Convection stability in the Taupo Volcanic Zone,New Zealand     

J.G. McLellan  N.H.S. Oliver  B.E. Hobbs  J.V. Rowland 《Journal of Geochemical Exploration》2009

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The mass and dynamical state of Abell 2218     

D. B. Cannon  T. J. Ponman  I. S. Hobbs 《Monthly notices of the Royal Astronomical Society》1999,302(1):9-21

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Pressure and equilibrium in deforming rocks          下载免费PDF全文

Bruce E. Hobbs  Alison Ord 《Journal of Metamorphic Geology》2017,35(9):967-982

It is widely proposed that tectonic pressure (the difference between the mean stress and the pressure arising from a lithostatic load) is large, and has a significant influence on mineral phase equilibria in deforming metamorphic rocks. The implication/assertion is that the mean stress is equivalent to the thermodynamic pressure which characterizes mineral phase equilibria and is a measure of how the energy changes as the volume changes. We distinguish two useful thermodynamic pressures. The first is an equilibrium thermodynamic pressure, characteristic of non‐dissipative systems and related directly to equilibrium values of the chemical potentials that define stable, equilibrium phase assemblages. The second is a non‐equilibrium thermodynamic pressure characteristic of dissipative systems with zero net entropy production and related to non‐equilibrium chemical potentials that define stable non‐equilibrium phase assemblages. In many dissipative metamorphic systems discussed in the literature, the concepts of thermodynamic pressure and chemical potential are not usefully defined because the system is not at equilibrium and/or no volume change is involved in the deformation. The conclusion of this note is that the influence of tectonic pressure on phase equilibria is minor. The role of tectonic pressure is an important issue but is only relevant to phase equilibrium when an equilibrium thermodynamic pressure can be defined; in such cases, the influence of tectonic pressure is small compared to many proposals in the literature. Except for elastic deformations, the mean stress is not useful in discussing mineral phase equilibrium.  相似文献   

Evidence for alignment of the rotation and velocity vectors in pulsars – II. Further data and emission heights     

Simon Johnston  M. Kramer  A. Karastergiou  G. Hobbs  S. Ord  J. Wallman 《Monthly notices of the Royal Astronomical Society》2007,381(4):1625-1637

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Millimeter-wave experiments for cometary space missions     

Robert W. Hobbs  John C. Brandt  Stephen P. Maran  Jan M. Hollis 《Icarus》1981,47(3):434-440

Predicted brightness temperatures for a variety of cometary nucleus models, consisting of homogeneous layers comprised of mixtures of water ice and refractory grains, are presented as functions of wavelength. These illustrative spectra are computed using simple radiative transfer techniques adapted from modeling of terrestrial ice and snow fields. The computed millimeter-wave spectra are sensitive to the values of physically significant nucleus parameters such as crust thickness, the subsurface temperature gradient, and the boundary temperature of the sublimating surface. It appears that millimeter-wave sensing from an interplanetary spacecraft is an effective means for distinguishing between alternate models of the nucleus and for inferring the rough physical state of substrata; modern theories on the nature of the nucleus indicate that sublimation from the substrata provides the gas phase cometary volatiles that are actually observed from ground-based and Earth-orbiting instruments. Antenna beam dilution is a major obstacle for ground-based molecular spectral line radio observations (e.g., water and ammonia) of comets but a modest millimeter-wave radiometer system in the near vicinity of the comet would not be subject to this problem. Such a system can make definitivebservations of several candidate parent molecules in the gas phase and should contribute to the understanding of the physics of the inner coma.  相似文献   

The Parkes Multibeam Pulsar Survey – II. Discovery and timing of 120 pulsars     

D. J. Morris  G. Hobbs  A. G. Lyne  I. H. Stairs  F. Camilo  R. N. Manchester  A. Possenti  J. F. Bell  V. M. Kaspi  N. D' Amico  N. P. F. McKay  F. Crawford  M. Kramer 《Monthly notices of the Royal Astronomical Society》2002,335(2):275-290

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Seismic attenuation in the continental crust SW of England     

Daniel S. Scheirer  Richard W. Hobbs 《Geophysical Journal International》1990,103(2):533-540

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Li production in the big bang     

Douglas K. Duncan  L. M. Hobbs 《Journal of Astrophysics and Astronomy》1987,8(2):83-87

Li abundance is determined for 23 halo subdwarfs. About half of the stars show [Fe/H] < −1.4 and a space velocityV > 160 km s⁻¹ Li appears to be present in all our halo stars, with an abundance within about ± 0.2 dex of the value logn (Li) = 2.0 found by Spite & Spite (1982). Thus our results provide confirmation of the main conclusion of Spite & Spite.  相似文献   

Homochirality as the signature of life: the SETH Cigar     

MacDermott AJ  Barron LD  Brack A  Buhse T  Drake AF  Emery R  Gottarelli G  Greenberg JM  Haberle R  Hegstrom RA  Hobbs K  Kondepudi DK  McKay C  Moorbath S  Raulin F  Sandford M  Schwartzman DW  Thiemann WH  Tranter GE  Zarnecki JC 《Planetary and Space Science》1996,44(11):1441-1446

A characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. It is therefore suggested that a search for extra-terrestrial life can be approached as a Search for Extra-Terrestrial Homochirality (SETH). A novel miniaturized space polarimeter, called the SETH Cigar, is described which could he used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. It is believed that homochirality will be found in the subsurface layers on Mars as a relic of extinct life.  相似文献   

Coulomb constitutive laws for friction: Contrasts in frictional behavior for distributed and localized shear   总被引：2，自引：0，他引：2  

Chris Marone  B. E. Hobbs  A. Ord 《Pure and Applied Geophysics》1992,139(2):195-214

We describe slip-rate dependent friction laws based on the Coulomb failure criteria. Frictional rate dependence is attributed to a rate dependence of cohesionc and friction angle . We show that differences in the stress states developed during sliding result in different Coulomb friction laws for distributed shear within a thick gouge layer versus localized shear within a narrow shear band or between bare rock surfaces. For shear within gouge, shear strength is given by =c cos + _n sin, whereas for shear between bare rock surfaces the shear strength is =c cos + _n tan, where and _n are shear and normal stress, respectively. In the context of rate-dependent Coulomb friction laws, these differences mean that for a given material and rate dependence of the Coulomb parameters, pervasive shear may exhibit velocity strengthening frictional behavior while localized shear exhibits velocity weakening behavior. We derive from experimental data the slip-rate dependence and evolution ofc and for distributed and localized shear. The data show a positive rate dependence for distributed shear and a negative rate dependence for localized shear, indicating that the rate dependence ofc and are not the same for distributed and localized shear, even after accounting for differences in stress state. Our analysis is consistent with the well-known association of instability with shear localization in simulated fault gouge and the observation that bare rock surfaces exhibit predominantly velocity weakening frictional behavior whereas simulated fault gouge exhibits velocity strengthening followed by a transition to velocity weakening with increasing displacement. Natural faults also exhibit displacement dependent frictional behavior and thus the results may prove useful in understanding the seismic evolution of faulting.  相似文献