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Melt retention and segregation beneath mid-ocean ridges

NATURE 2001年第6831期410卷 920-923页

作者： Faul, UH Australian Natl Univ Res Sch Earth Sci Canberra ACT 0200 Australia

Geochemical models of melting at mid-ocean ridges-particularly those based on trace elements and uranium-decay-series isotopes-predict that melt segregates from the matrix at very low porosities(1-8), of order 0.1%. Some of these models also require that the melt ascends rapidly(3,5). But these predictions appear to conflict with seismic data obtained by the mantle electromagnetic and tomography (MELT) experiment(9). These data reveal, beneath the East Pacific Rise (at 17 degreesS), a region of low velocities several hundred kilometres wide, which is best explained by the presence of 1-2% melt, distributed on a grain scale in disk-shaped geometries(10). Here I show that these apparently contradictory constraints can be reconciled by taking into account the geometry and resulting permeability of the intergranular network of melt, together with the changing character of the melt as it ascends. A deep, volatile-rich melt with low viscosity and density is mobile at 0.1% porosity, but basaltic melt only becomes mobile at a porosity above 1%. While the volumetric contribution of the volatile-rich melt to the erupted basalts is small, the isotopic disequilibria (except for radium) generated by porous flow of this melt are preserved if melt transport is rapid at the onset of high-productivity melting. Also, because of incomplete extraction, some melt is retained in a broad zone, consistent with the MELT observations.

关键词： Oceans Geology computer based modeling Permeability

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The concepts of model in information systems engineering: a proposal for an ontology of models

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KNOWLEDGE ENGINEERING REVIEW 2009年第1期24卷 5-21页

作者： Sanchez, Diana M. Maria Cavero, Jose Marcos, Esperanza Rey Juan Carlos Univ Sch Comp Sci Engn Dept Comp Languages & Syst 2 Kybele Res Grp Madrid 28933 Spain

Modelling is one of the most frequent tasks in the area of information systems (ISs), with models such as schemata, ontologies, patterns and architectures forming the bases for their creation. Very often, however, the difference between these types of models is not clear and causes confusion and erratic use of the terms. The aim of tills paper is to clarify the concept of model through a Study of some of the more common ones used in ISs. Tills proposal is presented through an ontology, where we show how we conceptualize models according to their role in the development of an IS: the model understood as the representation of a domain or as a reality serving as an example.

关键词： Information systems computer based modeling Ontology Systems design

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Cloud resolving modeling of the ARM summer 1997 IOP: Model formulation, results, uncertainties, and sensitivities

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2003年第4期60卷 607-625页

作者： Khairoutdinov, MF Randall, DA Colorado State Univ Dept Atmospher Sci Ft Collins CO 80523 USA

A new three-dimensional cloud resolving model (CRM) has been developed to study the statistical properties of cumulus convection. The model was applied to simulate a 28-day evolution of clouds over the Atmospheric Radiation Measurement Program (ARM) Southern Great Plains site during the summer 1997 Intensive Observation Period. The model was forced by the large-scale advective tendencies and surface fluxes derived from the observations. The sensitivity of the results to the domain dimensionality and size, horizontal grid resolution, and parameterization of microphysics has been tested. In addition, the sensitivity to perturbed initial conditions has also been tested using a 20-member ensemble of runs. The model captures rather well the observed temporal evolution of the precipitable water and precipitation rate, although it severely underestimates the shaded cloud fraction possibly because of an inability to account for the lateral advection of clouds over the ARM site. The ensemble runs reveal that the uncertainty of the simulated precipitable water due to the fundamental uncertainty of the initial conditions can be as large as 25% of the mean values. Even though the precipitation rates averaged over the whole simulation period were virtually identical among the ensemble members, the timing uncertainty of the onset and reaching the precipitation maximum can be as long as one full day. Despite the predictability limitations, the mean simulation statistics are found to be almost insensitive to the uncertainty of the initial conditions. The overall effects of the third spatial dimension are found to be minor for simulated mean fields and scalar fluxes but are quite considerable for velocity and scalar variances. Neither changes in a rather wide range of the domain size nor the horizontal grid resolution have any significant impact on the simulations. Although a rather strong sensitivity of the mean hydrometeor profiles and, consequently, cloud fraction to the microphy

关键词： Clouds computer based modeling Climate change

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modeling of stress and narrow-width effects in shallow trench isolation

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SOLID STATE TECHNOLOGY 2010年第2期53卷 19-+页

作者： Borges, Ricardo Synopsys Inc Prod Mkt Silicon Engn Grp Mountain View CA 94043 USA

Shallow trench isolation (STI) is a key process component in CMOS technologies because it provides electrical isolation between transistors. Although its function is intended to be electrically passive, as device dimensions shrink, the influence of STI on the transistor characteristics becomes stronger. This article describes two such examples of interaction between STI and transistor performance. The first example examines the impact of STI on the threshold voltage of narrow-width transistors-the so-called narrow-width effect. The second example addresses a larger area by considering the stresses induced by STI on nearby transistors. Both effects can be accurately simulated with TCAD, allowing technologists to optimize the process to account for and mitigate the impact of these effects. Compact modeling approaches to account for the effect in design flows are also described.

关键词： CMOS Semiconductor research computer based modeling Transistors computer aided design--CAD Stress analysis

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Sensitivity of age-of-air calculations to the choice of advection scheme

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2000年第19期57卷 3185-3201页

作者： Eluszkiewicz, J Hemler, RS Mahlman, JD Bruhwiler, L Takacs, LL Atmospher & Environm Res Inc Cambridge MA 02139 USA NOAA Geophys Fluid Dynam Lab Princeton NJ USA NOAA Climate Monitoring & Diagnost Lab Boulder CO 80303 USA NASA Goddard Space Flight Ctr Data Assimilat Off Greenbelt MD 20771 USA

The age of air has recently emerged as a diagnostic of atmospheric transport unaffected by chemical parameterizations, and the features in the age distributions computed in models have been interpreted in terms of the models' large-scale circulation field. This study shows, however, that in addition to the simulated large-scale circulation, three-dimensional age calculations can also be affected by the choice of advection scheme employed in solving the tracer continuity equation. Specifically, using the 3.0 degrees latitude x 3.6 degrees longitude and 40 vertical level version of the Geophysical Fluid Dynamics Laboratory SKYHI GCM and six online transport schemes ranging from Eulerian through semi-Lagrangian to fully Lagrangian, it will be demonstrated that the oldest ages are obtained using the nondiffusive centered-difference schemes while the youngest ages are computed with a semi-Lagrangian transport (SLT) scheme. The centered-difference schemes are capable of producing ages older than 10 years in the mesosphere, thus eliminating the "young bias" found in previous age-of-air calculations. At this stage, only limited intuitive explanations can be advanced for this sensitivity of age-of-air calculations to the choice of advection scheme. In particular, age distributions computed online with the National Center for Atmospheric Research Community Climate Model (MACCM3) using different Varieties of the SLT scheme are substantially older than the SKYHI SLT distribution. The different varieties, including a noninterpolating-in-the-vertical version (which is essentially centered-difference in the vertical), also produce a narrower range of age distributions than the suite of advection schemes employed in the SKYHI model. While additional MACCM3 experiments with a wider range of schemes would be necessary to provide more definitive insights, the older and less variable MACCM3 age distributions can plausibly be interpreted as being due to the semi-implicit semi-Lagrangian

关键词： Atmosphere Simulation computer based modeling

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Increasing risk of great floods in a changing climate

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NATURE 2002年第6871期415卷 514-517页

作者： Milly, PCD Wetherald, RT Dunne, KA Delworth, TL US Geol Survey GFDL NOAA Princeton NJ 08542 USA NOAA Geophys Fluid Dynam Lab Princeton NJ 08542 USA

Radiative effects of anthropogenic changes in atmospheric composition are expected to cause climate changes, in particular an intensification of the global water cycle(1) with a consequent increase in flood risk(2). But the detection of anthropogenically forced changes in flooding is difficult because of the substantial natural variability(3);the dependence of streamflow trends on flow regime(4,5) further complicates the issue. Here we investigate the changes in risk of great floods-that is, floods with discharges exceeding 100-year levels from basins larger than 200,000 km(2)-using both streamflow measurements and numerical simulations of the anthropogenic climate change associated with greenhouse gases and direct radiative effects of sulphate aerosols(6). We find that the frequency of great floods increased substantially during the twentieth century. The recent emergence of a statistically significant positive trend in risk of great floods is consistent with results from the climate model, and the model suggests that the trend will continue.

关键词： Floods Climate change computer based modeling Forecasting

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Measurement of microenvironmental ozone concentrations in Durham, North Carolina, using a 2B Technologies 205 Federal Equivalent Method monitor and an interference-free 2B Technologies 211 monitor

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JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION 2014年第3期64卷 360-371页

作者： Johnson, Ted Capel, Jim Ollison, Will TRJ Environm Inc Chapel Hill NC 27514 USA Amer Petr Inst Washington DC USA

During August and September of 2012, researchers conducted a microenvironmental (ME) monitoring study in Durham, North Carolina, using two 2B Technologies O-3 monitors: a dual-beam model 205 Federal Equivalent Method (FEM) 254 nm photometer and a newly developed model 211 interference-free dual-beam photometer. The two monitors were mounted in a wheeled, fan-cooled suitcase together with a battery, a disposable N2O cartridge for the model 211 monitor, and filtered sample lines. A scripted technician made paired O-3 measurements in a variety of MEs within 2 miles of a fixed-site FEM O-3 photometer at the Durham National Guard Armory. The ratio of the 211 to Armory O-3 concentrations tended to be lowest (<0.3) for 45 indoor MEs and highest (>0.8) for 104 outdoor MEs. The mean values of the ratio for in-vehicle MEs tended to fall between 0.2 and 0.7the mean for all 27 in-car tests was 0.3. The ratio values for indoor MEs tended to be higher when the enclosure was well ventilated. The outdoor ratios tended to be lower when the measurement was made downwind of nearby roadways, likely due to exhaust NO. The in-vehicle ratios tended to be larger with windows open than closed;the smallest occurred with closed windows, active air conditioning, and vent recirculation. The 205-211 measurement differences were generally small, with 94% of the 176 sample differences below 5 ppb. Five differences were above 10 ppb with the largest values (173.9 and 63.6 ppb) occurring inside a violin repair shop. Roadway proximity tended to increase the differences for outdoor locations. The largest in-vehicle difference (6 ppb) occurred at a convenience store service station. As addressed in regulatory models, such differences may reduce estimated population O-3 exposure by 30-50% in indoor and in-vehicle MEs where individuals spend more than 80% of their time. Implications: computer models used to estimate exposures of human populationssuch as the Air Pollution

关键词： Ozone Outdoor air quality Environmental monitoring computer based modeling Indoor air quality

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Foamed cement solves producing, injection problems

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OIL & GAS JOURNAL 1998年第2期96卷 41-45页

作者： Creel, P Crook, R Halliburton Energy Serv Inc Duncan OK 73536 USA

Three production and injection examples from the Permian basin demonstrate how advanced technology identifies problems that can be treated with foamed cement. The process involves computer simulation (modeling), log analysis, and tracer surveys. Operators of these wells identified conformance-control problems caused by fractures, interwell communication, and flooding fluid breakthrough. After circulating the open hole clean, the operator noted that the open hole section had been totally consolidated with its caliper being bit-sized. The well was placed on injection and began taking fluid at the required daily injection rate below fracture pressure. The final injection test was after follow-up perforating gained entry into selected portions of the open hole.

关键词： Oil wells Drilling Studies Technological change Cement computer based modeling Petroleum production Technology Offshore oil wells

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Precise inhibition is essential for microsecond interaural time difference coding

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NATURE 2002年第6888期417卷 543-547页

作者： Brand, A Behrend, O Marquardt, T McAlpine, D Grothe, B Max Planck Inst Neurobiol D-82152 Martinsried Germany UCL Dept Physiol London WC1E 6BT England

Microsecond differences in the arrival time of a sound at the two ears (interaural time differences, ITDs) are the main cue for localizing low-frequency sounds in space. Traditionally, ITDs are thought to be encoded by an array of coincidence-detector neurons, receiving excitatory inputs from the two ears via axons of variable length ('delay lines'), to create a topographic map of azimuthal auditory space(1,2). Compelling evidence for the existence of such a map in the mammalian ITD detector, the medial superior olive (MSO), however, is lacking. Equally puzzling is the role of a-temporally very precise(3)-glycine-mediated inhibitory input to MSO neurons. Using in vivo recordings from the MSO of the Mongolian gerbil, we found the responses of ITD-sensitive neurons to be inconsistent with the idea of a topographic map of auditory space. Moreover, local application of glycine and its antagonist strychnine by iontophoresis (through glass pipette electrodes, by means of an electric current) revealed that precisely timed glycine-controlled inhibition is a critical part of the mechanism by which the physiologically relevant range of ITDs is encoded in the MSO. A computer model, simulating the response of a coincidence-detector neuron with bilateral excitatory inputs and a temporally precise contralateral inhibitory input, supports this conclusion.

关键词： Sound Neurology Neurons Rodents Simulation computer based modeling

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Tropospheric aerosol optical thickness from the GOCART model and comparisons with satellite and Sun photometer measurements

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2002年第3期59卷 461-483页

作者： Chin, M Ginoux, P Kinne, S Torres, O Holben, BN Duncan, BN Martin, RV Logan, JA Higurashi, A Nakajima, T NASA Goddard Space Flight Ctr Greenbelt MD 20771 USA Georgia Inst Technol Sch Earth & Atmospher Sci Atlanta GA 30332 USA Univ Maryland Baltimore Cty JCET Baltimore MD USA Harvard Univ Dept Earth & Planetary Sci Cambridge MA 02138 USA Natl Inst Environm Studies Tsukuba Ibaraki Japan Univ Tokyo Ctr Climate Syst Res Tokyo Japan

The Georgia Institute of Technology-Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model is used to simulate the aerosol optical thickness tau for major types of tropospheric aerosols including sulfate, dust, organic carbon (OC), black carbon (BC), and sea salt. The GOCART model uses a dust emission algorithm that quantifies the dust source as a function of the degree of topographic depression, and a biomass burning emission source that includes seasonal and interannual variability based on satellite observations. Results presented here show that on global average, dust aerosol has the highest tau at 500 nm (0.051), followed by sulfate (0.040), sea salt (0.027), OC (0.017), and BC (0.007). There are large geographical and seasonal variations of tau, controlled mainly by emission, transport, and hygroscopic properties of aerosols. The model calculated total taus at 500 nm have been compared with the satellite retrieval products from the Total Ozone Mapping Spectrometer (TOMS) over both land and ocean and from the Advanced Very High Resolution Radiometer (AVHRR) over the ocean. The model reproduces most of the prominent features in the satellite data, with an overall agreement within a factor of 2 over the aerosol source areas and outflow regions. While there are clear differences among the satellite products, a major discrepancy between the model and the satellite data is that the model shows a stronger variation of tau from source to remote regions. Quantitative comparison of model and satellite data is still difficult, due to the large uncertainties involved in deriving the tau values by both the model and satellite retrieval, and by the inconsistency in physical and optical parameters used between the model and the satellite retrieval. The comparison of monthly averaged model results with the sun photometer network [Aerosol Robotics Network (AERONET)] measurements shows that the model reproduces the seasonal variations at most of the sites

关键词： Aerosols Atmosphere computer based modeling Climate change

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