Marsh筒法和净浆流动度法用于水泥与减水剂适应性测试的比较

通过Marsh筒法和净浆流动度法用于水泥与减水剂适应性测试比较发现,采用Marsh筒法无论在测定减水剂饱和掺量点、对经时损失的敏感性上,还是与水泥标准稠度用水量和胶砂流动度的相关性上都优于净浆流动度法。     

Enhancement in magnetic permeability of Ni-Co-Zn ferrites using CuO doping for RF and microwave devices

Novel soft magnetic ferrite materials will play a crucial role in next-generation trillion-dollar sensor technologies related to 5G communications and internet of things as these materials can achieve improved wireless power/signal transfer efficiency with high operation frequency. In this work, Ni_0.4Co_0.25Zn_0.35Fe₂O₄ ferrites with high permeability and low magnetic loss were prepared for RF and microwave device applications. Composition and microstructure control is crucial to obtain the desired magnetic and loss properties. CuO dopant (x = 0 wt% to 20 wt%) were employed during the synthesis of Ni_0.4Co_0.25Zn_0.35Fe₂O₄ ferrite specimens to modify the microstructures, thus improving the magnetic properties of the ferrites. High value of measured relative permeability (μ’ of 4-10) and relatively low magnetic loss tangent ( of 0.01-0.1) has been achieved at frequency range between 100 and 800 MHz. Addition of CuO, especially up to 3 wt%, can cause a significant increase in permeability. Real part of the permeability of 3.87 and 10.9 has been achieved for undoped and 3 wt% CuO doped specimens, while noticeable reduction in magnetic losses has been observed for the doped sample measured at 400 MHz. The resonance frequency of synthesized ferrites has also been shifted into GHz range, when higher concentration of CuO dopants (>5 wt%) were employed.     

Soy protein combined with copper and boron compounds for providing effective wood preservation

Chromated copper arsenate (CCA), an arsenicbased wood preservative, is toxic to human health and the environment. Although CCA is stable in seasoned wood, there are potential dangers during CCA manufacture, lumber treatment, and waste disposal. This research was conducted to study the effectiveness of soy products to replace toxic chromium and arsenic compounds in wood preservative formulations. Three soy product (Arpro 2100, HM 90, and Supro 760) were used as fixative agents in preservative solutions containing anhydrous CuSO₄ and Na₂B₄O₇·10H₂O. The decay resistance of treated wood blocks was measured by a soil-block culture method. Despite the large molecular sizes of copper-protein and copper-boron-protein complexes, southern pine sapwood was treatable with these preservative formulations. Wood samples treated with >6 kg°m⁻³ CuSO₄ and 7.5 kg·m⁻³ soy product, and subsequently leached for 3 d and exposed to the decay fungus Gloeophyllum trabeum (Fr.) Mur., sustained only 0.5% weight loss over 12 wk. Wood samples needed 40 kg·m⁻³ CuSO₄ and 50 kg·m⁻³ soy protein to resist the copper-tolerant decay fungus Postia placenta (Fr.) M. Lars. & Lomb. These results suggest that soy-based wood preservatives can prevent wood products from fungal attack and can replace CCA.     

Determination of dinitrogen emission and retention in floodwater and porewater of a lowland rice field fertilized with15N-urea

This paper reports a study on the distribution of dinitrogen between the atmosphere, floodwater and porewater of the soil in a flooded rice field after addition of¹⁵N-labelled urea into the floodwater.Microplots (0.086 m²) were established in a rice field near Griffith, N.S.W., and labelled urea (80 kg N ha^–1 containing 79.25 atoms %¹⁵N) was added to the floodwater when the rice was at the panicle initiation stage. Emission of nitrous oxide and dinitrogen was measured directly during the day and overnight, using a cover collection method and gas chromatographic and mass spectrometric analytical methods. Ammonia volatilization was calculated with a bulk aerodynamic method from measurements of wind speed and floodwater pH, temperature and ammoniacal nitrogen concentration. Seven days after urea application the¹⁵N₂ content of the floodwater and soil porewater was determined and total fertilizer nitrogen loss was calculated from an isotopic balance.Throughout the experimental period gas fluxes were low; nitrous oxide, ammonia and dinitrogen flux densities were less than 5, 170 and 720 g N ha^–1 d^–1, respectively. The greatest dinitrogen flux density was observed two days after urea addition and this declined to ~ 100 g ha^–1 d^–1 after seven days.The data indicate that, of the urea nitrogen added, 0.02% was lost to the atmosphere as nitrous oxide, 0.9% was lost by ammonia volatilization, and 3.6% was lost as dinitrogen gas during the 7 days of measurement. At the end of this period 0.028% and 0.002% of the added nitrogen was retained as dinitrogen gas in the floodwater and soil porewater respectively. Recovery of the¹⁵N applied as nitrogen gases, plant uptake, and soil and floodwater constituents totaled about 94% of the nitrogen added.     

氰酸酯树脂的性能与应用

氰酸酯树脂具有较低的介质损耗因数和低而稳定的介电常数，使用频带宽，力学性能好，吸水率低，是新一代航空航天雷达天线罩理想的基体材料。介绍了该树脂的制备途径、性能和应用，并指出合成中应注意的问题。     

基于糊模ID3算法的高校学生流失数据挖掘研究

目前高校不断扩招,生源却逐渐减少,于是预防和减少学生流失正成为各高校必须面对的问题。通过对高校学生流失情况进行数据挖掘,可发现一些有价值的信息,为解决高校学生流失问题提供帮助。基于糊模理论提出了糊模ID3算法,并将该算法运用于分析高校学生流失原因之中。通过实验证明,该算法生成的决策树更加合理,分类速度更快,为解决高校学生流失问题提供了理论依据。     

Dielectric loss and phase transition of sodium potassium niobate ceramic investigated by impedance spectroscopy

The dielectric permittivity of Na_0.80K_0.20NbO₃ ceramic was investigated by impedance spectroscopy. The dielectric characterization was performed from room temperature to 800 °C, in the frequency range 5 Hz–13 MHz. The bulk permittivity was derived by the variation of the imaginary part of the impedance as a function of reciprocal angular frequency. The permittivity values as a function of temperature showed two maxima. The first maximum is very similar at 200 °C and the second one positioned at around 400 °C, which was associated to Curie’s temperature. The evolution of the complex permittivity as a function of frequency and temperature was investigated. At low frequency dispersion was investigated in terms of dielectric loss. The Na_0.80K_0.20NbO₃ showed a dissipation factor between 5 and 40 over a frequency range from 1 to 10² kHz.     

丙烯酸酯聚氨酯/SiO2纳米复合涂层结构与形态对其耐刮伤性影响研究

以四乙氧基硅烷(TEOS)作为主要前驱体,通过改变溶胶-凝胶工艺参数制得了结构和形态各异的丙烯酸酯聚氨酯/SiO2纳米复合涂层,利用TEM、SAXS等手段表征涂层的结构与形态,由洗刷前后涂层的失光率来表征耐刮伤性,详细探讨了纳米复合涂层耐刮伤性与SiO2相特征、有机无机相作用力及SiO2质量分数之间的关系。研究表明:丙烯酸酯聚氨酯涂层中引入纳米SiO2相后,耐刮伤性明显提高。有机相与SiO2相之间的作用力是影响涂层耐刮伤性的最重要因素,作用力越强,耐刮伤性越好。网络状纳米SiO2与颗粒状纳米SiO2相比,更有利于耐刮伤性的提高,且网络状纳米SiO2质量分数越大,耐刮伤性越佳,但SiO2相的致密度和尺寸对耐刮伤性影响较小。对于颗粒状胶体SiO2,在15~160 nm范围内,粒径对耐刮伤性没有明显影响;随着胶体SiO2粒子的质量分数增加,耐刮伤性先增大后减小。     

Effect of green manure on the yield,N uptake and floodwater properties of a flooded rice,wheat rotation receiving15N urea on a highly permeable soil

Field studies were conducted for two years on a rapidly percolating loamy sand (Typic Ustochrept) to evaluate the effect of green manure (GM) on the yield,¹⁵N recovery from urea applied to flooded rice, the potential for ammonia loss and uptake of residual fertilizer N by succeeding crops. The GM crop ofSesbania aculeata was grownin situ and incorporated one day before transplanting rice. Urea was broadcast in 0.05 m deep floodwater, and incorporated with a harrow. Green manure significantly increased the yield and N uptake by rice and substituted for a minimum of 60 kg fertilizer N ha^–1. The recovery of fertilizer N as indicated by¹⁵N recovery was higher in the GM + urea treatments. The grain yield and N uptake by succeeding wheat in the rotation was slightly higher with GM. The recovery of residual fertilizer N as indicated by the¹⁵N recovery in the second, third and fourth crops of wheat, rice and wheat was only 3, 1 and 1 per cent of the urea fertilizer applied to the preceding rice crop. Floodwater chemistry parameters showed that the combined use of the GM and 40 kg N ha^–1 as urea applied at transplanting resulted in a comparatively higher potential for NH₃ loss immediately after fertilizer application. The actual ammonia loss as suggested by the¹⁵N recoveries in the rice crop, however, did not appear to be appreciably larger in the GM treatment. It appeared the ammonia loss was restricted by low ammoniacal-N concentration maintained in the floodwater after 2 to 3 days of fertilizer application.