FeCo基纳米晶合金高温交换耦合作用机理

研究了500和600℃真空退火后的纳米晶Fe_38.4Co₄₀Si₉B₉Nb_2.6Cu合金初始磁导率随温度的变化规律,发现较高温度(600℃)退火的FeCo基纳米晶合金,在非晶相居里温度以上较宽温度范围内磁导率没有明显的衰减,这是在双相纳米晶合金中观察到的一种新现象,其磁特性不同于Fe基纳米晶合金.为了探明这种现象的起源,估算了与剩余非晶相同成分的非晶合金的居里温度及纳米晶粒间发生交换耦合作用的参数 关键词： 交换耦合作用 非晶相居里温度 交换耦合穿透深度     

Polygonal invariant curves for a planar piecewise isometry

We investigate a remarkable new planar piecewise isometry whose generating map is a permutation of four cones. For this system we prove the coexistence of an infinite number of periodic components and an uncountable number of transitive components. The union of all periodic components is an invariant pentagon with unequal sides. Transitive components are invariant curves on which the dynamics are conjugate to a transitive interval exchange. The restriction of the map to the invariant pentagonal region is the first known piecewise isometric system for which there exist an infinite number of periodic components but the only aperiodic points are on the boundary of the region. The proofs are based on exact calculations in a rational cyclotomic field. We use the system to shed some light on a conjecture that PWIs can possess transitive invariant curves that are not smooth.

     

Fluidized beds in flow analysis: use with ion-exchange separation for spectrophotometric determination of zinc in plant digests

A novel strategy for utilization of solid reagents in flow analysis is proposed. Establishment of diffuse and reproducible geometry enables the solid particles to be maintained in constant floating, reflux, and circulating motion inside a mini-chamber. This is efficiently accomplished with pulsed flows, a characteristic of multi-pumping flow systems. Drawbacks inherent in solid-phase packed columns, for example backpressure, preferential pathways, swelling, etc., and some limitations inherent in immobilized reagents are minimised. Spectrophotometric determination of zinc in plants was selected as an application of the technique. Dowex 1-X8 anionic resin was kept freely inside a mini-chamber. Zinc chloro-complexes were adsorbed on the moving particles and derivatization with zincon was performed after elution. Analytical figures of merit and the potential and limitations of the approach are discussed.     

Preparation, preservation and application of pure isotope-enriched phenyltin species

A method combining liquid/liquid extraction and chromatographic fractionation has been developed for the preparation of pure monophenyltin (MPhT), diphenyltin (DPhT), and triphenyltin (TPhT), synthesized from isotope-enriched Sn metal using phenylation of SnI₄ in diethylether (DEE) followed by quenching with HBr and water. After two successive extractions of the aqueous HBr phase with DEE, >99% of both DPhT and TPhT was recovered in the combined DEE phase and 94% of the MPhT remained in the aqueous phase. The MPhT in the aqueous phase was extracted into dichloromethane. The organic phases were vaporized and the PhTs were redissolved in MeOH/water/acetic acid/sodium acetate (59/30/6/8, v/v/v/w), which was also used as storing solution. Aliquots of the two solutions containing either DPhT and TPhT or MPhT were injected into a silica-based C₁₈ column for isolating and purifying single species. The yields of pure MPhT, DPhT, and TPhT, each synthesized from isotope-enriched ¹¹⁸Sn metal, ¹²²Sn metal, and ¹²⁴Sn metal, were better than 99%. After chromatographic separation, the single phenyltin compounds were mixed to prepare a spike for multiple-isotope species-specific isotope dilution (MI-SSID). MI-SSID was successfully used to determine phenyltin compounds in the certified reference material, mussel tissue BCR CRM-477. At −20 °C, all of the fractionated phenyltin species were stable in the storage solution for at least 197 days. When these standards were stored at 4 °C or 22 °C, 4–6% of the DPhT and TPhT degraded within 27 days. The degradation of DPhT and TPhT increased with the ionic strength and acidity of the storage solution.      

Establishing a chromium-reactor design for measuring δ2H values of solid polyhalogenated compounds using direct elemental analysis and stable isotope ratio mass spectrometry

²H/¹H isotope ratios of polyhalogenated compounds were determined by elemental analysis and isotope ratio mass spectrometry (EA-IRMS). Initial measurements with standard EA-IRMS equipment, which used high-temperature pyrolysis to convert the organic compounds into hydrogen, did not achieve significant signals for polychlorinated pesticides and related compounds, presumably due to the formation of HCl instead of hydrogen. To reverse this problematic reaction, a chromium reactor was incorporated into the element analyzer system, which scavenged Cl, forming chromium chloride and releasing hydrogen again in the form of H₂. The optimized system therefore allowed the δ²H values of polyhalogenated compounds to be determined. A quality assurance program was developed based on several parameters. (i) Each compound was analyzed using a sequence of five injections, where the first measurement was discarded. (ii) Recovery of H (when calculated relative to acetanilide) had to be >90% for all replicates in a sequence. (iii) All δ-values within a sequence had to vary by less than 10‰. (iv) Results had to be reproducible on another day with a different sample scheme. Once this reproducibility had been established, variabilities in the δ²H values of organohalogen standards were investigated using the technique. The highest δ²H value of +75‰ was found for o,p′-DDD, whereas the strongest depletion in deuterium was found for Melipax (–181‰). The most important results for comparable compounds were as follows. DDT-related compounds gave δ²H values of between +59 and +75‰ (technical DDT, o,p′- and p,p′-DDD) or in the range of approximately −1‰, indicative of the different sources/methods of producing this compound. Four HCH isomers from the same supplier showed relatively similar hydrogen isotope distributions, whereas two lindane (γ–HCH) standards from other sources had 39‰ less deuterium. This difference is likely due to different purification steps during the isolation of pure lindane from the technical HCH mixture. An even greater difference was observed between the δ²H values of Toxaphene (US product dating from 1978) and Melipax (product from the former East Germany, dating from 1979), which gave δ²H values of –101‰ and –181‰, respectively, meaning that both products were easily distinguished via δ²H-IRMS. Fractioning of hydrogen isotopes in the atmospheric water cycle was suggested as one reason for the different values. In this theory, the water (which had different δ²H values depending on where it was taken from) was incorporated during the biosynthesis of camphene, which is the natural product used to produce both products. These results indicate that hydrogen isotope-specific analysis can be a valuable tool for tracing the origins of a compound in certain cases.     

C and N stable isotope variation in urine and milk of cattle depending on the diet

The stable carbon and nitrogen isotopic composition of urine and milk samples from cattle under different feeding regimes were analysed over a period of six months. The isotope ratios were measured with isotope ratio mass spectrometry (IRMS). The δ ¹³C values of milk and urine were dependent on different feeding regimes based on C₃ or C₄ plants. The δ ¹³C values are more negative under grass feeding than under maize feeding. The δ ¹³C values of milk are more negative compared to urine and independent of the feeding regime. Under grass feeding the analysed milk and urine samples are enriched in ¹³C relative to the feed, whereas under maize feeding the ¹³C/¹²C ratio of urine is in the same range and milk is depleted in ¹³C relative to the diet. The difference between the ¹⁵N/¹⁴N ratios for the two feeding regimes is less pronounced than the ¹³C/¹²C ratios. The δ ¹⁵N values in urine require more time to reach the new equilibrium, whereas the milk samples show no significant differences between the two feeding regimes.     

Rigorous spectral representation of relativistic random phase approximation for finite nuclei

By using the rigorous spectral representation of relativistic random phase approximation, the low-lying excitation of finite nuclei and its longitudinal response function for quasielastic electron scattering are calculated in the σ-ω model of quantum hadrodynamics. It is shown that the reproduction of the correct order of the 1- and 3- excitation states of 16O is due to the contribution of the exchange vertex. There is no significant influence of the retardation effect on the low-lying excitation states. In contrast, the retardation effect plays an important role in the electron scattering process of nuclei. The theoretical longitudinal responses of 12C and 40Ca, including the contributions of the exchange vertex and the retardation effect, are suppressed and reproduce the experimental data better than the results excluding them.     

Spin-dependent proximity effects in ferromagnetic semiconductor/superconductor structures

Proximity effects in normal metal/insulator/ferromagnetic semiconductor/superconductor (NM/I/FS/SC) and NM/I/SC/FS junctions are studied based on an extended Blonder-Tinkham-Klapwijk (BTK) theory. It is found that the magnitude of the proximity effects depends to a great extent on the mismatches of the effective mass and band between the FS and SC. For NM/I/FS/SC junction, the transition of the tunneling conductance from “0” to “π” state is determined by the mass, magnetic exchange energy in FS and the thickness of FS. For NM/I/SC/FS junctions, the conductance spectrum is spin-dependent, indicating a local coexistence of weak ferromagnetism and s-wave superconductivity.     

Magnetooptical activity of spinel type crystals with complex mixed-valence lattice irregularities

In this Letter we analyze the peculiarities of the Faraday rotation in the imperfect spinel type crystals for which the lattice irregularities are represented by the mixed valence clusters of transition metal ions. A such kind of complex system with the electronic configuration (for example, Mn2+Mn2+Mn3+) is considered in detail. The model takes into account the cubic and low symmetry crystal fields acting on the metal ions, migration of the “extra” hole as well as the orientational degeneracy (hidden optical anisotropy). The electric dipole transitions in these types of clusters with migrating hole coupled to the spin core through the double exchange mechanism are shown to lead to a significant magnetooptical activity in the visible range of spectrum. The intensity of these transitions can be comparable or higher than those for the magnetic dipole ones in the same range of frequencies. The electric dipole mechanism of the magnetooptical effects manifests itself in a highly anisotropic character of the spectra.     

A new formulation of Kapila’s five-equation model for compressible two-fluid flow,and its numerical treatment

A new formulation of Kapila’s five-equation model for inviscid, non-heat-conducting, compressible two-fluid flow is derived, together with an appropriate numerical method. The new formulation uses flow equations based on conservation laws and exchange laws only. The two fluids exchange momentum and energy, for which exchange terms are derived from physical laws. All equations are written as a single system of equations in integral form. No equation is used to describe the topology of the two-fluid flow. Relations for the Riemann invariants of the governing equations are derived, and used in the construction of an Osher-type approximate Riemann solver. A consistent finite-volume discretization of the exchange terms is proposed. The exchange terms have distinct contributions in the cell interior and at the cell faces. For the exchange-term evaluation at the cell faces, the same Riemann solver as used for the flux evaluation is exploited. Numerical results are presented for two-fluid shock-tube and shock-bubble-interaction problems, the former also for a two-fluid mixture case. All results show good resemblance with reference results.