Charged tensor matter fields and Lorentz symmetry violation via spontaneous symmetry breaking

We consider a model with a charged vector field along with a Cremmer-Scherk-Kalb-Ramond (CSKR) matter field coupled to a U(1) gauge potential. We obtain a natural Lorentz symmetry violation due to the local U(1) spontaneous symmetry breaking mechanism triggered by the imaginary part of the vector matter. The choice of the unitary gauge leads to the decoupling of the gauge-KR sector from the Higgs-KR sector. The excitation spectrum is carefully analyzed and the physical modes are identified. We propose an identification of the neutral massive spin-1 Higgs-like field with the massive Z boson of the so-called mirror matter models.Received: 30 October 2003, Revised: 16 March 2004, Published online: 23 June 2004     

Biased bilayer graphene: semiconductor with a gap tunable by the electric field effect

We demonstrate that the electronic gap of a graphene bilayer can be controlled externally by applying a gate bias. From the magnetotransport data (Shubnikov-de Haas measurements of the cyclotron mass), and using a tight-binding model, we extract the value of the gap as a function of the electronic density. We show that the gap can be changed from zero to midinfrared energies by using fields of less, approximately < 1 V/nm, below the electric breakdown of SiO2. The opening of a gap is clearly seen in the quantum Hall regime.     

电阻式核磁共振测量的最新进展

电阻式核磁共振(RDNMR)测量是1988年由德国马普所的von Klitzing研究小组针对GaAs二维电子气中少量核自旋的探测而提出的一种具有超高灵敏度的实验技术. 目前, RDNMR已经成为研究单层或双层GaAs二维电子气核自旋和电子自旋特性的重要手段. 由于为实现电阻式核磁共振测量所建立的动态核极化方法强烈依赖于GaAs特有的材料属性, 至今这一技术一直没有扩展应用到其他半导体低维系统中. 最近,本研究小组发展了一种动态核极化新方法,成功实现了对典型窄带半导体锑化铟(InSb) 二维电子气的电阻式核磁共振测量.本文在介绍电阻式核磁共振测量工作原理及已建立的典型动态核极化方法的基础上,着重讨论所提出的动态核极化新方法的机理、 实验结果以及对今后研究的展望.     

Effects of the piezoelectric field on the modulation of exciton–polaritons by surface acoustic waves

Surface acoustic waves (SAWs) provide a powerful tool for the modulation of polaritons in GaAs-based microcavities. In this contribution, we compare the modulation introduced by SAWs propagating along piezoelectric and non-piezoelectric crystal directions of the sample surface. Strain calculations reveal that the type-I band-gap modulation induced by the strain field is comparable for both SAW types. Piezoelectric SAWs have, however, an intrinsic longitudinal electric field, which can dissociate quantum well (QW) excitons and, thus, degrade the modulation. Images of the polariton far-field photoluminescence reveal this behavior for different excitation conditions.     

Evidence of surface active sites on NaY zeolite by a model reaction

Owing to the development of a new test reaction, namely the isomerization of 1-dodecene, it becomes possible to characterize the activity of cationic zeolites under conditions close to those of industrial adsorption and separation processes (temperature around 150-200 °C and liquid phase). Indeed, 1-dodecene is highly active and still in a liquid state at 150 °C. Furthermore, by comparing the reactivity of NaY before and after treatments applied to reduce its activity ((i) passivation of the external surface by deposition of TetraEthylOrthoSiloxane (TEOS) and (ii) washing the zeolite with a basic or neutral solution), we are able to propose a nature and localization for the residual active sites of this zeolite. Indeed, the evolution of the NaY activity in their function indicates that the active sites are located both at the external and internal surfaces of NaY and that two types of sites can be described: OH groups and structure defects.     

Mössbauer investigation of maghemite-based glycolic acid nanocomposite

Transmission electron microscopy, X-ray diffraction and Mössbauer spectroscopy were used in the characterization of a nanocomposite containing magnetic nanoparticles dispersed in a glycolic acid-based template. Maghemite nanoparticles were identified as the iron oxide phase dispersed in the polymeric template. From the low-temperature Mössbauer data the amount of the iron-based, non-magnetic material at the nanoparticle surface was estimated as roughly one monolayer in thickness.     

Spatial characterization of the laser-induced plasma plumes generated by IR CO2 pulsed laser on carbon targets

We have used ferrocene and paraffin wax as novel precursor and solvent for the growth of iron oxide nanoparticles. The proposed method of growth has several advantages over existing methods of growth using iron pentacarbonyl a precursor. Highly crystalline and monodispersed particles are obtained which assemble in two- and three-dimensional hexagonal closed packed superlattices. Growth kinetics has been studied by varying concentration of the precursor and time of growth. A phenomenological model has been proposed to explain the growth kinetics.     

Should Epstein strip arrangement be changed?

The paper describes effect of texture on the anisotropy of magnetic properties and shows that an Epstein strip arrangement including strips cut in a direction 45° to the rolling direction gives property values that are closer to the average values than the traditional RD+TD arrangement.     

Pre-relaxation Processes in a Radiating Relativistic Sphere

The influence of processes occurring before the system relaxes into diffusion, on the evolution of a radiating sphere, is exhibited in a specific example. The luminosity profiles, and consequently the general evolution of the object, are shown to be quite sensitive to the value of relaxation time.