6,611 research outputs found
Fatigue assessment of trailing suction hopper dredgers: A study on the contribution of the dredging cycle to the fatigue damage in the bottom door openings
No full textSince the 19th century hopper dredgers have been used for civil operations such as land reclamation and water way maintenance. In the past 25 years a trend of scale enlargement of hopper dredgers driven by economic and productivity reasons is seen. Scaling of the designs has effect on strength and fatigue assessment as well on settling of particles which affect the rate op production. This thesis is focussed on the fatigue assessment of the hopper dredger. Cracked damages in coaming and bottom door areas have been found in relatively large hopper dredgers that are classed by Bureau Veritas. According to Bureau Veritas rules for steel ships fatigue assessment is required if the ship has length greater than 170 m but damages have also been observed in hopper dredgers with a smaller length. This indicates that the hopper dredger design demands for a specific fatigue assessment procedure. The hopper dredger has a unique characteristic load profile consisting of loading and unloading cargo several times a day in combination with small wave heights due to reduced freeboard regulations. Special interest is given on the effect of the loading and unloading cycle in the corners of the bottom discharge openings. It is suspected that the effect of this characteristic cycle may be underestimated and requires an alternative assessment procedure. The main question is what the contribution of this cycle is and how it should be assessed. The relatively low frequency of the cycle raises the suspicion of low-cycle fatigue and this phenomenon is therefore investigated. It is concluded that the loading and unloading cycle has a major contribution to the fatigue damage in the bottom opening corners. In fact 97% of the fatigue damage is induced by the dredging cycle and therefore this cycle could be seen as the sole cause for fatigue cracks in the bottom opening corner structural details. The high stress ranges confirm the suspicion of a low-cycle fatigue phenomenon and therefore further research is done on how to approach this type of fatigue. A method is proposed to take into account bi-axial cyclic plasticity and material hardening based on the use of a maximum principal hot spot stress range. Linear-elastic stresses are corrected to pseudo elastic stresses and effects of SN-curve selection, material selection, bi-axiallity and residual stress are analysed. Based on the found pseudo hot spot stress ranges it is concluded that the linear-elastic stresses in the analysed hopper are not high enough to demand for such a low-cycle fatigue assessment approach. The bi-axial ratio between the two multi-axial plane stress components has no effect on this conclusion
Search for same-sign top production at the LHC
No full textAn inclusive search for same-sign top-quark pair production
in pp collisions at sqrt(s) = 7 TeV is performed using data samples recorded with the ATLAS and CMS detectors at the Large Hadron Collider.
These searches are motivated by the hypothesis of Flavor Changing Neutral Currents (FCNC) in the top sector, which would imply enhancement of same-sign top-pair production in
pp or ppbar collisions by the exchange of a hypothetical massive Z' boson. As no excess of events is observed, the ATLAS and CMS analyses constrain the FCNC models as a function of the mass the Z' boson and its couplings.
The observed limits disfavor the FCNC interpretation of the Tevatron results and limits are set on the cross section of same-sign top production at the Large Hadron Collider
CMS General Brochure
No full textThe CMS General Brochure developed in 2006 (EN, FR, IT updated in 2009). Available in multiple languages: English (updated in Sept 2015) - D. Barney, J. Virdee French (updated in Sept 2015) - C. Pralavorio, P. Bloch, M.Della-Negra Italian (updated in Sept 2015) - F. Cavallari et al German (updated in Sept 2015) - C. Wulz et al Dutch (2006) - F. Blekman, B. Van Konigsveld Greek (2006) - P. Vichoudis, E. Petrakou, E. Symeonidou, N. Tracas Spanish (2006) - J. Puerta-Pelayo, P. Garcia Finnish (2006) - J. Tuominiemi, K. Aspola Polish (2006) - M. Lapka, G.Wrochna Portuguese (2006) - C. Lourenco Serbian (2006) - D. Lazic, P. Milenovic, D. Maletic, A. Vitlic Turkish (2006) - Erhan Gulmez et a
Prospectives for stop searches at ATLAS and CMS
No full textThis talk describes the searches for supersymmetric stop squark within the mSUGRA model at ATLAS and CMS detectors. Results of simulation studies are presented. Search for the light stop squark in the Low Mass SUSY model, originating from the gluino decay, using the final state tb invariant mass at ATLAS is described. Inclusive stop search in the intermediate scenario, using the events with top candidate, leptons and missing energy at CMS is also presented. The discovery prospects with early data in both studies are discussed
Top Secrets: long-lived ALPs in top production
No full textAbstract We investigate the discovery potential for long-lived particles produced in association with a top-antitop quark pair at the (High-Luminosity) LHC. Compared to inclusive searches for a displaced vertex, top-associated signals offer new trigger options and an extra handle to suppress background. We design a search strategy for a displaced di-muon vertex in the tracking detectors, in association with a reconstructed top-antitop pair. For axion-like particles with masses above the di-muon threshold, we find that the (High-Luminosity) LHC can probe effective top-quark couplings as small as |c tt |/f a = 0.03 (0.002)/TeV and proper decay lengths as long as 20 (300) m, assuming a cross section of 1 fb, with data corresponding to an integrated luminosity of 150 fb −1 (3 ab −1). Our predictions suggest that searches for top-associated displaced di-muons will explore new terrain in the current sensitivity gap between searches for prompt di-muons and missing energy
Application of pivoting adversarial networks in search for four top quark production in CMS
No full textOne burden of high energy physics data analysis is uncertainty within the measurement, both systematically and statistically. Even with sophisticated neural network techniques that are used to assist in high energy physics measurements, the resulting measurement may suffer from both types of uncertainties. Fortunately, most types of systematic uncertainties are based on knowledge from information such as theoretical assumptions, for which the range and behaviour are known. It has been proposed to mitigate such systematic uncertainties by using a new type of neural network called adversarial neural network (ANN) that would make the discriminator less sensitive to these uncertainties, but this has not yet been demonstrated in a real-life LHC analysis. This work investigates ANNs using as a benchmark the search for the production of four top quarks, an extremely rare physics process at the LHC and one of the important processes that can prove or disprove the Standard Model. The search for four top quarks in some cases is sensitive to large systematic uncertainties. The expected cross section upper limit for four top quark production is calculated using traditional neural networks and adversarial neural networks based on simulated proton-proton collisions within the Compact Muon Solenoid detector within Large Hadron Collider, and are compared to existing results. The improvement and further considerations to the search for rare processes at the LHC will be discussed
Search for the standard model Higgs boson produced in association with W and Z bosons in pp collisions at √s=7 TeV
No full textChatrchyan, S., Khachatryan, V., Sirunyan, A.M., Tumasyan, A., Adam, W., Aguilo, E., Bergauer, T., Dragicevic, M., Erö, J., Fabjan, C., Friedl, M., Frühwirth, R., Ghete, V.M., Hammer, J., Hörmann, N., Hrubec, J., Jeitler, M., Kiesenhofer, W., Knünz, V., Krammer, M., Liko, D., Mikulec, I., Pernicka, M., Rahbaran, B., Rohringer, C., Rohringer, H., Schöfbeck, R., Strauss, J., Taurok, A., Waltenberger, W., Walzel, G., Widl, E., Wulz, C.-E., Mossolov, V., Shumeiko, N., Suarez Gonzalez, J., Bansal, S., Cornelis, T., De Wolf, E.A., Janssen, X., Luyckx, S., Mucibello, L., Ochesanu, S., Roland, B., Rougny, R., Selvaggi, M., Staykova, Z., Van Haevermaet, H., Van Mechelen, P., Van Remortel, N., Van Spilbeeck, A., Blekman, F., Blyweert, S., D'Hondt, J., Gonzalez Suarez, R., Kalogeropoulos, A., Maes, M., Olbrechts, A., Van Doninck, W., Van Mulders, P., Van Onsem, G.P., Villella, I., Clerbaux, B., De Lentdecker, G., Dero, V., Gay, A.P.R., Hreus, T., Léonard, A., Marage, P.E., Reis, T., Thomas, L., Vander Velde, C., Vanlaer, P., Wang, J., Adler, V., Beernaert, K., Cimmino, A., Costantini, S., Garcia, G., Grunewald, M., Klein, B., Lellouch, J., Marinov, A., McCartin, J., Ocampo Rios, A.A., Ryckbosch, D., Strobbe, N., Thyssen, F., Tytgat, M., Verwilligen, P., Walsh, S., Yazgan, E., Zaganidis, N., Basegmez, S., Bruno, G., Castello, R., Ceard, L., Delaere, C., Du Pree, T., Favart, D
Evidence for the 125 GeV Higgs boson decaying to a pair of τ leptons
No full textOpen Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.A search for a standard model Higgs boson decaying into a pair of τ leptons is performed using events recorded by the CMS experiment at the LHC in 2011 and 2012. The dataset corresponds to an integrated luminosity of 4.9 fb−1 at a centre-of-mass energy of 7 TeV and 19.7 fb−1 at 8 TeV. Each τ lepton decays hadronically or leptonically to an electron or a muon, leading to six different final states for the τ -lepton pair, all considered in this analysis. An excess of events is observed over the expected background contributions, with a local significance larger than 3 standard deviations for m H values between 115 and 130 GeV. The best fit of the observed H → τ τ signal cross section times branching fraction for m H = 125 GeV is 0.78 ± 0.27 times the standard model expectation. These observations constitute evidence for the 125 GeV Higgs boson decaying to a pair of τ leptons
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