Electron Spin Resonance (ESR) measurements of the polydiacetylene 4BCMU in the solid-state indicate the presence of a thermally activated paramagnetic center with g ≈ 2.002 and first-derivative peak-to-peak linewidth of ≈ 17G. An abrupt and irreversible decrease in ESR signal intensity is observed at ca. 400 K, and appears to be associated with the solid-state planar-nonplanar conformational transformation manifested by an irreversible color change from metallic brown to red. 相似文献
We consider the different characterizations of harmonic and subharmonic functions in terms of their mean values in balls and
on spheres. In particular, we prove a converse of an inequality of Beardon’s for subharmonic functions, and extend Rao’s integral
inequalities of Harnack type between these two means in general domains. 相似文献
AbstractThis article presents an overview of optical methodologies to aid the diagnosis and differentiation of thyroid and parathyroid tissues. In particular, we review the several techniques and associated methodologies that allow in vivo and ex vivo optical characterization of thyroid and parathyroid tissues. Emphasis is placed on the research potential of these techniques and whether intrinsic characteristics can provide useful contrast for the diagnosis of human thyroid and parathyroid malignant lesions. 相似文献
Despite the importance of a complete characterization of dendritic patterns in castings, the availability of studies on the development of tertiary dendrite arms is scarce in the literature. In the present study, the tip cooling rate, local solidification time, primary and tertiary dendrite arm spacings have been determined in Pb–Sb alloys castings directionally solidified under unsteady-state heat flow conditions. The alloys compositions experimentally examined are widely used in the as-cast condition for the manufacture of positive and negative grids of lead-acid batteries. The initial growth of tertiary dendritic arms from the secondary branches was found to occur only for a Pb–3.5 wt% Sb alloy at cooling rates in the range 0.4–0.2?K/s, with no evidence of this spacing pattern for Pb–Sb alloys having lower solute content. Tertiary dendritic branches have been observed along the entire casting lengths for alloys of the Pb–Sb hypoeutectic range having compositions higher than 4.0 wt% Sb. It is shown that a power function experimental law with a characteristic ?0.55 exponent is able to characterize the tertiary spacing evolution with the solidification cooling rate for alloys compositions ≥4.0 wt% Sb. The only exception was the Pb–3.5 wt% Sb alloy for which λ3 exhibited significant lower values when compared with the experimental values obtained for the other Pb–Sb alloys for a same solidification cooling rate. 相似文献
MnNi and MnPt become antiferromagnetic (AFM) when annealed at high enough temperatures, for which a face-centered cubic (fcc) to face-centered tetragonal (fct) structural transition occurs. Thus, structural information is essential when optimizing exchange bias in these materials. We performed structural (X-ray diffraction), magnetic (Magneto-Optical Kerr effect) and magneto-transport (magnetoresistance) measurements on MnNi based spin valves subjected to different annealing procedures and MnPt/CoFe bilayers with different MnPt thicknesses. We show that high annealing temperatures can in fact lead to the fct antiferromagnetic phase in both materials, but the annealing procedure is also an important factor on the obtained exchange field values. Also, MnPt/CoFe bilayers allowed us to probe the influence of average AFM-grain size on exchange bias. 相似文献
The use of agricultural wastes for energy conversion has been widely studied as renewable and carbon neutral energy sources. This paper aims to evaluate the energetic potential of six agricultural wastes—sugarcane bagasse, bean pods, corn stover, pineapple crown leaves, white cotton and natural coloured cotton stalks, through their characterization and pyrolysis kinetic study. The energetic potential of biomasses was evaluated by ultimate and proximate analysis, higher heating value (HHV), apparent density, and kinetic parameters of conversion and apparent activation energy (Ea) determined by Model-Free kinetics though thermogravimetric analysis data. The results indicate energetic density for dry basis biomasses, such as moisture content less than 7%, volatiles higher than 77% and moderate ash content. The HHVs were higher for the biomass with low O:C ratio. The Ea values increased with increasing O:C ratio and were also influenced by the biomass ash content. Among the studied biomasses, PCL are less explored for energy application, although the results confirm its potential for application in thermochemical processes such as pyrolysis or combustion.
The Perlin effect and its analog for fluorinated compounds (the fluorine Perlin-like effect) manifest on one-bond C─H (C─F for the fluorine Perlin-like effect) spin–spin coupling constants (SSCCs) in six-membered rings. These effects can be useful to probe the stereochemistry (axial or equatorial) of the C─H and C─F bonds, respectively. The origin of these effects has been debatable in the literature as being due to hyperconjugative interactions, dipolar effects, and induced current density. Accordingly, a variety of model compounds has been used to probe such effects since the cyclohexanone carbonyl group and the endocyclic heteroatom lone pairs play different roles on the above-mentioned effects. Thus, the 1JC─F SSCC in fluorinated lactams and lactones were theoretically studied to gain further insight on the nature of the fluorine Perlin-like effect. In addition, because the intramolecular α-effect has recently gained attention for its importance in the reactivity and stereoelectronic interactions in peroxide compounds, some fluorinated 1,2-dioxanes and 1,2-dithianes were studied to evaluate the role of the α-effect on the behavior of 1JC─F SSCCs. Differently from fluorinated ketones and ethers, the fluorine Perlin-like effect in the amides and esters cannot be explained by hyperconjugative or dipolar interactions alone, because the resonance in these groups affect the 1JC─F values. The O─O and S─S-containing systems exhibit a strong fluorine Perlin-like effect, but unlike the α-effect, this behavior cannot be explained neither by hyperconjugation nor by dipolar interactions alone; the spatial proximity of the C─F and O─O/S─S bonds is proposed to affect the magnitude of the 1JC─F SSCC. 相似文献