Top-dressing nitrogen fertilizer rate contributes to decrease culm physical strength by reducing structural carbohydrate content in japonica rice

Lodging is an important factor limiting rice yield and quality by bending or breaking stem in japonica rice（Oryza sativa L.） production. The objectives of this study were to determine the mechanism of lodging resistance in japonica rice as affected by carbohydrate components, especially its related arrangement in culm tissue and response to top-dressing nitrogen（N） fertilizer. Field experiments were conducted in Danyang County, Jiangsu Province, China, by using two japonica rice varieties Wuyunjing 23（lodging-resistance variety） and W3668（lodging-susceptible variety） with three top-dressing N fertilizer rates（0, 135 and 270 kg N ha^（-1）） in 2013 and 2014. Lodging related physical parameters, morphological characteristics and stem carbohydrate components were investigated at 30 d after full heading stage. Results showed that with increasing N fertilizer rates, the lodging rate and lodging index increased rapidly primarily due to significant reduction of breaking strength in two japonica rice varieties. Correlation analysis revealed that breaking strength was significantly and positively correlated with bending stress, but negatively correlated with section modulus, except for significant correlation at W3668 in 2014. Higher stem plumpness status and structural carbohydrate contents significantly enhanced stem stiffness, despite of lower non-structural carbohydrate. With higher N fertilizer rate, the culm wall thickness was almost identical, and culm diameter increased slightly. The structural carbohydrates, especially for lignin content in culm, reduced significantly under high N rate. Further histochemical staining analysis revealed that high N treatments decreased the lignin deposition rapidly in the sclerenchyma cells of mechanical tissue, large vascular bundle and small vascular bundle region, which were consistent with reduction of bending stress, especially for W3668 and thus, resulted in poor stem strength and higher lodging index. These results suggested that structural carbohydrate plays a vital role for improving stem strength in japonica rice. N rate decreased lodging resistance primarily due to poor stem stiffness, by reducing structural carbohydrate content and lignin deposition in the secondary cell wall of lower internode culm tissue.

Nitrogen Concentration in Subtending Cotton Leaves in Relation to Fiber Strength in Different Fruiting Branches

Nitrogen（N） fertilizer experiments were conducted to investigate the optimal subtending leaf N concentration for fiber strength,and its relationship with activities of key enzymes（sucrose synthase and β-1,3-glucanase） and contents of key constituents（sucrose and β-1,3-glucan） involved in fiber strength development in the lower,middle and upper fruiting branches of two cotton cultivars（Kemian 1 and NuCOTN 33B）.For each sampling day,we simulated changes in fiber strength,activity of sucrose synthase and β-1,3-glucanase and levels of sucrose and β-1,3-glucan in response to leaf N concentration using quadratic eqs.;the optimal subtending leaf N concentrations were deduced from the eqs.For the same fruiting branch,changes in the optimal leaf N concentration based on fiber development（DPA） could be simulated by power functions.From these functions,the average optimal subtending leaf N concentrations during fiber development for the cultivar,Kemian 1,were 2.84% in the lower fruiting branches,3.15% in the middle fruiting branches and 3.04% in the upper fruiting branches.For the cultivar,NuCOTN 33B,the optimum concentrations were 3.04,3.28 and 3.18% in the lower,middle and upper fruiting branches,respectively.This quantification may be used as a monitoring index for evaluating fiber strength and its related key enzymes and constituents during fiber formation at the lower,middle and upper fruiting branches.

Development of High Strength Steel Designed for Carbonitriding with High Nitrogen Content to Be Used for Automatic Transmission Gears

To downsize and lighten automatic transmission components, the gears installed must be strengthened in terms of pitting endurance and/or wear resistance. The most important metallurgical factor affecting fractures is well known to be resistance to softening when steel is tempered at approximately 573 K. Carbonitriding with a high amount of nitrogen is a very effective production technique because nitrogen increases the resistance during tempering. However, structural anomalies begin to appear in the surface layer when the nitrogen content exceeds 0.6 mass% in the chromium steel generally used. To address this, we have developed new high-strength chromium steel with an optimized chemical composition that effectively inhibits anomalies even when Carbonitriding with a nitrogen content of more than 0.6 mass%. We performed a drivetrain durability test on an automatic transmission component designed to have excellent contact fatigue strength and a tooth root bending impact and fatigue strength. We found that the developed steel that was carbonitrided with a content of about 0.9 mass%, and then shot peened hard, has a pitting life of roughly 4.5 times that of conventionally manufactured steel.

Strain rate and cold rolling dependence of tensile strength and ductility in high nitrogen nickel-free austenitic stainless steel

The tensile strength and ductility of a high nitrogen nickel-free austenitic stainless steel with solution and cold rolling treatment were investigated by performing tensile tests at different strain rates and at room temperature. The tensile tests demonstrated that this steel exhibits a significant strain rate and cold rolling dependence of the tensile strength and ductility.With the increase of the strain rate from 10^-4s^-1to 1 s^-1, the yield strength and ultimate tensile strength increase and the uniform elongation and total elongation decrease. The analysis of the double logarithmic stress–strain curves showed that this steel exhibits a two-stage strain hardening behavior, which can be well examined and analyzed by using the Ludwigson equation. The strain hardening exponents at low and high strain regions（n2and n1） and the transition strain（εL） decrease with increasing strain rate and the increase of cold rolling RA. Based on the analysis results of the stress–strain curves, the transmission electron microscopy characterization of the microstructure and the scanning electron microscopy observation of the deformation surfaces, the significant strain rate and cold rolling dependence of the strength and ductility of this steel were discussed and connected with the variation in the work hardening and dislocation activity with strain rate and cold rolling.

高氮奥氏体不锈钢的研究进展及展望

高氮奥氏体不锈钢强韧性高,耐磨耐蚀性强,同时,具有非铁磁性及良好的生物相容性。在海洋工程、能源化工、国防航空、生物医疗等诸多领域获得了广泛的关注。然而,其在制备过程中仍面临增氮水平控制不精确、高氮钢液凝固过程氮气易析出形成气孔,以及热加工过程中粗大氮化物析出等一系列问题与技术挑战,在一定程度上限制了其大规模发展与应用。本文系统性地阐述了高氮奥氏体不锈钢的发展现状、制备工艺及强化机理。首先,综述了高氮奥氏体不锈钢的国内外发展历史和研究现状;其次,对高氮奥氏体不锈钢的生产制备工艺进行了总结,概括了熔铸法制备工艺,如大熔池法、加压感应熔炼、加压钢包吹洗、加压电渣重熔以及加压等离子弧熔炼,并对其优缺点进行对比分析;此外,针对高氮奥氏体不锈钢粉末冶金制备工艺进行概述,包括机械合金化法、氮气雾化法、等离子旋转电极雾化法以及固态粉末渗氮法,并围绕粉末热等静压、放电等离子烧结、注射成型、热压烧结、冷压成型以及增材制造等成型工艺进行了总结。最后,探讨了氮在奥氏体不锈钢固溶强化、细晶强化、应变硬化、沉淀强化等强化机制方面的作用机理,并针对当前高氮奥氏体不锈钢在发展过程中存在的主要问题进行了探讨及展望。

Microstructures and Properties of 550 MPa Grade High Strength Thin-walled H-beam Steel

The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.

Effect of Different Nitrogen Application Rate on Rice Stem Characteristics

The effects of different nitrogen application rate on the physical characteristics and anatomic structure of rice stems were investigated with rice cultivars Guangliangyou 1128 （with high resistance） and Zhunliangyou 527 （with low resistance） as materials. The results showed that, firstly, plant height, gravity center height and basal internode length of the 2 rice cultivars increased with the increase of nitrogen application rate, while wall thickness and internode filling degree decreased. The breaking-resistance strength per stem and thrust-resistance strength of plants declined with the increase of nitrogen application rate. Secondly, as nitrogen input increased, the number of vascular bundles and the area of vascular bundles increased between the 2 rice cultivars. Thirdly, with the increase of nitrogen application rate, the stem section area of Guangliangyou 1128, which had strong lodging resistance, gradually increased, while that of Zhunliangyou 527 increased firstly and then decreased. The maximum application amount of nitrogen was 240 kg/hm 2. Nitrogen fertilizer mainly affected the relative gravity center height, stem wall thickness and internode filling degree of the 2 cultivars, thereby reducing the basal stem breaking resistance and plant thrust-resistance strength.

氮对07Cr18Ni11Nb不锈钢组织和性能影响

通过热力学计算软件Thermo-Calc 2023a、场发射扫描电子显微镜(FESEM)等进行第二相析出模拟和金相、性能检测分析:氮含量在0.013%时,07Cr18Ni11Nb凝固时氮的析出相主要有Nb(CN)、(Cr∶Ni∶Si∶N)复合相和σ相。随着氮含量增加到0.055%时,氮的析出相主要有Nb(CN)、(Cr∶Ni∶Si∶N)复合相,Z相也出现,晶粒有逐渐减小的趋势。室温25℃和高温600℃下屈服强度和抗拉强度都有所增加,但是屈服强度增加的幅度较抗拉强度多。

不同施氮水平下硅肥对谷子抗倒伏能力、产量和品质的影响

[目的]倒伏严重影响谷子产量和品质。探究不同施氮水平下硅肥提高谷子茎秆强度、产量及品质的作用,为谷子高产高效施肥提供技术方案。[方法]以晋谷21和张杂13为供试谷子品种,在山西太谷进行大田试验。在常规施氮量N_(1)(180 kg/hm^(2))和高施氮量N_(2)(450 kg/hm^(2))下,分别设置不施硅、施用硅酸钠(Si_(1),SiO_(2) 68.85 kg/hm^(2))和硅钙肥(Si_(2),SiO_(2) 67.2 kg/hm^(2)),共6个处理。在谷子成熟期测量其株高、抗倒伏能力相关指标、光合特性、产量和品质相关指标,并观察茎秆横切面显微结构。[结果]N_(1)水平下,施用硅肥降低了谷子基节长度,增加了茎粗、茎秆抗折力和穿刺力,晋谷21和张杂13两品种前五基节的节间长度分别降低了4.1%~30.1%和9.5%~11.5%,茎粗分别增加5.3%~19.4%和13.0%~34.1%;晋谷21抗倒性在N_(1)-Si_(1)处理较强,第一、第二基节抗倒伏指数较N_(1)-Si_0处理分别增加37.4%和35.8%,张杂13在N_(1)-Si_(2)处理时较强,第一、第二基节抗倒伏指数较N_(1)-Si_0处理分别增加136.0%和94.7%。N_(2)水平下,施用硅肥后晋谷21和张杂13前五基节的节间长度分别降低了9.6%~30.3%和10.6%~14.9%,茎粗分别增加了9.56%~23.9%和16.2%~31.0%,茎秆扁平度降低。硅钙肥对谷子茎秆强度影响大于硅酸钠,N_(2)-Si_(2)处理晋谷21的第二基节抗折力、穿刺力和抗倒伏指数比N_(2)-Si_0分别增加97.9%、77.6%和83.3%,张杂13的第一基节抗折力、穿刺力和抗倒伏指数比N_(2)-Si_0分别增加74.0%、66.8%和128%。施硅后谷子茎秆中机械组织增厚,维管束数量增多且排列均匀,向茎秆中心延伸,且在N_(2)水平下,硅钙肥作用效果优于硅酸钠。硅可促进谷子穗码发育,增加穗粗、穗粒数和千粒重,在高氮水平下硅钙肥处理使晋谷21和张杂13的产量分别增加23.8%和24.0%。施用硅肥能够提高谷子脂肪、蛋白质和氨基酸含量,在高氮水平下可以降低谷子直链淀粉/支链淀粉值。[结论]在高氮条件下,施用硅钙肥使谷子前五基节长度降低,茎粗增加,机械强度增加,进而提高抗倒伏能力;施用硅肥还可增加光合速率和蒸腾速率,促进物质积累和运输,增加产量,改善品质。

不同肥密措施对南疆水稻抗倒伏及干物质生产特性和产量的影响

以新稻36号为材料,在南疆地区进行了以氮肥水平(N)作为主区、栽插密度(D)作为副区的田间裂区试验。结果表明,随施氮量增加,第1节间长度、第2节间长度、弯曲力矩、株高和重心高度显著增加,抗折力则先增后降以N2处理(纯N 240 kg/hm^(2))最高;合理密植能够控制个体发育,降低节间长度、弯曲力矩、株高与重心高度;茎秆倒伏指数由上述因素共同影响,施氮量240 kg/hm^(2)、栽插密度20.83~27.78万丛/hm^(2)的处理抗倒伏性较优。花后干物质积累量对籽粒贡献占比为51.69%~76.14%,是籽粒干物质积累量的主要来源,适当增施氮肥能够提高花后干物质积累量与积累率;过量施肥则会使干物质在花前的积累量增大,多用于营养器官生长,不利于向籽粒转运。适度密植有利于提高花后干物质积累量,D4处理(27.78万丛/hm^(2))较其他处理提高18.06%~30.22%,同时也促进了干物质向籽粒的转运。综合来看,施氮量240 kg/hm^(2)、栽插密度27.78万丛/hm^(2)时能显著改善水稻地上部分干物质的比例及干物质分配,且未发生倒伏,有利于产量提高。

碳化硼陶瓷与高氮钢钎焊接头组织和性能

使用Ag-Cu-Ti钎料实现了碳化硼(B_(4)C)陶瓷与高氮钢之间的可靠钎焊连接,研究了Ti元素含量对Ag-Cu-Ti钎料润湿铺展性能的影响,分析了Ti元素影响钎焊接头界面组织的作用机制,并在室温条件下测试了钎焊接头的抗剪强度.结果表明,当钎料Ag-Cu-Ti钎料中的Ti元素含量为4.5%时,钎料在B_(4)C陶瓷与高氮钢上均表现出良好的润湿性能,铺展形貌良好,铺展面积更大,在钎焊温度910℃,保温时间25 min的焊接条件下,Ti元素含量为4.5%的钎料与B_(4)C陶瓷和高氮钢均实现了良好的冶金结合,显微组织分析结果表明,钎焊接头组织在陶瓷侧反应层存在TiB和TiC,而在高氮钢侧反应层中出现了TiFe_(2),TiN和CuTi_(2),B_(4)C陶瓷/高氮钢钎焊接头的最大抗剪强度为54 MPa.

烧结气压对氮化硅陶瓷力学性能的影响

在氮化硅陶瓷气压烧结制备过程中,除烧结加热制度外,氮气压力对其性能影响也很大,为了制备出性能更为优异的氮化硅陶瓷,本文采用气压烧结法在不同压力下制备氮化硅陶瓷材料,研究氮气压力对氮化硅陶瓷材料力学性能的影响。结果表明:当氮气压力达到4 MPa左右时,获得的氮化硅陶瓷材料综合性能最佳,α相几乎全部转变为β相,β-Si_(3)N_(4)晶粒长径比约为5.5,相对密度约为97.9%,抗弯强度约为(671.83±30.00)MPa、维氏硬度(HV)约为1670.25±50.00、断裂韧性约为(7.83±0.3.0)MPa·m1/2;通过分析氮化硅陶瓷材料腐蚀面和压痕裂纹的微观结构,发现适当的氮气压力能促使裂纹在扩展路径上更易发生偏转、分叉等增韧机制,消耗裂纹扩散能量,从而提高氮化硅陶瓷材料的断裂韧性,本研究对氮化硅陶瓷材料的增韧具有一定的指导意义。

负载S-g-C_(3)N_(4)/MgAl-CLDH光催化砂浆的去污及水化性能研究

本研究合成了硫掺杂氮化碳/煅烧镁铝水滑石(S-g-C_(3)N_(4)/MgAl-CLDH)新型光催化复合材料,通过内掺的方式将其负载在水泥砂浆上,并测试了光催化砂浆的氮氧化物(NO_(x))降解性能和水化性能。结果表明,当光催化剂掺量小于5%(质量分数)时,S-g-C_(3)N_(4)/MgAl-CLDH掺量与砂浆的NO_(x)降解率成正比。当光催化剂掺量超过5%时,砂浆的NO_(x)降解性能开始下降。适量的S-g-C_(3)N_(4)/MgAl-CLDH使水泥早期(1 d)水化程度显著提升,过量的S-g-C_(3)N_(4)/MgAl-CLDH使水泥后期水化程度下降。当光催化剂掺量为7%时,水泥砂浆的28 d强度较对照组砂浆显著下降。此外,适量(3%)S-g-C_(3)N_(4)/MgAl-CLDH能够改善砂浆的28 d强度。

高强度安全型柱塞式氮气弹簧优化设计与仿真

为解决氮气弹簧缸筒由于损伤破坏导致的安全隐患问题,文中采用有限元仿真方法找到了与实际损伤一致的关键隐患点,并优化设计出一种新的高强度安全型柱塞式氮气弹簧结构。仿真结果表明:仿真可有效地反映出安全问题关键所在;优化后的氮气弹簧结构与原结构相比,柱塞杆上最大应力从501.36 MPa减小至183 MPa,大大提高了柱塞杆结构强度;新结构中端盖应力最大,且柱塞杆的两级凸台具有应力差,可在危机时实现卸压保护和多级防脱功能;该新结构满足实际工作要求,并具有较高的强度及更好的安全性。

电晕老化对纳米复合PI薄膜介电性能的影响

高温超导非晶合金变压器作为低温运行设备具有节能降耗的功能。选择耐低温的聚酰亚胺(PI)薄膜为高温超导非晶合金变压器主绝缘材料,改进PI薄膜的制备工艺,搭建电晕老化系统,对PI薄膜进行电晕老化预处理。对经电晕老化预处理后的薄膜的介电特性进行研究,发现液氮环境中电晕老化薄膜的介质损耗角正切值要低于常温环境,在质量分数小于或等于5%时纳米粒子填充PI薄膜的介质损耗角正切值小于处理前薄膜的质损耗角正切值。

黄土水泥复合材料的孔隙结构演化与强度特征研究

黄土作为一种孔隙结构发育的特殊土壤,具有渗透性、湿陷性、崩解性等特性,容易引发地面裂缝、地表的不均匀沉降等问题。通过氮气吸附、硬度测试和SEM等室内试验对不同掺量水泥黄土孔隙结构和强度特征进行研究。结果表明:随着水泥掺量的逐渐增大,黄土水泥复合材料总孔容逐渐降低,水泥掺量为25%时总孔容较水泥掺量为10%时降低了40%;黄土水泥复合材料压痕硬度和强度与水泥掺量存在明显的正相关性,通过SEM从微观角度直观分析得出黄土水泥复合材料是通过改变土体颗粒大小、形状、连接方式,胶结物填充状态等来改变原土体的物理力学性质。研究可为黄土地区注浆材料的研发提供技术参考。

冷轧DC01钢板屈服强度偏高的原因

冷轧DC01钢板屈服强度高于要求的≤240 MPa。为此对屈服强度偏高的冷轧DC01钢板进行了化学成分分析、金相检验以及冷轧压下率、退火工艺和平整延伸率的复查。结果表明:钢板的含氮量偏高,退火过程中析出的AlN量过多,阻碍晶粒的回复和再结晶,导致其屈服强度偏高。通过控制DC01钢的含氮量≤60×10^(-6)和调整退火工艺,冷轧DC01钢板的屈服强度达到了要求。

外部水源作用下岩石液氮冻结试验研究

地下工程施工常遇到砂土交错和地下水丰富的软弱地层问题,液氮低温可使岩土体迅速冻结以达到土层稳定和加固目的,但液氮在快速冻结的同时也会导致周围岩土体物理力学性质受到劣化,因此,探究超低温作用下外部水源对岩石劣化作用的影响对于工程施工的长期稳定和安全具有重要意义。为研究外部水源对岩石低温劣化作用影响,对不同饱水条件下的岩样进行液氮冷浸处理后开展超声波试验、核磁共振试验和单轴压缩试验。试验结果表明:①岩样在冻结状态下仍存在损伤,且损伤程度随岩样恢复室温后进一步增加;②液氮冷浸时间40 min左右对岩样劣化作用最明显;③外部水环境导致干燥岩样劣化程度增加、而饱和岩样劣化程度降低;④当岩石外部存在水源时,长时间(>30 min)的液氮冷浸作用会增加岩石的强度,而短时间(≤30 min)的液氮冷浸处理会劣化岩石的强度。

SPA-H强度偏低分析与研究

对SPA-H工艺过程进行跟踪,结合金相组织及非金属夹杂物分析强度不稳定的原因。研究分析表明,SPA-H强度偏低主要集中在连铸开浇和热换炉次,因保护浇铸不当,造成板坯成分N含量偏高,有效Ti含量降低,导致钢种强度偏低。

洱海罗时江湿地表层沉积物氨氮释放特征及影响因素

以洱海上游的罗时江湿地为研究对象,基于为期半年的野外监测,弄清湿地水体和表层沉积物中氨氮(NH_(3)-N)的时空分异规律,借助摇瓶试验法探究湿地入口沉积物NH_(3)-N的释放特征及水体离子强度(IS)和pH的影响.结果表明:(1)罗时江湿地上覆水和表层沉积物NH_(3)-N浓度变化范围分别为0.14-1.45 mg·L^(−1)和0.23-8.89 mg·kg^(−1),干湿季差异均不显著(P>0.05);上覆水和表层沉积物NH_(3)-N浓度均沿水流方向显著下降(P<0.05),出水口NH_(3)-N平均浓度分别是入水口的59.2%和49.9%,湿地对水体NH_(3)-N有截留效果.(2)模拟试验条件下,沉积物NH_(3)-N累积释放量的变化范围为412.9-653.7 mg·kg^(−1),随提取次数的增加单次释放量逐渐降低;NH_(3)-N累积释放量湿地入口显著高于其他样点,干季高于湿季.(3)上覆水IS升高促进沉积物NH_(3)-N的持续释放,增加快速释放NH_(3)-N占比;上覆水处于弱酸条件下更利于沉积物NH_(3)-N的持续释放,同时提高快速释放NH_(3)-N占比.研究结果显示,表流湿地入水口沉积物是NH_(3)-N的主要富集场所,水化学条件变化导致NH_(3)-N向上覆水释放可能引起二次污染.