Small polaron formation in many-particle states of the Hubbard-Holstein model: The one-dimensional case

We investigate polaron formation in a many-electron system in the presence of a local repulsion sufficiently strong to prevent local-bipolaron formation. Specifically, we consider a Hubbard-Holstein model of interacting electrons coupled to dispersionless phonons of frequency $\omega_0$. Numerically solving the model in a small one-dimensional cluster, we find that in the nearly adiabatic case $\omega_0 < t$, the necessary and sufficient condition for the polaronic regime to occur is that the energy gain in the atomic (i.e., extremely localized) regime ${\cal E}_{pol}$ overcomes the energy of the purely electronic system ${\cal E}_{el}$. In the antiadiabatic case, $\omega_0 > t$, polaron formation is instead driven by the condition of a large ionic displacement $g/\omega_0 >1$ ($g$ being the electron-phonon coupling). Dynamical properties of the model in the weak and moderately strong coupling regimes are also analyzed

Temporary extra jobs for immigrants: Merging lane to employment or dead-end road in welfare?

We evaluate the effects of the most frequently used German welfare-to-work program on the employment chances of immigrant welfare recipients. In particular, we investigate whether program effects differ between immigrants and natives and what might cause these potential differences. Our results reveal that the program fails to achieve its objectives. The effects are more adverse for natives, but the program does not help otherwise identical immigrants to leave the welfare system either. Therefore, the program is a dead-end road rather than a merging lane to regular employment both for natives and for immigrants. --Immigrants,employment programs,evaluation,decomposition of effects,Germany

Intensifying the Use of Benefit Sanctions – An Effective Tool to Shorten Welfare Receipt and Speed up Transitions to Employment?

Benefitt sanctions imposed on non-compliant welfare recipients are a new element in the German welfare system. In practice, the sanction policy and the application of sanctions vary considerably across the 439 welfare agencies. Based on combined administrative and survey data, these differences are used as instrumental variables to estimate the effect of sanctions on the drop-out from welfare and the transition to employment. The estimated local average treatment effect (LATE) is an estimate of the effectiveness of an intensifed use of sanctions. The results show that tightening sanction policy would be quite eective.benefit sanctions, welfare recipients, IV, LATE

Cowden syndrome - Diagnostic skin signs

Cowden syndrome is a rare autosomal dominant familial cancer syndrome with a high risk of breast cancer. The most important clinical features include carcinomas of the breast and thyroid, and hamartomatous polyps of the gastrointestinal tract. There are characteristic mucocutaneous features which allow early recognition of the disease and are generally present before internal malignancies develop. We report on a woman in whom the diagnosis of Cowden syndrome was first made after she had been treated for both breast cancer and melanoma. Copyright (C) 2001 S. KargerAG, Basel

Intensifying the Use of Benefit Sanctions: An Effective Tool to Shorten Welfare Receipt and Speed Up Transitions to Employment?

Benefit sanctions imposed on non-compliant welfare recipients are a new element in the German welfare system. In practice, the sanction policy and the application of sanctions vary considerably across the 439 welfare agencies. Based on combined administrative and survey data, these differences are used as instrumental variables to estimate the effect of sanctions on the drop-out from welfare and the transition to employment. The estimated local average treatment effect (LATE) is an estimate of the effectiveness of an intensified use of sanctions. The results show that tightening sanction policy would be quite effective.benefit sanctions, welfare recipients, IV, LATE

Intensifying the use of benefit sanctions: an effective tool to shorten welfare receipt and speed up transitions to employment?

Benefit sanctions imposed on non-compliant welfare recipients are a new element in the German welfare system. In practice, the sanction policy and the application of sanctions vary considerably across the 439 welfare agencies. Based on combined administrative and survey data, these differences are used as instrumental variables to estimate the effect of sanctions on the drop-out from welfare and the transition to employment. The estimated local average treatment effect (LATE) is an estimate of the effctiveness of an intensified use of sanctions. The results show that tightening sanction policy would be quite effective. --benefit sanctions,welfare recipients,IV,LATE

Short-term training programs for immigrants: do effects differ from natives and why?

We evaluate the effects of different short-term training programs on the employment chances of immigrant and native welfare recipients in Germany. In particular, we investigate whether program effects differ between both groups and what might cause these potential differences. In a first step, we evaluate program effects separately for immigrants and natives using propensity score matching estimators. To explain potential differences in effects between the groups, we suggest and apply a decomposition method based on the matching procedure that allows identification of differences due to observable characteristics and differences related to an immigrant fixed effect in a second step. --Immigrants,short-term training programs,evaluation,decomposition,matching,Germany

Singular order parameter interaction at nematic quantum critical point in two dimensional electron systems

We analyze the infrared behavior of effective N-point interactions between order parameter fluctuations for nematic and other quantum critical electron systems with a scalar order parameter in two dimensions. The interactions exhibit a singular momentum and energy dependence and thus cannot be represented by local vertices. They diverge for all N greater or equal 4 in a collinear static limit, where energy variables scale to zero faster than momenta, and momenta become increasingly collinear. The degree of divergence is not reduced by any cancellations and renders all N-point interactions marginal. A truncation of the order parameter action at quartic or any other finite order is therefore not justified. The same conclusion can be drawn for the effective action describing fermions coupled to a U(1) gauge field in two dimensions.Comment: 18 pages, 1 figur

Cross-stream transport of asymmetric particles driven by oscillating shear

We study the dynamics of asymmetric, deformable particles in oscillatory, linear shear flow. By simulating the motion of a dumbbell, a ring polymer, and a capsule we show that cross-stream migration occurs for asymmetric elastic particles even in linear shear flow if the shear rate varies in time. The migration is generic as it does not depend on the particle dimension. Importantly, the migration velocity and migration direction are robust to variations of the initial particle orientation, making our proposed scheme suitable for sorting particles with asymmetric material properties.Comment: 5 pages, 4 figure