Integrating Dynamics and Wear Modelling to Predict Railway Wheel Profile Evolution

The aim of the work described was to predict wheel profile evolution by integrating multi-body dynamics simulations of a wheelset with a wear model. The wear modelling approach is based on a wear index commonly used in rail wear predictions. This assumes wear is proportional to Tγ, where T is tractive force and γ is slip at the wheel/rail interface. Twin disc testing of rail and wheel materials was carried out to generate wear coefficients for use in the model. The modelling code is interfaced with ADAMS/Rail, which produces multi-body dynamics simulations of a railway wheelset and contact conditions at the wheel/rail interface. Simplified theory of rolling contact is used to discretise the contact patches produced by ADAMS/Rail and calculate traction and slip within each. The wear model combines the simplified theory of rolling contact, ADAMS/Rail output and the wear coefficients to predict the wear and hence the change of wheel profile for given track layouts

Avian interactions with renewable energy infrastructure: An update

Energy infrastructure is widespread worldwide. Renewable energy technologies, which are expanding their footprint on the landscape and their contribution to energy availability, represent a different kind of infrastructure from extractive energy technologies. Although renewable energy sources may offer a ‘greener alternative’ to traditional extractive energy sources, mounting evidence suggests that renewable energy infrastructure, and the transmission lines needed to convey energy from renewable energy facilities to users, may impact birds. Peer-reviewed literature historically has focused on the direct effects of electrocution and, to a lesser extent, collisions with overhead power systems, and on avian collisions at wind energy facilities, with less consideration of indirect effects or other energy sectors. Here, we review studies that have examined direct and indirect effects on birds at utility-scale onshore windand solar-energy facilities, including their associated transmission lines. Although both direct and indirect effects appear site-, species-, and infrastructure-specific, generalities across energy sectors are apparent. For example, largebodied species with high wing loading and relatively low maneuverability appear to be especially susceptible to direct effects of tall structures, and the risk of collision is likely greater when structures are placed perpendicular to flight paths or in areas of high use. Given that all infrastructure types result in direct loss or fragmentation of habitat and may affect the distribution of predators, indirect effects mediated by these mechanisms may be pervasive across energy facilities. When considered together, the direct and indirect effects of renewable energy facilities, and the transmission lines serving these facilities, are likely cumulative. Ultimately, cross-facility and cross-taxon meta-analyses will be necessary to fully understand the cumulative impacts of energy infrastructure on birds. Siting these facilities in a way that minimizes avian impacts will require an expanded understanding of how birds perceive facilities and the mechanisms underlying direct and indirect effects. La infraestructura energ´etica esta´ ampliamente distribuida en todo el mundo. Las tecnolog´ıas de energ´ıa renovable esta´n expandiendo su huella en el paisaje y su contribuci ´on a la disponibilidad de energ´ıa, y representan un tipo diferente de infraestructura a la de las tecnolog´ıas extractivas de energ´ıa. Aunque las fuentes de energ´ıa renovable ofrecen una ‘‘alternativa ma´s verde’’ en comparaci ´on con las fuentes tradicionales de extracci ´on de energ´ıa, existe bastante evidencia que sugiere que la infraestructura de energ´ıa renovable y las l´ıneas de transmisi ´on necesarias para transportar la energ´ıa hacia los usuarios podr´ıan afectar a las aves. La literatura cient´ıfica tradicionalmente se ha enfocado en los efectos directos de la electrocuci ´on y, en menor medida, en las colisiones con los sistemas a´ereos de energ´ıa y con las estructuras de energ´ıa e ´ olica. En cambio, ha habido escasa consideraci ´on de sus efectos indirectos y de otros sectores energ´ eticos. En este trabajo revisamos estudios que investigaron los efectos directos e indirectos sobre las aves a la escala de instalaciones terrestres de energ´ıa e ´ olica y solar, incluyendo sus l´ıneas de transmisi ´ on. Aunque los efectos directos e indirectos parecen ser espec´ıficos para cada sitio, especie y tipo de energ´ıa, existen generalidades evidentes entre diferentes sectores energ´ eticos. Por ejemplo, las especies de mayor tama˜ no, con alta carga alar y maniobrabilidad relativamente baja parecen ser especialmente susceptibles a los efectos directos de las estructuras altas, y el riesgo de colisi ´on probablemente es mayor cuando las estructuras se ubican perpendiculares al sentido del vuelo o en a´reas con alto uso. Dado que todos los tipos de infraestructura resultan en la p´erdida directa del ha´bitat o en su fragmentaci ´on y podr´ıan afectar la distribuci ´on de los depredadores, los efectos indirectos mediados por estos mecanismos pueden ser comunes entre diferentes instalaciones energ´ eticas. Cuando se consideran en conjunto, los efectos directos e indirectos en las instalaciones de energ´ıa renovable y en las l´ıneas de transmisi ´on asociadas probablemente son acumulativos. Finalmente, sera´ necesario hacer meta ana´ lisis a trav´es de varios tipos de instalaciones y taxones para entender completamente los impactos acumulativos de la infraestructura energ´etic

Neutron Calibration Sources in the Daya Bay Experiment

We describe the design and construction of the low rate neutron calibration sources used in the Daya Bay Reactor Anti-neutrino Experiment. Such sources are free of correlated gamma-neutron emission, which is essential in minimizing induced background in the anti-neutrino detector. The design characteristics have been validated in the Daya Bay anti-neutrino detector.Comment: 13 pages, 7 figure

Surface Hydrogen Modeling of Super Soft X-ray Sources: Are They Supernova Ia Progenitors?

Nova explosions occur on the white dwarf (WD) component of a Cataclysmic Variable stellar system which is accreting matter lost by a companion. A Type Ia supernova explosion is thought to result when a WD, in a similar binary configuration, grows in mass to the Chandrasekhar Limit. Here, we present calculations of accretion of Solar matter, at a variety of mass accretion rates, onto hot ($2.3 \times 10^{5}$K), luminous (30L$_\odot$), massive (1.25M$_\odot$, 1.35M$_\odot$) Carbon-Oxygen WDs. In contrast to our nova simulations where the WD has a low initial luminosity and a thermonuclear runaway (TNR) occurs and ejects material, these simulations do not eject material (or only a small fraction of the accreted material) and the WD grows in mass. A hydrogen TNR does not occur because hydrogen fuses to helium in the surface layers, and we call this process Surface Hydrogen Burning (SHB). As the helium layer grows in mass, it gradually fuses either to carbon and oxygen or to more massive nuclei depending on the WD mass and mass accretion rate. If such a WD were to explode in a SN Ia event, therefore, it would show neither hydrogen nor helium in its spectrum as is observed. Moreover, the luminosities and effective temperatures of our simulations agree with the observations of some of the Super Soft X-ray Binary Sources and, therefore, our results strengthen previous speculation that some of them (CAL 83 and CAL 87 for example) are probably progenitors of SN Ia explosions. Finally, we have achieved SHB for values of the mass accretion rate that almost span the observed values of the Cataclysmic Variables.Comment: Accepted by APJL, 4 pages, 1 figure, LaTex (uses emulateapj.sty

Correlated defects, metal-insulator transition, and magnetic order in ferromagnetic semiconductors

The effect of disorder on transport and magnetization in ferromagnetic III-V semiconductors, in particular (Ga,Mn)As, is studied theoretically. We show that Coulomb-induced correlations of the defect positions are crucial for the transport and magnetic properties of these highly compensated materials. We employ Monte Carlo simulations to obtain the correlated defect distributions. Exact diagonalization gives reasonable results for the spectrum of valence-band holes and the metal-insulator transition only for correlated disorder. Finally, we show that the mean-field magnetization also depends crucially on defect correlations.Comment: 4 pages RevTeX4, 5 figures include

Auto-calibration of ultrasonic lubricant-film thickness measurements

The measurement of oil film thickness in a lubricated component is essential information for performance monitoring and design. It is well established that such measurements can be made ultrasonically if the lubricant film is modelled as a collection of small springs. The ultrasonic method requires that component faces are separated and a reference reflection recorded in order to obtain a reflection coefficient value from which film thickness is calculated. The novel and practically useful approach put forward in this paper and validated experimentally allows reflection coefficient measurement without the requirement for a reference. This involves simultaneously measuring the amplitude and phase of an ultrasonic pulse reflected from a layer. Provided that the acoustic properties of the substrate are known, the theoretical relationship between the two can be fitted to the data in order to yield reflection coefficient amplitude and phase for an infinitely thick layer. This is equivalent to measuring a reference signal directly, but importantly does not require the materials to be separated. The further valuable aspect of this approach, which is demonstrated experimentally, is its ability to be used as a self-calibrating routine, inherently compensating for temperature effects. This is due to the relationship between the amplitude and phase being unaffected by changes in temperature which cause unwanted changes to the incident pulse. Finally, error analysis is performed showing how the accuracy of the results can be optimized. A finding of particular significance is the strong dependence of the accuracy of the technique on the amplitude of reflection coefficient input data used. This places some limitations on the applicability of the technique. © 2008 IOP Publishing Ltd