The association between gas and galaxies - I. CFHT spectroscopy and pair analysis

We show that the combination of a weak magnetic propeller and accretion disc resonances can effectively halt accretion in short-period cataclysmic variables (CVs) for large fractions of their lifetimes. This may help to explain the discrepancy between the observed and predicted orbital period distributions of CVs at short periods. Orbital resonances cause the disc to become eccentric, allowing material to fall back on to the donor star or out of the system. A weak magnetic field on a rapidly spinning primary star propels disc material outwards, allowing it to access these resonances. Numerical and analytic calculations show that this state can be long lived (1011 yr). This is because the magnetic propeller is required only to maintain access to the resonances, and not to push matter out of the Roche lobe, so that the spin-down time-scale is much longer than that for a classical propeller model

Boronic Acid Derivatives Targeting HIV-1

A series of novel boronic acid derivatives containing either a pyrimidine or purine base was synthesized. The preparation involved the condensation of 4-bromobutyl boronic acid with the appropriate base. These acyclic nucleosides were designed as potential antiviral agents especially targeting the human immunodeficiency virus. Two analogues, 6-chloro-9-(4-dihydroxyborylbutyl)purine and 2,6-dichloro-9-(4-dihydroxyborylbutyl)purine, exhibited EC50 values of 7.7 µM and 0.99 µM, respectively, in an HIV-1 syncytial plaque reduction assay

The VLT LBG redshift survey – VI. Mapping H i in the proximity of z ∼ 3 LBGs with X-Shooter

We present an analysis of the spatial distribution and dynamics of neutral hydrogen gas around galaxies using new X-Shooter observations of z ∼ 2.5–4 quasars. Adding the X-Shooter data to our existing data set of high-resolution quasar spectroscopy, we use a total sample of 29 quasars alongside ∼1700 Lyman Break Galaxies (LBGs) in the redshift range 2 ≲ z ≲ 3.5. We measure the Lyα forest auto-correlation function, finding a clustering length of s0 = 0.081 ± 0.006 h−1 Mpc, and the cross-correlation function with LBGs, finding a cross-clustering length of s0 = 0.27 ± 0.14 h−1 Mpc and power-law slope γ = 1.1 ± 0.2. Our results highlight the weakly clustered nature of neutral hydrogren systems in the Lyα forest. Building on this, we make a first analysis of the dependence of the clustering on absorber strength, finding a clear preference for stronger Lyα forest absorption features to be more strongly clustered around the galaxy population, suggesting that they trace on average higher mass haloes. Using the projected and 2-D cross-correlation functions, we constrain the dynamics of Lyα forest clouds around z ∼ 3 galaxies. We find a significant detection of large-scale infall of neutral hydrogen, with a constraint on the Lyα forest infall parameter of βF = 1.02 ± 0.22

Null energy condition and superluminal propagation

We study whether a violation of the null energy condition necessarily implies the presence of instabilities. We prove that this is the case in a large class of situations, including isotropic solids and fluids relevant for cosmology. On the other hand we present several counter-examples of consistent effective field theories possessing a stable background where the null energy condition is violated. Two necessary features of these counter-examples are the lack of isotropy of the background and the presence of superluminal modes. We argue that many of the properties of massive gravity can be understood by associating it to a solid at the edge of violating the null energy condition. We briefly analyze the difficulties of mimicking $\dot H>0$ in scalar tensor theories of gravity.Comment: 46 pages, 6 figure

Do Young Children Consider Similarities or Differences When Responding to Referential Questions?

YesYoung children often struggle with referential communications because they fail to compare all valid referents. In two studies, we investigated this comparison process. In Study 1, 4- to 7-year-olds (N=114) were asked to categorize pairs of objects according to their similarities or differences, and then identified a unique quality of one of the objects by responding to a referential question. Children found it easier to judge the differences between objects than similarities. Correct judgments of differences predicted accurate identifications. In Study 2, 4- to 5-year-olds (N=36) again categorized according to similarities or differences, but this time were asked for verbal explanations of their decisions. Recognition of differences was easier than recognition of similarities. Explanations of errors were either: a) ambiguous; b) color error: c) thematic (creative imaginative explanations). Children offered thematic explanations when they failed to recognize similarities between objects, but not for errors of difference

Determination of superconducting anisotropy from magnetization data on random powders as applied to LuNi2_2B2_2C, YNi2_2B2_2C and MgB2_2

The recently discovered intermetallic superconductor MgB2 appears to have a highly anisotopic upper critical field with Hc2(max)/Hc2(min} = \gamma > 5. In order to determine the temperature dependence of both Hc2(max) and Hc2(min) we propose a method of extracting the superconducting anisotropy from the magnetization M(H,T) of randomly oriented powder samples. The method is based on two features in dM/dT the onset of diamagnetism at Tc(max), that is commonly associated with Hc2, and a kink in dM/dT at a lower temperature Tc(min). Results for LuNi2B2C and YNi2B2C powders are in agreement with anisotropic Hc2 obtained from magneto-transport measurements on single crystals. Using this method on four different types of MgB2 powder samples we are able to determine Hc2(max)(T) and Hc2(min)(T) with \gamma \approx 6

On the connection between the intergalactic medium and galaxies: the H I–galaxy cross-correlation at z ≲ 1

We present a new optical spectroscopic survey of 1777 ‘star-forming’ (‘SF’) and 366 ‘non-star-forming’ (‘non-SF’) galaxies at redshifts z ∼ 0-1 (2143 in total), 22 AGN and 423 stars, observed by instruments such as the Deep Imaging Multi-Object Spectrograph, the Visible Multi-Object Spectrograph and the Gemini Multi-Object Spectrograph, in three fields containing five quasi-stellar objects (QSOs) with Hubble Space Telescope (HST) ultraviolet spectroscopy. We also present a new spectroscopic survey of 173 ‘strong’ (1014 ≤ NHI≲ 1017 cm−2) and 496 ‘weak’ (1013 ≲ NHI 50 per cent of ‘weak’ H i systems reside within galaxy voids (hence not correlated with galaxies), and are confined in dark matter haloes of masses smaller than those hosting ‘strong’ systems and/or galaxies. We speculate that H i systems within galaxy voids might still be evolving in the linear regime even at scales ≲2 Mpc