Time–frequency analysis of various simulated and experimental signals due to elastic wave scattering from damage are performed using wavelet transform (WT) and Hilbert–Huang transform (HHT) and their ...performances are compared in context of quantifying the damages. Spectral finite element method is employed for numerical simulation of wave scattering. An analytical study is carried out to study the effects of higher-order damage parameters on the reflected wave from a damage. Based on this study, error bounds are computed for the signals in the spectral and also on the time–frequency domains. It is shown how such an error bound can provide an estimate of error in the modelling of wave propagation in structure with damage. Measures of damage based on WT and HHT is derived to quantify the damage information hidden in the signal. The aim of this study is to obtain detailed insights into the problem of (1) identifying localised damages (2) dispersion of multifrequency non-stationary signals after they interact with various types of damage and (3) quantifying the damages. Sensitivity analysis of the signal due to scattered wave based on time–frequency representation helps to correlate the variation of damage index measures with respect to the damage parameters like damage size and material degradation factors.
Use of smart sensor technology along with intelligent signal processing plays a crucial role in the implementation and working of ultrasonic wave based damage detection system. In this work, the ...interaction of A0 Lamb mode with damages like crack and delamination are studied. Piezoelectric Wafer Active Sensors (PWAS) are used for generation of Lamb waves to detect damages in metal and composite structures. Experiments were conducted on aluminum plates to study the interaction of Lamb wave with crack oriented at different angles and on a titanium turbine blade of complex geometry with a fine surface crack. A geodesic based Lamb wave approach was employed to locate a crack in an aluminum plate. The existing geodesic algorithm is improved by replacing the Dijkstra’s algorithm with the accurate fast marching method. Further, the interactions of A0 mode with multiple layer delaminations in glass fiber epoxy composite laminates were studied. Spectral Finite Element Method (SFEM) is used for numerical simulation to validate the experimental results. Time-frequency analysis techniques, namely Wavelet Transform (WT) and Hilbert Huang transform (HHT) are used to study the experimental signals and their performances were compared. This study provides significant insight into the problem of identifying localized damages in the structure using integrated PWAS and dispersion of multi-frequency signal after they interact with different types of damage.
The most precise measurements to date of the $^{3}_{Λ}$H lifetime τ and Λ separation energy BΛ are obtained using the data sample of Pb–Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV collected by ALICE ...at the LHC. The $^{3}_{Λ}$H is reconstructed via its charged two-body mesonic decay channel ($^{3}_{Λ}$H → 3He + π– and the charge-conjugate process). The measured values τ = 253 ± 11 (stat.) ± 6(syst.) ps and BΛ = 102 ± 63 (stat.) ± 67 (syst.) keV are compatible with predictions from effective field theories and confirm that the $^{3}_{Λ}$H structure is consistent with a weakly-bound system.
The transverse-momentum (p_{T}) spectra and coalescence parameters B_{2} of (anti)deuterons are measured in p-p collisions at sqrts=13 TeV for the first time in and out of jets. In this measurement, ...the direction of the leading particle with the highest p_{T} in the event (p_{T}^{lead}>5 GeV/c) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions, and the jet signal is obtained as the difference between the toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons in the jet cone as compared with the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase-space distributions of nucleons are generated using pythia8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in pythia8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the B_{2}^{Jet} is not reproduced by the models, which instead give a decreasing trend.
The ALICE Collaboration reports three measurements in ultraperipheral proton-lead collisions at forward rapidity. The exclusive two-photon process γγ → μ+μ- and the exclusive photoproduction of J/ψ ...are studied. J/ψ photoproduction with proton dissociation is measured for the first time at a hadron collider. The cross section for the two-photon process of dimuons in the invariant mass range from 1 to 2.5 GeV/c2 agrees with leading-order quantum electrodynamics calculations. The exclusive and dissociative cross sections for J/ψ photoproductions are measured for photon-proton center-of-mass energies from 27 to 57 GeV. They are in good agreement with HERA results.
Through the marriage of microelectronics and molecular biology, a miniaturized device is presented for ultrasensitive detection of labeled molecules. The novelty of the approach is the direct ...integration of a charge-coupled device (CCD) and a probe-based assay. Specifically, a CCD detector serves as an active solid support that quantitatively detects and images the distribution of labeled target molecules near the spatially addressable pixels. The device exploits the inherent characteristics of microelectronics that accommodate highly parallel assays, ultrasensitive detection, high throughput, integrated data acquisition and computation. Hence, the technology presented offers substantial practical utility to both research and clinical diagnostic applications that require quantitative analysis of bound molecules. Specifically for probe-based assays such as reverse dot blots, hybridization of radiolabeled or fluorescently labeled, target DNA can be quantitatively assessed within seconds due to the high sensitivity and direct coupling employed.
The pseudorapidity density of charged particles with minimum transverse momentum (pT) thresholds of 0.15, 0.5, 1, and 2 GeV/c is measured in pp collisions at the center of mass energies of $\sqrt{s}$ ...= 5.02 and 13 TeV with the ALICE detector. The study is carried out for inelastic collisions with at least one primary charged particle having a pseudorapidity (η) within ± 0.8 and pT larger than the corresponding threshold. In addition, measurements without pT-thresholds are performed for inelastic and nonsingle-diffractive events as well as for inelastic events with at least one charged particle having |η| < 1 in pp collisions at $\sqrt{s}$ = 5.02 TeV for the first time at the LHC. These measurements are compared to the pythia 6, pythia 8, and epos-lhc models. In general, the models describe the η dependence of particle production well. However, discrepancies are observed for the highest transverse momentum threshold (pT > 2 GeV/c), highlighting the importance of such measurements for tuning event generators. The new measurements agree within uncertainties with results from the ATLAS and CMS experiments obtained at $\sqrt{s}$ =13 TeV .
Measurement of the Λ hyperon lifetime Alizadehvandchali, N.; Alkin, A.; Alocco, G. ...
Physical review. D,
08/2023, Volume:
108, Issue:
3
Journal Article
Peer reviewed
Open access
A new, more precise measurement of the Λ hyperon lifetime is performed using a large data sample of Pb-Pb collisions at $\sqrt{s_{NN}}$=5.02 TeV with ALICE. The Λ and $\bar{Λ}$ hyperons are ...reconstructed at midrapidity using their two-body weak decay channel Λ→p+π- and $\bar{Λ}$→$\bar{p}$+π+. The measured value of the Λ lifetime is τΛ=261.07±0.37(stat.)±0.72(syst.) ps. The relative difference between the lifetime of Λ and $\bar{Λ}$, which represents an important test of CPT invariance in the strangeness sector, is also measured. The obtained value (τΛ-τ$\bar{Λ}$)/τΛ=0.0013±0.0028(stat.)±0.0021(syst.) is consistent with zero within the uncertainties. Both measurements of the Λ hyperon lifetime and of the relative difference between τΛ and τ$\bar{Λ}$ are in agreement with the corresponding world averages of the Particle Data Group and about a factor of three more precise.
The first measurement of the cross section for incoherent photonuclear production of J/ψ vector mesons as a function of the Mandelstam |t| variable is presented. The measurement was carried out with ...the ALICE detector at midrapidity, |y|<0.8, using ultraperipheral collisions of Pb nuclei at a center-of-mass energy per nucleon pair of sqrts_{NN}=5.02 TeV. This rapidity interval corresponds to a Bjorken-x range (0.3-1.4)×10^{-3}. Cross sections are given in five |t| intervals in the range 0.04<|t|<1 GeV^{2} and compared to the predictions by different models. Models that ignore quantum fluctuations of the gluon density in the colliding hadron predict a |t| dependence of the cross section much steeper than in data. The inclusion of such fluctuations in the same models provides a better description of the data.
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