动物蛋白水解酶法制备梅鱼鲜味酶解液的研究

以梅鱼为原料,采用动物蛋白水解酶,以鲜甜味游离氨基酸总量为指标,水解制备梅鱼鲜味酶解液。在单因素的基础上,采用响应面分析法得出酶解的最佳条件:温度40.7℃、pH7.68、[E]/[S]0.84%,时间4 h,制得的酶解液鲜甜味游离氨基酸总量为115.159μg/mL,海鲜味特征明显。     

软土粗颗粒含量对杂填土与软土地基互嵌沉降影响的试验分析

为实现对杂填土与软土地基互嵌过程的实时沉降分析,探究软土粗颗粒含量变化对互嵌沉降和软土固结沉降的作用,借助自主研制的杂填土与软土互嵌试验仪,通过室内试验定量区分互嵌沉降和软土固结沉降,设计正交试验组对照分析2种粒径杂填土颗粒(5、10 mm)与5种粗颗粒含量软土(0、3%、6%、9%、12%)在一定荷载下的沉降发展规律,总结总沉降、互嵌沉降、软土固结沉降的最终沉降量和瞬时沉降量的差异。试验结果表明：软土中存在粗颗粒时,总沉降和互嵌沉降在各阶段均较无粗颗粒情况下增长量更大且发展更快,在粗颗粒含量6%时总沉降和互嵌沉降有极大值,粗颗粒含量对软土固结沉降的影响并不明显。     

Crystal–quasicrystal transition depending on cooling rates in directionally solidified Al–3Mn–7Be (at.%) alloy

The transition of primary phases from the crystalline approximant phase to icosahedral quasicrystal phase (I-phase) is observed in the directional solidified Al–3Mn–7Be (at.%) alloy. The structures of I-phase and approximant phases are characterized by SEM, TEM and HRTEM. The addition of Be significantly enhances the formation ability of I-phase, combining with the directional solidification method where the growth rates and temperature gradients can be separately controlled, giving rise to a promising way to prepare quasicrystal-reinforced Al-matrix composite.     

Temperature-dependent mechanical properties of alpha-/beta-Nb5Si3 phases from first-principles calculations

The temperature-dependent structural properties and anisotropic thermal expansion coefficients of α-/β-Nb₅Si₃ phases have been determined by minimizing the non-equilibrium Gibbs free energy as functions of crystallographic deformations. The results indicate that the crystal anisotropy of α-Nb₅Si₃ phase is much more temperature dependence than that of β-Nb₅Si₃ phase. The total/partial density of states of α-/β-Nb₅Si₃ phases are discussed in detail to analyze their electronic hybridizations. It is demonstrated that the bonding of the two phases is mainly contributed from the hybridization between Nb-4d and Si-3p electronic states. The temperature-dependent mechanical properties of α-/β-Nb₅Si₃ phases are further investigated via the quasi-harmonic approximation method in coupling with continuum elasticity theory. The calculated single-crystalline and polycrystalline elasticity shows that both phases are mechanically stable and exhibit the intrinsic brittleness. The results also suggest that α-Nb₅Si₃ phase possesses a superior ability of compression resistance but an inferior ability of high-temperature resistance of mechanical properties than those of β-Nb₅Si₃ phase. The bonding features of α-/β-Nb₅Si₃ phases are discussed by means of charge density difference analysis in order to explain the difference of the temperature-dependent mechanical properties between the two phases.     

Martensitic transformation behavior of Ti–Ni–Ag alloys

Microstructures and martensitic transformation behavior of Ti–Ni–Ag alloys prepared by arc melting were investigated by means of scanning electron microscopy (SEM), electron probe micro analysis (EPMA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and thermal cycling tests under constant load. Ti–Ni–Ag alloys consisted of Ti–Ni–Ag matrices, Ti₂Ni and TiAg phases. Ti–Ni–Ag matrices contained 0.27–0.52 at.% of solute Ag atoms depending on alloy compositions. The B2–B19′ transformation occurred in Ti–50.1Ni–0.7Ag, Ti–49.2Ni–0.9Ag, Ti–49.2Ni–0.6Ag and Ti–49.0Ni–0.7Ag alloys, while the B2-R-B19′ transformation did in Ti–47.5Ni–1.3Ag and Ti–44.4Ni–1.1Ag alloys. Thermo-mechanical treatment separated the B2-R from the R–B19′ transformation clearly and improved shape recovery by increasing the critical stress for slip deformation in a Ti–50.0Ni–0.7Ag alloy.     

Phase equilibria and thermodynamic calculation of the Co–Ta binary system

Experimental investigation and thermodynamic evaluation of the Co–Ta binary phase diagram was carried out. Equilibrium compositions obtained in two-phase alloys and diffusion couples were measured by electron probe microanalyzer (EPMA). A very narrow λ₃(C36) + λ₂(C15) two-phase region is confirmed to be present around 26.5 at.% Ta at temperatures between 950 °C and 1448 °C. Equilibrium relationships above 1500 °C among the liquid, Laves (λ₁(C14), λ₂ and λ₃, whose stoichiometry is described by Co₂Ta), μ(D8_b) and CoTa₂(C16) phases were investigated by microstructural examination in as-cast Co-(24–60 at.%)Ta alloys. The solvus temperature of the γ′ Co₃Ta (L1₂) phase precipitated in the 5.8 at.%Ta γ(Co) and the peritectoid temperature of the Co₇Ta₂ phase in an 8.5 at.%Ta alloy were determined to be 1013 °C and 1033 °C, respectively, by differential scanning calorimeter (DSC). Fine precipitates of the γ′ phase precipitated in the γ (A1) matrix were observed by transmission electron microscope (TEM). Analyzing the present experimental results synthetically, the γ′ Co₃Ta phase was identified to be a metastable phase, of which the γ/γ′ transition temperature of the stoichiometric Co₃Ta alloy was estimated to be 2000 °C. Thermodynamic assessment of the Co–Ta binary system was carried out based on the present results as well as on experimental data in the literature. Calculated results of not only stable but also metastable equilibria were found to be in good agreement with the revised phase diagram. The evaluated stability of the metastable γ′ Co₃Ta coincides with the enthalpy of formation (ΔH(γ'Co₃Ta) = −23.44 kJ/mol) calculated by the ab initio method.     

Microstructure and martensitic transformation of an ultrafine-grained TiNiNb shape memory alloy processed by equal channel angular pressing

Microstructure, martensitic transformation and mechanical properties of an ultrafine-grained Ti₄₄Ni₄₇Nb₉ shape memory alloy processed by equal channel angular pressing were investigated. The as-ECAP processed sample is characterized by an inhomogeneous and refined microstructure. In β-Nb phase-rich region, the grains of matrix are elongated with high density dislocations. In β-Nb phase-free region, the microstructure is partial recovery and characterized by near-equiaxed grains. The heterogeneous microstructure is attributed to presence of β-Nb phase. Martensitic transformation behavior of the as-ECAP processed sample is characterized by a single-stage transformation. The thermal cycling stability of transformation and the mechanical properties are considerably improved due to a strengthening effect resulting from refined grain size and high dislocation density.     

Partitioning and site occupancy of Ta and Mo in Co-base γ/γ′ alloys studied by atom probe tomography

The detailed understanding of solute partitioning and site occupancies of these solutes within the ordered γ′ (L1₂) precipitates holds a key role in the development of cobalt-base γ/γ′ alloys with optimized properties. The present atom probe tomography study utilizes both structural and compositional information to determine the partitioning behavior of transition elements like Ta and Mo between γ matrix and γ′ precipitates and their site occupancy within the γ′ phase. The addition of Ta, which enhances the formation of γ′, to a ternary Co–Al–W alloy with stoichiometric Co₃(Al,W) precipitates, results in the substitution of only the W in the γ′ precipitates to form Co₃(Al, W, Ta) precipitates. Interestingly, Mo, typically considered a γ solid solution strengthener in nickel-base alloys, also partitions strongly to γ′ precipitates when added to the Co–Al–W alloy and displaces only the W atoms. The experimentally observed equal atomic substitution of W by both Ta and Mo, without any change in the Al content within the γ′ precipitates, gives insights into the energetics of relative site substitutions in this ordered compound.     

Effect of the tetragonal distortion on the electronic structure,phonons and superconductivity in the Mo3Sb7 superconductor

Effect of tetragonal distortion on the electronic structure, dynamical properties and superconductivity in Mo₃Sb₇ is analyzed using first principles electronic structure and phonon calculations. Rigid muffin tin approximation (RMTA) and McMillan formulas are used to calculate the electron–phonon coupling constant λ and superconducting critical temperature. Our results show, that tetragonal distortion has small, but beneficial effect on superconductivity, slightly increasing λ, and the conclusion that the electron–phonon mechanism is responsible for the superconductivity in Mo₃Sb₇ is supported. The spin-polarized calculations for the ordered (ferromagnetic or antiferromagnetic), as well as disordered (disordered local moment) magnetic states yielded non-magnetic ground state. We point out that due to its experimentally observed magnetic properties the tetragonal Mo₃Sb₇ might be treated as noncentrosymmetric superconductor, which could have influence for the pairing symmetry. In this context the relativistic band structure is calculated and spin–orbit interaction effects are discussed.     

颗粒组成对杂填土与软土互嵌沉降的影响试验研究

在受到上覆荷载作用时,杂填土地基下敷淤泥软土会轻易挤入杂填土颗粒之间的孔隙中,造成互嵌沉降,在传统地基沉降计算中这部分沉降未被考虑。而杂填土级配不均,其孔隙率与粒径组分密切相关。选取4种不同粒径颗粒组,以不同粒径的杂填土颗粒组成的二元混合物为研究对象,利用自制互嵌仪进行互嵌试验,揭示二元混合颗粒中不同粒径比、小颗粒含量下杂填土与软土的总沉降与互嵌沉降发展规律。研究结果表明：二元混合颗粒组成中,当小颗粒占主体时,互嵌沉降随着小颗粒粒径的增大而增大;当大小颗粒含量相同时,随着小颗粒粒径的增大,互嵌沉降呈先减小后增大的趋势;当小颗粒含量较少时,互嵌沉降随着小颗粒粒径的增大而减小。而在杂填土大小颗粒含量变化过程中,小颗粒粒径较小时,互嵌沉降随着颗粒含量的增加而减小;小颗粒粒径较大时,颗粒含量的增加对杂填土与软土的互嵌沉降影响不大。