9C: a survey of radio sources at 15 GHz with the Ryle Telescope

The fields chosen for the first observations of the cosmic microwave background with the Very Small Array have been surveyed with the Ryle Telescope at 15 GHz. We have covered three regions around RA  00^h 20^m Dec. +30°  , RA  09^h 40^m Dec. +32°  and RA  15^h 40^m Dec. +43° (J2000.0)  , an area of  520 deg²  . There are 465 sources above the current completeness limit of  ≈25 mJy  , although a total of  ≈760  sources have been detected, some as faint as 10 mJy. This paper describes our techniques for observation and data analysis; it also includes source counts and some discussion of spectra and variability. Preliminary source lists are presented.     

Error analysis for the evaluation of model performance: rainfall–runoff event summary variables

This paper provides a procedure for the evaluation of model performance for rainfall–runoff event summary variables, such as total discharge or peak runoff. The procedure is based on the analysis of model errors, defined as the differences between observed values and values predicted by a simulation model. Model errors can (i) indicate whether and where the model can be improved, (ii) be used to measure the performance of a model, and (iii) be used to compare model simulations. In this paper, both statistical and graphical methods are used to characterize model errors. We explore model recalibration by relating model errors to the model predictions, and to external, independent variables. The R‐5 catchment data sets that we used in this study include summary variables for 72 rainfall–runoff events. The simulations used in this study were previously conducted with the quasi‐physically based rainfall–runoff model QPBRRM for 11 different characterizations of the R‐5 catchment, each with increasing information or a refined spatial discretization of the overland flow planes. This paper is about proposing model diagnostics and not about procedures for using diagnostics for model modification. Copyright © 2007 John Wiley & Sons, Ltd.     

Methane hydrate in the global organic carbon cycle

The global occurrence of methane hydrate in outer continental margins and in polar regions, and the magnitude of the amount of methane sequestered in methane hydrate suggest that methane hydrate is an important component in the global organic carbon cycle. Various versions of this cycle have emphasized the importance of methane hydrate, and in the latest version the role of methane hydrate is considered to be analogous to the workings of an electrical circuit. In this circuit the methane hydrate is a condenser and the consequences of methane hydrate dissociation are depicted as a resistor and inductor, reflecting temperature change and changes in earth surface history. These consequences may have implications for global change including global climate change.
Terra Nova, 14, 302–306, 2002     

Equilibrium figures of spinning bodies with self-gravity

The study of the equilibrium and stability of spinning ellipsoidal fluid bodies with gravity began with Newton in 1687, and continues to the present day. However, no smaller bodies of the Solar System are fluid. Here I model those bodies as elastic-plastic solids using a cohesionless Mohr-Coulomb yield envelope characterized by an angle of friction. This study began in Holsapple 2001. Here new closed-form algebraic formulas for the spin limits of ellipsoidal shapes are derived using an energy method. The fluid results of Maclaurin and Jacobi are again recovered as special cases. I then consider the stability of those equilibrium states. For elastic-plastic solids the common methods cannot be used, because the constitutive equations lack sufficient smoothness at the limiting plastic states. Therefore, I propose and study a new measure of the stability of dynamic processes in general bodies. An energy-based approach is introduced which is shown to include stability approaches used in the statics of nonlinear elastic and elastic-plastic bodies, spectral definitions and the Liapunov methods used for finite-dimensional dynamical systems. The method is applied to spinning, solid, strained bodies. In contrast to the special fluid case, it is found that the strain energy term of solid materials generally induces stability of all equilibrium shapes, except for two possible cases. First, strain softening in the elastic-plastic law can result in instability at the plastic limit spin. Second, a loss of shear stiffness can give unstable states at specific spins less than the limit equilibrium spins. In the latter case, a solid spinning ellipsoidal body without elastic shear stiffness can spin no faster than with a period of about 3.7 hr, else it will fail by shearing deformations. That is distinctly slower than the oft-quoted limit of 2.1 hr at which material would be flung off the equator by tensile forces. However, the final conclusion is that neither cohesion nor tensile strength is required for the shapes and spins of almost all of the larger observed asteroids: we cannot rule out rubble-pile structures.