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[en] Highlights: •A modified α − k power iteration method is presented for computing the time-eigenvalue. •It is not required to provide the initial values of α for the modified method. •Computational experiences validate the validity and efficiency of the new method. -- Abstract: A modified α − k power iteration method is presented for the prediction of time-eigenvalue(α) of the neutron transport equation. By developing a direct relationship between K-eigenvalue and α-eigenvalue, a new formula is introduced to estimate the value of α. Compared with the conventional method, it is not required to provide the initial values of α for the modified method. Since it is always difficult to guess the suitable initial values, the modified method is more convenient for solving time-eigenvalue problems. Computational experiences show that the accuracy of the modified method is the same as the conventional method.
[en] SGRD (Spectroscopy, Gamma rays, Rapid Deterministic) code is used to infer the dimensions of a one-dimensional model of a shielded gamma ray source. The method is based on the simulation of the un-collided leakage current of discrete gamma lines that are produced by nuclear decay. Experimentally, the unscattered gamma lines leakage current is obtained by processing high precision gamma spectroscopy measurements. The material thicknesses are computed with SGRD using a fast ray-tracing algorithm embedded in a non-linear multidimensional iterative optimization procedure that minimizes the error metric between calculated and measured signatures. For verification, numerical results on a test problem are presented. The test problem is a spherical natural shell surrounded by polyethylene (CH2) and an aluminium cover. The gamma source is due to uranium radioactive decay and 5 characteristic lines are chosen for the optimization. The comparison between the initial and the optimized gamma line spectra with measurement simulated by direct transport calculation shows that the optimization method works well
[en] Nuclear reactor physics deals with the solution of the neutron transport equation, for which several numerical methods and resulting calculation codes exist. Using parallel programming to multiply the resources available to these codes, it is possible to increase their computational power, thus improving their modelling capabilities. This work focuses on the optimization of neutron transport algorithms by means of parallel programming techniques. For cell calculations, the collision probabilities and heterogeneous response (HRM) methods are considered, including the associated multigroup scheme, as implemented in INVAP’s cell calculation code, CONDOR. The diffusion method in a finite difference formulation, used in CITVAP for core calculations, is optimized as well. The parallel methods obtained are implemented in OpenMP, an application for parallel programming in shared memory computers. (author)
[es]La física de reactores está basada en la resolución de la ecuación de transporte de neutrones, para la cual existen diversos esquemas numéricos y códigos de cálculo que los implementan. La programación en paralelo permite aumentar la velocidad de estos códigos mediante la utilización de múltiples unidades de procesamiento, mejorando la capacidad de modelado. En este trabajo se estudió la paralelización de distintos algoritmos asociados a la ecuación de transporte. Para la etapa de cálculos de celda fueron considerados los métodos de probabilidades de colisión y de respuesta heterogénea (HRM), incluyendo el esquema multigrupo asociado, y su implementación en el código CONDOR, desarrollado en INVAP. El método de difusión en diferencias finitas implementado en el código CITVAP fue analizado para los cálculos de núcleo. La programación de los algoritmos desarrollados se realizó en OpenMP, una herramienta de procesamiento en paralelo en el modelo de memoria compartida. (author)
[en] Road transport aspects are becoming increasingly important due to their high impact on economic, environmental and social sustainability. Considering the triple bottom line approach, best practices play a fundamental role within organisations. The purpose of this paper is to analyse several sustainable initiatives in road transport adopted by companies. Design/methodology/approach: The findings were developed and evaluated based on empirical data captured through a survey of 98 professionals involved in logistics and transport activities. Additionally, key literature on transport initiatives was reviewed to supplement the framework for the implementation of best practices in road transport.The exploratory study shows the importance of each best practice and determines the level of implementation of each initiative, comparing the results among different dealers (retailers, wholesalers, carriers and manufacturers), type of transport fleet and companies’ revenues. Research limitations/implications: The sample of 98 companies was based on simple search filters and the group is not wholly representative of all sectors. Respondents were mainly managers from Spain involved in logistics and transport activities. Surveyed companies included manufacturing, retailers, wholesalers and third-party logistics providers. Practical implications: The most common best practices in road transport are identified, including initiatives related to: efficiency, reusability, safety, optimization, emissions, waste and recycling. Initiatives that influence road transport are ranked by their degree of implementation in the companies analysed.
[en] We investigate transport theory for anisotropic transport of neutrons in finite medium or injected externally. When anisotropic transport is treated by the usual transport equation, on which reversibility of collisions is shown imposed, successive collisions always induce 'self-collision' or sham collision; the fact is unavoidable as long as statistical ensemble is constructed from the reductionistic mechanical-systems. Then, irreductionistic elements, or spatial cells containing assembly of free neutrons (and implicit medium nuclei) uniformly are introduced, from which alternative Liouville equation is constructed. Successive collisions are expressed by fusing three cells; for reviving mechanical law in the collisions the law of action and reaction is applied to between first fused-cell and third cell. Extended transport equation can thus describe the process of chaotically mixing anisotropic momentum, i.e., the well-known deep penetration. (author)
[en] Global confinement properties of the limiter plasmas of the first operational campaign of W7-X are investigated with special focus on the energy confinement and possible operational limits. The energy confinement time was found to be close to expectations from the empirical ISS04 scaling for stellarators. Absolute values up to were achieved. This can be considered as a great success for the initial operation of the device. However, a clear degradation of the performance was observed when radiative losses became significant, which was typically the case at low heating power. While a significant improvement of the plasma purity is expected during divertor operation, the presented results underline the importance of the impurity dynamics for the development of high-performance steady-state scenarios in W7-X. Furthermore, comparisons of the global performance properties with neoclassical transport modeling are presented. These studies are not yet fully conclusive, which could indicate that anomalous transport may have played an essential role in the low-density OP1.1 plasmas. (paper)
[en] Traffic regulations on the roads mostly aim to ensure the safety of road users. Vehicles may come across many traffic lights (TL) on their way, and some of them will reach TLs in the green phase when others are in yellow/red phases. Reaching a traffic light on the yellow or the red phase means a loss of inertia or kinetic energy that could also be interpreted as a loss of fuel because after the light turns green, the vehicle will resume its normal speed using extra fuel (compared to moving without stopping at traffic light). The economic reasoning may seem negligible to some, but in case of heavy cars or trucks, stopping can be very expensive, especially when fully loaded. Another effect of such movement interruptions is safety leakages. In some cases, drivers could simply be late after a slow down. Moreover, the slowing down that is required to stop the vehicle at traffic lights forces the driver to undergo unhealthy deceleration. One of the simple solutions of the given problem is to change the route from a disallowed to an allowed one at traffic lights; in contrast to moving directly on the route that will require the driver to stop and wait for a red light, a heavy truck can turn right or left in order to take a slightly longer route if possible, thereby increasing its travel distance but saving inertia. This study proposed an alternative solution to the described problem as an intelligent speed control that mostly relies on knowing the traffic light's state and aims to control the vehicle's speed in such a way that it always tries to reach the traffic light in its green phase. (author)
[en] RANKERN 16 is the latest version of the point-kernel gamma radiation transport Monte Carlo code from AMEC Foster Wheeler's ANSWERS Software Service. RANKERN is well established in the UK shielding community for radiation shielding and dosimetry assessments. Many important developments have been made available to users in this latest release of RANKERN. The existing general 3D geometry capability has been extended to include import of CAD files in the IGES format providing efficient full CAD modelling capability without geometric approximation. Import of tetrahedral mesh and polygon surface formats has also been provided. An efficient voxel geometry type has been added suitable for representing CT data. There have been numerous input syntax enhancements and an extended actinide gamma source library. This paper describes some of the new features and compares the performance of the new geometry capabilities. (authors)
[en] We propose a new method to control the directed quantum transport of ultracold atoms in a one-dimensional optical lattice. In this proposal, the effective tunneling between the neighboring sites can be adjusted via coherent destruction of tunneling by tuning the phase of the external field, instead of using the driving field intensity or the frequency, thus the directed quantum transport of ultracold atoms can be coherently controlled in a much easier manner. Our proposal overcomes the major drawback of the method used by Creffield et al. [Phys. Rev. Lett. 99 (2007) 110501], and can be implemented, in principle, in any one-dimensional optical lattice. Some potential applications of the scheme are also discussed. (authors)