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If a Hertzian contact is loaded by a tangential force which varies direction in time, the classical solution due to Cattaneo and Mindlin does not hold, and a numerical solution is needed. Here, we deal with the important practical case when the force describes an ellipse in the loading space, that is, the components have harmonic variation, with the in-phase (uniaxial) case being the limiting Cattaneo–Mindlin problem. We observe convergence to a steady state within the second cycle of oscillatory loading, and we describe the dependence of frictional dissipation, important both as a source of structural damping and as an indicator of potential fretting damage, on the parameters of the problem. The results show that the dissipation depends significantly on the biaxiality ratio between the tangential load components, particularly so when their amplitude is close to the full sliding limit. We find steady-state dissipation to be higher than the corresponding Cattaneo–Mindlin case for low tangential forces (with a maximum of dissipation for a rotating load). The increase is of the order of 15% only, whereas the decrease for large tangential forces seems to be more significant. This is vaguely similar to the case recently studied when the tangential force was of constant direction, but normal and tangential loads were oscillating harmonically and out of phase: this suggests that in the general case, the dissipation may be significantly larger when all the loads are out of phase. [ABSTRACT FROM PUBLISHER]

The problem of the detachment of a flat indenter from a plane adhesive viscoelastic strip of thickness " b " is studied. For any given retraction speed, three different detachment regimes are found: (i) for very small " b " the detachment stress is constant and equal to the theoretical strength of the interface, (ii) for intermediate values of " b " the detachment stress decays approximately as b − 1 / 2 , (iii) for thick layers a constant detachment stress is obtained corresponding to case the punch is detaching from a halfplane. By using the boundary element method a comprehensive numerical study is performed which assumes a linear viscoelastic material with a single relaxation time and a Lennard-Jones force-separation law. Pull-off stress is found to consistently and monotonically increase with unloading rate, but to be almost insensitive to the history of the contact. Due to viscoelasticity, unloading at high enough retraction velocity may allow punches of macroscopic size to reach the theoretical strength of the interface. Finally, a corrective term in Greenwood or Persson theories considering finite size effects is proposed with good agreement between theoretical and numerical results. [Display omitted] • Ultra-strong adhesion is reached unloading from very thin soft viscoelastic layers. • Macroscopic flat punches may reach the theoretical interfacial adhesive strength. • Viscoelastic crack propagation theories are extended to finite size systems. [ABSTRACT FROM AUTHOR]

Recently, generalizing the solution of the adhesiveless random rough contact proposed by Xu, Jackson, and Marghitu (XJM model), the first author has obtained a model for adhesive contact near full contact, under the Johnson, Kendall, and Roberts (JKR) assumptions, which leads to quite strong effect of the fractal dimension. We extend here the results with closed-form equations, including both loading and unloading which were not previously discussed, showing that the conclusions are confirmed. A large effect of hysteresis is found, as was expected. The solution is therefore competitive with Persson's JKR solution, at least in the range of nearly full contact, with an enormous advantage in terms of simplicity. Two examples of real surfaces are discussed. [ABSTRACT FROM AUTHOR]

T-cell acute lymphoblastic leukemia (T-ALL) is a T-cell malignancy characterized by cell subsets and enriched with leukemia-initiating cells (LICs). β-Catenin modulates LIC activity in T-ALL. However, its role in maintaining established leukemia stem cells remains largely unknown. To identify functionally relevant protein interactions of β-catenin in T-ALL, we performed coimmunoprecipitation followed by liquid chromatography-mass spectrometry. Here, we report that a noncanonical functional interaction of β-catenin with the Forkhead box O3 (FOXO3) transcription factor positively regulates LIC-related genes, including the cyclin-dependent kinase 4, which is a crucial modulator of cell cycle and tumor maintenance. We also confirm the relevance of these findings using stably integrated fluorescent reporters of β-catenin and FOXO3 activity in patient-derived xenografts, which identify minor subpopulations with enriched LIC activity. In addition, gene expression data at the single-cell level of leukemic cells of primary patients at the time of diagnosis and minimal residual disease (MRD) up to 30 days after the standard treatments reveal that the expression of β-catenin- and FOXO3-dependent genes is present in the CD82+CD117+ cell fraction, which is substantially enriched with LICs in MRD as well as in early T-cell precursor ALL. These findings highlight key functional roles for β-catenin and FOXO3 and suggest novel therapeutic strategies to eradicate aggressive cell subsets in T-ALL., (© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)