A Novel Approach to Extract Morphological Variables in Crystalline Polymers from Time-Resolved Synchrotron SAXS Data

A novel approach to extract morphological variables in crystalline polymers from time-resolved SAXS data using the method of correlation and interface distribution functions has been devised. The principle of the calculation is based on two alternative expressions of Porod's law using the form of the interference function. The approach enables the continuous estimate of the Porod constant, and corrections for liquid scattering and finite interface between the two phases, from the time-resolved data. A model of lamellar morphology has been implemented to interpret the calculated correlation and interface distribution functions. Many detailed morphological variables such as lamellar long period, thicknesses of crystal and amorphous phases, interface thickness, and scattering invariant can be estimated. An example analysis of isothermal crystallization in PET measured by synchrotron SAXS is demonstrated

Characterizing the Low-Redshift Intergalactic Medium towards PKS1302-102

We present a detailed analysis of the intergalactic metal-line absorption systems in the archival HST/STIS and FUSE ultraviolet spectra of the low-redshift quasar PKS1302-102 (z_QSO = 0.2784). We supplement the archive data with CLOUDY ionization models and a survey of galaxies in the quasar field. There are 15 strong Lya absorbers with column densities logN_HI > 14. Of these, six are associated with at least CIII 977 absorption (logN(C^++) > 13); this implies a redshift density dN_CIII/dz = 36+13/-9 (68% confidence limits) for the five detections with rest equivalent width W_r > 50 mA. Two systems show OVI 1031,1037 absorption in addition to CIII (logN(O^+5) > 14). One is a partial Lyman limit system (logN_HI = 17) with associated CIII, OVI, and SiIII 1206 absorption. There are three tentative OVI systems that do not have CIII detected. For one OVI doublet with both lines detected at 3 sigma with W_r > 50 mA, dN_OVI/dz = 7+9/-4. We also search for OVI doublets without Lya absorption but identify none. From CLOUDY modeling, these metal-line systems have metallicities spanning the range -4 < [M/H] < -0.3. The two OVI systems with associated CIII absorption cannot be single-phase, collisionally-ionized media based on the relative abundances of the metals and kinematic arguments. From the galaxy survey, we discover that the absorption systems are in a diverse set of galactic environments. Each metal-line system has at least one galaxy within 500 km/s and 600 h^-1 kpc with L > 0.1 L_*.Comment: 21 pages in emulatepj form, 24 figures, 10 tables, accepted to Ap

Shear-Enhanced Crystallization in Isotactic Polypropylene. 3. Evidence for a Kinetic Pathway to Nucleation

In situ rheo-optical techniques are combined with synchrotron wide-angle X-ray diffraction (WAXD) to investigate the oriented crystallization precursors that develop upon strongly shearing an isothermal melt of polydisperse isotactic polypropylene (iPP). The “short-term shearing” experimental protocol, developed by Janeschitz-Kriegl and co-workers, is used under conditions previously determined to induce oriented crystallite growth. Surprisingly, the time for these precursors to appear decreases with increasing temperature, tracking the melt dynamics of the polymer moleculesa behavior unanticipated by current models. Thus, nucleation proceeds via a “nonclassical” kinetic pathway that effectively eliminates the activation barrier for nucleation. To characterize the importance of chain length distribution for the formation of nucleation precursors, experiments were performed with model bidisperse systems containing a small percentage of high molecular weight iPP blended with lower molecular weight iPP of matched stereoregularity. Oriented crystallization was not observed for the individual components of the blend under the most extreme experimental conditions investigated, but it was readily observed for the bidisperse blend. This suggests that, under intense shear, nucleation of oriented crystallites is governed by the rheologically determined formation of a critical anisotropic configuration of polymer chains in the melt

Characterizing Circumgalactic Gas around Massive Ellipticals at z~0.4 - II. Physical Properties and Elemental Abundances

We present a systematic investigation of the circumgalactic medium (CGM) within projected distances d<160 kpc of luminous red galaxies (LRGs). The sample comprises 16 intermediate-redshift (z=0.21-0.55) LRGs of stellar mass M_star>1e11 M_sun. Combining far-ultraviolet Cosmic Origin Spectrograph spectra from the Hubble Space Telescope and optical echelle spectra from the ground enables a detailed ionization analysis based on resolved component structures of a suite of absorption transitions, including the full HI Lyman series and various ionic metal transitions. By comparing the relative abundances of different ions in individually-matched components, we show that cool gas (T~1e4 K) density and metallicity can vary by more than a factor of ten in in an LRG halo. Specifically, metal-poor absorbing components with <1/10 solar metallicity are seen in 50% of the LRG halos, while gas with solar and super-solar metallicity is also common. These results indicate a complex multiphase structure and poor chemical mixing in these quiescent halos. We calculate the total surface mass density of cool gas, \Sigma_cool, by applying the estimated ionization fraction corrections to the observed HI column densities. The radial profile of \Sigma_cool is best-described by a projected Einasto profile of slope \alpha=1 and scale radius r_s=48 kpc. We find that typical LRGs at z~0.4 contain cool gas mass of M_cool= (1-2) x1e10 M_sun at d<160 kpc (or as much as 4x1e10 M_sun at d<500 kpc), comparable to the cool CGM mass of star-forming galaxies. Furthermore, we show that high-ionization OVI and low-ionization absorption species exhibit distinct velocity profiles, highlighting their different physical origins. We discuss the implications of our findings for the origin and fate of cool gas in LRG halos.Comment: Accepted for publication in MNRAS after a minor revision. 23 pages, 14 figures, and a 29-page Appendix with 27 additional figure

Probing the IGM-Galaxy Connection Toward PKS0405-123 II : A Cross-Correlation Study of Lya Absorbers and Galaxies at z<0.5

We present a pilot study of the clustering properties of Lya absorbers with respect to known galaxies based on 112 Lya absorbers and 482 galaxies identified at z<0.5 along the sightline toward PKS0405-123. The principal goal is to determine the origin of Lya absorbers based on their cross-correlation amplitude with known galaxies and investigate a possible N(HI) dependence of the cross-correlation function. The main results of our study are as follows. (1) The cross-correlation function xi_{ga} measured using only emission-line dominated galaxies and Lya absorbers of log N(HI) >= 14 shows a comparable strength to the galaxy auto-correlation function xi_{gg} on co-moving, projection distance scales < 1 h^{-1} Mpc, while there remains a lack of cross-correlation signal when using only absorption-line dominated galaxies. This signifies a morphology-dependent xi_{ga} and indicates that strong absorbers of log N(HI) >= 14 and emission-line galaxies reside in the same halo population. (2) A maximum-likelihood analysis shows that Lya absorbers of log N(HI) < 13.6 are consistent with being more randomly distributed with respect to known galaxies. Finally, (3) we find based on this single sightline that the amplitude of xi_{ga} does not depend sensitively on N(HI) for strong absorbers of log N(HI) >= 13.6.Comment: 5 pages, including 2 figures; to appear in ApJ Letters, the 2005 August 10 issu

Characterizing Circumgalactic Gas around Massive Ellipticals at z ~ 0.4 I. Initial Results

We present a new Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) absorption-line survey to study halo gas around 16 luminous red galaxies (LRGs) at z=0.21-0.55. The LRGs are selected uniformly with stellar mass Mstar>1e11 Msun and no prior knowledge of the presence/absence of any absorption features. Based on observations of the full Lyman series, we obtain accurate measurements of neutral hydrogen column density N(HI) and find that high-N(HI) gas is common in these massive quiescent halos with a median of <log N(HI)> = 16.6 at projected distances d<~160 kpc. We measure a mean covering fraction of optically-thick gas with log N(HI)>~17.2 of LLS=0.44^{+0.12}_{-0.11} at d<~160 kpc and LLS=0.71^{+0.11}_{-0.20} at d<~100 kpc. The line-of-sight velocity separations between the HI absorbing gas and LRGs are characterized by a mean and dispersion of =29 km/s and \sigma_v_{gas-gal}=171 km/s. Combining COS FUV and ground-based echelle spectra provides an expanded spectral coverage for multiple ionic transitions, from low-ionization MgII and SiII, to intermediate ionization SiIII and CIII, and to high-ionization OVI absorption lines. We find that intermediate ions probed by CIII and SiIII are the most prominent UV metal lines in LRG halos with a mean covering fraction of _{0.1}=0.75^{+0.08}_{-0.13} for W(977)>=0.1 Ang at d<160 kpc, comparable to what is seen for CIII in L* and sub-L* star-forming and red galaxies but exceeding MgII or OVI in quiescent halos. The COS-LRG survey shows that massive quiescent halos contain widespread chemically-enriched cool gas and that little distinction between LRG and star-forming halos is found in their HI and CIII content.Comment: 19 pages, 6 figures, accepted by MNRA

The Cosmic Ultraviolet Baryon Survey (CUBS) I. Overview and the diverse environments of Lyman limit systems at z<1

We present initial results from the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS is designed to map diffuse baryonic structures at redshift z<~1 using absorption-line spectroscopy of 15 UV-bright QSOs with matching deep galaxy survey data. CUBS QSOs are selected based on their NUV brightness to avoid biases against the presence of intervening Lyman Limit Systems (LLSs) at zabs~ 17.2 over a total redshift survey pathlength of dz=9.3, and a number density of n(z)=0.43 (-0.18, +0.26). Considering all absorbers with log N(HI)/cm^-2 > 16.5 leads to n(z)=1.08 (-0.25, +0.31) at z<1. All LLSs exhibit a multi-component structure and associated metal transitions from multiple ionization states such as CII, CIII, MgII, SiII, SiIII, and OVI absorption. Differential chemical enrichment levels as well as ionization states are directly observed across individual components in three LLSs. We present deep galaxy survey data obtained using the VLT-MUSE integral field spectrograph and the Magellan Telescopes, reaching sensitivities necessary for detecting galaxies fainter than 0.1L* at d<~300 physical kpc (pkpc) in all five fields. A diverse range of galaxy properties is seen around these LLSs, from a low-mass dwarf galaxy pair, a co-rotating gaseous halo/disk, a star-forming galaxy, a massive quiescent galaxy, to a galaxy group. The closest galaxies have projected distances ranging from d=15 to 72 pkpc and intrinsic luminosities from ~0.01L* to ~3L*. Our study shows that LLSs originate in a variety of galaxy environments and trace gaseous structures with a broad range of metallicities.Comment: 26 pages, 14 figures, MNRAS in pres

Dislocation-Controlled Perforated Layer Phase in a Peo-B-Ps Diblock Copolymer

Small angle x-ray analyses show that the shear-induced hexagonal perforated layer phase in a poly(ethylene oxide)-b-polystyrene diblock copolymer consists of trigonal (R3(overbar)m) twins and a hexagonal (P6(3)/mmc) structure, with trigonal twins being majority components. Transmission electron microscopy reveals that the hexagonal structure is generated through sequential intrinsic stacking faults on the second layer from a previous edge dislocation line, while the trigonal twins are formed by successive intrinsic stacking faults on neighboring layers due to the plastic deformation under mechanical shear