Cooperation on Competition: The Multistate Tax Commission and State Corporate Tax Uniformity

This report explores how interstate uniformity of state corporate income taxes has varied over time, the role played by the MTC, and how likely it is that uniformity will be achieved. FRC Report 11

On the mechanism of branching in negative ionization fronts

We explain a mechanism for branching of a planar negative front. Branching occurs as the result of a balance between the destabilizing effect of impact ionization and the stabilizing effect of electron diffusion on ionization fronts. The dispersion relation for transversal perturbation is obtained analytically and reads: $s = |k|/[2 (1 + |k|)] - D |k|^2$, where $D$, which is assumed to be small, is the ratio between the electron diffusion coefficient and the intensity of the externally imposed electric field. We estimate the spacing $\lambda$ between streamers in a planar discharge and deduce a scaling law $\lambda \sim D^{1/3}$

The timing of maternal depressive symptoms and child cognitive development: a longitudinal study.

Background: Maternal depression is known to be associated with impairments in child cognitive development, although the effect of timing of exposure to maternal depression is unclear. Methods: Data collected for the Avon Longitudinal Study of Parents and Children, a longitudinal study beginning in pregnancy, included self-report measures of maternal depression the Edinburgh Postnatal Depression Scale, completed on 6 occasions up to 3 years of age, and IQ of the index child (WISC) measured at aged 8 years. We used these data to assign women to 8 groups according to whether depression occurred in the antenatal, postnatal, preschool period, any combination of these times, or not at all. We compared a model comprising all patterns of depression (saturated model) with models nested within this to test whether there is a relationship between depression and child cognitive development and, if so, whether there is a sensitive period. We then investigated the relationship with child IQ for each model, following adjustment for confounders. Results: Six thousand seven hundred and thirty-five of 13,615 children from singleton births (49.5%, of eligible core sample) attended a research clinic at 8 years and completed a WISC with a score ≥ 70. A total of 5,029 mothers of these children had completed mood assessments over the 3 time periods. In unadjusted analyses, all three sensitive period models were as good as the saturated model, as was an accumulation model. Of the sensitive period models, only that for antenatal exposure was a consistently better fit than the accumulation model. After multiple imputation for missing data (to n = 6,735), there was no effect of postnatal depression on child IQ independent of depression at other times [-0.19 IQ points, 95% confidence interval (CI) -1.5 to 1.1 points]. There was an effect of antenatal depression (-3.19 IQ points, 95% CI: -4.33 to -2.06) which attenuated following adjustment (-0.64 IQ points, 95% CI: -1.68 to 0.40). Conclusions: The postnatal period is not a sensitive one for the effect of maternal depression on child cognitive development. © 2011 The Authors. Journal of Child Psychology and Psychiatry

Probing the evolution of Stark wave packets by a weak half cycle pulse

We probe the dynamic evolution of a Stark wave packet in cesium using weak half-cycle pulses (HCP's). The state-selective field ionization(SSFI) spectra taken as a function of HCP delay reveal wave packet dynamics such as Kepler beats, Stark revivals and fractional revivals. A quantum-mechanical simulation explains the results as multi-mode interference induced by the HCP.Comment: 4 pages, incl. 3 figures, submitted to PR

Nonlinear Ionic Conductivity of Thin Solid Electrolyte Samples: Comparison between Theory and Experiment

Nonlinear conductivity effects are studied experimentally and theoretically for thin samples of disordered ionic conductors. Following previous work in this field the {\it experimental nonlinear conductivity} of sodium ion conducting glasses is analyzed in terms of apparent hopping distances. Values up to 43 \AA are obtained. Due to higher-order harmonic current density detection, any undesired effects arising from Joule heating can be excluded. Additionally, the influence of temperature and sample thickness on the nonlinearity is explored. From the {\it theoretical side} the nonlinear conductivity in a disordered hopping model is analyzed numerically. For the 1D case the nonlinearity can be even handled analytically. Surprisingly, for this model the apparent hopping distance scales with the system size. This result shows that in general the nonlinear conductivity cannot be interpreted in terms of apparent hopping distances. Possible extensions of the model are discussed.Comment: 7 pages, 6 figure

Information hiding and retrieval in Rydberg wave packets using half-cycle pulses

We demonstrate an information hiding and retrieval scheme with the relative phases between states in a Rydberg wave packet acting as the bits of a data register. We use a terahertz half-cycle pulse (HCP) to transfer phase-encoded information from an optically accessible angular momentum manifold to another manifold which is not directly accessed by our laser pulses, effectively hiding the information from our optical interferometric measurement techniques. A subsequent HCP acting on these wave packets reintroduces the information back into the optically accessible data register manifold which can then be `read' out.Comment: 4 pages, 4 figure