Multiple electron trapping in the fragmentation of strongly driven molecules

We present a theoretical quasiclassical study of the formation, during Coulomb explosion, of two highly excited neutral H atoms (double H$^{*}$) of strongly driven H$_2$. In this process, after the laser field is turned off each electron occupies a Rydberg state of an H atom. We show that two-electron effects are important in order to correctly account for double H$^{*}$ formation. We find that the route to forming two H$^{*}$ atoms is similar to pathway B that was identified in Phys. Rev. A {\bf 85} 011402 (R) as one of the two routes leading to single H$^{*}$ formation. However, instead of one ionization step being "frustrated" as is the case for pathway B, both ionization steps are "frustrated" in double H$^{*}$ formation. Moreover, we compute the screened nuclear charge that drives the explosion of the nuclei during double H$^{*}$ formation.Comment: 4 pages, 6 figure

HAMSTRINGS COACTIVATION IN TRAINED LONG JUMPERS AND UNTRAINED INDIVIDUALS DURING DROP JUMPING

The purpose of this study was to examine the EMG activity patterns of the hamstrings during drop jumping from different heights in trained longer jumpers and controls. A group of trained long jumpers and a group of untrained subjects performed maximal drop jumps from 20cm, 40cm and 60 cm on a force platform. The surface EMG activity of the hamstrings was recorded using bipolar electrodes. The ground reaction forces (GRF) and 3-D kinematic data were also recorded. Two-way analysis of variance tests indicated non-significant differences in hamstring EMG amplitude between trained and untrained athletes. However, the long jumpers had significantly higher vertical GRF values and some kinematic differences compared to untrained individuals. The absence of higher hamstrings activity in the long jumpers may have been a contributing factor in their higher performance compared to controls. However, the same result indicates that this increased performance may be accompanied by a possible increased risk of knee joint instability

The Coulomb four-body problem in a classical framework: Triple photoionization of lithium

Formulating a quasiclassical approach we determine the cross section for the complete four-body break-up of the lithium ground state following single photon absorption from threshold up to 220 eV excess energy. In addition, we develop a new classification scheme for three-electron ionizing trajectories in terms of electron-electron collisions, thereby identifying two main ionization paths which the three electrons in the ground state of lithium follow to escape to the continuum. The dominant escape paths manifest themselves in a characteristic ``T-shape'' break-up pattern of the three electrons which implies observable structures in the electronic angular correlation probability. This break-up pattern prevails for excess energies so low that the Wannier threshold law $\sigma\propto E^{\alpha}$ describes already the triple ionization cross section, whose predicted value $\alpha=2.16$ we can confirm quantitatively

Classical Scattering for a driven inverted Gaussian potential in terms of the chaotic invariant set

We study the classical electron scattering from a driven inverted Gaussian potential, an open system, in terms of its chaotic invariant set. This chaotic invariant set is described by a ternary horseshoe construction on an appropriate Poincare surface of section. We find the development parameters that describe the hyperbolic component of the chaotic invariant set. In addition, we show that the hierarchical structure of the fractal set of singularities of the scattering functions is the same as the structure of the chaotic invariant set. Finally, we construct a symbolic encoding of the hierarchical structure of the set of singularities of the scattering functions and use concepts from the thermodynamical formalism to obtain one of the measures of chaos of the fractal set of singularities, the topological entropy.Comment: accepted in Phy. Rev.

Streaking single-electron ionization in open-shell molecules driven by X-ray pulses

We obtain continuum molecular wavefunctions for open-shell molecules in the Hartree-Fock framework. We do so while accounting for the singlet or triplet total spin symmetry of the molecular ion, that is, of the open-shell orbital and the initial orbital where the electron ionizes from. Using these continuum wavefunctions, we obtain the dipole matrix elements for a core electron that ionizes due to single-photon absorption by a linearly polarized X-ray pulse. After ionization from the X-ray pulse, we control or streak the electron dynamics using a circularly polarized infrared (IR) pulse. For a high intensity IR pulse and photon energies of the X-ray pulse close to the ionization threshold of the $1{\sigma}$ or $2{\sigma}$ orbitals, we achieve control of the angle of escape of the ionizing electron by varying the phase delay between the X-ray and IR pulses. For a low intensity IR pulse, we obtain final electron momenta distributions on the plane of the IR pulse and we find that many features of these distributions correspond to the angular patterns of electron escape solely due to the X-ray pulse.Comment: 13 pages, 7 figure

Imaging Ca2+ concentration changes at the secretory vesicle surface with a recombinant targeted cameleon

AbstractRegulated exocytosis involves the Ca2+-triggered fusion of secretory vesicles with the plasma membrane, by activation of vesicle membrane Ca2+-binding proteins [1]. The Ca2+-binding sites of these proteins are likely to lie within 30 nm of the vesicle surface, a domain in which changes in Ca2+ concentration cannot be resolved by conventional fluorescence microscopy. A fluorescent indicator for Ca2+ called a yellow ‘cameleon’ (Ycam2) – comprising a fusion between a cyan-emitting mutant of the green fluorescent protein (GFP), calmodulin, the calmodulin-binding peptide M13 and an enhanced yellow-emitting GFP – which is targetable to specific intracellular locations, has been described [2]. Here, we generated a fusion between phogrin, a protein that is localised to secretory granule membranes [3], and Ycam2 (phogrin–Ycam2) to monitor changes in Ca2+ concentration ([Ca2+]) at the secretory vesicle surface ([Ca2+]gd) through alterations in fluorescence resonance energy transfer (FRET) between the linked cyan and yellow fluorescent proteins (CFP and YFP, respectively) in Ycam2. In both neuroendocrine PC12 and MIN6 pancreatic β cells, apparent resting values of cytosolic [Ca2+] and [Ca2+]gd were similar throughout the cell. In MIN6 cells following the activation of Ca2+ influx, the minority of vesicles that were within ∼1 μm of the plasma membrane underwent increases in [Ca2+]gd that were significantly greater than those experienced by deeper vesicles, and greater than the apparent cytosolic [Ca2+] change. The ability to image both global and compartmentalised [Ca2+] changes with recombinant targeted cameleons should extend the usefulness of these new Ca2+ probes

Quasiclassical double photoionization from the 2^{1,3}S excited states of helium including shakeoff

We account for the different symmetries of the 2^{1,3}S helium excited states in a quasiclassical description of the knockout mechanism augmented by a quantum shakeoff contribution. We are thus able to formulate the separate contribution of the knockout and shakeoff mechanisms for double photoionization for any excess energy from the 2^{1,3}S states. Photoionization ratios and singly differential cross sections calculated for the 2^{1,3}S excited states of helium are found to be in very good agreement with recent theoretical results.Comment: 9 pages, 5 figure