of observed luminosities of bursts allows us to place statistical, model-dependent limits that are typically <~1e25 cm^{-2} for less luminous bursts, and as low as ~1e24 cm$^{-2} for the most luminous. Using the shape of the high-energy broadband spectrum, however, in some favourable cases, limits as low as ~5e24 cm^{-2} can placed on individual bursts, implying metallicity lower limits from X- and gamma-rays alone from 0 up to 0.01 Z/Zsun. At extremely high redshifts, this limit would be at least 0.02 Z/Z_sun, enough to discriminate population III from non-primordial GRBs.Comment: 4 pages, 4 figures, submitted to A&A letter

Lyman alpha Resonant Scattering in Young Galaxies - Predictions from Cosmological Simulations

We present results obtained with a 3D, Ly alpha radiative transfer code, applied to a fully cosmological galaxy formation simulation. The developed Monte Carlo code is capable of treating an arbitrary distribution of source Ly alpha emission, neutral hydrogen density, temperature, and peculiar velocity of the interstellar medium. We investigate the influence of resonant scattering on the appearance and properties of young galaxies by applying the code to a simulated "Lyman Break Galaxy" at redshift z = 3.6, and of star formation rate 22 M_sun/yr and total Ly alpha luminosity 2.0 X 10^43 erg/s. It is found that resonant scattering of Ly alpha radiation can explain that young galaxies frequently are observed to be more extended on the sky in Ly alpha than in the optical. Moreover, it is shown that, for the system investigated, due to the anisotropic escape of the photons, the appearent maximum surface brightness can differ by a factor of ~15, and the total derived luminosity by a factor of ~4, depending on the orientation of the system relative to the observer.Comment: Letter updated to match version published in Ap

Deep rest-frame far-UV spectroscopy of the giant Lyman-alpha emitter 'Himiko'

We present deep 10h VLT/XSHOOTER spectroscopy for an extraordinarily luminous and extended Lya emitter at z=6.595 referred to as Himiko and first discussed by Ouchi et al. (2009), with the purpose of constraining the mechanisms powering its strong emission. Complementary to the spectrum, we discuss NIR imaging data from the CANDELS survey. We find neither for HeII nor any metal line a significant excess, with 3 sigma upper limits of 6.8, 3.1, and 5.8x10^{-18} erg/s/cm^2 for CIV $\lambda$1549, HeII $\lambda$1640, CIII] $\lambda$1909, respectively, assuming apertures with 200 km/s widths and offset by -250 km/s w.r.t to the peak Lya redshift. These limits provide strong evidence that an AGN is not a major contribution to Himiko's Lya flux. Strong conclusions about the presence of PopIII star-formation or gravitational cooling radiation are not possible based on the obtained HeII upper limit. Our Lya spectrum confirms both spatial extent and flux (8.8+/-0.5x10^{-17} erg/s/cm^2) of previous measurements. In addition, we can unambiguously exclude any remaining chance of it being a lower redshift interloper by significantly detecting a continuum redwards of Lya, while being undetected bluewards

Finite-Element Limit Analysis of the Tucker High School Gymnasium Roof Failure

The Randolph Tucker High School gymnasium roof failure of 1970 has received much scholarly attention. This study will provide a conclusion to a large body of previously published works by means of limit state analysis of the roof failure using state of the art parametric finite-element modeling. Parametric modeling within a general purpose finite-element analysis program allows for extremely rapid changes to the model because key terms are objects or parameters that can be adjusted internally by the program, rather than laboriously entered by the user. The failure of the roof was investigated by means of a limit state analysis, which accurately captured the cracking of the concrete and the yielding of the reinforcing steel. Concrete creep and shrinkage and relaxation of the prestressing steel were also accounted for. Finally, the authors also studied the idea that camber in the roof geometry might have prevented collapse

Supertertiary protein structure affects an allosteric network

The notion that protein function is allosterically regulated by structural or dynamic changes in proteins has been extensively investigated in several protein domains in isolation. In particular, PDZ domains have represented a paradigm for these studies, despite providing conflicting results. Furthermore, it is still unknown how the association between protein domains in supramodules, consitituting so-called supertertiary structures, affects allosteric networks. Here, we experimentally mapped the allosteric network in a PDZ:ligand complex, both in isolation and in the context of a supramodular structure, and show that allosteric networks in a PDZ domain are highly dependent on the supertertiary structure in which they are present. This striking sensitivity of allosteric networks to the presence of adjacent protein domains is likely a common property of supertertiary structures in proteins. Our findings have general implications for prediction of allosteric networks from primary and tertiary structures and for quantitative descriptions of allostery

Seeking allosteric networks in PDZ domains

Ever since Ranganathan and coworkers subjected the covariation of amino acid residues in the postsynaptic density-95/Discs large/Zonula occludens 1 (PDZ) domain family to a statistical correl- ation analysis, PDZ domains have represented a paradigmatic family to explore single domain protein allostery. Nevertheless, several theoretical and experimental studies in the past two dec- ades have contributed contradicting results with regard to structural localization of the allosteric networks, or even questioned their actual existence in PDZ domains. In this review, we first describe theoretical and experimental approaches that were used to probe the energetic network (s) in PDZ domains. We then compare the proposed networks for two well-studied PDZ domains namely the third PDZ domain from PSD-95 and the second PDZ domain from PTP-BL. Our analysis highlights the contradiction between the different methods and calls for additional work to better understand these allosteric phenomena

Overdreven tillid til jordbundsanalysen

Overdreven tillid til jordbundsanalyse

Galaxy Counterparts of metal-rich Damped Lyman-alpha Absorbers - I: The case of the z=2.35 DLA towards Q2222-0946

We have initiated a survey using the newly commissioned X-shooter spectrograph to target candidate relatively metal-rich damped Lyman-alpha absorbers (DLAs). The spectral coverage of X-shooter allows us to search for not only Lyman-alpha emission, but also rest-frame optical emission lines. We have chosen DLAs where the strongest rest-frame optical lines ([OII], [OIII], Hbeta and Halpha) fall in the NIR atmospheric transmission bands. In this first paper resulting from the survey, we report on the discovery of the galaxy counterpart of the z_abs = 2.354 DLA towards the z=2.926 quasar Q2222$-0946. This DLA is amongst the most metal-rich z>2 DLAs studied so far at comparable redshifts and there is evidence for substantial depletion of refractory elements onto dust grains. We measure metallicities from ZnII, SiII, NiII, MnII and FeII of -0.46+/-0.07, -0.51+/-0.06, -0.85+/-0.06, -1.23+/-0.06, and -0.99+/-0.06, respectively. The galaxy is detected in the Lyman-alpha, [OIII] lambda4959,5007 Halpha emission lines at an impact parameter of about 0.8 arcsec (6 kpc at z_abs = 2.354). We infer a star-formation rate of 10 M_sun yr^-1, which is a lower limit due to the possibility of slit-loss. Compared to the recently determined Halpha luminosity function for z=2.2 galaxies the DLA-galaxy counterpart has a luminosity of L~0.1L^*_Halpha. The emission-line ratios are 4.0 (Lyalpha/Halpha) and 1.2 ([OIII]/Halpha). The Lyalpha line shows clear evidence for resonant scattering effects, namely an asymmetric, redshifted (relative to the systemic redshift) component and a much weaker blueshifted component. The fact that the blueshifted component is relatively weak indicates the presence of a galactic wind. The properties of the galaxy counterpart of this DLA is consistent with the prediction that metal-rich DLAs are associated with the most luminous of the DLA-galaxy counterparts.Comment: 9 pages, 7 figures. Accepted for publication in MNRA

Assessment of Modeling Strategies for Lightly Reinforced Concrete Shear Walls

element detailing, which suggest they are susceptible to brittle, compression-controlled failure modes, and deemed deficient by industry practitioners. Researchers at the California Polytechnic State University [1], San Luis Obispo (Cal Poly), recently tested a slender RC wall with vertical and horizontal reinforcement ratios approaching ACI 318-14 [2] code minimum (ρl= ρh= 0.37%) and no boundary elements. Results from this wall test will be presented and contrasted with a set of lightly reinforced walls, specimens C1-C3 tested by Lu et al. [3] at the University of Auckland, New Zealand, with higher levels of reinforcement (ρl= 0.53%). This paper will examine the Cal Poly and Lu et al. walls by comparing experimental test results. It will also comment on the accuracy of current modelling strategies used by industry practitioners to estimate the strength, stiffness, and ductility of existing lightly reinforced walls. Finally, it will make recommendations for the necessary model calibrations to achieve accurate prediction of the response of the lightly reinforced walls using PERFORM-3D [4], as a refinement of Lowes et al. [5] modeling recommendations for this wall type. The overall goal with this study is to facilitate accurate modeling that will provide detailed understanding of the wall response, and to inform the industry practitioner about the need for retrofitting to meet modern standards