Adsorption and mobility of metals in build-up on road surfaces

The study investigated the adsorption and bioavailability characteristics of traffic generated metals common to urban land uses, in road deposited solids particles. To validate the outcomes derived from the analysis of field samples, adsorption and desorption experiments were undertaken. The analysis of field samples revealed that metals are selectively adsorbed to different charge sites on solids. Zinc, copper, lead and nickel are adsorbed preferentially to oxides of manganese, iron and aluminium. Lead is adsorbed to organic matter through chemisorption. Cadmium and chromium form weak bonding through cation exchange with most of the particle sizes. Adsorption and desorption experiments revealed that at high metal concentrations, chromium, copper and lead form relatively strong bonds with solids particles while zinc is adsorbed through cation exchange with high likelihood of being released back into solution. Outcomes from this study provide specific guidance for the removal of metals from stormwater based on solids removal.

Changing travel patterns and journeys to health services in Great Britain 1985-2012: An examination health service utilisation using the National Travel Survey

Background This paper examines changing patterns in the utilisation and geographic access to health services in Great Britain using National Travel Survey data (1985-2012). The National Travel Survey (NTS) is a series of household surveys designed to provide data on personal travel and monitor changes in travel behaviour over time. The utilisation rate was derived using the proportion of journeys made to access health services. Geographic access was analysed by separating the concept into its accessibility and mobility dimensions. Methods Variables from the PSU, households, and individuals datasets were used as explanatory variables. Whereas, variables extracted from the journeys dataset were used as dependent variables to identify patterns of utilisation i.e. the proportion of journeys made by different groups to access health facilities in a particular journey distance or time band or by mode of transport; and geographic access to health services. A binary logistic regression analysis was conducted to identify the utilisation rate over the different time periods between different groups. This analysis shows the Odds Ratios (ORs) for different groups making a trip to utilise health services compared to their respective counterparts. Linear multiple regression analyses were conducted to then identify patterns of change in the accessibility and mobility level. Results Analysis of the data has shown that that journey distances to health facilities were signi fi cantly shorter and also gradually reduced over the period in question for Londoners, females, those without a car or on low incomes, and older people. Although rates of utilisation of health services we re Oral Abstracts / Journal of Transport & Health 2 (2015) S5 – S63 S43 signi fi cantly lower because of longer journey times. These fi ndings indicate that the rate of utilisation of health services largely depends on mobility level although previous research studies have traditionally overlooked the mobility dimension. Conclusions This fi nding, therefore, suggests the need to improve geographic access to services together with an enhanced mobility option for disadvantaged groups in order for them to have improved levels of access to health facilities. This research has also found that the volume of car trips to health services also increased steadily over the period 1985-2012 while all other modes accounted for a smaller number of trips. However, it is dif fi cult to conclude from this research whether this increase in the volume of car trips was due to a lack of alternative transport or due to an increase in the level of car-ownership.

Stability and mobility of sand-bed channels affected by seepage

Seepage effects on the stability, mobility, and incipient motion of sand-bed particles are experimentally investigated. Seepage through a sand bed in a downward direction (suction) reduces the stability of particles, and it can even initiate their movement. The bed erosion is increased with the increased rates of suction. Whereas the seepage in an upward direction (injection) increases the stability of bed particles, it does not aid initiating their movement. The rate of bed erosion is reduced or even stopped by the increased infection rates. Hydrodynamic conditions leading to the so-called "pseudoincipient motion'' with suction (for the initiation of particles movement that are otherwise at rest under no-seepage conditions), and with injection (for only arresting the particles movement that are otherwise moving initially) are evaluated. The conventional Shields curve cannot be used to predict such pseudoincipient motion conditions with seepage. The concepts thus developed are useful for a better understanding of the sediment transport mechanics and in the design of stable alluvial channels affected by seepage.

Carrier lifetime and mobility enhancement in nearly defect-free core-shell nanowires measured using time-resolved terahertz spectroscopy.

We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.

Noncontact measurement of charge carrier lifetime and mobility in GaN nanowires

The first noncontact photoconductivity measurements of gallium nitride nanowires (NWs) are presented, revealing a high crystallographic and optoelectronic quality achieved by use of catalyst-free molecular beam epitaxy. In comparison with bulk material, the NWs exhibit a long conductivity lifetime (>2 ns) and a high mobility (820 ± 120 cm 2/(V s)). This is due to the weak influence of surface traps with respect to other III-V semiconducting NWs and to the favorable crystalline structure of the NWs achieved via strain-relieved growth. © 2012 American Chemical Society.

Sorption, degradation and mobility of microcystins in Chinese agriculture soils: Risk assessment for groundwater protection

In the present paper, sorption, persistence, and leaching behavior of three microcystin variants in Chinese agriculture soils were examined. Based on this study, the values of capacity factor and slope for three MCs variants in three soils ranged from 0.69 to 6.00, and 1.01 to 1.54, respectively. The adsorption of MCs in the soils decreased in the following order: RR > Dha(7) LR > LR. Furthermore, for each MC variant in the three soils, the adsorption rate in the soils decreased in the following order: soil A > soil C > soil B. The calculated half-time ranged between 7.9 and 17.8 days for MC-RR, 6.0-17.1 days for MC-LR, and 7.1-10.2 days for MC-Dha(7) LR. Results from leaching experiments demonstrated that recoveries of toxins in leachates ranged from 0-16.7% for RR, 73.2-88.9% for LR, and 8.9-73.1% for Dha 7 LR. The GUS value ranged from 1.48 to 2.06 for RR, 1.82-2.88 for LR, and 1.76-2.09 for Dha(7) LR. Results demonstrated the use of cyanobacterial collections as plant fertilizer is likely to be unsafe in soils. (c) 2006 Elsevier Ltd. All rights reserved.

Distribution and mobility of metals in agricultural soils near a copper smelter in South China

The distribution and mobility of heavy metals in the paddy soils surrounding a copper smelting plant in south China was investigated. We assessed the degree of metal contamination using an index of geoaccumulation. The metals were divided into two groups: (1) Cu, Zn, Pb and Cd, whose concentrations were heavily affected by anthropogenic inputs, and (2) Ni, Co and Cr, which were mainly of geochemical origin. Concentrations of Cu, Cd, Zn, and Pb in the polluted soils were higher than the Chinese soil quality criteria. The chemical partitioning patterns of Pb, Zn and Cu indicated that Pb was largely associated with the residual and NH2OH HCl extractable fractions. In contrast, Cd was predominantly associated with the MgCl2 extractable fraction. A large proportion of Cu was bound to the acidic H2O2 extractable fractions, while Zn was predominantly found in the residual phase. The fraction of mobile species, which potentially is the most harmful to the environment, was found to be elevated compared to unpolluted soils in which heavy metals are more strongly bound to the matrix. The mobility of the metals was studied by water extraction using a modification of Tessier's procedure, and the order of mobility was Zn > Cd > Cu > Ce > Pb.

On the Cost of Supporting Multihoming and Mobility

As the Internet has evolved and grown, an increasing number of nodes (hosts or autonomous systems) have become multihomed, i.e., a node is connected to more than one network. Mobility can be viewed as a special case of multihoming—as a node moves, it unsubscribes from one network and subscribes to another, which is akin to one interface becoming inactive and another active. The current Internet architecture has been facing significant challenges in effectively dealing with multihoming (and consequently mobility). The Recursive INternet Architecture (RINA) [1] was recently proposed as a clean-slate solution to the current problems of the Internet. In this paper, we perform an average-case cost analysis to compare the multihoming / mobility support of RINA, against that of other approaches such as LISP and MobileIP. We also validate our analysis using trace-driven simulation.