Phase transitions and noise crosscorrelations in a model of directed polymers in a disordered medium

We show that effective interactions mediated by disorder between two directed polymers can be modelled as the crosscorrelation of noises in the Kardar-Parisi-Zhang (KPZ) equations satisfied by the respective free energies of these polymers. When there are two polymers, disorder introduces attractive interactions between them. We analyze the phase diagram in details and show that these interactions lead to new phases in the phase diagram. We show that, even in dimension $d=1$, the two directed polymers see the attraction only if the strength of the disorder potential exceeds a threshold value. We extend our calculations to show that if there are $m$ polymers in the system then $m$-body interactions are generated in the disorder averaged effective free energy.Comment: To appear in Phys. Rev. E(2000

Interface Depinning in the Absence of External Driving Force

We study the pinning-depinning phase transition of interfaces in the quenched Kardar-Parisi-Zhang model as the external driving force $F$ goes towards zero. For a fixed value of the driving force we induce depinning by increasing the nonlinear term coefficient $\lambda$, which is related to lateral growth, up to a critical threshold. We focus on the case in which there is no external force applied (F=0) and find that, contrary to a simple scaling prediction, there is a finite value of $\lambda$ that makes the interface to become depinned. The critical exponents at the transition are consistent with directed percolation depinning. Our results are relevant for paper wetting experiments, in which an interface gets moving with no external driving force.Comment: 4 pages, 3 figures included, uses epsf. Submitted to PR

The Importance of Monomeric Anthocyanins in the Definition of Wine Colour Properties

Monomeric anthocyanins are the main contributor of colour in young red wines. To study the importance of monomeric anthocyanins to the wine colour, 41 wines of Vitis vinifera L. Cabernet Sauvignon, Cabernet Gernischt and Merlot were examined. Seven monomeric anthocyanins were isolated and applied as standards in HPLC analysis. Multiple linear regression (MLR) and partial least squares regression (PLSR) were performed to relate and validate the correlations between the monomeric anthocyanins and CIELab colour parameters. Malvidin-3-O-glucoside (Mv3g) was the most abundant anthocyanin in all tested wines, but not the anthocyanin that showed the highest correlation with the colour parameters evaluated. L*, b* and h were shown to be correlated significantly with mainly the anthocyanins for Cabernet Sauvignon, L* with the anthocyanins for Cabernet Gernischt and h with the anthocyanins for Merlot. MLR and PLSR both successfully predicted the colour from the anthocyanin composition of the wine. Delphinidin-3-glucoside (Dp3g), malvidin-3-O-acetylglucoside (Mv3ac) and Dp3g were the most important monomeric anthocyanins contributing to the prediction of the wine colour of Cabernet Sauvignon, Cabernet Gernischt and Merlot respectively. Different grape varieties had profound influences on the correlation of wine colour with anthocyanin composition

Inter-layer Hall effect in double quantum wells subject to in-plane magnetic fields

We report on a theoretical study of the transport properties of two coupled two-dimensional electron systems subject to in-plane magnetic fields. The charge redistribution in double wells induced by the Lorenz force in crossed electric and magnetic fields has been studied. We have found that the redistribution of the charge and the related inter-layer Hall effect originate in the chirality of diamagnetic currents and give a substantial contribution to the conductivity.Comment: 7 RevTex pages, 4 figures, appendix added and misprint in Eq. (11) correcte

Scaling determination of the nonlinear I-V characteristics for 2D superconducting networks

It is shown from computer simulations that the current-voltage ($I$-$V$) characteristics for the two-dimensional XY model with resistively-shunted Josephson junction dynamics and Monte Carlo dynamics obeys a finite-size scaling form from which the nonlinear $I$-$V$ exponent $a$ can be determined to good precision. This determination supports the conclusion $a=z+1$, where $z$ is the dynamic critical exponent. The results are discussed in the light of the contrary conclusion reached by Tang and Chen [Phys. Rev. B {\bf 67}, 024508 (2003)] and the possibility of a breakdown of scaling suggested by Bormann [Phys. Rev. Lett. {\bf 78}, 4324 (1997)].Comment: 6 pages, to appear in PR

Gravitational Contributions to the Running of Gauge Couplings

Gravitational contributions to the running of gauge couplings are calculated by using different regularization schemes. As the $\beta$ function concerns counter-terms of dimension four, only quadratic divergences from the gravitational contributions need to be investigated. A consistent result is obtained by using a symmetry-preserving loop regularization with string-mode regulators which can appropriately treat the quadratic divergences and preserve non-abelian gauge symmetry. The harmonic gauge condition for gravity is used in both diagrammatical and background field calculations, the resulting gravitational corrections to the $\beta$ function are found to be nonzero, which is different from previous results presented in the existing literatures.Comment: 5 pages, 2 figures, published versio

Induced four fold anisotropy and bias in compensated NiFe/FeMn double layers

A vector spin model is used to show how frustrations within a multisublattice antiferromagnet such as FeMn can lead to four-fold magnetic anisotropies acting on an exchange coupled ferromagnetic film. Possibilities for the existence of exchange bias are examined and shown to exist for the case of weak chemical disorder at the interface in an otherwise perfect structure. A sensitive dependence on interlayer exchange is found for anisotropies acting on the ferromagnet through the exchange coupling, and we show that a wide range of anisotropies can appear even for a perfect crystalline structure with an ideally flat interface.Comment: 7 pages, 7 figure