Packing of balls into a jar: first ask if the balls are all the same size

EGR1074

- How spheres pack into containers is a problem that’s been studied for decades. Recent computer simulations show that such packings appear to have large-scale density fluctuations if the spheres aren’t all exactly the same size. More significantly, the simulations show that careful consideration of each particle’s size reveals that the density fluctuations are smoother than they first appear. However, it is very hard to detect subtle particle size differences in experiments. Previously experiments had to assume all particles are the same, which is an approximation; the simulations showed that this approximation is an unfortunate one to have to make. We imaged half a million microscopic spheres in a container and developed a novel method for determination of each particle’s size. Using our data, we confirmed the prior computer simulation results. We expect our method will be quite useful for a variety of experimental studies of sand and particle suspensions.

Attosecond intramolecular electron dynamics observed

LF13695

- The current article provides an exceptional view into the microscopic,
ultrafast world of one single electron inside nature's most simple
molecule.

Our experimental and theoretical work shows how an ultrashort and strong
laser drives the only electron in the chemical bond of a hydrogen
molecular ion on an attosecond time scale (1 attosecond = 10^{-18}
seconds), makes it slosh around and finally splashes it out of the
molecule. This wild splashing electron waves come as a surprise to
scientists who previously assumed that a laser field frees electrons
gently through a narrow tunnel "drilled" into the molecule by the light.
Our work further shows the exciting prospect that the invisible dynamics
of the electron inside a molecule can be mapped onto the momenta of the
electron once it left the molecule and where they become observable.