Force measurement on coupled flapping flags in uniform flow

An experimental study on the coupled flapping of two identical flags arranged in parallel, tandem, and staggered positions in uniform flow was conducted in a wind tunnel. The dynamic characteristics of each flag were measured using an in-house designed balance and the flapping modes were analyzed through a high-speed video recording technique and a "Spatio-Temporal Evolution" software. For the side-by-side arrangement, the dependences of the kinematic and dynamic parameters on the flow speed and on the mutual distance were observed. The results indicated that the coupling motion and dynamics of two parallel flags in uniform flow were mainly affected by their mutual position. Significant drag reductions were observed when the flags flapped in the in-phase mode for a relatively small separation. For two flags in tandem arrangement, both the upstream and downstream flags experienced a drag reduction compared to the scenario of a single flag in the same flow. Especially, for relatively large separation the upstream flag had a smaller drag coefficient than that of the downstream one. For very small separation, the drag coefficient of the upstream flag was larger than that of the downstream one. Finally, for two flags arranged in a staggered configuration, an anomalous drag distribution was found. This work provides valuable experimental data and casts insight into the coupling mechanism of multiple flexible structures in an air flow

Momentum scale calibration of the LHCb spectrometer

For accurate determination of particle masses accurate knowledge of the momentum scale of the detectors is crucial. The procedure used to calibrate the momentum scale of the LHCb spectrometer is described and illustrated using the performance obtained with an integrated luminosity of 1.6 fb-1 collected during 2016 in pp running. The procedure uses large samples of J/ψ → μ + μ - and B+ → J/ψ K + decays and leads to a relative accuracy of 3 × 10-4 on the momentum scale

Helium identification with LHCb

The identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using pp collision data at √(s) = 13 TeV recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of 5.5 fb-1. A total of around 105 helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately 50% with a corresponding background rejection rate of up to O(10^12). These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei

Curvature-bias corrections using a pseudomass method

Momentum measurements for very high momentum charged particles, such as muons from electroweak vector boson decays, are particularly susceptible to charge-dependent curvature biases that arise from misalignments of tracking detectors. Low momentum charged particles used in alignment procedures have limited sensitivity to coherent displacements of such detectors, and therefore are unable to fully constrain these misalignments to the precision necessary for studies of electroweak physics. Additional approaches are therefore required to understand and correct for these effects. In this paper the curvature biases present at the LHCb detector are studied using the pseudomass method in proton-proton collision data recorded at centre of mass energy √(s)=13 TeV during 2016, 2017 and 2018. The biases are determined using Z→μ + μ - decays in intervals defined by the data-taking period, magnet polarity and muon direction. Correcting for these biases, which are typically at the 10-4 GeV-1 level, improves the Z→μ + μ - mass resolution by roughly 18% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass

The effect of particle deformation on densification of 316L stainless steel under Micro-FAST

The importance of the effect of particle deformation under Micro-forming Fields Activated Sintering Technology (Micro-FAST) has been summarized in this paper. Micro-FAST is involved in the coupling of stress field, temperature field and electric field wherein these fields work simultaneously rather than independently. By using Gleeble-1500D thermal simulation instrument, the micro-cylinders with size of Φ1.0mm×1.0mm were formed from 316L stainless steel powders. It has been found that the maximum relative density of sintered samples reaches up to 99.2% close to the full density. Moreover, the microstructure of specimens has also been investigated. Especially, the metal powders have been simulated as globular plasticine particles in the structure to elucidate the deformation of particle under Micro-FAST