Modeling of centrifugal filtration in unsaturated deformable porous media     

Jacob Bear 《Advances in water resources》1984,7(4):150-167

  相似文献   

The occurrence and distribution of Mo and molybdenite in unaltered peralkaline rhyolites from Pantelleria,Italy   总被引：4，自引：0，他引：4  

Jacob B. Lowenstern  Gail A. Mahood  Richard L. Hervig  Joel Sparks 《Contributions to Mineralogy and Petrology》1993,114(1):119-129

Small hexagonal and triangular platelets of molybdenite (MoS₂), 5 to 25 m in diameter, were identified in phenocrysts and matrix glass of unaltered felsic volcanic rocks from Pantelleria, Italy. The MoS₂ occurs commonly in pantellerites (peralkaline rhyolites), rarely in pantelleritic trachytes, and never in trachytes. The occurrence of euhedral MoS₂ platelets in all phenocryst phases, in matrix glass, and even in some melt inclusions indicates that MoS₂ precipitated directly from the peralkaline melt. Despite MoS₂ saturation, the melt (glass) contains greater than 95% of the Mo in Pantellerian rocks: X-ray fluorescence analyses of 20 whole rocks and separated glasses show that whole rocks consistently contain less Mo than corresponding matrix glasses, the differences being in proportion to phenocryst abundances. The Mo contents increase with differentiation from trachytes (2–12 ppm) to pantellerites (15–25 ppm) and correlate positively with incompatible elements such as Th, Y, and Nb. The Mo concentrations, as determined by secondary ion mass spectrometry, are essentially the same in matrix glasses and melt inclusions, showing that Mo did not partition strongly into a volatile fluid phase during outgassing. The high Mo contents of the pantellerites (relative to metaluminous magmas with 1–5 ppm) may be due to several factors: (1) the enhanced stability of highly charged cations (such as Mo⁶⁺, U⁴⁺, and Zr⁴⁺) in peralkaline melts; (2) the rarity of Fe-Ti oxides and litanite into which Mo might normally partition; (3) reduced volatility of Mo in low fO₂, H₂O-poor (1–2 wt%) peralkaline magmas. Geochemical modeling indicates that the precipitation of MoS₂ can be explained simply by the drop in temperature during magmatic differentiation. The occurrence of MoS₂ in pantellerites may result from their high Mo concentrations and low redox state (Ni/NiO=-2.5) relative to metaluminous magmas, causing them to reach MoS₂ saturation at magmatic temperatures. The apparent absence of MoS₂ microphenocrysts in more oxidized, metaluminous rhyolites may indicate that Mo is dissolved primarily as a hexavalent ion in those magmas.  相似文献   

Model employers and model cities?: Bangalore’s public sector and the rise of the neoliberal city     

H. Jacob Carlson 《Urban geography》2018,39(5):726-745

Bangalore is held up as a model for how cities, particularly in the global south, should develop in the globalized information age, in which entrepreneurs with new access to international capital fuel service-sector-driven development. Expanding market forces cultivate cities of skilled middle-class workers whose increased consumption generates broad developmental benefits. Now known as the “Silicon Valley of India,” Bangalore was previously the capital of India’s public sector enterprises (PSEs), which laid important groundwork for the city of today, including the IT sector. I show how, by providing access to homeownership along with high wages and benefits tied to secure employment, Bangalore’s PSEs created the foundation for the city today and its middle-class character. The skilled workforce that PSEs created helped the IT sector emerge in the city. By examining this erased history, we see the role of the state in development projects, and consider alternative models for urban change.  相似文献   

ENVIRONMENTAL DEGRADATION IN BRAZILIAN AMAZONIA: PERSPECTIVES IN US NEWS MEDIA*     

Jacob Bendix  Carol M. Liebler 《The Professional geographer》1991,43(4):474-485

While news media play a major role in shaping public opinion and government policy, existing literature suggests that coverage of both the third world and environmental issues is superficial and crisis-oriented. This study uses the example of Amazonian deforestation to explore the quantity and content of coverage in influential American newspapers. We found that coverage included a wide range of (sometimes) contradictory theories regarding the causes of deforestation, and that the amount, but not the nature, of the coverage changed in response to a “crisis.”  相似文献   

Multisite campaign on the open cluster M67 – III. δ Scuti pulsations in the blue stragglers     

H. Bruntt  D. Stello  J. C. Suárez  T. Arentoft  T. R. Bedding  M. Y. Bouzid  Z. Csubry  T. H. Dall  Z. E. Dind  S. Frandsen  R. L. Gilliland  A. P. Jacob  H. R. Jensen  Y. B. Kang  S.-L. Kim  L. L. Kiss  H. Kjeldsen  J.-R. Koo  J.-A. Lee  C.-U. Lee  J. Nuspl  C. Sterken  R. Szabó 《Monthly notices of the Royal Astronomical Society》2007,378(4):1371-1384

  相似文献   

The influence of atmospheric dust on limb darkening of M-type Mira variables     

T.R. Bedding †  A.P. Jacob  M. Scholz †  P.R. Wood 《Monthly notices of the Royal Astronomical Society》2001,325(4):1487-1496

We explore the occurrence of dust in M-type Mira atmospheres and its effect on limb darkening under schematic assumptions about dust temperatures and dust particle properties. Dust particles that are thermodynamically coupled to the surrounding gas may form and may affect limb darkening, though only by very little in infrared continuum bandpasses. Dust particles that assume the equilibrium temperature given by the mean intensity of the radiation field only form under rare circumstances. Unexpectedly large or wavelength-dependent infrared continuum radii observed by interferometry are unlikely to be caused by atmospheric dust, except possibly near 1 μm; however, radius measurements may be significantly affected by molecular band contamination.  相似文献   

Improved methods for isolating and validating indigenous biomarkers in Precambrian rocks   总被引：1，自引：0，他引：1  

Laura S. Sherman  Jacob R. Waldbauer  Roger E. Summons   《Organic Geochemistry》2007,38(12):1987-2000

Hydrocarbon biomarkers in highly mature Precambrian rocks have the potential to provide important information about the diversity ecology, and evolution of early life, but studying them presents special analytical challenges. Extractable hydrocarbons are present in Archean and most Paleoproterozoic sedimentary rocks in such trace concentration that even slight contamination from petroleum-derived materials in situ or during drilling, storage, sampling, handling and laboratory analysis would compromise the results and, thereby, any consequent inferences. Here we report protocols that we have developed for the analysis of cores from several recently completed deep-time scientific drilling initiatives. By paying special attention to cutting, cleaning, crushing and extraction, it is possible to significantly reduce laboratory blanks to acceptable levels. When these methods are utilized, meaningful variations in the patterns of biomarkers over stratigraphic and lithologic boundaries provide compelling evidence for syngeneity.  相似文献   

Gradient in the climate change signal of European discharge predicted by a multi-model ensemble     

Stefan Hagemann  Daniela Jacob 《Climatic change》2007,81(1):309-327

In order to perform hydrological studies on the PRUDENCE regional climate model (RCM) simulations, a special focus was put on the discharge from large river catchments located in northern and central Europe. The discharge was simulated with a simplified land surface (SL) scheme and the Hydrological Discharge (HD) model. The daily fields of precipitation, 2 m temperature and evapotranspiration from the RCM simulations were used as forcing. Therefore the total catchment water balances are constrained by the hydrological cycle of the different RCMs. The validation of the simulated hydrological cycle from the control simulations shows that the multi-model ensemble mean is closer to the observations than each of the models, especially if different catchments and hydrological variables are considered. Therefore, the multi-model ensemble mean can be used to largely reduce the uncertainty that is introduced by a single RCM. This also provides more confidence in the future projections for the multi-model ensemble means. The scenario simulations predict a gradient in the climate change signal over Northern and Central Europe. Common features are the overall warming and the general increase of evapotranspiration. But while in the northern parts the warming will enhance the hydrological cycle leading to an increased discharge, the large warming, especially in the summer, will slow down the hydrological cycle caused by a drying in the central parts of Europe which is accompanied by a reduction of discharge. The comparison of the changes predicted by the multi-model ensemble mean to the changes predicted by the driving GCM indicates that the RCMs can compensate problems that a driving GCM may have with local scale processes or parameterizations.  相似文献   

X‐ray fluorescence measurements of the surface elemental composition of asteroid 433 Eros     

Larry R. Nittler  Richard D. Starr  Lucy Lim  Timothy J. Mccoy  Thomas H. Burbine  Robert C. Reedy  Jacob I. Trombka  Paul Gorenstein  Steven W. Squyres  William V. Boynton  Timothy P. Mcclanahan  Jesse S. Bhangoo  Pamela E. Clark  Mary Ellen Murphy  Rosemary Killen 《Meteoritics & planetary science》2001,36(12):1673-1695

Abstract— We report major element ratios determined for the S‐class asteroid 433 Eros using remote‐sensing x‐ray fluorescence spectroscopy with the near‐Earth asteroid rendezvous Shoemaker x‐ray spectrometer (XRS). Data analysis techniques and systematic errors are described in detail. Data acquired during five solar flares and during two extended “quiet Sun” periods are presented; these results sample a representative portion of the asteroid's surface. Although systematic uncertainties are potentially large, the most internally consistent and plausible interpretation of the data is that Eros has primitive Mg/Si, Al/Si, Ca/Si and Fe/Si ratios, closely similar to H or R chondrites. Global differentiation of the asteroid is ruled out. The S/Si ratio is much lower than that of chondrites, probably reflecting impact‐induced volatilization and/or photo‐ or ion‐induced sputtering of sulfur at the surface of the asteroid. An alternative explanation for the low S/Si ratio is that it reflects a limited degree of melting with loss of an FeS‐rich partial melt. Size‐sorting processes could lead to segregation of Fe‐Ni metal from silicates within the regolith of Eros; this could indicate that the Fe/Si ratios determined by the x‐ray spectrometer are not representative of the bulk Eros composition.  相似文献   

A multi-site campaign on the long period variable subdwarf b star PG 1627+017     

Suzanna Randall  Gilles Fontaine  Elizabeth Green  Dave Kilkenny  Lisa Crause  Oliver Cordes  Simon O’Toole  Lázló Kiss  Bi-Qing For  Pierre-Olivier Quirion 《Astrophysics and Space Science》2004,291(3-4):465-471

We report on the outcome of the first major multi-site campaign on a long-period variable subdwarf B star. The target PG 1627+017 was observed for a total of 334 h during April/May/June 2003 from the lynchpin observatory at Mt. Bigelow, Arizona, with important contributions coming from co-observations at SAAO, Calar Alto and Siding Spring. Preliminary analysis indicates the presence of 8–10 probable periods in the range ～4500 to ～8900 s with relative amplitudes between 0.1 and 0.5%;. The range over which the periods are found is in qualitative agreement with theoretical predictions and the number of periods found shows potential for an in-depth asteroseismological analysis. Multi-colour observations show that the relative amplitudes of pulsation are larger in the U-band than in the R, which again is in agreement with theory. However, more multi-colour observations are needed to be able to make statements at the quantitative level.  相似文献