Critical Casimir Forces in Colloidal Suspensions

Some time ago, Fisher and de Gennes pointed out that long-ranged correlations in a fluid close to its critical point Tc cause distinct forces between immersed colloidal particles which can even lead to flocculation [C. R. Acad. Sc. Paris B 287, 207 (1978)]. Here we calculate such forces between pairs of spherical particles as function of both relevant thermodynamic variables, i.e., the reduced temperature t = (T-Tc)/Tc and the field h conjugate to the order parameter. This provides the basis for specific predictions concerning the phase behavior of a suspension of colloidal particles in a near-critical solvent.Comment: 29 pages, 14 figure

Supervisory Performance and Satisfaction in Relation to Supervisory Style Interactions at Adjacent Levels of Management

The present study examined, for a range of industrial management positions, the relationship of supervisory style patterns at adjacent managerial levels to supervisory performance and job satisfaction. It also investigated the utility of Fiedler’s Contingency Model for determining the supervisory style associated with optimal work group performance at the middle levels of industrial management. Supervisory style was viewed as the extent to which a supervisor’s job related behaviour was basically task-oriented or human relations-oriented. One hundred and twenty-four production supervisory staff representing six manufacturing companies and six organizational levels completed a multi-faceted questionnaire. Measurement devices included: three indices of supervisory style, measures of satisfaction with four separate aspects of the job, two higher management ratings of job performance and independent ratings of position power and job task structure. The results suggested that, for most levels of industrial management, a subordinate manager’s similarity to his immediate supervisor was unrelated to the subordinate’s job satisfaction. At the third level of management similarity of supervisory style was positively related to this manager’s satisfaction with his work and his coworkers. The results provided considerable support for earlier findings which showed that subordinate job satisfaction was positively related to the supervisor’s “consideration” behaviour as perceived by the subordinate manager. Analysis of data related to the Contingency Model provided little support for the model’s validity in terms of the present sample

Modeling the mid-infrared optical gap in La2−xSrxCuO4

In this work, we used a periodic lattice potential in order to model the infrared optical data of the high-temperature superconductor La2−xSrxCuO4. This potential consists of a two-dimensional array of double-well potentials, which simulate the CuO2 layers. It is obtained by assembling Cu-O-Cu units rather than Cu and O single atoms in the tight-binding approach. A gap separating two energy bands can be obtained and is used to fit the infrared (IR) optical gap of this cuprate. We derived the dielectric function and showed that in the classical limit it reduces to the one consisting of a Drude term plus a number of lorentz components, equivalent to the dielectric function used empirically by several authors in their fits of the reflectivity. By refitting available reflectance data, we deduced a simple law for the doping dependence of the optical gap in La2−xSrxCuO4. In the present study, we argue that the optical gap is distinct from the pseudogap or the two-magnon gap, because it characterizes La2−xSrxCuO4 for all doping regimes.In this work, we used a periodic lattice potential in order to model the infrared optical data of the high-temperature superconductor La2−xSrxCuO4. This potential consists of a two-dimensional array of double-well potentials, which simulate the CuO2 layers. It is obtained by assembling Cu-O-Cu units rather than Cu and O single atoms in the tight-binding approach. A gap separating two energy bands can be obtained and is used to fit the infrared (IR) optical gap of this cuprate. We derived the dielectric function and showed that in the classical limit it reduces to the one consisting of a Drude term plus a number of lorentz components, equivalent to the dielectric function used empirically by several authors in their fits of the reflectivity. By refitting available reflectance data, we deduced a simple law for the doping dependence of the optical gap in La2−xSrxCuO4. In the present study, we argue that the optical gap is distinct from the pseudogap or the two-magnon gap, because it characterizes La2−xSrxCuO4 for all doping regimes

Comment on "Quantum Monte Carlo Evidence for Superconductivity in the Three-Band Hubbard Model in Two Dimensions"

In a recent Letter, Kuroki and Aoki [Phys. Rev. Lett. 76, 440 (1996)] presented quantum Monte-Carlo (QMC) results for pairing correlations in the three-band Hubbard model, which describes the Cu-d_{x^2-y^2} and O-p_{x,y} orbitals present in the CuO_2 planes of high-T_c materials. In this comment we argue that (i) the used parameter set is not appropriate for the description of high-T_c materials since it does not satisfy the minimal requirement of a charge-transfer gap at half-filling, and (ii) the observed increase in the d_{x^2-y^2} channel is dominantly produced by the pair-field correlations without the vertex part. Hence, the claim of evidence of ODLRO is not justified.Comment: 1 page latex and 2 eps-figures, uses epsfig, submitted to PR

Polarization anisotropy in the optical properties of silicon ellipsoids

A new real space quantum mechanical approach with local field effects included is applied to the calculation of the optical properties of silicon nanocrystals. Silicon ellipsoids are studied and the role of surface polarization is discussed in details. In particular, surface polarization is shown to be responsible for a strong optical anisotropy in silicon ellipsoids, much more pronounced with respect to the case in which only quantum confinement effects are considered. The static dielectric constant and the absorption spectra are calculated, showing that the perpendicular and parallel components have a very different dependence on the ellipsoid aspect ratio. Then, a comparison with the classical dielectric model is performed, showing that the model only works for large and regular structures, but it fails for thin elongated ellipsoids.Comment: 5 pages, 4 figures, International Conference on NANO-Structures Self-Assemblin

Resistance Breeding in Apple at Dresden-Pillnitz

Resistance breeding in apple has a long tradition at the Institute of Fruit Breeding now Julius Kuehn-institute in Dresden-Pillnitz. The breeding was aimed at the production of multiple resistance cultivars to allow a more sustainable and environmentally friendly production of apple. In the last decades a series of resistant cultivars (Re®-cultivars) bred in Dresden-Pillnitz has been released, ‘Recolor’ and ‘Rekarda’ in 2006. The main topic in the resistance breeding programme was scab resistance and the donor of scab resistance in most cultivars was Malus x floribunda 821. Due to the development of strains that are able to overcome resistance genes inherited by M. x floribunda 821 and due to the fact that single resistance genes can be broken easily, pyramiding of resistance genes is necessary. Besides scab, fire blight and powdery mildew are the main disease for which a pyramiding of genes is aspired in Pillnitz. Biotechnical approaches are necessary for the early detection of pyramided resistance genes in breeding clones. This paper will give an overview of the resistance breeding of apple in Pillnitz and the methods used

A Dynamical Quantum Cluster Approach to Two-Particle Correlation Functions in the Hubbard Model

We investigate the charge- and spin dynamical structure factors for the 2D one-band Hubbard model in the strong coupling regime within an extension of the Dynamical Cluster Approximation (DCA) to two-particle response functions. The full irreducible two-particle vertex with three momenta and frequencies is approximated by an effective vertex dependent on the momentum and frequency of the spin/charge excitation. In the spirit of the DCA, the effective vertex is calculated with quantum Monte Carlo methods on a finite cluster. On the basis of a comparison with high temperature auxiliary field quantum Monte Carlo data we show that near and beyond optimal doping, our results provide a consistent overall picture of the interplay between charge, spin and single-particle excitations.Comment: 8 pages, 11 figure

Comment on "Why is the DNA denaturation transition first order?"

In this comment we argue that while the conclusions in the original paper (Y. Kafri, D. Mukamel and L. Peliti, Phys. Rev. Lett. 85, 4988 (2000)) are correct for asymptotically long DNA chains, they do not apply to the chains used in typical experiments. In the added last paragraph, we point out that for real DNA the average distance between denatured loops is not of the order of the persistence length of a single-stranded chain but much larger. This corroborates our reasoning that the double helix between loops is quite rigid, and thereby our conclusion.Comment: 1 page, REVTeX. Last paragraph adde