Point-to-curve raytracing by algebraic rasterization     

T.J. Moser 《Studia Geophysica et Geodaetica》2006,50(3):399-416

Boundary-value raytracing problems can be concatenated to a smooth one-parameter family of problems, that can be solved by continuation. This has been the purpose of point-to-curve raytracing. A global approach, based on algorithms taken from computer graphics (algebraic rasterization of implicit curves), has several advantages. Subject to relatively mild assumptions-Lipschitz continuity of the emergence point as function of initial parameters-all solution branches are found, there are no problems with initialization, bifurcation, or closed loop solutions. The algebraic rasterization benefits to boundary value raytracing problems in a wide range of applications: shot-to-profile shooting, VSP raytracing, normal raytracing, and more. The algorithm is sufficiently robust to continue even beyond points where the Lipschitz continuity does not apply, such as faults.  相似文献   

19th century eutrophication of a remote boreal lake: a consequence of climate warming?     

K.A. Moser  J.P. Smol  G.M. MacDonald  C.P.S. Larsen 《Journal of Paleolimnology》2002,28(2):269-281

To investigate the response of a remote boreal lake to recent climate warming, a 200-year varved sediment record from Rainbow Lake A (RLA), located in the northern boreal forest of Wood Buffalo National Park, straddling northern Alberta and the Northwest Territories (Canada), was investigated using diatom assemblages and biogenic silica concentrations. Diatom community composition, trends in diatom-inferred total phosphorus (TP) and biogenic silica levels all showed significant changes beginning between circa 1830 and 1840, coincident with the onset of increasingly warm June/July temperatures in northern Canada. We evaluated several hypotheses which may have caused these nutrient changes, including local anthropogenic disturbances, forest fires, increased atmospheric deposition of nutrients or pollen, and internal sources of nutrient regeneration. We concluded that TP is likely increasing as a result of enhanced internal cycling of phosphorus due to either increased thermal stratification in response to warmer summer temperatures and/or decreased meromictic stability. The results presented here, in combination with other recent paleolimnological research in northern latitude regions, suggest widespread aquatic response to increasing temperatures beginning in the 19th century.  相似文献   

Microbial hydrocarbon gases in the Witwatersrand Basin, South Africa: Implications for the deep biosphere     

J.A Ward  D.P Moser  G Lacrampe-Couloume  M Davidson  B Mislowack  T.C Onstott 《Geochimica et cosmochimica acta》2004,68(15):3239-3250

In this study, compositions and δ¹³C and δ²H isotopic values of hydrocarbon gases from 5 mines in the Witwatersrand basin, South Africa, support the widespread occurrence of microbially produced methane in millions of years-old fissure waters. The presence of microbial methane is, to a large extent, controlled by the geologic formations in which the gases are found. Samples from the Witwatersand Supergroup have the largest microbial component based on δ¹³C and δ²H signatures and CH₄/C₂+ values. Based on mixing between a microbial CH₄ component and a more ¹³C-enriched and ²H-depleted C₂+-rich end member, conservative estimates of the % contribution of microbial CH₄ to the gas samples range from >90% microbial CH₄ at Beatrix, Masimong, and Merriespruit, to between 5 and 80% microbial CH₄ at Evander, and <18% microbial CH₄ at Kloof. The Witwatersrand basin’s history of thermal alteration of organic-rich ancient sedimentary units suggests a thermogenic origin for this ¹³C-enriched end member. Alternatively, the potential for an abiogenic origin similar to hydrocarbon gases produced by water-rock interaction at other Precambrian Shield mines is discussed. Microbial methane is predominantly found in paleo-meteoric fissure waters with δ¹⁸O and δ²H values that fall on the meteoric waterline, and have temperatures between 30 to 40°C. In contrast, fissure waters with a larger component of nonmicrobial hydrocarbon gases show a trend towards more enriched δ¹⁸O and δ²H values that fall well above the meteoric waterline, and temperatures of 45 to 60°C. The enrichment in ¹⁸O and ²H in these samples, and their high salinity, are similar to the isotopic and compositional characteristics of saline groundwaters and brines produced by water-rock interaction at Precambrian Shield sites elsewhere. The reported 100 Ma ages of fissure waters from the Witwatersrand and Ventersdorp formations suggest that these microbial hydrocarbon gases are the product of in situ methanogenic communities in the deep subsurface of the Witswaterand basin. Small subunit ribosomal RNA genes were amplified using archaeal-specific primer sets from DNA extracts derived from several of these waters. Fissure waters with a high proportion of microbial methane also contained sequences resembling those of known methanogens.  相似文献   

Kinetics of crystallization: example of micro-crystallization in basalt lava   总被引：1，自引：0，他引：1  

Dorothee J. Burkhard 《Contributions to Mineralogy and Petrology》2002,142(6):724-737

The kinetics of crystallization of basalt glass from Kilauea, Hawaii, was investigated to derive time and temperature dependence of growth rates, and to relate these results to crystallization characteristics that develop during in-place cooling of lava and isothermal re-heating in the lab. The choice of temperatures of re-heating was based on observations that pyroxene and Fe-Ti oxide production starts at about 850 °C and plagioclase above 920 °C. Crystallization parameters were determined by the crystal size distribution method (CSD), which allows one to derive growth (G) and nucleation (J) rates, if the residence time within the temperature interval of crystallization is known. For the in-place cooled lava, the residence time was determined from cooling rates that could be derived from literature data of temperature measurements in the upper 2 cm of lava lobes. Re-heating of basalt glass as a function of time shows a linear relationship between log G and log (time): % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabiabaaGcbaGaciiBaiaac+ % gacaGGNbGaam4raiabg2da9iabgkHiTiaadggaciGGSbGaai4Baiaa % cEgacaWG0bGaeyOeI0Iaam4AamaaBaaaleaacaaIXaaabeaaaaa!42ED! logG = - alogt - k₁\log G = - a\log t - k_1 . This observation was possible because the time scale of crystallization was similar to the observational time scale, a condition usually not given for cooling processes. The time dependence of G is shown to correspond to a decrease in G (and J) from the original surface-air interface to the interior of the lava: a change that occurs concomitant with an increase in crystal size and number density. Hence, it is the time dependence of G that explains the hitherto well-observed relationship with cooling rate along a temperature gradient in magmatic bodies. Moreover, the log-linear relationship between time and growth rate is suggested to describe heterogeneous nucleation and growth, which is independent of the process, i.e. cooling or metamorphism. Isothermal re-heating extinguishes the high growth rate signatures of cooling. Temperature dependence of growth rates, carried out at 24 h, shows minimum temperatures of 900-950 °C, which, because of the time dependence of growth, refers to the nucleation and crystallization maximum, and is in agreement with results from differential scanning calorimetry.  相似文献   

Geotechnical aspects of soil slips in Alpine regions     

M. Moser  F. Hohensinn 《Engineering Geology》1983,19(3):185-211

Slope movements are due to many different causes. Numerous investigations carried out during the last ten years have led to the supposition that almost all slope movements, and particularly those occurring in soils, are conditioned by a significant combination of factors.For the Alpine regions, quantity, duration and kind of precipitation have to be considered as direct mechanical causes. Combined with such contributing factors as geological and soil-mechanical properties, aspect, vegetation, slope inclination and slope morphology, they will determine the type, dimensions and process of slope movements.The detailed investigation of 140 slope movements in slightly cohesive soils show that the process of movement is represented by sliding and flow events. In particular it was found out that shallow scars with planar slides predominate so that the supposition of an infinite slope model for slope stability appears to be justified. In many cases debris flows and debris avalanches continued downslope of the source area of the scars.  相似文献   

Making Alzheimer’s disease matter. Enacting, interfering and doing politics of nature     

Ingunn Moser 《Geoforum》2008,39(1):98-110

This article contributes to recent discussions about the politics of nature by exploring how Alzheimer’s disease is being shaped as a ‘matter of concern’. Drawing on work on differences in medicine from science and technology studies, and from the geographies of naturecultures, it explores the ‘mattering’ of this disease in a number of locations including: an international Alzheimer’s patients’ movement; a medical textbook; laboratory science; daily care practice; an advertisement for anti-dementia medication; general practice; parliamentary politics; and a conference on dementia. It explores how these locations interfere and co-exist with one another and argues against the ‘science centrism’ of science and technology studies which contributes to the dominance of science and medicine by granting these analytical privilege. The same problem is posed in the recent STS turn from science to politics - the danger is that politics is similarly privileged.  相似文献   

The impact of errors in polar motion and nutation on UT1 determinations from VLBI Intensive observations   总被引：2，自引：2，他引：0  

Axel Nothnagel  Dorothee Schnell 《Journal of Geodesy》2008,82(12):863-869

The earth’s phase of rotation, expressed as Universal Time UT1, is the most variable component of the earth’s rotation. Continuous monitoring of this quantity is realised through daily single-baseline VLBI observations which are interleaved with VLBI network observations. The accuracy of these single-baseline observations is established mainly through statistically determined standard deviations of the adjustment process although the results of these measurements are prone to systematic errors. The two major effects are caused by inaccuracies in the polar motion and nutation angles introduced as a priori values which propagate into the UT1 results. In this paper, we analyse the transfer of these components into UT1 depending on the two VLBI baselines being used for short duration UT1 monitoring. We develop transfer functions of the errors in polar motion and nutation into the UT1 estimates. Maximum values reach 30 [μs per milliarcsecond] which is quite large considering that observations of nutation offsets w.r.t. the state-of-the-art nutation model show deviations of as much as one milliarcsecond.  相似文献   

Forest city,Malaysia, and Chinese expansionism   总被引：2，自引：2，他引：0  

Sarah Moser 《Urban geography》2018,39(6):935-943

Over the past decade, an acceleration of Chinese state and private investment in urban infrastructure and real estate has transformed many skylines around the world. In 2014, a private Chinese company in collaboration with Malaysia’s Sultan of Johor state started construction on Forest City, a private gated luxury mega-development for 700,000 people on four reclaimed islands in the narrow strait that separates Malaysia and Singapore. While the official material for Forest City claims it is for all nationalities, it is being marketed predominantly in China and to ethnic Chinese communities in Southeast Asia. This paper investigates the broader implications for Singapore, Malaysia, and the region and makes two key arguments. First, I suggest Forest City is more than a Chinese-financed real estate development, rather it constitutes a Chinese neocolonial outpost to which Malaysia has largely conceded sovereignty and advances China’s expansionist agenda. Second, Forest City challenges current geopolitical dynamics and threatens to undermine Malaysia’s relationships with neighbouring countries.  相似文献   

The relationship between the landslide frequency and hydrogeological aspects: a case study from a hilly region in Northern Bavaria (Germany)     

Johannes Wiedenmann  Joachim Rohn  Michael Moser 《Environmental Earth Sciences》2016,75(7):609

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Calcium Isotopic Composition of Various Reference Materials and Seawater   总被引：1，自引：0，他引：1  

Dorothee Hippler  Anne-Désirée Schmitt  Nikolaus Gussone  Alexander Heuser  Peter Stille  Anton Eisenhauer  Thomas F. Nägler 《Geostandards and Geoanalytical Research》2003,27(1):13-19

A compilation of δ^44/40Ca (δ^44/40Ca) data sets of different calcium reference materials is presented, based on measurements in three different laboratories (Institute of Geological Sciences, Bern; Centre de Géochimie de la Surface, Strasbourg; GEOMAR, Kiel) to support the establishment of a calcium isotope reference standard. Samples include a series of international and internal Ca reference materials, including NIST SRM 915a, seawater, two calcium carbonates and a CaF₂ reference sample. The deviations in δ^44/40Ca for selected pairs of reference samples have been defined and are consistent within statistical uncertainties in all three laboratories. Emphasis has been placed on characterising both NIST SRM 915a as an internationally available high purity Ca reference sample and seawater as representative of an important and widely available geological reservoir. The difference between δ^44/40Ca of NIST SRM 915a and seawater is defined as -1.88 O.O4%o (δ^44/42Ca_{NISTSRM915a/Sw}= -0.94 0.07%o). The conversion of values referenced to NIST SRM 915a to seawater can be described by the simplified equation δ^44/40Ca_Sa/Sw=δ^44/40Ca_{Sa/NIST SRM 915a} - 1.88 (δ^44/42Ca_Sa/Sw=δ^44/42Ca_{Sa/NIST SRM 915a} - 0.94). We propose the use of NIST SRM 915a as general Ca isotope reference standard, with seawater being defined as the major reservoir with respect to oceanographic studies.  相似文献