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81.
Anomalous behavior of the resistivity at or just below the Néel temperature in antiferromagnetic metals is usually attributed to the formation of superzone gaps. However, we find that RMn12-xFex alloys which have no such gaps exhibit a similarly anomalous resistivity. We show that electron scattering by substitutional spin disorder can account for such behavior of itinerant magnets. This mechanism, which has not been studied before, leads to a relaxation rate that is proportional to x(12-x)m(2), where m is the staggered magnetization. Together with spin fluctuations, phonon, and impurity scattering, it accounts well for the resistivity data we obtain for HoMn12-xFex, for 0< or =x< or =9, in the temperature range of 4 to 400 K. 相似文献
82.
Armando Herize José R. Mora Jesus Lezama Edgar Marquez Tania Córdova Gabriel Chuchani 《Journal of Physical Organic Chemistry》2009,22(2):170-176
The elimination kinetic of methyl carbazate in the gas phase was determined in a static system over the temperature range of 340–390 °C and pressure range of 47–118 Torr. The reaction is homogeneous, unimolecular, and obeys a first order rate law. The decomposition products are methyl amine, nitrous acid, and CO gas. The variation of the rate coefficients with temperatures is given by the Arrhenius expression: log k1 (s?1) = (11.56 ± 0.34) ? (180.7 ± 4.1) kJ mol?1(2.303 RT)?1. The estimated kinetics and thermodynamics parameters are in good agreement to the experimental values using B3LYP/6‐31G (d,p), and MP2/6‐31G (d,p) levels of theory. These calculations imply a molecular mechanism involving a concerted non‐synchronous quasi three‐membered ring cyclic transition state to give an unstable intermediate, 1,2‐oxaziridin‐3‐one. Bond order analysis and natural charges implies that polarization of O (alkyl)? C (alkyl) bond of the ester is rate determining in this reaction. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
83.
Human serum albumin consists of a single polypeptide of 585 amino acid residues with 1 Trp residue. In the present work, we
measured fluorescence lifetimes of the protein in both native and denatured states. The results indicate that Trp emission
occurs with three lifetimes in both states. Lifetimes values and contribution to the global emission decay differ between
the two states. Data are interpreted as the results of an emission occurring from three substructures of the tryptophan formed
in the excited state. Two of these substructures are already present for the tryptophan free in solution. The third lifetime
is the result of the interaction between the tryptophan residue and surrounding microenvironment. The populations of these
substructures characterized by the pre-exponential parameters of the fluorescence lifetimes are dependent on the fluorophore
microenvironment and on the global protein structure. 相似文献
84.
85.
This work investigates different hemp surface modifications (mercerization, maleated polyethylene (MAPE) addition in solution or in melt blending) to improve the properties of linear medium density polyethylene (LMDPE). From the composites produced, a complete morphological and tensile characterization was performed for a fixed hemp content (30% wt.). The morphological analysis showed that both the direct (melt blending) and solution modifications were able to significantly improve the composites interface quality and therefore the tensile properties (151% increase in modulus and 36% increase in strength over the neat matrix) within the range of conditions tested. 相似文献
86.
87.
88.
89.
Santos Regis C. Maia José R. da S. Abras Anuar Filgueiras Carlos A. L. 《Hyperfine Interactions》2002,142(3-4):495-501
Several novel tin(IV) adducts of amidines, [SnClPh3L], [SnCl2Ph2L] and [SnBr4L] {L=N,N-diphenylacetamidine (Hdpac) or N,N-diphenylbenzamidine (Hdpba)}, were prepared and investigated by Mössbauer spectroscopy which was an important tool for the elucidation of bonding and structural features. The resulting Mössbauer data also led to the conclusion that the tin(IV) centre for the adduct [SnClPh3L] is pentacoordinated in a trigonal bipyramidal arrangement and hexacoordinated for [SnCl2Ph2L] and [SnBr4L] in a geometric patterns of an octahedral. The amidines act as monodentate ligands to the metal centre for the former and bidentate for the latter. 相似文献
90.
José Maria Esbrí Anna Bernaus Marta ávila David Kocman Eva M. García‐Noguero Beatriz Guerrero Xavier Gaona Rodrigo álvarez Gustavo Perez‐Gonzalez Manuel Valiente Pablo Higueras Milena Horvat Jorge Loredo 《Journal of synchrotron radiation》2010,17(2):179-186
The mobility, bioavailability and toxicity of mercury in the environment strongly depend on the chemical species in which it is present in soil, sediments, water or air. In mining districts, differences in mobility and bioavailability of mercury mainly arise from the different type of mineralization and ore processing. In this work, synchrotron‐based X‐ray absorption near‐edge spectroscopy (XANES) has been taken advantage of to study the speciation of mercury in geological samples from three of the largest European mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). XANES has been complemented with a single extraction protocol for the determination of Hg mobility. Ore, calcines, dump material, soil, sediment and suspended particles from the three sites have been considered in the study. In the three sites, rather insoluble sulfide compounds (cinnabar and metacinnabar) were found to predominate. Minor amounts of more soluble mercury compounds (chlorides and sulfates) were also identified in some samples. Single extraction procedures have put forward a strong dependence of the mobility with the concentration of chlorides and sulfates. Differences in efficiency of roasting furnaces from the three sites have been found. 相似文献