Elastic Differential Cross Sections for Space Radiation Applications

The eikonal, partial wave (PW) Lippmann-Schwinger, and three-dimensional Lippmann- Schwinger (LS3D) methods are compared for nuclear reactions that are relevant for space radiation applications. Numerical convergence of the eikonal method is readily achieved when exact formulas of the optical potential are used for light nuclei (A $\le$ 16), and the momentum-space representation of the optical potential is used for heavier nuclei. The PW solution method is known to be numerically unstable for systems that require a large number of partial waves, and, as a result, the LS3D method is employed. The effect of relativistic kinematics is studied with the PW and LS3D methods and is compared to eikonal results. It is recommended that the LS3D method be used for high energy nucleon-nucleus reactions and nucleus-nucleus reactions at all energies because of its rapid numerical convergence and stability

The combinatorial lexicon: Priming derivational affixes

In earlier research we argued for a morphemically decomposed account of the mental representation of semantically transparent derived forms, such as happiness, rebuild, and punishment. We proposed that such forms were represented as stems linked to derivational affixes, as in {happy} + {-ness} or {re-} + {build}. A major source of evidence for this was the pattern of priming effects, between derived forms and their stems, in a cross-modal repetition priming task. In two new experiments we investigated the prediction of this account that derivational affixes, such as {-ness} or {re-}, should also exist as independent entities in the mental lexicon, and should also be primable. We tested both prefixes and suffixes, split into productive and unproductive groups (where "unproductive" means no longer used to form new words), and found significant priming effects in the same cross-modal task. These effects were strongest for the productive suffixes and prefixes, as in prime-target pairs such as darkness/toughness and rearrange/rethink, where the overall effects were as strong as those for derived/stem pairs such as absurdity/absurd, and where possible phonological effects are ruled out by the absence of priming in phonological control and pseudo-affix conditions. We interpret this as evidence for a combinatorial approach to lexical representation

Snapshots of a protein folding intermediate

We have investigated the folding dynamics of Thermus thermophilus cytochrome c_(552) by time-resolved fluorescence energy transfer between the heme and each of seven site-specific fluorescent probes. We have found both an equilibrium unfolding intermediate and a distinct refolding intermediate from kinetics studies. Depending on the protein region monitored, we observed either two-state or three-state denaturation transitions. The unfolding intermediate associated with three-state folding exhibited native contacts in β-sheet and C-terminal helix regions. We probed the formation of a refolding intermediate by time-resolved fluorescence energy transfer between residue 110 and the heme using a continuous flow mixer. The intermediate ensemble, a heterogeneous mixture of compact and extended polypeptides, forms in a millisecond, substantially slower than the ∼100-μs formation of a burst-phase intermediate in cytochrome c. The surprising finding is that, unlike for cytochrome c, there is an observable folding intermediate, but no microsecond burst phase in the folding kinetics of the structurally related thermostable protein