Volatile organic sulfur compounds as biomarkers complementary to methane: Infrared absorption spectroscopy of CH3SH enables insitu measurements on Earth and Mars     

Steve Vance  Lance E. Christensen  Christopher R. Webster  Keeyoon Sung 《Planetary and Space Science》2011,59(2-3):299-303

As universal products of biological processes, volatile organic sulfur compounds such as methyl mercaptan (CH₃SH) may be essential in the search for signs of life on Mars and in exoplanet atmospheres. Methyl mercaptan is implicated in the origin of life at sites of low-temperature hydrothermal activity driven by serpentinization. Serpentinization may occur on Mars, in icy satellite oceans, and in other small wet bodies to a greater extent than on Earth, with important implications for life. We characterized absorption features in pure laboratory sample spectra of CH₃SH using the Carbon Isotope Laser Spectrometer (CILS), an infrared $(3.27\mathrm{\mu }\mathrm{m})$ tunable diode laser spectrometer with capabilities nearly identical to those of the Tunable Laser Spectrometer (TLS) instrument on the Mars Science Laboratory. The molecular species proves detectable by CILS and TLS at the sensitivities approaching the level of parts per trillion with pre-concentration. These measurements demonstrate the possibility for detection of methyl mercaptan, with implications for its possible use as an in situ biosignature for Earth-based and extraterrestrial exploration.  相似文献   

Framing the use of geo-information in government: a tale of two perspectives     

Yola Georgiadou  Gianluca Miscione  Kate Lance  Walter de Vries 《Earth Science Informatics》2009,2(4):271-282

While commercial virtual globes (e.g. Google Earth) and global scientific cyber-infrastructures (e.g. Digital Earth) are revolutionizing the way we use and produce geo-information, we still lack a rich conceptual understanding of how genuine human actors use geo-information and associated technologies in real work settings. In this paper, we conceptualize the use of geo-information as encompassing people’s actual use practices, the values to which people aspire through geo-information use, and the rules that either legally prescribe or just encourage optimal use. Values, practices and rules can be illuminated from two perspectives (or lenses), the market and the polis, resulting in radically different insights on the use of geo-information as a social phenomenon. We argue that with a polis lens we stand a chance to explain how authentic human actors, groups and communities with different values, interests and motivations use geo-information, and how societal benefits materialize or not as a result. Seen from a polis lens, values are not easily measurable standards of goodness, dominant public management ideas can be the source of technical-organizational change in government while policies can be fruitfully examined as persuasive arguments to target audiences. With a polis lens, we are more likely to understand the emergence of new practices, value contests and global rules underpinning commercial virtual globes and scientific cyber-infrastructures.  相似文献   

Near-Earth asteroid surface roughness depends on compositional class   总被引：1，自引：0，他引：1  

Lance A.M. Benner  Steven J. Ostro  Michael C. Nolan  Jon D. Giorgini  Jean-Luc Margot  Michael W. Busch 《Icarus》2008,198(2):294-304

Radar observations of 214 near-Earth asteroids (NEAs) reveal a very strong correlation of circular polarization ratio with visible-infrared taxonomic class, establishing distinct differences in the centimeter-to-several-decimeter structural complexity of objects in different spectral classes. The correlation may be due to the intrinsic mechanical properties of different mineralogical assemblages but also may reflect very different formation ages and collisional histories. The highest ratios are measured for groups associated with achondritic igneous rocky meteorites: the E class, whose parent body may be 3103 Eger, and the V class, derived from the mainbelt asteroid (and Dawn mission target) 4 Vesta.  相似文献   

Cosmological evolution and hierarchical galaxy formation     

Will Percival  Lance Miller 《Monthly notices of the Royal Astronomical Society》1999,309(4):823-832

We calculate the rate at which dark matter haloes merge to form higher mass systems. Two complementary derivations using Press–Schechter theory are given, both of which result in the same equation for the formation rate. First, a derivation using the properties of the Brownian random walks within the framework of Press–Schechter theory is presented. We then use Bayes' theorem to obtain the same result from the standard Press–Schechter mass function. The rate obtained is shown to be in good agreement with results from Monte Carlo and N -body simulations. We illustrate the usefulness of this formula by calculating the expected cosmological evolution in the rate of star formation that is due to short-lived, merger-induced starbursts. The calculated evolution is well-matched to the observed evolution in ultraviolet luminosity density, in contrast to the lower rates of evolution that are derived from semi-analytic models that do not include a dominant contribution from starbursts. Hence we suggest that the bulk of the observed ultraviolet starlight at z >1 arises from merger-induced starbursts. Finally, we show that a simple merging-halo model can also account for the bulk of the observed evolution in the comoving quasar space density.  相似文献   

U-Pb zircon dating of mafic dykes and its application to the Proterozoic geological history of the Vestfold Hills,East Antarctica   总被引：3，自引：0，他引：3  

Ruth Lanyon  Lance P. Black  Hans-Michael Seitz 《Contributions to Mineralogy and Petrology》1993,115(2):184-203

The Vestfold Hills, one of several Archaean cratonic blocks within the East Antarctic Shield, comprises a high-grade metamorphic basement complex intruded by at least nine generations of Early to Middle Proterozoic mafic dykes. Extensive U-Pb ion microprobe (SHRIMP) analyses of zircons, derived predominantly from late-stage felsic differentiates of the mafic dykes, provide precise crystallisation ages for several dyke generations. These new ages enable constraints to be placed on both the history of mafic magmatism in the Vestfold Hills and the timing of the various interspersed Proterozoic deformation events. In addition to demonstrating the utility of zircons derived from felsic late-stage differentiates for the dating of co-genetic mafic dykes, this study also places doubt on previous wholerock Rb-Sr dating of mafic dyke suites in this and other areas of East Antarctica. The ²⁰⁷Pb/²⁰⁶Pb zircon ages of 2241±4 Ma and 2238±7 Ma for the Homogeneous and Mottled Norites, respectively, provide a younger emplacement age for associated group 2 High-Mg tholeiite dykes than the whole-rock Rb-Sr date (2424±72 Ma) originally interpreted as the age of all high-Mg intrusives in the Vestfold Hills. Zircon ages of 1754±16 Ma and 1832±72 Ma confirm the previously defined Rb-Sr age of the group 2 Fe-rich tholeiites. Two later dyke generations, the group 3 and 4 Fe-rich tholeiites, are distinguished on the basis of field orientations and cross-cutting relationships, and yield zircon emplacement ages of 1380±7 Ma and 1241±5 Ma which also define minimum ages for two suites of lamprophyre dykes. Xenocrystic zircons within both felsic segregations and mafic dykes yield zircon ages of 2478±5 Ma to 2740 Ma, indicating the presence of Archaean crustal source rocks of this antiquity beneath the Vestfold Hills.  相似文献   

An empirical attenuation relationship for Northwestern Turkey ground motion using a random effects approach   总被引：2，自引：0，他引：2  

Cem zbey  Ali Sari  Lance Manuel  Mustafa Erdik  Yasin Fahjan 《Soil Dynamics and Earthquake Engineering》2004,24(2):115-125

Using a random effects model that takes into consideration the correlation of data recorded by a single seismic event, a database consisting of 195 recordings from 17 recent events is employed to develop empirical attenuation relationships for the geometric mean of horizontal peak ground acceleration and 5-percent damped spectral acceleration (S_a). The recordings employed are obtained from strong motion stations operating in Northwestern Turkey and resulted from events that include the Kocaeli (M_w=7.4) and the Düzce (M_w=7.1) earthquakes and their aftershocks as well as other events. By studying differences in standard errors, the random effects model is compared with a fixed effects model that does not account for distinctions between intra- and inter-event variability. Effects of local site conditions are included in the empirical relationships developed. The dependence on frequency of the various model parameters is also studied. Frequency-dependent attenuation coefficients for the proposed random effects models developed are summarized in tables to facilitate their use.  相似文献   

Reef parameterisation schemes with applications to tidal modelling     

Lance Bode  Luciano B. Mason  Jason H. Middleton 《Progress in Oceanography》1997,40(1-4)

A variety of analytical models is used to investigate the effects on tidal propagation of a barrier reef system. These models specify reef geometry by two parameters. They can accommodate cases where water flows over reefs, as well as through inter-reef gaps, and also incorporate quadratic bottom friction. Although based on a one-dimensional approach, adaptations of a solution by Huthnance are used to account for the additional blockage effects associated with two-dimensional flow patterns near reef barriers. The present work adopts the philosophy that only a numerical approach can cope with the wide variations in reef geometry that are encountered in areas such as the Great Barrier Reef (GBR) region of Australia. Moreover, since typical model grids cannot resolve inter-reef gaps and other features with sufficient accuracy, a parameterised approach is needed to accommodate the conflicting demands of reef geometry and an economically feasible model resolution. The formulation of the analytical models is such that they can be applied immediately to standard numerical algorithms. Numerical experiments for flow in a channel, with a reef barrier across its centre, are used to test the parameterisation schemes. Comparison of the results for parameterised reefs with those obtained using extremely fine grids, shows convincing evidence of the success of the schemes. A separate method for automatically generating reef parameters has simplified the task of applying the methodology to real reefal systems. A tidal model of the Southern GBR, a region which exhibits unusual tidal behaviour, but which also has ample field data available for model testing, is used to demonstrate the accuracy that can be attained with the parameterised approach. Although tides are considered specifically in the present work, the formulation should be applicable with equal ease to the many other significant classes of low frequency motions in the GBR.  相似文献   

The integration of South African fisheries into the global economy: Past,present and future     

David Crosoer  Lance van Sittert  Stefano Ponte 《Marine Policy》2006

The integration of the South African fisheries into the global economy has operated as a powerful constraint on post-apartheid fisheries reform. The shedding of South Africa's international pariah status and currency depreciation enhanced access to and competitiveness on global markets, sparking a demersal-led export boom, which has favoured incumbent producers. Increased exports have also allowed the post-apartheid state and nascent black capital to maximise their returns from the fisheries through cost recovery and share purchases. The protection and promotion of the fisheries’ “international competitiveness”, inter alia sought through “sustainable fishery” certification of the hake industry with the Maritime Stewardship Council (MSC), has in turn provided a cover-all for the refusal of populist redistribution demands and special treatment for black small capital.  相似文献   

Cyclic Loading Effects on the Creep and Dilation of Salt Rock     

Lance A. Roberts  Stuart A. Buchholz  Kirby D. Mellegard  Uwe Düsterloh 《Rock Mechanics and Rock Engineering》2015,48(6):2581-2590

  相似文献   

The Deposition and Chronology of Cenote T’isil: A Multiproxy Study of Human/Environment Interaction in the Northern Maya Lowlands of Southeast Mexico     

Lance Wollwage  Scott Fedick  Sergey Sedov  Elizabeth Solleiro‐Rebolledo 《Geoarchaeology》2012,27(5):441-456

Cenotes (natural wells or sinkholes) comprise the most common landscape features in the northern Maya Lowlands of the Yucatán Peninsula, México. Detailed study of dated soil‐sedimentary sequences, recovered from a cenote at the archaeological site T’isil and nearby wetlands, allows a partial reconstruction of environmental variability at the site for the last 2000 years. Biogenic calcite sedimentation and Calcisol development occur during three intervals of increased inundation in cenote and wetland environments, ca. A.D. 300, A.D. 1000, and A.D. 1300. Periods of increased inundation in the cenote and wetlands correlate with wetter climatic intervals, and periods of Maya occupation at sites in the Yalahau region. Evidence for Maya modification of the cenote environment may relate to regional wetland agricultural practices.  相似文献