Microbial survival in space shuttle crash     

McLean RJ  Welsh AK  Casasanto VA 《Icarus》2006,181(1):323-325

A slow growing, heat resistant bacterium, identified by 16S rRNA gene sequencing as Microbispora sp., was recovered from the wreckage of the ill-fated space shuttle Columbia (STS-107). As this organism survived disintegration of the space craft, heat of reentry, and impact, it supports the possibility of a natural mechanism for the interplanetary spread of life by meteorites.  相似文献   

Bedform response to flow variability     

J. M. Nelson  B. L. Logan  P. J. Kinzel  Y. Shimizu  S. Giri  R. L. Shreve  S. R. McLean 《地球表面变化过程与地形》2011,36(14):1938-1947

Laboratory observations and computational results for the response of bedform fields to rapid variations in discharge are compared and discussed. The simple case considered here begins with a relatively low discharge over a flat bed on which bedforms are initiated, followed by a short high‐flow period with double the original discharge, during which the morphology of the bedforms adjusts, followed in turn by a relatively long period of the original low discharge. For the grain size and hydraulic conditions selected, the Froude number remains subcritical during the experiment, and sediment moves predominantly as bedload. Observations show rapid development of quasi‐two‐dimensional bedforms during the initial period of low flow with increasing wavelength and height over the initial low‐flow period. When the flow increases, the bedforms rapidly increase in wavelength and height, as expected from other empirical results. When the flow decreases back to the original discharge, the height of the bedforms quickly decreases in response, but the wavelength decreases much more slowly. Computational results using an unsteady two‐dimensional flow model coupled to a disequilibrium bedload transport model for the same conditions simulate the formation and initial growth of the bedforms fairly accurately and also predict an increase in dimensions during the high‐flow period. However, the computational model predicts a much slower rate of wavelength increase, and also performs less accurately during the final low‐flow period, where the wavelength remains essentially constant, rather than decreasing. In addition, the numerical results show less variability in bedform wavelength and height than the measured values; the bedform shape is also somewhat different. Based on observations, these discrepancies may result from the simplified model for sediment particle step lengths used in the computational approach. Experiments show that the particle step length varies spatially and temporally over the bedforms during the evolution process. Assuming a constant value for the step length neglects the role of flow alterations in the bedload sediment‐transport process, which appears to result in predicted bedform wavelength changes smaller than those observed. However, observations also suggest that three‐dimensional effects play at least some role in the decrease of bedform wavelength, so incorporating better models for particle hop lengths alone may not be sufficient to improve model predictions. Published in 2011. This article is a US Government work and is in the public domain in the USA.  相似文献   

A catalog of Kazarian galaxies     

M. A. Kazarian  V. Zh. Adibekyan  B. McLean  R. J. Allen  A. R. Petrosian 《Astrophysics》2010,53(1):57-69

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From Dispossession to Compensation: a political ecology of the Ord Final Agreement as a partial success story for Indigenous traditional owners     

Jessica McLean 《The Australian geographer》2012,43(4):339-355

The recent digging of a new channel for water delivery to expand irrigation in the Ord provides a good opportunity for unearthing the native title agreement that allows for intensification of agriculture there. Initial irrigation development in this north-eastern Australian catchment did not include recognition of, consultation with, or distribution of benefits to Indigenous people impacted by dam creation and land flooding. Forming agreement between those affected by previous dispossessions, and associated accumulation of wealth via mining and irrigation, with those initiating such activities was an important and challenging process. The Ord Final Agreement (OFA), formalised in 2006, came from negotiations between Miriuwung and Gajerrong traditional owners and government and private interests. Through qualitative research, I dissect the context and content of the OFA to identify the strengths and weaknesses therein. While the agreement does allow for co-management of significant land- and waterscapes, it does not provide for Indigenous water rights, showing one instance of loose ends and missing links within the Ord.  相似文献   

U‐Pb Geochronological and Thermochronological Time–Temperature Constraints of 40Ar/39Ar Hornblende Reference Material HB3gr          下载免费PDF全文

Terrence Blackburn  Noah McLean  Samuel A. Bowring 《Geostandards and Geoanalytical Research》2017,41(3):325-334

Hornblende from the Lone Grove Pluton, Llano Uplift, Texas, has served as an irradiation reference material in ⁴⁰Ar/³⁹Ar studies for decades. In order to evaluate the apparent age bias that currently exists between the U‐Pb and ⁴⁰Ar/³⁹Ar systems, zircon and titanite were dated by isotope dilution‐thermal ionisation mass spectrometry (ID‐TIMS) from the same rock from which the hornblende ⁴⁰Ar/³⁹Ar reference material HB3gr is derived. Zircon U‐Pb data indicate initial crystallisation at 1090.10 ± 0.16 Ma (2s), a date that is 1.7% older than the accepted K‐Ar date (1072 ± 14 Ma, 2s) for HB3gr; an offset that exceeds the typical 0.5–1% bias between the two systems, though remaining within uncertainty due to the large uncertainties in the ⁴⁰K decay constant. Zircon data are presented using both EARTHTIME tracers ET535 and ET2535 and are statistically indistinguishable. Single grain titanite analyses range between 1082 ± 0.75 and 1086 ± 0.81 Ma (2s) and are interpreted to record the subsequent cooling following crystallisation at rates between 30 and 50 °C Ma^?1. This is supported by the observation that hornblende ⁴⁰Ar/³⁹Ar dates corrected for decay constant bias are resolvably younger than the zircon U‐Pb date and in good agreement with titanite U‐Pb dates, permitting the conclusion that both titanite U‐Pb and hornblende ⁴⁰Ar/³⁹Ar systems provide a record of cooling.  相似文献   

Non-existence of linear polarization in type III solar bursts at 80 MHz     

R. J. M. Grognard  D. J. McLean 《Solar physics》1973,29(1):149-161

A search for linear polarization showing the effect of Faraday rotation has been made at 80 MHz in type III solar radio bursts. A novel autocorrelation technique was employed. The results were entirely negative, contrary to what was expected on the ground of earlier, less sophisticated experiments. However, there are convincing theoretical reasons why no linear polarization should be expected.Radiophysics Publication RPP 1642, September, 1972.  相似文献   

The Rest-Frame Optical Spectrum of MS 1512-cB58     

Teplitz HI  McLean IS  Becklin EE  Figer DF  Gilbert AM  Graham JR  Larkin JE  Levenson NA  Wilcox MK 《The Astrophysical journal》2000,533(1):L65-L68

Moderate-resolution, near-IR spectroscopy of MS 1512-cB58 is presented, obtained during commissioning of the near-infrared spectrometer (NIRSPEC) on the Keck II telescope. The strong lensing of this z=2.72 galaxy by the foreground cluster MS 1512+36 makes it the best candidate for detailed study of the rest-frame optical properties of Lyman-break galaxies. In 80 minutes of on-source integration, we have detected Halpha, [N ii] lambdalambda6583, 6548, [O i] lambda6300, He i lambda5876, [O iii] lambdalambda5007, 4959, Hbeta, Hgamma, [O ii] lambda3727, and a strong continuum signal in the range of 1.29-2.46 μm. A redshift of z=2.7290+/-0.0007 is inferred from the emission lines, in contrast to the z=2.7233 calculated from UV observations of interstellar absorption lines. Using the Balmer line ratios, we find an extinction of E(B-V) = 0.27. Using the line strengths, we infer a star formation rate (SFR) of 620+/-18 M middle dot in circle yr-1 (H0=75, q0=0.1, and Lambda=0), which is a factor of 2 higher than that measured from narrowband imaging observations of the galaxy but is a factor of almost 4 lower than the SFR inferred from the UV continuum luminosity. The width of the Balmer lines yields a mass of Mvir=1.2x1010 M middle dot in circle. We find that the oxygen abundance is 13 solar, in good agreement with other estimates of the metallicity. However, we infer a high nitrogen abundance, which may argue for the presence of an older stellar population.  相似文献   

Miocene Blanca Fan,Northern Channel Islands,California: Small fans reflecting tectonism and volcanism     

Hugh McLean  D. G. Howell 《Geo-Marine Letters》1983,3(2-4):161-166

Blanca fan is a submarine fan composed of Miocene volcaniclastic strata. Parts of the fan system are exposed on Santa Cruz and Santa Rosa Islands, and possibly correlative strata crop out on San Miguel and Santa Catalina Islands. The Blanca fan and underlying breccia reflect regional transcurrent faulting in the California Continental Borderland and development of a system of rapidly subsiding basins and uplifted linear ridges during early and middle Miocene time. Erosion of uplifted crystalline basement rocks followed by the onset of silicic volcanism created linear sediment sources for the alluvial and submarine fans, respectively.  相似文献   

Double-averaged velocity profiles over fixed dune shapes     

Stephen R. McLean  Vladimir I. Nikora  Stephen E. Coleman 《Acta Geophysica》2008,56(3):669-697

Spatially averaged profiles of time averaged velocity, using integrals over thin horizontal slabs (Cartesian double average), are employed in characterizing the flow over fixed dune shapes. For comparison the spatial averaging method of Smith and McLean (1977) that averages along lines at constant distance from the local bed elevation is also investigated. The Cartesian double averaged profiles of the inverse of the velocity shear are nearly constant below the crest elevation, but increase rapidly above the crest level. This results in velocity profiles that increase linearly with distance from the bed below the crest. Above the crest it can be argued that the velocity increases logarithmically, but a power law profile can also be argued. Spatially averaged eddy viscosity profiles are calculated by multiplying the average Reynolds stress by the inverse shear. The resulting profile is more complex than the uniform flow counterpart.  相似文献   

Studies on the larva of Oniscigaster wakefieldi (Ephemeroptera: Siphlonuridae) in Waitakere stream,Auckland     

J. A. McLean 《新西兰海洋与淡水研究杂志》2013,47(1):36-45

The larva of the primitive mayfly Oniscigaster wakefieldi, McLachlan 1873 (Ephemeroptera: Siphlonuridae) was studied in the Waitakere Stream, near Auckland, New Zealand, over a 17‐month period extending from July 1965— November 1966. A wide‐mouthed dragnet enabled monthly samples (average 46 specimens) to be collected for detailed studies of the larval growth pattern; this collecting method revealed that the species, previously thought to be rare, is numerous both in the study area and elsewhere in North Island, New Zealand.

O. wakefieldi has a univoltine life cycle with 20–25 larval instars. The larvae prefer different habitats according to their age and can be divided into three distinct groups: larvae 1–10 mm in length are found on finer sediments in quiet shallow water; 11–18 mm in length inhabit waters up to 50 cm deep where the substratum is mainly of pebbles (0.4–4.0 cm diameter) set in a silt matrix; and mature larvae 19–26 mm in length are found adjacent to dry emergent boulders, often at the base of riffles.

Three larval characters are described for the first time to separate the larvae of O. wakefieldi and O. distans. Sexual dimorphism is evident in O. wakefieldi populations by size difference; in the last larval instar, females average 4 mm longer than males. The known distribution of the species in North Island is illustrated.  相似文献