Dynamic Alignment of Single-Walled Carbon Nanotubes in Pulsed Magnetic Fields

We have used linear dichroism spectroscopy to measure the dynamic alignment of single-walled carbon nanotubes (SWNT) in pulsed magnetic fields up to 55 T. We make use of the fact that SWNTs absorb light only when the electric-field vector is oriented parallel to the tube axis. SWNTs thus produce a polarization dependent change of the optical transmission, that permits precise measurements of their orientation. In order to distinguish the influence of different mechanisms governing the alignment such as the external magnetic field, Brownian motion or the tube length, we have systematically varied parameters such as the viscosity of the aqueous solution and the sample temperature.     

Effects of core excess reactivity and coolant average temperature on maximum operable time of NIRR-1 miniature neutron source reactor

We appraised in this study the effects of core excess reactivity and average coolant temperature on the operable time of the Nigeria Research Reactor-1 (NIRR-1), which is a miniature neutron source reactor (MNSR). The duration of the reactor operating time and fluence depletion under different operation mode as well as change in core excess reactivity with temperature coefficient was investigated over a period of five years. Our result shows that there is a strong dependence of reactor operating time on core excess reactivity and temperature coefficient. It was observed in 2004 that with a cold core excess reactivity of 3.77 mk, at full-power flux of 1.0 × 10¹² n cm⁻² s⁻¹ the reactor operated for 5 continues hours. At half-power flux of 0.5 × 10¹² n cm⁻² s⁻¹ and under the same excess reactivity condition, the reactor reaches 8 h of operation. However, re-measurements done in 2009 shows that excess reactivity of the reactor has reduced to 2.80 mk, the operable time at full flux dropped to 3.5 h while that of half-power became 7 h. We also investigated the reactor's energy consumption within the period under study and found to be much more in 2008 compared to the previous years. We infer that the amount of fluence consumed and the excessive reactor usage in 2008 has contributed significantly to the reduction of the reactor's excess reactivity in that year. The results obtained here revels that for an MNSR with a clean core excess reactivity between 3.5 mk and 4.0 mk, 5 and 8 h are the maximum operable times under full and half-power flux conditions, respectively. Negative deviation from these optimum times is therefore an indication of a drop in excess reactivity and the need for beryllium shims addition.     

Investigative studies on effect of reflector thickness on the performance of low enriched uranium-fueled miniature neutron source reactors

Neutronics analyses were performed on the 30 kW(th) GHARR-1 facility to investigate the effects on increased beryllium annular reflector thickness on nuclear criticality safety and on the neutron flux levels in the experimental channels. The investigative study was carried out using the Monte Carlo code MCNP on a hypothetical LEU UO₂ core theoretically enriched to 12.6% and having the same core configuration as the present 90.2% enriched HEU U-Al core. The analyses were performed on four models consisting of a reference model with 10.2 cm annular reflector thickness and three new design modification models with increased reflector thickness of 10.3, 10.4 and 10.5 cm respectively. The simulations indicated average thermal neutron fluxes of (9.80 ± 0.0017)E+11 n/cm² s in the inner irradiation channels for the reference model, indicating a 2% decrease with respect to the nominal flux of 1.00E+12 n/cm² s. Relatively lower neutron fluxes were obtained for the modification models with an average of (9.79 ± 0.0017)E+11 n/cm² s, representing losses of 2.01% and 0.01% with respect to the HEU core and reference LEU model.     

Accident risk and risk-taking behaviour among young drivers

This paper reviews the evidence relevant to the hypotheses that young (16-25) drivers are at greater risk of being involved in a casualty accident than older drivers and this greater risk is primarily a function of their propensity to take risks while driving. The first hypothesis is clearly supported by epidemiological research even when controlling for differences in the quantity and quality of road travel and driving experience. The second hypothesis is also supported by observational and self-report surveys of driving behaviour. Some of the research and theory bearing on risk perception and risk utility, possible mediators of risk-taking, is also reviewed.     

The effectiveness of the Canadian mandatory seat belt use laws

The impact of four provincial mandatory seat belt use laws passed in 1976 and 1977 on seat belt use and on motor vehicle occupant casualties is examined. Subsequent to the passage of the laws, belt use typically increased from 20 to the 70% level dropping to around 50% over the next several years. Ontario exhibited a clear drop in the fatality and injury rates in the years following the introduction of the law. Quebec experienced little reduction in casualties. The changes in casualties for British Columbia and Saskatchewan were mixed with the former showing a drop only in the fatality rate subsequent to the seat belt law, while the latter experienced a reduction only in the injury rate. The provinces without seat belt use laws also enjoyed some reductions in occupant casualty rates. The changes in occupant casualties in the legislated provinces were also examined relative to the changes in non-occupant casualties and relative to the unlegislated provinces. It was concluded that three provinces experienced some reductions as a result of legislation but not as much as anticipated. It is speculated that the impact of the seat belt use laws fell short of expectations because it was mainly the safe drivers who buckled up in response to the laws.     

SPROUT—A Modeling Language for SEED

An important capability of the SEED system is rapid generation of internal design representations, including design alternatives, that can be evaluated in terms of a broad range of criteria. It consists of modules that must communicate with each other and remain extensible. From a software engineering perspective, there exists no single programming language or database management system, commercial or research-based, that provides all the needed support. In this paper, we describe the SPROUT modeling language, the cornerstone of efforts to bridge this gap. It supports the specification of a system information model, which contains a building product model as a subset. Developments are discussed that lead to the current language design as well as the support for case-based design, persistent storage of objects, management of versions and alternatives, and communication between different SEED modules (i.e., agents). Emphasis is placed on the automatic generation of computer programs and database schemas from a SPROUT specification. Lastly, this effort is compared to other comparable efforts including PDES∕STEP.     

A LINEAR CORRELATION FOR SOLID SOLUBILITIES IN SUPERCRITICAL GASES

A previously derived equation (Jonah, 1986) for solid solubilities in supercritical gases is tested in empirically abbreviated form against experimental data on six solutes in supercritical ethylene and carbon dioxide. The solids considered are benzoic acid, 2,3- and 2,6-dimethylnaphthalene, naphthalene, phenanthrene and anthracene.

Our equation correlates these solid solubilities linearly with certain functions of pure solvent thermodynamic properties, thereby making possible the interpolation and extrapolation of sparse experimental data.     

Geometric characterization of nanoporous metals

Nanoporous metals made by dealloying possess significant geometric complexity—they are random, bicontinuous structures that also possess bubbles within ligaments, regions of very high negative, positive, and saddlepoint curvature, and significant polyfaceting. Here we introduce methods to geometrically quantify the structure of nanoporous metals employing simulated model nanoporous metals generated via large-scale kinetic Monte Carlo simulations as the basis of discussion. A method is introduced to transform these simulated structures into smooth triangulated meshes using new mesh-smoothing algorithms that hybridize mean curvature flow and signal processing approaches to mesh fairing. The technique is assessed by comparing the exact genus of high-genus meshes with the genus calculated via the Gauss–Bonnet formula, and works well to find the local curvature at all points of simulated surfaces of high topological genus. Specific geometric quantification of nanoporous metals is discussed for two quantities: (i) the relative surface area fraction of different crystal facets, which is important for catalysis; and (ii) the curvature distribution on the surface of porous metals, important for applications in which high curvature features are active (e.g. optical sensing).