On the redshift cut-off for steep-spectrum radio sources

We use three samples (3CRR, 6CE and 6C*) selected at low radio frequency to constrain the cosmic evolution in the radio luminosity function (RLF) for the 'most luminous' steep-spectrum radio sources. Though intrinsically rare, such sources give the largest possible baseline in redshift for the complete flux-density-limited samples currently available. Using parametric models to describe the RLF, incorporating distributions in radio spectral shape and linear size, as well as the usual luminosity and redshift, we find that the data are consistent with a constant comoving space density between     and     . We find that this model is favoured over a model with similar evolutionary behaviour to that of optically selected quasars (i.e., a roughly Gaussian distribution in redshift) with probability ratios of     and     for spatially flat cosmologies with     and     respectively. Within the uncertainties, this evolutionary behaviour may be reconciled with the shallow decline preferred for the comoving space density of flat-spectrum sources by Dunlop & Peacock and Jarvis & Rawlings, in line with the expectations of unified schemes.     

I C and RC band time-series observations of some bright ultracool dwarfs

The results of more than 100 h of CCD photometric monitoring of 10 L dwarfs and two T dwarfs are presented. Reasonable evidence is shown for I _C band variability in DENIS 0255−4700, DENIS 1705−0516 and 2M 2104−1037. Substantial brightening of the T dwarf binary ε Indi Bab was observed over the course of 3.6 h; it is unlikely that this could have been caused by surface spots. No unequivocal variability could be detected in the R _C band.     

Bias properties of logarithmic and asinh magnitudes at very low flux levels

The observation of flux sources near the limit of detection requires a careful evaluation of possible biases in magnitude determination. Both the traditional logarithmic magnitudes and the recently proposed inverse hyperbolic sine (asinh) magnitudes are considered. Formulae are derived for three different biasing mechanisms: the statistical spread of the observed flux values arising from e.g. measurement error; the dependence of these errors on the true flux; and the dependence of the observing probability on the true flux. As an example of the results, it is noted that biases at large signal-to-noise ratios R , at which the two types of magnitude are similar, are of the order of −( p +1)/ R ², where the exponent p parametrizes a power-law dependence of the probability of observation on the true flux.     

Kinematics of the Galactic halo from horizontal branch stars in the Hamburg/ESO survey

Large samples of field horizontal branch (FHB) stars make excellent tracers of the Galactic halo; by studying their kinematics, one can infer important physical properties of our Galaxy. Here we present the results of a medium-resolution spectroscopic survey of 530 FHB stars selected from the Hamburg/ESO survey. The stars have a mean distance of ∼7 kpc and thus probe the inner parts of the Milky Way halo. We measure radial velocities from the spectra in order to test the model of Sommer-Larsen et al., who suggested that the velocity ellipsoid of the halo changes from radially dominated orbits to tangentially dominated orbits as one proceeds from the inner to the outer halo. We find that the present data are unable to discriminate between this model and a more simple isothermal ellipsoid; we suggest that additional observations towards the Galactic Centre might help to differentiate them.     

Systematic variations in xenocryst mineral composition at the province scale, Buffalo Hills kimberlites, Alberta, Canada

The Buffalo Hills kimberlites define a province of kimberlite magmatism occurring within and adjacent to Proterozoic crystalline basement termed the Buffalo Head Terrane in north-central Alberta, Canada. The kimberlites are distinguished by a diverse xenocryst suite and most contain some quantity of diamond. The xenocryst assemblage in the province is atypical for diamondiferous kimberlite, including an overall paucity of mantle indicator minerals and the near-absence of compositionally subcalcic peridotitic garnet (G10). The most diamond-rich bodies are distinguished by the presence of slightly subcalcic, chromium-rich garnet and the general absence of picroilmenite, with the majority forming a small cluster in the northwestern part of the province. Barren and near-barren pipes tend to occur to the south, with increasing proximity to the basement structure known as the Peace River Arch. Niobian picroilmenite, compositionally restricted low-to moderate-Cr peridotitic garnet, and megacrystal titanian pyrope occur in kimberlites closest to the arch. Major element data for clinopyroxene and trace element data for garnet from diamond-rich and diamond-poor kimberlites suggests that metasomatism of lithospheric peridotite within the diamond stability field may have caused destruction of diamond, and diamond source rocks proximal to the arch were the most affected.     

Application of the Maslov Seismogram Method in Three Dimensions

Asymptotic methods provide an efficient way to compute seismograms in heterogeneous media. However, zeroth-order ray theory, the simplest of the asymptotic methods, often fails because of the presence of caustics. Maslov theory is an extension of zeroth-order ray theory, which gives a uniformly valid expression of the wavefield everywhere, including the caustics. This result is given in terms of an integral of ray data over one or two ray parameters. It is shown in this paper how geometrical arrivals are constructed in the one and two-parameter Maslov integrals.In practice Maslov seismograms have been computed using only one ray parameter. However, in three-dimensional media two parameters are needed to uniquely define a ray. In this paper we present an efficient algorithm to compute two-parameter Maslov integrals. The Maslov integral is evaluated by computing the frequency-to-time Fourier transform prior to integration over the ray parameters. The wavefield is then discretized by smoothing with a boxcar function. The resulting expression, which only requires the results of ordinary kinematic and dynamic ray tracing, cen be computed efficiently and robustly. A numerical example is given that illustrates the use of this algorithm.     

Real-Time GPS Data Transmission Using VSAT Technology

The University NAVSTAR Consortium (UNAVCO) Boulder Facility is assessing Very Small Aperture Terminal (VSAT) technology for near real-time transmission of GPS data from a remote receiver to a central processing facility. The study is motivated by the need for a robust, cost-effective data communications solutions to transfer GPS data from remote sites where no other communication alternatives exist. Future large-scale plate boundary deformation initiatives using spatially dense networks of GPS will require receivers to be located where the science dictates, and not the power or communications infrastructure. For other applications, such as determining rapid GPS orbits and time transfer, there is a push toward reducing the latency in GPS data used to produce GPS data products and differential corrections (Talaya & Bosch, 1999; Jackson, Meertens, & Rocken, 2000; Muellerschoen, Bar-Sever, Bertiger, & Stowers, 2001), and to support upcoming Low Earth Orbiting (LEO) missions requiring low latency, 1-s GPS data. In this paper we evaluate two Ku-band systems, the Nanometrics Libra VSAT and the StarBand 2-way satellite Internet VSAT. The Nanometrics system test results show that continuous, 1-s GPS data can be streamed from multiple remote stations within the VSAT footprint, quality checked, and delivered for processing with a <2.5-s latency (mean 1.2 s) and a 99.8% reliability. Benefits of the Nanometrics system include global coverage, control of bandwidth allocation and data hub, and the low power draw of the system. Negatives include the cost of hub and remote infrastructure and the need to negotiate landing rights issues on a country-by-country basis. The UNAVCO Facility currently operates a Nanometrics hub and three remote VSAT systems. The StarBand system showed 98.9% reliability with a maximum latency of 10.2 s (mean latency 1.7 s) for 1-Hz GPS data and an average uplink speed of 31.7 kbps. Benefits of the StarBand system include the cost and small profile of the remote antenna. Negatives include coverage limited to coterminous United States and the high power draw of remote systems. ? 2002 Wiley Periodicals, Inc.     

Climatic Implications of the Kyoto Protocol: The Contribution of International Spillover

We explore the long-run impact of the Kyoto Protocol commitments to limit greenhouse gas emissions under various assumptions about the international spillover arising from actions led by the industrialised countries. International spillover comprises many complex processes including substitution due to price effects, diffusion of technology innovations, and policy and political spillovers. We represent these in terms of their aggregate impact on emission intensities over the next century. Limiting industrialised country emissions alone has limited environmental benefit if there is no international spillover; in our base case atmospheric concentrations by the end of the century rise to 730 ppm. However, this implies a large divergence of emission intensities, contrary to both empirical long term aggregate trends, and to identifiable influences towards convergence associated with economic globalisation. In contrast, if spillover leads to convergence of emission intensities by 2100, atmospheric concentrations are kept to below 560 ppm and are close to stabilising. Weargue that zero or negative international spillover, as assumed in manyanalyses, is not credible; we estimate the most likely range for the international spillover parameter in our model to be 0.5–1.0. For our base scenario this would imply a mean global average temperature change from pre-industrial levels by 2100 of 2.7–3.4 °C instead of 4.2 °C,and rising at only 0.15–0.29 °C/decade instead of 0.45 °C/decade.Long-run sea-level rise is greatly curtailed. The regional benefits to the industrialised countries are also magnified because of the spillover to developing county emissions. Although the aggregate degree of spillover is uncertain, the available evidence suggests that it will be important and environmentally beneficial in aggregate. Spillover will help to spread the global effectiveness of the Kyoto first period and subsequent commitments, and deserves much further scrutiny.