Simulations of structure and transport in polymer electrolytes

Simulations implementing both Monte Carlo (MC) and molecular dynamics (MD) techniques were used to explore various aspects of polymer electrolytes. Evidence is presented to support the conclusion that collective behavior of ions determines much of the behavior of these complex materials. Simple theories attributing ion transport to either single ions or clusters of three ions are inadequate to explain ion transport behavior; in particular, the Nernst-Einstein relation commonly used to discuss polymer electrolytes is almost certainly quantitatively inappropriate for these materials.

Relationships of land use mix with walking for transport : do land uses and geographical scale matter?

Physical activity and public health recommendations now emphasize the creation of activity-friendly neighborhoods. Mixed land use in a neighborhood is important in this regard, as it reflects the availability of destinations to which residents can walk or ride bicycles, and thus is likely to contribute to residents’ active lifestyles that in turn will influence their overall health. Relationships between land use mix (LUM) and physical activity have not been apparent in some studies, which may be because geographical scale and the specificity of hypothesized environment–behavior associations are not taken into account. We compared the strength of association of four Geographic Information Systems-derived LUM measures with walking for transport and perceived proximity to destinations. We assessed physical activity behaviors of 2,506 adults in 154 Census Collection Districts (CCDs) in Adelaide, Australia, for which ‘‘original’’ LUM measures were calculated, and then refined by either: accounting for the geographic scale of measurement; including only the most-relevant land uses; or, both. The refined (but not the ‘‘original’’) LUM measures had significant associations with the frequency of walking for transport (p < 0.05) and area-corrected measures had significant associations with the duration of walking for transport. All LUM measures had significant associations with perceived proximity to destinations, but stronger associations were seen when using the refined measures compared with the original LUM. Identifying the LUM attributes most strongly associated with walking for transport is a priority and can inform environmental and policy initiatives that are needed to promote health-enhancing physical activity.

Perceptions of representatives of public, private, and community sector institutions of the barriers and enablers for physically active transport

Active transport bridges many shared concerns in the public health and transport sectors. To positively affect opportunities for active transport, public health and transport professionals are engaging with other sectors, including urban planning, housing, recreation, retail, education, and employer groups. A first step in such inter-sectoral collaboration is to understand the perceptions of key players in all of these sectors. This paper describes the results of structured interviews with senior and middle-level administrators from public, private, and community groups in a rapidly developing region in Queensland, Australia, to assess the perceived barriers and enablers to active transport. Key themes emerged relating to infrastructure delivery, public transport services, walk- and cycle-friendly community attributes, political leadership and government coordination, and societal travel norms and culture. There were also themes relating to limits due to resources and limited relevant technical expertise, institutional and practitioner cultures, and agencies not identifying with their roles in active transport. Policies and cross-government initiatives were seen to hold promise, including economic incentives and built environment guidelines, campaigns targeting public attitudes and opinions, and community participation in policy-making. These elements are potential keys to positively promoting comprehensive active transport initiatives among gatekeepers and leaders across different sectors.

Aggregation, ageing and transport properties of surface modified fumed silica dispersions

We have investigated the aggregation, ageing and transport properties of surface modified silica dispersions in DMSO by photon correlation spectroscopy and conductivity measurements. The surface modification introduces Li+-ions that dissociate in the dispersion creating a single Li+-ion conducting electrolyte. We show that the surface modification changes the aggregation and ageing properties of the material. There is a pronounced ageing observed for the modified silica dispersions. At high concentrations of fumed silica a gel state is found, which in the case of the surface modified silica is a very weak gel that can be rejuvenated by ultrasonic treatment. The key parameter controlling the aggregation in this system is hydrogen bonding and the surface modification results in a very low number of sites for hydrogen bonding. In addition there is a contribution from repulsive electrostatic interactions in the surface modified silica dispersions due to the highly charged surfaces of these particles. Furthermore, the Li+-ion diffusion, at low silica concentration, is three orders of magnitude faster than that of the silica particles and in the gel state the silica particles are immobile. We also find that the Li+-ion diffusion is virtually independent of the silica concentration in the dispersions.

Investigation of proton dynamics and the proton transport pathway in choline dihydrogen phosphate using solid-state NMR

Choline dihydrogen phosphate has previously been shown to be a good ionic conductor as well as an excellent host for acid doping, leading to high proton conductivities required for e.g., electrochemical devices including proton membrane fuel cells and sensors. A combination of variable-temperature ¹H solid-state NMR and 2D NMR pulse sequences, including ³¹P and ¹³C CODEX and ¹H BaBa, show that the proton conduction mechanism primarily involves assisted transport via a restricted three-site motion of the phosphate unit around the P–O bond that is hydrogen bonded to the choline and exchange of protons between these anions. In other words, proton transport at ambient temperatures appears to occur most favorably along the crystallographic b axis, from phosphate dimer to dimer. At elevated temperatures exchange between the protons of the hydroxyl group on the choline cation and the hydrogen-bonded dihydrogen phosphate groups also contributes to the structural diffusion of the protons in this solid state conductor.

Proton transport in choline dihydrogen phosphate/H3PO4 mixtures

Mixtures of the plastic crystal material choline dihydrogen phosphate [Choline][DHP] and phosphoric acid, from 4.5 mol% to 18 mol% H₃PO₄, were investigated and shown to have significantly higher proton conductivity compared to the pure [Choline][DHP]. This was particularly evident from the electrochemical hydrogen reduction reaction and the proton NMR diffusion measurements, in addition to ionic conductivity measured from the impedance spectroscopy. The ionic conductivity was observed to increase by more than an order of magnitude in phase I (i.e. the highest temperature solid phase in [Choline][DHP]) reaching up to 10⁻² S cm⁻¹. The multinuclear NMR spectroscopy data suggest that, at least on the timescale of the NMR measurement, the H⁺ cations and [DHP] anions are equivalent in both phases. The pulsed field gradient NMR diffusion measurements of the 18 mol% acid sample indicate that all three ions are mobile, however the H⁺ diffusion coefficient is an order of magnitude higher than for the [Choline] cation or the [DHP] anion, and therefore conduction in these materials is dominated by proton conductivity. The thermal stability, as measured by TGA, is unaffected with increasing acid additions and remains high; i.e. no significant mass loss below 200 °C.

Associations between intrapersonal and neighborhood environmental characteristics and cycling for transport and recreation in adults : baseline results from the RESIDE study

Background: This study investigated the relationship between individual and neighborhood environmental factors and cycling for transport and for recreation among adults living in Perth, Western Australia.
Methods: Baseline cross-sectional data from 1813 participants (40.5% male; age range 18 to 78 years) in the Residential Environment (RESIDE) project were analyzed. The questionnaire included information on cycling behavior and on cycling-specific individual, social environmental, and neighborhood environmental attributes. Cycling for transport and recreation were dichotomized as whether or not individuals cycled in a usual week.
Results: Among the individual factors, positive attitudes toward cycling and perceived behavioral control increased the odds of cycling for transport and for recreation. Among the neighborhood environmental attributes, leafy and attractive neighborhoods, access to bicycle/walking paths, the presence of traffic slowing devices and having many 4-way street intersections were positively associated with cycling for transport. Many alternative routes in the local area increased the odds of cycling for recreation.
Conclusions: Effective strategies for increasing cycling (particularly cycling for transport) may include incorporating supportive environments such as creating leafy and attractive neighborhood surroundings, low traffic speed, and increased street connectivity, in addition to campaigns aimed at strengthening positive attitudes and confidence to cycle.

Assessing cost-effectiveness in obesity : active transport program for primary school children— TravelSMART schools curriculum program

Background: To assess from a societal perspective the cost-effectiveness of a school program to increase active transport in 10- to 11-year-old Australian children as an obesity prevention measure.
Methods: The TravelSMART Schools Curriculum program was modeled nationally for 2001 in terms of its impact on Body Mass Index (BMI) and Disability-Adjusted Life Years (DALYs) measured against current practice. Cost offsets and DALY benefits were modeled until the eligible cohort reached age 100 or died. The intervention was qualitatively assessed against second stage filter criteria (‘equity,’ ‘strength of evidence,’ ‘acceptability to stakeholders,’ ‘feasibility of implementation,’ ‘sustainability,’ and ‘side-effects’) given their potential impact on funding decisions.
Results: The modeled intervention reached 267,700 children and cost $AUD13.3M (95% uncertainty interval [UI] $6.9M; $22.8M) per year. It resulted in an incremental saving of 890 (95%UI –540; 2,900) BMI units, which translated to 95 (95% UI –40; 230) DALYs and a net cost per DALY saved of $AUD117,000 (95% UI dominated; $1.06M).
Conclusions: The intervention was not cost-effective as an obesity prevention measure under base-run modeling assumptions. The attribution of some costs to nonobesity objectives would be justified given the program’s multiple benefits. Cost-effectiveness would be further improved by considering the wider school community impacts.

Proton transport properties in zwitterion blends with brønsted acids

We describe zwitterion, 3-(1-butyl-1H-imidazol-3-ium-3-yl)propane-1-sulfonate (Bimps), mixtures with 1,1,1-trifluoro-N-(trifluoromethylsulfonyl)methanesulfoneamide (HN(Tf)₂) as new proton transport electrolytes. We report proton transport mechanisms in the mixtures based on results from several methods including thermal analyses, the complex-impedance method, and the pulsed field gradient spin echo NMR (pfg-NMR) method. The glass transition temperature (Tg) of the mixtures decreased with increasing HN(Tf)₂ concentration up to 50 mol %. The Tg remained constant at −55 °C with further acid doping. The ionic conductivity of HN(Tf)₂ mixtures increased with the HN(Tf)₂ content up to 50 mol %. Beyond that ratio, the mixtures showed no increase in ionic conductivity (10⁻⁴ S cm⁻¹ at room temperature). This tendency agrees well with that of Tg. However, the self-diffusion coefficients obtained from the pfg-NMR method increased with HN(Tf)₂ content even above 50 mol % for all component ions. At HN(Tf)₂ 50 mol %, the proton diffusion of HN(Tf)₂ was the fastest in the mixture. These results suggest that Bimps cannot dissociate excess HN(Tf)₂, that is, the excess HN(Tf)₂ exists as molecular HN(Tf)₂ in the mixtures. The zwitterion, Bimps, forms a 1:1 complex with HN(Tf)₂ and the proton transport property in this mixture is superior to those of other mixing ratios. Furthermore, CH₃SO₃H and CF₃SO₃H were mixed with Bimps for comparison. Both systems showed a similar tendency, which differed from that of the HN(Tf)₂ system. The Tg decreased linearly with increasing acid content for every mixing ratio, while the ionic conductivity increased linearly. Proton transport properties in zwitterion/acid mixtures were strongly affected by the acid species added.

High performance BaBiScCo hollow fibre membranes for oxygen transport

Here we report the production of novel high performance BaBi_0.05Sc_0.1Co_0.85O_3-3 (BaBiScCo) hollow fibres delivering oxygen fluxes of 11.4 ml cm^-2 min^-1 at 950 °C. The doping of bismuth, a highly ionic conductor, at the B-site of a barium based perovskite overcame oxygen ionic transport limitations even at temperatures as low as 600 °C.

Computational modeling aspects of photon transport equations in biological media

This paper presents an overview of modeling light propagation through biological media by solving the photon transport equation. Different variants of the photon transport equation (PTE) are discussed. Several methods for modeling static distributions and the transient response are presented. A discussion on how to mix and match electromagnetic problems with the PTE is also provided.