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251.
Jessica K Graybill 《Area》2007,39(1):6-19
Environmental studies conducted worldwide often overlook the knowledge traditions of the locales where they are conducted. Addressing this issue, I investigated the geographic journal literature of late Soviet (1980–1989) and post-Soviet (1990–2003) Russia. Notable trends are increasing criticism of environmental and resource management in Russia and a (re)turn to pre-socialist Russian theorizations of society–nature interactions. Specifically, the noösphere, ethnogenesis and geosystems are trends in the literature that signify how Russian geographers (re)construct environmental knowledge. For non-Russian geographers working in Russia, awareness of these trends situates place-based knowledge relative to multiple cultures (ethnic, scientific) and time periods, promoting cross-cultural understanding of different traditions of geographic inquiry. 相似文献
252.
We have experimentally studied the process of bubble coalescence in rhyolite and phonolite melts of natural composition. The experiments involved decompression of water-saturated melts equilibrated at pressures and temperatures from 100 to 150 MPa and 775 to 840 °C in vertically oriented, rapid-quench capable, cold seal pressure vessels. One type of experiments (rhyolite MCR-100, 120, 150 and phonolite LSP-120 series') approximates a “static” bubble coalescence case, where we held the decompressed samples for ∼5 seconds to 4320 minutes (3 days) before quenching. The second type (rhyolite LPC-100 series) replicates an “expanding” bubble coalescence environment, where we continually decompressed the experiments at a rate of 0.5 MPa/s, examining samples quenched at ending pressures between 10 and 80 MPa. Our “static” case (MCR-100, 120, and 150, and LSP-120) results show significant increases in the modal bubble sizes and in the sizes of the largest bubbles, corresponding to measurable broadening in the size distributions. Their bubble number densities (NV) decrease as a function of hold time at their final pressures (PF), and can be fit well by power law functions. Our “expanding” case experiments (LPC-100) show a significant drop in NV during the duration of the experiments that can be fit by an exponential equation as NV vs. either time or PF. Average estimates of bulk coalescence rates indicate a ∼1 order of magnitude drop in NV for “static” case rhyolites in a 2-3 day period, and ∼2 orders of magnitude for phonolites within a 3 day period. Despite a ∼2 order of magnitude difference in viscosity, coalescene in the phonolite is only slightly faster than the rhyolite. The “expanding” case experiments show a ∼1 order of magnitude drop in NV over 180 seconds. Thus, NV's decrease 4 orders of magnitude faster in expanding vs. static bubbly rhyolite melts. Our results imply that significant bubble coalescence can occur in rhyolite magmas at relatively fast (∼20 m/s) ascent rates in the conduit. Thus, bubble interconnectivity, leading to high permeability, is possible during ascent. Bubble coalescence may occur during second boiling in magma bodies that are stalled in the crust. The timescales over which this occurs is much faster than the estimated rise rates for bubbles to reach the top of the magma chamber. 相似文献
253.
Daniel D. Huppert Rebecca L. Johnson Jessica Leahy Kathleen Bell 《Estuaries and Coasts》2003,26(4):994-1009
This paper explores social, and economic aspects of coastal communities crucial to the management of estuaries in the Pacific Northwest. These aspects include the changing demographics and economies of coastal communities, and the public perceptions, attitudes, and values pertaining to estuarine ecosystems. Information from Willapa Bay and Grays Harbor in Washington and Tillamook, Yaquina, and Coos Bays in Oregon shows that the coastal communities are growing more slowly than the states overall., that the populations are relatively old, and that, although the local economies continue to rely on them, the extractive natural resource industries (fishing, aquaculture, agriculture, forest products) are declining in importance relative to tourism, recreation, and retirement industries. These trends suggest that human uses of the estuaries are changing in character, and altering the management problems. Coastal residents choose to live in these communities to enjoy the views and scenery, to experience rural living, to be near the ocean, and to recreate outdoors. People express coherent perceptions of risks to the estuaries, especially the threats of declining fish habitats, oil spills, shoreline development, invasive species, and logging in upland areas> Residential land values are enhanced by the presence of wetlands and forests and are diminished by the presence of hazardous waste sites. We conclude that, if recent trends in population age structure, income sources, and employment status continue, public attitudes and values will move towards stronger environmental protection. Because ecosystem management involves local public participation and collaboration, estuarine managers will be faced with both increased demands and opportunities. 相似文献
254.
From experimental data in the systems Na2O-Al2O3-SiO2-H2O, K2O-Al2O3-SiO2-H2O at 1100°C, and CaO-Al2O3-SiO2-H2O at 1200°C in the 1-2 GPa pressure range, the solution behavior of the individual oxides in coexisting H2O-saturated silicate melts and silicate-saturated aqueous fluids appears to be incongruent. Recalculated on an anhydrous basis, in the CaO-Al2O3-SiO2-H2O system, CaOfluid/CaOmelt < 1, whereas in the Na2O-Al2O3-SiO2-H2O and K2O-Al2O3-SiO2-H2O systems, K2Ofluid/K2Omelt and Na2Ofluid/Na2Omelt both are greater than 1. The aqueous fluids are depleted in alumina relative to silicate melt.In the Na2O-Al2O3-SiO2-H2O, K2O-Al2O3-SiO2-H2O, and CaO-Al2O3-SiO2-H2O systems, fluid/melt partition coefficients for the individual oxides range between ∼0.005 and 0.35 depending on oxide, bulk composition and pressure. The alkali partition coefficients are about an order of magnitude higher than that of CaO. Alumina and silica partition coefficient values in the CaO-Al2O3-SiO2-H2O system are 10-20% of the values for the same oxides in the Na2O-Al2O3-SiO2-H2O and K2O-Al2O3-SiO2-H2O systems.Positive correlations among individual partition coefficients and oxide concentrations in the aqueous fluids are consistent with complexing in the fluid that involves silicate polymers associated with alkalis and alkaline earths and aluminosilicate complexes where alkalis and alkaline earths may serve to charge-balance Al3+, which is, perhaps, in tetrahedral coordination. Alkali aluminosilicate complexes in aqueous fluid appear more stable than Ca-aluminosilicate complexes. 相似文献
255.
Jessica M. Bartlett Jon S. Dougherty-Page Nigel B. W. Harris Chris J. Hawkesworth M. Santosh 《Contributions to Mineralogy and Petrology》1998,131(2-3):181-195
The technique of single zircon dating from the thermal evaporation of 207Pb/206Pb (Kober 1986, 1987) provides a means of dating successive periods of growth and nucleation of zircons in polymetamorphic
assemblages. In contrast Nd model ages may provide a measure of the period of crustal residency for the sample or its protolith.
These two techniques have been combined to elucidate the tectonic history of the Proterozoic mobile belt of southern India,
exposed south of the Palghat-Cauvery Shear Zone that marks the southern boundary of the Archaean craton of Karnataka. The
two main tectonic units of this mobile belt comprise the Madurai and Trivandrum Blocks, both of which are characterised by
massive charnockite uplands and low-lying polymetamorphic metasedimentary belts that have undergone a complex tectonic history
throughout the Proterozoic. Evidence for early Palaeoproterozoic magmatism is restricted to the Madurai Block where single
zircon evaporation ages from a metagranite (2436 ± 4 Ma) are similar to model Nd ages from a range of lithologies suggesting
crustal growth at that time. The Trivandrum Block, to the south of the Achankovil shear zone, is comprised of the Kerala Khondalite
Belt, the Nagercoil charnockites and the Achankovil metasediments. Single zircon evaporation ages, together with conventional
zircon and garnet chronometry, suggest that all three units underwent upper-amphibolite facies metamorphism at ∼1800 Ma, an
event unrecorded in the metagranite from the Madurai Block. This implies that the Madurai and Trivandrum blocks represent
distinct terrains throughout the Palaeoproterozoic. Model Nd ages from the Achankovil metasediments are much younger (1500–1200
Ma) than those from the adjacent Kerala Khondalite Belt and Madurai Blocks (3000–2100 Ma), but there is no evidence for zircon
growth in these metasediments during the Mesoproterozoic. Hence the comparatively young model Nd ages of the metasediments
are indicative of a mixed provenance rather than a discrete period of crustal growth. Zircon overgrowths from the Madurai
Block (547 ± 17 Ma) and Achankovil metasediments (530 ± 21 Ma) suggest that all tectonic units of the Proterozoic mobile belt
of South India shared the same metamorphic history from the early Palaeozoic. This event has been recognised in the basement
lithologies of Sri Lanka and East Antarctica, confirming that the constituent terrains of East Gondwana had assembled by this
time.
Received: 10 October 1995 / Accepted: 27 October 1997 相似文献
256.
Mountain rivers can be subject to strong constraints imposed by changes in gradient and grain size supplied by processes such as glaciation and rockfall. Nonetheless, adjustments in the channel geometry and hydraulics of mountain rivers at the reach scale can produce discernible patterns analogous to those in fully alluvial rivers. Mountain rivers can differ in that imposed reach‐scale gradient is an especially important control on reach‐scale channel characteristics, as indicated by examination of North St Vrain Creek in Colorado. North St Vrain Creek drains 250 km2 of the Rocky Mountains. We used 25 study reaches within the basin to examine controls on reach‐scale channel geometry. Variables measured included channel geometry, large woody debris, grain size, and mean velocity. Drainage area at the study reaches ranged from 2·2 to 245 km2, and gradient from 0·013 to 0·147 m m?1. We examined correlations among (1) potential reach‐scale response variables describing channel bankfull dimension and shape, hydraulics, bedform wavelength and amplitude, grain size, ?ow resistance, standard deviation of hydraulic radius, and volume of large woody debris, and (2) potential control variables that change progressively downstream (drainage area, discharge) or that are likely to re?ect a reach‐speci?c control (bed gradient). We tested the hypothesis that response variables correlate most strongly with local bed gradient because of the segmented nature of mountain channels. Results from simple linear regression analyses indicate that most response variables correlate best with gradient, although channel width and width/depth ratio correlate best with discharge. Multiple regression analyses using Mallow's Cp selection criterion and log‐transformation of all variables produced similar results in that most response variables correlate strongly with gradient. These results suggest that the hypothesis is partially supported: channel bed gradient is likely to be a good predictor for many reach‐scale response variables along mountain rivers, but discharge is also an important predictor for some response variables. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
257.
Jessica Craig Alan J. Jamieson Rory Hutson Alain F. Zuur Imants G. Priede 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(11):1474-1484
Measurements of the density of deep pelagic bioluminescent zooplankton (BL) were made with the Intensified Silicon Intensifier Target (ISIT) profiler in the Ligurian, Tyrrhenian, Adriatic, Ionian Seas and the Strait of Sicily from ~300 m to near seafloor. Mean BL densities ranged from 2.61 m?3 at 500–1000 m depth in the Adriatic Sea to 0.01 m?3 at 4000–5000 m depth in the E Ionian Sea. We investigated drivers of spatial variation of deep pelagic BL density. Linear regression was applied between surface chlorophyll a (Chl a) concentration and underlying BL density. Chl a values were determined from satellite derived 100 km radius composites (six 10-day means per ISIT deployment, over preceding 60 days). At 500–1000 m depth we found a significant positive relationship between mean BL density and mean Chl a in the period prior to 0–10 days (at 1% level) and prior to 10–40 days (at 5% level). Beyond 40 days no relationship between BL density and Chl a was found at this depth. At depths 1000–1500 m BL density values were low and no significant relationship with Chl a was detected. Generalised additive modelling (GAM) was used to assess the influence of benthic hotspots (seamount; cold water coral mound; mud volcano) on overlying BL density. A reduction in BL density was found downstream of the Palinuro seamount from 300 to 600 m. No effect on BL density in the overlying water column was detected from the presence of cold water corals. Higher BL densities were detected over the W Madonna dello Ionio mud volcano than at other sites sampled in the NW Ionian Sea. We find surface Chl a to be a good predictor of BL density in the mesopelagic zone; below this depth we hypothesise that processes affecting the efficiency of particle export to deep water may exert greater influence on BL density. 相似文献
258.
Frank J. Tipler Jessica Graber Matthew McGinley Joshua Nichols-Barrer Christopher Staecker 《Monthly notices of the Royal Astronomical Society》2007,379(2):629-640
We show that it is possible for the information paradox in black hole evaporation to be resolved classically. Using standard junction conditions, we attach the general closed spherically symmetric dust metric to a space–time satisfying all standard energy conditions but with a single point future c-boundary. The resulting Omega Point space–time, which has NO event horizons, nevertheless has black hole type trapped surfaces and hence black holes. However, since there are no event horizons, information eventually escapes from the black holes. We show that a scalar quintessence field with an appropriate exponential potential near the final singularity would give rise to an Omega Point final singularity. 相似文献
259.
Jessica Saïag Pierre‐Yves Collin Jean‐Pierre Sizun Frdric Herbst Ophlie Faÿ‐Gomord Carmela Chateau Smith Bruno Caline ric Lasseur 《Sedimentology》2019,66(7):2976-3007
Microtexture describes the type of particles and their arrangement in matrix samples at scanning electron microscopy scale. Although a microtexture classification exists for micritic limestone, it cannot be directly applied to chalk. This study therefore proposes a classification of chalk microtextures and discusses the origin of microtexture variability. Chalk was sampled at thirteen spatio‐temporal locations along the coastline of northern France (Cenomanian–Santonian). Four criteria are defined to describe, characterize and determine chalk matrix microtexture: (i) mineralogical content; (ii) biogenic fraction; (iii) micritic fraction; and (iv) cement fraction. From these criteria, two major groups are defined: Pure Chalk Microtexture Group, with seven classes, and Impure Chalk Microtexture Group, divided into two subgroups: Argillaceous Microtexture with four classes and Siliceous Microtexture with two classes. Microtexture variability is related both to initial sedimentation and to diagenesis. Sedimentological conditions (for example, climate and distance from shore) affect chalk composition (carbonate content and type of insoluble particles), thus influencing microtexture. Changes in Pure Chalk Microtexture are the result of increasing diagenetic intensity. This classification can also be used to characterize the microtexture of subsurface chalk reservoirs. Reservoir quality depends on the petrophysical and mechanical properties of reservoir rocks, which can be better understood by exploring their sedimentary and diagenetic history, revealed by the study of chalk microtexture variability. 相似文献
260.
Jessica D. Tomkins Dermot Antoniades Scott F. Lamoureux Warwick F. Vincent 《Journal of Paleolimnology》2008,40(1):577-582
We describe a method for preserving the upper sediments of fragile sediment cores during transport from field sites and assess
potential effects on subsequent laboratory analyses. This method addresses the need to minimize disturbance to the surfaces
of unfrozen sediment cores used for paleoenvironmental or other high-resolution sedimentological analyses during transport.
A polymer gel (sodium polyacrylate) applied above the sediment surface acts as a barrier to movement while also preserving
surface undulations. The gel seal can preserve even exceptionally fine sedimentary structures (<0.2 mm) in the upper sediments
of lacustrine and fiord sediment cores, but may react with organic material (e.g. algal mats) present on some sediment surfaces.
This reaction creates an adhesive layer at the gel’s base but it can be handled effectively during sampling. The gel seal
minimizes surface deformation and preserves surficial sediments better than traditional seals made of water-absorbent floral
foam, wax or paper towel. In addition to permitting detailed sedimentary and subfossil investigations of the sediment–water
interface, this method shows no detectable effects on measurements of total organic carbon or total nitrogen values in the
sediment. This method is inexpensive, non-hazardous and applicable to many coring systems and sediment types. 相似文献