25 research outputs found
Rheology of a confined granular material
We study the rheology of a granular material slowly driven in a confined
geometry. The motion is characterized by a steady sliding with a resistance
force increasing with the driving velocity and the surrounding relative
humidity. For lower driving velocities a transition to stick-slip motion
occurs, exhibiting a blocking enhancement whith decreasing velocity. We propose
a model to explain this behavior pointing out the leading role of friction
properties between the grains and the container's boundary.Comment: 9 pages, 3 .eps figures, submitted to PR
Slow dynamics and aging of a confined granular flow
We present experimental results on slow flow properties of a granular
assembly confined in a vertical column and driven upwards at a constant
velocity V. For monodisperse assemblies this study evidences at low velocities
() a stiffening behaviour i.e. the stress necessary to obtain
a steady sate velocity increases roughly logarithmically with velocity. On the
other hand, at very low driving velocity (), we evidence a
discontinuous and hysteretic transition to a stick-slip regime characterized by
a strong divergence of the maximal blockage force when the velocity goes to
zero. We show that all this phenomenology is strongly influenced by surrounding
humidity. We also present a tentative to establish a link between the granular
rheology and the solid friction forces between the wall and the grains. We base
our discussions on a simple theoretical model and independent grain/wall
tribology measurements. We also use finite elements numerical simulations to
confront experimental results to isotropic elasticity. A second system made of
polydisperse assemblies of glass beads is investigated. We emphasize the onset
of a new dynamical behavior, i.e. the large distribution of blockage forces
evidenced in the stick-slip regime
Mechanisms for slow strengthening in granular materials
Several mechanisms cause a granular material to strengthen over time at low
applied stress. The strength is determined from the maximum frictional force
F_max experienced by a shearing plate in contact with wet or dry granular
material after the layer has been at rest for a waiting time \tau. The layer
strength increases roughly logarithmically with \tau -only- if a shear stress
is applied during the waiting time. The mechanisms of strengthening are
investigated by sensitive displacement measurements and by imaging of particle
motion in the shear zone. Granular matter can strengthen due to a slow shift in
the particle arrangement under shear stress. Humidity also leads to
strengthening, but is found not to be its sole cause. In addition to these time
dependent effects, the static friction coefficient can also be increased by
compaction of the granular material under some circumstances, and by cycling of
the applied shear stress.Comment: 21 pages, 11 figures, submitted to Phys. Rev.
Infrastructure for Detector Research and Development towards the International Linear Collider
The EUDET-project was launched to create an infrastructure for developing and
testing new and advanced detector technologies to be used at a future linear
collider. The aim was to make possible experimentation and analysis of data for
institutes, which otherwise could not be realized due to lack of resources. The
infrastructure comprised an analysis and software network, and instrumentation
infrastructures for tracking detectors as well as for calorimetry.Comment: 54 pages, 48 picture
Autoantibodies against type I IFNs in patients with life-threatening COVID-19
Interindividual clinical variability in the course of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is vast. We report that at least 101 of 987 patients with life-threatening coronavirus disease 2019 (COVID-19) pneumonia had neutralizing immunoglobulin G (IgG) autoantibodies (auto-Abs) against interferon-w (IFN-w) (13 patients), against the 13 types of IFN-a (36), or against both (52) at the onset of critical disease; a few also had auto-Abs against the other three type I IFNs. The auto-Abs neutralize the ability of the corresponding type I IFNs to block SARS-CoV-2 infection in vitro. These auto-Abs were not found in 663 individuals with asymptomatic or mild SARS-CoV-2 infection and were present in only 4 of 1227 healthy individuals. Patients with auto-Abs were aged 25 to 87 years and 95 of the 101 were men. A B cell autoimmune phenocopy of inborn errors of type I IFN immunity accounts for life-threatening COVID-19 pneumonia in at least 2.6% of women and 12.5% of men
Gaia Early Data Release 3: The celestial reference frame (Gaia-CRF3)
Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. Aims. We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Methods. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). Results. Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13-21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 ÎŒas yr-1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution
Dynamic and Transient Analysis of Silicon-Based Thin-Film Transistors: Channel Propagation Model
International audienceThe quasi-static approach in the dynamic modeling considers that a thin-film transistor (TFT) reaches the steady-state instantaneously, and how to insert its behavior before steady-state is an important issue. In this paper, dynamic responses of silicon-based TFTs under gate-voltage pulse are studied in details. We experimentally distinguish quasi-static and non-quasi-static cases and we identify two charging regimes of the channel formation: channel propagation and charging of the fully propagated channel. We propose a model for the channel propagation, with a compact model-like approach to take into account the effect of defect states