Motion of a sphere through an aging system

We have investigated the drag on a sphere falling through a clay suspension that has a yield stress and exhibits rheological aging. The drag force increases with both speed and the rest time between preparation of the system and the start of the experiment, but there exists a nonzero minimum speed below which steady motion is not possible. We find that only a very thin layer of material around the sphere is fluidized when it moves, while the rest of suspension is deformed elastically. This is in marked contrast to what is found for yield-stress fluids that do not age.Comment: latex, 4 figure

On the order of a non-abelian representation group of a slim dense near hexagon

We show that, if the representation group $R$ of a slim dense near hexagon $S$ is non-abelian, then $R$ is of exponent 4 and $|R|=2^{\beta}$, $1+NPdim(S)\leq \beta\leq 1+dimV(S)$, where $NPdim(S)$ is the near polygon embedding dimension of $S$ and $dimV(S)$ is the dimension of the universal representation module $V(S)$ of $S$. Further, if $\beta =1+NPdim(S)$, then $R$ is an extraspecial 2-group (Theorem 1.6)

Deceleration of Relativistic Radio Components and the morphologies of Gigahertz Peaked Spectrum Sources

A relativistic radio component, which moves in a direction close to the sky plane, will increase in flux density when it decelerates. This effect is the basis for the qualitative model for GPS galaxies we present in this paper, which can explain their low-variability convex spectrum, their compact double or compact symmetric morphology, and the lack of GPS quasars at similar redshifts. Components are expelled from the nucleus at relativistic speeds at a large angle to the line of sight, and are decelerated (eg. by ram-pressure or entrainment of the external gas) before contributing to a mini-lobe. The young components are Doppler boosted in the direction of motion but appear fainter for the observer. The non-relativistic mini-lobes dominate the structure and are responsible for the low variability in flux density and the convex radio spectrum as well as the compact double angular morphology. Had the same source been orientated at a small angle to the line of sight, the young components would be boosted in the observer's direction resulting in a flat and variable radio spectrum at high frequencies. Hence the characteristic convex spectrum of a GPS source would not be seen. These sources at small angles to the line of sight are probably identified with quasars, and are not recognized as GPS sources, but are embedded in the large population of flat spectrum variable quasars and BL Lac objects. This leads to a deficiency in GPS/CSOs identified with quasars.Comment: 11 pages, LaTeX, accepted by A&A 26/Jan/199

Observation of the B + → Jψη′K + decay

The B + → Jψη′K + decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb −1. The branching fraction of this decay is measured relative to the known branching fraction of the B + → ψ(2S)K + decay and found to be B(B+→Jψη′K+)B(B+→ψ(2S)K+)=(4.91±0.47±0.29±0.07)×10−2, where the first uncertainty is statistical, the second is systematic and the third is related to external branching fractions. A first look at the J/ψη′ mass distribution is performed and no signal of intermediate resonances is observed