Resistance due to vortex motion in the ν=1\nu=1 bilayer quantum Hall superfluid

The longitudinal and Hall resistances have recently been measured for quantum Hall bilayers at total filling $\nu=1$ in the superfluid state with interlayer pairing, both for currents flowing parallel to one another and for "counterflowing" currents in the two layers. Here I examine the contribution to these resistances from the motion of unpaired vortices in these systems, developing some possible explanations of various qualitative features of these data.Comment: 4 pages, slightly revised, accepted to PR

Comparing Nonparametric Regression Quantiles

This paper investigates how conditional quantiles of a given distribution relate to each other. Given two conditional quantiles estimated nonparametrically, we investigate their relation by linking them through a parametric transformation. Asymptotic normality of the associated parameter vector is established, and the method is illustrated with data from the Family Expenditure Survey (FES) of UK households. The FES records expenditures of households on six broad categories of goods (alcohol, clothing, food, fuel, transport, and "other goods"), and the methodology is applied by estimating and comparing the conditional quantiles of the Engel relation. The only category for which expenditure can explain the shift in the quantile curves is for "other goods" relationship, indicating an increase in heterogeneity for better off households, suggesting a "taste for variety" effect as the expenditure level increases. For the remaining categories one cannot reject the null of a parallel shift of the quantile curvesQuantile Regression, Semiparametric Estimation, Specification Testing, Engel Curve, Household Expenditure, Budget Shares.

Localization of interacting fermions at high temperature

We suggest that if a localized phase at nonzero temperature $T>0$ exists for strongly disordered and weakly interacting electrons, as recently argued, it will also occur when both disorder and interactions are strong and $T$ is very high. We show that in this high-$T$ regime the localization transition may be studied numerically through exact diagonalization of small systems. We obtain spectra for one-dimensional lattice models of interacting spinless fermions in a random potential. As expected, the spectral statistics of finite-size samples cross over from those of orthogonal random matrices in the diffusive regime at weak random potential to Poisson statistics in the localized regime at strong randomness. However, these data show deviations from simple one-parameter finite-size scaling: the apparent mobility edge ``drifts'' as the system's size is increased. Based on spectral statistics alone, we have thus been unable to make a strong numerical case for the presence of a many-body localized phase at nonzero $T$

Superdiffusive nonequilibrium motion of an impurity in a Fermi sea

We treat the nonequilibrium motion of a single impurity atom in a low-temperature single-species Fermi sea, interacting via a contact interaction. In the nonequilibrium regime, the impurity does a superdiffusive geometric random walk where the typical distance traveled grows with time as $\sim t^{d/(d+1)}$ for the $d$-dimensional system with $d\geq 2$. For nonzero temperature $T$, this crosses over to diffusive motion at long times with diffusivity $D\sim T^{-(d-1)/2}$. These results apply also to a nonzero concentration of impurity atoms as long as they remain dilute and nondegenerate.Comment: 5 pages, 1 figure, to appear in Phys. Rev.

Institutional complementarities and gender diversity on boards: a configurational approach

Manuscript Type: Empirical Research Question/Issue: To address the lack of a complementarities-based approach in studies of board diversity, this paper seeks to understandwhether and howcertain country-level factors are causally and jointly related towomen on boards and the nature of their complementarities (are they synergic or substitutes?). Moreover, we intend to learn more about the adoption/diffusion of board gender quotas, by taking into account their role in the existing national configurations (whether they are necessary and/or sufficient conditions). Research Findings/Insights: Using fs/QCA, our findings reveal a particular configuration of country-level conditions that supports the existence of a joint causal relation between given institutional arrangements. Furthermore, we find that board gender quota legislation is not a sufficient condition on its own to achieve a higher number of women on boards. Such evidence suggests that its diffusion across countries could be the result of institutional isomorphismor social legitimacy more than to rational reasons. Theoretical/Academic Implications: For scholars, our paper refines and expands insights from the extant comparative corporate governance literature. By finding support for the “bundled” or jointly causal nature of given institutional factors,we open a window for further research that investigates board-level phenomena in a complementarities-based perspective. Practitioner/Policy Implications: For policymakers, this study provides some insights that could better drive their choice about which mix of policies is necessary to improve female representation on boards, and especially in which institutional areas they should be implemented. It is particularly relevant, because once gender quotas are endorsed at board level, they could have ambiguous effects on firm performance and corporate governance

Evaporative depolarization and spin transport in a unitary trapped Fermi gas

We consider a partially spin-polarized atomic Fermi gas in a high-aspect-ratio trap, with a flux of predominantly spin-up atoms exiting the center of the trap. We argue that such a scenario can be produced by evaporative cooling, and we find that it can result in a substantially non-equilibrium polarization pattern for typical experimental parameters. We offer this as a possible explanation for the quantitative discrepancies in recent experiments on spin-imbalanced unitary Fermi gases.Comment: 6 pages, 3 figures; published versio