The importance of interactions for mass loss from satellite galaxies in cold dark matter haloes     

Alexander Knebe  Chris Power  Stuart P. D. Gill  Brad K. Gibson 《Monthly notices of the Royal Astronomical Society》2006,368(2):741-750

We investigate the importance of interactions between dark matter substructures for the mass loss they suffer whilst orbiting within a sample of high-resolution galaxy cluster mass cold dark matter (CDM) haloes formed in cosmological N -body simulations. We have defined a quantitative measure that gauges the degree to which interactions are responsible for mass loss from substructures. This measure indicates that interactions are more prominent in younger systems when compared to older more relaxed systems. We show that this is due to the increased number of encounters a satellite experiences and a higher mass fraction in satellites. This is in spite of the uniformity in the distributions of relative distances and velocities of encounters between substructures within the different host systems in our sample.
Using a simple model to relate the net force felt by a single satellite to the mass loss it suffers, we show that interactions with other satellites account for ∼30 per cent of the total mass loss experienced over its lifetime. The relation between the age of the host and the importance of interactions increases the scatter about this mean value from ∼25 per cent for the oldest to ∼45 per cent for the youngest system we have studied. We conclude that satellite interactions play a vital role in the evolution of substructure in dark matter haloes and that a significant fraction of the tidally stripped material can be attributed to these interactions.  相似文献   

Thermal structure and CO distribution for the Venus mesosphere/lower thermosphere: 2001–2009 inferior conjunction sub-millimeter CO absorption line observations     

R. Todd Clancy  Brad J. Sandor  Gerald Moriarty-Schieven 《Icarus》2012,217(2):779-793

Sub-millimeter ¹²CO (346 GHz) and ¹³CO (330 GHz) line absorptions, formed in the mesosphere and lower thermosphere of Venus (70–120 km), have been mapped across the nightside Venus disk during 2001–2009 inferior conjunctions, employing the James Clerk Maxwell Telescope (JCMT). Radiative transfer analysis of these thermal line absorptions supports temperature and CO mixing profile retrievals, as well as Doppler wind fields (described in the companion paper, Clancy et al., 2012). Temporal sampling over the hourly, daily, weekly and interannual timescales was obtained over 2001–2009. On timescales inferred as several weeks, we observe changes between very distinctive CO and temperature nightside distributions. Retrieved nightside CO, temperature distributions for January 2006 and August 2007 observations display strong local time, latitudinal gradients consistent with early morning (2–3 am), low-to-mid latitude (0–40NS) peaks of 100–200% in CO and 20–30 K in temperature. The temperature increases are most pronounced above 100 km altitudes, whereas CO variations extend from 105 km (top altitude of retrieval) down to below 80 km in the mesosphere. In contrast, the 2004 and 2009 periods of observation display modest temperature (5–10 K) and CO (30–60%) increases, that are centered on antisolar (midnight) local times and equatorial latitudes. Doppler wind derived global (zonal and should be SSAS) circulations from the same data do not exhibit variations correlated with these CO, temperature short-term variations. However, large-scale residual wind fields not fit by the zonal, SSAS circulations are observed in concert with the strong temperature, CO gradients observed in 2006 and 2007 (Clancy et al., 2010). These short term variations in nightside CO, temperature distributions may also be related to observed nightside variations in O₂ airglow (Hueso, H., Sánchez-Lavega, A., Piccioni, G., Drossart, P., Gérard, J.C., Khatuntsev, I., Zasova, L., Migliorini, A. [2008]. J. Geophys. Res. 113, E00B02. doi:10.1029/2008JE003081) and upper mesospheric SO and SO₂ layers (Sandor, B.J., Clancy, R.T., Moriarty-Schieven, G.H., Mills, F.P. [2010]. Icarus 208, 49–60).The retrieved temperature profiles also exhibit 20 K long-term (2001–2009) variations in nightside (whole disk) average mesospheric (80–95 km) temperatures, similar to 1982–1991 variations identified in previous millimeter CO line observations (Clancy et al., 1991). Global average diurnal variations in lower thermospheric temperatures and mesospheric CO abundances decreased by a factor-of-two between 2000–2002 versus 2007–2009 periods of combined dayside and nightside observations. The infrequency and still limited temporal extent of the observations make it difficult to assign specific timescales to such longer term variations, which may be associated with longer term variations observed for cloud top SO₂ (Esposito, L.W., Bertaux, J.-L., Krasnopolsky, V., Moroz, V.I., Zasova, L.V. [1997]. Chemistry of lower atmosphere and clouds. In: Bougher, S.W., Hunten, D.M., Phillips, R.J. (Eds.), VENUS II, 1362pp) and mesospheric water vapor (Sandor, B.J., Clancy, R.T. [2005]. Icarus 177, 129–143) abundances.  相似文献   

Evolution of the winonaite parent body: Clues from silicate mineral trace element distributions     

Christine FLOSS  Ghislaine CROZAZ  Brad JOLLIFF  Gretchen BENEDIX  Shannon COLTON 《Meteoritics & planetary science》2008,43(4):657-674

Abstract— We have measured the trace element compositions of individual plagioclase, pyroxene, and olivine grains in 6 different winonaites that span the range of textures and mineralogies observed in these meteorites. Textural evidence in these meteorites, including the presence of a plagioclase/clinopyroxene‐rich lithology and coarse‐grained olivine lithologies, suggests that they may have experienced some silicate partial melting. However, trace element distributions in these lithologies do not show any clear signatures for such an event. Pyroxene trace element compositions do exhibit systematic trends, with abundances generally lowest in Pontlyfni and highest in Winona. The fact that the same trends are present for both incompatible and compatible trace elements suggests, however, that the systematics are more likely the result of equilibration of minerals with initially heterogeneous and distinct compositions, rather than partial melting of a compositionally homogeneous precursor. The winonaites have experienced brecciation and mixing of lithologies, followed by varying degrees of thermal metamorphism on their parent body. These factors probably account for the variable bulk rare earth element (REE) patterns noted for these meteorites and may have led to re‐equilibration of trace elements in different lithologies.  相似文献   

Titanite dates crystallization: Slow Pb diffusion during super‐solidus re‐equilibration     

Michael I. H. Hartnady  Christopher L. Kirkland  Chris Clark  Catherine V. Spaggiari  R. Hugh Smithies  Noreen J. Evans  Brad J. McDonald 《Journal of Metamorphic Geology》2019,37(6):823-838

Titanite can be found in rocks of wide compositional range, is reactive, growing or regrowing during metamorphic and hydrothermal events, and is generally amenable to U–Pb geochronology. Experimental evidence suggest that titanite has a closure temperature for Pb ranging from 550 to 650°C, and thus titanite dates are commonly interpreted as cooling ages. However, this view has been challenged in recent years by evidence from natural titanite which suggests the closure temperature may be significantly higher (up to 800°C). Here, we investigate titanite in an enclave of migmatitic gneiss included within a granite intrusion. The titanite crystals exhibit textural features characteristic of fluid‐mediated mass transfer processes on length scales of <100 µm. These textural features are associated with variation in both Pb concentrations and distinct U–Pb isotopic compositions. Zr‐in‐titanite thermometry indicates that modification of the titanite occurred at temperatures in excess of 840°C, in the presence of a high‐T silicate melt. The Pb concentration gradients preserved in these titanite crystals are used to determine the diffusivity of Pb in titanite under high‐T conditions. We estimate diffusivities ranging from 2 × 10^?22 to 5 × 10^?25 m²/s. These results are significantly lower than experimental data predict yet are consistent with other empirical data on natural titanites, suggesting that Pb diffusivity is similar to that of Sr. Thus our data challenge the wide‐held assumption that U–Pb titanite dates only reflect cooling ages.  相似文献   

QUANTIFYING AND MITIGATING FLOOD RISK IN RAPIDLY AGGRADING FLUVIAL SYSTEMS     

Brad R. HALL 《国际泥沙研究》1999,(2)

ILOWERGUADALUPERIVER,SANJOSECALIFORNIATheLowerGuadalupeRiverProjectAreadoesnothavetheabilitytoconveytheflowofthe100-yearfloodevent.LocatedbetweentheSanrranciscoBayandDowntownSanJose,theLowerGuadalupeRiverProjectareaissubjecttomanynaturalandman-inducedagentsandnaturalphysicalprocessesthataffectthehydraulicandsedimenttransportcharacteristicsoftheRiver.Themostsignificantagentsandprocessesincludethelocalgeology,regionalseismicity,tidalprocesses,pastsubsidenceintheregion,risings…  相似文献   

Ecohydrologic feedbacks controlling sizes of cypress wetlands in a patterned karst landscape     

Xiaoli Dong  A. Brad Murray  James B. Heffernan 《地球表面变化过程与地形》2019,44(5):1178-1191

Many landforms on Earth are profoundly influenced by biota. In particular, biota play a significant role in creating karst biogeomorphology, through biogenic CO₂ accelerating calcite weathering. In this study, we explore the ecohydrologic feedback mechanisms that have created isolated depressional wetlands on exposed limestone bedrock in South Florida – Big Cypress National Preserve –as a case study for karst biogeomorphic processes giving rise to regularly patterned landscapes. Specifically, we are interested in: (1) whether cypress depressions on the landscape have reached (or will reach) equilibrium size; (2) if so, what feedback mechanisms stabilize the size of depressions; and (3) what distal interactions among depressions give rise to the even distribution of depressions in the landscape. We hypothesize three feedback mechanisms controlling the evolution of depressions and build a numerical model to evaluate the relative importance of each mechanism. We show that a soil cover feedback (i.e. a smaller fraction of CO₂ reaches the bedrock surface for weathering as soil cover thickens) is the major feedback stabilizing depressions, followed by a biomass feedback (i.e. inhibited biomass growth with deepening standing water and extended inundation period as depressions expand in volume). Strong local positive feedback between the volume of depressions and rate of volume expansion and distal negative feedback between depressions competing for water likely lead to the regular patterning at the landscape scale. The individual depressions, however, are not yet in steady state but would be in ~0.2–0.4 million years. This represents the first study to demonstrate the decoupling of landscape-scale self-organization and the self-organization of its constituent agents. © 2018 John Wiley & Sons, Ltd.  相似文献   

Effectiveness of Monitored Natural Attenuation (MNA) as a Groundwater Remedy for Arsenic in Phosphatic Wastes     

Brad A. Bessinger  Remy J.-C. Hennet 《Ground Water Monitoring & Remediation》2019,39(4):52-68

A study was conducted to evaluate monitored natural attenuation (MNA) as a remedy for arsenic in groundwater at a former phosphate mining and manufacturing facility. The mineralogy, speciation, and lability of arsenic in phosphatic wastes present in soils were characterized using sequential extraction procedures, leaching experiments, batch adsorption tests, and microchemical speciation analysis. A PHREEQC-based reactive transport model was also parameterized using these laboratory results, and it was used to evaluate the importance of identified attenuation mechanisms on arsenic concentrations along a vertical flow path from a shallow, alluvial aquifer to the underlying Floridan aquifer. Arsenic was found to occur in several chemical forms in phosphatic wastes, including unstable sulfide minerals, adsorbed surface complexes, and relatively insoluble phosphate and oxide minerals. Most arsenic was associated with stable minerals. The reactive transport model predicted that historical leaching of solid-phase waste materials in soils would not have generated enough arsenic to explain the concentrations observed in downgradient groundwater; instead, the source of arsenic to groundwater was likely acidic and saline process water that infiltrated though unlined ponds and ditches during historical manufacturing operations. A key factor affecting the long-term effectiveness of natural attenuation of arsenic in groundwater is the occurrence and stability of iron oxyhydroxides in aquifer sediments. According to laboratory and reactive transport model results, sufficient levels were found to be present at the site to effectively limit arsenic migration at concentrations exceeding drinking water standards in the future in the Floridan aquifer. This study presents the geochemical evaluations that are needed to satisfy EPA guidelines on determining whether or not MNA is an acceptable remedy for a site. It specifically details the characterization and modeling that were used to demonstrate effectiveness at a site where MNA was ultimately selected as the remedy for arsenic in groundwater.  相似文献   

Recent shifts in coastline change and shoreline stabilization linked to storm climate change   总被引：1，自引：0，他引：1       下载免费PDF全文

Jennifer M. Johnson  Laura J. Moore  Kenneth Ells  A. Brad Murray  Peter N. Adams  Richard A. MacKenzie III  John M. Jaeger 《地球表面变化过程与地形》2015,40(5):569-585

Since cuspate coastlines are especially sensitive to changes in wave climate, they serve as potential indicators of initial responses to changing wave conditions. Previous work demonstrates that Cape Hatteras and Cape Lookout, North Carolina, which are largely unaffected by shoreline stabilization efforts, have become increasingly asymmetric over the past 30 years, consistent with model predictions for coastline response to increases in Atlantic Ocean summer wave heights and resulting changes in the distribution of wave‐approach angles. Historic and recent shoreline change observations for Cape Fear, North Carolina, and model simulations of coastline response to an increasingly asymmetric wave climate in the presence of beach nourishment, produce comparable differences in shoreline change rates in response to changes in wave climate. Results suggest that the effect of beach nourishment is to compensate for – and therefore to mask – natural responses to wave climate change that might otherwise be discernible in patterns of shoreline change alone. Therefore, this case study suggests that the effects of wave climate change on human‐modified coastlines may be detectable in the spatial and temporal patterns of shoreline stabilization activities. Similar analyses of cuspate features in areas where the change in wave climate is less pronounced (i.e. Fishing Point, Maryland/Virginia) and where local geology appears to exert control on coastline shape (i.e. Cape Canaveral, Florida), suggest that changes in shoreline configuration that may be arising from shifting wave climate are currently limited to sandy wave‐dominated coastlines where the change in wave climate has been most pronounced. However, if hurricane‐generated wave heights continue to increase, large‐scale shifts in patterns of erosion and accretion will likely extend beyond sensitive cuspate features as the larger‐scale coastline shape comes into equilibrium with changing wave conditions. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Quantifying the rate and depth dependence of bioturbation based on optically‐stimulated luminescence (OSL) dates and meteoric 10Be          下载免费PDF全文

Michelle O. Johnson  Simon M. Mudd  Brad Pillans  Nigel A. Spooner  L. Keith Fifield  Mike J. Kirkby  Manuel Gloor 《地球表面变化过程与地形》2014,39(9):1188-1196

Both the rate and the vertical distribution of soil disturbance modify soil properties such as porosity, particle size, chemical composition and age structure; all of which play an important role in a soil's biogeochemical functioning. Whereas rates of mixing have been previously quantified, the nature of bioturbation's depth dependence remains poorly constrained. Here we constrain, for the first time, the relationship between mixing rate and depth in a bioturbated soil in northeast Queensland, Australia using a novel method combining OSL (optically‐stimulated luminescence) ages and meteoric beryllium‐10 (¹⁰Be) inventories. We find that the best fit mixing rate decreases non‐linearly with increasing soil depth in this soil and the characteristic length scale of 0.28 m over which the mixing coefficient decays is comparable to reported rooting depth coefficients. In addition we show that estimates of surface mixing rates from OSL data are highly dependent on erosion rate and that erosion rate must be constrained if accurate mixing rates are to be quantified. We calculate surface diffusion‐like mixing coefficients of 1.8 × 10^?4 and 2.1 × 10^?4 m² yr^?1 for the studied soil for two different estimates of soil erosion. © 2014 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.  相似文献   

Comments on Rebuttal of M. Sagir     

Mufide Banar  Barbaros Murat Kose  Aysun Ozkan  Ilgın Poyraz Acar 《Environmental Geology》2009,58(5):1143-1144

This rebuttal was written in response to the rebuttal of the paper “choosing a municipal landfill site by analytic network process” published in 2007 by M. Sagir. This study was conducted as an application for the landfill site selection in the environmental engineering discipline. Since ANP was only the “instrument” used in our study, the details of this existing methodology were referenced, and not presented, due to page limitations and to match the content of the journal. Responses to M. Sagir’s comments are discussed within the body of this rebuttal.  相似文献