Microwave properties of composites with glass coated amorphous magnetic microwires

The complex permittivity and permeability of composites filled with Fe-based microwires are measured in a coaxial line at frequencies from 0.01 to 10 GHz.The samples under study consist of closely packed wire sections with various orientations relative to wave vector. The composites, where the wires are collinear to the coaxial axis, are found to be low permeable. Their permittivity has frequency dispersion governed by the length of the wire and its linear impedance. The middle section of the wire has higher impedance than that of the end sections where the regular domain structure is distorted. Magnetic bias parallel to the wire axis affects the linear impedance and parameters of dielectric absorption of a composite, the effect is proportional to bias strength. The samples of a coil-type structure, where the wires are wound around the coaxial axis, display the intensive magnetic absorption attributed to the domain wall motion. The absorption takes place in the megahertz band, at microwaves the permeability is close to unity. The microwave properties of diluted composites filled with randomly oriented permeable wires are discussed.     

A wire trap for neutral atoms

We present new ways of trapping a neutral atom with static electric and magnetic fields. We discuss the interaction of a neutral atom with the magnetic field of a current carrying wire and the electric field of a charged wire. Atoms can be trapped by the 1/r magnetic field of a current-carrying wire in a two-dimensional trap. The atoms move in Kepler-like orbits around the wire and angular momentum prevents them from being absorbed at the wire. Trapping was demonstrated in an experiment by guiding atoms along a 1 m long current-carrying wire. Stable traps using the interaction of a polarizable atom with the electric field of a charged wire alone are not possible because of the 1/r ² form of the interaction potential. Nevertheless, we show that one can build a microscopic trap with a combination of a magnetic field generated by a current in a straight wire and the static electric field generated by a concentric charged ring which provides the longitudinal confinement. In all of these traps, the neutral atoms are trapped in a region of maximal field, in theirhigh-field seeking state.Dedicated to H. Walther on the occasion of his 60th birthday     

Narrow transmission bands of quasi-1D comb-like photonic waveguides containing negative index materials

Using the interface response theory, we investigate the band structure and transmission of quasi-1D comb-like photonic waveguides with side branches composed of negative index materials. Numerical results exhibit the existence of discrete modes in band structure. These discrete modes are corresponding to narrow transmission bands which separated by large forbidden band in the transmission spectrum. Meanwhile it is shown that the narrow transmission bands become narrower with the increase of the number of side branches. The above properties are still maintained when the negative index materials are dispersive and lossy.     

Selective cell culture on UV transparent polymer by F2 laser surface modification

A microchip made of UV transparent polymer (CYTOP) that can perform selective cell culture has been fabricated by F₂ laser surface modification. The refractive index of CYTOP is almost the same as that of culture medium, which is essential for three-dimensional (3D) observation of cells. The F₂ laser modification of CYTOP achieves hydrophilicity only on the laser irradiated area with little deterioration of the optical properties and surface smoothness. After the laser modification, HeLa cells were successfully cultured and strongly adhered only on the modified area of CYTOP. The cells patterned on CYTOP were applied for clear 3D observation using an optical microscope in phase contrast mode.     

Gauss-Bonnet and Lovelock Gravities and the Generalized Second Law of Thermodynamics

It has been shown [Chin. Phys. Lett.25 （2008） 4199] that the generalized second law of thermodynamics holds in Einstein gravity. Here we extend this procedure for Gauss-Bonnet and Lovelock gravities. It is shown that by employing the general expression for temperature Th =｜κ｜/2π= 1/2πτA （1-τA/2HτA） associated with the apparent horizon of a Friedman Robertson-Walker （FRW） universe and assuming Tm = bTh, we are able to construct conditions for which the generalized second law holds in Gauss Bonnet and Lovelock gravities, where Tm and Th are the temperatures of the source and the horizon respectively.     

Effect of the ceramic grain size and concentration on?the?dynamical mechanical and dielectric behavior of?poly(vinilidene fluoride) Pb(Zr0.53Ti0.47)O3 composites

In this work, poly(vinilidene fluoride)/Pb(Zr_0.53Ti_0.47)O₃([PVDF]_1−x /[PZT] _x ) composites of volumetric fractions x and (0–3) type connectivity were prepared in the form of thin films. PZT powder of crystallite size of 0.84, 1.68, and 2.35 μm in different amounts of PZT (10, 20, 30, and 40%) was mixed with the polymeric matrix. The crystalline phase of the polymeric matrix was the nonpolar α-phase and the polar β-phase. Dielectric and dynamic mechanical (DMA) measurements were performed to these composites in order to evaluate the influence of particle size and the amount of PZT filler with respect to the PVDF matrix. The inclusion of ceramic particles in the PVDF polymer matrix increases the complex dielectric constant and dynamical mechanical response of the composites. A similar behavior is observed for the α- or β-phase of the polymeric matrix indicating that the PVDF polymer matrix is not particularly relevant for the composite behavior. On the other hand, ceramic size and especially content play the major role in the increase of the dielectric response and the room temperature storage modulus. In particular, the storage modulus increases with increasing PZT concentration, but this increase is more pronounced, in terms of maximum value, for the sample with 2.35 μm particle size; DMA reveals two main relaxations in the analyzed samples. A low-temperature process maximum at ca. −40°C, usually labeled by β or α _a associated to the T _g of the polymer and the α-relaxation at temperatures above 30°C. The β-relaxation is also observed in the dielectric measurements. The models used to asses the dielectric behavior of the samples with increasing PZT concentration indicate that the particle–matrix interaction plays a relevant role, as well as the particle asymmetry and relative orientation, being the Yamada model the most appropriate to describe the composite behavior. An erratum to this article can be found at     

Synthesis and characterization of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>–Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> magnetoelectric composites with dielectric and magnetic properties

Composite structures consisting of (001)-oriented SrTiO₃ (STO)/La_0.7Sr_0.3MnO₃ (LSMO) films of 30 nm thickness, grown on an (001) Pb(Mg_1/3Nb_2/3)TiO₃– 28 mol.% PbTiO₃ piezoelectric relaxor-ferroelectric single-crystalline wafer were investigated by means of Wide-Angle X-ray Diffraction (WAXRD) in situ under influence of a d.c. electric field with strength E up to ±18 kV/cm. The WAXRD measurements of the films and substrate reflection profiles resulted in a determination of the strain s in the films and the substrate separately. The strained state of the STO/LSMO films is effectively controlled by a huge converse piezoelectric effect of the PMN-PT substrate. The coefficients of coupling between electric-field-induced out-of-plane strain in the films and in the substrate for the composite system STO/LSMO/PMN-PT are obtained.     

Rapid and efficient synthesis of colloidal gold nanoparticles by?arc discharge method

The microstructural (XRD and SEM) and dielectric behavior of Pb(Zr_0.54Ti_0.46)O₃ (PZT 54/46) ceramic system with donor (La, Nb and La+Nb) doping was studied. For all Nb-doped PZT samples, only one (tetragonal) phase was found, which confirms the compositional shifts near the morphotropic phase boundary. For La- and La+Nb-doped samples, there are two (rhombohedral and tetragonal) phases. Dielectric characteristic behavior (1/ε) for La- and La+Nb-doped PZT was associated with two-phase transitions: Ferro–Ferro at low temperature and Ferro–Para at Curie temperature. For Nb-doped samples, only one phase transition is observed, which indicates the presence of a single ferroelectric phase.     

Effect of laser melting on plasma-sprayed aluminum oxide coatings reinforced with carbon nanotubes

The effect of laser melting on the microstructure and mechanical properties of plasma-sprayed aluminum oxide composite coating reinforced with 4 wt% multi-walled carbon nanotubes (CNTs) is reported. Laser-melted layer consists of dense, coarse columnar microstructure which is significantly different from plasma-sprayed coating that consists of splats and porosity. CNTs retained their original cylindrical graphitic structure after undergoing laser irradiation. Three dimensional heat flow model has been developed to estimate temperature variation in the laser-melted composite layer. Laser-melted layers show an increase in the microhardness at the expanse of degradation of fracture toughness. Nanoindentation study indicates an increase in the elastic modulus and yield strength of the laser-melted layer which is attributed to dense microstructure with absence of weak-bonding splats and porosity.     

Probing spin-orbit quenching in Cl (2P) + H2 via crossed molecular beam scattering

In our previous work we investigated electronically non-adiabatic effects in using crossed molecular beam scattering coupled with velocity mapped ion imaging. The prior experiments placed limits on the cross-section for electronically non-adiabatic spin-orbit excitation and electronically non-adiabatic spin-orbit quenching . In the present work, we investigate electronically non-adiabatic spin-orbit quenching for which is the required first step for the reaction of Cl^* to produce ground state HCl+H products. In these experiments we collide Cl (²P) with H₂ at a series of fixed collision energies using a crossed molecular beam machine with velocity mapped ion imaging detection. Through an analysis of our ion images, we determine the fraction of electronically adiabatic scattering in Cl^* +H₂, which allows us to place limits on the cross-section for electronically non-adiabatic scattering or quenching. We determine the following quenching cross-sections σ _quench(2.1 kcal/mol) = 26 ± 21 ?², σ _quench(4.0 kcal/mol) = 21 ± 49 ?², and σ _quench(5.6 kcal/mol) = 14 ± 41 ?².