Comparative study of the temporal evolution of atmospheric lead deposition in Scotland and eastern Canada using blanket peat bogs

The temporal evolution of atmospheric lead deposition and its possible sources were assessed in eastern Canada and in western Scotland, using blanket peat bogs as geochemical archives. Short cores were taken from two remote sites located close to the sea. Significant lead enrichments in the upper layers at both sites reflect the increasing emission of lead into the atmosphere due to anthropogenic activities during the last century. At the Scottish site, a region under aeolian influence from Europe, anthropogenic derived lead could be recognized by the distinctive unradiogenic composition (206Pb/207Pb ratios down to approximately 1.115), being clearly different from the pre-industrial values (206Pb/207Pb approximately 1.166). In contrast, the lead pollution in eastern Canada (influenced by North American sources) is identified by a more radiogenic lead isotope composition (206Pb/207Pb ratios up to approximately 1.199) compared to preindustrial values (206Pb/207Pb approximately 1.161). Emission inventories and isotope characteristics suggest that industrial (coal burning, mining) and traffic (leaded gasoline) outputs are the most likely sources during the first and the second half of the 20th century, respectively, in both, western Scotland and eastern Canada alike. The Scottish record is in line with previous studies of past atmospheric lead deposition. However, the Canadian deposit suggests that the wind derived, pre-industrial lead, is less radiogenic as previously implied using sediment archives. These results are thus the first to report pre-industrial lead isotope ratios and concentrations of atmospheric derived aerosols in North America.     

A global comparison of national biodiesel production potentials

This study presents a consistent, national-level evaluation of potential biodiesel volumes and prices, replicated across 226 countries, territories, and protectorates. Utilizing all commercially exported lipid feedstocks from existing agricultural lands, we compare the upper-limit potential for expanded biodiesel production in terms of absolute biodiesel volumes, profitable potential from biodiesel exports, and potential from expanded vegetable oil production through agricultural yield increases. Country findings are compared across a variety of economic, energy, and environmental metrics. Our results show an upper-limit worldwide volume potential of 51 billion liters from 119 countries; 47 billion of which could be produced profitably at today's import prices. Also significant production gains are possible through increasing agricultural yields: a 12-fold increase over existing potential, primarily hinging on better management of tropical oilseed varietals.     

TBT causes regime shift in shallow lakes

Tributyltin (TBT) is an organotin compound used since the early 1960s as a biocide in boat antifouling paints. Its use has been linked to a host of negative effects in marine ecosystems including malformations and imposex in Mollusca and acute toxicity in many other aquatic animals. Yet, the consequences of TBT use in freshwaters are largely unknown. Here, for the first time we reveal that TBT may have caused hitherto unsuspected damage to freshwater ecosystems. Through an analysis of dated sediment cores collected from a system of recreationally boated, shallow lakes, we show that first evidence of TBT is associated with a dramatic loss of submerged vegetation and associated diverse animal communities. Cause and effect are difficult to unravel in our study. However, we hypothesize that TBT, through reducing populations of grazing organisms in lakes already affected by eutrophication, promoted the replacement of macrophytes by phytoplankton, ultimately leading to a regime shift in the ecosystem. Our findings may have parallels in freshwater ecosystems all over the world.     

On the geometrical dependence of low-frequency noise in SiGe HBTs

We present an investigation of the dependence of low-frequency noise on device geometry in advanced npn silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs). The devices examined in this work have fixed emitter width (W_E = 0.4 μm), but varying emitter length (0.5 μm  L_E  20.0 μm), and thus the ratio of the emitter perimeter (P_E) to the emitter area (A_E) varies widely, making it ideal for examining geometrical effects. The SPICE noise parameter A_F extracted from these devices decreases with increasing L_E. Furthermore, the low-frequency noise measured on SiGe HBTs with significantly different P_E/A_E ratios suggests a possibility that the fundamental noise source for the diffusion base current may be located at the emitter periphery. Transistors with different distances between the emitter edge and the shallow trench edge (XEC), and shallow trench edge to deep trench edge (XTC), are also investigated. The SiGe HBTs with a smaller value of XEC have higher low-frequency noise, but no significant difference is found in devices with varying XTC. Explanations of the observed noise behavior are suggested.     

Design equations for optimized PEM fuel cell electrodes

This paper presents simple mathematical expressions that can be used for optimizing fuel cell electrode structures, specifically polymer electrolyte membrane fuel cells (PEMFCs). Based on the effectiveness factor, equations relate current density to catalyst utilization and a mass transfer coefficient. These can be used to screen new materials or identify which specific processes need to be improved in an existing electrode design. The optimum thickness, or catalyst loading, and maximum current that can be achieved with a given set of materials can be calculated from a simple set of equations based on the mass transfer characteristics of the electrode materials. These methods can save considerable experimental time and cost during electrode development.     

Mobile Software Agents for Control in Telecommunications Networks

Distributed control can, in principle, have advantages in terms of speed of response and robustness over centralised control. However, the benefits of robustness are not realised automatically, and, due to its more complex dynamics, distributed control can be just as brittle as centralised control. Distribution of control can also result in sub-optimal performance since global information is not normally available to each controlling process.     

Treatment of an Iron-rich ARD Using Waste Carbonate Rock: Bench-Scale Reactor Test Results

The treatment of acid rock drainage (ARD) places extraordinary financial burdens on governments and companies worldwide, and an improved efficiency in treatment by as little as 1% can save many millions of dollars in rehabilitation. We investigated a system for treating Fe-rich ARD using a three-stage reactor design. In the first reaction cell, Fe-rich ARD was partially neutralised using rapid periodic carbonate resuspension with a rotating axial mixer. This was followed by an air-sparged oxidation chamber and then a second reaction cell, with more carbonate periodically resuspended until a pH of 6.3 was reached, which was followed by a settlement chamber. This reactor design has a high capacity for neutralisation, with an efficiency of ≈70% of acidity neutralised by the acid neutralising capacity (g of CaCO₃ equivalent) added to the reactor. Axial mixers were tested because of their low-energy requirements and their high reliability. The intermediate chamber effectively removes Fe by oxidising Fe(II) to Fe(III). Given the amount of acidity neutralised, the sludge volume produced was low compared to other technologies, providing further potential savings in sludge handling. Waste carbonate rock proved to be an effective neutralising agent, even though it was about 60% dolomite and 40% magnesite, with minor calcite, and despite the fact that magnesite has substantially slower dissolution kinetics compared to the more dominant dolomite. The mixed waste carbonates were capable of raising the pH sufficiently to reduce the heavy metal loadings in Fe-rich ARD by more than two orders of magnitude. The final settlement stage of the process was shown to be essential for metal precipitation, for the carry-over of fine carbonates, and CO₂ loss. This was associated with a rise in pH, from 6.3 to 7.5. In addition, residual slow-reacting magnesite from the mixed carbonate remains in the sludge from the first reactor and provides acid buffering capacity within the sludge, which is commonly lacking in the ARD neutralisation sludge of other systems.     

Potential for reducing electricity demand for lighting in households: An exploratory socio-technical study

Illuminance data were collected from 18 UK dwellings during 1-week periods in spring 2007, to establish when luminaires were used and to calculate electricity consumption for lighting. Householders were also interviewed about lighting use and choices. The potential for reducing lighting electricity consumption by replacing incandescent bulbs with compact fluorescent lamps (CFLs) is assessed. Mean weekly electricity consumption for lighting was 3.756 kW h and mean proportion of total electricity consumption used for lighting was 6.55%. It is notable, however, that participants generally expressed high levels of environmental awareness and that electricity consumption figures for less environmentally-aware households may differ. On average, households could have reduced lighting electricity consumption by 50.9% if all incandescent bulbs were replaced with CFLs. Even householders making extensive use of efficient lighting technologies expressed concerns about these technologies’ performance, but seemed willing to tolerate perceived shortcomings for environmental reasons. However, the study raises questions about whether people without strong environmental motivations can be convinced that efficient lighting technologies will meet their needs. It also raises questions about the effectiveness of policies phasing out general lighting service incandescent bulbs, as there is a risk that householders may switch to tungsten halogen bulbs rather than low-energy options.     

Dynamics of Peer Education in Cooperative Learning Workgroups

Many recent studies demonstrate that cooperative learning provides a variety of educational advantages over more traditional instructional models, both in general and specifically in engineering education. Little is known, however, about the interactional dynamics among students in engineering work groups. To explore these dynamics and their implications for engineering education, we analyzed work sessions of student groups in a sophomore‐level chemical engineering course at North Carolina State University. Using conversation analysis as a methodology for understanding how students taught and learned from one another, we found that group members generally engaged in two types of teaching‐learning interactions. In the first type, transfer‐of‐knowledge (TK) sequences, they took on distinct teacher and pupil roles, and in the second, collaborative sequences (CS), they worked together with no clear role differentiation. The interactional problems that occurred during the work sessions were associated primarily with TK sequences, and had to do with students who either habitually assumed the pupil's role (constant pupils) or habitually discouraged others' contributions (blockers). Our findings suggest that professors can facilitate student group interactions by introducing students to the two modes of teaching interaction so group members can effectively manage exchanges of knowledge, and also by helping students distribute tasks in a way that minimizes role imbalances.