X-ray induced electron and ion fragmentation dynamics in IBr

Characterization of the inner-shell decay processes in molecules containing heavy elements is key to understanding x-ray damage of molecules and materials and for medical applications with Auger-electron-emitting radionuclides. The 1s hole states of heavy atoms can be produced by absorption of tunable x-rays and the resulting vacancy decays characterized by recording emitted photons, electrons, and ions. The 1s hole states in heavy elements have large x-ray fluorescence yields that transfer the hole to intermediate electron shells that then decay by sequential Auger-electron transitions that increase the ion's charge state until the final state is reached. In molecules the charge is spread across the atomic sites, resulting in dissociation to energetic atomic ions. We have used x-ray/ion coincidence spectroscopy to measure charge states and energies of I$^{q+}$ and Br$^{q'+}$ atomic ions following 1s ionization at the I and Br \textit{K}-edges of IBr. We present the charge states and kinetic energies of the two correlated fragment ions associated with core-excited states produced during the various steps of the cascades. To understand the dynamics leading to the ion data, we develop a computational model that combines Monte-Carlo/Molecular Dynamics simulations with a classical over-the-barrier model to track inner-shell cascades and redistribution of electrons in valence orbitals and nuclear motion of fragments

Leaders' achievement goals and their integrative management of creative ideas voiced by subordinates or superiors

The purpose of this research was to examine the joint impact of leader achievement goals and hierarchical position of the voicer of creative ideas (subordinate vs. superior) on the extent to which leaders (intent to) integrate these voiced creative ideas with their own ideas (integrative idea management). In a scenario-based survey (study 1; N=189), in which we measured participants' achievement goals, we found that the relationship between leaders' performance goals and their intention to integrate voiced creative ideas is contingent on the hierarchical position of the idea voicer. Similarly, in an experimental study (study 2; N=94), in which we experimentally induced achievement goals, we found that leaders display lower integrative intentions when ideas are voiced by a subordinate rather than a superior, but this was only true for leaders pursuing performance goals. Furthermore, the results of an additional, exploratory analysis suggest that the hierarchical position of the voicer of creative ideas had an indirect effect on integrative behavior through integrative intentions for performance goal leaders and no effect for mastery goal leaders. Together, these findings advance our understanding of how middle management leaders are influenced by their own achievement goals when managing the creative ideas voiced by subordinates and superiors.</p

Spin-state studies with XES and RIXS: From static to ultrafast

We report on extending hard X-ray emission spectroscopy (XES) along with resonant inelastic X-ray scattering (RIXS) to study ultrafast phenomena in a pump-probe scheme at MHz repetition rates. The investigated systems include low-spin (LS) Fe-II complex compounds, where optical pulses induce a spin-state transition to their (sub)nanosecond-lived high-spin (HS) state. Time-resolved XES clearly reflects the spin-state variations with very high signal-to-noise ratio, in agreement with HS-LS difference spectra measured at thermal spin crossover, and reference HS-LS systems in static experiments, next to multiplet calculations. The 1s2p RIXS, measured at the Fe Is pre-edge region, shows variations after laser excitation, which are consistent with the formation of the HS state. Our results demonstrate that X-ray spectroscopy experiments with overall rather weak signals, such as RIXS, can now be reliably exploited to study chemical and physical transformations on ultrafast time scales. (C) 2012 Elsevier B.V. All rights reserved

Identifying ‘win-win-win’ futures from inequitable value chain trade-offs: A system dynamics approach

Context There is growing recognition that food systems must adapt to become more sustainable and equitable. Consequently, in developing country contexts, there is increasing momentum away from traditional producer-facing value chain upgrades towards efforts to increase both the availability and affordability of nutritious foods at the consumer level. However, such goals must navigate the inherent complexities of agricultural value chains, which involve multiple interactions, feedbacks and unintended consequences, including important but often surprising trade-offs between producers and consumers. Objective and methods Based around the 'Loop' horticultural aggregation scheme of Digital Green in Bihar, India, we develop a system dynamics modelling framework to survey the value chain trade-offs emerging from upgrades that aim to improve the availability of fruits and vegetables in small retail-oriented markets. We model the processes of horticultural production, aggregation, marketing, and retailing – searching for futures that are ‘win-win-win’ for: (i) the availability of fruits and vegetables in small retail markets, (ii) the profits of farmers participating in aggregation, and (iii) the sustainability of the initial scheme for Digital Green as an organisation. We simulate two internal upgrades to aggregation and two upgrades to the wider enabling environment through a series of 5000 Monte Carlo trajectories – designed to explore the plausible future dynamics of the three outcome dimensions relative to the baseline. Results We find that ‘win-win-win’ futures cannot be achieved by internal changes to the aggregation scheme alone, emerging under a narrow range of scenarios that boost supplies to the small retail market whilst simultaneously supporting the financial takeaways of farmers. In contrast, undesirable producer versus consumer trade-offs emerge as unintended consequences of scaling-up aggregation and the introduction of market-based cold storage. Significance This approach furthers ongoing efforts to capture complex value chain processes, outcomes and upgrades within system dynamics modelling frameworks, before scanning the horizon of plausible external scenarios, internal dynamics and unintended trade-offs to identify ‘win-win-win’ futures for all

Femtosecond Operation of the LCLS for User Experiments

In addition to its normal operation at 250pC, the LCLS has operated with 20pC bunches delivering X-ray beams to users with energies between 800eV and 2 keV and with bunch lengths below 10 fs FWHM. A bunch arrival time monitor and timing transmission system provide users with sub 50 fs synchronization between a laser and the X-rays for pump/probe experiments. We describe the performance and operational experience of the LCLS for short bunch experiments

Class, Ethnicity, and Socialist Politics: St. Louis, 1876-1881

[No abstract

DETERMINATION OF THE MOLECULAR STRUCTURE OF SEVERAL CARBO-CATIONS VIA THE ``COULOMB EXPLOSION'' TECHNIQUE

$^{1}$ E. P. Kanter, Z. Vager, G. Both, and D. Zajman, J. Chem. Phys. 85, 7487 (1986). $^{2}$ G. P. Raine and H. F. Schaefer, J. Chem. Phys. 81, 4034 (1984). $^{3}$ J. Pople, private communication.Author Institution: Argonne National Laboratory, 9700 S. Cass Ave.; Argonne National Laboratory, The Weizmann Institute of ScienceSeveral important carbo-cations such as $C_{2}H_{3}{^{+1}}$ and $CH_{5}^{+}$ have been studied by this radically new technique which obtains direct three-dimensional images of small molecules. Protonated acetylene has been a molecule of extreme interest because of the possibility of it assuming nonclassical ""bridged"" and classical ""nonbridged"" configurations. Our data is consistent with having the proton in the bridged position; the spatial geometry obtained is in quite reasonable agreement with ab $initio^{2,3}$ calculations. This work supported by the U. S. Department of Energy, Office of Basic Energy Sciences, under Contract W-31-109-ENG-38