Effect of temperature and mass transport on transition metal isotope fractionation during electroplating     

Jay R. Black  Seth John  Abby Kavner 《Geochimica et cosmochimica acta》2010,74(18):5187-715

Transition metal stable isotope signatures can be useful for tracing both natural and anthropogenic signals in the environment, but only if the mechanisms responsible for fractionation are understood. To investigate isotope fractionations due to electrochemistry (or redox processes), we examine the stable isotope behavior of iron and zinc during the reduction reaction  + 2e⁻ = M_metal as a function of electrochemical driving force, temperature, and time. In all cases light isotopes are preferentially electroplated, following a mass-dependent law. Generally, the extent of fractionation is larger for higher temperatures and lower driving forces, and is roughly insensitive to amount of charge delivered. The maximum fractionations are δ^56/54Fe = −4.0‰ and δ^66/64Zn = −5.5‰, larger than observed fractionations in the natural environment and larger than those predicted due to changes in speciation. All the observed fractionation trends are interpreted in terms of three distinct processes that occur during an electrochemical reaction: mass transport to the electrode, chemical speciation changes adjacent to the electrode, and electron transfer at the electrode. We show that a large isotope effect adjacent the electrode surface arises from the charge-transfer kinetics, but this effect is attenuated in cases where diffusion of ions to the electrode surface becomes the rate-limiting step. Thus while a general increase in fractionation is observed with increasing temperature, this appears to be a result of thermally enhanced mass transport to the reacting interface rather than an isotope effect associated with the charge-transfer kinetics. This study demonstrates that laboratory experiments can successfully distinguish isotopic signatures arising from mass transport, chemical speciation, and electron transfer. Understanding how these processes fractionate metal isotopes under laboratory conditions is the first step towards discovering what role these processes play in fractionating metal isotopes in natural systems.  相似文献   

The consumption of space: Land, capital and place in the New Zealand wine industry   总被引：1，自引：0，他引：1  

John Overton 《Geoforum》2010,41(5):752-762

Geographers have developed a keen interest in the social production of space - in the way meanings and values are ascribed to places as a result of changing social, cultural and political processes. There is a need to explore this approach further, seeing how social and economic values of places are inter-related and how these values are constructed in often deliberate and concerted ways. There is also a need to explore how such values are consumed: how the values in place are traded, appropriated and redistributed, both through the products of places and in land markets. This paper examines the New Zealand wine industry where certain wine regions have been identified and developed in ways which attempt to emphasise their distinctiveness in terms of wine quality and thus enhance the value of the wine produced. Different strategies have been employed in this process of place construction and this reflects the differential role of capital, striving on the one hand to increase the price and marketability of the products of distinctive places but, on the other, careful not to over-inflate land values and thus restrict further expansion. The paper suggests that the issue of consumption of space, involving a complex relationship amongst land, capital and place, is worthy of further exploration.  相似文献   

翼龙重建：方法论的一个研究例子     

John A. CONWAY 《地球学报》2010,31(Z1):14-14

Reconstructions of fossil animals are widespread and often very high profile, yet many of these reconstructions exhibit low standards of scientific accuracy.  相似文献   

Trinitite—the atomic rock     

Nelson Eby  Robert Hermes  Norman Charnley  John A. Smoliga 《Geology Today》2010,26(5):180-185

On 16 July 1945, the first atomic bomb was detonated at the Alamogordo Bombing range in New Mexico, USA. Swept up into the nuclear cloud was the surrounding desert sand, which melted to form a green glassy material called ‘trinitite’. Contained within the glass are melted bits of the first atomic bomb and the support structures and various radionuclides formed during the detonation. The glass itself is marvelously complex at the tens to hundreds of micrometre scale, and besides glasses of varying composition also contains unmelted quartz grains. Air transport of the melted material led to the formation of spheres and dumbbell shaped glass particles. Similar glasses are formed during all ground level nuclear detonations and contain forensic information that can be used to identify the atomic device.  相似文献   

The construction and development of SHRIMP I: An historical outline     

John J. Foster 《Precambrian Research》2010

In 1973 Bill Compston advocated the building of an ion microprobe at the Research School of Earth Sciences (RSES) at the Australian National University (ANU). The commercial ion probes available at this time were too small to have sufficient sensitivity for trace element analysis and too low in mass resolution to avoid molecular interferences. The project commenced in 1974 with the appointment of a former ANU PhD student Steve Clement who had expertise in beam transport theory. To achieve high sensitivity and high mass resolution, beam transport theory indicated that a much larger magnet than in any commercially available mass spectrometer would be required. Clement chose an ion optical design, by Professor Matsuda of Osaka University in 1974, which had the required combination of high mass resolution and high transmission. Clement's job was to produce the detailed scientific designs and machine drawings for the new instrument as well as testing the completed instrument. Clement coined the term SHRIMP-Sensitive High Resolution Ion MicroProbe. By the end of 1977 nearly all the components had been manufactured and the big electromagnet had been successfully tested. In the following year the secondary mass analyzer was assembled and tested using a thermal ionization source and showed great promise with flat-topped peaks at 5000 resolution and 50% transmission with 50 V energy spread. At this stage the machine had far exceeded the specifications for the available commercial ion probes. Continued development during 1981 to the point where the original design specifications were fully realized was time consuming since learning how to use the entirely novel instrument was no simple task; no one else had an instrument like SHRIMP. The application of the instrument to zircon U–Pb geochronology established the necessary operating conditions for measuring Pb isotopic compositions and the elemental ratios Pb/U and U/Zr from 20 μm diameter spots on single zircon grains. Application of this in the early 1980s started a revolution in Precambrian geology by the ability to produce rapidly accurate and precise age determinations on structurally complex zircon samples.  相似文献   

Got green? addressing environmental justice in park provision   总被引：3，自引：0，他引：3  

Chona Sister  Jennifer Wolch  John Wilson 《GeoJournal》2010,75(3):229-248

We present a pragmatic approach to assist planners in addressing racial inequities in park access. Utilizing the Los Angeles metropolitan region as an example, we used Thiessen polygons to delineate a service area for each park, and described potential park congestion or ‘pressure’ in each park service area. Results show that Latinos, African-Americans, and low-income groups in general were likely to live close to parks with higher potential park congestion. On the other hand, predominantly White, high-income areas were typically located close to parks with lower potential park congestion levels. The park service area analysis presented here facilitates the identification of areas with greater park need and provides a pragmatic way to redress existing disparities in park access. Built into a set of web-based decision support tools, the approach fosters greater community participation and empowers local stakeholders in the process of park provision.  相似文献   

Geochemical processes controlling arsenic mobility in groundwater: A case study of arsenic mobilization and natural attenuation     

Y. Thomas He  Arthur G. Fitzmaurice  Azra Bilgin  Sunkyung Choi  Peggy O’Day  John Horst  James Harrington  H. James Reisinger  David R. Burris  Janet G. Hering 《Applied Geochemistry》2010

The behavior of As in the subsurface environment was examined along a transect of groundwater monitoring wells at a Superfund site, where enhanced reductive dechlorination (ERD) is being used for the remediation of groundwater contaminated with chlorinated solvents. The transect was installed parallel to the groundwater flow direction through the treatment area. The ERD technology involves the injection of organic C (OC) to stimulate in situ microbial dechlorination processes. A secondary effect of the ERD treatment at this site, however, is the mobilization of As, as well as Fe and Mn. The concentrations of these elements are low in groundwater collected upgradient of the ERD treatment area, indicating that, in the absence of the injected OC, the As that occurs naturally in the sediment is relatively immobile. Batch experiments conducted using sediments from the site inoculated with an Fe(III)- and As(V)-reducing bacterium and amended with lactate resulted in mobilization of As, Fe and Mn, suggesting that As mobilization in the field is due to microbial processes.  相似文献   

Aquifer Storage Recovery (ASR) of chlorinated municipal drinking water in a confined aquifer     

John A. Izbicki  Christen E. Petersen  Kenneth J. Glotzbach  Loren F. Metzger  Allen H. Christensen  Gregory A. Smith  David O’Leary  Miranda S. Fram  Trevor Joseph  Heather Shannon 《Applied Geochemistry》2010

About 1.02 × 10⁶ m³ of chlorinated municipal drinking water was injected into a confined aquifer, 94–137 m below Roseville, California, between December 2005 and April 2006. The water was stored in the aquifer for 438 days, and 2.64 × 10⁶ m³ of water were extracted between July 2007 and February 2008. On the basis of Cl⁻ data, 35% of the injected water was recovered and 65% of the injected water and associated disinfection by-products (DBPs) remained in the aquifer at the end of extraction. About 46.3 kg of total trihalomethanes (TTHM) entered the aquifer with the injected water and 37.6 kg of TTHM were extracted. As much as 44 kg of TTHMs remained in the aquifer at the end of extraction because of incomplete recovery of injected water and formation of THMs within the aquifer by reactions with free-chlorine in the injected water. Well-bore velocity log data collected from the Aquifer Storage Recovery (ASR) well show as much as 60% of the injected water entered the aquifer through a 9 m thick, high-permeability layer within the confined aquifer near the top of the screened interval. Model simulations of ground-water flow near the ASR well indicate that (1) aquifer heterogeneity allowed injected water to move rapidly through the aquifer to nearby monitoring wells, (2) aquifer heterogeneity caused injected water to move further than expected assuming uniform aquifer properties, and (3) physical clogging of high-permeability layers is the probable cause for the observed change in the distribution of borehole flow. Aquifer heterogeneity also enhanced mixing of native anoxic ground water with oxic injected water, promoting removal of THMs primarily through sorption. A 3 to 4-fold reduction in TTHM concentrations was observed in the furthest monitoring well 427 m downgradient from the ASR well, and similar magnitude reductions were observed in depth-dependent water samples collected from the upper part of the screened interval in the ASR well near the end of the extraction phase. Haloacetic acids (HAAs) were completely sorbed or degraded within 10 months of injection.  相似文献   

Groundwater recharge in natural dune systems and agricultural ecosystems in the Thar Desert region, Rajasthan, India   总被引：2，自引：1，他引：1  

Bridget R. Scanlon  Abhijit Mukherjee  John Gates  Robert C. Reedy  Amarendra K. Sinha 《Hydrogeology Journal》2010,18(4):959-972

Water and nutrient availability for crop production are critical issues in (semi)arid regions. Unsaturated-zone Cl tracer data and nutrient (NO₃ and PO₄) concentrations were used to quantify recharge rates using the Cl mass balance approach and nutrient availability in the Thar Desert, Rajasthan, India. Soil cores were collected in dune/interdune settings in the arid Thar Desert (near Jaisalmer) and in rain-fed (nonirrigated) and irrigated cropland in the semiarid desert margin (near Jaipur). Recharge rates were also simulated using unsaturated zone modeling. Recharge rates in sparsely vegetated dune/interdune settings in the Jaisalmer study area are 2.7–5.6 mm/year (2–3% of precipitation, 165 mm/year). In contrast, recharge rates in rain-fed agriculture in the Jaipur study area are 61–94 mm/year (10–16% of precipitation, 600 mm/year). Minimum recharge rates under current freshwater irrigated sites are 50–120 mm/year (8–20% of precipitation). Nitrate concentrations are low at most sites. Similarity in recharge rates based on SO₄ with those based on Cl is attributed to a meteoric origin of SO₄ and generally conservative chemical behavior in these sandy soils. Modeling results increased confidence in tracer-based recharge estimates. Recharge rates under rain-fed agriculture indicate that irrigation of 20–40% of cultivated land with 300 mm/year should be sustainable.  相似文献   

Two-dimensional horizontal modeling of fine-sediment transport at the South Channel–North Passage of the partially mixed Changjiang River estuary,China     

John Z. Shi  Hong-Qiang Zhou  Hua Liu  Yong-Gang Zhang 《Environmental Earth Sciences》2010,61(8):1691-1702

Tidal flow and fine-sediment transport at the South Channel–North Passage of the partially-mixed Changjiang River estuary were studied using a two-dimensional horizontal (2DH) numerical model. This 2DH model was achieved by depth-integrating the momentum and convection–diffusion equations. The Alternating Direction Implicit scheme was used to solve the governing equations. The iterative method was adopted for the calculation of convection and diffusion terms of momentum equation. Comparisons between calculated and measured results (tidal elevations and depth-averaged velocities) have shown reasonable agreement. Horizontal distributions of tidal current velocity and suspended sediment concentration were qualitatively consistent with observations. Those modeled results were analyzed to elucidate the mechanisms for the formation of the turbidity maximum and intratidal variations in fine-sediment transport processes.  相似文献