236 research outputs found
"Studs": a squat-type defect in rails
In the mid-2000s a rail defect that was classified as a "squat" became increasingly common on London Underground's track. By 2006 there were about 600 of these and they had become the Underground's single most common rail defect. This defect occurred almost exclusively on lines carrying relatively new rolling stock. The work reported here was undertaken initially to characterize this defect, advise as to whether it was indeed a squat and propose a hypothesis that explained its mechanism of formation. The paper includes observations and measurements from track and initial results of metallurgical analysis. The hypothesis for formation of the defects is presented, and both similarities and differences are discussed between these defects and the classical "squat". The defect on London Underground appears to be the same as that described by Marich and his colleagues in Australia and by Li and his colleagues in the Netherlands. It is evidently not a rolling contact fatigue defect. In order to avoid confusion arising from simple misuse of an established term, it is proposed that these defects be given a different name, for which “stud” is proposed. Evidence to date is that the "stud" is a significantly more benign defect than a "squat"
Kinetic equations for thermal degradation of polymers
Kinetic equations are analyzed for thermal degradation of polymers. The
governing relations are based on the fragmentation-annihilation concept.
Explicit solutions to these equations are derived in two particular cases of
interest. For arbitrary values of adjustable parameters, the evolution of the
number-average and mass-average molecular weights of polymers is analyzed
numerically. Good agreement is demonstrated between the results of numerical
simulation and experimental data. It is revealed that the model can correctly
predict observations in thermo-gravimetric tests when its parameters are
determined by matching experimental data for the decrease in molecular weight
with exposure time
Prediction of RCF Damage on Underground Metro Lines
London Underground (LUL) is one of the largest metro networks in the world and carried nearly 1.5 billion passengers in 2015. This increasing passenger demand leads to higher axle loads and shorter headways in the railway operations. However, this has a detrimental impact on the damage generated at the wheel-rail interface. In spite of the advances in rolling stock and track engineering, new developments in material manufacturing methods and rail inspection technology, cracking in rails still remains a major concern for infrastructure managers in terms of safety and maintenance costs. In this study, field data from two metro lines on the LUL network was analysed to identify the distribution and severity of the different damage types. Detailed vehicle dynamics route simulations were conducted for the lines and the calculated wheel-rail forces were investigated to assess the applicability current models for the prediction of rail damage on metro lines. These models include the Whole Life Rail Model (WLRM), previously developed for Great Britain (GB) main line tracks, and Shakedown theory. The influence of key factors such as curve radius, different friction conditions, track irregularities and wheel-rail profiles on the wheel-rail contact interface have been evaluated and compared with outputs from simulations on mainline routes. The study found that the contact patch energy (Tγ) and the interaction between wear and RCF in rails were highly influenced by the characteristics of metro tracks. It was also shown that both the Tγ and Shakedown methods can provide successful prediction of damage susceptibility of rails. However, in order to increase the accuracy of damage predictions and to ascertain the severity of different damage types, the duty conditions which are observed by the rail and the changes in contact conditions resulting from the successive vehicle passes should be considered in the modelling
Study of Vibrations in a Short-Span Bridge Under Resonance Conditions Considering Train-Track Interaction
[EN] Resonance is a phenomenon of utmost importance in railways engineering, leading to vast damages both in track and vehicles. A short-span bridge has been modeled by means of a finite elements method model, calibrated and validated with real data, to study resonance vibrations induced by the passage of trains. Furthermore, the influence of vehicle speed and track damping on the vibrations registered on the rail, the sleeper and the bridge has been assessed. Different track and vehicle pathologies have been proposed and their effect on the resonance of the bridge has been evaluated.Ribes-Llario, F.; Velarte-González, JL.; Pérez-Garnes, JL.; Real Herráiz, JI. (2016). Study of Vibrations in a Short-Span Bridge Under Resonance Conditions Considering Train-Track Interaction. Latin American Journal of Solids and Structures. 13(7):1236-1249. doi:10.1590/1679-78252773S12361249137Ahlström, J., & Karlsson, B. (1999). Microstructural evaluation and interpretation of the mechanically and thermally affected zone under railway wheel flats. Wear, 232(1), 1-14. doi:10.1016/s0043-1648(99)00166-0Bian, X., Chao, C., Jin, W., & Chen, Y. (2011). A 2.5D finite element approach for predicting ground vibrations generated by vertical track irregularities. Journal of Zhejiang University-SCIENCE A, 12(12), 885-894. doi:10.1631/jzus.a11gt012Grassie, S. L., & Kalousek, J. (1993). Rail Corrugation: Characteristics, Causes and Treatments. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 207(1), 57-68. doi:10.1243/pime_proc_1993_207_227_02Gupta, A., & Singh Ahuja, A. (2014). Dynamic Analysis of Railway Bridges under High Speed Trains. Universal Journal of Mechanical Engineering, 2(6), 199-204. doi:10.13189/ujme.2014.020604Ju, S. H., & Lin, H. T. (2003). Resonance characteristics of high-speed trains passing simply supported bridges. Journal of Sound and Vibration, 267(5), 1127-1141. doi:10.1016/s0022-460x(02)01463-3Kwark, J. W., Choi, E. S., Kim, Y. J., Kim, B. S., & Kim, S. I. (2004). Dynamic behavior of two-span continuous concrete bridges under moving high-speed train. Computers & Structures, 82(4-5), 463-474. doi:10.1016/s0045-7949(03)00054-3Lu, Y., Mao, L., & Woodward, P. (2012). Frequency characteristics of railway bridge response to moving trains with consideration of train mass. Engineering Structures, 42, 9-22. doi:10.1016/j.engstruct.2012.04.007Makino, T., Yamamoto, M., & Fujimura, T. (2002). Effect of material on spalling properties of railroad wheels. Wear, 253(1-2), 284-290. doi:10.1016/s0043-1648(02)00117-5Mao, L., & Lu, Y. (2013). Critical Speed and Resonance Criteria of Railway Bridge Response to Moving Trains. Journal of Bridge Engineering, 18(2), 131-141. doi:10.1061/(asce)be.1943-5592.0000336Museros, P., Romero, M. ., Poy, A., & Alarcón, E. (2002). Advances in the analysis of short span railway bridges for high-speed lines. Computers & Structures, 80(27-30), 2121-2132. doi:10.1016/s0045-7949(02)00261-4Pal, S., Valente, C., Daniel, W., & Farjoo, M. (2012). Metallurgical and physical understanding of rail squat initiation and propagation. Wear, 284-285, 30-42. doi:10.1016/j.wear.2012.02.013Sheng, X., Jones, C. J. C., & Thompson, D. J. (2004). A theoretical model for ground vibration from trains generated by vertical track irregularities. Journal of Sound and Vibration, 272(3-5), 937-965. doi:10.1016/s0022-460x(03)00782-xSimon, S., Saulot, A., Dayot, C., Quost, X., & Berthier, Y. (2013). Tribological characterization of rail squat defects. Wear, 297(1-2), 926-942. doi:10.1016/j.wear.2012.11.011Wang, Y., Wei, Q., Shi, J., & Long, X. (2010). Resonance characteristics of two-span continuous beam under moving high speed trains. Latin American Journal of Solids and Structures, 7(2), 185-199. doi:10.1590/s1679-78252010000200005Xia, H., Zhang, N., & Guo, W. W. (2006). Analysis of resonance mechanism and conditions of train–bridge system. Journal of Sound and Vibration, 297(3-5), 810-822. doi:10.1016/j.jsv.2006.04.022Yang, Y. B., & Lin, C. W. (2005). Vehicle–bridge interaction dynamics and potential applications. Journal of Sound and Vibration, 284(1-2), 205-226. doi:10.1016/j.jsv.2004.06.03
Graviton Resonances in E+ E- -> MU+ MU- at Linear Colliders with Beamstrahlung and ISR Effects
Electromagnetic radiation emitted by the colliding beams is expected to play
an important role at the next generation of high energy e^+ e^- linear
collider(s). Focusing on the simplest process e+e- -> mu+ mu-, we show that
radiative effects like initial state radiation (ISR) and beamstrahlung can lead
to greatly-enhanced signals for resonant graviton modes of the Randall-Sundrum
model.Comment: 20 pages Latex, 7 eps figure
Radiative decay of the lightest neutralino in an R-parity violating supersymmetric theory
In an R-parity violating supersymmetric scenario, the lightest neutralino
is no longer a stable particle. We calculate the branching
ratio for the decay mode which
occurs at the one-loop level. Taking into account bilinear as well as trilinear
lepton number violating interactions as the sources of R-parity violation, we
make a detailed scan of the parameter space, both with and without gaugino mass
unification and including the constraints on the neutrino sector from the
recent Superkamiokande results. This study enables one to suggest interesting
experimental signals distinguishing between the two types of R-parity breaking,
and also to ascertain whether such radiative decays can give rise to collider
signals of the type + from pair-produced
neutralinos.Comment: 25 pages, LaTex including postscript figures. Uses axodraw.sty. Minor
typographic errors correcte
Enhanced superconducting pairing interaction in indium-doped tin telluride
The ferroelectric degenerate semiconductor SnTe exhibits
superconductivity with critical temperatures, , of up to 0.3 K for hole
densities of order 10 cm. When doped on the tin site with greater
than indium atoms, however, superconductivity is observed up
to 2 K, though the carrier density does not change significantly. We present
specific heat data showing that a stronger pairing interaction is present for
than for . By examining the effect of In dopant atoms on
both and the temperature of the ferroelectric structural phase
transition, , we show that phonon modes related to this transition are
not responsible for this enhancement, and discuss a plausible candidate
based on the unique properties of the indium impurities.Comment: 7 page
Relating the CMSSM and SUGRA models with GUT scale and Super-GUT scale Supersymmetry Breaking
While the constrained minimal supersymmetric standard model (CMSSM) with
universal gaugino masses, m_{1/2}, scalar masses, m_0, and A-terms, A_0,
defined at some high energy scale (usually taken to be the GUT scale) is
motivated by general features of supergravity models, it does not carry all of
the constraints imposed by minimal supergravity (mSUGRA). In particular, the
CMSSM does not impose a relation between the trilinear and bilinear soft
supersymmetry breaking terms, B_0 = A_0 - m_0, nor does it impose the relation
between the soft scalar masses and the gravitino mass, m_0 = m_{3/2}. As a
consequence, tan(\beta) is computed given values of the other CMSSM input
parameters. By considering a Giudice-Masiero (GM) extension to mSUGRA, one can
introduce new parameters to the K\"ahler potential which are associated with
the Higgs sector and recover many of the standard CMSSM predictions. However,
depending on the value of A_0, one may have a gravitino or a neutralino dark
matter candidate. We also consider the consequences of imposing the
universality conditions above the GUT scale. This GM extension provides a
natural UV completion for the CMSSM.Comment: 16 pages, 11 figures; added erratum correcting several equations and
results in Sec.2, Sec.3 and 4 remain unaffected and conclusions unchange
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