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排序方式: 共有2621条查询结果,搜索用时 27 毫秒
1.
某电力公司变电站用铝合金设备线夹在运行过程发生批次开裂事故,通过宏观观察、断口分析、化学成分分析、力学性能测试、冷冻模拟试验等方法,对设备线夹的开裂原因和开裂机理进行了分析。结果表明:设备线夹焊缝存在焊接缺陷,导致焊缝强度下降;设备线夹接线管底部存在积水空间,寒冷天气下积水结冰,体积膨胀,使焊缝承受设计工况外的负载而过载开裂,造成了线夹开裂。 相似文献
2.
Hydrogen storage in liquid state is considered key feature to its efficient volumetric density for transportation applications. However, there are several hazards associated with handling liquid hydrogen, e.g. fire, explosion, asphyxiation in indoor accidents, and frostbites due to exposure in extremely low temperatures. Predictive capabilities of liquid hydrogen dispersion are essential for developing emergency response plans and facilitate the understanding of the physical problem. In the present study, the Computational Fluid Dynamics (CFD) methodology is employed to simulate the dispersion of liquid hydrogen based on experiment conducted by the Health Safety Laboratory (HSL), in order to investigate several factors that greatly influence dispersion modeling. The flashed vapour fraction at the pipe exit is estimated assuming isenthalpic expansion combined with the NIST equation of state. Modeling the condensation of ambient humidity and air components (nitrogen and oxygen) and imposing transient wind profile are the main issues addressed by the present study. The Homogeneous Equilibrium Model (HEM model) is compared against the Non-Homogeneous Equilibrium Model (NHEM model) to account for slip effects of the non-vapour phase. To estimate the slip velocity in the NHEM model a methodology (momentum slip model) is employed, which solves along with the conservation equations for the mixture the momentum conservation equation of the non-vapour phase. Comparison of the momentum slip model with the algebraic slip model shows that the latter overestimates the slip velocity for large particles and thus its use needs special attention. Overall satisfactory agreement was found with the experimental data when all the above parameters were modelled. 相似文献
3.
文章分析了3a马尔康国家基准气候站AG2.0型超声波蒸发传感器观测数据,结果表明:蒸发传感器遇低温结冰时段自动观测数据偏大。对1d中部分时间段内蒸发水结冰、融化以及冬季全天结冰期很短的观测数据进行了分析,分析认为数据偏大主要是因为蒸发桶和测量筒的材料物理性质以及测量的水体面积不同。最后提出了数据记录处理建议。 相似文献
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Michael Wisniewski Timothy Artlip Jia Liu Jing Ma Erik Burchard John Norelli Christopher Dardick 《International journal of molecular sciences》2020,21(24)
Malus sieversii is considered the progenitor of modern apple (Malus pumila) cultivars and to represent a valuable source of genetic diversity. Despite the importance of M. sieversii as a source of disease resistance, stress tolerance, and novel fruit traits, little is known about gene function and diversity in M. sieversii. Notably, a publicly annotated genome sequence for this species is not available. In the current study, the FOX (Full-length cDNA OvereXpressing) gene hunting system was used to construct a library of transgenic lines of Arabidopsis in which each transgenic line overexpresses a full-length gene obtained from a cDNA library of the PI619283 accession of M. sieversii. The cDNA library was constructed from mRNA obtained from bark tissues collected in late fall–early winter, a time at which many abiotic stress-adaptative genes are expressed. Over 4000 apple FOX Arabidopsis lines have been established from the pool of transgenic seeds and cDNA inserts corresponding to various Gene Ontology (GO) categories have been identified. A total of 160 inserts appear to be novel, with no or limited homology to M. pumila, Arabidopsis, or poplar. Over 1300 lines have also been screened for freezing resistance. The constructed library of transgenic lines provides a valuable genetic resource for exploring gene function and diversity in Malus sieversii. Notably, no such library of t-DNA lines currently exists for any Malus species. 相似文献
6.
Yanhuizhi Feng Huai-Ling Gao Di Wu Yu-Teng Weng Ze-Yu Wang Shu-Hong Yu Zuolin Wang 《Advanced functional materials》2021,31(43):2105348
Mucogingival surgery has become a common procedure for soft gingival tissue reparation in dental clinical practice, which mainly relies on autograft or commercial collagen membranes (CM). However, the autograft faces grand challenges in source availability and long-term post-surgery pain management, and the CM is restricted by its poor mechanical properties in an aqueous environment. Here, it is reported that a bio-inspired lamellar chitosan scaffold (LCS) with long range ordered porous structure, manufactured through a bidirectional freezing method, can serve as a promising gingival tissue engineering material. The LCS not only exhibits excellent mechanical properties in the hydrated state but also accelerates vessel formation and soft tissue regeneration in vivo. Most interestingly, the LCS is found to be capable of inducing macrophage differentiation to M2 macrophages, which is thought to play an important role in tissue regeneration. These advantages combined with its easy and low-cost preparation process make the LCS a promising candidate for dental clinical applications. 相似文献
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速冻机宽度方向上流场的实验分析 总被引:1,自引:0,他引:1
在速冻机宽度方向上,速冻机两侧的冻品冻结速率远大于速冻机中心,为解决速冻机宽度方向上冻品冻结速率不均匀的问题,通过实验分析沿速冻机宽度方向上冻结速率差别较大的原因及速冻区域内气流的稳定性。研究表明:在速冻机宽度方向上,速冻机中心流速最低,两侧流速最高;靠近压力出口,喷嘴出口流速为19.11 m/s;远离压力出口,喷嘴出口流速为14.03 m/s。测点S_1、S_2、S_3和S_4的速度不均匀度为32%、99.92%、31.81%和79.62%。速度不均匀度是引起冻结速率不同的关键因素。速冻区域内气流的不稳定性会削弱换热,降低冻结速率,测点S_1、S_2、S_3和S_4的速度极差数值反映了气流的波动性。波动性最小的是S_1点,极差最小值为0.69 m/s。 相似文献
9.
为研究低压静电场辅助冷冻对竹笋冻结特性的影响,以冻结曲线、硬度、水分损失率、水分迁移、冰晶形态和组织微观结构为指标,探究低压静电场辅助冷冻(-35 ℃)和普通冷冻(-35 ℃)条件下竹笋品质的变化规律。结果表明:低压静电场辅助冷冻提高了冻结效率,改变了冰晶形态及分布,减轻了组织微观结构破损程度,改善了解冻汁液流失情况。与静电板间距10、20、30、40 cm处的冷冻竹笋解冻后水分损失率分别为14.16%、12.58%、9.73%、10.44%,显著低于对照组(21.01%)(P<0.05),硬度分别为461.19、507.48、496.65 g和455.31 g,显著高于对照组(350.70 g)(P<0.05)。低场核磁共振分析结果表明,在低压静电场辅助冷冻下竹笋解冻后汁液流失减少,扫描电子显微镜观察结果显示,竹笋纤维排列整齐,组织微观结构保持较好。低压静电场辅助冷冻可有效改善竹笋品质,可为利用低压静电场进行果蔬的冷冻贮藏和冷链运输提供参考。 相似文献
10.
Xi Zhao Hongyue Li Fangchao Cui Jinxiang Wang Shumin Yi Hongbo Mi Yanfang Lv Xuepeng Li Jianrong Li 《International Journal of Food Science & Technology》2022,57(7):4400-4410
Taking air freezing (AF) as the reference, the effects of four types of multi-compound freezing medium for cryogenic liquid quick-freezing (immersion freezing, IF) on the freezing rate, quality and myofibrillar protein (MP) denaturation of red drum (Sciaenops ocellatus) fillets during frozen storage (−18°C) from days 0 to 90 were studied. Samples were gathered on days 0, 15, 30, 45, 60 and 90 for analysis. The results showed that IF groups (IF-1: 20% ethanol, 30% propylene glycol, 10% sodium chloride aqueous solution; IF-2: 20% ethanol, 20% propylene glycol, 10% glycerol, 10% sodium chloride aqueous solution; IF-3: 20% ethanol, 20% propylene glycol, 10% polyethylene glycol, 10% sodium chloride aqueous solution; IF-4: 20% ethanol, 20% propylene glycol, 5% glycerol, 5% polyethylene glycol, 10% sodium chloride aqueous solution) significantly shortened the time to cross the formation zone of maximum ice crystals while the freezing rate was 6.13 times higher than the AF group after adding 30% propylene glycol as the freezing medium. Furthermore, compared with the AF group, the IF groups significantly reduced losses in the water-holding capacity, the myofibrillar fragmentation index, microstructure damage, texture characteristics, drip loss and water migration (P < 0.05). In addition, the MP of IF groups had higher maximum transition temperatures (Tmax1 and Tmax2), total sulfhydryl content, Ca2+-ATPase activity and relative α-helix content compared with the AF group. In conclusion, IF could significantly increase the freezing rate of red drum fillets, and slow down quality deterioration and denaturation of MP during frozen storage for 90 days (−18°C). In particular, IF-2 (20% ethanol, 20% propylene glycol, 10% glycerol, 10% sodium chloride aqueous solution) was found to be more suitable for the immersion freezing of marine fish among the four multi-compound freezing medium. 相似文献