Monte‐Carlo simulations predict that a local correlated disorder is responsible for many of the novel transport and magnetic properties of colossal magnetoresistance (CMR) materials such as manganites. One important prediction of these models is that the resistivity at the metal–insulator transition (MIT) in manganites depends strongly on the correlated quenched disorder. However, experimental confirmation has been challenging since it is difficult to control the amount of disorder in these compounds. We carried out experiments on Sm0.55Sr0.45MnO3, a prototypical CMR manganite with a sharp MIT, whereby the oxygen‐related disorder is systematically enhanced by low temperature thermal activation. We observe dramatic changes in the temperature dependence of resistivity at the MIT as the amount of quenched disorder is increased, occurring in a manner that is in agreement with theoretical predictions.
The acceleration of high-energy ion beams following the interaction of short (t < 1 ps) and intense (Iλ2 > 1018 W cm-2 μm2) laser pulses with solid targets is a field of research currently attracting high interest in the scientific community, due
to some of the unique properties of these ion sources, promising routes toward the optimization of their energy content, and
a number of possible, innovative applications in the scientific, technological and medical areas. Work on the characterization
and development of these sources has progressed enormously over the past few years, thanks to the contribution of many groups
worldwide. This paper will report some recent results, obtained in experiments carried out at the RAL and LULI laboratories,
in which we investigated the ion acceleration mechanism, developed a technique to control the ion beam divergence and energy
spectrum, and applied a proton radiography technique to investigate electric and magnetic field production following laser-matter
interaction. 相似文献
The ultra-high fields of high-power short-pulse lasers are expected to contribute to understanding fundamental properties of the quantum vacuum and quantum theory in very strong fields. For example, the neutral QED vacuum breaks down at the Schwinger field strength of 1.3×1018 V/m, where a virtual e+e- pair gains its rest mass energy over a Compton wavelength and materializes as a real pair. At such an ultra-high field strength, an electron experiences an acceleration of aS=2×1028g and hence fundamental phenomena such as the long predicted Unruh effect start to play a role. The Unruh effect implies that the accelerated electron experiences the vacuum as a thermal bath with the Unruh temperature. In its accelerated frame the electron scatters photons off the thermal bath, corresponding to the emission of an entangled pair of photons in the laboratory frame. While it remains an experimental challenge to reach the critical Schwinger field strength within the immediate future even in view of the enormous thrust in high-power laser developments in recent years, the near-future laser technology may allow to probe the signatures of the Unruh effect mentioned above. Using a laser-accelerated electron beam (γ~300) and a counter-propagating laser beam acting as optical undulator should allow to create entangled Unruh photon pairs (i.e., signatures of the Unruh effect) with energies of the order of several hundred keV. An even substantially improved experimental scenario can be realized by using a brilliant 20 keV photon beam as X-ray undulator together with a low-energy (γ≈2) electron beam. In this case the separation of the Unruh photon pairs from background originating from linearly accelerated electrons (classical Larmor radiation) is significantly improved. Detection of the Unruh photons may be envisaged by Compton polarimetry in a 2D-segmented position-sensitive germanium detector. 相似文献
An atomic-scale picture of the strain-mediated magnetoelectric (ME) coupling is delineated by carefully examining the effect of an applied electric field on the extended X-ray absorption fine structure (EXAFS) spectra of a CoFe2O4-dispersed Pb(Zr,Ti)O3 matrix (CFO-PZT) composite. These studies demonstrated a tensile-compressive strain relation between the PZT matrix and the dispersed CFO phase, thereby providing an X-ray spectroscopic evidence of the interfacial strain-mediated ME coupling. Both the dielectric anomaly observed at ∼480 °C and the decrease in the remanent magnetization under an applied electric field support the strain-mediated ME coupling in the CFO-PZT composite. 相似文献
(Ca1−x,Eux)MgSi2yO6+δ blue phosphor was prepared by spray pyrolysis and the photoluminescence properties were optimized by controlling concentration of Si element and the activator content. At y=1.0, the concentration quenching in the luminescent intensity appeared when the Eu2+ content (x) was 0.01 (1 at%). Such quenching concentration was changed with the concentration of silicon (y), which was increased with an increase in the quantity of excess Si (y>1.0). The highest luminescent intensity was achieved when the Eu2+ content (x) and the Si concentration (y) were 0.04 and 1.3, respectively. According to X-ray diffraction (XRD) analysis, the tetragonal SiO2 phase was formed as a minor phase when the y value was larger than 1.3. The formation of SiO2 phase, however, did not reduce but increased the luminescent intensity when the Eu2+ content was optimized again. As a result, the luminescent intensity of the phosphor particles optimized in the content of both Si and Eu2+ was about 150% improved compared with that of the CaMgSi2O6:Eu sample (x=0.01, y=1.0). 相似文献
SrTi1?xFexO3?δ (STF) model cathodes, with compositions of x = 0.05 to 0.80 were deposited onto single crystal yttria stabilized zirconia by pulsed layer deposition as dense films with well defined area and thickness and studied by electrochemical impedance spectroscopy as a function of electrode geometry, temperature and pO2. The STF cathode was observed to exhibit typical mixed ionic-electronic behavior with the electrode reaction occurring over the full electrode surface area rather than being limited to the triple phase boundary. The electrode impedance was observed to be independent of electrode thickness and to the introduction of CGO interlayers and inversely proportional to the square of the electrode diameter, pointing to surface exchange limited kinetics. Values for the surface exchange coefficient, k, were calculated and found to be comparable in magnitude to those exhibited by other popular mixed ionic-electronic conductors such as (La,Sr)(Co,Fe)O3, thereby, confirming the suitability of STF as a model mixed conducting cathode material. The surface exchange coefficient, k, was also found to be insensitive to orders of magnitude change in both bulk electronic and ionic conductivities. 相似文献
A sequential separation procedure has been developed for the determination of transuranic elements and fission products in
uranium metal ingot samples from an electrolytic reduction process for a metallization of uranium dioxide to uranium metal
in a medium of LiCl-Li2O molten salt at 650 °C. Pu, Np and U were separated using anion-exchange and tri-n-butylphosphate (TBP) extraction chromatography.
Cs, Sr, Ba, Ce, Pr, Nd, Sm, Eu, Gd, Zr and Mo were separated in several groups from Am and Cm using TBP and di(2-ethylhexyl)phosphoric
acid (HDEHP) extraction chromatography. Effect of Fe, Ni, Cr and Mg, which were corrosion products formed through the process,
on the separation of the analytes was investigated in detail. The validity of the separation procedure was evaluated by measuring
the recovery of the stable metals and 239Pu, 237Np, 241Am and 244Cm added to a synthetic uranium metal ingot dissolved solution. 相似文献
The objective of this study was to evaluate the performance of a photocatalysis/H2O2/metal membrane hybrid system in the degradation of humic acid. A metal membrane of nominal pore size 0.5 μm was used in the
experiment for separation of TiO2 particles. Hydrogen peroxide was tested as an oxidant. The efficiency of removal of CODCr and color increased rapidly for initial hydrogen peroxide concentrations up to 50 mg L−1. The efficiency of removal of CODCr and color by 50 mg L−1 initial hydrogen peroxide concentration was approximately 95 and 98%, respectively. However, addition of hydrogen peroxide
over 50 mg L−1 inhibited the efficiency of the system. Addition of hydrogen peroxide to a UV/TiO2 system enhanced efficiency of removal of CODCr and color compared with no addition of hydrogen peroxide. This may be ascribed to capture electrons ejected from TiO2 and to the production of OH radicals. Application of the metal membrane in the UV/TiO2/H2O2 system enhanced the efficiency of removal of CODCr and color because of adsorption by the metal membrane surface and the production of OH radicals. By application of a metal
membrane with a nominal pore size of 0.5 μm, TiO2 particles were effectively separated from the treated water by metal membrane rejection. The photocatalytic metal membrane
had much less resistance than the humic acid, TiO2, and humic acid/TiO2 because of the degradation of humic acid by the photocatalytic reaction. 相似文献
We describe a simple method to fabricate an array of polystyrene microbeads (PS μbeads) conjugated with an elastin-like polypeptide (ELP) on a glass surface using a removable polymer template (RPT). A thin layer of adhesive was spun-cast on glass and cured by UV radiation. Micropatterns of an RPT were then transferred onto the surface by microcontact printing. The adhesion of PS μbeads on the surface depended on the adhesion performance of the adhesive layer, which could be adjusted by irradiation time. An array of PS μbeads conjugated with ELP was used for a smart immunoassay of prostate-specific antigen (PSA), a cancer marker. By controlling the phase transition of ELP molecules, PSA molecules were selectively adhered or released from the bead surface. The selective and reversible binding of PSA molecules on the bead surface was characterized with fluorescence microscopy. 相似文献