Disorder-induced freezing of dynamical spin fluctuations in underdoped cuprates

We study the dynamical spin susceptibility of a correlated d-wave superconductor (dSC) in the presence of disorder, using an unrestricted Hartree-Fock approach. This model provides a concrete realization of the notion that disorder slows down spin fluctuations, which eventually "freeze out". The evolution of disorder-induced spectral weight transfer agrees qualitatively with experimental observations on underdoped cuprate superconductors. For sufficiently large disorder concentrations, static spin density wave (SDW) order is created when droplets of magnetism nucleated by impurities overlap. We also study the disordered stripe state coexisting with a dSC and compare its magnetic fluctuation spectrum to that of the disorder-generated SDW phase.Comment: 5 pages, 4 figure

How to portray men and women in advertisements? Explicit and implicit evaluations of ads depicting different gender roles.

The purpose of the current study was to gain more insight in the evaluation of advertisements containing different gender role portrayals (stereotypical/a-stereotypical) by examining explicit and implicit processes of ad evaluation. The results of two experiments showed an explicit preference for ads containing a-stereotypical images. Implicitly, we found a preference for 'warm' ads irrespective of the degree of gender stereotypicality of the ad. These findings suggest that complex stimuli such as ads may inhibit implicit gender stereotype activation. At an implicit level, warmth seems a better predictor of ad evaluation.Ad evaluation; Evaluation; Gender role portrayal; Image; Implicit association test; Implicit attitudes; Implicit stereotyping; Preference; Processes; Research; Roles; Studies;

Doe one need to go a long way to dig deep? An empirical comparison of online and traditional focus groups.

We evaluate the potential of online focus groups to trigger deep level customer information, which is the major aim of focus groups. We do so by comparing its yield to that of its traditional counterpart. The traditional focus group substantially outperforms online focus groups in level of disclosure, in number of words generated, and in number of ideas generated. However, participants do not reveal these differences in their self-reports. Further, in line with the view that disclosure requires gradual warming up, we find increases in disclosure during the interview in traditional focus groups but not in online focus groups. We conclude that in its present form, the online focus group is not particularly suitable to yield deep level customer information. Starting from our finding that the difference in communication speed explains the differences in disclosure, we suggest some methodological improvements to online focus groups that might increase their yield.Characteristics; Communication; Disclosure; Focus groups; Group dynamics; Implications;

Analytic expression for Taylor-Couette stability boundary

We analyze the mechanism that determines the boundary of stability in Taylor-Couette flow. By simple physical argument we derive an analytic expression to approximate the stability line for all radius ratios and all speed ratios, for co- and counterrotating cylinders. The expression includes viscosity and so generalizes Rayleigh's criterion. We achieve agreement with linear stability theory and with experiments in the whole parameter space. Explicit formulae are given for limiting cases.Comment: 6 pages (LaTeX with REVTEX) including 4 figures (Postscript) Revised, discussion of two additional references. See also http://staff-www.uni-marburg.de/~esse

Computational error bounds for multiple or nearly multiple eigenvalues

AbstractIn this paper bounds for clusters of eigenvalues of non-selfadjoint matrices are investigated. We describe a method for the computation of rigorous error bounds for multiple or nearly multiple eigenvalues, and for a basis of the corresponding invariant subspaces. The input matrix may be real or complex, dense or sparse. The method is based on a quadratically convergent Newton-like method; it includes the case of defective eigenvalues, uncertain input matrices and the generalized eigenvalue problem. Computational results show that verified bounds are still computed even if other eigenvalues or clusters are nearby the eigenvalues under consideration

Variational Monte-Carlo studies of Gossamer Superconductivity

We use a partially Gutzwiller projected BCS d-wave wavefunction with an antiferromagentic weighting factor to study the ground state phase diagram of a half filled Hubbard-Heisenberg model in a square lattice with nearest neighbor hopping $t$ and a diagonal hopping $t'$. The calculations are carried out by using variational Monte Carlo method which treats the Gutzwiller projection explicitly. At large on-site Coulomb interaction $U$, the ground state is antiferromagnetic. As $U$ decreases, the ground state becomes superconducting and eventually metallic. The phase diagram is obtained by extensive calculations. As compared to the strong effect of $U/t$, the phase boundaries turn out to be less sensitive to $t'/t$. The result is consistent with the phase diagram in layered organic conductors, and is compared to the earlier mean field result based on the Gutzwiller approximation.Comment: 5 pages, 4 figure