A tidally interacting disk in the young triple system WL 20?

We present high-resolution λ = 2.7 mm imaging of the close triple pre-main-sequence system WL 20. Compact dust emission with integrated flux density of 12.9 ± 1.3 mJy is associated with two components of the triple system, WL 20W and WL 20S. No emission above a 3 σ level of 3.9 mJy is detected toward the third component, WL 20E, which lies 3."17 (400 AU) due east in projection from its neighbors. A possibly warped structure of ~0.1 M_☉ and ≤3."2 extent encompasses WL 20W and WL 20S, which have a projected separation of 2."25 (~280 AU) along a north-south axis. This structure is most likely a tidally disrupted disk surrounding WL 20S. New near-infrared spectra of the individual components show a remarkable similarity between the two T Tauri stars of the system: WL 20E has a K7 spectral type (T_eff = 4040 K) with r_K = 0.2, and WL 20W has an M0 spectral type (T_eff = 3800 K) with r_K = 0.2. The spectrum of WL 20S is consistent with that of a source intrinsically similar to WL 20W, with r_K < 0.9, but seen through an A_V = 25 in addition to the A_V = 16.3 to the system as a whole. Taken together, these millimeter and infrared data help explain the peculiar nature of the infrared companion, WL 20S, as resulting from a large enhancement in its dusty, circumstellar environment in relation to its companions

A Re-examination Of The Quantitative Infrared Absorption Cross-sections Of Isobutane

Recently published work\footnote {DM Hewett, PF Bernath, BE Billinghurst. 2019 “Infrared absorption cross sections of isobutane with hydrogen and nitrogen as broadening gases.” \emph{Journal of Quantitative Spectroscopy and Radiative Transfer} 227:226–229.} has called into question the absolute infrared absorption cross-section values for isobutane presented in the Northwest Infrared (NWIR) database. As a result, we have remeasured these cross-sections. In all, four data sets were acquired, analyzed and compared to the original NWIR database with excellent agreement. All new data sets were measured with a nominal pathlength of 20 cm and sample temperature of 25.0 $^{\circ}$C. Three data sets were acquired using a Bruker IFS 125HR spectrometer equipped with a HgCdTe detector. Spectra were first recorded between 600 and 5000 \wn at 0.112 \wn instrument resolution using thirteen burdens of isobutane (0.3 to 22 Torr), each pressure-broadened to one atmosphere using N$_{2}$ gas. The second and third data sets were recorded using thirteen burdens of isobutane (0.1 to 23 Torr), at an instrument resolution of 0.01 \wn. A spectrum of each sample was recorded neat and then recorded pressure-broadened to one atmosphere using N$_{2}$ gas, producing two data sets. A fourth data set, using eleven burdens of neat isobutane (0.5 to 23 Torr) was recorded using a Bruker IFS 66v/S with a DTGS detector. Spectra were recorded between 400 and 6500 \wn at 2 \wn instrument resolution. Each of the four data sets was fitted using a weighted linear least squares algorithm and resulted in a “composite” log$_{10}$ absorbance spectrum of isobutane with concentration-pathlength units of ppm$^{-1}$ m$^{-1}$. The wavenumber axis is in units of \wn. For the 125HR data sets, the integrated band strengths for both the C-H stretch and CH$_{2}$ bend regions are within 2\% of the original NWIR integrated band strengths, and the 66v/S integrated band strengths for both spectral regions are within 5\% of the NWIR data. The agreement between the original and new cross-section data is close to the original experimental error, 3\%, reported for the NWIR database

Modelling the Fluid Mechanics of Cilia and Flagella in Reproduction and Development

Cilia and flagella are actively bending slender organelles, performing functions such as motility, feeding and embryonic symmetry breaking. We review the mechanics of viscous-dominated microscale flow, including time-reversal symmetry, drag anisotropy of slender bodies, and wall effects. We focus on the fundamental force singularity, higher order multipoles, and the method of images, providing physical insight and forming a basis for computational approaches. Two biological problems are then considered in more detail: (1) left-right symmetry breaking flow in the node, a microscopic structure in developing vertebrate embryos, and (2) motility of microswimmers through non-Newtonian fluids. Our model of the embryonic node reveals how particle transport associated with morphogenesis is modulated by the gradual emergence of cilium posterior tilt. Our model of swimming makes use of force distributions within a body-conforming finite element framework, allowing the solution of nonlinear inertialess Carreau flow. We find that a three-sphere model swimmer and a model sperm are similarly affected by shear-thinning; in both cases swimming due to a prescribed beat is enhanced by shear-thinning, with optimal Deborah number around 0.8. The sperm exhibits an almost perfect linear relationship between velocity and the logarithm of the ratio of zero to infinite shear viscosity, with shear-thickening hindering cell progress.Comment: 20 pages, 24 figure

Demonstration of Robust Quantum Gate Tomography via Randomized Benchmarking

Typical quantum gate tomography protocols struggle with a self-consistency problem: the gate operation cannot be reconstructed without knowledge of the initial state and final measurement, but such knowledge cannot be obtained without well-characterized gates. A recently proposed technique, known as randomized benchmarking tomography (RBT), sidesteps this self-consistency problem by designing experiments to be insensitive to preparation and measurement imperfections. We implement this proposal in a superconducting qubit system, using a number of experimental improvements including implementing each of the elements of the Clifford group in single `atomic' pulses and custom control hardware to enable large overhead protocols. We show a robust reconstruction of several single-qubit quantum gates, including a unitary outside the Clifford group. We demonstrate that RBT yields physical gate reconstructions that are consistent with fidelities obtained by randomized benchmarking

TEXES Observations of Pure Rotational H_2 Emission from AB Aurigae

We present observations of pure rotational molecular hydrogen emission from the Herbig Ae star, AB Aur. Our observations were made using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility and the Gemini North Observatory. We searched for H_2 emission in the S(1), S(2), and S(4) lines at high spectral resolution and detected all three. By fitting a simple model for the emission in the three transitions, we derive T = 670 ± 40 K and M = 0.52 ± 0.15 M_⊙ for the emitting gas. On the basis of the 8.5 km s^(-1) FWHM of the S(2) line, assuming the emission comes from the circumstellar disk, and with an inclination estimate of the AB Aur system taken from the literature, we place the location for the emission near 18 AU. Comparison of our derived temperature to a disk structure model suggests that UV and X-ray heating are important in heating the disk atmosphere

Clustering of photometric luminous red galaxies I : Growth of Structure and Baryon Acoustic Feature

The possibility of measuring redshift space (RSD) distortions using photometric data have been recently highlighted. This effect complements and significantly alters the detectability of baryon acoustic oscillations (BAO) in photometric surveys. In this paper we present measurements of the angular correlation function of luminous red galaxies (LRGs) in the photometric catalog of the final data release (DR7) of the Sloan Digital Sky Survey II (SDSS). The sample compromise ~ 1.5 x 10^6 LRGs distributed in 0.45 < z < 0.65, with a characteristic photometric error of ~ 0.05. Our measured correlation centered at z=0.55 is in very good agreement with predictions from standard LCDM in a broad range of angular scales, $0.5^\circ < \theta < 6^\circ$. We find that the growth of structure can indeed be robustly measured, with errors matching expectations. The velocity growth rate is recovered as $f \sigma_8 = 0.53 \pm 0.42$ when no prior is imposed on the growth factor and the background geometry follows a LCDM model with WMAP7+SNIa priors. This is compatible with the corresponding General Relativity (GR) prediction $f \sigma_8 = 0.45$ for our fiducial cosmology. If we adopt a parametrization such that $f=\Omega ^\gamma_m(z)$, with $\gamma \approx 0.55$ in GR, and combine our $f\sigma_8$ measurement with the corresponding ones from spectroscopic LRGs at lower redshifts we obtain $\gamma=0.54 \pm 0.17$. In addition we find evidence for the presence of the baryon acoustic feature matching the amplitude, location and shape of LCDM predictions. The photometric BAO feature is detected with 98 % confidence level at z=0.55.Comment: 16 pages, 19 figures, minor changes to text to match accepted version by MNRA

The Angular Power Spectra of Photometric SDSS LRGs

We construct new galaxy angular power spectra based on the extended, updated and final SDSS II Luminous Red Galaxy (LRG) photometric redshift survey: MegaZ DR7. Encapsulating 7746 deg^{2} we utilise 723,556 photometrically determined LRGs between 0.45 < z < 0.65 in a 3.3 (Gpc h^{-1})^3 spherical harmonic analysis of the galaxy distribution. By combining four photometric redshift bins we find preliminary parameter constraints of f_{b} = \Omega_{b}/\Omega_{m} = 0.173 +/- 0.046 and \Omega_{m} = 0.260 +/- 0.035 assuming H_{0} = 75 km s^{-1} Mpc^{-1}, n_{s}=1 and \Omega_{k} = 0. These limits are consistent with the CMB and the previous data release (DR4). The C_{\ell} are sensitive to redshift space distortions and therefore we also recast our constraints into a measurement of \beta ~ \Omega_{m}^{0.55}/b in different redshift shells. The robustness of these power spectra with respect to a number of potential systematics such as extinction, photometric redshift and ANNz training set extrapolation are examined. The latter includes a cosmological comparison of available photometric redshift estimation codes where we find excellent agreement between template and empirical estimation methods. MegaZ DR7 represents a methodological prototype to next generation surveys such as the Dark Energy Survey (DES) and, furthermore, is a photometric precursor to the spectroscopic BOSS survey. Our galaxy catalogue and all power spectra data can be found at http://zuserver2.star.ucl.ac.uk/~sat/MegaZ/MegaZDR7.tar.gz.Comment: MNRAS Accepted: 20 pages - Galaxy catalogue and power spectra included onlin