Five WC9 stars discovered in the AAO/UKST Hα survey     

E. C. Hopewell  M. J. Barlow  J. E. Drew  Y. C. Unruh  Q. A. Parker  M. J. Pierce  P. A. Crowther  C. Knigge  S. Phillipps  A. A. Zijlstra 《Monthly notices of the Royal Astronomical Society》2005,363(3):857-866

We report the discovery of five massive Wolf–Rayet (WR) stars resulting from a programme of follow-up spectroscopy of candidate emission-line stars in the Anglo-Australian Observatory United Kingdom Schmidt Telescope (AAO/UKST) Southern Galactic Plane Hα survey. The 6195–6775 Å spectra of the stars are presented and discussed. A WC9 class is assigned to all five stars through comparison of their spectra with those of known late-type WC stars, bringing the known total number of Galactic WC9 stars to 44. Whilst three of the five WC9 stars exhibit near-infrared (NIR) excesses characteristic of hot dust emission (as seen in the great majority of known WC9 stars), we find that two of the stars show no discernible evidence of such excesses. This increases the number of known WC9 stars without NIR excesses to seven. Reddenings and distances for all five stars are estimated.  相似文献   

Variability in concentration of suspensates in an estuarine environment     

J. W. Pierce  D. L. Correll  B. Goldberg  W. H. Klein 《Geo-Marine Letters》1984,4(3-4):153-155

Three data sets of suspensate concentrations, collected under different sampling plans, were analyzed to develop a minimal sampling period, consistent with a predetermined precision. Individual samples collected during any part of a given day were within ±50% of the daily average. In the main channel of the estuary, a monthly sampling scheme closely approximated a weekly pattern; however, seasonal sampling was unsatisfactory. Outside the main channel, weekly, monthly, and seasonal sampling patterns did not differ greatly. Variability in suspensate concentrations must be considered when calculating sediment flux in estuarine and coastal waters.  相似文献   

Spatial and temporal patterns of cuttlefish (Sepia officinalis) abundance and environmental influences - a case study using trawl fishery data in French Atlantic coastal, English Channel, and adjacent waters   总被引：1，自引：0，他引：1  

Wang  Jianjun; Pierce  Graham J; Boyle  Peter R; Denis  Vincent; Robin  Jean-Paul; Bellido  Jose M 《ICES Journal of Marine Science》2003,60(5):1149-1158

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Extreme value estimates for arbitrary bandwidth Gaussian processes using the analytic envelope     

Robert D. Pierce 《Ocean Engineering》1985,12(6):493-529

A procedure is presented for the estimation of extreme values of stationary Gaussian random processes with arbitrary bandwidths. This approach is based on the analytic envelope defined by the Hilbert Transform; this envelope is Rayleigh distributed regardless of bandwidth. For experimentally derived data that has been converted into digital form, the Hilbert Transform is approximated using algorithms implemented on a digital computer to produce samples of the envelope's time history. Next, the degree of correlation between these envelope samples is taken into account using a method developed from simulation studies of a series of synthetic Gaussian time histories with varying bandwidths. Once this correlation effect has been estimated, the standard methods of order statistics are applied to these samples using the Rayleigh probability density function. Examples of applying this procedure to experimentally derived data are presented.  相似文献   

The observed limb effect in Fraunhofer lines,I     

A. Keith Pierce 《Solar physics》1991,133(2):215-225

The absolute limb effect is presented for Fei lines 3767 and 3969; for five Tii lines of multiplet 42 near 4535 and one Tiii line at 4534; two lines of Mgi, 4571 and 5172; two lines of Baii at 5854 and 6497. The scattered light of the McMath solar telescope is illustrated by several figures but not applied to the limb-effect observations. It is suggested that the supergravity shift at the limb is the result of scattering of the atoms in anisotropic velocity field.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.  相似文献   

A comparative error analysis of manual versus automated methods of data acquisition for algebraic strain estimation   总被引：1，自引：0，他引：1  

Kingshuk Roy Choudhury  Kieran Mulchrone   《Tectonophysics》2006,421(3-4):209-230

This paper presents a statistical analysis of the algebraic strain estimation algorithm of Shimamoto and Ikeda [Shimamoto, T., Ikeda, Y., 1976. A simple algebraic method for strain estimation from deformed eillipsoidal objects: 1. Basic theory. Tectonophysics 36, 315–337]. It is argued that the error in their strain estimation procedure can be quantified using an expected discrepancy measure. An analysis of this measure demonstrates that the error is inversely proportional to the number of clasts used. The paper also examines the role of measurement error, in particular that incurred under (i) a moment based and (ii) manual data acquisition methods. Detailed analysis of these two acquisition methods shows that in both cases, the effect of measurement error on the expected discrepancy is small relative to the effect of the sample size (number of objects). Given their relative speed advantage, this result favours the use of automated measurement methods even if they incur more measurement error on individual objects. Validation of these results is carried out by means of a simulation study, as well as by reference to studies appearing in previous literature. The results are also applied to obtain an upper bound on the error of strain estimation for various studies published in the literature on strain analysis.  相似文献   

Exploration and discovery in Yellowstone Lake: results from high-resolution sonar imaging, seismic reflection profiling, and submersible studies     

L. A. Morgan  W. C. Shanks  III  D. A. Lovalvo  S. Y. Johnson  W. J. Stephenson  K. L. Pierce  S. S. Harlan  C. A. Finn  G. Lee  M. Webring  B. Schulze  J. Dühn  R. Sweeney  L. Balistrieri 《Journal of Volcanology and Geothermal Research》2003,122(3-4):221-242

‘No portion of the American continent is perhaps so rich in wonders as the Yellow Stone’ (F.V. Hayden, September 2, 1874)Discoveries from multi-beam sonar mapping and seismic reflection surveys of the northern, central, and West Thumb basins of Yellowstone Lake provide new insight into the extent of post-collapse volcanism and active hydrothermal processes occurring in a large lake environment above a large magma chamber. Yellowstone Lake has an irregular bottom covered with dozens of features directly related to hydrothermal, tectonic, volcanic, and sedimentary processes. Detailed bathymetric, seismic reflection, and magnetic evidence reveals that rhyolitic lava flows underlie much of Yellowstone Lake and exert fundamental control on lake bathymetry and localization of hydrothermal activity. Many previously unknown features have been identified and include over 250 hydrothermal vents, several very large (>500 m diameter) hydrothermal explosion craters, many small hydrothermal vent craters (1–200 m diameter), domed lacustrine sediments related to hydrothermal activity, elongate fissures cutting post-glacial sediments, siliceous hydrothermal spire structures, sublacustrine landslide deposits, submerged former shorelines, and a recently active graben. Sampling and observations with a submersible remotely operated vehicle confirm and extend our understanding of the identified features. Faults, fissures, hydrothermally inflated domal structures, hydrothermal explosion craters, and sublacustrine landslides constitute potentially significant geologic hazards. Toxic elements derived from hydrothermal processes also may significantly affect the Yellowstone ecosystem.  相似文献   

Discrete element method modeling of inherently anisotropic rocks under uniaxial compression loading          下载免费PDF全文

K. Duan  C.Y. Kwok  M. Pierce 《国际地质力学数值与分析法杂志》2016,40(8):1150-1183

A new numerical approach is proposed in this study to model the mechanical behaviors of inherently anisotropic rocks in which the rock matrix is represented as bonded particle model, and the intrinsic anisotropy is imposed by replacing any parallel bonds dipping within a certain angle range with smooth‐joint contacts. A series of numerical models with β = 0°, 15°, 30°, 45°, 60°, 75°, and 90° are constructed and tested (β is defined as the angle between the normal of weak layers and the maximum principal stress direction). The effect of smooth‐joint parameters on the uniaxial compression strength and Young's modulus is investigated systematically. The simulation results reveal that the normal strength of smooth‐joint mainly affects the behaviors at high anisotropy angles (β > 45°), while the shear strength plays an important role at medium anisotropy angles (30°–75°). The normal stiffness controls the mechanical behaviors at low anisotropy angles. The angle range of parallel bonds being replaced plays an important role on defining the degree of anisotropy. Step‐by‐step procedures for the calibration of micro parameters are recommended. The numerical model is calibrated to reproduce the behaviors of different anisotropic rocks. Detailed analyses are conducted to investigate the brittle failure process by looking at stress‐strain behaviors, increment of micro cracks, initiation and propagation of fractures. Most of these responses agree well with previous experimental findings and can provide new insights into the micro mechanisms related to the anisotropic deformation and failure behaviors. The numerical approach is then applied to simulate the stress‐induced borehole breakouts in anisotropic rock formations at reduced scale. The effect of rock anisotropy and stress anisotropy can be captured. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

The relation of Holocene fluvial terraces to changes in climate and sediment supply,South Fork Payette River,Idaho     

Jennifer L. Pierce  Grant A. Meyer  Tammy Rittenour 《Quaternary Science Reviews》2011,30(5-6):628-645

Well-preserved Holocene terraces along the South Fork Payette River in central Idaho provide a record of fluvial system behavior in a steep mountain watershed characterized by weathered and erodible Idaho Batholith granitic rocks. Terrace deposit ages were provided by ¹⁴C dating of charcoal fragments and optically stimulated luminescence (OSL) dating of sandy sediments. Along with pairing of many terrace tread heights, these data indicate episodic downcutting during the Holocene, with a mean incision rate of ～0.9 m/ka from ～7 ka to present. Prior to 7 ka, the river incised to within～3 m of current bankfull, but then aggraded by ～5 m over at least a ～10 km-long reach in an episode centered ～7–6 ka. Aggradation may relate to (1) increased hillslope sediment input from landslides and debris flows in steep tributary basins with abundant grussified granitic bedrock, (2) possible local landslide-damming of the channel, (3) decreased peak discharge, or (4) a combination of these factors. Middle Holocene channel aggradation ca. 7–6 ka corresponds with a period of prolonged and widespread aridity in the northern Rocky Mountains. Between ～5 and 1.3 ka, the river aggraded slightly and then remained stable, forming a prominent terrace tread at ～3 m above current bankfull. Modest aggradation to vertical stability of the South Fork Payette River at the 1.5 m terrace level ～1.0–0.7 ka corresponds with large fire-related debris flows in tributaries during Medieval droughts. Three intervals of incision (～5.5–5 ka, 1.3–1.0 ka and 0.5 ka) correspond with frequent but small fire-related sedimentation events and generally cooler, wetter conditions suggesting increased snowmelt runoff discharges. Other possible drivers of channel incision include an increase in stochastic or climate-modulated large storms and floods and a reduction in delivery of hillslope sediment to the channel. Aggradation is more confidently tied to climate through increases in hillslope sediment delivery and (or) decreased stream power, both likely related to warmer, drier conditions (including high-severity fires) that reduce snowmelt and decrease vegetation cover on steep slopes. Thus, the Holocene terraces of the South Fork Payette River do not reflect simple stepwise incision with periods of vertical stability and lateral migration, but record substantial episodes of aggradation as well. We infer that increases in hillslope erosion and mass movements combined with reduced discharges during prolonged droughts episodically reverse the post-glacial trend of downcutting, in particular during the middle Holocene. The present bedrock-dominated channel implies a strong tendency toward incision in the late Holocene.  相似文献   

Kinematics and shear heat pattern of ductile simple shear zones with ‘slip boundary condition’     

Kieran F. Mulchrone  Soumyajit Mukherjee 《International Journal of Earth Sciences》2016,105(3):1015-1020

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