Search results for "Phase"
showing 10 items of 6344 documents
Improving the solid-phase extraction of “quat” pesticides from water samples
1998
A novel strategy, based on the addition of a cationic surfactant, for preventing the interferences associated with a diminution in the efficacy of solid-phase extraction (SPE) with silica cartridges of diquat, paraquat and difenzoquat in water is developed. Conditions for extraction are optimised with respect to pH, cationic surfactant and its concentration. Humic acids, anionic surfactants, inorganic salts and other organic contaminants like pesticides, phenols, polycyclic aromatic hydrocarbons and polychlorinated biphenyls produce the studied interferences. The best performance is shown in the improvement of the "quats" recovery from waters with high levels of humic acids and anionic surf…
Polarization Switching in Heterophase Nanostructures: PLZT Relaxor Ceramics
2005
The polarization switching is experimentally investigated in hot-pressed PLZT-x/65/35 ceramics with a lanthanum content from 5 to 12 at. %. The specific features in the temperature dependence of the polarization switching in a heterophase state are interpreted by analyzing the change in the switched charge measured over wide ranges of fields and temperatures. Particular emphasis is placed on the role of depolarization fields induced by interphase boundaries. A model of the evolution of polydomain nanostructures with a change in the temperature and in the response to an external field is considered. It is assumed that the low-temperature dielectric anomaly and the temperature hysteresis are …
The Induction Phase as a Critical Transition for Newly Qualified Teachers
2012
This chapter addresses the issue of becoming a teacher, with the induction phase as a critical transition from initial teacher education to the lifelong professional learning of teachers, and mentoring as a tool of support. It presents newly qualified teachers’ views on initial teacher education and discusses the need for fostering the connection between teacher training and the induction year. New teachers’ views on teacher induction and mentoring are based on research findings in Finland and other Nordic countries. Another important question addresses how initial teacher education can facilitate the metamorphosis of a student teacher into an autonomous teacher. The new teachers’ experienc…
Oxidative halogenation of substituted pyrroles with Cu(II). PartIII. Bromination and chlorination of 2-benzoylpyrrole
1992
The bromination of 2-benzoylpyrrole with copper(II) bromide in the homogeneous and the heterogeneous phase is described, giving 4- and 5-monobromo derivatives whose ratio decreases as the temperature is increased. The same reaction with copper(II) chloride in acetonitrile at 60° produces 5-chloro-2-benzoylpyrrole as the major product. 4,5-Dihalopyrroles in good yields are obtained with an excess of halogenating agent.
Notice of Removal: Stochastic generation of the phononic band structure of lossy and infinite crystals
2017
The concept of the band structure is central to the field of phononic crystals. Indeed, capturing the dispersion of Bloch waves — the eigenmodes of propagation in periodic media — gives invaluable information on allowed propagation modes, their phase and group velocities, local resonances, and band gaps. Band structures are usually obtained by solving an eigenvalue problem defined on a closed and bounded domain, which results in a discrete spectrum. There are at least two cases, however, that cannot be reduced to a simple eigenvalue problem: first, when materials showing dispersive loss are present and second, when the unit-cell extends beyond any bound, as in the case of phononic crystal o…
The influence of topological phase transition on the superfluid density of overdoped copper oxides
2017
We show that a topological quantum phase transition, generating flat bands and altering Fermi surface topology, is a primary reason for the exotic behavior of the overdoped high-temperature superconductors represented by $\rm La_{2-x}Sr_xCuO_4$, whose superconductivity features differ from what is described by the classical Bardeen-Cooper-Schrieffer theory [J.I. Bo\^zovi\'c, X. He, J. Wu, and A. T. Bollinger, Nature 536, 309 (2016)]. We demonstrate that 1) at temperature $T=0$, the superfluid density $n_s$ turns out to be considerably smaller than the total electron density; 2) the critical temperature $T_c$ is controlled by $n_s$ rather than by doping, and is a linear function of the $n_s$…
On the blue phase structure of hydrogen-bonded liquid crystals via 19F NMR
2018
Abstract 19 F NMR spectra are simulated for blue phase I of FPHG( St 1.5 ∗ Ap 1.5 ) based on a model of a double-twisted substructure inside cylinders that form a body-centred cubic lattice. A kinetic matrix is included to describe jump processes over quarter pitch lengths. Though the lines in the NMR spectra are broad and featureless, changes in the widths and positions with temperature are well described by the blue phase model structure. The spectra in the chiral nematic N∗ phase are also simulated. Dynamics in the BP I are found to be slower than in the N∗ phase.
Bose-Einstein Condensation in an electro-pneumatically transformed quadrupole-Ioffe magnetic trap
2014
We report a novel approach for preparing a Bose-Einstein condensate (BEC) of $^{87}$Rb atoms using electro-pneumatically driven transfer of atoms into a Quadrupole-Ioffe magnetic trap (QUIC Trap). More than 5$\times$$10^{8}$ atoms from a Magneto-optical trap are loaded into a spherical quadrupole trap and then these atoms are transferred into an Ioffe trap by moving the Ioffe coil towards the center of the quadrupole coil, thereby, changing the distance between quadrupole trap center and the Ioffe coil. The transfer efficiency is more than 80 \%. This approach is different from a conventional approach of loading the atoms into a QUIC trap wherein the spherical quadrupole trap is transformed…
Role of image charges in ionic liquid confined between metallic interfaces.
2020
The peculiar properties of ionic liquids in confinement have not only become essential for energy storage, catalysis and tribology, but still pose fundamental questions. Recently, an anomalous liquid-solid phase transition has been observed in atomic force microscopy experiments for 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), the transition being more pronounced for metallic surfaces. Image charges have been suggested as the key element driving the anomalous freezing. Using atomistic molecular dynamics simulations, we investigate the impact of image charges on structure, dynamics and thermodynamics of [BMIM][BF4] confined between gold electrodes. Our results not only unveil…
Metrological performances of voltage and current instrument transformers in harmonics measurements
2018
In the new electrical system scenario, the increasing presence of non-linear loads and renewable energy sources makes the measurement of harmonics an essential task. The accuracy of harmonic measurement firstly depends on the used instrument transformers for voltage and current sensing. Since the behavior of instrument transformers in non-sinusoidal conditions is not always well defined, this paper presents an experimental study on the metrological performances of current and voltage instrument transformers (CTs and VTs) in the presence of harmonics. Proper tests procedures are defined and measurement setups are developed for both CTs and VTs calibration. The analysis is carried out by usin…