Statistical cosmology with quadratic density fields     

Peter Watts  Peter Coles 《Monthly notices of the Royal Astronomical Society》2003,338(3):806-815

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Middle-ear stiffness of the bottlenose dolphin tursiops truncatus     

Miller  B.S. Zosuls  A.L. Ketten  D.R. Mountain  D.C. 《Oceanic Engineering, IEEE Journal of》2006,31(1):87-94

Previous research on the cetacean auditory system has consisted mostly of behavioral studies on a limited number of species. Little quantitative physiologic data exists on cetacean hearing. The frequency range of hearing varies greatly across different mammalian species. Differences among species correlate with differences in the middle-ear transfer function. Middle-ear transfer functions depend on the mechanical stiffness of the middle ear and the cochlear input impedance. The purpose of this study was to measure the middle-ear stiffness for the bottlenose dolphin (Tursiops truncatus), a species specialized for underwater high-frequency hearing and echolocation. Middle-ear stiffness was measured with a force probe that applied a known displacement to the stapes and measured the restoring force. The average middle-ear stiffness in ten dolphin ears was 1.37 N//spl mu/m, which is considerably higher than that reported for most terrestrial mammals. The relationship between middle-ear stiffness and low-frequency hearing cutoff in Tursiops was shown to be comparable to that of terrestrial mammals.  相似文献   

Understanding the behavior of Prometheus and Pandora     

Alison J. Farmer  Peter Goldreich 《Icarus》2006,180(2):403-411

We revisit the dynamics of Prometheus and Pandora, two small moons flanking Saturn's F ring. Departures of their orbits from freely precessing ellipses result from mutual interactions via their 121:118 mean motion resonance. Motions are chaotic because the resonance is split into four overlapping components. Orbital longitudes were observed to drift away from predictions based on Voyager ephemerides. A sudden jump in mean motions took place close to the time at which the orbits' apses were antialigned in 2000. Numerical integrations reproduce both the longitude drifts and the jumps. The latter have been attributed to the greater strength of interactions near apse antialignment (every 6.2 yr), and it has been assumed that this drift-jump behavior will continue indefinitely. We re-examine the dynamics of the Prometheus-Pandora system by analogy with that of a nearly adiabatic, parametric pendulum. In terms of this analogy, the current value of the action of the satellite system is close to its maximum in the chaotic zone. Consequently, at present, the two separatrix crossings per precessional cycle occur close to apse antialignment. In this state libration only occurs when the potential's amplitude is nearly maximal, and the “jumps” in mean motion arise during the short intervals of libration that separate long stretches of circulation. Because chaotic systems explore the entire region of phase space available to them, we expect that at other times the Prometheus-Pandora system would be found in states of medium or low action. In a low action state it would spend most of the time in libration, and separatrix crossings would occur near apse alignment. We predict that transitions between these different states can happen in as little as a decade. Therefore, it is incorrect to assume that sudden changes in the orbits only happen near apse antialignment.  相似文献   

The 2dF QSO Redshift Survey – XII. The spectroscopic catalogue and luminosity function     

S. M. Croom  R. J. Smith  B. J. Boyle  T. Shanks  L. Miller  P. J. Outram  N. S. Loaring 《Monthly notices of the Royal Astronomical Society》2004,349(4):1397-1418

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QUEST on DASI: a South Pole CMB polarization experiment     

Sarah Church  Peter Ade  James Bock  Melanie Bowden  John Carlstrom  Ken Ganga  Walter Gear  James Hinderks  Wayne Hu  Brian Keating  John Kovac  Andrew Lange  Eric Leitch  Olivier Mallie  Simon Melhuish  Anthony Murphy  Ben Rusholme  Creidhe O&#x;Sullivan  Lucio Piccirillo  Clem Pryke  Andy Taylor  Keith Thompson 《New Astronomy Reviews》2003,47(11-12):1083

QUEST on DASI is a ground-based, high-sensitivity, high-resolution (ℓ_max2500) experiment designed to map CMB polarization at 100 and 150 GHz and to measure the power spectra from E-modes, B-modes from lensing of the CMB, and B-modes from primordial gravitational waves. The experiment comprises a 2.6 m Cassegrain optical system, equipped with an array of 62 polarization-sensitive bolometers (PSBs), located at the South Pole. The instrument is designed to minimize systematic effects; features include differencing of pairs of orthogonal PSBs within a single feed, a rotatable achromatic waveplate, and axisymmetric rotatable optics. In addition the South Pole location allows both repeatable and highly controlled observations. QUEST on DASI will commence operation in early 2005.  相似文献   

The 2dF QSO Redshift Survey – X. Lensing of background QSOs by galaxy groups     

A. D. Myers  P. J. Outram  T. Shanks  B. J. Boyle  S. M. Croom  N. S. Loaring  L. Miller  R. J. Smith 《Monthly notices of the Royal Astronomical Society》2003,342(2):467-482

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Mesoscale linear streaks on Mars: environments of dust entrainment     

P.C Thomas  P Gierasch  D.S Miller  B Cantor 《Icarus》2003,162(2):242-258

Variable surface albedo features on Mars are likely caused by the entrainment and deposition of dust by the wind. Most discrete markings are associated with topographic forms or with regional slopes that serve to alter the effective wind shear stress on the surface. Some of the largest variable features, here termed mesoscale linear streaks, are up to 400 km in length and repeatedly occur in one of the smoothest regions of Mars: Amazonis Planitia. Their orientations and apparent season of variability as observed by Viking and Mars Orbiter cameras indicate linear streak formation by enhanced surface wind stresses during regional or local dust storms and during the initial stages of global dust storms. They provide an example of the ability of large-scale winds, without significant local enhancement, to initiate dust motion on Mars. The sizes and spacing of the linear streaks may be controlled by boundary layer rolls. The repetitive formation of these streaks, over a span of more than 11 Mars years, gives one measure of the stability of Mars’ eolian processes.  相似文献   

Magnetic remanence in the Murchison meteorite     

Gunther KLETETSCHKA  Tomas KOHOUT  Peter J. WASILEWSKI 《Meteoritics & planetary science》2003,38(3):399-405

Abstract— The Murchison meteorite is a carbonaceous chondrite containing a small amount of chondrules, various inclusions, and matrix with occasional porphyroblasts of olivine and/or pyroxene. It also contains amino acids that may have served as the necessary components for the origin of life. Magnetic analyses of Murchison identify an ultrasoft magnetic component due to superparamagnetism as a significant part of the magnetic remanence. The rest of the remanence may be due to electric discharge in the form of lightning bolts that may have formed the amino acids. The level of magnetic remanence does not support this possibility and points to a minimum ambient field of the remanence acquisition. We support our observation by showing that normalized mineral magnetic acquisition properties establish a calibration curve suitable for rough paleofield determination. When using this approach, 1–2% of the natural remanence left in terrestrial rocks with TRM and/or CRM determines the geomagnetic field intensity irrespective of grain size or type of magnetic mineral (with the exception of hematite). The same method is applied to the Murchison meteorite where the measured meteorite remanence determines the paleofield minimum intensity of 200–2000 nT during and/or after the formation of the parent body.  相似文献   

Origin of chaos in the Prometheus-Pandora system     

Peter Goldreich  Nicole Rappaport 《Icarus》2003,166(2):320-327

We demonstrate that the chaotic orbits of Prometheus and Pandora are due to interactions associated with the 121:118 mean motion resonance. Differential precession splits this resonance into a quartet of components equally spaced in frequency. Libration widths of the individual components exceed the splitting, resulting in resonance overlap which causes the chaos. Mean motions of Prometheus and Pandora wander chaotically in zones of width 1.8 and 3.1 deg yr⁻¹, respectively. A model with 1.5 degrees of freedom captures the essential features of the chaotic dynamics. We use it to show that the Lyapunov exponent of 0.3 yr⁻¹ arises because the critical argument of the dominant member of the resonant quartet makes approximately two separatrix crossings every 6.2 year precessional cycle.  相似文献   

Journeyman Editor     

Peter J. Taylor 《The Professional geographer》1990,42(3):359-360

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