A state-of-the-art review of curve squeal noise: Phenomena, mechanisms, modelling and mitigation

[EN] Curve squeal is an intense tonal noise occurring when a rail vehicle negotiates a sharp curve. The phenomenon can be considered to be chaotic, with a widely differing likelihood of occurrence on different days or even times of day. The term curve squeal may include several different phenomena with a wide range of dominant frequencies and potentially different excitation mechanisms. This review addresses the different squeal phenomena and the approaches used to model squeal noise; both time-domain and frequency-domain approaches are discussed and compared. Supporting measurements using test rigs and field tests are also summarised. A particular aspect that is addressed is the excitation mechanism. Two mechanisms have mainly been considered in previous publications. In many early papers the squeal was supposed to be generated by the so-called falling friction characteristic in which the friction coefficient reduces with increasing sliding velocity. More recently the mode coupling mechanism has been raised as an alternative. These two mechanisms are explained and compared and the evidence for each is discussed. Finally, a short review is given of mitigation measures and some suggestions are offered for why these are not always successful.Squicciarini, G.; Thompson, D.; Ding, B.; Baeza González, LM. (2018). A state-of-the-art review of curve squeal noise: Phenomena, mechanisms, modelling and mitigation. Notes on Numerical Fluid Mechanics and Multidisciplinary Design. 139:3-41. https://doi.org/10.1007/978-3-319-73411-8_1S341139Anderson, D., Wheatley, N., Fogarty, B., Jiang, J., Howie, A., Potter, W.: Mitigation of curve squeal noise in Queensland, New South Wales and South Australia. In: Conference on Railway Engineering. pp. 625–636, Perth, Australia (2008)Hanson, D., Jiang, J., Dowdell, B., Dwight, R.: Curve squeal: causes, treatments and results. 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Development of a vehicle track interaction model to predict the vibratory benefits of rail grinding in the time domain

Imperfections in the wheel-rail contact are one of the main sources of generation of railway vibrations. Consequently, it is essential to take expensive corrective maintenance measures, the results of which may be unknown. In order to assess the effectiveness of these measures, this paper develops a vehicle-track interaction model in the time domain of a curved track with presence of rail corrugation on the inner rail. To characterize the behavior of the track, a numerical finite element model is developed using ANSYS software, while the behavior of the vehicle is characterized by a unidirectional model of two masses developed with VAMPIRE PRO software. The overloads obtained with the dynamic model are applied to the numerical model and then, the vibrational response of the track is obtained. Results are validated with real data and used to assess the effectiveness of rail grinding in the reduction of wheel-rail forces and the vibration generation phenomenon.Real Herráiz, JI.; Zamorano, C.; Velarte, JL.; Blanco, AE. (2015). Development of a vehicle track interaction model to predict the vibratory benefits of rail grinding in the time domain. Journal of Modern Transportation. 23(3):189-201. doi:10.1007/s40534-015-0078-yS189201233Grassie SL, Kalousek J (1993) Rail corrugation: characteristics, causes and treatments. Proc Inst Mech Eng Part F: J Rail Rapid Transit 207:57–68Grassie SL (2005) Rail corrugation: advances in measurement, understanding and treatment. Wear 258:1224–1234Grassie SL (2009) Rail corrugation: characteristics, causes and treatments. Proc Inst Mech Eng Part F: J Rail Rapid Transit 223:581–596Suda Y, Komine H, Iwasa T, Terumichi Y (2002) Experimental study on mechanism of rail corrugation using corrugation simulator. Wear 253:162–171Jin XS, Wen ZF, Wang KY, Zhou ZR, Liu QY, Li CH (2006) Three-dimensional train–track model for study of rail corrugation. J Sound Vib 293(3):830–855Zhao X, Li Z, Esveld C, Dollevoet R (2007) The dynamic stress state of the wheel–rail contact. In: Proceedings of the 2nd IASME/WSEAS international conference on continuum mechanicsTorstensson P, Nielsen J (2011) Simulation of dynamic vehicle-track interaction on small radius curves. Veh Syst Dyn 49(11):1711–1732Hawari HM, Murray MH (2008) Effects of train characteristics on the rate of deterioration of track roughness. J Eng Mech 134(3):234–239Ling L, Li W, Shang H, Xiao X, Wen Z, Jin X (2014) Experimental and numerical investigation of the effect of rail corrugation on the behaviour of rail fastenings. Veh Syst Dyn 52(9):1211–1231Collette C, Horodinca M, Preumont A (2009) Rotational vibration absorber for the mitigation of rail rutting corrugation. Veh Syst Dyn 47:641–659Egaña J, Viñolas J, Gil-Negrete L (2005) Effect of liquid high positive friction (HPF) modifier on wheel-rail contact and rail corrugation. Tribol Int 38:769–774Real Herraiz JI, Galisteo Cabeza A, Real T, Zamorano Martin C (2012) Study of wave barriers design for the mitigation of railway ground vibrations. J Vibroeng 14(1):408–422Real JI, Zamorano C, Hernandez C, Comendador R, Real T (2014) Computational considerations of 3-D finite element method models of railway vibration prediction in ballasted tracks. J Vibroeng 16(4):1709–1722Andersen L, Jones CJ (2001) Three-dimensional elastodynamic analysis using multiple boundary element domains. ISVR Technical Memorandum, University of Southampton, SouthamptonLópez Pita A (2006) Infraestructuras Ferroviarias. Universitat Politècnica de Catalunya, BarcelonaAlves P, Calçada R, Silva A (2011) Vibrations induced by railway traffic: influence of the mechanical properties of the train on the dynamic excitation mechanism. In: Proceedings of the 8th international conference on structural dynamics, EURODYN 2011, Leuven, BelgiumFerrara R, Leonardi G, Jourdan F (2012) Numerical modelling of train induced vibrations. In: SIIV-5th international congress—sustainability of road infrastructures, Rome, ItalyUzzal RU, Ahmed AK, Bhat RB (2013) Modelling, validation and analysis of a three-dimensional railway vehicle–track system model with linear and nonlinear track properties in the presence of wheel flats. Veh Syst Dyn 51(11):1695–1721Eadie DT, Kalousek J, Chiddick KC (2002) The role of high positive friction (HPF) modifier in the control of short pitch corrugations and related phenomena. Wear 253:185–19

Shedding Light on the Galaxy Luminosity Function

From as early as the 1930s, astronomers have tried to quantify the statistical nature of the evolution and large-scale structure of galaxies by studying their luminosity distribution as a function of redshift - known as the galaxy luminosity function (LF). Accurately constructing the LF remains a popular and yet tricky pursuit in modern observational cosmology where the presence of observational selection effects due to e.g. detection thresholds in apparent magnitude, colour, surface brightness or some combination thereof can render any given galaxy survey incomplete and thus introduce bias into the LF. Over the last seventy years there have been numerous sophisticated statistical approaches devised to tackle these issues; all have advantages -- but not one is perfect. This review takes a broad historical look at the key statistical tools that have been developed over this period, discussing their relative merits and highlighting any significant extensions and modifications. In addition, the more generalised methods that have emerged within the last few years are examined. These methods propose a more rigorous statistical framework within which to determine the LF compared to some of the more traditional methods. I also look at how photometric redshift estimations are being incorporated into the LF methodology as well as considering the construction of bivariate LFs. Finally, I review the ongoing development of completeness estimators which test some of the fundamental assumptions going into LF estimators and can be powerful probes of any residual systematic effects inherent magnitude-redshift data.Comment: 95 pages, 23 figures, 3 tables. Now published in The Astronomy & Astrophysics Review. This version: bring in line with A&AR format requirements, also minor typo corrections made, additional citations and higher rez images adde

Antimutagenic compounds and their possible mechanisms of action

Mutagenicity refers to the induction of permanent changes in the DNA sequence of an organism, which may result in a heritable change in the characteristics of living systems. Antimutagenic agents are able to counteract the effects of mutagens. This group of agents includes both natural and synthetic compounds. Based on their mechanism of action among antimutagens, several classes of compounds may be distinguished. These are compounds with antioxidant activity; compounds that inhibit the activation of mutagens; blocking agents; as well as compounds characterized with several modes of action. It was reported previously that several antitumor compounds act through the antimutagenic mechanism. Hence, searching for antimutagenic compounds represents a rapidly expanding field of cancer research. It may be observed that, in recent years, many publications were focused on the screening of both natural and synthetic compounds for their beneficial muta/antimutagenicity profile. Thus, the present review attempts to give a brief outline on substances presenting antimutagenic potency and their possible mechanism of action. Additionally, in the present paper, a screening strategy for mutagenicity testing was presented and the characteristics of the most widely used antimutagenicity assays were described

The interstitium in cardiac repair: role of the immune-stromal cell interplay

Cardiac regeneration, that is, restoration of the original structure and function in a damaged heart, differs from tissue repair, in which collagen deposition and scar formation often lead to functional impairment. In both scenarios, the early-onset inflammatory response is essential to clear damaged cardiac cells and initiate organ repair, but the quality and extent of the immune response vary. Immune cells embedded in the damaged heart tissue sense and modulate inflammation through a dynamic interplay with stromal cells in the cardiac interstitium, which either leads to recapitulation of cardiac morphology by rebuilding functional scaffolds to support muscle regrowth in regenerative organisms or fails to resolve the inflammatory response and produces fibrotic scar tissue in adult mammals. Current investigation into the mechanistic basis of homeostasis and restoration of cardiac function has increasingly shifted focus away from stem cell-mediated cardiac repair towards a dynamic interplay of cells composing the less-studied interstitial compartment of the heart, offering unexpected insights into the immunoregulatory functions of cardiac interstitial components and the complex network of cell interactions that must be considered for clinical intervention in heart diseases

PYRAZOLYL-BRIDGED IRIDIUM DIMERS .2. CONTRASTING MODES OF 2-CENTER OXIDATIVE ADDITION TO A BIMETALLIC SYSTEM AND REDUCTIVE ACCESS TO THE STARTING COMPLEX - 3 KEY DIIRIDIUM STRUCTURES REPRESENTING SHORT NON-BONDING AND LONG AND SHORT BONDING METAL-METAL INTERACTIONS

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