Evolution of Structure and Superconductivity in Ba(Ni1−x_{1-x}Cox_x)2_2As2_2

The effects of Co-substitution on Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ ($0\leq x\leq 0.251$) single crystals grown out of Pb flux are investigated via transport, magnetic, and thermodynamic measurements. BaNi$_2$As$_2$ exhibits a first order tetragonal to triclinic structural phase transition at $T_s=137 K$ upon cooling, and enters a superconducting phase below $T_c=0.7 K$. The structural phase transition is sensitive to cobalt content and is suppressed completely by $x\geq0.133$. The superconducting critical temperature, $T_c$, increases continuously with $x$, reaching a maximum of $T_c=2.3 K$ at the structural critical point $x=0.083$ and then decreases monotonically until superconductivity is no longer observable well into the tetragonal phase. In contrast to similar BaNi$_2$As$_2$ substitutional studies, which show an abrupt change in $T_c$ at the triclinic-tetragonal boundary that extends far into the tetragonal phase, Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ exhibits a dome-like phase diagram centered around the first-order critical point. Together with an anomalously large heat capacity jump $\Delta C_e/\gamma T\sim 2.2$ at optimal doping, the smooth evolution of $T_c$ in the Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ system suggests a mechanism for pairing enhancement other than phonon softening.Comment: 7 pages, 8 figure

Intraflagellar transport delivers tubulin isotypes to sensory cilium middle and distal segments.

Sensory cilia are assembled and maintained by kinesin-2-dependent intraflagellar transport (IFT). We investigated whether two Caenorhabditis elegans α- and β-tubulin isotypes, identified through mutants that lack their cilium distal segments, are delivered to their assembly sites by IFT. Mutations in conserved residues in both tubulins destabilize distal singlet microtubules. One isotype, TBB-4, assembles into microtubules at the tips of the axoneme core and distal segments, where the microtubule tip tracker EB1 is found, and localizes all along the cilium, whereas the other, TBA-5, concentrates in distal singlets. IFT assays, fluorescence recovery after photobleaching analysis and modelling indicate that the continual transport of sub-stoichiometric numbers of these tubulin subunits by the IFT machinery can maintain sensory cilia at their steady-state length

A Numerical Study of the Effects of Wave-Induced Fluid Flow in Porous Media: Linear Solver

In this paper, we present a computational method to simulate wave propagation in porous rocks saturated with Newtonian fluids over a range of frequencies of interest. The method can use a digital representation of a rock sample where distinct material phase and properties at each volume cell are identified and model the dynamic response of the rock to an acoustic excitation mathematically with a coupled equation system: elastic wave equation in solid matrix and viscous wave equation in fluid. The coupled wave equations are solved numerically with a rotated-staggered-grid finite difference scheme. We simulate P-wave propagation through an idealized porous medium of periodically alternating solid and fluid layers where an analytical solution is available and obtain excellent agreements between numerical and analytical solutions. The method models the effect of pore fluid motion on the rock dynamic response more accurately with a linearized Navier-Stokes equation than with the viscoelastic model of the generalized Maxwell body, a low frequency approximation commonly used to overcome the difficulty of modeling frequency-dependent fluid shear modulus in time domain.Schlumberger Doll ResearchMassachusetts Institute of Technology. Earth Resources Laborator

The Relationship Between Galaxies and Low Redshift Weak Lyman alpha Absorbers in the Directions of H1821+643 and PG1116+215

To study the nature of low z Lya absorbers in the spectra of QSOs, we have obtained high signal-to-noise UV spectra of H 1821+643 (z = 0.297) and PG 1116+215 (z = 0.177) with the GHRS on the HST. The spectra have minimum S/N of 70-100 and 3 sigma limiting equivalent widths of 50-75 mA. We detect 26 Lya lines with Wr > 50 mA toward H1821+643 and 13 toward PG1116+215, which implies a density of 102+/-16 lines per unit redshift. The two-point correlation function shows marginal evidence of clustering on ~500 km/s scales, but only if the weakest lines are excluded. We have also used the WIYN Observatory to measure galaxy redshifts in the ~1 degree fields centered on each QSO. We find 17 galaxy-absorber pairs within projected distances of 1 Mpc with velocity separations of 350 km/s or less. Monte Carlo simulations show that if the Lya lines are randomly distributed, the probability of observing this many close pairs is 3.6e-5. We find that all galaxies with projected distances of 600 kpc or less have associated Lya absorbers within 1000 km/s, and the majority of these galaxies have absorbers within 350 km/s. We also find that the Lya equivalent width is anticorrelated with the projected distance of the nearest galaxy out to at least 600 kpc, but this should be interpreted cautiously because there are potential selection biases. Statistical tests using the entire sample also indicate that the absorbers are not randomly distributed. We discuss the nature of the Lya absorbers in light of the new data.Comment: Accepted for publication in ApJ. 17 pages plus 11 tables and 17 figure

The UCSD Radio-Selected Quasar Survey for Damped Lyman alpha System

As large optical quasar surveys for damped Lya become a reality and the study of star forming gas in the early Universe achieves statistical robustness, it is now vital to identify and quantify the sources of systematic error. Because the nature of optically-selected quasar surveys makes them vulnerable to dust obscuration, we have undertaken a radio-selected quasar survey for damped Lya systems to address this bias. We present the definition and results of this survey. We then combine our sample with the CORALS dataset to investigate the HI column density distribution function f(N) of damped Lya systems toward radio-selected quasars. We find that f(N) is well fit by a power-law f(N) = k_1 N^alpha_1, with log k_1 = 22.90 and alpha_1 = -2.18. This power-law is in excellent agreement with that of optically-selected samples at low N(HI), an important yet expected result given that obscuration should have negligible effect at these gas columns. However, because of the relatively small size of the radio-selected sample, 26 damped Lya systems in 119 quasars, f(N) is not well constrained at large N(HI) and the first moment of the HI distribution function, Omega_g, is, strictly speaking, a lower limit. The power-law is steep enough, however, that extrapolating it to higher column densities implies only a modest, logarithmic increase in Omega_g. The radio-selected value of Omega_g = 1.15 x 10^-3, agrees well with the results of optically-selected surveys. While our results indicate that dust obscuration is likely not a major issue for surveys of damped Lya systems, we estimate that a radio-selected sample of approximately 100 damped Lya systems will be required to obtain the precision necessary to absolutely confirm an absence of dust bias.Comment: 12 pages, 9 Figures. Accepted to ApJ April 11, 200

Pengaruh Substitusi Tepung Ikan Dengan Tepung Kepala Ikan Teri Terhadap Pertumbuhan Ikan Nila (Oreochromis SP.)

Salah satu faktor penting dalam budidaya ikan nila adalah ketersediaan pakan yang memadai. Ikan nila (Oreochromis sp.) merupakan ikan air tawar yang memiliki nilai ekonomis tinggi dan banyak dibudidayakan, namun pembudidaya sering mengalami kendala karena harga pakan yang tinggi. Hal ini terjadi karena bahan baku pakan seperti tepung ikan masih diimpor. Untuk mengatasinya perlu alternatif sumber bahan baku salah satunya adalah memanfaatkan limbah kepala ikan teri. Penelitian ini bertujuan untuk memperoleh formulasi pakan yang terbaik untuk pertumbuhan ikan nila, menggunakan Rancangan Acak Lengkap dengan 5 perlakuan dan 3 kali ulangan A (tepung ikan 100%), B (tepung kepala ikan teri 25% dan tepung ikan 75%), C (tepung kepala ikan teri 50% dan tepung ikan 50%), D (tepung kepala ikan teri 75% dan tepung ikan 25%), E (tepung kepala ikan teri 100%). Data yang diperoleh dianalisis ragam dan dilanjutkan dengan uji BNT. Parameter yang diamati berupa: pertumbuhan, retensi protein, feed convertion ratio (FCR), dan survival rate (SR). hasil pengamatan menunjukkan bahwa penggunaan tepung kepala ikan teri dalam pakan buatan pada perlakuan E memberikan pengaruh nyata dibandingkan perlakuan A, B, C, dan D yakni didapat pertumbuhan, dan retensi protein tinggi, sedangkan nilai FCR rendah. Hal tersebut menyatakan bahwa tepung kepala ikan teri mampu menggantikan tepung ikan

Variable O VI and N V emission from the X-ray binary LMC X-3 : heating of the black hole companion

Based on high-resolution ultraviolet spectroscopy obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Cosmic Origins Spectrograph, we present new detections of Ovi and Nv emission from the black hole X-ray binary (XRB) system LMCX-3. We also update the ephemeris of the XRB using recent radial velocity measurements obtained with the echelle spectrograph on the Magellan-Clay telescope. We observe significant velocity variability of the UV emission, and we find that the Ovi and Nv emission velocities follow the optical velocity curve of the XRB. Moreover, the Ovi and Nv intensities regularly decrease between binary phase=0.5 and 1.0, which suggests that the source of the UV emission is increasingly occulted as the B star in the XRB moves from superior to inferior conjunction. These trends suggest that illumination of the B star atmosphere by the intense X-ray emission from the accreting black hole creates a hot spot on one side of the B star, and this hot spot is the origin of the Ovi and Nv emission. However, the velocity semiamplitude of the ultraviolet emission, K-UV approximate to 180 km s(-1), is lower than the optical semiamplitude; this difference could be due to rotation of the B star. Comparison of the FUSE observations taken in 2001 November and 2004 April shows a significant change in the Ovi emission characteristics: in the 2001 data, the Ovi region shows both broad and narrow emission features, while in 2004 only the narrow Ovi emission is clearly present. Rossi X-ray Timing Explorer data show that the XRB was in a high/soft state in the 2001 November epoch but was in a transitional state in 2004 April, so the shape of the X-ray spectrum might change the properties of the region illuminated on the B star and thus change the broad versus narrow characteristics of the UV emission. If our hypothesis about the origin of the highly ionized emission is correct, then careful analysis of the emission occultation could, in principle, constrain the inclination of the XRB and the mass of the black hole