[en] Given the difference between peak and off-peak occupancy rates in public transport, emissions per traveller kilometre are lower in the peak than in the off-peak period, whereas the opposite pattern is observed for cars. It is argued that it is much more fruitful to analyse environmental effects in marginal terms. This calls for a careful analysis of capacity management policies of public transport suppliers that are facing increased demand during both peak and off-peak periods. A detailed analysis of capacity management by the Netherlands Railways (NS) revealed that off-peak capacity supply is mainly dictated by the demand levels during the peak period. The analysis included the effects of increased frequency and increased vehicle size on environmental impacts, while environmental economies of vehicle size were also taken into account. The main conclusion is that the marginal environmental burden during the peak hours is much higher than is usually thought, whereas it is almost zero during the off-peak period. This implies a pattern that is the precise opposite of the average environmental burden. Thus, an analysis of environmental effects of public transport based on average performance would yield misleading conclusions

[en] Arguments for and against the highly controversial levy approved by Translink, the transportation authority in Greater Vancouver, are discussed. This highly controversial plan will cost car owners in the Greater Vancouver Regional District up to $120 per year for transportation improvements to roads, public transit and bicycle paths. Supporters of the levy contend that divisive as the levy may be, it is a bold first step towards a user-pay system. The GVRD transportation system is badly in need of improvement and the levy is a quick and temporary way to finance the necessary work. However, even supporters of the scheme suggest that the levy should not be seen as the final solution. Instead, they urge Translink to move towards a usage-pay system, including a fuel tax, combined with road and bridge tolls. A pay-as-you-go system would encourage residents to drive less, or to drive more fuel-efficient vehicles. Regardless of how the public reacts to the levy system, Translink should commit to building a more equitable system to pay for the transportation improvements needed by the region

[en] In the Matrix MOC a linear algebraic equation system can be constructed by sweeping only once, and then solving the linear system takes the place of repeatedly characteristics sweeping. Traditionally, k_e_f_f is computed by power iteration (PI), whose convergence rate depends on the dominance ratio deeply. Large problems of practical interest often have dominance ratios close to 1, leading to slow convergence of PI. Combined with multi-group GMRES coupling all groups directly, Wielandt iteration is studied for accelerating Matrix MOC. Numerical results of several benchmarks demonstrate that Wielandt iteration combined with multi-group GMRES can obtain good accuracy and higher efficiency compared with PI. (authors)

[en] The Monte Carlo generalized rejection technique provides a continuous passage from the inverse equation sampling method to the uniform sampling rejection method; it is well known that the nonuniform rejection method can be used to achieve very significant increases in sampling efficiency. The nonuniform rejection method was applied to the Klein--Nishina probability density function, and improved efficiencies were obtained over the uniform sampling method of up to 100 percent at high gamma-ray energies and 10 to 60 percent improved efficiencies in the energy range from 0.3 to 1.5 MeV, respectively

[en] New estimation approaches for nuclear reactor calculations by Monte Carlo are developed and investigated, with the purpose of surmounting or alleviating existing difficulties facing the application of the Monte Carlo Method. Bias-free estimators which extract more information on a given particle tract than currently used estimators are deduced. These depend on estimating separately the different Neumann series terms of the solution to the Boltzmann Transport Equation, and are based on underlying absorbing or nonabsorbing Markov Chain random walk models. They are applied to representative slowing-down and deep penetration problems. Effective biases arising from application of currently used methods are highly suppressed. Comparison to analytical solutions and to currently used methods shows their distinctive advantages. An approach for the systematic determination of optimal biasing parameters in importance sampling calculations, depending on particle tracks scaling; which avoids the effective biases and infinite variances in these calculations, is developed and applied to the deep penetration problem of particle transport. The use of stationary functionals from variational theory for variance reduction in Monte Carlo calculations is discussed. Suggestions for alternative error estimation methods in Monte Carlo calculations, based on functionals of the second moment for the collision and last collision estimators, or on reconstructing the sample distributions from sample moments, are exposed. Implementation of the suggested new approaches in future Monte Carlo calculations is discussed

[en] A simple extension of the discrete ordinates method for solving the transport equation with quadrilateral meshes in X-Y and R-Z geometry is described. Numerical results of some benchmark problems are presented for showing the adequacy of the modified scheme. (author)

[en] The critical slab problem has been studied in the one-speed neutron transport equation with isotropic scattering by using the first kind of Chebyshev Polynomials. The moment criticality solutions were obtained for the uniform finite slab using Mark and Marshak type vacuum boundary conditions. The results obtained by this approximation are presented in tables which also include the results obtained by the P_N method for comparison. (orig.)

[en] I calculated neutron and gamma-ray equivalent doses leaking through a variety of infinite (laminate) slab-shields. In the shield computations, I used, as the incident neutron spectrum, the leakage spectrum (<20 MeV) calculated for the LANSCE tungsten production target at 90 degree to the target axis. The shield thickness was fixed at 60 cm. The results of the shield calculations show a minimum in the total leakage equivalent dose if the shield is 40-45 cm of iron followed by 20-15 cm of borated (5% B) polyethylene. High-performance shields can be attained by using multiple laminations. The calculated dose at the shield surface is very dependent on shield material. 4 refs., 4 figs., 1 tab

[en] A finite element method is introduced for solving the neutron transport equations. Our method falls into the category of Petrov-Galerkin solution, since the trial space differs from the test space. The close relationship between this method and the discrete ordinate method is discussed, and the methods are compared for simple test problems

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