On the observation of 92Nb and 94Nb in nature     

K.E Apt  J.D Knight  D.C Camp  E.W Perkins 《Geochimica et cosmochimica acta》1974,38(9):1485-1488

Radioactivity measurements have shown evidence for long-lived ⁹²Nb and $\text{2.03 × 10}{}^4\text{yr}{}^{94}\text{Nb}$ in natural niobium. The specific activity of ⁹⁴Nb was observed to be 0.32 ± 0.03 dis/min. kg Nb and that of ⁹²Nb to be 0.058 ± 0.035 dis/min. kg Nb. With $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ taken as ≈ 1.7 × 10⁸yr, the isotopic abundance of ⁹⁸Nb is 1.2 × 10^?10 per cent.  相似文献   

A Jar for Culturing Small Pelagic Marine Organisms in Running Water during Shipboard or Laboratory Studies     

Schumann  George O.; Perkins  Herbert C. 《ICES Journal of Marine Science》1966,30(2):171-176

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Pore-scale and continuum simulations of solute transport micromodel benchmark experiments     

M. Oostrom  Y. Mehmani  P. Romero-Gomez  Y. Tang  H. Liu  H. Yoon  Q. Kang  V. Joekar-Niasar  M. T. Balhoff  T. Dewers  G. D. Tartakovsky  E. A. Leist  N. J. Hess  W. A. Perkins  C. L. Rakowski  M. C. Richmond  J. A. Serkowski  C. J. Werth  A. J. Valocchi  T. W. Wietsma  C. Zhang 《Computational Geosciences》2016,20(4):857-879

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Thermochemistry of (Fe2+, Mg)SiO3 orthopyroxene     

C. Chatillon-Colinet  R.C. Newton  D. Perkins  O.J. Kleppa 《Geochimica et cosmochimica acta》1983,47(9):1597-1603

Enthalpies of solution in eutectic (Li, Na)₂B₂O₄ melts at 1023 K were measured for five synthetic orthopyroxenes on the join MgSiO₃-FeSiO₃. The pyroxenes were synthesized at 1120°C and 20 kbar and thus were presumed to be highly disordered. The measurements indicate a small positive enthalpy of mixing, with W_H = 950 cal/MSiO₃.Enthalpy of solution measurements were made on a natural, well-ordered orthopyroxene near the composition En_52.5Fs_47.5 and on this material after heat-treatment at 1150°C and 20 kbar. Irreversible expansion of the unit-cell constants of the natural pyroxene after heat-treatment at various temperatures was used to characterize the degree of M-site disorder. The observed enthalpy of solution decrement of 0.85 kcal/MSiO₃ between the natural En_52.5 and the same material heated at 1150° corresponds to about half of the maximum possible disordering, or ΔX_Fe^M1? 0.25, which leads to a ΔH of 7.5 kcal/M₂Si₂O₆, for the exchange reaction: Fe(M2) + Mg(Ml) = Fe(Ml) + Mg(M2) if M-site interaction energy terms are ignored. This ΔH is larger than inferred from any of the analyses of site-occupancy data except that of Besancon (1981), who gave a very similar value. The measured ΔH of disorder and the W_H of mixing together indicate a large ΔH as great as 3.2 kcal for the reciprocal reaction: Fe₂Si₂O₆ + Mg₂Si₂O₆ = Fe(M2)Mg(M1)Si₂O₆ + Fe(M1)Mg(M2)Si₂O₆ as anticipated by Sack (1980).As a consequence of the inferred magnitudes of ΔHof the exchange and reciprocal reactions, departures from ideality of Gibbs energy of mixing of orthopyroxene are very small at 700°–1000°C. Activities of MgSiO₃ and FeSiO₃ may be replaced by their mol fractions at all temperatures in most petrologic calculations.  相似文献   

Errata     

Dexter Perkins III  Steve J. Chipera 《Contributions to Mineralogy and Petrology》1985,89(4):410-410

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Cytosolic metal distribution as an indicator of toxicity in sea urchins from the Southern California Bight     

Kenneth D. Jenkins  David A. Brown  Philip S. Oshida  Edwin M. Perkins 《Marine pollution bulletin》1982,13(12):413-421

Sea urchins (Strongylocentrotus purpuratus) were collected from intertidal stations at Point Dume, Redondo Beach and White's Point in the Southern California Bight. Cytosolic metal levels varied both within and between stations, with the highest levels found in organisms from White's Point. Examination of the cytosolic metal distribution by Sephadex G-75 gel chromatography indicated that organisms adapted to increased levels of trace metals by producing more of a metallothionein-like metal-binding protein. Histological and histochemical examinations indicated that these organisms were not stressed over the range of metal concentrations encountered in this study.  相似文献   

A seismic hazard map of India and adjacent areas   总被引：1，自引：0，他引：1  

K.N. Khattri  A.M. Rogers  D.M. Perkins  S.T. Algermissen 《Tectonophysics》1984,108(1-2)

We have produced a probabilistic seismic hazard map showing peak ground accelerations in rock for India and neighboring areas having a 10% probability of being exceeded in 50 years. Seismogenic zones were identified on the basis of historical seismicity, seismotectonics and geology of the region. Procedures for reducing the incompleteness of earthquake catalogs were followed before estimating recurrence parameters. An eastern United States acceleration attenuation relationship was employed after it was found that intensity attenuation for the Indian region and the eastern United States was similar. The largest probabilistic accelerations are obtained in the seismotectonic belts of Kirthar, Hindukush, Himalaya, Arakan-Yoma, and the Shillong massif where values of over 70% g have been calculated.  相似文献   

The Al2O3 contents of enstatite in equilibrium with garnet in the system MgO-Al2O3-SiO2 at 15–40 kbar and 900°–1,600° C     

D. Perkins III  T. J. B. Holland  R. C. Newton 《Contributions to Mineralogy and Petrology》1981,78(1):99-109

Forty-six reversed determinations of the Al₂O₃content of enstatite in equilibrium with garnet were made in the P/T range 15–40 kbar/900–1,600° C in the MgO-Al₂O₃-SiO₂ system. Starting materials were mixtures of synthetic pyrope+Al-free enstatite and pyrope+enstatite (5–12% Al₂O₃). Al₂O₃ contents in reversal run pairs closely approached common values from both the high- and low-Al sides. Most experiments were done in a piston-cylinder device using a NaCl medium; some runs at very high temperatures were made in pyrex/NaCl or pyrex/talc assemblies. The measured enstatite compositions, expressed as mole fractions of Mg₂(MgAl)(AlSi₃)O₁₂(X _Opy ^En ) were fitted by a Monte-Carlo method to the equilibrium condition: $$\begin{gathered} \Delta H_{970}^0 - 970\Delta S_{970}^0 \hfill \\ + \mathop \smallint \limits_1^P \Delta V_{970}^0 dP - \mathop \smallint \limits_{970}^T \Delta S_T^0 dT + RT\ln X_{Opy}^{En} = 0 \hfill \\ \end{gathered}$$ where the best fit parameters of ΔH, ΔS and ΔV (1 bar, 970 K) for the reaction pyrope=opy are 2,040 cal/mol, 2.12 eu and 9.55 cc/mol. In addition to the determination of Al₂O₃ contents of enstatite, the univariant reaction pyrope+forsterite=enstatite+spinel was reversibly located in the range 1,100–1,400°C. A “best-fit” line passes through 22, 22.5 and 25 kbar at 1,040, 1,255 and 1,415°C, respectively. Our results for the univariant reaction are in agreement with previous studies of MacGregor (1974) and Haselton (1979). However, comparison of the experimentally determined curve with thermochemical calculations suggests that there may be a small error in the tabulated ΔH _f(970,1) ⁰ value for enstatite. A value of?8.32 rather than?8.81 kcal/mole (Charlu et al. 1975) is consistent with the present data. Application of garnet-enstatite-spinel-forsterite equilibria to natural materials is fraught with difficulties. The effects of nonternary components are poorly understood, and the low solubilities of Al₂O₃ in enstatite under most geologically reasonable conditions make barometric or thermometric calculations highly sensitive. More detailed studies, including reversed determinations in low-friction assemblies, are sorely needed before the effects of important diluents such as Fe, Ca and Cr can be fully understood.  相似文献   

Ecologies of actor-networks and (non)social labor within the urban political economies of nature     

Harold A. Perkins   《Geoforum》2007,38(6):1152-1162

On September 16th, 2005 the United States began restricting the entry of commodities shipped from abroad in wood packaging materials that do not conform to phytosanitation measures meant to prevent the spread of pests and pathogens. This action results from expensive lessons learned as global commerce facilitates pandemics like Dutch elm disease. Marxist political ecology is well suited to investigate such scenarios with its emphasis on the social production of nature within accumulation regimes. Some scholars contend, however, that Marxist accounts of the contradictions that result from nature’s commodification relegate nonhuman organisms to an apolitical role in environmental transformation while reinforcing the nature/society dichotomy. Often viewed as antithetical to Marxism, actor-network theory or ANT emphasizes the ability of actants (both human and nonhuman) to enroll other actants into heterogeneous assemblages or networks. Thus, it is claimed that nonhuman organisms can be attributed ontological status in processes of environmental change, much like their human counterparts. Despite this apparent theoretical discord, political ecologists are increasingly integrating aspects of both Marx and ANT into their analyses. But a more explicit articulation of the ontological basis and epistemic import of theoretical synthesis is warranted. This paper therefore prioritizes and links the ontological status of labor in both of these theories in order to expand the definition of urban environmental politics to include the role of nonhuman organisms. By demonstrating the laboring capacity of Dutch elm disease within the networks of urban political economy, the epistemology of environmental politics is thus expanded.  相似文献   

Groundwater recharge amidst focused stormwater infiltration          下载免费PDF全文

Aditi S. Bhaskar  Dianna M. Hogan  John R. Nimmo  Kimberlie S. Perkins 《水文研究》2018,32(13):2058-2068

Distributed, infiltration‐based approaches to stormwater management are being implemented to mitigate effects of urban development on water resources. One of the goals of this type of storm water management, sometimes called low impact development or green infrastructure, is to maintain groundwater recharge and stream base flow at predevelopment levels. However, the connection between infiltration‐based stormwater management and groundwater recharge is not straightforward. Water infiltrated through stormwater facilities may be stored in soil moisture, taken up by evapotranspiration or contribute to recharge and eventually base flow. This study focused on a 1.1 km² suburban, low impact development watershed in Clarksburg, Maryland, USA, that was urbanized and contained 73 infiltration‐based stormwater facilities. Continuous water table measurements were used to quantify the movement of infiltrated stormwater. Time series analyses were performed on hydrographs of 7 wells, and the episodic master recession method was used. Persistence in water levels, as measured by autocorrelation function, was found to be positively related to depth to water. Storm properties (precipitation rate and duration) and well location (proximity to the nearest stream) were significant in driving episodic recharge to precipitation ratios. The well that had the highest recharge to precipitation ratios and water table rises of up to 1.5 m in response to storm events was located furthest from the stream and down gradient of stormwater infiltration locations. This work may be considered in evaluating the effects of planned watershed‐scale infiltration‐based stormwater management on groundwater flow systems.  相似文献