Search results for "composites"

Preparation and x-ray pole-figure characterization of DC-sputtered Bi-2201, Bi-2212 and Bi-2223 thin films

1997

Thin films of the three members of the superconducting series , n = 1,2,3, were prepared by diode sputtering. X-ray characterization shows that all the films are single phase and c-axis oriented and in addition they are epitaxially grown. The latter is found by x-ray pole-figure measurements taken with a four-circle diffractometer. These are emphasized in this work. AC susceptibility measurements show that, while the 2201 films are not superconducting until 4 K, the transition temperatures of the 2212 films are 82 K - 90 K and of the 2223 films 84 K - 89 K.

High quality superconducting titanium nitride thin film growth using infrared pulsed laser deposition

2018

The quantum phase slip phenomenon in superconducting nanowires with a low-Ohmic environment

2012

In a number of recent experiments it has been demonstrated that in ultra-narrow superconducting channels quantum fluctuations of the order parameter, alternatively called quantum phase slips, are responsible for the finite resistance well below the critical temperature. The acceptable agreement between those experiments and the models describing quantum fluctuations in quasi-one-dimensional superconductors has been established. However the very concept of the phase slip is justified when these fluctuations are the relatively rare events, meaning that the effective resistance of the system should be much smaller than the normal state equivalent. In this paper we study the limit of the strong…

Field-induced suppression of the pi-band superconductivity and magnetic hysteresis in the microwave surface resistance of MgB_2 at temperatures near …

2009

We report on the magnetic-field-induced variations of the microwave surface resistance, R_s, in a polycrystalline MgB_2 sample, at different values of temperature. We have detected a magnetic hysteresis in R_s, which exhibits an unexpected plateau on decreasing the DC magnetic field below a certain value. In particular, at temperatures near T_c the hysteresis manifests itself only through the presence of the plateau. Although we do not quantitatively justify the anomalous shape of the magnetic hysteresis, we show that the results obtained in the reversible region of the R_s(H) curve can be quite well accounted for by supposing that, in this range of magnetic field, the pi-gap is almost supp…

Self-assembled dimers with supramolecular chirality

2003

The possibilities to form dimeric capsules with supramolecular chirality from tetraurea calix[4]arenes composed of two different phenolic urea units are discussed in general and demonstrated experimentally for various selected examples.

Hybrid approach to surface roughness evaluation in multistage machining processes

2003

Abstract An assessment of surface quality in turned, ground and honed specimens is made by means of a computer-based processing of digitised surface profiles. Three different methods of surface finish characterisation, i.e. statistical, fractal and neural network-based approaches are examined and compared. Correlations between some representative roughness parameters and the fractal dimension (D) values estimated were found. Consequently, they can be converted to their corresponding roughness parameters, i.e. Ra, Rz and RΔa. Finally, a set of parameters including the minimum surface finish data for machining of external cylindrical surfaces when using complex technological process, is propo…

First-Principles Calculations of SrZrO3 (001) Surfaces

2011

The results of calculations of surface relaxations, rumplings, and charge distribution for the SrZrO3 (001) surface using ab initio code CRYSTAL and a hybrid description of exchange and correlation are presented. Both SrO and ZrO2 terminations of the SrZrO3 (001) surface are considered. On the (001) surfaces all upper and third layer atoms relax inward, while outward relaxations of all atoms in the second layer are found with the sole exception of SrO-terminated SrZrO3 (001) surface second layer O atom. Calculated surface rumpling for the SrO-terminated SrZrO3 (001) surface 6.77% of the lattice constant is by a factor of ten larger than the surface rumpling for the ZrO2-terminated SrZrO3 (0…

AB INITIO CALCULATIONS OF SrTiO3, BaTiO3, PbTiO3, CaTiO3 AND BaZrO3 (001) AND (011) SURFACES

2009

I present results of calculations of surface relaxations and rumplings for the (001) and (011) surfaces of BaZrO3 and ATiO3 perovskites (A = Sr, Ba, Pb and Ca) using a hybrid B3PW description of exchange and correlation. The (001) surface energies of AO, TiO2 and ZrO2 terminations are found to be comparable with each other for all five materials. The surface energies for BaZrO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (011) surfaces for all terminations are considerably larger than for (001) surfaces. We predict a considerable increase in the Ti-O (Zr-O) chemical bond covalency near the (011) surface as compared both to the bulk and to the (001) surface.

Surface Anisotropy in the Expansion Behavior of Laminated Quasi-Isotropic Composites

1984

Mesure a l'aide d'un extensometre des deformations thermiques superficielles de deux materiaux stratifies resine epoxy-fibre de graphite. Les resultats dependent de la direction de mesure, l'anisotropie superficielle associee est inversement proportionnelle aux dimensions de l'echantillon et proportionnelle au rapport d'anisotropie d'une lamelle isolee. Comparaison avec la theorie des stratifications

Effective elastic properties of biocomposites using 3D computational homogenization and X-ray microcomputed tomography

2021

A 3D computational homogenization method based on X-ray microcomputed tomography (μCT) was proposed and implemented to investigate how the fiber weight fraction, orthotropy and orientation distribution affect the effective elastic properties of regenerated cellulose fiber-polylactic acid (PLA) biocomposites. Three-dimensional microstructures reconstructed by means of the X-ray μCT were used as the representative volume elements (RVEs) and incorporated into the finite element solver within the computational homogenization framework. The present method used Euclidean bipartite matching technique so as to eliminate the generation of artificial periodic boundaries and use the in-situ solution d…