We present strontium (Sr) isotope ratios that, unlike traditional 87 Sr/ 86 Sr data, are not normalized to a fixed 88 Sr/ 86 Sr ratio of 8.375209 (defined as d 88/86 Sr = 0 relative to NIST SRM 987). Instead, we correct for isotope fractionation during mass spectrometry with a 87 Sr-84 Sr double spike. This technique yields two independent ratios for 87 Sr/ 86 Sr and 88 Sr/ 86 Sr that are reported as ( 87 Sr/ 86 Sr*) and (d 88/86 Sr), respectively. The difference between the traditional radiogenic ( 87 Sr/ 86 Sr normalized to 88 Sr/ 86 Sr = 8.375209) and the new 87 Sr/ 86 Sr* values reflect natural mass-dependent isotope fractionation. In order to constrain glacial/interglacial changes in the marine Sr budget we compare the isotope composition of modern seawater (( 87 Sr/ 86 Sr*, d 88/86 Sr) Seawater ) and modern marine biogenic carbonates (( 87 Sr/ 86 Sr*, d 88/86 Sr) Carbonates ) with the corresponding values of river waters (( 87 Sr/ 86 Sr*, d 88/86 Sr) River ) and hydrothermal solutions (( 87 Sr/ 86 Sr*, d 88/86 Sr) HydEnd ) in a triple isotope plot. The measured ( 87 Sr/ 86 Sr*, d 88/86 Sr) River values of selected rivers that together account for $18% of the global Sr discharge yield a Sr flux-weighted mean of (0.7114 (8), 0.315(8)&). The average ( 87 Sr/ 86 Sr*, d 88/86 Sr) HydEnd values for hydrothermal solutions from the Atlantic Ocean are (0.7045(5), 0.27(3)&). In contrast, the ( 87 Sr/ 86 Sr*, d 88/86 Sr) Carbonates values representing the marine Sr output are (0.70926(2), 0.21(2)&). We estimate the modern Sr isotope composition of the sources at (0.7106(8), 0.310(8)&).The difference between the estimated ( 87 Sr/ 86 Sr*, d 88/86 Sr) input and ( 87 Sr/ 86 Sr*, d 88/86 Sr) output values reflects isotope disequilibrium with respect to Sr inputs and outputs. In contrast to the modern ocean, isotope equilibrium between inputs and outputs during the last glacial maximum (10-30 ka before present) can be explained by invoking three times higher Sr inputs from a uniquely "glacial" source: weathering of shelf carbonates exposed at low sea levels. Our data are also consistent with the "weathering peak" hypothesis that invokes enhanced Sr inputs resulting from weathering of postglacial exposure of abundant fine-grained material.

We demonstrate that the use of time-dependent light polarization opens a new level of control over quantum systems. With potassium dimer molecules from a supersonic molecular beam, we show that a polarization-shaped laser pulse increases the ionization yield beyond that obtained with an optimally shaped linearly polarized laser pulse. This is due to the different multiphoton ionization pathways in K2 involving dipole transitions which favor different polarization directions of the exciting laser field. This experiment is a qualitative extension of quantum control mechanisms which opens up new directions giving access to the three-dimensional temporal response of molecular systems.

Here, using a quantitative in vivo assay, we map three regions in the carboxy terminus of conventional kinesin that are involved in cargo association, folding and regulation, respectively. Using C-terminal and internal deletions, point mutations, localization studies, and an engineered 'minimal' kinesin, we identify five heptads of a coiled-coil domain in the kinesin tail that are necessary and sufficient for cargo association. Mutational analysis and in vitro ATPase assays highlight a conserved motif in the globular tail that is involved in regulation of the motor domain; a region preceding this motif participates in folding. Although these sites are spatially and functionally distinct, they probably cooperate during activation of the motor for cargo transport.

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Coherent control beyond population control and spectral interferences is demonstrated on the interferences and intensity of the two Autler-Townes ͑AT͒ components in the photoelectron spectrum of K atoms, using a sequence of two intense time-delayed femtosecond laser pulses. Photoelectron spectra were taken at various delay times between the two laser pulses and at different laser intensities at a fixed delay time. With respect to the interferences in the AT doublet the role of time delay and laser intensity is interchangeable for (n ϩ0.5) excitation. Strong laser fields or the optical phase of the delayed laser pulse allow the quantum mechanical phase of an atomic state to be manipulated in a symmetrical fashion. The observations are discussed in terms of a two-level model coupled to the continuum. For suitable combinations of the laser intensity of the first pulse and the time delay, the second laser pulse leaves the excited state population unchanged.