Dynamics of shallow impact cratering.

We present data for the time dependence of wooden spheres penetrating into a loose noncohesive packing of glass beads. The stopping time is a factor of 3 longer than the time d/v0 needed to travel the total penetration distance d at the impact speed v0. The acceleration decreases monotonically throughout the impact. These kinematics are modeled by a position- and velocity-dependent stopping force that is constrained to reproduce prior observations for the scaling of the penetration depth with the total drop distance.

Penetration depth for shallow impact cratering.

We present data for the penetration of a variety of spheres, dropped from rest, into a loose noncohesive granular medium. We improve upon earlier work [J. S. Uehara, Phys. Rev. Lett. 90, 194301 (2003)] in three regards. First, we explore the behavior vs sphere diameter and density more systematically, by holding one of these parameters constant while varying the other. Second, we prepare the granular medium more reproducibly and, third, we measure the penetration depth more accurately. The new data support the previous conclusion that the penetration depth is proportional to the 1/2 power of sphere density, the 2/3 power of sphere diameter, and the 1/3 power of total drop distance.

Low-speed impact craters in loose granular media.

We report on craters formed by balls dropped into dry, noncohesive, granular media. By explicit variation of ball density rho(b), diameter D(b), and drop height H, the crater diameter is confirmed to scale as the 1/4 power of the energy of the ball at impact: D(c) approximately equal (rho(b)D(3)(b)H)(1/4). Against expectation, a different scaling law is discovered for the crater depth: d approximately equal (rho(3/2)(b)D(2)(b)H)(1/3). The scaling with properties of the medium is also established. The crater depth has significance for granular mechanics in that it relates to the stopping force on the ball.

Exposure to paraphenylendiamine in hairdressing parlours.

Synopsis A certain number of hairdressing parlour employers have been taken to court because their employees allegedly suffered from lung allergies caused by the vapours from PPD (paraphenylendiamine) which allegedly developed when applying hair dyes. These conclusions may be reached if the specific hazards of the rubber and particularly leather and fur dyeing industry are extrapolated as is widely reported in literature, to hairdressing employees. The purpose of this study is to assess the actual exposure rate to PPD vapours of hairdressing employees during a working day, on the basis of the type and characteristics of the salon (small, medium and large), the number of dye applications per day and the chemical-physical characteristics of the oxidation dyes. The results prove that, even under the hypothesis of experimental conditions pushed to the extreme, it is not reasonable to speak of exposure to PPD through the lungs of hairdressing employees.