Rolling friction of a hard cylinder on a viscous plane

The resistance against rolling of a rigid cylinder on a flat viscous surface is investigated. We found that the rolling-friction coefficient reveals strongly non-linear dependence on the cylinder's velocity. For low velocity the rolling-friction coefficient rises with velocity due to increasing deformation rate of the surface. For larger velocity, however, it decreases with velocity according to decreasing contact area and deformation of the surface.Comment: 7 pages, 3 figure

Coefficient of tangential restitution for the linear dashpot model

The linear dashpot model for the inelastic normal force between colliding spheres leads to a constant coefficient of normal restitution, $\epsilon_n=$const., which makes this model very popular for the investigation of dilute and moderately dense granular systems. For two frequently used models for the tangential interaction force we determine the coefficient of tangential restitution $\epsilon_t$, both analytically and by numerical integration of Newton's equation. Although $\epsilon_n=$const. for the linear-dashpot model, we obtain pronounced and characteristic dependencies of the tangential coefficient on the impact velocity $\epsilon_t=\epsilon_t(\vec{g})$. The results may be used for event-driven simulations of granular systems of frictional particles.Comment: 12 pages, 12 figure

Chains of Viscoelastic Spheres

Given a chain of viscoelastic spheres with fixed masses of the first and last particles. We raise the question: How to chose the masses of the other particles of the chain to assure maximal energy transfer? The results are compared with a chain of particles for which a constant coefficient of restitution is assumed. Our simple example shows that the assumption of viscoelastic particle properties has not only important consequences for very large systems (see [1]) but leads also to qualitative changes in small systems as compared with particles interacting via a constant restitution coefficient.Comment: 11 pages, 6 figure

Scaling properties of granular materials

Given an assembly of viscoelastic spheres with certain material properties, we raise the question how the macroscopic properties of the assembly will change if all lengths of the system, i.e. radii, container size etc., are scaled by a constant. The result leads to a method to scale down experiments to lab-size.Comment: 4 pages, 2 figure

Impact of the atmospheric circulation on the Arctic snow cover and ice thickness variability

The Arctic sea ice cover and thickness have significantly declined since the 1970s, while exhibiting large interannual variability. Snow cover on sea ice, acting as an insulating barrier, was shown to be instrumental in driving the variability and trends in sea-ice thickness. Yet, the Arctic snow depth remains scarcely measured and overlooked in climate models, which translates to “very limited predictive skill” according to the IPCC (Special Report on the Ocean and Cryosphere in a Changing Climate). Moreover, sea-ice thickness initialization has been shown to be an important element for skilful sea-ice forecasts, and it appears plausible that the same holds for the snow layer on top. Here, we investigate the role of atmospheric circulation anomalies in shaping the Arctic snow-cover and sea-ice thickness anomalies. In this preparatory work, spectral nudging of the large-scale atmospheric circulation towards ERA5 reanalysis data is applied to the fully coupled AWI Climate Model (AWI-CM-3). We examine the variability and trends of Arctic snowfall, snow depth, sea ice cover and thickness over a 42-year period (1979-2021), and in particular the reproduction of observed anomalies. Two nudging configurations are used, differing in strength by their relaxation timescale τ and spectral truncation wavenumber T (namely τ=24 h, T20 and τ=1 h, T159). We demonstrate the importance of atmospheric circulation anomalies in shaping variations of snow and ice thickness at sub-seasonal to interannual scales, and discuss the potential of spectral nudging as a tool to improve the initialization of sea ice forecasts

Coefficient of normal restitution of viscous particles and cooling rate of granular gases

We investigate the cooling rate of a gas of inelastically interacting particles. When we assume velocity dependent coefficients of restitution the material cools down slower than with constant restitution. This behavior might have large influence to clustering and structure formation processes.Comment: 3 figures, Phys. Rev. E (in press

Aurora A phosphorylation of TACC3/maskin is required for centrosome-dependent microtubule assembly in mitosis

Centrosomes act as sites of microtubule growth, but little is known about how the number and stability of microtubules emanating from a centrosome are controlled during the cell cycle. We studied the role of the TACC3–XMAP215 complex in this process by using purified proteins and Xenopus laevis egg extracts. We show that TACC3 forms a one-to-one complex with and enhances the microtubule-stabilizing activity of XMAP215 in vitro. TACC3 enhances the number of microtubules emanating from mitotic centrosomes, and its targeting to centrosomes is regulated by Aurora A–dependent phosphorylation. We propose that Aurora A regulation of TACC3 activity defines a centrosome-specific mechanism for regulation of microtubule polymerization in mitosis

Self-diffusion in granular gases

The coefficient of self-diffusion for a homogeneously cooling granular gas changes significantly if the impact-velocity dependence of the restitution coefficient $\epsilon$ is taken into account. For the case of a constant $\epsilon$ the particles spread logarithmically slow with time, whereas the velocity dependent coefficient yields a power law time-dependence. The impact of the difference in these time dependences on the properties of a freely cooling granular gas is discussed.Comment: 6 pages, no figure

Simulation for the oblique impact of a lattice system

The oblique collision between an elastic disk and an elastic wall is numerically studied. We investigate the dependency of the tangential coefficient of restitution on the incident angle of impact. From the results of simulation, our model reproduces experimental results and can be explained by a phenomenological theory of the oblique impact.Comment: 30 pages, 9 figures, submitted to J. Phys. Soc. Japa

Les immunothérapies spécifiques dans le traitement des cancers

The offer of anti-cancer drugs has recently been disrupted by the introduction of checkpoint inhibitors on the market. Currently, one anti-CTLA-4, two anti-PD-1 and two anti-PD-L1 are authorized in the European Union, in seven different types of cancer. The clinical development of these therapies is still in full swing: in July 2017, more than 1 500 clinical trials were evaluating anti-PD-1, anti-PD-L1 and anti-CTLA-4 drugs in about twenty different locations and this number continues to increase. In the short term in France, other immunotherapies, the CAR-T cells, will complete this therapeutic arsenal. These immunotherapies appear as a real revolution in the treatment of some cancers. Nevertheless, many issues are associated with these therapies, particularly regarding the identification of good responders, the proper use of these drugs including the management of therapeutic strategies and safety profile, as well as the organization of care. In addition, the expenses associated with ipilimumab, nivolumab and pembrolizumab are substantial and almost tripled in one year, going from 120 million euros in 2015 to more than 340 million euros in 2016. This raises the question of the ability of the current healthcare system to maintain equitable access to innovation and best treatments for all patients. For all these reasons, the French National Cancer Institute decided to dedicate its thematic annual report on these innovative immunotherapies, targeting in particular checkpoint inhibitors and CAR-T cells, in order to produce an inventory of current data and an analysis regarding the different issues associated with these therapies