非诺贝特对小鼠急性局灶性脑缺血再灌注损伤的保护作用

目的研究非诺贝特(fenofibrate,Fen)对小鼠急性局灶性脑缺血再灌注损伤的保护作用及机制。方法线栓法制备小鼠大脑中动脉栓塞模型,缺血90 min后再灌注。非诺贝特(10,80 mg.kg-1)再灌注同时及再灌后2 h各灌胃给药1次。再灌注后24 h,测定小鼠神经功能缺失评分、脑梗死体积及脑水肿程度,实时逆转录多聚酶链反应(RT-PCR)法检测过氧化物酶体增殖物激活受体α(PPARα)mRNA的表达水平,生化法测定脑组织丙二醛(maiondialdehyde,MDA)含量及超氧化物歧化酶(superoxide dismutase,SOD)的活性,伊文思蓝(Evans blue,EB)法观察血脑屏障破坏程度;应用过氧化物酶体增殖物激活受体α拮抗剂MK886(10 mg.kg-1),观察过氧化物酶体增殖物激活受体α是否参与非诺贝特的脑保护作用。结果非诺贝特(80 mg.kg-1)可改善小鼠神经功能缺失,减小脑梗死体积,减轻脑水肿程度,减少脑缺血后脑内伊文思蓝的渗漏,上调脑损伤后脑内过氧化物酶体增殖物激活受体αmRNA的表达,减轻脑组织的脂质过氧化。MK886可拮抗非诺贝特的保护作用。结论非诺贝特可通过上调过氧化物酶体增殖物激活受体αmRNA表达、减轻脂质过氧化损伤而对小鼠急性局灶性脑缺血再灌注损伤发挥保护作用

前胡甲素对小鼠局灶性脑缺血的保护作用

目的观察前胡甲素(Pd-Ia)对小鼠局灶性脑缺血损伤的保护作用及特点。方法线栓法制备小鼠大脑中动脉栓塞脑缺血损伤模型。Pd-Ia(1,5,10mg/kg)在缺血前0.5h腹腔给药1次;或在缺血前1,0.5h、缺血同时、再灌注同时、再灌后0.5h及再灌后1h各腹腔给予Pd-Ia5mg/kg。脑缺血1.5h,再灌注24h后,测定小鼠神经功能缺失评分、脑梗死体积、脑水肿等评定脑缺血损伤的指标;测定血清中丙二醛(MDA)和超氧化物岐化酶(SOD)的活性。结果Pd-Ia(5,10mg/kg)缺血前0.5h给药及Pd-Ia5mg/kg缺血前0.5h、缺血同时、再灌注同时及再灌后0.5h给药可明显改善小鼠神经功能损伤,减小脑梗死体积和减轻脑水肿程度,且以再灌注同时单次给药效果最为显著;Pd-Ia(5,10mg/kg)能够明显提高脑缺血损伤小鼠血清中SOD活性,降低MDA含量。结论Pd-Ia保护小鼠局灶性脑缺血急性损伤,最佳剂量为5mg/kg,最佳治疗时间点为再灌注同时;其保护脑缺血损伤的机制可能与抑制脂质过氧化、提高氧化酶的活性有关

油酰乙醇胺在小鼠急性局灶性脑缺血再灌注损伤中的作用及机制

目的研究油酰乙醇胺(OEA)在脑缺血再灌注损伤中的作用及机制。方法线栓法制备小鼠大脑中动脉栓塞模型,缺血90 min后再灌注。应用HPLC-MS/MS方法测定脑组织内OEA的含量。给予OEA(5,10,40 mg/kg,ig)或OEA水解酶抑制剂URB597(1 mg/kg,ig),观察其对小鼠急性脑缺血再灌注损伤的影响。测定脑组织丙二醛(MDA)含量,超氧化物歧化酶(SOD)及过氧化氢酶(CAT)的活性。观察MK886对OEA抗脂质过氧化损伤的影响。结果脑缺血再灌注后6 h,损伤侧脑内OEA含量开始升高,再灌注后24 h升高最明显。脑缺血再灌注后给予OEA(40 mg/kg)或URB597(1 mg/kg)可减少神经功能缺失评分,减小脑梗死体积,减轻脑水肿程度。OEA可减少脑内MDA含量,增加抗氧化酶SOD的活性。OEA这一抗氧化作用可被MK886所取消。结论脑缺血再灌注可增加脑内OEA的含量,OEA通过激动PPARα,减轻脂质过氧化损伤发挥抗脑缺血再灌注损伤作用

油酰乙醇胺对小鼠局灶性脑缺血的保护作用

目的观察新型PPARα激动剂油酰乙醇胺(oleoyleth-anolamide,OEA)对小鼠局灶性脑缺血损伤的保护作用及特点。方法线栓法制备小鼠大脑中动脉栓塞模型诱导脑缺血。OEA(10、20、40mg·kg-1)在术前3d开始每天灌胃给药1次;或在缺血前0.5h、1h、再灌注同时、再灌后1h,各单次灌胃给予OEA40mg·kg-1。脑缺血1.5h,再灌注24h后,测定小鼠神经功能缺失评分、脑梗死体积、脑水肿等评定脑缺血损伤的指标。结果OEA(20、40mg·kg-1)术前多次给药及OEA(40mg·kg-1)缺血前0.5h或再灌注同时单次给药可明显改善小鼠神经功能损伤,减小脑梗死体积和减轻脑水肿程度,且以再灌注同时单次给药效果最为明显。结论OEA剂量及时间依赖性的保护小鼠局灶性脑缺血急性损伤,有效剂量为20mg·kg-1和40mg·kg-1,最佳治疗时间点为再灌注同时

面向对象的高分辨率影像单值分类耕地提取方法研究

遥感技术已广泛应用于土地覆盖/土地利用分类中。在专题应用中,用户只对某一类地物感兴趣,如耕地提取,即单类别分类问题。随着影像分辨率的提高,基于像元的分类算法难以满足高分辨率影像高精度信息提取的需求。本文采用结合面向对象分类思想和基于正样本、未标记样本遥感单值(PUL)分类方法从多源高分辨率影像中提取耕地信息,并与基于像素的分类试验进行对比分析。结果表明,在缺少部分地类的不完全训练集下,基于面向对象的单值分类较传统神经网络分类有更较稳定的表现,并且远优于基于像素的分类结果

Simultaneous Improvement of Yield Strength and Ductility at Cryogenic Temperature by Gradient Structure in 304 Stainless Steel

The tensile properties and the corresponding deformation mechanism of the graded 304 stainless steel (ss) at both room and cryogenic temperatures were investigated and compared with those of the coarse-grained (CGed) 304 ss. Gradient structures were found to have excellent synergy of strength and ductility at room temperature, and both the yield strength and the uniform elongation were found to be simultaneously improved at cryogenic temperature in the gradient structures, as compared to those for the CG sample. The hetero-deformation-induced (HDI) hardening was found to play a more important role in the gradient structures as compared to the CG sample and be more obvious at cryogenic temperature as compared to that at room temperature. The central layer in the gradient structures provides stronger strain hardening during tensile deformation at both temperatures, due to more volume fraction of martensitic transformation. The volume fraction of martensitic transformation in the gradient structures was found to be much higher at cryogenic temperature, resulting in a much stronger strain hardening at cryogenic temperature. The amount of martensitic transformation at the central layer of the gradient structures is observed to be even higher than that for the CG sample at cryogenic temperature, which is one of the origins for the simultaneous improvement of strength and ductility by the gradient structures at cryogenic temperature

Excellent tensile properties induced by heterogeneous grain structure and dual nanoprecipitates in high entropy alloys

Both heterogeneous grain structure and dual nanoprecipitates (B2 and L12) have been designed and obtained in a FCC-based Al0.5Cr0.9FeNi2.5V0.2 high entropy alloy (HEA). The volume fraction of B2 phase is nearly unchanged, while the average size and volume fraction for L12 particles become larger after aging, resulting in a more severe heterogeneity. The aged samples display a better synergy of strength and ductility than the corresponding unaged samples. The aged samples show a transient up-turn strain hardening behavior and a higher hardening rate as compared to the corresponding unaged samples. The hetero-deformation-induced hardening plays a more important role in the aged samples than in the unaged samples, producing higher density of geometrically necessary dislocations for better tensile properties. Orowan-type bowing hardening and shearing hardening mechanisms are observed for B2 and L12 nano-particles, respectively. The size and interspacing of B2 and L12 particles are at nanometer scale, which should be very effective on hardening and strengthening by accumulating dislocations at phase interfaces. A theoretical analysis based on dislocation strengthening, grain boundary strengthening, Orowan-type bowing strengthening of B2 nano-particles, shearing strengthening of L12 nanoparticles and strengthening of chemical short-range order has been found to provide well prediction on strength

<p>Designing structures with combined gradients of grain size and precipitation in high entropy alloys for simultaneous improvement of strength and ductility & nbsp;</p>

Suppressing the early strain localization at the nanostructured topmost layer is crucial for achieving better tensile ductility in the gradient structure. Thus, structures with combined gradient distributions along the depth for both grain size and volume fraction of precipitates were designed and introduced in a high entropy alloy by surface mechanical attrition treatment and aging. Yield strength and uniform elongation were observed to be simultaneously improved in the structures with combined gradients as compared to the corresponding structures with only grain size gradient. More severe strain gradients and higher density of geometrically necessary dislocations were observed to be produced at various domain boundaries in the structures with combined gradients, resulting in stronger hetero-deformation-induced (HDI) extra hardening for better tensile properties. Shearing and bowing hardening mechanisms were observed for L1( 2) and B2 precipitates, respectively. Higher volume fractions of B2 and L1( 2) phases at the topmost layer induce stronger precipitation hardening, which compensates the diminished strain hardening due to the reduced grain size at the topmost layer for better tensile ductility in the structures with combined gradients. The observed higher yield strength in the structures with combined gradients have been discussed based on mechanisms of dislocation strengthening, precipitation strengthening and HDI strengthening. (C)& nbsp;2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.& nbsp

Superior dynamic shear properties by structures with dual gradients in medium entropy alloys

Structures with single gradient and dual gradients have been designed and fabricated in an Al 0.5 Cr 0.9 FeNi 2.5 V 0.2 medium entropy alloy. Structures with dual gradients (with increasing grain size and a decreasing volume fraction of nanoprecipitates from the surface to the center) were observed to show much better dynamic shear properties compared to both structures with single grain size gradient and coarse grained structures with homogeneously distributed nanoprecipitates. Thus, the dual gradients have a synergetic strengthening/toughening effect as compared to the sole effect of a single gradient and the sole precipitation effect. Initiation of the adiabatic shear band (ASB) is delayed and propagation of ASB is slowed down in structures with dual gradients compared to structures with single gradients, resulting in better dynamic shear properties. A higher magnitude of strain gradient and higher density of geometrically necessary dislocations are induced in the structures with dual gradients, resulting in extra strain hardening. Higher density dislocations, stacking faults, and Lomer Cottrell locks can be accumulated by the interactions between these defects and B2/L1 2 precipitates, due to the higher volume fraction of nanoprecipitates in the surface layer of the structures with dual gradients, which could retard the early strain localization in the surface layer for better dynamic shear properties. (c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology

Superior dynamic shear properties and deformation mechanisms in a high entropy alloy with dual heterogeneous structures

Both heterogeneous grain structure and dual nanoprecipitates were designed in a Al-0.5 Cr0.9FeNi2.5V0.2 high entropy alloy (HEA), and the dynamic shear responses were investi-gated by hat-shaped specimens in split Hopkinson pressure bar tests. The present HEA with heterogeneous structure displays an unprecedented synergy of dynamic shear strength and ductility, as compared to the literature data for other metals and alloys. The excellent dynamic shear properties in the unaged samples could be due to the dynamical grain refinement, the dislocations hardening, and the precipitation hardening. The aged samples with a higher volume fraction of coherent L1(2) nanoprecipitates display even better dynamic shear properties, as compared to the unaged samples, which can be attributed to the triggered planar dislocation slip, the stored higher density of dislocations, the formation of dislocation substructure and the more pronounced precipitation hardening for postponing the occurrence of the adiabatic shear band (ASB). The high strain rate, high strain/stress magnitude, high adiabatic temperature rise, and fast-cooling process within ASB were observed to induce the dynamic recrystallization and the phase transformation from FCC phase to B2 phase, and this newly observed phase transformation phenomenon was not observed before under quasi-static deformation conditions. (C) 2022 The Author(s). Published by Elsevier B.V