Young people’s experiences using electric powered indoor-outdoor wheelchairs (EPIOCs): Potential for enhancing users’ development?

Purpose: To examine the experiences of severely physically disabled young people using electric powered indoor/outdoor chairs (EPIOCs). Methods: A priori interview questions examined young people’s functioning with EPIOCs, pain and discomfort with EPIOC use and accidents or injuries resulting from EPIOC use. Eighteen young people (13 males and 5 females) aged 10 -18 (mean 15) years were interviewed by telephone using a qualitative framework approach. Participants were interviewed 10 -19 (mean 14.5) months after delivery of the chair. Diagnoses included muscular dystrophy (n = 10), cerebral palsy (n = 5), and ‘other’ (n =3). Results: Many children reported positive functioning following EPIOC use, including increased independence and social activities like wheelchair football. However, EPIOC use was also associated with pain and discomfort, as well as perceived lack of safety, and minor accidents. Most young people and their families were fairly satisfied with the service and provision of their wheelchairs. Conclusions: The findings suggest that disabled children’s development may benefit from the use of electric powered indoor/outdoor wheelchairs, although the advantages may come at certain costs to young people’s perceived and real safety. Recommendations to powered wheelchair providers include the demonstrated need for additional driving training as these young people mature

Ischemic Heart Disease Incidence in Relation to Fine versus Total Particulate Matter Exposure in a U.S. Aluminum Industry Cohort.

Ischemic heart disease (IHD) has been linked to exposures to airborne particles with an aerodynamic diameter <2.5 μm (PM2.5) in the ambient environment and in occupational settings. Routine industrial exposure monitoring, however, has traditionally focused on total particulate matter (TPM). To assess potential benefits of PM2.5 monitoring, we compared the exposure-response relationships between both PM2.5 and TPM and incidence of IHD in a cohort of active aluminum industry workers. To account for the presence of time varying confounding by health status we applied marginal structural Cox models in a cohort followed with medical claims data for IHD incidence from 1998 to 2012. Analyses were stratified by work process into smelters (n = 6,579) and fabrication (n = 7,432). Binary exposure was defined by the 10th-percentile cut-off from the respective TPM and PM2.5 exposure distributions for each work process. Hazard Ratios (HR) comparing always exposed above the exposure cut-off to always exposed below the cut-off were higher for PM2.5, with HRs of 1.70 (95% confidence interval (CI): 1.11-2.60) and 1.48 (95% CI: 1.02-2.13) in smelters and fabrication, respectively. For TPM, the HRs were 1.25 (95% CI: 0.89-1.77) and 1.25 (95% CI: 0.88-1.77) for smelters and fabrication respectively. Although TPM and PM2.5 were highly correlated in this work environment, results indicate that, consistent with biologic plausibility, PM2.5 is a stronger predictor of IHD risk than TPM. Cardiovascular risk management in the aluminum industry, and other similar work environments, could be better guided by exposure surveillance programs monitoring PM2.5

Dislocation loops as a mechanism for thermoelectric power factor enhancement in silicon nano-layers

A more than 70% enhancement in the thermoelectric power factor of single-crystal silicon is demonstrated in silicon nano-films, a consequence of the introduction of networks of dislocation loops and extended crystallographic defects. Despite these defects causing reductions in electrical conductivity, carrier concentration, and carrier mobility, large corresponding increases in the Seebeck coefficient and reductions in thermal conductivity lead to a significant net enhancement in thermoelectric performance. Crystal damage is deliberately introduced in a sub-surface nano-layer within a silicon substrate, demonstrating the possibility to tune the thermoelectric properties at the nano-scale within such wafers in a repeatable, large-scale, and cost-effective way

On the effectiveness of the thermoelectric energy filtering mechanism in low-dimensional superlattices and nano-composites

Electron energy filtering has been suggested as a promising way to improve the power factor and enhance the ZT figure of merit of thermoelectric materials. In this work, we explore the effect that reduced dimensionality has on the success of the energy-filtering mechanism for power factor enhancement. We use the quantum mechanical non-equilibrium Green's function method for electron transport including electron-phonon scattering to explore 1D and 2D superlattice/nanocomposite systems. We find that, given identical material parameters, 1D channels utilize energy filtering more effectively than 2D as they: (i) allow one to achieve the maximal power factor for smaller well sizes/smaller grains which are needed to maximize the phonon scattering, (ii) take better advantage of a lower thermal conductivity in the barrier/boundary materials compared to the well/grain materials in both: enhancing the Seebeck coefficient; and in producing a system which is robust against detrimental random deviations from the optimal barrier design. In certain cases, we find that the relative advantage can be as high as a factor of 3. We determine that energy-filtering is most effective when the average energy of carrier flow varies the most between the wells and the barriers along the channel, an event which occurs when the energy of the carrier flow in the host material is low, and when the energy relaxation mean-free-path of carriers is short. Although the ultimate reason for these aspects, which cause a 1D system to see greater relative improvement than a 2D, is the 1D system's van Hove singularity in the density-of-states, the insights obtained are general and inform energy-filtering design beyond dimensional considerations

Simulations of nanowire transistors: Atomistic vs. Effective Mass Models

As device sizes shrink towards the nanoscale, CMOS development investigates alternative structures and devices. Existing CMOS devices will evolve to 3D non-planar devices at nanometer sizes. They will operate under strong confinement and strain, regimes where atomistic effects are important. This work investigates atomistic effects in the transport properties of nanowire devices by using a nearest-neighbor tight binding (TB) model (sp3s*d5-SO) [1] for electronic structure calculation, coupled to a 2D Poisson solver for electrostatics. The 2D cross section of a 3D device is described with an arbitrary geometrical shape such as rectangular, cylindrical and tri-gate/FinFET type of structures (Fig. 1(a-d)) using a finite element mesh. Upon convergence, the ballistic transport characteristics are calculated with a semi-classical ballistic model [2]. Comparisons to the effective mass approach (EM) are discussed. Finally, the nonequilibrium Greens’ function (NEGF) approach is used to obtain the transmission coefficients for nanowires in different orientations. This approach will be deployed on nanoHUB.org as an enhancement of the existing Bandstructure Lab [3]

Thermal rectification optimization in nanoporous Si using Monte Carlo simulations

We investigate thermal rectification in nanoporous silicon using a semiclassical Monte Carlo simulation method. We consider geometrically asymmetric nanoporous structures and investigate the combined effects of porosity, interpore distance, and pore position relative to the device boundaries. Two basis geometries are considered, one in which the pores are arranged in rectangular arrays and ones in which they form triangular arrangements. We show that systems (i) with denser, compressed pore arrangements (i.e., with smaller interpore distances), (ii) with the pores positioned closer to the device edge/contact, and (iii) with the pores in a triangular arrangement can achieve rectification of over 55%. Introducing smaller pores into existing porous geometries in a hierarchical fashion increases rectification even further to over 60%. Importantly, for the structures we simulate, we show that sharp rectifying junctions, separating regions of long from short phonon mean-free-paths, are more beneficial for rectification than spreading the asymmetry throughout the material along the heat direction in a graded fashion

Numerical study of the thermoelectric power factor in ultra-thin Si nanowires

Low dimensional structures have demonstrated improved thermoelectric (TE) performance because of a drastic reduction in their thermal conductivity, {\kappa}l. This has been observed for a variety of materials, even for traditionally poor thermoelectrics such as silicon. Other than the reduction in {\kappa}l, further improvements in the TE figure of merit ZT could potentially originate from the thermoelectric power factor. In this work, we couple the ballistic (Landauer) and diffusive linearized Boltzmann electron transport theory to the atomistic sp3d5s*-spin-orbit-coupled tight-binding (TB) electronic structure model. We calculate the room temperature electrical conductivity, Seebeck coefficient, and power factor of narrow 1D Si nanowires (NWs). We describe the numerical formulation of coupling TB to those transport formalisms, the approximations involved, and explain the differences in the conclusions obtained from each model. We investigate the effects of cross section size, transport orientation and confinement orientation, and the influence of the different scattering mechanisms. We show that such methodology can provide robust results for structures including thousands of atoms in the simulation domain and extending to length scales beyond 10nm, and point towards insightful design directions using the length scale and geometry as a design degree of freedom. We find that the effect of low dimensionality on the thermoelectric power factor of Si NWs can be observed at diameters below ~7nm, and that quantum confinement and different transport orientations offer the possibility for power factor optimization.Comment: 42 pages, 14 figures; Journal of Computational Electronics, 201

Incident Ischemic Heart Disease After Long-Term Occupational Exposure to Fine Particulate Matter: Accounting for 2 Forms of Survivor Bias.

Little is known about the heart disease risks associated with occupational, rather than traffic-related, exposure to particulate matter with aerodynamic diameter of 2.5 µm or less (PM2.5). We examined long-term exposure to PM2.5 in cohorts of aluminum smelters and fabrication workers in the United States who were followed for incident ischemic heart disease from 1998 to 2012, and we addressed 2 forms of survivor bias. Left truncation bias was addressed by restricting analyses to the subcohort hired after the start of follow up. Healthy worker survivor bias, which is characterized by time-varying confounding that is affected by prior exposure, was documented only in the smelters and required the use of marginal structural Cox models. When comparing always-exposed participants above the 10th percentile of annual exposure with those below, the hazard ratios were 1.67 (95% confidence interval (CI): 1.11, 2.52) and 3.95 (95% CI: 0.87, 18.00) in the full and restricted subcohorts of smelter workers, respectively. In the fabrication stratum, hazard ratios based on conditional Cox models were 0.98 (95% CI: 0.94, 1.02) and 1.17 (95% CI: 1.00, 1.37) per 1 mg/m(3)-year in the full and restricted subcohorts, respectively. Long-term exposure to occupational PM2.5 was associated with a higher risk of ischemic heart disease among aluminum manufacturing workers, particularly in smelters, after adjustment for survivor bias

Dependence of DC characteristics of CNT MOSFETs on bandstructure models

http://www.gianlucafiori.org/articles/CNTieeenano.pd