Two-Particle Microrheology of quasi-2D Viscous Systems

We study the correlated motions of colloidal particles in a quasi-2D system (Human Serum Albumin (HSA) protein molecules at an air-water interface) for different surface viscosities $\eta_{s}$. We observe a transition in the behavior of the correlated motion, from 2-D interface dominated at high $\eta_{s}$ to bulk fluid-dependent at low $\eta_{s}$. The correlated motions can be scaled onto a master curve which captures the features of this transition. This master curve also characterizes the spatial dependence of the flow field of a viscous interface in response to a force. From the flow field and the correlated particle motions, we calculate a two-particle MSD (mean square displacement) for direct comparison with rheological measurements.Comment: 4 pages, 4 figures, submitted to PR

Magnetic behavior of EuCu2As2: Delicate balance between antiferromagnetic and ferromagnetic order

The Eu-based compound, EuCu2As2, crystallizing in the ThCr2Si2-type tetragonal structure, has been synthesized and its magnetic behavior has been investigated by magnetization (M), heat-capacity (C) and electrical resistivity (rho) measurements as a function of temperature (T) and magnetic field (H) as well as by 151Eu Moessbauer measurements. The results reveal that Eu is divalent ordering antiferromagnetically below 15 K in the absence of magnetic field, apparently with the formation of magnetic Brillouin-zone boundary gaps. A fascinating observation is made in a narrow temperature range before antiferromagnetism sets in: That is, there is a remarkable upturn just below 20 K in the plot of magnetic susceptibility versus T even at low fields, as though the compound actually tends to order ferromagnetically. There are corresponding anomalies in the magnetocaloric effect data as well. In addition, a small application of magnetic field (around 1 kOe at 1.8 K) in the antiferromagnetic state causes spin-reorientation effect. These results suggest that there is a close balance between antiferromagnetism and ferromagnetism in this compoundComment: Phys. Rev. B, in pres

New excitations in bcc 4^{4}He - an inelastic neutron scattering study

We report neutron scattering measurements on bcc solid $^{4}$% He. We studied the phonon branches and the recently discovered ''optic-like'' branch along the main crystalline directions. In addition, we discovered another, dispersionless "optic-like'' branch at an energy around 1 meV ($\sim$~11K). The properties of the two "optic-like" branches seem different. Since one expects only 3 acoustic phonon branches in a monoatomic cubic crystal, these new branches must represent different type of excitations. One possible interpretation involves localized excitations unique to a quantum solid.Comment: 4 pages, 3 figures, accepted by PRB, Rapid Communication

Testing T Invariance in the Interaction of Slow Neutrons with Aligned Nuclei

The study of five-fold (P even, T odd) correlation in the interaction of slow polarized neutrons with aligned nuclei is a possible way of testing the time reversal invariance due to the expected enhancement of T violating effects in compound resonances. Possible nuclear targets are discussed which can be aligned both dynamically as well as by the "brute force" method at low temperature. A statistical estimation is performed of the five-fold correlation for low lying p wave compound resonances of the $^{121}$Sb, $^{123}$Sb and $^{127}$I nuclei. It is shown that a significant improvement can be achieved for the bound on the intensity of the fundamental parity conserving time violating (PCTV) interaction.Comment: 22 pages, 5 figures, published versio

Influência da época do ano e das diferentes formas de aplicação de ácido naftaleno acético (ANA) no enraizamento de Mikania micrantha Kunth.

Mikania micrantha Kunth é uma espécie nativa do Brasil, heliófila e de hábito rasteiro. É amplamente difundida na medicina popular e potencialmente utilizada na recuperação de áreas degradadas. O objetivo deste trabalho foi verificar a influência de diferentes formulações e vias de aplicação de ácido naftaleno acético (NAA) no enraizamento de estacas caulinares de Mikania micrantha Kunth coletadas nas quatro estações do ano. Estacas herbáceas provenientes de plantas matrizes nativas da região de Colombo - Paraná foram coletadas na primavera/2002, verão/2003, outono/2003 e inverno/2003, confeccionadas com 10 cm de comprimento e uma folha cortada pela metade mantida no ápice, desinfestadas e submetidas aos seguintes tratamentos (T): T, (Omg Kg-lANA), T2 (5000 mg Kg-l ANA), T3 (5000 mg Kg-1ANA- RAIZON 05@),T4 (5000 mg L-I ANA), T, (O mg L-' ANA) e Te (água). O plantio foi realizado em tubetes de polipropileno (55 crn-) contendo vermiculita de granulometria média, sendo as estacas mantidas em casa-devegetação com nebulização intermitente. Após 20 dias foram avaliadas as seguintes características: porcentagem de estacas enraizadas, número e comprimento das três maiores raízes por estaca, porcentagem de estacas vivas (sem raiz e sem calos) e porcentagem de estacas mortas. A análise estatística constou de um delineamento inteiramente casualizado (DIC) composto por seis tratamentos com quatro repetições de 24 estacas por parcela. A espécie foi considerada de fácil enraizamento, apresentando as maiores porcentagens na primavera, verão e outono (superiores a 86%), dispensando o uso de regulador vegetal para a indução radicial

Measuring Dislocation Density in Aluminum with Resonant Ultrasound Spectroscopy

Dislocations in a material will, when present in enough numbers, change the speed of propagation of elastic waves. Consequently, two material samples, differing only in dislocation density, will have different elastic constants, a quantity that can be measured using Resonant Ultrasound Spectroscopy. Measurements of this effect on aluminum samples are reported. They compare well with the predictions of the theory.Comment: 4 pages, 2 figure